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Sample records for pulses initial structural

  1. Fast initial continuous current pulses versus return stroke pulses in tower-initiated lightning

    NASA Astrophysics Data System (ADS)

    Azadifar, Mohammad; Rachidi, Farhad; Rubinstein, Marcos; Rakov, Vladimir A.; Paolone, Mario; Pavanello, Davide; Metz, Stefan

    2016-06-01

    We present a study focused on pulses superimposed on the initial continuous current of upward negative discharges. The study is based on experimental data consisting of correlated lightning current waveforms recorded at the instrumented Säntis Tower in Switzerland and electric fields recorded at a distance of 14.7 km from the tower. Two different types of pulses superimposed on the initial continuous current were identified: (1) M-component-type pulses, for which the microsecond-scale electric field pulse occurs significantly earlier than the onset of the current pulse, and (2) fast pulses, for which the onset of the field matches that of the current pulse. We analyze the currents and fields associated with these fast pulses (return-stroke type (RS-type) initial continuous current (ICC) pulses) and compare their characteristics with those of return strokes. A total of nine flashes containing 44 RS-type ICC pulses and 24 return strokes were analyzed. The median current peaks associated with RS-type ICC pulses and return strokes are, respectively, 3.4 kA and 8 kA. The associated median E-field peaks normalized to 100 km are 1.5 V/m and 4.4 V/m, respectively. On the other hand, the electric field peaks versus current peaks for the two data sets (RS-type ICC pulses and return strokes) are characterized by very similar linear regression slopes, namely, 3.67 V/(m kA) for the ICC pulses and 3.77 V/(m kA) for the return strokes. Assuming the field-current relation based on the transmission line model, we estimated the apparent speed of both the RS-type ICC pulses and return strokes to be about 1.4 × 108 m/s. A strong linear correlation is observed between the E-field risetime and the current risetime for the ICC pulses, similar to the relation observed between the E-field risetime and current risetime for return strokes. The similarity of the RS-type ICC pulses with return strokes suggests that these pulses are associated with the mixed mode of charge transfer to ground.

  2. EVOLUTION OF FAST MAGNETOACOUSTIC PULSES IN RANDOMLY STRUCTURED CORONAL PLASMAS

    SciTech Connect

    Yuan, D.; Li, B.; Pascoe, D. J.; Nakariakov, V. M.; Keppens, R. E-mail: bbl@sdu.edu.cn

    2015-02-01

    We investigate the evolution of fast magnetoacoustic pulses in randomly structured plasmas, in the context of large-scale propagating waves in the solar atmosphere. We perform one-dimensional numerical simulations of fast wave pulses propagating perpendicular to a constant magnetic field in a low-β plasma with a random density profile across the field. Both linear and nonlinear regimes are considered. We study how the evolution of the pulse amplitude and width depends on their initial values and the parameters of the random structuring. Acting as a dispersive medium, a randomly structured plasma causes amplitude attenuation and width broadening of the fast wave pulses. After the passage of the main pulse, secondary propagating and standing fast waves appear. Width evolution of both linear and nonlinear pulses can be well approximated by linear functions; however, narrow pulses may have zero or negative broadening. This arises because narrow pulses are prone to splitting, while broad pulses usually deviate less from their initial Gaussian shape and form ripple structures on top of the main pulse. Linear pulses decay at an almost constant rate, while nonlinear pulses decay exponentially. A pulse interacts most efficiently with a random medium with a correlation length of about half of the initial pulse width. This detailed model of fast wave pulses propagating in highly structured media substantiates the interpretation of EIT waves as fast magnetoacoustic waves. Evolution of a fast pulse provides us with a novel method to diagnose the sub-resolution filamentation of the solar atmosphere.

  3. Ultrashort pulse propagation in multiple-grating fiber structures.

    PubMed

    Chen, L R; Benjamin, S D; Smith, P W; Sipe, J E; Juma, S

    1997-03-15

    We propose a multiple-grating fiber structure that decomposes an ultrashort broadband optical pulse simultaneously in both wavelength and time. As an initial demonstration, we used a transform-limited 1-ps Gaussian pulse centered at 1.55 mu;m as the ultrashort broadband input into a three-grating fiber structure and generated three output pulses separated in wavelength and time with good correlation between experimental results and simulations. This device structure can be used to generate a multiwavelength train of pulses for use in wavelength-division-multiplexed systems or to implement frequency-domain encoding of coherent pulses for optical code-division multiple access. PMID:18183215

  4. Initial Black Pulse Findings, Bulletin No. l.

    ERIC Educational Resources Information Center

    National Urban League, Inc., Washington, DC. Research Dept.

    In 1979, the National Urban League and its local affiliates launched the Black Pulse, a nationwide survey designed to (1) assess the needs and status of blacks in such areas as employment, housing, child care, education, health, crime, political participation, family patterns, and discrimination; and (2) determine the extent to which major…

  5. A physics-based model of the electric field pulses occurring during the lightning initiation

    NASA Astrophysics Data System (ADS)

    Kaspar, Petr; Santolik, Ondrej; Kolmasova, Ivana

    2016-04-01

    We investigate properties of the electric field pulses observed during the lightning initiation using a generalization of electrostatic and transmission-line models. In the model, the initial leader has a finite conductivity, the current in the channel is inducted owing to an ambient field generated by charge structure inside a thundercloud, and the electric field is computed by a formula derived from exact solution of the Maxwell's equations for a given inducted current. We show how the shape of electric field waveform of individual pulses depends on various parameters of the model with an emphasis on the thundercloud charge structure. We generalize the model to include sequences of several electric field pulses. We show how the peak current pulse is related to the preliminary breakdown electric field peak pulse and we compare this estimation with observations.

  6. Physical Mechanism of Initial Breakdown Pulses in Lightning Discharges

    NASA Astrophysics Data System (ADS)

    Da Silva, C.; Pasko, V. P.

    2014-12-01

    The initial breakdown stage of a lightning flash encompasses its first several to tens of milliseconds and it is characterized by a sequence of pulses typically detected with electric field change sensors on the ground [e.g., Villanueva et al., JGR, 99, D7, 1994]. A typical (referred to as "classical") initial breakdown pulse (IBP) has duration of tens of microseconds and it is one of the largest pulses at the beginning of a lightning flash, but a wide range of pulse durations and amplitudes also occur [e.g., Nag et al., Atmos. Res., 91, 316, 2009]. Recent results by Marshall et al. [JGR, 119, 445, 2014] suggest that IBPs should be observable in all lightning discharges. Complementarily, Stolzenburg et al. [JGR, 118, 2918, 2013] correlated individual IBPs to bursts of light that appear to be illumination of a lightning leader channel and Karunarathne et al. [JGR, 118, 7129, 2013] have determined that as a flash evolves the location of IBP sources inside the cloud coincide with the position of negative leaders as determined by a VHF lightning mapping system. In view of the above listed properties of IBPs, we have developed a new numerical model to investigate the electromagnetic signatures associated with these events and to relate them to the initial lightning leader development. The model is built on a bidirectional (zero-net-charge) lightning leader concept [e.g., Mazur and Ruhnke, JGR, 103, D18, 1998]. We simulate a finite-length finite-conductivity leader elongating in the thunderstorm electric field and we solve a set of integro-differential equations to retrieve the full dynamics of charges and currents induced in it. Our proposed approach is a generalization of the transmission-line [e.g., Nag and Rakov, JGR, 115, D20102, 2010] and electrostatic [e.g., Pasko, GRL, 41, 179, 2014] approximations used for analysis of in-cloud discharge processes. We also allow for different propagation mechanisms at the different polarity leader extremities, i.e., continuous

  7. Luminosity Coincident with Initial Breakdown Pulses in Lightning

    NASA Astrophysics Data System (ADS)

    Stolzenburg, M.; Marshall, T.; Karunarathne, S.; Karunarathna, N.; Vickers, L.; Warner, T. A.; Orville, R. E.; Betz, H.

    2012-12-01

    Time correlated high-speed video and electromagnetic data for 15 cloud-to-ground and intracloud lightning flashes reveal bursts of light, bright enough to be seen through intervening cloud, during the initial breakdown (IB) stage and within the first 3 ms after flash initiation. Each sudden increase in luminosity is coincident with a CG-type (12 cases) or IC-type (3 cases) IB pulse in fast electric field change records. Some of these IB pulses have a coincident VLF/LF (LINET) or a VHF (LDAR2) radiation source. The luminosity bursts of 14 CG flashes occur 11-340 ms before the first return stroke, at altitudes of 4-8 km, and at 4-41 km range from the camera. In seven cases, streamer-type linear segments visibly advance away from the first light burst for 55-200 μs, then the entire length dims, then the luminosity sequence repeats along the same path. These visible initial streamers lengthen intermittently to about 300-1500 m. Their estimated 2-D speeds are 4 to 18 x 10^5 m/s over the first few hundred microseconds and decrease by about 50% over the first 2 ms. In other cases, only a bright spot or a broad area of diffuse light, presumably scattered by intervening cloud, is visible. The bright area grows larger over 20-60 μs before the luminosity fades in about 100 μs, then this sequence may repeat several times. In several of the flashes a 1-2 ms period of little or no luminosity and small E-change is observed following the IB stage prior to stepped leader development. In this presentation we will show examples of the IB luminosity and coincident electromagnetic data.

  8. Locating initial breakdown pulses using electric field change network

    NASA Astrophysics Data System (ADS)

    Karunarathne, Sumedhe; Marshall, Thomas C.; Stolzenburg, Maribeth; Karunarathna, Nadeeka; Vickers, Lauren E.; Warner, Tom A.; Orville, Richard E.

    2013-07-01

    Initial breakdown pulses (IBPs) observed in the fast electric field change (E-change) at the beginning of intracloud (IC) and cloud-to-ground (CG) lightning flashes are located using a time-of-arrival technique called Position By Fast Antenna (PBFA) with data from a network of 10 E-change sensors located at Kennedy Space Center. Location errors, estimated using a Monte Carlo method, are usually less than 100 m for horizontal coordinates and several hundreds of meters for altitude, depending on distance to the sensors and altitude of the source. Comparison of PBFA source locations to locations from a VHF lightning mapping system (Lightning Detection and Ranging II (LDAR2)) shows that PBFA locates most of the "classic" IBPs while LDAR2 locates only a few percent of them. As the flash develops during the IB stage, PBFA and LDAR2 obtain similar locations when they detect the same IBPs. The overall vertical motion indicated by the PBFA positions of IBPs was downward with time for CG flashes and upward with time for IC flashes. Location of the fast pulses due to return strokes of CG flashes is also determined using PBFA. Comparison to locations from the Cloud-to-Ground Lightning Surveillance System (CGLSS) shows that PBFA reliably locates ground strokes. These results are verified using ground truth data acquired with a high-speed video camera. After cross calibration with the CGLSS data set, peak currents of return strokes are also determined.

  9. Spacecraft attitude pulse-width control at initial, service and emergency modes

    NASA Astrophysics Data System (ADS)

    Somov, Sergey

    2012-11-01

    Problems of nonlinear modeling, dynamic analysis and simulation of spatial motion by a spacecraft with a flexible weak damping structure, are considered. Attitude motion of a flexible spacecraft with pulse-width control, spin-up rotors of six single-gimbal control moment gyros (CMGs) at the initial, service and emergency modes, is studied. Results on analysis of the spacecraft nutation and flexible oscillations, are represented.

  10. Inertial cavitation initiated by polytetrafluoroethylene nanoparticles under pulsed ultrasound stimulation.

    PubMed

    Jin, Qiaofeng; Kang, Shih-Tsung; Chang, Yuan-Chih; Zheng, Hairong; Yeh, Chih-Kuang

    2016-09-01

    Nanoscale gas bubbles residing on a macroscale hydrophobic surface have a surprising long lifetime (on the order of days) and can serve as cavitation nuclei for initiating inertial cavitation (IC). Whether interfacial nanobubbles (NBs) reside on the infinite surface of a hydrophobic nanoparticle (NP) and could serve as cavitation nuclei is unknown, but this would be very meaningful for the development of sonosensitive NPs. To address this problem, we investigated the IC activity of polytetrafluoroethylene (PTFE) NPs, which are regarded as benchmark superhydrophobic NPs due to their low surface energy caused by the presence of fluorocarbon. Both a passive cavitation detection system and terephthalic dosimetry was applied to quantify the intensity of IC. The IC intensities of the suspension with PTFE NPs were 10.30 and 48.41 times stronger than those of deionized water for peak negative pressures of 2 and 5MPa, respectively. However, the IC activities were nearly completely inhibited when the suspension was degassed or ethanol was used to suspend PTFE NPs, and they were recovered when suspended in saturated water, which may indicates the presence of interfacial NBs on PTFE NPs surfaces. Importantly, these PTFE NPs could sustainably initiate IC for excitation by a sequence of at least 6000 pulses, whereas lipid microbubbles were completely depleted after the application of no more than 50 pulses under the same conditions. The terephthalic dosimetry has shown that much higher hydroxyl yields were achieved when PTFE NPs were present as cavitation nuclei when using ultrasound parameters that otherwise did not produce significant amounts of free radicals. These results show that superhydrophobic NPs may be an outstanding candidate for use in IC-related applications. PMID:27150739

  11. Preliminary breakdown of intracloud lightning: Initiation altitude, propagation speed, pulse train characteristics, and step length estimation

    NASA Astrophysics Data System (ADS)

    Wu, Ting; Yoshida, Satoru; Akiyama, Yasuhiro; Stock, Michael; Ushio, Tomoo; Kawasaki, Zen

    2015-09-01

    Using a low-frequency lightning location system comprising 11 sites, we located preliminary breakdown (PB) processes in 662 intracloud (IC) lightning flashes during the summer of 2013 in Osaka area of Japan. On the basis of three-dimensional location results, we studied initiation altitude and upward propagation speed of PB processes. PB in most IC flashes has an initiation altitude that ranges from 5 to 10 km with an average of 7.8 km. Vertical speed ranges from 0.5 to 17.8 × 105 m/s with an average of 4.0 × 105 m/s. Vertical speed is closely related with initiation altitude, with IC flashes initiated at higher altitude having lower vertical speed during PB stage. Characteristics of PB pulse trains including pulse rate, pulse amplitude, and pulse width are also analyzed. The relationship between pulse rate and vertical speed has the strongest correlation, suggesting that each PB pulse corresponds to one step of the initial leader during the PB stage. Pulse rate, pulse amplitude, and pulse width all show decreasing trends with increasing initiation altitude and increasing trends with increasing vertical speed. Using a simple model, the step length of the initial leader during the PB stage is estimated. Most of initial leaders have step lengths that range from 40 to 140 m with an average of 113 m. Estimated step length has a strong correlation with initiation altitude, indicating that leaders initiated at higher altitude have longer steps. Based on the results of this study, we speculate that above certain altitude (~12 km), initial leaders in PB stages of IC flashes may only have horizontal propagations. PB processes at very high altitude may also have very weak radiation, so detecting and locating them would be relatively difficult.

  12. Pulsed dye laser fragmentation of ureteral calculi: initial clinical experience.

    PubMed

    Dretler, S P; Watson, G; Parrish, J A; Murray, S

    1987-03-01

    The pulsed dye laser, emitting at wavelengths of 504 nm. for 1 microsecond. at a frequency of 5 Hz. transmitted via a 250 mu in diameter silicon-coated quartz fiber, was passed into the ureter through the working channel of a 9.5F rigid ureteroscope. Seventeen patients with ureteral calculi too large to be extracted directly, who were unable to be treated by extracorporeal shock wave lithotripsy or who otherwise would have required transureteral or percutaneous ultrasonic stone removal, underwent attempted stone fragmentation by pulsed dye laser application. Of the 17 calculi 16 were fragmented to spontaneously passable or easily extractable fragments. There was no significant ureteral injury, thermal or otherwise, attributable to laser energy action. At 3-month followup 15 of the 17 ureters had improved and 2 showed evidence of ureterscopic injury. The mechanism of stone fragmentation by laser is small volume "shock wave" formation. PMID:3820363

  13. Initiation complex structure and promoter proofreading.

    PubMed

    Liu, Xin; Bushnell, David A; Silva, Daniel-Adriano; Huang, Xuhui; Kornberg, Roger D

    2011-07-29

    The initiation of transcription by RNA polymerase II is a multistage process. X-ray crystal structures of transcription complexes containing short RNAs reveal three structural states: one with 2- and 3-nucleotide RNAs, in which only the 3'-end of the RNA is detectable; a second state with 4- and 5-nucleotide RNAs, with an RNA-DNA hybrid in a grossly distorted conformation; and a third state with RNAs of 6 nucleotides and longer, essentially the same as a stable elongating complex. The transition from the first to the second state correlates with a markedly reduced frequency of abortive initiation. The transition from the second to the third state correlates with partial "bubble collapse" and promoter escape. Polymerase structure is permissive for abortive initiation, thereby setting a lower limit on polymerase-promoter complex lifetime and allowing the dissociation of nonspecific complexes. Abortive initiation may be viewed as promoter proofreading, and the structural transitions as checkpoints for promoter control. PMID:21798951

  14. Pulsed oxygen-iodine chemical laser initiated by an electrical discharge

    SciTech Connect

    Zhang Rongyao; Chen Fang; Song Xueqin; Xu Qingzhou; Huan Changqing; Zhuang Qi; Zhang Cunhao

    1988-08-01

    This paper demonstrates for the first time the feasibility of an electrically initiated, pulsed oxygen-iodine laser which can be initiated efficiently by low energy electrons. By electrical initiation, an O/sub 2/(/sup 1/..delta..)--CH/sub 3/I--N/sub 2/ mixture has been made to lase with an output energy of 130 mJ. The efficiency of the electrical initiation is 350 times higher than that obtained with photo-initiation.

  15. Polarization sensitive anisotropic structuring of silicon by ultrashort light pulses

    SciTech Connect

    Zhang, Jingyu; Drevinskas, Rokas Beresna, Martynas; Kazansky, Peter G.

    2015-07-27

    Imprinting of anisotropic structures on the silicon surface by double pulse femtosecond laser irradiation is demonstrated. The origin of the polarization-induced anisotropy is explained in terms of interaction of linearly polarized second pulse with the wavelength-sized symmetric crater-shaped structure generated by the linearly polarized first pulse. A wavefront sensor is fabricated by imprinting an array of micro-craters. Polarization controlled anisotropy of the structures can be also explored for data storage applications.

  16. Charge Migration in Phenylalanine Initiated by Attosecond Pulses

    NASA Astrophysics Data System (ADS)

    Greenwood, Jason; Trabattoni, Andrea; Ayuso, David; Belshaw, Louise; de Camillis, Simone; Anumula, Sunil; Frassetto, Fabio; Poletto, Luca; Palacios, Alicia; Declava, Piero; Martin, Fernando; Calegari, Francesca; Nisoli, Mauro

    2015-05-01

    In the past few years attosecond techniques have been implemented for the investigation of ultrafast dynamics in molecules. The generation of isolated attosecond pulses characterized by a relatively high photon flux has opened up new possibilities in the study of molecular dynamics. We report on experimental and theoretical results of ultrafast charge dynamics in a biochemically relevant molecule, namely, the amino acid phenylalanine. The data represent the first experimental demonstration of the generation and observation of a charge migration process in a complex molecule, where electron dynamics precede nuclear motion. The application of attosecond technology to the investigation of electron dynamics in biologically relevant molecules represents a multidisciplinary work, which can open new research frontiers: those in which few femtosecond and even sub-femtosecond electron processes determine the fate of biomolecules.

  17. Quantitative effect of initial current rise on pumping the double-pulsed copper chloride laser

    NASA Technical Reports Server (NTRS)

    Vetter, A. A.

    1977-01-01

    The laser energy at optimum time delay of a double-pulsed CuCl laser was experimentally determined to be a logarithmic function of the initial current rise of the pumping pulse over the total circuit inductance range 1 to 12 microhenrys. The minimum delay was found to decrease with initial current rise, which implies that faster rising current pulses are more efficient at pumping copper atoms from the ground state to the upper laser level because lasing threshold occurs with a higher population in the lower laser level.

  18. Real-time study of bulk damage formation in glass initiated by intense femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Kudriašov, V.; Gaižauskas, E.; Sirutkaitis, V.

    2005-12-01

    Dynamics of damage formation by focusing intense femtosecond pulses inside the fused silica glass is studied in wide energy range. Damage usually is initiated in the zone near geometrical focus, which is preceded by the zone where beam propagates in the form of multiple filaments. For high repetition rate pulses damage appears as an extended narrow track along the beam path, which forms due to the propagation of the initial damage zone toward the laser source. For low repetition rate pulses extended damage tracks don't form.

  19. Probabilistic SSME blades structural response under random pulse loading

    NASA Technical Reports Server (NTRS)

    Shiao, Michael; Rubinstein, Robert; Nagpal, Vinod K.

    1987-01-01

    The purpose is to develop models of random impacts on a Space Shuttle Main Engine (SSME) turbopump blade and to predict the probabilistic structural response of the blade to these impacts. The random loading is caused by the impact of debris. The probabilistic structural response is characterized by distribution functions for stress and displacements as functions of the loading parameters which determine the random pulse model. These parameters include pulse arrival, amplitude, and location. The analysis can be extended to predict level crossing rates. This requires knowledge of the joint distribution of the response and its derivative. The model of random impacts chosen allows the pulse arrivals, pulse amplitudes, and pulse locations to be random. Specifically, the pulse arrivals are assumed to be governed by a Poisson process, which is characterized by a mean arrival rate. The pulse intensity is modelled as a normally distributed random variable with a zero mean chosen independently at each arrival. The standard deviation of the distribution is a measure of pulse intensity. Several different models were used for the pulse locations. For example, three points near the blade tip were chosen at which pulses were allowed to arrive with equal probability. Again, the locations were chosen independently at each arrival. The structural response was analyzed both by direct Monte Carlo simulation and by a semi-analytical method.

  20. Anode initiated impulse breakdown in water: the dependence on pulse rise time for nanosecond and sub-nanosecond pulses and initiation mechanism based on electrostriction

    NASA Astrophysics Data System (ADS)

    Seepersad, Yohan; Fridman, Alexander; Dobrynin, Danil

    2015-10-01

    The effect of the voltage rise time on nanosecond and sub-nanosecond impulse breakdown of distilled water is studied. The dependence of anode initiated streamer inception on this parameter is shown to be more intricate than previously reported, particularly as it relates to mechanisms directly in the liquid phase. Dynamics of the emission phase for sub-nanosecond pulses with 600 ps rise time are presented to enable comparison with previous work on nanosecond initiation features. Schlieren imaging is also used to show the development of optical density perturbations and rarefactions as a result of electrostriction in the liquid which were previously found for nanosecond pulses as well. The mechanism of nanopore generation in the liquid due to fast impulses proposed by Shneider, Pekker and Fridman is used to explain the results.

  1. Sprite streamer initiation from natural mesospheric structures.

    PubMed

    Liu, Ningyu; Dwyer, Joseph R; Stenbaek-Nielsen, Hans C; McHarg, Matthew G

    2015-01-01

    Sprites are large, luminous electrical discharges in the upper atmosphere caused by intense cloud-to-ground lightning flashes, manifesting an impulsive coupling mechanism between lower and upper atmospheric regions. Their dynamics are governed by filamentary streamer discharges whose propagation properties have been well studied by past work. However, how they are initiated is still under active debate. It has recently been concluded that ionospheric/mesospheric inhomogeneities are required for their initiation, but it is an open question as to what the sources of those inhomogeneities are. Here we present numerical simulation results to demonstrate that naturally-existing, small-scale mesospheric structures such as those created by gravity waves via instability and breaking are viable sources. The proposed theory is supported by a recent, unique high-speed observation from aircraft flying at 14-km altitude. The theory naturally explains many aspects of observed sprite streamer initiation and has important implications for future observational work. PMID:26118893

  2. Intensity improvement in the attosecond pulse generation with the coherent superposition initial state

    NASA Astrophysics Data System (ADS)

    Feng, Liqiang; Chu, Tianshu

    2012-03-01

    We investigate the coherent superposition initial state effect and found that when the initial active electron state is prepared in the coherent superposition of the 1s and 2s states of the He+ ion and the chirp parameter of the fundamental field in the two-color scheme is chosen to be β=0.3, the harmonic cutoff energy is remarkably extended and the harmonic yield is enhanced by at least 6 orders of magnitude compared with the case of the single 1s ground state with chirp-free pulse. An ultrabroad supercontinuum with a 458 eV bandwidth is formed, directly producing an intense isolated 34 as pulse.

  3. On the percentage of lightning flashes that begin with initial breakdown pulses

    NASA Astrophysics Data System (ADS)

    Marshall, T.; Schulz, W.; Karunarathna, N.; Karunarathne, S.; Stolzenburg, M.; Vergeiner, C.; Warner, T.

    2014-01-01

    The initial breakdown (IB) stage of lightning flashes typically occurs in the first 20 ms of a flash and includes a series of IB pulses often detected with electric field change sensors. There is disagreement about the percentage of negative cloud-to-ground (CG) flashes that begin with IB pulses. This study includes new data on IB pulses in 198 CG flashes in Austria (latitude ~48˚N), Florida, USA (~29˚N) and South Dakota, USA (~44˚N) with, respectively, 100%, 100%, and 95% of the flashes having IB pulses. The data indicate that the amplitude of the largest IB pulse, range normalized to 100 km, is often weak, < 0.5 V m-1, with the lower latitude having a greater percentage (36%) of these weak maximum IB pulses than the higher latitude (11%). Since sensor noise levels are often larger than this value, detection of smaller amplitude IB pulses may be difficult. A similar result is seen in the amplitude ratio of the largest IB pulse to the first return stroke: at the lower latitude, 50% of flashes had a ratio < 0.1 versus 8% of flashes at the higher latitude. However, comparisons of the amplitude ratios from Austria (~48˚) and South Dakota (~44˚) do not support a simple latitude dependence. The data also show that 5-10% of IB pulses occur more than 100 ms before the first return stroke. These findings may explain why some previous studies found percentages <100%. Overall, the results indicate that all negative CG flashes probably begin with IB pulses.

  4. Double pulse laser-induced breakdown spectroscopy of explosives: Initial study towards improved discrimination

    NASA Astrophysics Data System (ADS)

    De Lucia, Frank C.; Gottfried, Jennifer L.; Munson, Chase A.; Miziolek, Andrzej W.

    2007-12-01

    Detecting trace explosive residues at standoff distances in real-time is a difficult problem. One method ideally suited for real-time standoff detection is laser-induced breakdown spectroscopy (LIBS). However, atmospheric oxygen and nitrogen contributes to the LIBS signal from the oxygen- and nitrogen-containing explosive compounds, complicating the discrimination of explosives from other organic materials. While bathing the sample in an inert gas will remove atmospheric oxygen and nitrogen interference, it cannot practically be applied for standoff LIBS. Alternatively, we have investigated the potential of double pulse LIBS to improve the discrimination of explosives by diminishing the contribution of atmospheric oxygen and nitrogen to the LIBS signal. These initial studies compare the close-contact (< 1 m) LIBS spectra of explosives using single pulse LIBS in argon with double pulse LIBS in atmosphere. We have demonstrated improved discrimination of an explosive and an organic interferent using double pulse LIBS to reduce the air entrained in the analytical plasma.

  5. Note: Design and initial results of a multi-pulsed intense electron beam source

    NASA Astrophysics Data System (ADS)

    Xia, L.; Zhang, H.; Yang, A.; Shen, Y.; Wang, W.; Wen, L.; Zhang, K.; Shi, J.; Zhang, L.; Deng, J.

    2014-06-01

    A multi-pulsed intense electron beam source is introduced, including the design and the initial experimental results. The source can generate a burst of three pulses of intense electron beams with energy of 2-3 MeV and beam intensities of around 2.5 kA. An inductive adder is chosen to generate the pulsed diode voltages and a dispenser cathode is chosen to emit electron beams. The test results indicate that the design of the source is reliable. The multi-pulsed diode voltage is up to 2.5 MV and the beam intensities are more than 2 kA at the exit of the source with small variation.

  6. Note: Design and initial results of a multi-pulsed intense electron beam source.

    PubMed

    Xia, L; Zhang, H; Yang, A; Shen, Y; Wang, W; Wen, L; Zhang, K; Shi, J; Zhang, L; Deng, J

    2014-06-01

    A multi-pulsed intense electron beam source is introduced, including the design and the initial experimental results. The source can generate a burst of three pulses of intense electron beams with energy of 2-3 MeV and beam intensities of around 2.5 kA. An inductive adder is chosen to generate the pulsed diode voltages and a dispenser cathode is chosen to emit electron beams. The test results indicate that the design of the source is reliable. The multi-pulsed diode voltage is up to 2.5 MV and the beam intensities are more than 2 kA at the exit of the source with small variation. PMID:24985872

  7. Dislocation structure produced by an ultrashort shock pulse

    SciTech Connect

    Matsuda, Tomoki Hirose, Akio; Sano, Tomokazu; Arakawa, Kazuto

    2014-11-14

    We found an ultrashort shock pulse driven by a femtosecond laser pulse on iron generates a different dislocation structure than the shock process which is on the nanosecond timescale. The ultrashort shock pulse produces a highly dense dislocation structure that varies by depth. According to transmission electron microscopy, dislocations away from the surface produce microbands via a network structure similar to a long shock process, but unlike a long shock process dislocations near the surface have limited intersections. Considering the dislocation motion during the shock process, the structure near the surface is attributed to the ultrashort shock duration. This approach using an ultrashort shock pulse will lead to understanding the whole process off shock deformation by clarifying the early stage.

  8. Luminosity with Intracloud-Type Initial Breakdown Pulses and Terrestrial Gamma-ray Flash Candidates

    NASA Astrophysics Data System (ADS)

    Stolzenburg, Maribeth; Marshall, Thomas; Karunarathne, Sumedhe; Orville, Richard

    2016-04-01

    High-speed video data for three hybrid lightning flashes show luminosity increases at visible wavelengths that are time-correlated with large, intracloud (IC) type initial breakdown (IB) pulses in electric field change (E-change) data. In one case, a diffuse luminosity increase is visible for 280-300 us, apparently centered near 9 km altitude. At the same time, locations of VHF sources and E-change pulses indicate breakdown activity occurring at altitudes of 9.2-10.2 km altitude, and the initial leader was developing rapidly upward. The second case has a diffuse luminosity increase at the time of three large IC-type IB pulses, while the initial leader is advancing upward from about 7 km altitude. In the third example, a series of luminosity bursts are visible at the times of several large-amplitude IC-type IB pulses, although the center of the activity is apparently above the video frame. In all three hybrid flashes, the luminous IC-type IB pulses are relatively complicated and large in E-change amplitude, and most have distinct electrostatic offset at horizontal distances of 20-25 km from a sensor. Such large amplitude IB pulses have been associated with the production of terrestrial gamma ray flashes (TGFs) in prior work [Marshall et al., 2013, doi:10.1002/jgrd.50866]. No satellite or ground-based TGF observations were available for these events, hence it is not known if these TGF candidates produced gammas or other high energy radiation. This presentation describes the video and E-change observations during the intracloud and cloud-to-ground initial breakdown periods of these flashes and implications for TGF production.

  9. Investigating short-pulse shock initiation in HMX-based explosives with reactive meso-scale simulations

    NASA Astrophysics Data System (ADS)

    Springer, H. K.; Tarver, C. M.; Reaugh, J. E.; May, C. M.

    2014-05-01

    We performed reactive meso-scale simulations of short-pulse experiments to study the influence of flyer velocity and pore structure on shock initiation of LX-10 (95wt% HMX, 5wt% Viton A). Our calculations show that the reaction evolution fit a power law relationship in time and increases with increasing porosity, decreasing pore size, and increasing flyer velocity. While heterogeneous shock initiation modes, dependent on hot spot mechanisms, are predicted at lower flyer velocities, mixed heterogeneous-homogeneous shock initiation modes, less dependent on hot spots, are predicted at higher velocities. These studies are important because they enable the development of predictive shock initiation models that incorporate complex microstructure and can be used to optimize performance-safety characteristics of explosives.

  10. Transcription initiation complex structures elucidate DNA opening.

    PubMed

    Plaschka, C; Hantsche, M; Dienemann, C; Burzinski, C; Plitzko, J; Cramer, P

    2016-05-19

    Transcription of eukaryotic protein-coding genes begins with assembly of the RNA polymerase (Pol) II initiation complex and promoter DNA opening. Here we report cryo-electron microscopy (cryo-EM) structures of yeast initiation complexes containing closed and open DNA at resolutions of 8.8 Å and 3.6 Å, respectively. DNA is positioned and retained over the Pol II cleft by a network of interactions between the TATA-box-binding protein TBP and transcription factors TFIIA, TFIIB, TFIIE, and TFIIF. DNA opening occurs around the tip of the Pol II clamp and the TFIIE 'extended winged helix' domain, and can occur in the absence of TFIIH. Loading of the DNA template strand into the active centre may be facilitated by movements of obstructing protein elements triggered by allosteric binding of the TFIIE 'E-ribbon' domain. The results suggest a unified model for transcription initiation with a key event, the trapping of open promoter DNA by extended protein-protein and protein-DNA contacts. PMID:27193681

  11. Implementation of STUD Pulses at the Trident Laser and Initial Results

    NASA Astrophysics Data System (ADS)

    Johnson, R. P.; Shimada, T.; Montgomery, D. S.; Afeyan, B.; Hüller, S.

    2012-10-01

    Controlling and mitigating laser-plasma instabilities such as stimulated Brillouin scattering, stimulated Raman scattering, and crossed-beam energy transfer is important to achieve high-gain inertial fusion using laser drivers. Recent theory and simulations show that these instabilities can be largely controlled using laser pulses consisting of spike trains of uneven duration and delay (STUD) by modulating the laser on a picosecond time scale [1,2]. We have designed and implemented a STUD pulse generator at the LANL Trident Laser Facility using Fourier synthesis to produce a 0.5-ns envelope of psec-duration STUD pulses using a spatial light modulator. Initial results from laser propagation tests and measurements as well as initial laser-plasma characterization experiments will be presented.[4pt] [1] B. Afeyan and S. H"uller, ``Optimal Control of Laser Plasma Instabilities using STUD pulses,'' IFSA 2011, P.Mo.1, to appear in Euro. Phys. J. Web of Conf. (2012).[2] S. H"uller and B. Afeyan, ``Simulations of drastically reduced SBS with STUD pulses,'' IFSA 2011, O.Tu8-1, to appear in Euro. Phys. J. Web of Conf. (2012).

  12. Receiver Function Study of the Peruvian Flat-Slab Region: Initial Results from PULSE

    NASA Astrophysics Data System (ADS)

    Bishop, B.; Beck, S. L.; Zandt, G.; Kumar, A.; Wagner, L. S.; Long, M. D.; Tavera, H.

    2013-12-01

    corresponding to locations of Miocene and Pleistocene to Holocene volcanics. The most prominent low velocity body occurs northeast of Lima under the Western Cordillera arc that shut off ~10 Ma presumably due to the onset of flat subduction. Deeper, we interpret a discontinuous P-to-S conversion at ~ 80 km as the Moho in the downgoing slab. South of the Nazca Ridge this correlates well with relocated intermediate depth earthquakes recorded by PULSE, and is similar to prior estimates of the slab depth based on global subduction zone models. North of the ridge, the slab Moho appears more discontinuous and 'broken' and potentially shallower than estimated in global models. We compare these initial findings with available studies of the structural geology and magmatism in the region and kinematic reconstructions of the subduction of the Nazca Ridge to better understand the nature of the interaction between the flat slab and the upper plate.

  13. Nanosecond Pulsed Discharge in Water without Bubbles: A Fundamental Study of Initiation, Propagation and Plasma Characteristics

    NASA Astrophysics Data System (ADS)

    Seepersad, Yohan

    The state of plasma is widely known as a gas-phase phenomenon, but plasma in liquids have also received significant attention over the last century. Generating plasma in liquids however is theoretically challenging, and this problem is often overcome via liquid-gas phase transition preceding the actual plasma formation. In this sense, plasma forms in gas bubbles in the liquid. Recent work at the Drexel Plasma Institute has shown that nanosecond pulsed electric fields can initiate plasma in liquids without any initial cavitation phase, at voltages below theoretical direct-ionization thresholds. This unique regime is poorly understood and does not fit into any current descriptive mechanisms. As with all new phenomena, a complete fundamental description is paramount to understanding its usefulness to practical applications. The primary goals of this research were to qualitatively and quantitatively understand the phenomenon of nanosecond pulsed discharge in liquids as a means to characterizing properties that may open up niche application possibilities. Analysis of the plasma was based on experimental results from non-invasive, sub-nanosecond time-resolved optical diagnostics, including direct imaging, transmission imaging (Schlieren and shadow), and optical emission spectroscopy. The physical characteristics of the plasma were studied as a function of variations in the electric field amplitude and polarity, liquid permittivity, and pulse duration. It was found that the plasma size and emission intensity was dependent on the permittivity of the liquid, as well as the voltage polarity, and the structure and dynamics were explained by a 'cold-lightning' mechanism. The under-breakdown dynamics at the liquid-electrode interface were investigated by transmission imaging to provide evidence for a novel mechanism for initiation based on the electrostriction. This mechanism was proposed by collaborators on the project and developed alongside the experimental work in this

  14. The potential for biological structure determination with pulsed neutrons

    SciTech Connect

    Wilson, C.C.

    1994-12-31

    The potential of pulsed neutron diffraction in structural determination of biological materials is discussed. The problems and potential solutions in this area are outlined, with reference to both current and future sources and instrumentation. The importance of developing instrumentation on pulsed sources in emphasized, with reference to the likelihood of future expansion in this area. The possibilities and limitations of single crystal, fiber and powder diffraction in this area are assessed.

  15. Radiative Characteristics of the Pulse-Periodic Discharge Plasma Initiated by Runaway Electrons

    NASA Astrophysics Data System (ADS)

    Lomaev, M. I.; Beloplotov, D. V.; Tarasenko, V. F.; Sorokin, D. A.

    2016-07-01

    Results of experimental investigations of amplitude-temporal and spectral characteristics of radiation of a pulse-periodic discharge plasma initiated in nitrogen by runaway electrons are presented. The discharge was initiated by high-voltage nanosecond voltage pulses with repetition frequency of 60 Hz in a sharply inhomogeneous electric field in a gap between the conic potential cathode and the planar grounded aluminum anode. It is established that intensive lines of Al I atoms and Al II atomic ions, lines of N I atoms and N II ions, bands of the first (1+) and second positive (2+) nitrogen systems, as well as bands of cyanogen CN are observed in the emission spectrum of the discharge plasma under the given excitation conditions.

  16. Optimization of single attosecond x-ray pulses by genetic algorithm control of the chirp and initial phase of 5 fs laser pulses

    SciTech Connect

    Xiao Jun; Sun Zhenrong; Zhang Xiangyun; Wang Yufeng; Zhang Weiping; Wang Zugeng; Li Ruxin; Xu Zhizhan

    2006-04-15

    We show that the peak intensity of single attosecond x-ray pulses is enhanced by 1 or 2 orders of magnitude, the pulse duration is greatly compressed, and the optimal propagation distance is shortened by genetic algorithm optimization of the chirp and initial phase of 5 fs laser pulses. However, as the laser intensity increases, more efficient nonadiabatic self-phase matching can lead to a dramatically enhanced harmonic yield, and the efficiency of optimization decreases in the enhancement and compression of the generated attosecond pulses.

  17. Fibonacci-like photonic structure for femtosecond pulse compression.

    PubMed

    Makarava, L N; Nazarov, M M; Ozheredov, I A; Shkurinov, A P; Smirnov, A G; Zhukovsky, S V

    2007-03-01

    The compression of femtosecond laser pulses by linear quasiperiodic and periodic photonic multilayer structures is studied both experimentally and theoretically. We compare the compression performance of a Fibonacci and a periodic structure with similar total thickness and the same number of layers, and find the performance to be higher in the Fibonacci case, as predicted by numerical simulation. This compression enhancement takes place due to the larger group velocity dispersion at a defect resonance of the transmission spectrum of the Fibonacci structure. We demonstrate that the Fibonacci structure with the thickness of only 2.8 microm can compress a phase-modulated laser pulse by up to 30%. The possibility for compression of laser pulses with different characteristics in a single multilayer is explored. The operation of the compressor in the reflection regime has been modeled, and we show numerically that the reflected laser pulse is subjected to real compression: not only does its duration decrease but also its amplitude rises. PMID:17500811

  18. The initial stage of surface modification of magnesium alloys by high intensity pulse ions beam

    NASA Astrophysics Data System (ADS)

    Li, P.; Liu, Z. H.; Zhang, Z. P.

    2016-06-01

    The initial stage of high intensity pulsed ion beam irradiated magnesium alloys was studied by MD simulation. Specimens containing Mg17Al12 precipitation were modeled to investigate the evolution of magnesium alloys during several picoseconds after a high-energy ion impacting. It was found that the Mg17Al12 precipitation has little effects on the kinetic energy evolution in the heat zone, but considerable effects on strength of kinetic energy peak moving to the deep matrix and on the surface morphology of the magnesium alloy at thermal equilibrium state. The thickness of the heat zone is independent on the temperature of surface region.

  19. Ultrashort pulse lasers for precise processing: overview on a current German research initiative

    NASA Astrophysics Data System (ADS)

    Nolte, S.

    2014-03-01

    Ultrashort laser pulses provide a powerful means of processing a wide variety of materials with highest precision and minimal damage. In order to exploit the full potential of this technology, the German Federal Ministry of Education and Research has launched an initiative with 20 Million EUR funding about two years ago. Within 9 joint research projects, different aspects from novel concepts for robust and powerful laser sources to reliable components with high damage thresholds and dynamic beam shaping and steering are investigated. Applications include eye surgery as well as the processing of semiconductors, carbon fiber reinforced plastics and metals. The paper provides an overview on the different projects and highlights first results.

  20. Health monitoring of operational structures: Initial results

    NASA Astrophysics Data System (ADS)

    James, G.; Mayes, R.; Carne, T.; Simmermacher, T.; Goodding, J.

    Two techniques for damage localization (structural translational and rotational error checking - STRECH, and matrix completion - MAXCON) are described and applied to operational structures. The structures include a horizontal axis wind turbine (HAWT) blade undergoing a fatigue test and a highway bridge undergoing an induced damage test. STRECH is seen to provide a global damage indicator to assess the global damage state of a structure. STRECH is also seen to provide damage localization for static flexibility shapes or the first mode of simple structures. MAXCON is a robust damage localization tool using the higher order dynamics of a structure. Several options arc available to allow the procedure to be tailored to a variety of structures.

  1. Health monitoring of operational structures -- Initial results

    SciTech Connect

    James, G.; Mayes, R.; Carne, T.; Simmermacher, T.; Goodding, J.

    1995-03-01

    Two techniques for damage localization (Structural Translational and Rotational Error Checking -- STRECH and MAtriX COmpletioN -- MAXCON) are described and applied to operational structures. The structures include a Horizontal Axis Wind Turbine (HAWT) blade undergoing a fatigue test and a highway bridge undergoing an induced damage test. STRECH is seen to provide a global damage indicator to assess the global damage state of a structure. STRECH is also seen to provide damage localization for static flexibility shapes or the first mode of simple structures. MAXCON is a robust damage localization tool using the higher order dynamics of a structure. Several options arc available to allow the procedure to be tailored to a variety of structures.

  2. A Search for Structure in Gamma Ray Burst X-ray Flares Confirming Whether They Are Similar To The Three Pulse Structure Found In Propt Emission Pulses

    NASA Astrophysics Data System (ADS)

    Baron, Jason; Racusin, Judith L.; Morris, David C.

    2016-01-01

    Gamma Ray Bursts (GRBs) are the the most luminous electromagnetic events known to occur throughout the Universe. These violent explosions produce relativistic jets in a short burst of prompt emission and are followed by an afterglow emitted across the electromagnetic spectrum. During the afterglow, there are periods of sporadic increase in the X-ray flux, known as flares. Only ~1/2 of all GRBs produce flares. We present a sample selection of the brightest isolated flares observed by the Swift X-Ray Telescope (XRT). Using light curves from the XRT Team repository at the University of Leicester between 2005 and 2014, and our own light curve fits, the sample was filtered using a stringent set of criteria. We selected bursts that: 1) had a high peak flare flux to afterglow ratio, and/or 2) a high fluence (integrated flux). By further analyzing these flares, we will study the structure of flares, searching for the three components that have been seen in isolated prompt emission pulses: an initial small rapidly decaying pulse, followed by the main flare which then decays over time and is followed by another small but slower decaying pulse. Seeing a similar behavior in X-ray flares as we see in prompt pulses will inform models for the physics of relativistic shocks.

  3. Ignition and Growth Modeling of Short Pulse Duration Shock Initiation Experiments on HNS IV

    NASA Astrophysics Data System (ADS)

    Tarver, Craig; Chidester, Steven

    2013-06-01

    Short pulse duration shock initiation experiments on 1.60 g/cm3 density (92% TMD) HNS IV have been reported by Schwarz, Bowden et al., Dudley et al., Goveas et al., Greenaway et al., and others. This flyer threshold velocity for detonation/failure data plus measured unreacted HNS Hugoniot data and detonation cylinder test product expansion data were used as the experimental basis for the development of an Ignition and Growth reactive flow model for the shock initiation of HNS IV. The resulting Ignition and Growth HNS IV model parameters yielded good overall agreement with all of this experimental data. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.: Explosive, HNS IV, shock to detonation transition, Ignition and Growth: 82.33.Vx, 82.40.Fp.

  4. Initial carrier-envelope phase of few-cycle pulses determined by terahertz emission from air plasma

    NASA Astrophysics Data System (ADS)

    Xu, Rongjie; Bai, Ya; Song, Liwei; Liu, Peng; Li, Ruxin; Xu, Zhizhan

    2013-08-01

    The evolution of THz waveform generated in air plasma provides a sensitive probe to the variation of the carrier envelope phase (CEP) of propagating intense few-cycle pulses. Our experimental observation and calculation reveal that the number and positions of the inversion of THz waveform are dependent on the initial CEP, which is near 0.5π constantly under varied input pulse energies when two inversions of THz waveform in air plasma become one. This provides a method of measuring the initial CEP in an accuracy that is only limited by the stability of the driving few-cycle pulses.

  5. Scattering pulse of label free fine structure cells to determine the size scale of scattering structures

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Chen, Xingyu; Zhang, Zhenxi; Chen, Wei; Zhao, Hong; Zhao, Xin; Li, Kaixing; Yuan, Li

    2016-04-01

    Scattering pulse is sensitive to the morphology and components of each single label-free cell. The most direct detection result, label free cell's scattering pulse is studied in this paper as a novel trait to recognize large malignant cells from small normal cells. A set of intrinsic scattering pulse calculation method is figured out, which combines both hydraulic focusing theory and small particle's scattering principle. Based on the scattering detection angle ranges of widely used flow cytometry, the scattering pulses formed by cell scattering energy in forward scattering angle 2°-5° and side scattering angle 80°-110° are discussed. Combining the analysis of cell's illuminating light energy, the peak, area, and full width at half maximum (FWHM) of label free cells' scattering pulses for fine structure cells with diameter 1-20 μm are studied to extract the interrelations of scattering pulse's features and cell's morphology. The theoretical and experimental results show that cell's diameter and FWHM of its scattering pulse agree with approximate linear distribution; the peak and area of scattering pulse do not always increase with cell's diameter becoming larger, but when cell's diameter is less than about 16 μm the monotone increasing relation of scattering pulse peak or area with cell's diameter can be obtained. This relationship between the features of scattering pulse and cell's size is potentially a useful but very simple criterion to distinguishing malignant and normal cells by their sizes and morphologies in label free cells clinical examinations.

  6. Nanosecond pulsed laser generation of holographic structures on metals

    NASA Astrophysics Data System (ADS)

    Wlodarczyk, Krystian L.; Ardron, Marcus; Weston, Nick J.; Hand, Duncan P.

    2016-03-01

    A laser-based process for the generation of phase holographic structures directly onto the surface of metals is presented. This process uses 35ns long laser pulses of wavelength 355nm to generate optically-smooth surface deformations on a metal. The laser-induced surface deformations (LISDs) are produced by either localized laser melting or the combination of melting and evaporation. The geometry (shape and dimension) of the LISDs depends on the laser processing parameters, in particular the pulse energy, as well as on the chemical composition of a metal. In this paper, we explain the mechanism of the LISDs formation on various metals, such as stainless steel, pure nickel and nickel-chromium Inconel® alloys. In addition, we provide information about the design and fabrication process of the phase holographic structures and demonstrate their use as robust markings for the identification and traceability of high value metal goods.

  7. Effect of initial phase on error in electron energy obtained using paraxial approximation for a focused laser pulse in vacuum

    SciTech Connect

    Singh, Kunwar Pal; Arya, Rashmi; Malik, Anil K.

    2015-09-14

    We have investigated the effect of initial phase on error in electron energy obtained using paraxial approximation to study electron acceleration by a focused laser pulse in vacuum using a three dimensional test-particle simulation code. The error is obtained by comparing the energy of the electron for paraxial approximation and seventh-order correction description of the fields of Gaussian laser. The paraxial approximation predicts wrong laser divergence and wrong electron escape time from the pulse which leads to prediction of higher energy. The error shows strong phase dependence for the electrons lying along the axis of the laser for linearly polarized laser pulse. The relative error may be significant for some specific values of initial phase even at moderate values of laser spot sizes. The error does not show initial phase dependence for a circularly laser pulse.

  8. Pulse

    MedlinePlus

    Heart rate; Heart beat ... The pulse can be measured at areas where an artery passes close to the skin. These areas include the: ... side of the foot Wrist To measure the pulse at the wrist, place the index and middle ...

  9. Experimental investigation of jet pulse control on flexible vibrating structures

    NASA Astrophysics Data System (ADS)

    Karaiskos, Grigorios; Papanicolaou, Panos; Zacharopoulos, Dimitrios

    2016-08-01

    The feasibility of applying on-line fluid jet pulses to actively control the vibrations of flexible structures subjected to harmonic and earthquake-like base excitations provided by a shake table is explored. The operating principles and capabilities of the control system applied have been investigated in a simplified small-scale laboratory model that is a mass attached at the top free end of a vertical flexible slender beam with rectangular cross-section, the other end of which is mounted on an electrodynamic shaker. A pair of opposite jets placed on the mass at the top of the cantilever beam applied the appropriate forces by ejecting pressurized air pulses controlled by on/off solenoid electro-valves via in house developed control software, in order to control the vibration caused by harmonic, periodic and random excitations at pre-selected frequency content provided by the shaker. The dynamics of the structure was monitored by accelerometers and the jet impulses by pressure sensors. The experimental results have demonstrated the effectiveness and reliability of Jet Pulse Control Systems (JPCS). It was verified that the measured root mean square (RMS) vibration levels of the controlled structure from harmonic and earthquake base excitations, could be reduced by approximately 50% and 33% respectively.

  10. Effect of powerful pulsed and continuous ion beams on the Al- Cu-Mg alloy structure

    NASA Astrophysics Data System (ADS)

    Gushchina, N. V.; Makhin'ko, F. F.; Ovchinnikov, V. V.; Gusel'nikov, V. I.; Remnev, G. E.

    2016-02-01

    The paper considers the results of an electron microscopy study of the VD1 alloy of the Al-Cu-Mg system after cold working and subsequent irradiation with a powerful pulsed ion beam (70% C+ + 30% H+, E = 180 keV) in the pulsed-periodic mode (t = 80 ns, f = 0.1 Hz, j = 200 A/cm2, F = 1-1014 cm-2) and under the conditions of the generation of only one pulse (t = 180 ns, j = 100 A/cm2, F = 2-1015 cm-2). It is established that this irradiation noticeably affects the microstructure of the cold-worked 3 mm thick sheets of VD1 alloy. The initial cellular dislocation structure transforms into a subgrain one. The intensity of structural transformations in the alloy increases with ion current density of a pulse. A similar transformation of a dislocation structure over the entire thickness of the sample is observed under irradiation with continuous Ar+ ion beams (E = 20-40 keV) with not high fluences (1015-1016 cm-2).

  11. Investigation of honeycomb structure using pulse infrared thermography method

    NASA Astrophysics Data System (ADS)

    Li, Huijuan

    2010-11-01

    To reduce weight and improve strength in the aerospace industry, composite structure has gained popularity as a replacement for conventional materials and structures, such as adhesive bonding and honeycomb structure. Honeycomb structures composed by a honeycomb core between two facesheets are very common on aerospace parts. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining methods. With the large increase in the use of composite materials and honeycomb structures, the need for high speed, large area inspection for fracture critical, sub-surface defects in aircraft, missiles and marine composites led to broad acceptance of infrared based NDT methods. Infrared thermography is one of several non-destructive testing techniques which can be used for defect detection in aircraft materials. Infrared thermography can be potentially useful, as it is quick, real time, non-contact and can examine over a relatively large area in one inspection procedure. In this paper, two kinds of defects which are of various size, shape and location below the test surface are planted in the honeycomb structure, they are all tested by pulsed thermography, analyze the thermal sequence and intensity graph got by this methods, it shows that pulsed thermography is an effective nondestructive technique for inspecting disbonding defect, can distinguish the location and the dimension of the defect exactly.

  12. Dispersion, damping and confinement of propagating pulses in large space structures

    NASA Technical Reports Server (NTRS)

    Zak, Michail

    1988-01-01

    Pulse propagations in large space structures caused by repeated pulse excitations are studied analytically (by using the Z-transforms) and numerically. It is found that resonance regimes can be generated not only by periodical, but also by non-periodical repeated pulses; the conditions for such regimes are derived. Special attention is paid to the dispersion of propagating pulses due to structural irregularities, to damping of pulses due to appropriate combination of elastic and viscous properties of joints between structural members, and to the protection of certain areas of Large Space Structures (LSS) from impacts provided by a pulse trapping effect.

  13. Magnetic structures of actinide materials by pulsed neutron diffraction

    SciTech Connect

    Lawson, A.C.; Goldstone, J.A.; Huber, J.G.; Giorgi, A.L.; Conant, J.W.; Severing, A.; Cort, B.; Robinson, R.A.

    1990-01-01

    We describe some attempts to observe magnetic structure in various actinide (5f-electron) materials. Our experimental technique is neutron powder diffraction as practiced at a spallation (pulsed) neutron source. We will discuss our investigations of {alpha}-Pu, {delta}-Pu, {alpha}-UD{sub 3} and {beta}-UD{sub 3}. {beta}-UD{sub 3} is a simple ferromagnet: surprisingly, the moments on the two non-equivalent uranium atoms are the same within experimental error. {alpha}-UD{sub 3}, {alpha}-Pu and {delta}-Pu are non-magnetic, within the limits of our observations. Our work with pulsed neutron diffraction shows that it is a useful technique for research on magnetic materials.

  14. Structure of Microgravity Transitional and Pulsed Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Bahadori, M. Yousef; Hegde, Uday; Stocker, Dennis P.

    1997-01-01

    This paper describes results obtained in a study of pulsed gas jet diffusion flames to better characterize the recently observed vortex/flame interactions in microgravity transitional and turbulent diffusion flames, and to improve the understanding of large-scale structures in corresponding normal-gravity flames. In preparation for a space experiment, tests were conducted in the 5.18-Second Zero-Gravity Facility of the NASA Lewis Research Center. Both unpulsed and pulsed laminar flames were studied and numerical modeling of these flames was carried out for data comparison and model validation. In addition, complementary tests for a series of unpulsed flames were conducted on-board the NASA KC-135 research aircraft. The microgravity transitional and turbulent gas-jet diffusion flames have been observed to be dominated by large-scale disturbances, or structures. These structures first appear intermittently in the flame at Reynolds numbers (based on the cold jet injection properties) of about 2100. With increase in injection Reynolds number, the rate of intermittent disturbances increases until the generation becomes continuous at Reynolds numbers of 3000 and higher. The behavior of these structures depends upon the velocity and temperature characteristics of the jet/flame shear layer. These characteristics are different in normal gravity and microgravity.

  15. Generation of Rydberg states of hydrogen atoms with intense laser pulses: The roles of Coulomb force and initial lateral momentum

    NASA Astrophysics Data System (ADS)

    Zhang, Bin; Chen, Wenbo; Zhao, Zengxiu

    2014-08-01

    We investigate the generation of Rydberg states of hydrogen atoms with intense laser pulses by solving the time-dependent Schrödinger equation and by means of classical-trajectory Monte Carlo simulations. Both linearly polarized multicycle pulses and pairs of optical half-cycle pulses are used. Comparisons between these methods show that both the Coulomb force and initial lateral momentum, which have effects on the n distribution and l distribution of the population of excited states, are important in the generation of Rydberg states.

  16. Surface mico-structures on amorphous alloys induced by vortex femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ran, Ling-Ling; Qu, Shi-Liang; Guo, Zhong-Yi

    2010-03-01

    This paper investigates the generation of self-organized surface structures on amorphous alloys by vortex femtosecond laser pulses. The scanning electron microscope characterizations show that the as-formed structures are periodic ripples, aperiodic ripples, and 'coral-like' structures. Optimal conditions for forming these surface structures are determined in terms of pulses number at a given pulse energy. The applicable mechanism is suggested to interpret the formation and evolution of the 'coral-like' structures.

  17. Compressive strength evaluation of structural lightweight concrete by non-destructive ultrasonic pulse velocity method.

    PubMed

    Bogas, J Alexandre; Gomes, M Glória; Gomes, Augusto

    2013-07-01

    In this paper the compressive strength of a wide range of structural lightweight aggregate concrete mixes is evaluated by the non-destructive ultrasonic pulse velocity method. This study involves about 84 different compositions tested between 3 and 180 days for compressive strengths ranging from about 30 to 80 MPa. The influence of several factors on the relation between the ultrasonic pulse velocity and compressive strength is examined. These factors include the cement type and content, amount of water, type of admixture, initial wetting conditions, type and volume of aggregate and the partial replacement of normal weight coarse and fine aggregates by lightweight aggregates. It is found that lightweight and normal weight concretes are affected differently by mix design parameters. In addition, the prediction of the concrete's compressive strength by means of the non-destructive ultrasonic pulse velocity test is studied. Based on the dependence of the ultrasonic pulse velocity on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless the type of concrete and its composition. More than 200 results for different types of aggregates and concrete compositions were analyzed and high correlation coefficients were obtained. PMID:23351273

  18. Pulse swallowing frequency divider with low power and compact structure

    NASA Astrophysics Data System (ADS)

    Haijun, Gao; Lingling, Sun; Chaobo, Cai; Haiting, Zhan

    2012-11-01

    A pulse swallowing frequency divider with low power and compact structure is presented. One of the DFFs in the divided by 2/3 prescaler is controlled by the modulus control signal, and automatically powered off when it has no contribution to the operation of the prescaler. The DFFs in the program counter and the swallow counter are shared to compose a compact structure, which reduces the power consumption further. The proposed multi-modulus frequency divider was implemented in a standard 65 nm CMOS process with an area of 28 × 22 μm2. The power consumption of the divider is 0.6 mW under 1.2 V supply voltage when operating at 988 MHz.

  19. Ultra-short Pulse Laser Structuring of Molding Tools

    NASA Astrophysics Data System (ADS)

    Conrad, Daniel; Richter, Lars

    The machining of highly filled abrasive polymer plastics in injection molding processes determines high resistant tools in the industrial production. One of the most important points is a long durability of the molding tools to reduce the costs of production. Thus, the adhesion force and abrasion will be reduced with the help of defined surface properties. To achieve appropriate surface conditions, an ultra-short pulse laser is used for a micro structuring. Additional a laser polishing of the micro-structured surfaces to optimize the frictional properties is presented. This paper shows the research results of investigations on the laser modification of steel surfaces, to generate high-quality and wear-resistant surfaces for injection molding tools.

  20. Pulse

    MedlinePlus

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... rate gives information about your fitness level and health.

  1. Monitoring of concrete structures using the ultrasonic pulse velocity method

    NASA Astrophysics Data System (ADS)

    Karaiskos, G.; Deraemaeker, A.; Aggelis, D. G.; Van Hemelrijck, D.

    2015-11-01

    Concrete is the material most produced by humanity. Its popularity is mainly based on its low production cost and great structural design flexibility. Its operational and ambient loadings including environmental effects have a great impact in the performance and overall cost of concrete structures. Thus, the quality control, the structural assessment, the maintenance and the reliable prolongation of the operational service life of the existing concrete structures have become a major issue. In the recent years, non-destructive testing (NDT) is becoming increasingly essential for reliable and affordable quality control and integrity assessment not only during the construction of new concrete structures, but also for the existing ones. Choosing the right inspection technique is always followed by a compromise between its performance and cost. In the present paper, the ultrasonic pulse velocity (UPV) method, which is the most well known and widely accepted ultrasonic concrete NDT method, is thoroughly reviewed and compared with other well-established NDT approaches. Their principles, inherent limitations and reliability are reviewed. In addition, while the majority of the current UPV techniques are based on the use of piezoelectric transducers held on the surface of the concrete, special attention is paid to a very promising technique using low-cost and aggregate-size piezoelectric transducers embedded in the material. That technique has been evaluated based on a series of parameters, such as the ease of use, cost, reliability and performance.

  2. Control structure interactions in large space structures Analysis using energy approach. [for constant and pulsed thrusters

    NASA Technical Reports Server (NTRS)

    Shrivastava, S. K.; Ried, R. C.; Manoharan, M. G.

    1983-01-01

    A simple energy approach to study the problem of control structure interactions in large space structures is presented. For the illustrative cases of free-free beam and free rectangular plate, the vibrational energy imparted during operation of constant and pulsed thrusters is found in a nondimensional form. Then based on a parametric study, suggestions are made on the choice of the thruster location and parameters to minimize the control structure interactions.

  3. Dying Pulse Trains in Cygnus XR-1: Initial Results of X-Ray Searches

    NASA Technical Reports Server (NTRS)

    Dolan, Joseph F.

    2003-01-01

    Dying pulse trains (DPT's) are a signature of a black hole as described by general relativity. Detecting DPT's would establish the existence of black holes by ruling out more exotic objects in systems in which a neutron star or white dwarf component has already been excluded by maximum mass arguments. The positive identification of a black hole would also be an additional test of general relativity. Two possible DPT's were detected in W photometry of Cygnus XR-1, the leading candidate for a stellar mass sized BH, in 3 hours of observational data. A search of X-ray photometry of Cygnus XR-1 from the Ross1 X-ray Timing Explorer (RXTE) has begun. No DPT's have been detected in the first 4 hours of data searched. Because of the low event rate detected in the W data, these initial results are consistent with such disparate scenarios as the rate of DPT occurrence being dependent on the luminosity state of the system; or being more difficult to detect in the X-ray region relative to the W region; or occurring at the same rate in the W and X-ray regions; or even not occurring at all from Cygnus XR-1. The search for DPT's in RXTE photometry is continuing.

  4. The structure and photoconductivity of SiGe/Si epitaxial layers modified by single-pulse laser radiation

    NASA Astrophysics Data System (ADS)

    Ivlev, G. D.; Kazuchits, N. M.; Prakopyeu, S. L.; Rusetsky, M. S.; Gaiduk, P. I.

    2014-12-01

    The effect of nanosecond pulses of ruby laser radiation on the structural state and morphology of the epitaxial layers of a SiO0.5Ge0.5 solid solution on silicon with the initiation of a crystal-melt phase transition has been studied by electron microscopy. Data on the photoelectric parameters of the laser-modified layers having a cellular structure owing to the segregation of germanium during the solidification of the binary melt have been derived.

  5. Spatial structure of the arc in a pulsed GMAW process

    NASA Astrophysics Data System (ADS)

    Kozakov, R.; Gött, G.; Schöpp, H.; Uhrlandt, D.; Schnick, M.; Häßler, M.; Füssel, U.; Rose, S.

    2013-06-01

    A pulsed gas metal arc welding (GMAW) process of steel under argon shielding gas in the globular mode is investigated by measurements and simulation. The analysis is focussed on the spatial structure of the arc during the current pulse. Therefore, the radial profiles of the temperature, the metal vapour species and the electric conductivity are determined at different heights above the workpiece by optical emission spectroscopy (OES). It is shown that under the presence of metal vapour the temperature minimum occurs at the centre of the arc. This minimum is preserved at different axial positions up to 1 mm above the workpiece. In addition, estimations of the electric field in the arc from the measurements are given. All these results are compared with magneto-hydrodynamic simulations which include the evaporation of the wire material and the change of the plasma properties due to the metal vapour admixture in particular. The experimental method and the simulation model are validated by means of the satisfactory correspondence between the results. Possible reasons for the remaining deviations and improvements of the methods which should be aspired are discussed.

  6. Pulsed phase thermography for defect detection of honeycomb structure

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Feng, Lichun; Li, Yanhong; Zhang, Cunlin

    2009-07-01

    Pulse Phase Thermography (PPT) has been reported as a powerful technique of the thermal NDE. In this paper, the authors show that the original phase-images of two kinds of honeycomb structure defects by PPT based on Fast Fourier Transform (FFT) for the signal of temperature-time of each pixel. One is the artificial defects in honeycomb structure core under surface skin, and the defects can be identified easily. The other is disbonding defect between surface skin and core, and the difference is apparent compared with bonding and no-bonding between surface skin and core. To improve the signal to noise ratio for defect inspection of honeycomb structure, the temperature decay curve of each pixel is smoothed by moving average filter and then fitted by exponential function. After FFT on the fitted data of temperature, the fitted phase-images of two kinds of honeycomb structure defects are given. Compared with the original thermal-images of PT and original phase-images, the calculated phase-images are much more improved. Another advantage is the data could be represented by coefficients of fitting functions, and the storage of data could be greatly reduced. At last, the calculation process of temperature decay curve and analysis of the influence caused by increasing sampling time and frequency are given.

  7. Initial Results From The Micro-pulse Lidar Network (MPL-Net)

    NASA Astrophysics Data System (ADS)

    Welton, E. J.; Campbell, J. R.; Berkoff, T. A.; Spinhirne, J. D.; Ginoux, P.

    2001-12-01

    The micro-pulse lidar system (MPL) was developed in the early 1990s and was the first small, eye-safe, and autonomous lidar built for fulltime monitoring of cloud and aerosol vertical distributions. In 2000, a new project using MPL systems was started at NASA Goddard Space Flight Center. This new project, the Micro-pulse Lidar Network or MPL-Net, was created to provide long-term observations of aerosol and cloud vertical profiles at key sites around the world. This is accomplished using both NASA operated sites and partnerships with other organizations owning MPL systems. The MPL-Net sites are co-located with NASA AERONET sunphotometers to provide aerosol optical depth data needed for calibration of the MPL. In addition to the long-term sites, MPL-Net provides lidar support for a limited number of field experiments and ocean cruises each year. We will present an overview of the MPL-Net project and show initial results from the first two MPL-Net sites at the South Pole and at Goddard Space Flight Center. Observations of dust layers transported from the desert regions of China, across the Pacific Ocean, to the east coast of the United States will also be shown. MPL-Net affiliated instruments were in place at the desert source region in China, on a research vessel in the Sea of Japan, at ARM sites in Alaska and Oklahoma, and finally at our home site in Maryland (GSFC) during the massive dust storms that occurred in April 2001. The MPL observations of dust layers at each location are shown in comparison to dust layers predicted using the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport model (GOCART). Finally, the MPL-Net project is the primary ground-validation program for the Geo-Science Laser Altimeter System (GLAS) satellite lidar project (launch date 2002). We will present an overview demonstrating how MPL-Net results are used to help prepare the GLAS data processing algorithms and assist in the calibration/validation of the GLAS data

  8. Initial Results from the Micro-pulse Lidar Network (MPL-Net)

    NASA Technical Reports Server (NTRS)

    Welton, Ellsworth J.; Campbell, James R.; Berkoff, Timothy A.; Spinhirne, James D.; Ginoux, Paul; Starr, David OC. (Technical Monitor)

    2001-01-01

    The micro-pulse lidar system (MPL) was developed in the early 1990s and was the first small, eye-safe, and autonomous lidar built for full time monitoring of cloud and aerosol vertical distributions. In 2000, a new project using MPL systems was started at NASA Goddard Space Flight Center. This new project, the Micro-pulse Lidar Network or MPL-Net, was created to provide long-term observations of aerosol and cloud vertical profiles at key sites around the world. This is accomplished using both NASA operated sites and partnerships with other organizations owning MPL systems. The MPL-Net sites are co-located with NASA AERONET sunphotometers to provide aerosol optical depth data needed for calibration of the MPL. In addition to the long-term sites, MPL-Net provides lidar support for a limited number of field experiments and ocean cruises each year. We will present an overview of the MPL-Net project and show initial results from the first two MPL-Net sites at the South Pole and at Goddard Space Flight Center. Observations of dust layers transported from the Gobi desert, across the Pacific Ocean, to the east coast of the United States will also be shown. MPL-Net affiliated instruments were in place at the desert source region in China, on a research vessel in the Sea of Japan, at ARM sites in Alaska and Oklahoma, and finally at our home site in Maryland (GSFC) during the massive dust storms that occurred in April 2001. The MPL observations of dust layers at each location are shown in comparison to dust layers predicted using the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport model (GOCART). Finally, the MPL-Net project is the primary ground-validation program for the Geo-Science Laser Altimeter System (GLAS) satellite lidar project (launch date 2002). We will present an overview demonstrating how MPL-Net results are used to help prepare the GLAS data processing algorithms and assist in the calibration/validation of the GLAS data products.

  9. Spectral evolution of pulse structures in gamma-ray bursts

    NASA Technical Reports Server (NTRS)

    Norris, J. P.; Share, G. H.; Messina, D. C.; Dennis, B. R.; Desai, U. D.; Cline, T. L.

    1986-01-01

    The Hard X-Ray Burst Spectrometer (HXRBS) and Gamma-Ray Spectrometer (GRS) data from the Solar Maximum Mission satellite have been searched for gamma-ray bursts with sufficient intensities and relatively simple time profiles such that their spectral behavior may be studied on a time scale of about 1 s. Ten such events were observed with the GRS experiment, and four of these were also detected within the HXRBS field of view. Details are presented for two moderately intense bursts with relatively simple structure. The spectral evolutions of the remaining events are summarized briefly. Results suggest a pattern in the spectral evolution within burst pulses: a tendency for the high-energy emission to lead the low-energy emission, in contrast to the correlation of intensity and spectral hardness reported by Golenetskii et al. (1983).

  10. Characterization of multiple twinned structural units in pulse-electrodeposited nickel

    NASA Astrophysics Data System (ADS)

    Klement, U.; Kahrimanidis, A.; Yao, Y.

    2015-04-01

    The investigation was performed on pulse-electrodeposited Nickel with submicrocrystalline microstructure containing slightly elongated grains having a <110> fibre texture in growth direction. Structural units in form of groups of elongated grains possessing a common <110>-zone axis in growth direction and CSL boundaries (in some cases twins) between them have been found in the microstructure by use of EBSD. Grain growth sets in above 325°C but the texture is conserved up to at least 600°C. This means that the arrangement of twins and other CSL boundaries stabilized the structural units; there is no orientation change (by further twinning) when grain growth occurs as seen in previous studies on Ni and Ni-Fe of different initial texture. The observed structural units were characterized in detail and the occurring grains and grain boundaries are described.

  11. The impact of structure dimensions on initial bacterial adhesion.

    PubMed

    Helbig, Ralf; Günther, Denise; Friedrichs, Jens; Rößler, Florian; Lasagni, Andrés; Werner, Carsten

    2016-07-21

    Substrate topography can have profound effects on initial bacterial adhesion during biofilm formation. We applied Staphylococcus epidermidis and Escherichia coli cells onto periodically structured substrates with different structure dimensions, structure types and wetting properties. We found a strong dependence of cell retention on the structure dimensions of the applied substrates. Periodicities in the range of the cell size increased, whereas smaller periodicities decreased cell retention, independent of contact time (minutes to hours) and hydrophobicity. These novel insights on the role of surface topography on bacterial retention might facilitate the development of non-fouling surfaces in the future. PMID:27232637

  12. Sensitivity of a Wave Structure to Initial Conditions

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.; Duval, Walter M. B. (Technical Monitor)

    2000-01-01

    Microgravity experiments aimed at quantifying effects of gentler via controlled sinusoidal forcing transmitted on the interface between two miscible liquids have shown the evolution of a quasi -stationary four-mode wave structure oriented vertically. The sensitivity of the wave structure to phase angle variation is investigated computationally. We show that a slight variation of the phase angle is sufficient to cause a bifurcation to a two-mode structure. The dependence of phase angle on wave structure is attributed to sensitivity on initial conditions due to the strong nonlinearity of the coupled field equations for the parametric space of interest.

  13. Saturable inductor and transformer structures for magnetic pulse compression

    DOEpatents

    Birx, Daniel L.; Reginato, Louis L.

    1990-01-01

    Saturable inductor and transformer for magnetic compression of an electronic pulse, using a continuous electrical conductor looped several times around a tightly packed core of saturable inductor material.

  14. Sub-diffraction limited structuring of solid targets with femtosecond laser pulses.

    PubMed

    Korte, F; Adams, S; Egbert, A; Fallnich, C; Ostendorf, A; Nolte, S; Will, M; Ruske, J P; Chichkov, B; Tuennermann, A

    2000-07-17

    Possibilities to produce sub-diffraction limited structures in thin metal films and bulk dielectric materials using femtosecond laser pulses are investigated. The physics of ultrashort pulse laser ablation of solids is outlined. Results on the fabrication of sub-micrometer structures in 100-200 nm chrome-coated surfaces by direct ablative writing are reported. Polarization maintaining optical waveguides produced by femtosecond laser pulses inside crystalline quartz are demonstrated. PMID:19404368

  15. INITIAL EVALUATION OF A PULSED WHITE SPECTRUM NEUTRON GENERATOR FOR EXPLOSIVE DETECTION

    SciTech Connect

    King, Michael J.; Miller, Gill T.; Reijonen, Jani; Ji, Qing; Andresen, Nord; Gicquel,, Frederic; Kavlas, Taneli; Leung, Ka-Ngo; Kwan, Joe

    2008-06-02

    Successful explosive material detection in luggage and similar sized containers is acritical issue in securing the safety of all airline passengers. Tensor Technology Inc. has recently developed a methodology that will detect explosive compounds with pulsed fast neutron transmission spectroscopy. In this scheme, tritium beams will be used to generate neutrons with a broad energy spectrum as governed by the T(t,2n)4He fission reaction that produces 0-9 MeV neutrons. Lawrence Berkeley National Laboratory (LBNL), in collaboration with Tensor Technology Inc., has designedand fabricated a pulsed white-spectrum neutron source for this application. The specifications of the neutron source are demanding and stringent due to the requirements of high yield and fast pulsing neutron emission, and sealed tube, tritium operation. In a unique co-axial geometry, the ion source uses ten parallel rf induction antennas to externally couple power into a toroidal discharge chamber. There are 20 ion beam extraction slits and 3 concentric electrode rings to shape and accelerate the ion beam into a titanium cone target. Fast neutron pulses are created by using a set ofparallel-plate deflectors switching between +-1500 volts and deflecting the ion beams across a narrow slit. The generator is expected to achieve 5 ns neutron pulses at tritium ion beam energies between 80 - 120 kV. First experiments demonstrated ion source operation and successful beam pulsing.

  16. Open Access Initiatives in Africa--Structure, Incentives and Disincentives

    ERIC Educational Resources Information Center

    Nwagwu, Williams E.

    2013-01-01

    Building open access in Africa is imperative not only for African scholars and researchers doing scientific research but also for the expansion of the global science and technology knowledgebase. This paper examines the structure of homegrown initiatives, and observes very low level of awareness prevailing in the higher educational institutions…

  17. Multiple attractors in stage-structured population models with birth pulses.

    PubMed

    Tang, Sanyi; Chen, Lansun

    2003-05-01

    In most models of population dynamics, increases in population due to birth are assumed to be time-independent, but many species reproduce only during a single period of the year. A single species stage-structured model with density-dependent maturation rate and birth pulse is formulated. Using the discrete dynamical system determined by its Poincaré map, we report a detailed study of the various dynamics, including (a) existence and stability of nonnegative equilibria, (b) nonunique dynamics, meaning that several attractors coexist, (c) basins of attraction (defined as the set of the initial conditions leading to a certain type of attractor), (d) supertransients, and (e) chaotic attractors. The occurrence of these complex dynamic behaviour is related to the fact that minor changes in parameter or initial values can strikingly change the dynamic behaviours of system. Further, it is shown that periodic birth pulse, in effect, provides a natural period or cyclicity that allows multiple oscillatory solutions in the continuous dynamical systems. PMID:12749535

  18. Generation and structure of extremely large clusters in pulsed jets.

    PubMed

    Rupp, Daniela; Adolph, Marcus; Flückiger, Leonie; Gorkhover, Tais; Müller, Jan Philippe; Müller, Maria; Sauppe, Mario; Wolter, David; Schorb, Sebastian; Treusch, Rolf; Bostedt, Christoph; Möller, Thomas

    2014-07-28

    Extremely large xenon clusters with sizes exceeding the predictions of the Hagena scaling law by several orders of magnitude are shown to be produced in pulsed gas jets. The cluster sizes are determined using single-shot single-particle imaging experiments with short-wavelength light pulses from the free-electron laser in Hamburg (FLASH). Scanning the time delay between the pulsed cluster source and the intense femtosecond x-ray pulses first shows a main plateau with size distributions in line with the scaling laws, which is followed by an after-pulse of giant clusters. For the extremely large clusters with radii of several hundred nanometers the x-ray scattering patterns indicate a grainy substructure of the particles, suggesting that they grow by cluster coagulation. PMID:25084909

  19. Generation and structure of extremely large clusters in pulsed jets

    SciTech Connect

    Rupp, Daniela Adolph, Marcus; Flückiger, Leonie; Müller, Jan Philippe; Müller, Maria; Sauppe, Mario; Wolter, David; Möller, Thomas; Gorkhover, Tais; Schorb, Sebastian; Treusch, Rolf; Bostedt, Christoph

    2014-07-28

    Extremely large xenon clusters with sizes exceeding the predictions of the Hagena scaling law by several orders of magnitude are shown to be produced in pulsed gas jets. The cluster sizes are determined using single-shot single-particle imaging experiments with short-wavelength light pulses from the free-electron laser in Hamburg (FLASH). Scanning the time delay between the pulsed cluster source and the intense femtosecond x-ray pulses first shows a main plateau with size distributions in line with the scaling laws, which is followed by an after-pulse of giant clusters. For the extremely large clusters with radii of several hundred nanometers the x-ray scattering patterns indicate a grainy substructure of the particles, suggesting that they grow by cluster coagulation.

  20. Narrow bipolar pulse locations compared to thunderstorm radar echo structure

    NASA Astrophysics Data System (ADS)

    Karunarathna, Nadeeka; Marshall, Thomas C.; Stolzenburg, Maribeth; Karunarathne, Sumedhe

    2015-11-01

    The locations of 172 positive narrow bipolar pulses (NBPs) found on one day in Florida are superimposed on radar reflectivity data from that day. All 172 NBPs were found within the reflectivity of a thundercloud or at the edge of the reflectivity. The NBPs were classified into three groups: (I) in or above the high-reflectivity core of the storm, (II) in the convective region but not Group I, or (III) in the anvil region. Groups I, II, and III had, respectively, 79%, 17%, and 4% of the NBPs. Of the 136 NBPs in Group I, 43% occurred within the reflectivity core and 57% occurred above the core. A sequence of 34 positive NBPs during 1 h of one thunderstorm suggests that the majority of NBPs occurred during the rapid growth of two thunderstorm cells. Positive NBPs seem to recur in some storm locations; 67 (39%) of the NBPs were part of a recurrent set. We found 28 cases of NBPs recurring in approximately the same location, including 22 doublets, 3 triplets, 2 quadruplets, and 1 sextuplet. Analyses of one quadruplet and one sextuplet showed that these 10 positive NBPs occurred just above and/or right beside the high-reflectivity core on the downshear side of the core. Our data lead us to a hypothesis that NBPs occurring between the thunderstorm's upper positive charge and upper negative screening charge are initiated by small-scale charge regions with positive charge above negative charge, or opposite the orientation of the large-scale storm charges.

  1. Initial operation of high power ICRF system for long pulse in EAST

    SciTech Connect

    Qin, C. M. Zhao, Y. P.; Zhang, X. J.; Wan, B. N.; Gong, X. Z.; Mao, Y. Z.; Yuan, S.; Chen, G.

    2015-12-10

    The ICRF heating system on EAST upgraded by active cooling aims for long pulse operation. In this paper, the main technical features of the ICRF system are described. One of a major challenges for long pulse operation is RF-edge interactions induced impurity production and heat loading. In EAST, ICRF antenna protections and Faraday screen bars damaged due to LH electron beam are found. Preliminary results for the analysis of the interaction between LHCD and ICRF antenna are discussed. Increase of metal impurities in the plasma during RF pulse and in a larger core radiation are also shown. These RF-edge interactions at EAST and some preliminary results for the optimizing RF performance will be presented.

  2. Initial operation of high power ICRF system for long pulse in EAST

    NASA Astrophysics Data System (ADS)

    Qin, C. M.; Zhao, Y. P.; Zhang, X. J.; Wan, B. N.; Gong, X. Z.; Mao, Y. Z.; Yuan, S.; Chen, G.

    2015-12-01

    The ICRF heating system on EAST upgraded by active cooling aims for long pulse operation. In this paper, the main technical features of the ICRF system are described. One of a major challenges for long pulse operation is RF-edge interactions induced impurity production and heat loading. In EAST, ICRF antenna protections and Faraday screen bars damaged due to LH electron beam are found. Preliminary results for the analysis of the interaction between LHCD and ICRF antenna are discussed. Increase of metal impurities in the plasma during RF pulse and in a larger core radiation are also shown. These RF-edge interactions at EAST and some preliminary results for the optimizing RF performance will be presented.

  3. Template Reproduction of GRB Pulse Light Curves

    NASA Astrophysics Data System (ADS)

    Hakkila, Jon E.; Preece, R. D.; Loredo, T. J.; Wolpert, R. L.; Broadbent, M. E.

    2014-01-01

    A study of well-isolated pulses in gamma ray burst light curves indicates that simple models having smooth and monotonic pulse rises and decays are inadequate. Departures from the Norris et al. (2005) pulse shape are in the form of a wave-like pre-peak residual that is mirrored and stretched following the peak. Pulse shape departures are present in GRB pulses of all durations, but placement of the departures relative to pulse peaks correlates with asymmetry. This establishes an additional link between temporal structure and spectral evolution, as pulse asymmetry is related to initial hardness while pulse duration indicates the rate of hard-to-soft pulse evolution.

  4. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse.

    PubMed

    Szlachetko, J; Milne, C J; Hoszowska, J; Dousse, J-Cl; Błachucki, W; Sà, J; Kayser, Y; Messerschmidt, M; Abela, R; Boutet, S; David, C; Williams, G; Pajek, M; Patterson, B D; Smolentsev, G; van Bokhoven, J A; Nachtegaal, M

    2014-03-01

    Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10(-18) s) to femtoseconds (10(-15) s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments. PMID:26798772

  5. Structures of heterogeneous systems determined using XFEL pulses in the face of radiation damage

    NASA Astrophysics Data System (ADS)

    Young, Linda; Ho, Phay; Knight, Chris; Bostedt, Christoph; Faigl, Gyula; Tegze, Miklos

    2016-05-01

    Intense, femtosecond x-ray free-electron laser pulses are a promising tool for studying the structure and dynamics of complex systems at atomic resolution. Our previous efforts, using an atomistic quantum/classical model to track the dynamical evolution of ions and electrons throughout a femtosecond x-ray pulse and out to picosecond timescales, focused on quantifying the effects of radiation damage on homogeneous rare gas clusters for imaging applications in an ideal situation. In these studies, the entire 3D Q-space scattering pattern was computed and available for reconstruction of the initial structure. However, a realistic representation of an experiment would feature a collection of noisy 2D scattering patterns, from which orientation would first be required to generate the 3D Q-space distribution from which solution of the phase problem and reconstruction would then proceed. We will present the first results of these efforts on heterogeneous systems. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

  6. Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

    PubMed Central

    Szlachetko, J.; Milne, C. J.; Hoszowska, J.; Dousse, J.-Cl.; Błachucki, W.; Sà, J.; Kayser, Y.; Messerschmidt, M.; Abela, R.; Boutet, S.; David, C.; Williams, G.; Pajek, M.; Patterson, B. D.; Smolentsev, G.; van Bokhoven, J. A.; Nachtegaal, M.

    2014-01-01

    Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10−18 s) to femtoseconds (10−15 s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments. PMID:26798772

  7. Nanosecond Pulsed Discharges in Liquid Phase: Optical diagnostics of positive versus negative modes of initiation in water

    NASA Astrophysics Data System (ADS)

    Seepersad, Yohan; Fridman, Alexander; Dobrynin, Danil; Applied Physics Group Team

    2013-09-01

    Recent work on nanosecond pulsed discharges in liquids has shown the possibility of producing plasma directly in the liquid phase without bubble formation or heating of the liquid. Paramount to understanding the physical processes leading to this phenomenon is a thorough understanding of the way these discharges behave under various conditions. This work explores the development of nanosecond pulsed discharges in water, for both positively and negatively applied pulses in a pin-to-plane configuration. Time resolved nanosecond ICCD imaging is used to trace the development of the discharge for applied voltages up to 24 kV. From the results we are able to identify breakdown thresholds at which discharge is initiated for both modes. At voltages below the critical breakdown value, Schlieren and shadowgraphy techniques are used to investigate perturbations in the liquid layers near the electrode tip as a consequence of these fat rising pulses. This work was supported by Defense Advanced Research Projects Agency (grant #DARPA-BAA-11-31).

  8. Reaction enhancement of initially distant scalars by Lagrangian coherent structures

    SciTech Connect

    Pratt, Kenneth R. Crimaldi, John P.; Meiss, James D.

    2015-03-15

    Turbulent fluid flows have long been recognized as a superior means of diluting initial concentrations of scalars due to rapid stirring. Conversely, experiments have shown that the structures responsible for this rapid dilution can also aggregate initially distant reactive scalars and thereby greatly enhance reaction rates. Indeed, chaotic flows not only enhance dilution by shearing and stretching but also organize initially distant scalars along transiently attracting regions in the flow. To show the robustness of this phenomenon, a hierarchical set of three numerical flows is used: the periodic wake downstream of a stationary cylinder, a chaotic double gyre flow, and a chaotic, aperiodic flow consisting of interacting Taylor vortices. We demonstrate that Lagrangian coherent structures (LCS), as identified by ridges in finite time Lyapunov exponents, are directly responsible for this coalescence of reactive scalar filaments. When highly concentrated filaments coalesce, reaction rates can be orders of magnitude greater than would be predicted in a well-mixed system. This is further supported by an idealized, analytical model that was developed to quantify the competing effects of scalar dilution and coalescence. Chaotic flows, known for their ability to efficiently dilute scalars, therefore have the competing effect of organizing initially distant scalars along the LCS at timescales shorter than that required for dilution, resulting in reaction enhancement.

  9. Mechanisms of three-dimensional structuring of photo-polymers by tightly focussed femtosecond laser pulses.

    PubMed

    Malinauskas, Mangirdas; Zukauskas, Albertas; Bickauskaite, Gabija; Gadonas, Roaldas; Juodkazis, Saulius

    2010-05-10

    Three-dimensional (3D) micro/nano-structuring of photo-resists is systematically studied at the close-to-dielectric- breakdown irradiance. It is demonstrated that avalanche absorption is playing a major part in free electron generation and chemical bond breaking at these conditions. The steps of photo-initiation and chemical bond breaking in propagation of polymerization are altered as compared with photo-polymerization at low-irradiance and one-photon stereo-lithography. The avalanche dominates radical generation and promotion of polymerization at tight focusing and a high approximately TW/cm(2) irradiance. The rates of electron generation by two-photon absorption and avalanche are calculated for the experimental conditions. Simulation results are corroborated by 3D polymerization in three resists with different photo-initiators at two different wavelengths and pulse durations. The smallest feature sizes of 3D polymerized logpile structures are consistent with spectral dependencies of the two photon nonlinearities. Implications of these findings for achieving sub-100 nm resolution in 3D structuring of photo-polymers are presented. PMID:20588875

  10. Modeling the initiation and growth of delaminations in composite structures

    SciTech Connect

    Reedy, E.D. Jr.; Mello, F.J.; Guess, T.R.

    1996-01-01

    A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented. The laminate is divided into two or more sublaminates, with each sublaminate modeled with 4-noded quadrilateral shell elements. A special, 8-noded hex constraint element connects the sublaminates and makes them act as a single laminate until a prescribed failure criterion is attained. When the failure criterion is reached, the connection is broken, and a discrete delamination is initiated or grows. This approach has been implemented in a three-dimensional, finite element code. This code uses explicit time integration, and can analyze shell-like structures subjected to large deformations and complex contact conditions. Tensile, compressive, and shear laminate failures are also modeled. This paper describes the 8-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. In addition, calculated results for double cantilever beam and end notched flexure specimens are presented and compared to measured data to assess the ability of the present approach to reproduce observed behavior. Results are also presented for a diametrally compressed ring to demonstrate the capacity to analyze progressive failure in a highly deformed composite structure.

  11. Air nonlinear dynamics initiated by ultra-intense lambda-cubic terahertz pulses

    NASA Astrophysics Data System (ADS)

    Shalaby, Mostafa; Hauri, Christoph P.

    2015-05-01

    We report on the measurement of the instantaneous Kerr nonlinearity and the retarded alignment of air molecules CO2, N2, and O2 triggered by an intense, lambda-cubic terahertz pulse, a diffraction- and transform-limited single-cycle pulse. The strong-field, impulsive low-frequency excitation (3.9 THz) leads to field-free alignment dynamics of these molecules thanks to the terahertz-induced transient dipole moments in the otherwise non-polar molecules. The strong coupling to the terahertz electric transient results in the excitation of coherent large amplitude long-living rotational states at room temperature and ambient pressure. Beyond fundamental investigations of nonlinear properties in gases, our results suggest a route towards field-free molecular alignment at laser intensity well below the ionization threshold.

  12. Infrared nanosecond laser-metal ablation in atmosphere: Initial plasma during laser pulse and further expansion

    SciTech Connect

    Wu, Jian; Wei, Wenfu; Li, Xingwen; Jia, Shenli; Qiu, Aici

    2013-04-22

    We have investigated the dynamics of the nanosecond laser ablated plasma within and after the laser pulse irradiation using fast photography. A 1064 nm, 15 ns laser beam was focused onto a target made from various materials with an energy density in the order of J/mm{sup 2} in atmosphere. The plasma dynamics during the nanosecond laser pulse were observed, which could be divided into three stages: fast expansion, division into the primary plasma and the front plasma, and stagnation. After the laser terminated, a critical moment when the primary plasma expansion transited from the shock model to the drag model was resolved, and this phenomenon could be understood in terms of interactions between the primary and the front plasmas.

  13. Initial electronic coherence in molecular dissociation induced by an attosecond pulse

    NASA Astrophysics Data System (ADS)

    Medišauskas, Lukas; Patchkovskii, Serguei; Harvey, Alex; Brambila, Danilo S.; Neidel, Christian; Klei, Jesse; Rouzée, Arnaud; Vrakking, Marc J. J.; Ivanov, Misha Yu.

    2015-11-01

    We investigate the influence of the attosecond electron dynamics of photoionization on the femtosecond fragmentation of the molecular ion left behind. We consider the dissociative photoionization dynamics of the N2 molecule, induced by an attosecond extreme-ultraviolet (XUV) pulse in the presence of a moderately strong infrared (IR) laser field. We show that the kinetic energy spectrum of N+ fragments depends on (i) the phases between the different electronic states of N2 + established by the photoionization process and (ii) phases associated with the vibrational dynamics in the dissociating molecular ion. We show that the phase acquired during the photoionization can be obtained from the dependence of the N+ ion kinetic energy release spectra on the time delay between the XUV and IR pulses.

  14. Air nonlinear dynamics initiated by ultra-intense lambda-cubic terahertz pulses

    SciTech Connect

    Shalaby, Mostafa E-mail: christoph.hauri@psi.ch; Hauri, Christoph P. E-mail: christoph.hauri@psi.ch

    2015-05-04

    We report on the measurement of the instantaneous Kerr nonlinearity and the retarded alignment of air molecules CO{sub 2}, N{sub 2}, and O{sub 2} triggered by an intense, lambda-cubic terahertz pulse, a diffraction- and transform-limited single-cycle pulse. The strong-field, impulsive low-frequency excitation (3.9 THz) leads to field-free alignment dynamics of these molecules thanks to the terahertz-induced transient dipole moments in the otherwise non-polar molecules. The strong coupling to the terahertz electric transient results in the excitation of coherent large amplitude long-living rotational states at room temperature and ambient pressure. Beyond fundamental investigations of nonlinear properties in gases, our results suggest a route towards field-free molecular alignment at laser intensity well below the ionization threshold.

  15. Structural insights into transcription initiation by RNA polymerase II

    PubMed Central

    Grünberg, Sebastian; Hahn, Steven

    2013-01-01

    Transcriptional regulation is one of the most important steps in control of cell identity, growth, differentiation and development. Many signaling pathways controlling these processes ultimately target the core transcription machinery that, for protein coding genes, consists of RNA polymerase II (Pol II) and the general transcription factors (GTFs). New studies on the structure and mechanism of the core assembly and how it interfaces with promoter DNA and coactivator complexes have given tremendous insight into early steps in the initiation process, genome-wide binding, and mechanisms conserved for all nuclear and archaeal Pols. Here we review recent developments in dissecting the architecture of the Pol II core machinery with a focus on early and regulated steps in transcription initiation. PMID:24120742

  16. Structural basis of initial RNA polymerase II transcription

    PubMed Central

    Cheung, Alan C M; Sainsbury, Sarah; Cramer, Patrick

    2011-01-01

    During transcription initiation by RNA polymerase (Pol) II, a transient open promoter complex (OC) is converted to an initially transcribing complex (ITC) containing short RNAs, and to a stable elongation complex (EC). We report structures of a Pol II–DNA complex mimicking part of the OC, and of complexes representing minimal ITCs with 2, 4, 5, 6, and 7 nucleotide (nt) RNAs, with and without a non-hydrolyzable nucleoside triphosphate (NTP) in the insertion site +1. The partial OC structure reveals that Pol II positions the melted template strand opposite the active site. The ITC-mimicking structures show that two invariant lysine residues anchor the 3′-proximal phosphate of short RNAs. Short DNA–RNA hybrids adopt a tilted conformation that excludes the +1 template nt from the active site. NTP binding induces complete DNA translocation and the standard hybrid conformation. Conserved NTP contacts indicate a universal mechanism of NTP selection. The essential residue Q1078 in the closed trigger loop binds the NTP 2′-OH group, explaining how the trigger loop couples catalysis to NTP selection, suppressing dNTP binding and DNA synthesis. PMID:22056778

  17. Monitoring of initial patterns and structures in an artificial catchment

    NASA Astrophysics Data System (ADS)

    Schaaf, Wolfgang; Gerwin, Werner; Biemelt, Detlef; Fischer, Anton

    2010-05-01

    To combine process-oriented research on initial development of ecosystems with interactions and co-development of spatial patterns and structures the Transregional Collaborative Research Centre (SFB/TRR) 38 (www.tu-cottbus.de/sfb_trr) was established as an initiative of three universities (BTU Cottbus, TU Munich and ETH Zurich). The objective of the SFB/TRR 38 is to enhance our understanding of structure genesis in ecosystems and of process dynamics as well as their interactions during the initial development phase. The aim is to integrate these feedback mechanisms in the analysis of water and element budgets at the catchment scale and to implement them into models. To allow the clear definition of starting conditions at ´point zeró and to be able to integrate spatially distributed processes and patterns to larger units, an artificial catchment was constructed in the mining area of Lusatia/Germany as the main research site (Gerwin et al. 2009a). With an area of about 6 ha, this catchment ´Chicken Creeḱ is to our knowledge the largest artificial catchment worldwide. It was constructed as a 2-4 m layer of post-glacial sandy to loamy sediments overlying a 1-2 m layer of Tertiary clay that forms a shallow pan and seals the whole catchment at the base. No further measures of restoration like planting, amelioration or fertilization were carried out to allow natural succession and undisturbed development. Due to the artificial construction, boundary conditions of this site are clearly defined including well documented inner structures as compared to natural catchments. It is assumed that the interaction of patterns and processes during initial development will proceed from simpler to more complex states of the systems and that different stages along this phase can be identified at the catchment level. Changes within the catchment are intensively monitored since 2005, when construction finished (Gerwin et al. 2009b), including intensive on-site measurements and micro

  18. Development and initial testing of a pulse oximetry prototype for measuring dental pulp vitality

    NASA Astrophysics Data System (ADS)

    Cerqueira, M.; Ferreira, M.; Caramelo, F.

    2015-05-01

    The guiding principle of endodontic treatment is to preserve teeth while maintaining its aesthetic and functional roles. To accomplish this goal the assessment of teeth pulp vitality is very important since it will determine the procedures that should be adopted and define the therapy strategy. Currently, the most commonly tests for determining dental pulp state are the thermal and the electrical tests, which are based on nerve response and, because of that, have a relatively high rate of false positives and false negatives cases. In this work we present a simple test to be used in the clinical setting for evaluating noninvasively the existence of blood perfusion in dental pulp. This test is based on pulse oximetry principle that was devised to indirectly measure the amount of oxygen in blood. Although pulse oximetry has already demonstrated its usefulness in clinical environment its usage for the determination of dental pulp vitality has been frustrated by several factors, notably the absence of a suitable sensor to the complex shape of the various coronary teeth. We developed a suitable sensor and present the first trials with promising results, regarding the ability for distinguish teeth with and without blood perfusion.

  19. Structure of Shocks in Burgers Turbulencewith Stable Noise Initial Data

    NASA Astrophysics Data System (ADS)

    Bertoin, Jean

    Burgers equation can be used as a simplified model for hydrodynamic turbulence. The purpose of this paper is to study the structure of the shocks for the inviscid equation in dimension 1 when the initial velocity is given by a stable Lévy noise with index α∈ (1/2,2]. We prove that Lagrangian regular points exist (i.e. there are fluid particles that have not participated in shocks at any time between 0 and t) if and only if α<= 1 and the noise is not completely asymmetric, and that otherwise the shock structure is discrete. Moreover, in the Cauchy case α= 1, we show that there are no rarefaction intervals, i.e. at time t >0$, there are fluid particles in any non-empty open interval.

  20. Initial temporal and spatial changes of the refractive index induced by focused femtosecond pulsed laser irradiation inside a glass

    SciTech Connect

    Sakakura, Masaaki; Terazima, Masahide

    2005-01-01

    The temporal and spatial developments of the refractive-index change in a focal region of a femtosecond-laser pulse inside a soda-lime glass is investigated by the transient lens (TrL) method with a time resolution of subpicosecond. In the TrL signal, the oscillation with about an 800-ps period is observed until about 2000 ps. In order to explain the oscillation, the thermoelastic response of a heated material by a short pulsed laser is calculated. It is found that the TrL signal calculated based on the thermoelastic calculation reproduces the observed oscillating signal very well, even though the calculated density at the focal region does not oscillate. The essential feature of the oscillation can be explained in terms of the pressure wave generation and propagation in the outward direction from the irradiated region. Based on the pressure-wave propagation and the phase-retrieval method, the temporal evolution of the refractive-index distribution inside a glass is obtained from the probe-beam deformation (TrL image) at various delay times between the pump and probe pulses. Two phases of the refractive-index increase at the laser focal region were observed in a range of 20-100 and 500-700 ps, which may cause a permanent refractive-index increase in the laser focal region inside a glass. We discuss the effect of the laser pulse duration on the material deformation process in the laser-irradiated region. This study clearly shows the initial process of the material deformation dynamics inside a glass after femtosecond laser irradiation.

  1. Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

    PubMed

    Almeida, G F B; Martins, R J; Otuka, A J G; Siqueira, J P; Mendonca, C R

    2015-10-19

    We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring. PMID:26480419

  2. Domain structure of a human general transcription initiation factor, TFIIF.

    PubMed Central

    Yonaha, M; Aso, T; Kobayashi, Y; Vasavada, H; Yasukochi, Y; Weissman, S M; Kitajima, S

    1993-01-01

    The structural and functional domains of a general transcription initiation factor, TFIIF (RAP30/74, FC), have been investigated using various deletion mutants of each subunit, both in vivo and in vitro. An in vivo assay showed that the N-terminal sequence containing residues of 1-110 of RAP30 that is located close to a sigma homology region interacts with a minimum sequence of residues 62-171 of RAP74 to form a heteromeric interaction. Reconstitution of in vitro transcription activity by deletion mutants of RAP74 clearly indicated that both N-terminal residues 73-205 and C-terminal residues 356-517 are essential for full activity, the former interacting with RAP30, thus complexing with RNA polymerase II. From these data, the functional significance of domain structure of TFIIF is discussed in terms of its sigma homology sequences and complex formation with RNA polymerase II in the initiation and elongation of transcription. Images PMID:8441635

  3. Pulsed UV and ultrafast laser micromachining of surface structures

    NASA Astrophysics Data System (ADS)

    Apte, Paul; Sykes, Neil

    2015-07-01

    We describe and compare the cutting and patterning of various "difficult" materials using pulsed UV Excimer, picosecond and femtosecond laser sources. Beam delivery using both fast galvanometer scanners and scanning mask imaging are described. Each laser source has its own particular strengths and weaknesses, and the optimum choice for an application is also decided by financial constraints. With some materials notable improvements in process quality have been observed using femtosecond lasers compared to picosecond lasers, which makes for an interesting choice now that cost effective reliable femtosecond systems are increasingly available. By contrast Pulsed UV Excimer lasers offer different imaging characteristics similar to mask based Lithographic systems and are particularly suited to the processing of polymers. We discuss optimized beam delivery techniques for these lasers.

  4. Pulse-Like Rupture Induced by Three-Dimensional Fault Zone Flower Structures

    NASA Astrophysics Data System (ADS)

    Pelties, Christian; Huang, Yihe; Ampuero, Jean-Paul

    2015-05-01

    Faults are often embedded in low-velocity fault zones (LVFZ) caused by material damage. Previous 2D dynamic rupture simulations (H uang and A mpuero, 2011; H uang et al., 2014) showed that if the wave velocity contrast between the LVFZ and the country rock is strong enough, ruptures can behave as pulses, i.e. with local slip duration (rise time) much shorter than whole rupture duration. Local slip arrest (healing) is generated by waves reflected from the LVFZ-country rock interface. This effect is robust against a wide range of fault zone widths, absence of frictional healing, variation of initial stress conditions, attenuation, and off-fault plasticity. These numerical studies covered two-dimensional problems with fault-parallel fault zone structures. Here, we extend previous work to 3D and geometries that are more typical of natural fault zones, including complexities such as flower structures with depth-dependent velocity and thickness, and limited fault zone depth extent. This investigation requires high resolution and flexible mesh generation, which are enabled here by the high-order accurate arbitrary high-order derivatives discontinuous Galerkin method with an unstructured tetrahedral element discretization (P elties et al., 2012). We show that the healing mechanism induced by waves reflected in the LVFZ also operates efficiently in such three-dimensional fault zone structures and that, in addition, a new healing mechanism is induced by unloading waves generated when the rupture reaches the surface. The first mechanism leads to very short rise time controlled by the LVFZ width to wave speed ratio. The second mechanism leads to generally longer, depth-increasing rise times, is also conditioned by the existence of an LVFZ, and persists at some depth below the bottom of the LVFZ. Our simulations show that the generation of slip pulses by these two mechanisms is robust to the depth extent of the LVFZ and to the position of the hypocenter. The first healing

  5. Effect of laser-pulse structure and wavelength on wound healing

    NASA Astrophysics Data System (ADS)

    Fortune, D. S.; Huang, Shan; Bryant, G. L.; Garrett, C. Gaelyn; Reinisch, Lou

    1998-07-01

    We have investigated wound healing of incisions in the buccal mucosa of a canine model created with the Vanderbilt Free Electron Laser tuned to 6.1, 6.45 and 6.8 microns. We have also used a carbon dioxide laser, continuous wave and with a short-pulse structure (100 microseconds) to access wavelength and pulse structure components to wound healing from laser incisions. The tissue was evaluated histologically and with tensiometry acutely and at post operative days 3, 7, and 14. The data indicate that shorter laser pulse durations create less lateral thermal injury and wounds with greater tensile strength, resulting in earlier wound healing. Wound healing was only slightly dependent upon the wavelength of the laser. These results demonstrate that surgical carbon dioxide lasers with a short-pulse structure of approximately 100 microseconds or less could offer more prompt wound healing while maintaining the advantages of a 10.6 micron wavelength laser.

  6. Short pulse duration shock initiation experiments plus ignition and growth modeling on Composition B

    NASA Astrophysics Data System (ADS)

    May, Chadd M.; Tarver, Craig M.

    2014-05-01

    Composition B (63% RDX, 36% TNT, 1% wax) is still a widely used energetic material whose shock initiation characteristics are necessary to understand. It is now possible to shock initiate Composition B and other secondary explosives at diameters well below their characteristic failure diameters for unconfined self-sustaining detonation. This is done using very high velocity, very thin, small diameter flyer plates accelerated by electric or laser power sources. Recently experimental detonation versus failure to detonate threshold flyer velocity curves for Composition B using several KaptonTM flyer thicknesses and diameters were measured. Flyer plates with diameters of 2 mm successfully detonated Composition B, which has a nominal failure diameter of 4.3 mm. The shock pressures required for these initiations are greater than the Chapman-Jouguet (C-J) pressure in self-sustaining Composition B detonation waves. The initiation process is two-dimensional, because both rear and side rarefactions can affect the shocked Composition B reaction rates. The Ignition and Growth reactive flow model for Composition B is extended to yield accurate simulations of this new threshold velocity data for various flyer thicknesses.

  7. Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

    NASA Technical Reports Server (NTRS)

    Krause, David L.; Whittenberger, J. Daniel

    2002-01-01

    , which were not considered in the simplified computer models. The fatigue testing proved the value of redundancies since specimen strength was maintained even after the fracture of one or two ligaments. This ongoing test program is planned to continue through high-temperature testing. Also scheduled for testing are IN 718 lattice block panels with integral face sheets, as well as specimens cast from a higher temperature alloy. The initial testing suggests the value of this technology for large panels under low and moderate pressure loadings and for high-risk, damage-tolerant structures. Potential aeropropulsion uses for lattice blocks include turbine-engine actuated panels, exhaust nozzle flaps, and side panel structures.

  8. A spectroscopic study of the initial stages of pulsed glow discharges in noble gases

    NASA Astrophysics Data System (ADS)

    Demidov, V. I.; Adams, S. F.; Bogdanov, E. A.; Kudryavtsev, A. A.; Williamson, J. M.

    2011-10-01

    The dynamics of the rapid growth of electron and metastable atom densities at the beginning of a pulsed dc discharge in argon was explored by investigating the relationship between the strength of the applied electric field and the measured emission line intensities at 419.8 and 420.1 nm. Data showed that when the electric field strength was low, the growth of the metastable atom density began before the growth of the electron density. The opposite relationship was observed when a higher strength electric field was applied. This observed dependence can be confirmed by modeling the argon dc discharge. Furthermore, similar measurements for the 345.4 and 347.3 nm spectral lines in neon and the 480.7 and 467.2 nm spectral lines in xenon suggest analogous behaviors in these noble gases. Thus, spectral measurements of the above lines could be a sensitive indicator of the presence of noble gas metastable atoms in plasmas. This relationship could be used to control plasma properties, a tool that would be useful for many technological applications. This work was supported by the DOE (DE-SC0001939), NSF CBET-0903635, GK 14.740.11.0893 and AFOSR.

  9. Simulation and initial experiments of a high power pulsed TEA CO2 laser

    NASA Astrophysics Data System (ADS)

    Torabi, R.; Saghafifar, H.; Koushki, A. M.; Ganjovi, A. A.

    2016-01-01

    In this paper, the output characteristics of a UV pin array pre-ionized TEA CO2 laser have been simulated and compared with the associated experimental data. In our simulation, a new theoretical model has been improved for transient behavior analysis of the discharge current pulse. The laser discharge tube was modeled by a nonlinear RLC electric circuit as a real model for electron density calculation. This model was coupled with a six-temperature model (6TM) in order to simulation dynamic emission processes of the TEA CO2 laser. The equations were solved numerically by the fourth order Runge-Kutta numerical method and some important variables such as current and voltage of the main discharge, resistance of the plasma column and electron density in the main discharge region, were calculated as functions of time. The effects of non-dissociation factor, rotational quantum number and output coupler reflectivity were also studied theoretically. The experimental and simulation results are in good agreement.

  10. Mean maps for cosmic web structures in cosmological initial conditions

    NASA Astrophysics Data System (ADS)

    Aung, Han; Cohn, J. D.

    2016-02-01

    Haloes, filaments, sheets and voids in the cosmic web can be defined in terms of the eigenvalues of the smoothed shear tensor and a threshold λth. Using analytic methods, we construct mean maps centred on these types of structures for Gaussian random fields corresponding to cosmological initial conditions. Each map also requires a choice of shear at the origin; we consider three possibilities. We find characteristic sizes, shapes and other properties of the central objects in these mean maps and explore how these properties change with varying the threshold and smoothing scale, i.e. varying the separation of the cosmic web into different kinds of components. The mean maps become increasingly complex as the threshold λth decreases to zero. We also describe scatter around these mean maps, subtleties which can arise in their construction, and some comparisons between haloes in the maps and collapsed haloes at final times.

  11. Calibration of Tests for Time-Dilation in GRB Pulse Structures

    NASA Technical Reports Server (NTRS)

    Norris, J. P.; Bonnell, J. T.; Nemiroff, R. J.; Scargle, J. D.; Cuzzi, Jeffery N. (Technical Monitor)

    1995-01-01

    If gamma-ray bursts are at cosmological distances, then not only their constituent pulses but also the intervals between pulses should be time-dilated. Unlike time-dilation measures of pulse emission, intervals would appear to require less "K-correction" for redshift of narrower temporal structure from higher energy into the band of observation. However, stretching of pulse intervals is intrinsically difficult to measure without incurring a timescale-dependent bias since, as time profiles are stretched, more structure can appear at the limit of resolution. This problem is compounded in dimmer bursts since identification of significant structures is problematic. We have attempted to minimize brightness bias problems by equalizing the signal-to-noise level of all bursts. Then, analyzing wavelet-denoised profiles binned to several resolutions, we identify significant (3 - 4 sigma) fluctuations between pulse structures and interjacent valleys. When bursts are ranked by peak flux, an interval time-dilation signature is evident, but its measure is dependent upon choice of temporal resolution. This result appears to tentatively and qualitatively confirm the work of Davis, who found such a signature using a pulse fitting approach.

  12. Enhancement of initial equivalency for protein structure alignment based on encoded local structures.

    PubMed

    Hung, Kenneth; Wang, Jui-Chih; Chen, Cheng-Wei; Chuang, Cheng-Long; Tsai, Kun-Nan; Chen, Chung-Ming

    2012-11-01

    Most alignment algorithms find an initial equivalent residue pair followed by an iterative optimization process to explore better near-optimal alignments in the surrounding solution space of the initial alignment. It plays a decisive role in determining the alignment quality since a poor initial alignment may make the final alignment trapped in an undesirable local optimum even with an iterative optimization. We proposed a vector-based alignment algorithm with a new initial alignment approach accounting for local structure features called MIRAGE-align. The new idea is to enhance the quality of the initial alignment based on encoded local structural alphabets to identify the protein structure pair whose sequence identity falls in or below twilight zone. The statistical analysis of alignment quality based on Match Index (MI) and computation time demonstrated that MIRAGE-align algorithm outperformed four previously published algorithms, i.e., the residue-based algorithm (CE), the vector-based algorithm (SSM), TM-align, and Fr-TM-align. MIRAGE-align yields a better estimate of initial solution to enhance the quality of initial alignment and enable the employment of a non-iterative optimization process to achieve a better alignment. PMID:22717522

  13. Structural Analysis Using Phase-Stepped, Double Pulsed ESPI

    NASA Astrophysics Data System (ADS)

    Tyrer, John R.

    1990-04-01

    Optical whole-field testing techniques have been carrots dangled in front of engineers' noses for a considerable period of time. The promise of acquiring meaningful data without upsetting the component nor its environment, has significant attractions. ESPI technology has been modified and pursued with these goals in mind. This paper presents some of the recent work containing several developments which now make the engineering realisations a near term possibility. An overview of the correlation imaging mechanism is presented with a discussion on how this principle type of optical interferometer can be configured to provide the data necessary for analytical use. Attempts to produce instrumentation able to function outside the laboratory have required replacement of continuous wave lasers with Nd.YAG pulsed lasers. The new pulsed lasers are able to be combined with the computer based fringe pattern analysis which has been produced to suit the requirements of the engineer. Experimental results using such equipment are presented and further work is included which demonstrates the ability for speckle interferometry to produce three-dimensional analysis with the data being presented in conventional cartesian form.

  14. Pulse number controlled laser annealing for GeSn on insulator structure with high substitutional Sn concentration

    NASA Astrophysics Data System (ADS)

    Moto, Kenta; Matsumura, Ryo; Sadoh, Taizoh; Ikenoue, Hiroshi; Miyao, Masanobu

    2016-06-01

    Crystalline GeSn-on-insulator structures with high Sn concentration (>8%), which exceeds thermal equilibrium solid-solubility (˜2%) of Sn in Ge, are essential to achieve high-speed thin film transistors and high-efficiency optical devices. We investigate non-thermal equilibrium growth of Ge1-xSnx (0 ≤ x ≤ 0.2) on quartz substrates by using pulsed laser annealing (PLA). The window of laser fluence enabling complete crystallization without film ablation is drastically expanded (˜5 times) by Sn doping above 5% into Ge. Substitutional Sn concentration in grown layers is found to be increased with decreasing irradiation pulse number. This phenomenon can be explained on the basis of significant thermal non-equilibrium growth achieved by higher cooling rate after PLA with a lower pulse number. As a result, GeSn crystals with substitutional Sn concentration of ˜12% are realized at pulse irradiation of single shot for the samples with the initial Sn concentration of 15%. Raman spectroscopy and electron microscopy measurements reveal the high quality of the grown layer. This technique will be useful to fabricate high-speed thin film transistors and high-efficiency optical devices on insulating substrates.

  15. Temporal femtosecond pulse shaping dependence of laser-induced periodic surface structures in fused silica

    SciTech Connect

    Shi, Xuesong; Jiang, Lan; Li, Xin Zhang, Kaihu; Yu, Dong; Yu, Yanwu; Lu, Yongfeng

    2014-07-21

    The dependence of periodic structures and ablated areas on temporal pulse shaping is studied upon irradiation of fused silica by femtosecond laser triple-pulse trains. Three types of periodic structures can be obtained by using pulse trains with designed pulse delays, in which the three-dimensional nanopillar arrays with ∼100–150 nm diameters and ∼200 nm heights are first fabricated in one step. These nanopillars arise from the break of the ridges of ripples in the upper portion, which is caused by the split of orthogonal ripples in the bottom part. The localized transient electron dynamics and corresponding material properties are considered for the morphological observations.

  16. Classical-quantum correspondence in atomic ionization by midinfrared pulses: Multiple peak and interference structures

    NASA Astrophysics Data System (ADS)

    Lemell, Christoph; Burgdörfer, Joachim; Gräfe, Stefanie; Dimitriou, Konstantinos I.; Arbó, Diego G.; Tong, Xiao-Min

    2013-01-01

    Atomic ionization by strong and ultrashort laser pulses with frequencies in the midinfrared spectral region have revealed novel features such as the low-energy structures. We have performed fully three-dimensional quantum dynamical as well as classical trajectory Monte Carlo simulations for pulses with wavelengths from λ=2000 to 6000 nm. Furthermore, we apply distorted-wave quantum approximations. This allows to explore the quantum-classical correspondence as well as the (non) perturbative character of the ionization dynamics driven by long-wavelength pulses. We observe surprisingly rich structures in the differential energy and angular momentum distribution which sensitively depend on λ, the pulse duration τp, and the carrier-envelope phase ϕCEP.

  17. Suppression of beam induced pulse shortening modes in high power RF generator TW output structures

    SciTech Connect

    Haimson, J.; Mecklenburg, B.

    1992-12-31

    Several different style 11.4 GHz relativistic klystrons, operating with beam pulse widths of 50 ns and using large aperture, tapered phase-velocity TW structures,` have recently demonstrated output RF power levels in the range of 100 to 300 MW without breakdown or pulse shortening. To extend this performance into the long pulse regime (1 {mu}s) or to demonstrate a threefold increase in output power by using higher currents, the existing TW circuit designs must be modified (a) to reduce the cavity maximum surface E-fields by a factor of 2 to 3, and (b) to elevate the current threshold values of the beam induced higher order modes (HOM) to ensure avoidance of RF pulse shortening and associated instabilities. A technique for substantially elevating this threshold current is described, and microwave data and photographs are presented showing the degree of HOM damping achieved in a recently constructed 11.4 GHz TW structure.

  18. Time-resolved detection of structural change in polyethylene films using mid-infrared laser pulses

    SciTech Connect

    Ageev, Eduard; Mizobata, Keisuke; Nakajima, Takashi Zen, Heishun; Kii, Toshiteru; Ohgaki, Hideaki

    2015-07-27

    Some of the vibrational modes of crystalline organic polymers are known to be sensitive to the structural change from the crystalline phase to the amorphous phase, and vice versa. Using a mid-infrared (mid-IR) pulse from a free-electron laser as a probe, we demonstrate the time-resolved detection of structural change in crystalline polymer (polyethylene) films upon laser heating by a Q-switched Nd:YAG laser. Transmittance of the resonant mid-IR pulse almost instantaneously changes before and after the Nd:YAG laser pulse if its fluence is sufficient to induce the structural change in the film. The developed technique would be useful to study the time-dependent dynamics of the structural change in various materials.

  19. Magnetic structure of nickel nanowires after the high-density current pulse

    NASA Astrophysics Data System (ADS)

    Nurgazizov, N. I.; Bizyaev, D. A.; Bukharaev, A. A.

    2016-05-01

    Changes in the magnetic structure of nickel nanowires formed on a nonconductive surface after the high-density current pulse have been investigated using magnetic force microscopy and voltammetry. Based on the obtained experimental data and results of the computer simulation, it has been concluded that the main reason for the change in the magnetic structure is the heating of the nanowire by a current pulse. It has been shown that, during the subsequent cooling, the newly formed magnetic structure is pinned by surface roughnesses of the relief of the nanowire under investigation.

  20. Breakdown voltages for discharges initiated from plasma pulses produced by high-frequency excimer lasers

    SciTech Connect

    Yamaura, Michiteru

    2006-06-19

    The triggering ability under the different electric field was investigated using a KrF excimer laser with a high repetition rate of kilohertz order. Measurements were made of the magnitude of impulse voltages that were required to initiate a discharge from plasmas produced by a high-frequency excimer laser. Breakdown voltages were found to be reduced by 50% through the production of plasmas in the discharge gap by a high-frequency excimer laser. However, under direct-current electric field, triggering ability decreased drastically due to low plasma density. It is considered that such laser operation applied for laser-triggered lightning due to the produced location of plasma channel is formed under the impulse electric field since an electric field of the location drastically reduces temporary when the downward leader from thunderclouds propagates to the plasma channel.

  1. Crystal structure of eukaryotic translation initiation factor 2B.

    PubMed

    Kashiwagi, Kazuhiro; Takahashi, Mari; Nishimoto, Madoka; Hiyama, Takuya B; Higo, Toshiaki; Umehara, Takashi; Sakamoto, Kensaku; Ito, Takuhiro; Yokoyama, Shigeyuki

    2016-03-01

    Eukaryotic cells restrict protein synthesis under various stress conditions, by inhibiting the eukaryotic translation initiation factor 2B (eIF2B). eIF2B is the guanine nucleotide exchange factor for eIF2, a heterotrimeric G protein consisting of α-, β- and γ-subunits. eIF2B exchanges GDP for GTP on the γ-subunit of eIF2 (eIF2γ), and is inhibited by stress-induced phosphorylation of eIF2α. eIF2B is a heterodecameric complex of two copies each of the α-, β-, γ-, δ- and ε-subunits; its α-, β- and δ-subunits constitute the regulatory subcomplex, while the γ- and ε-subunits form the catalytic subcomplex. The three-dimensional structure of the entire eIF2B complex has not been determined. Here we present the crystal structure of Schizosaccharomyces pombe eIF2B with an unprecedented subunit arrangement, in which the α2β2δ2 hexameric regulatory subcomplex binds two γε dimeric catalytic subcomplexes on its opposite sides. A structure-based in vitro analysis by a surface-scanning site-directed photo-cross-linking method identified the eIF2α-binding and eIF2γ-binding interfaces, located far apart on the regulatory and catalytic subcomplexes, respectively. The eIF2γ-binding interface is located close to the conserved 'NF motif', which is important for nucleotide exchange. A structural model was constructed for the complex of eIF2B with phosphorylated eIF2α, which binds to eIF2B more strongly than the unphosphorylated form. These results indicate that the eIF2α phosphorylation generates the 'nonproductive' eIF2-eIF2B complex, which prevents nucleotide exchange on eIF2γ, and thus provide a structural framework for the eIF2B-mediated mechanism of stress-induced translational control. PMID:26901872

  2. Layered structure in the interaction of thin foil with two laser pulses

    SciTech Connect

    Yu, Yahong; Shen, Baifei E-mail: jill@siom.ac.cn; Yu, Wei; Wang, Wenpeng; Zhang, Xiaomei; Ji, Liangliang E-mail: jill@siom.ac.cn; Zhao, Xueyan; Wang, Xiaofeng; Yi, Longqing; Shi, Yin; Xu, Tongjun; Zhang, Lingang; Wen, Meng

    2014-02-15

    An interesting layered structure of multiple high density layers are formed when two counter-propagating circularly polarized laser pulses with the same polarization direction irradiate on an ultra-thin foil. This structure changes periodically. For light atoms most of which electrons may be fully ionized, this layered structure can keep for dozens of laser periods after the laser-foil interaction. This interesting structure may have potential applications.

  3. Local field enhancement on metallic periodic surface structures produced by femtosecond laser pulses

    SciTech Connect

    Ionin, Andrei A; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Mel'nik, N N; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Khmelnitskii, R A

    2013-04-30

    Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules. (extreme light fields and their applications)

  4. Nanofractal structure consisting of nanoparticles produced by ultrashort laser pulses

    SciTech Connect

    Nishikawa, Kumiko; Takano, Kei; Miyahara, Hidekazu; Kawamura, Tohru; Okino, Akitoshi; Hotta, Eiki; Nayuki, Takuya; Oishi, Yuji; Fujii, Takashi; Wang, Xiaofang; Nemoto, Koshichi

    2006-12-11

    By irradiating subpicosecond laser onto an iron plate, a nanofibrous structure consisting of iron nanoparticles with diameters less than 12 nm was produced. The nanofibrous structure was found to be three-dimensional fractal, and its fractal dimension measured from field-emission scanning electron microscopy images conserved the same fractal dimension of 1.73 in the wide-scale range from 30 nm to 60 {mu}m, and the smallest fractal structure was less than 10 nm. The growth of this fractal is related to the cluster-cluster aggregation model, and it suggests that the fractal structure grew by the attachment of clusters consisting of nanoparticles.

  5. Detection of cystic structures using pulsed ultrasonically induced resonant cavitation

    NASA Technical Reports Server (NTRS)

    Bar-Cohen, Yoseph (Inventor); Kovach, John S. (Inventor)

    2002-01-01

    Apparatus and method for early detection of cystic structures indicative of ovarian and breast cancers uses ultrasonic wave energy at a unique resonance frequency for inducing cavitation in cystic fluid characteristic of cystic structures in the ovaries associated with ovarian cancer, and in cystic structures in the breast associated with breast cancer. Induced cavitation bubbles in the cystic fluid implode, creating implosion waves which are detected by ultrasonic receiving transducers attached to the abdomen of the patient. Triangulation of the ultrasonic receiving transducers enables the received signals to be processed and analyzed to identify the location and structure of the cyst.

  6. Nonlinear magnetoelectric response of planar ferromagnetic-piezoelectric structures to sub-millisecond magnetic pulses.

    PubMed

    Kreitmeier, Florian; Chashin, Dmitry V; Fetisov, Yury K; Fetisov, Leonid Y; Schulz, Irene; Monkman, Gareth J; Shamonin, Mikhail

    2012-01-01

    The magnetoelectric response of bi- and symmetric trilayer composite structures to pulsed magnetic fields is experimentally investigated in detail. The structures comprise layers of commercially available piezoelectric (lead zirconate titanate) and magnetostrictive (permendur or nickel) materials. The magnetic-field pulses have the form of a half-wave sine function with duration of 450 µs and amplitudes ranging from 500 Oe to 38 kOe. The time dependence of the resulting voltage is presented and explained by theoretical estimations. Appearance of voltage oscillations with frequencies much larger than the reciprocal pulse length is observed for sufficiently large amplitudes (~1-10 kOe) of the magnetic-field pulse. The origin of these oscillations is the excitation of bending and planar acoustic oscillations in the structures. Dependencies of the magnetoelectric voltage coefficient on the excitation frequency and the applied magnetic field are calculated by digital signal processing and compared with those obtained by the method of harmonic field modulation. The results are of interest for developing magnetoelectric sensors of pulsed magnetic fields as well as for rapid characterization of magnetoelectric composite structures. PMID:23202188

  7. Nonlinear Magnetoelectric Response of Planar Ferromagnetic-Piezoelectric Structures to Sub-Millisecond Magnetic Pulses

    PubMed Central

    Kreitmeier, Florian; Chashin, Dmitry V.; Fetisov, Yury K.; Fetisov, Leonid Y.; Schulz, Irene; Monkman, Gareth J.; Shamonin, Mikhail

    2012-01-01

    The magnetoelectric response of bi- and symmetric trilayer composite structures to pulsed magnetic fields is experimentally investigated in detail. The structures comprise layers of commercially available piezoelectric (lead zirconate titanate) and magnetostrictive (permendur or nickel) materials. The magnetic-field pulses have the form of a half-wave sine function with duration of 450 μs and amplitudes ranging from 500 Oe to 38 kOe. The time dependence of the resulting voltage is presented and explained by theoretical estimations. Appearance of voltage oscillations with frequencies much larger than the reciprocal pulse length is observed for sufficiently large amplitudes (∼1–10 kOe) of the magnetic-field pulse. The origin of these oscillations is the excitation of bending and planar acoustic oscillations in the structures. Dependencies of the magnetoelectric voltage coefficient on the excitation frequency and the applied magnetic field are calculated by digital signal processing and compared with those obtained by the method of harmonic field modulation. The results are of interest for developing magnetoelectric sensors of pulsed magnetic fields as well as for rapid characterization of magnetoelectric composite structures. PMID:23202188

  8. Fabrication of a periodic structure with a high refractive-index difference by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Takeshima, Nobuhito; Kuroiwa, Yutaka; Narita, Yoshihiro; Tanaka, Shuhei; Hirao, Kazuyuki

    2004-08-01

    A microfabrication process using ultrafast laser pulses in glass was investigated. We investigated the formation of semiconductors by the irradiation of glasses with femtosecond laser pulses. ZnS- or PbS-doped SiO2-Al2O3-B2O3-CaO-ZnO-Na2O-K2O glasses were prepared by a melting method and irradiated by femtosecond laser pulses. Periodic structures in the sample glasses with a high refractive index difference were produced by femtosecond laser pulses. The maximum relative refractive index difference between the irradiated area and the nonirradiated areas was 20%. Diffraction gratings were also fabricated inside the ZnS- or PbS-doped silicate glasses. The diffraction efficiency of these gratings was approximately 90% in the infrared region.

  9. Universal pulse dependence of the low-energy structure in strong-field ionization

    NASA Astrophysics Data System (ADS)

    Zhang, Kaikai; Lai, Yu Hang; Diesen, Elias; Schmidt, Bruno E.; Blaga, Cosmin I.; Xu, Junliang; Gorman, Timothy T.; Légaré, Françis; Saalmann, Ulf; Agostini, Pierre; Rost, Jan M.; DiMauro, Louis F.

    2016-02-01

    We determine quantitatively the laser pulse duration dependence of the low-energy structure (LES) in strong-field atomic ionization and establish its universal character. The electron energy measurement is performed on krypton and argon by varying the duration of a 1.8 μ m midinfrared pulse from two to ten cycles. Comparing the experiment with analytical and numerical results, the soft-recollision mechanism leading to electron momentum bunching is confirmed as the origin of the LES. The universal behavior of the LES peak energy on pulse duration emerges from an analytical description as a product of two factors: one contains the influence of the laser parameters and the target, while the other one describes the pulse duration dependence in terms of optical cycles.

  10. Structure Fragmentation in a Subsurface Nickel Titanium Layer Caused by its Irradiation with Pulsed Silicon ion Fluxes

    NASA Astrophysics Data System (ADS)

    Meisner, S. N.

    2014-07-01

    Using the methods of electron backscatter diffraction, an investigation of variations in microstructure of the subsurface nickel titanium layer after its irradiation with pulsed, medium-energy silicon ion fluxes is performed. It is shown that following this ion-beam irradiation of the specimen surfaces, the subsurface-layer structure changes and undergoes fragmentation down to as deep as 5-15 μm, which is smaller than the average grain size of the initial alloy. It is found out that the fragmented-structure layer is characterized by the presence of a martensitic В19' phase and a high concentration of interfaces and grain boundaries; the linear dimensions of the fragments exceed 1 μm, the structure refinement in the layer below the irradiated surface is nonuniform and depends on crystallographic orientation of the initial grain. A reason for intensive fragmentation of individual grains of the initial B2 phase after ion-beam treatment is assumed to be the proximity of the orientation axes of the principal slip planes to that of the incident ion beam flux. This might have resulted in an earlier, compared to other grains, onset of plastic deformation in these grains and, as a result, partial fragmentation of their structure.

  11. Nanofabrication of tailored surface structures in dielectrics using temporally shaped femtosecond-laser pulses.

    PubMed

    Hernandez-Rueda, Javier; Götte, Nadine; Siegel, Jan; Soccio, Michelina; Zielinski, Bastian; Sarpe, Cristian; Wollenhaupt, Matthias; Ezquerra, Tiberio A; Baumert, Thomas; Solis, Javier

    2015-04-01

    We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses for producing nanostructures in two dielectric materials (sapphire and phosphate glass) with different characteristics in their response to pulsed laser radiation. For this purpose, laser pulses shaped by third-order dispersion (TOD) were used to generate temporally asymmetric excitation pulses, leading to the single-step production of subwavelength ablative and subablative surface structures. When compared to previous works on the interaction of tightly focused TOD-shaped pulses with fused silica, we show here that this approach leads to very different nanostructure morphologies, namely, clean nanopits without debris surrounding the crater in sapphire and well-outlined nanobumps and nanovolcanoes in phosphate glass. Although in sapphire the debris-free processing is associated with the much lower viscosity of the melt compared to fused silica, nanobump formation in phosphate glass is caused by material network expansion (swelling) upon resolidification below the ablation threshold. The formation of nanovolcanoes is a consequence of the combined effect of material network expansion and ablation occurring in the periphery and central part of the irradiated region, respectively. It is shown that the induced morphologies can be efficiently controlled by modulating the TOD coefficient of the temporally shaped pulses. PMID:25762003

  12. Generation of Initial Kinetic Distributions for Simulation of Long-Pulse Charged Particle Beams with High Space-Charge intensity

    SciTech Connect

    Lund, Steven M.; Kikuchi, Takashi; Davidson, Ronald C.

    2007-04-03

    Self-consistent Vlasov-Poisson simulations of beams with high space-charge intensity often require specification of initial phase-space distributions that reflect properties of a beam that is well adapted to the transport channel--both in terms of low-order rms (envelope) properties as well as the higher-order phase-space structure. Here, we first review broad classes of kinetic distributions commonly in use as initial Vlasov distributions in simulations of unbunched or weakly bunched beams with intense space-charge fields including: the Kapchinskij-Vladimirskij (KV) equilibrium, continuous-focusing equilibria with specific detailed examples, and various non-equilibrium distributions, such as the semi-Gaussian distribution and distributions formed from specified functions of linear-field Courant-Snyder invariants. Important practical details necessary to specify these distributions in terms of usual accelerator inputs are presented in a unified format. Building on this presentation, a new class of approximate initial kinetic distributions are constructed using transformations that preserve linear-focusing single-particle Courant-Snyder invariants to map initial continuous-focusing equilibrium distributions to a form more appropriate for non-continuous focusing channels. Self-consistent particle-in-cell simulations are employed to show that the approximate initial distributions generated in this manner are better adapted to the focusing channels for beams with high space-charge intensity. This improved capability enables simulation applications that more precisely probe intrinsic stability properties and machine performance.

  13. Electronic and Structural Response of InSb to Ultra-short and Ultra-intense Laser Pulses

    NASA Astrophysics Data System (ADS)

    Burzo, Andrea; Allen, Roland

    2002-03-01

    The present work is motivated in part by the increasing interest in a better understanding of the optical properties of InSb, the main material used to manufacture infrared detectors. In addition, there have been recent experimental studies of the behavior of InSb following application of ultra-short and ultra-intense laser pulses. Motivated directly by these experiments, we have performed simulations of the electron-ion dynamics of InSb subjected to femtosecond-scale laser pulses. These simulations employ a tight-binding approximation, and the time-dependent Schroedinger equation is solved with an adapted Cayley algorithm which conserves probability. The atomic forces are obtained from a generalized Hellmann-Feynman theorem, which may be also interpreted as a generalized Ehrenfest theorem. We find that above a certain threshold intensity the lattice loses its tetrahedral structure and becomes disrupted. In addition, the band gap collapses and the material becomes metallic. Comparison of our simulations with experiments involving measurements of the imaginary part of the dielectric function shows good agreement in all important aspects. Further investigation of microscopic quantities, such as the atomic pair correlation function, the occupancies of excited states, and the displacement of atoms from their initial positions, strengthens our conclusion that the semiconductor exhibits a nonthermal phase transition as the intensity of the laser pulse is increased.

  14. Pulsed Electron Double Resonance in Structural Studies of Spin-Labeled Nucleic Acids

    PubMed Central

    Fedorova, O. S.; Tsvetkov, Yu. D.

    2013-01-01

    This review deals with the application of the pulsed electron double resonance (PELDOR) method to studies of spin-labeled DNA and RNA with complicated spatial structures, such as tetramers, aptamers, riboswitches, and three- and four-way junctions. The use of this method for studying DNA damage sites is also described. PMID:23556128

  15. Pulsed terahertz time domain spectroscopy of vertically structured photoconductive antennas

    NASA Astrophysics Data System (ADS)

    Faulks, R.; Rihani, S.; Beere, H. E.; Evans, M. J.; Ritchie, D. A.; Pepper, M.

    2010-02-01

    We present a terahertz (THz) photoconductive emitter structure, which employs a n-doped layer underneath a low-temperature-grown GaAs region to enable the THz transient to couple vertically through a defined mesa. A nonlinear bias dependence is observed, yielding an order in magnitude improvement in power for a mesa device with a 100 μm2 area over a conventional planar control reference device at 32 V and 5 mW illumination power. We relate the bias dependence of the THz signal to the breakdown voltage observed in the current-voltage characteristic. Reducing the antenna gap size through reducing the thickness of the low temperature-GaAs region below 1 μm shows a large improvement in the bandwidth of the device, with an enhancement of the normalized intensity between 0.2 to 2 THz for a bow-tie antenna geometry.

  16. Low-Energy Peak Structure in Strong-Field Ionization by Mid-Infrared Laser Pulses

    NASA Astrophysics Data System (ADS)

    Lemell, C.; Dimitriou, K. I.; Arbó, D. G.; Tong, X.-M.; Kartashov, D.; Burgdörfer, J.; Gräfe, S.

    2013-03-01

    Using a quasiclassical approach, we demonstrate that the formation of the low-energy structure in above-threshold ionization spectra by intense, midinfrared laser pulses originates from a two-dimensional focusing of the strong-field dynamics in the energy-angular-momentum plane. We show that the low-energy structure is very sensitive to the carrier-envelope phase of the laser field.

  17. Analysis of Crystallographic Structure of a Japanese Sword by the Pulsed Neutron Transmission Method

    NASA Astrophysics Data System (ADS)

    Kino, K.; Ayukawa, N.; Kiyanagi, Y.; Uchida, T.; Uno, S.; Grazzi, F.; Scherillo, A.

    We measured two-dimensional transmission spectra of pulsed neutron beams for a Japanese sword sample. Atom density, crystalline size, and preferred orientation of crystals were obtained using the RITS code. The position dependence of the atomic density is consistent with the shape of the sample. The crystalline size is very small and shows position dependence, which is understood by the unique structure of Japanese swords. The preferred orientation has strong position dependence. Our study shows the usefulness of the pulsed neutron transmission method for cultural metal artifacts.

  18. Structural properties of silicon nanoparticles formed by pulsed laser ablation in liquid media

    NASA Astrophysics Data System (ADS)

    Eroshova, O. I.; Perminov, P. A.; Zabotnov, S. V.; Gongal'skii, M. B.; Ezhov, A. A.; Golovan', L. A.; Kashkarov, P. K.

    2012-11-01

    Silicon nanoparticles have been formed as a result of the irradiation of single-crystal silicon targets in distilled water and liquid nitrogen, by, respectively, picosecond and femtosecond laser pulses. The main structural properties of these nanoparticles have been investigated by atomic force microscopy, transmission electron microscopy, electron diffraction, Raman scattering, and photoluminescence spectroscopy. These particles are found to be mainly spherical. The presence of crystalline and amorphous silicon phases under picosecond ablation in water is established experimentally. Irradiation by femtosecond pulses in liquid nitrogen can yield nanoparticles smaller than 5 nm in size, which are quantum dots with a characteristic photoluminescence peak near 750 nm.

  19. Structure of the dense cores and ablation plasmas in the initiation phase of tungsten wire-array Z pinches

    SciTech Connect

    Douglass, J. D.; Hammer, D. A.; McBride, R. D.; Pikuz, S. A.; Shelkovenko, T. A.; Bland, S. N.; Bott, S. C.

    2007-01-15

    The early stages of tungsten (W) wire-array Z-pinch implosions have been studied using two-frame point projection x-ray backlighting on the 1 MA COBRA pulsed power generator [J. D. Douglass, J. B. Greenly, D. A. Hammer, and B. R. Kusse, in Proceedings of the 15th IEEE International Pulsed Power Conference, Monterey, 2005 (to be published)]. X-pinch backlighter images with subnanosecond time resolution and 4-10 {mu}m spatial resolution have been obtained of individual W exploding wires in 8-wire arrays that show evolution of wire-core and coronal plasma structures. The timing of the X-pinch x-ray bursts relative to the Z-pinch initiation time was adjusted over a 50 ns time interval by varying the X-pinch mass per unit length. Wire-cores seen in two images separated in view by 120 deg. show that the expansion is remarkably azimuthally symmetric. A strong correlation is observed between the structure on the dense exploding wire-cores and the structure of the {>=}10{sup 18}/cm{sup 3} ablation plasma being drawn from radial prominences. Plasma ablation velocity was estimated to have a lower bound of 24 km/s. The wire-core expansion rate was found to be approximately constant with time over the interval 50-100 ns after the start of the current pulse. Finally, micron-scale axial gaps, seen as early as 70 ns into the current pulse and persisting from that time, were observed along the wire-core.

  20. Three-dimensional micro-/nano-structuring via direct write polymerization with picosecond laser pulses.

    PubMed

    Malinauskas, Mangirdas; Danilevičius, Paulius; Juodkazis, Saulius

    2011-03-14

    We demonstrate capability to structure photo-polymers with sub-wavelength resolution, ∼200-500 nm, and retrieve three-dimensional (3D) structures using a picosecond laser exposure. This alternative to commonly used ultra-short femtosecond lasers extends accessibility of 3D direct write. A popular hybrid sol-gel resist SZ2080 was used for quantitative determination of structuring resolution at 1064 nm and 532 nm wavelengths and for pulses of 8-25 ps duration at the repetition rates of 0.2-1 MHz. Systematic study of feature size dependence of 3D suspended nano-rods shows that linear power dependence of photopolymerization on the dose-per-pulse becomes dominant at higher repetition rates (≥0.5 MHz) while the two-photon nonlinear absorption is still distinguishable at rates lower than 0.2 MHz and shorter pulses (≤8 ps). Thermal accumulation defines polymerization when cooling time of the focal volume is larger than separation between pulses. Photopolymerization and its scaling mechanisms, quality, and fidelity at tight focusing of fs-, ps-, and cw-laser radiation are revealed and explained. 3D scaffolds for biomedicine and microlenses for optical applications are fabricated by the ps-laser direct write. PMID:21445200

  1. Multiple quasi-monoenergetic electron beams from laser-wakefield acceleration with spatially structured laser pulse

    SciTech Connect

    Ma, Y.; Li, M. H.; Li, Y. F.; Wang, J. G.; Tao, M. Z.; Han, Y. J.; Zhao, J. R.; Huang, K.; Yan, W. C.; Ma, J. L.; Li, Y. T.; Chen, L. M.; Li, D. Z.; Chen, Z. Y.; Sheng, Z. M.; Zhang, J.

    2015-08-15

    By adjusting the focus geometry of a spatially structured laser pulse, single, double, and treble quasi-monoenergetic electron beams were generated, respectively, in laser-wakefield acceleration. Single electron beam was produced as focusing the laser pulse to a single spot. While focusing the laser pulse to two spots that are approximately equal in energy and size and intense enough to form their own filaments, two electron beams were produced. Moreover, with a proper distance between those two focal spots, three electron beams emerged with a certain probability owing to the superposition of the diffractions of those two spots. The energy spectra of the multiple electron beams are quasi-monoenergetic, which are different from that of the large energy spread beams produced due to the longitudinal multiple-injection in the single bubble.

  2. Time-resolved structural dynamics of thin metal films heated with femtosecond optical pulses

    PubMed Central

    Chen, Jie; Chen, Wei-Kan; Tang, Jau; Rentzepis, Peter M.

    2011-01-01

    We utilize 100 fs optical pulses to induce ultrafast disorder of 35- to 150-nm thick single Au(111) crystals and observe the subsequent structural evolution using 0.6-ps, 8.04-keV X-ray pulses. Monitoring the picosecond time-dependent modulation of the X-ray diffraction intensity, width, and shift, we have measured directly electron/phonon coupling, phonon/lattice interaction, and a histogram of the lattice disorder evolution, such as lattice breath due to a pressure wave propagating at sonic velocity, lattice melting, and recrystallization, including mosaic formation. Results of theoretical simulations agree and support the experimental data of the lattice/liquid phase transition process. These time-resolved X-ray diffraction data provide a detailed description of all the significant processes induced by ultrafast laser pulses impinging on thin metallic single crystals. PMID:22065752

  3. Time-resolved pulsed hydrogen/deuterium exchange mass spectrometry probes gaseous proteins structural kinetics.

    PubMed

    Rajabi, Khadijeh

    2015-01-01

    A pulsed hydrogen/deuterium exchange (HDX) method has been developed for rapid monitoring of the exchange kinetics of protein ions with D2O a few milliseconds after electrospray ionization (ESI). The stepwise gradual evolution of HDX of multiply charged protein ions was monitored using the pulsed HDX mass spectrometry technique. Upon introducing a very short pulse of D2O (in the μs to ms time scale) into the linear ion trap (LIT) of a time-of-flight (TOF) mass spectrometer, bimodal distributions were detected for the ions of cytochrome c and ubiquitin. Mechanistic details of HDX reactions for ubiquitin and cytochrome c in the gas phase were uncovered and the structural transitions were followed by analyzing the kinetics of HDX. PMID:25318698

  4. Time-Resolved Pulsed Hydrogen/Deuterium Exchange Mass Spectrometry Probes Gaseous Proteins Structural Kinetics

    NASA Astrophysics Data System (ADS)

    Rajabi, Khadijeh

    2015-01-01

    A pulsed hydrogen/deuterium exchange (HDX) method has been developed for rapid monitoring of the exchange kinetics of protein ions with D2O a few milliseconds after electrospray ionization (ESI). The stepwise gradual evolution of HDX of multiply charged protein ions was monitored using the pulsed HDX mass spectrometry technique. Upon introducing a very short pulse of D2O (in the μs to ms time scale) into the linear ion trap (LIT) of a time-of-flight (TOF) mass spectrometer, bimodal distributions were detected for the ions of cytochrome c and ubiquitin. Mechanistic details of HDX reactions for ubiquitin and cytochrome c in the gas phase were uncovered and the structural transitions were followed by analyzing the kinetics of HDX.

  5. Structural Influences on Initial Accent Placement in French

    ERIC Educational Resources Information Center

    Astesano, Corine; Bard, Ellen Gurman; Turk, Alice

    2007-01-01

    In addition to the phrase-final accent (FA), the French phonological system includes a phonetically distinct Initial Accent (IA). The present study tested two proposals: that IA marks the onset of phonological phrases, and that it has an independent rhythmic function. Eight adult native speakers of French were instructed to read syntactically…

  6. Turbulent structure and emissions of strongly-pulsed jet diffusion flames

    NASA Astrophysics Data System (ADS)

    Fregeau, Mathieu

    This current research project studied the turbulent flame structure, the fuel/air mixing, the combustion characteristics of a nonpremixed pulsed (unsteady) and unpulsed (steady) flame configuration for both normal- and microgravity conditions, as well as the flame emissions in normal gravity. The unsteady flames were fully-modulated, with the fuel flow completely shut off between injection pulses using an externally controlled valve, resulting in the generation of compact puff-like flame structures. Conducting experiments in normal and microgravity environments enabled separate control over the relevant Richardson and Reynolds numbers to clarify the influence of buoyancy on the flame behavior, mixing, and structure. Experiments were performed in normal gravity in the laboratory at the University of Washington and in microgravity using the NASA GRC 2.2-second Drop Tower facility. High-speed imaging, as well as temperature and emissions probes were used to determine the large-scale structure dynamics, the details of the flame structure and oxidizer entrainment, the combustion temperatures, and the exhaust emissions of the pulsed and steady flames. Of particular interest was the impact of changes in flame structure due to pulsing on the combustion characteristics of this system. The turbulent flame puff celerity (i.e., the bulk velocity of the puffs) was strongly impacted by the jet-off time, increasing markedly as the time between pulses was decreased, which caused the degree of puff interaction to increase and the strongly-pulsed flame to more closely resemble a steady flame. This increase occurred for all values of injection time as well as for constant fuelling rate and in both the presence and absence of buoyancy. The removal of positive buoyancy in microgravity resulted in a decrease in the flame puff celerity in all cases, amounting to as much as 40%, for both constant jet injection velocity and constant fuelling rate. The mean flame length of the strongly-pulsed

  7. Formation of nanoporous structures in metallic materials by pulse-periodic laser treatment

    NASA Astrophysics Data System (ADS)

    Murzin, Serguei P.

    2015-09-01

    A method of the formation of nanoporous structures in metallic materials by pulse-periodic laser treatment was developed. In this study, the multicomponent aluminum-iron brass was considered and the nanoporous structure across the entire cross section of the material with a thickness of 50 μm was formed. The method was implemented using a CO2 laser processing unit. The pulse-periodic laser treatment of the Cu-Zn-Al-Fe alloy with pulse frequency of 5 Hz has led to the formation of nanosized cavities due to accumulation of internal stresses during cyclic heating and cooling at high speeds. It was determined that the pores of a channel type with average widths of 80-100 nm are formed in the central region of the heat-affected zone during laser action with thermocycling. When implementing the chosen conditions of the pulse-periodic laser processing, the localness in depth and area of the physical processes occurring in the heat-affected zone is ensured, while maintaining the original properties of the material and the absence of significant deformations in the rest of the volume. This patented process is perspective for the production not only catalysts for chemical reactions, but for ultrafiltration and microfiltration membranes as well.

  8. Mathematical Constraints on the Use of Transmission Line Models for Simulating Initial Breakdown Pulses in Lightning Discharges

    NASA Astrophysics Data System (ADS)

    da Silva, C. L.; Merrill, R. A.; Pasko, V. P.

    2015-12-01

    A significant portion of the in-cloud lightning development is observed as a series of initial breakdown pulses (IBPs) that are characterized by an abrupt change in the electric field at a remote sensor. Recent experimental and theoretical studies have attributed this process to the stepwise elongation of an initial lightning leader inside the thunderstorm [da Silva and Pasko, JGR, 120, 4989-5009, 2015, and references therein]. Attempts to visually observe these events are hampered due to the fact that clouds are opaque to optical radiation. Due to this reason, throughout the last decade, a number of researchers have used the so-called transmission line models (also commonly referred to as engineering models), widely employed for return stroke simulations, to simulate the waveshapes of IBPs, and also of narrow bipolar events. The transmission line (TL) model approach is to prescribe the source current dynamics in a certain manner to match the measured E-field change waveform, with the purpose of retrieving key information about the source, such as its height, peak current, size, speed of charge motion, etc. Although the TL matching method is not necessarily physics-driven, the estimated source characteristics can give insights on the dominant length- and time-scales, as well as, on the energetics of the source. This contributes to better understanding of the environment where the onset and early stages of lightning development takes place.In the present work, we use numerical modeling to constrain the number of source parameters that can be confidently inferred from the observed far-field IBP waveforms. We compare different modified TL models (i.e., with different attenuation behaviors) to show that they tend to produce similar waveforms in conditions where the channel is short. We also demonstrate that it is impossible to simultaneously retrieve the speed of source current propagation and channel length from an observed IBP waveform, in contrast to what has been

  9. Structure of the Jovian Magnetodisk Current Sheet: Initial Galileo Observations

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Huddleston, D. E.; Khurana, K. K.; Kivelson, M. G.

    2001-01-01

    The ten-degree tilt of the Jovian magnetic dipole causes the magnetic equator to move back and forth across Jupiter's rotational equator and tile Galileo orbit that lies therein. Beyond about 24 Jovian radii, the equatorial current sheet thins and tile magnetic structure changes from quasi-dipolar into magnetodisk-like with two regions of nearly radial but antiparallel magnetic field separated by a strong current layer. The magnetic field at the center of the current sheet is very weak in this region. Herein we examine tile current sheet at radial distances from 24 55 Jovian radii. We find that the magnetic structure very much resembles tile structure seen at planetary magnetopause and tail current sheet crossings. Tile magnetic field variation is mainly linear with little rotation of the field direction, At times there is almost no small-scale structure present and the normal component of the magnetic field is almost constant through the current sheet. At other times there are strong small-scale structures present in both the southward and northward directions. This small-scale structure appears to grow with radial distance and may provide the seeds for tile explosive reconnection observed at even greater radial distances oil tile nightside. Beyond about 40 Jovian radii, the thin current sheet also appears to be almost constantly in oscillatory motion with periods of about 10 min. The amplitude of these oscillations also appears to grow with radial distance. The source of these fluctuations may be dynamical events in tile more distant magnetodisk.

  10. Differences between intra- and extra-cavity pulse time structure in a hole-coupled free-electron laser

    SciTech Connect

    Weits, H.H.; Knippels, G.M.H.; Werkhoven, G.H.C. van; Oepts, D.; Amersfoort, P.W. van

    1997-03-01

    In the strong-slippage regime of a free-electron laser, the optical pulse inside the resonator is composed of a series of subsequently growing and decaying subpulses due to a limit-cycle oscillation. The picosecond time structure of the outcoupled pulses can be quite different from that of the intracavity pulse, in case of outcoupling through a hole and for specific resonator parameters. This is demonstrated by autocorrelation measurements and corroborated by simulations.

  11. Spatial Moran models, II: cancer initiation in spatially structured tissue

    PubMed Central

    Foo, J; Leder, K

    2016-01-01

    We study the accumulation and spread of advantageous mutations in a spatial stochastic model of cancer initiation on a lattice. The parameters of this general model can be tuned to study a variety of cancer types and genetic progression pathways. This investigation contributes to an understanding of how the selective advantage of cancer cells together with the rates of mutations driving cancer, impact the process and timing of carcinogenesis. These results can be used to give insights into tumor heterogeneity and the “cancer field effect,” the observation that a malignancy is often surrounded by cells that have undergone premalignant transformation. PMID:26126947

  12. The structure of slip-pulses and supershear ruptures driving slip in bimaterial friction

    PubMed Central

    Shlomai, Hadar; Fineberg, Jay

    2016-01-01

    The most general frictional motion in nature involves bimaterial interfaces, when contacting bodies possess different elastic properties. Frictional motion occurs when the contacts composing the interface separating these bodies detach via propagating rupture fronts. Coupling between slip and normal stress variations is unique to bimaterial interfaces. Here we use high speed simultaneous measurements of slip velocities, real contact area and stresses to explicitly reveal this bimaterial coupling and its role in determining different classes of rupture modes and their structures. We directly observe slip-pulses, highly localized slip accompanied by large local reduction of the normal stress near the rupture tip. These pulses propagate in the direction of motion of the softer material at a selected (maximal) velocity and continuously evolve while propagating. In the opposite direction bimaterial coupling favors crack-like ‘supershear' fronts. The robustness of these structures shows the importance of bimaterial coupling to frictional motion and modes of frictional dissipation. PMID:27278687

  13. The structure of slip-pulses and supershear ruptures driving slip in bimaterial friction.

    PubMed

    Shlomai, Hadar; Fineberg, Jay

    2016-01-01

    The most general frictional motion in nature involves bimaterial interfaces, when contacting bodies possess different elastic properties. Frictional motion occurs when the contacts composing the interface separating these bodies detach via propagating rupture fronts. Coupling between slip and normal stress variations is unique to bimaterial interfaces. Here we use high speed simultaneous measurements of slip velocities, real contact area and stresses to explicitly reveal this bimaterial coupling and its role in determining different classes of rupture modes and their structures. We directly observe slip-pulses, highly localized slip accompanied by large local reduction of the normal stress near the rupture tip. These pulses propagate in the direction of motion of the softer material at a selected (maximal) velocity and continuously evolve while propagating. In the opposite direction bimaterial coupling favors crack-like 'supershear' fronts. The robustness of these structures shows the importance of bimaterial coupling to frictional motion and modes of frictional dissipation. PMID:27278687

  14. The structure of slip-pulses and supershear ruptures driving slip in bimaterial friction

    NASA Astrophysics Data System (ADS)

    Shlomai, Hadar; Fineberg, Jay

    2016-06-01

    The most general frictional motion in nature involves bimaterial interfaces, when contacting bodies possess different elastic properties. Frictional motion occurs when the contacts composing the interface separating these bodies detach via propagating rupture fronts. Coupling between slip and normal stress variations is unique to bimaterial interfaces. Here we use high speed simultaneous measurements of slip velocities, real contact area and stresses to explicitly reveal this bimaterial coupling and its role in determining different classes of rupture modes and their structures. We directly observe slip-pulses, highly localized slip accompanied by large local reduction of the normal stress near the rupture tip. These pulses propagate in the direction of motion of the softer material at a selected (maximal) velocity and continuously evolve while propagating. In the opposite direction bimaterial coupling favors crack-like `supershear' fronts. The robustness of these structures shows the importance of bimaterial coupling to frictional motion and modes of frictional dissipation.

  15. Surface modification of structural materials by low-energy high-current pulsed electron beam treatment

    SciTech Connect

    Panin, A. V. E-mail: kms@ms.tsc.ru; Kazachenok, M. S. E-mail: kms@ms.tsc.ru; Sinyakova, E. A.; Borodovitsina, O. M.; Ivanov, Yu. F.; Leontieva-Smirnova, M. V.

    2014-11-14

    Microstructure formation in surface layers of pure titanium and ferritic-martensitic steel subjected to electron beam treatment is studied. It is shown that low energy high-current pulsed electron beam irradiation leads to the martensite structure within the surface layer of pure titanium. Contrary, the columnar ferrite grains grow during solidification of ferritic-martensitic steel. The effect of electron beam energy density on the surface morphology and microstructure of the irradiated metals is demonstrated.

  16. Membrane-initiated estradiol actions mediate structural plasticity and reproduction

    PubMed Central

    Micevych, Paul; Christensen, Amy

    2012-01-01

    Over the years, our ideas about estrogen signaling have greatly expanded. In addition to estradiol having direct nuclear actions that mediate transcription and translation, more recent experiments have demonstrated membrane-initiated signaling. Both direct nuclear and estradiol membrane signaling can be mediated by the classical estrogen receptors, ERα and ERβ, which are two of the numerous putative membrane estrogen receptors. Thus far, however, only ERα has been shown to play a prominent role in regulating female reproduction and sexual behavior. Because ERα is a ligand-gated transcription factor and not a typical membrane receptor, trafficking to the cell membrane requires post-translational modifications. Two necessary modifications are palmitoylation and association with caveolins, a family of scaffolding proteins. In addition to their role in trafficking, caveolin proteins also serve to determine ERα interactions with metabotropic glutamate receptors (mGluRs). It is through these complexes that ERα, which cannot by itself activate G proteins, is able to initiate intracellular signaling. Various combinations of ERα-mGluR interactions have been demonstrated throughout the nervous system from hippocampus to striatum to hypothalamus to dorsal root ganglion (DRG) in both neurons and astrocytes. These combinations of ER and mGluR allow estradiol to have both facilitative and inhibitory actions in neurons. In hypothalamic astrocytes, the estradiol-mediated release of intracellular calcium stores regulating neurosteroid synthesis requires ERα-mGluR1a interaction. In terms of estradiol regulation of female sexual receptivity, activation of ERα-mGluR1a signaling complex leads to the release of neurotransmitters and alteration of neuronal morphology. This review will examine estradiol membrane signaling (EMS) activating a limbic-hypothalamic lordosis regulating circuit, which involves ERα trafficking, internalization, and modifications of neuronal morphology

  17. Structural basis for angiopoietin-1–mediated signaling initiation

    SciTech Connect

    Yu, Xuehong; Seegar, Tom C. M.; Dalton, Annamarie C.; Tzvetkova-Robev, Dorothea; Goldgur, Yehuda; Rajashankar, Kanagalaghatta R.; Nikolov, Dimitar B.; Barton, William A.

    2013-04-30

    Angiogenesis is a complex cellular process involving multiple regulatory growth factors and growth factor receptors. Among them, the ligands for the endothelial-specific tunica intima endothelial receptor tyrosine kinase 2 (Tie2) receptor kinase, angiopoietin-1 (Ang1) and Ang2, play essential roles in balancing vessel stability and regression during both developmental and tumor-induced angiogenesis. Despite possessing a high degree of sequence identity, Ang1 and Ang2 have distinct functional roles and cell-signaling characteristics. Here, we present the crystal structures of Ang1 both unbound and in complex with the Tie2 ectodomain. Comparison of the Ang1-containing structures with their Ang2-containing counterparts provide insight into the mechanism of receptor activation and reveal molecular surfaces important for interactions with Tie2 coreceptors and associated signaling proteins. Using structure-based mutagenesis, we identify a loop within the angiopoietin P domain, adjacent to the receptor-binding interface, which confers the specific agonist/antagonist properties of the molecule. We demonstrate using cell-based assays that an Ang2 chimera containing the Ang1 loop sequence behaves functionally similarly to Ang1 as a constitutive Tie2 agonist, able to efficiently dissociate the inhibitory Tie1/Tie2 complex and elicit Tie2 clustering and downstream signaling.

  18. A novel structure of transmission line pulse transformer with mutually coupled windings.

    PubMed

    Yu, Binxiong; Su, Jiancang; Li, Rui; Zhao, Liang; Zhang, Xibo; Wang, Junjie

    2014-03-01

    A novel structure of transmission line transformer (TLT) with mutually coupled windings is described in this paper. All transmission lines except the first stage of the transformer are wound on a common ferrite core for the TLT with this structure. A referral method was introduced to analyze the TLT with this structure, and an analytic expression of the step response was derived. It is shown that a TLT with this structure has a significantly slower droop rate than a TLT with other winding structures and the number of ferrite cores needed is largely reduced. A four-stage TLT with this structure was developed, whose input and output impedance were 4.2 Ω and 67.7 Ω, respectively. A frequency response test of the TLT was carried out. The test results showed that pulse response time of the TLT is several nanoseconds. The TLT described in this paper has the potential to be used as a rectangle pulse transformer with very fast response time. PMID:24689623

  19. Phase and frequency structure of superradiance pulses generated by relativistic Ka-band backward-wave oscillator

    NASA Astrophysics Data System (ADS)

    Rostov, V. V.; Romanchenko, I. V.; Elchaninov, A. A.; Sharypov, K. A.; Shunailov, S. A.; Ul'masculov, M. R.; Yalandin, M. I.

    2016-08-01

    Phase and frequency stability of electromagnetic oscillations in sub-gigawatt superradiance (SR) pulses generated by an extensive slow-wave structure of a relativistic Ka-band backward-wave oscillator were experimentally investigated. Data on the frequency tuning and radiation phase stability of SR pulses with a variation of the energy and current of electron beam were obtained.

  20. Initiation of simian virus 40 DNA replication in vitro: Pulse-chase experiments identify the first labeled species as topologically unwound

    SciTech Connect

    Bullock, P.A.; Seo, Yeon Soo; Hurwitz, J. )

    1989-06-01

    A distinct unwound form of DNA containing the simian virus 40 (SV40) origin is produced in replication reactions carried out in mixtures containing crude fractions prepared from HeLa cells. This species, termed form U{sub R}, comigrates on chloroquine-containing agarose gels with the upper part of the previously described heterogeneous highly unwound circular DNA, form U. As with form U, formation of form U{sub R} is dependent upon the SV40 tumor (T) antigen. Pulse-chase experiments demonstrate that the first species to incorporate labeled deoxyribonucleotides comigrates with form U{sub R}. Restriction analyses of the products of the pulse-chase experiments show that initiation occurs at the SV40 origin and then proceeds outward in a bidirectional manner. These experiments establish form U{sub R} as the earliest detectable substrate for SV40 DNA replication and suggest that SV40 DNA replication initiates on an unwound species.

  1. Periodic structure formation and surface morphology evolution of glassy carbon surfaces applying 35-fs-200-ps laser pulses

    NASA Astrophysics Data System (ADS)

    Csontos, J.; Toth, Z.; Pápa, Z.; Budai, J.; Kiss, B.; Börzsönyi, A.; Füle, M.

    2016-06-01

    In this work laser-induced periodic structures with lateral dimensions smaller than the central wavelength of the laser were studied on glassy carbon as a function of laser pulse duration. To generate diverse pulse durations titanium-sapphire (Ti:S) laser (center wavelength 800 nm, pulse durations: 35 fs-200 ps) and a dye-KrF excimer laser system (248 nm, pulse durations: 280 fs, 2.1 ps) were used. In the case of Ti:S laser treatment comparing the central part of the laser-treated areas a striking difference is observed between the femtoseconds and picoseconds treatments. Ripple structure generated with short pulse durations can be characterized with periodic length significantly smaller than the laser wavelength (between 120 and 165 nm). At higher pulse durations the structure has a higher periodic length (between 780 and 800 nm), which is comparable to the wavelength. In case of the excimer laser treatment the different pulse durations produced similar surface structures with different periodic length and different orientation. One of the structures was parallel with the polarization of the laser light and has a higher periodic length (~335 nm), and the other was perpendicular with smaller periodic length (~78-80 nm). The possible mechanisms of structure formation will be outlined and discussed in the frame of our experimental results.

  2. Initial phases for the development of a Structural Geology database

    NASA Astrophysics Data System (ADS)

    Tikoff, Basil; Babaie, Hassan; Clark, Ryan; Newman, Juile; Walker, Doug

    2014-05-01

    We are at the beginning stages of developing a Data System for Structural Geology and Tectonics (SG&T). This activity is prompted by the necessity of reporting our data from government-funded projects and the lack of any existing database. SG&T data is complex for a variety of reasons, including the wide range of temporal and spatial scales (many orders of magnitude each), the complex three-dimensional geometry of some geological structures, inherent spatial nature of the data, and the difficulty of making temporal inferences from spatial observations. To successful implement the step of developing a SG&T data system, we must simultaneously solve three problems: 1) How to digitize SG&T data; 2) How to design a software system that is applicable; and 3) How to construct a very flexible user interface. To address the first problem, we introduce the "Spot" concept, which allows tracking of hierarchical and spatial relations between structures at all scales, and will link map scale, mesoscale, and laboratory scale data. A Spot, in this sense, is analogous to the beam size of analytical equipment used for in situ analysis of rocks; it is the size over which a measurement or quantity is applicable. A Spot can be a single measurement, an aggregation of individual measurements, or even establish relationships between numerous other Spots. We propose to implement both a Spot and a more traditional Mapping mode for data input. The final challenge is to construct a user interface that is intuitive, open source, and spans as many operating systems and devices as possible. For these reasons, we propose to develop a web-application that can run in both a connected (on the internet) and disconnected mode. Our hope is to have extensive and international community input into the data system development process.

  3. Micro/Nano-Structuring of Medical Stainless Steel using Femtosecond Laser Pulses

    NASA Astrophysics Data System (ADS)

    Lin, C. Y.; Cheng, C. W.; Ou, K. L.

    The medical stainless steel (SUS 304) surface is irradiated by femtosecond laser pulses with linear or circular polarization to form nanostructure-covered conical microstructures. The mean spacing of the conical microstructures and the type of the nanostructure can be controlled by the laser-processing parameters. The liquid test (water and normal-saline solution) demonstrates that the process provides a fast single-step structuring method to generate hydrophobic-enhanced metal parts. The biocompatibility test demonstrated that the femtosecond laser micro/nano- structuring surfaces have excellent biocompatibility properties compared to an untreated surface.

  4. Lightning initiation from a tall structure in the Basque Country

    NASA Astrophysics Data System (ADS)

    López, J.; Montanyà, J.; Maruri, M.; De la Vega, D.; Aranda, J. A.; Gaztelumendi, S.

    2012-11-01

    Lightning detection in the Spanish Basque Country is performed using the LF TOA, VHF interferometer and the VLF lightning detection technologies in which two independent networks are based, providing a better detection quality due to the combination of these different techniques. Total lightning activity related to the tall structure of the weather radar operated by the Basque Meteorology Agency (Euskalmet) is presented. The tall structure is a 50 m tower located on the top of Kapildui Mountain (at about 1169.48 m ASL). Remarkable electrical activity associated to this place has been witnessed in the last two years. Two particular flashes during November 30th 2009 caused damage to the weather radar. Two different lightning detection networks detected five and six cloud-to-ground strokes, respectively. Only nine VHF sources were detected in the first flash without any VLF detection classified as intracloud. But for the second flash non VHF source was detected and two detections were reported by the VLF system. In both cases some intracloud detections were reported before cloud-to-ground strokes and some others during the flash. This paper presents the study of a winter episode with a special impact in the tower, the research carried out for characterizing the lightning events and the measures taken in order to achieve a better protection mechanism for the radar site.

  5. Structural basis for DNA binding by replication initiator Mcm10

    SciTech Connect

    Warren, Eric M.; Vaithiyalingam, Sivaraja; Haworth, Justin; Greer, Briana; Bielinsky, Anja-Katrin; Chazin, Walter J.; Eichman, Brandt F.

    2009-06-30

    Mcm10 is an essential eukaryotic DNA replication protein required for assembly and progression of the replication fork. The highly conserved internal domain (Mcm10-ID) has been shown to physically interact with single-stranded (ss) DNA, DNA polymerase alpha, and proliferating cell nuclear antigen (PCNA). The crystal structure of Xenopus laevis Mcm10-ID presented here reveals a DNA binding architecture composed of an oligonucleotide/oligosaccharide-fold followed in tandem by a variant and highly basic zinc finger. NMR chemical shift perturbation and mutational studies of DNA binding activity in vitro reveal how Mcm10 uses this unique surface to engage ssDNA. Corresponding mutations in Saccharomyces cerevisiae result in increased sensitivity to replication stress, demonstrating the functional importance of DNA binding by this region of Mcm10 to replication. In addition, mapping Mcm10 mutations known to disrupt PCNA, polymerase alpha, and DNA interactions onto the crystal structure provides insight into how Mcm10 might coordinate protein and DNA binding within the replisome.

  6. Pulsed modification of germanium films on silicon, sapphire, and quartz substrates: Structure and optical properties

    SciTech Connect

    Novikov, H. A.; Batalov, R. I. Bayazitov, R. M.; Faizrakhmanov, I. A.; Lyadov, N. M.; Shustov, V. A.; Galkin, K. N.; Galkin, N. G.; Chernev, I. M.; Ivlev, G. D.; Prokop’ev, S. L.; Gaiduk, P. I.

    2015-06-15

    The structural and optical properties of thin Ge films deposited onto semiconducting and insulating substrates and modified by pulsed laser radiation are studied. The films are deposited by the sputtering of a Ge target with a low-energy Xe{sup +} ion beam. Crystallization of the films is conducted by their exposure to nanosecond ruby laser radiation pulses (λ = 0.694 μm) with the energy density W = 0.2−1.4 J cm{sup −2}. During pulsed laser treatment, the irradiated area is probed with quasi-cw (quasi-continuous-wave) laser radiation (λ = 0.532 and 1.064 μm), with the reflectance recorded R(t). Experimental data on the lifetime of the Ge melt are compared with the results of calculation, and good agreement between them is demonstrated. Through the use of a number of techniques, the dependences of the composition of the films, their crystal structure, the level of strains, and the reflectance and transmittance on the conditions of deposition and annealing are established.

  7. Structural Biology of Replication Initiation Factor Mcm10

    PubMed Central

    Du, Wenyue; Stauffer, Melissa E.; Eichman, Brandt F.

    2016-01-01

    Minichromosome maintenance protein 10 (Mcm10) is a non-enzymatic replication factor required for proper assembly of the eukaryotic replication fork. Mcm10 interacts with single-stranded and double-stranded DNA, polymerase α, and Mcm2-7, and is important for activation of the pre-replicative complex and recruitment of subsequent proteins to the origin at the onset of S-phase. In addition, Mcm10 has recently been implicated in coordination of helicase and polymerase activities during replication fork progression. The nature of Mcm10's involvement in these activities, whether direct or indirect, remains unknown. However, recent biochemical and structural characterization of Mcm10 from multiple organisms has provided insights into how Mcm10 utilizes a modular architecture to act as a replisome scaffold, which helps to define possible roles in origin DNA melting, pol α recruitment and coordination of enzymatic activities during elongation. PMID:22918587

  8. Resistance to deformation of structural steels exposed to current pulses and cryogenic temperatures

    SciTech Connect

    Strizhalo, V.A.; Novogrudskii, L.S.; Znachkovskii, O.Y.

    1986-01-01

    This paper studies the resistance to deformation of structural materials acted upon by electric current at cryogenic temperatures in dependence on the magnitude of residual deformation, the degree of preliminary deformation, and other factors. The authors used an installation UTN-10 at temperatures of 293, 77, and 4.2 degrees K with fivefold specimens of chromenickel steel and chrome-manganese steel. The dependence of the change of resistance to deformation of steels on the residual deformation at which a current pulse was applied is shown. Lowering the temperature to 77 degrees K or less strengthens the role of the interaction between electrons and dislocations in reducing the resistance to deformation of steels 12Kh18N10T and 03Kh13AG19 at the instant when an electric-current pulse acts.

  9. Generation of periodic accelerating structures in plasma by colliding laser pulses.

    PubMed

    Shvets, G; Fisch, N J; Pukhov, A; Meyer-Ter-Vehn, J

    1999-08-01

    A mechanism for generating large (>1 GeV/m) accelerating wakes in a plasma is proposed. Two slightly detuned counterpropagating laser beams, an ultrashort timing pulse and a long pump, exchange photons and deposit the recoil momentum in plasma electrons. This produces a localized region of electron current, which acts as a virtual electron beam, inducing intense plasma wakes with phase velocity equal to the group velocity of the short pulse. Modulating the pumping beam generates periodic accelerating structures in the plasma ("plasma linac") which can be used for particle acceleration unlimited by the dephasing between the particles and the wake. An important difference between this type of plasma accelerator and the conventional wakefield accelerators is that this type can be achieved with laser intensities I<10(18) W/cm(2). PMID:11970016

  10. Refractive index-modified structures in glass written by 266nm fs laser pulses.

    PubMed

    Saliminia, Ali; Bérubé, Jean-Philippe; Vallée, Réal

    2012-12-01

    We demonstrate the inscription of embedded waveguides, anti-waveguides and Bragg gratings by use of intense femtosecond (fs) UV laser pulses at 266nm in pure fused silica, and for the first time, in bulk fused quartz and ZBLAN glasses. The magnitude of induced index changes, depends, besides pulse energy and translation speed, largely on writing depth and varies from ~10(-4) for smooth modifications to ~10(-3) for damaged structures. The obtained results are promising as they present the feasibility of fabrication of short (< 0.2μm) period first-order fiber Bragg gratings (FBGs) for applications such as in realization of all-fiber lasers operating at short wavelengths. PMID:23262691

  11. Resolution enhancement in long pulse OTDR for application in structural health monitoring

    NASA Astrophysics Data System (ADS)

    Bahrampour, Ali Reza; Maasoumi, Fatemeh

    2010-08-01

    To improve the range resolution in inexpensive conventional long pulse optical time domain reflectometer (OTDR) for application in structural health monitoring (SHM) and robotic neural network, the Fourier Wavelet Regularized Deconvolution (ForWaRD) based on the adaptive wavelet method is employed. Since Deconvolution is a noise sensitive process, employing the (ForWaRD) method enhances the signal to noise ratio. Simulation for long pulse OTDR system is done and ForWaRD method is employed to improve the resolution of the OTDR system to the order of several centimeters. In this method the resolution is limited by the bandwidth of detector, bandwidth of electronic circuit, and the sampling rate of analog to digital convertor.

  12. Structural and functional characterization of paramecium dynein: initial studies.

    PubMed

    Larsen, J; Barkalow, K; Hamasaki, T; Satir, P

    1991-01-01

    Dynein arms and isolated dynein from Paramecium tetraurelia ciliary axonemes are comparable in structure, direction of force generation, and microtubule translocation ability to other dyneins. In situ arms have dimensions and substructure similar to those of Tetrahymena. Based on spoke arrangement in intact axonemes, arms translocate axonemal microtubules in sliding such that active dynein arms are (-) end directed motors and the doublet to which the body and cape of the arms binds (N) translocates the adjacent doublet (N + 1) tipward. After salt extraction, based on ATPase activity, paramecium dynein is found as a 22S and a 14S species. The 22S dynein is a three-headed molecule that has unfolded from the in situ dimensions; the 14S dynein is single headed. Both dyneins can be photocleaved by UV light (350 nm) in the presence of Mg2+, ATP and vanadate; the photocleavage pattern of 22S dynein differs from that seen with Tetrahymena. Both isolated dyneins translocate taxol-stabilized, bovine brain microtubules in vitro. Under standard conditions, 22S dynein, like comparable dyneins from other organisms, translocates at velocities that are about three times faster than 14S dynein. PMID:1825507

  13. Origin of double-line structure in nonsequential double ionization by few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Huang, Cheng; Zhong, Mingmin; Wu, Zhengmao

    2016-07-01

    We investigate nonsequential double ionization (NSDI) of molecules by few-cycle laser pulses at the laser intensity of 1.2-1.5 × 1014 W/cm2 using the classical ensemble model. The same double-line structure as the lower intensity (1.0 × 1014 W/cm2) is also observed in the correlated electron momentum spectra for 1.2-1.4 × 1014 W/cm2. However, in contrast to the lower intensity where NSDI proceeds only through the recollision-induced double excitation with subsequent ionization (RDESI) mechanism, here, the recollision-induced excitation with subsequent ionization (RESI) mechanism has a more significant contribution to NSDI. This indicates that RDESI is not necessary for the formation of the double-line structure and RESI can give rise to the same type of structure independently. Furthermore, we explore the ultrafast dynamics underlying the formation of the double-line structure in RESI.

  14. Surface pressure profiles, vortex structure and initialization for hurricane prediction. Part II: numerical simulations of track, structure and intensity

    NASA Astrophysics Data System (ADS)

    Davidson, Noel E.; Ma, Yimin

    2012-07-01

    In part 1 of this study, an assessment of commonly used surface pressure profiles to represent TC structures was made. Using the Australian tropical cyclone model, the profiles are tested in case studies of high-resolution prediction of track, structure and intensity. We demonstrate that: (1) track forecasts are mostly insensitive to the imposed structure; (2) in some cases [here Katrina (2005)], specification of vortex structure can have a large impact on prediction of structure and intensity; (3) the forecast model mostly preserves the characteristics of the initial structure and so correct structure at t = 0 is a requirement for improved structure forecasting; and (4) skilful prediction of intensity does not guarantee skilful prediction of structure. It is shown that for Ivan (2004) the initial structure from each profile is preserved during the simulations, and that markedly different structures can have similar intensities. Evidence presented suggests that different initial profiles can sometimes change the timing of intensification. Thus, correct initial vortex structure is an essential ingredient for more accurate intensity and structure prediction.

  15. An investigation for structure transformation in electric pulse modified liquid aluminum

    NASA Astrophysics Data System (ADS)

    Qi, Jingang; Wang, Jianzhong; He, Lijia; Zhao, Zuofu; Du, Huiling

    2011-02-01

    The electric pulse (EP) modification of liquid metal is a novel method for grain refinement. In this work, the structure tests of EP-modified liquid aluminum were conducted and investigated using high-temperature X-ray diffractometer by virtue of the outstanding structural heredity of EP-modified liquid aluminum. The results show that the EP-modified liquid structure tends to be slack and unordered with increasing temperature similar to that of the unmodified. Nevertheless, the quantitative characterization denoted by the liquid structural parameters exhibits its discrepancy. At the modifying temperature of 750 °C, the order of degree of EP-modified liquid aluminum is remarkably strengthened and the value of average atomic number per cluster changes from 119 (no EP) up to 174 (EP) by an increase of 46%. These tests experimentally testified Wang's electric pulse modification (EPM) model that was built only by phenomenology, and hereby the mechanism of grain refinement resulting from EPM is further elucidated.

  16. Reversible Phase Change Characteristics of Cr-Doped Sb2Te3 Films with Different Initial States Induced by Femtosecond Pulses.

    PubMed

    Wang, Qing; Jiang, Minghui; Liu, Bo; Wang, Yang; Zheng, Yonghui; Song, Sannian; Wu, Yiqun; Song, Zhitang; Feng, Songlin

    2016-08-17

    As a kind of chalcogenide alloy, phase change material has been widely used as novel storage medium in optical disk or electrical memory. In this paper, femtosecond pulses are used to study the reversible phase transition processes of Cr-doped Sb2Te3 films with different initial states. The SET processes are all induced by multiple pulses and relate to the increase of crystallized partial in the irradiated spot. When the Cr concentration is 5.3 at % or 10.5 at %, the crystallization mechanism is still growth-dominated as Sb2Te3, which is beneficial for high speed and high density storage, whereas the necessary crystallization energy increases with more Cr-dopants, leading to higher amorphous thermal stability. RESET results by multiple pulses show that Cr-dopants will not increase the power consumption, and the increase in Cr-dopants could greatly increase the antioxidant capacity. Single-pulse experiments show that the RESET process involves the competition of melting/amorphization and recrystallization. The reversible SET/RESET results on different initial states are quite different from each other, which is mainly due to the different surroundings around the irradiated spot. Crystalline surroundings provide higher thermal conductivity and lead to easier crystallization, whereas amorphous surroundings were the reverse. All in all, Cr-doped Sb2Te3 films with suitable composition have advantages for storage with high density, better thermal stability, and lower power consumption; and the suitable initial states could ensure better reversible phase transition performances. PMID:27459421

  17. Ultrafast gigantic photo-response in (EDO-TTF)2PF6 initiated by 10-fs laser pulses

    SciTech Connect

    Schoenlein, Robert William; Itatani, Jiro; Rini, Matteo; Cavalleri, Andrea; Onda, Ken; Ishikawa, Tadahiko; Koshihara, Shin-ya; Shao, Xiangfeng; Yamochi, Hideki; Saito, Gunzi; Schoenlein, Robert W.

    2006-08-07

    We photo-exited a charge-ordered organic salt (EDO-TTF)2PF6 with sub-10-fs optical pulses. The photo-induced metallic phase appeared within 80-fs after pumping, characterized by large changes in reflectivity (DELTA R/R~0.8) followed by strong coherent phonon modulation

  18. Epitaxial Structure of (001)- and (111)-Oriented Perovskite Ferrate Films Grown by Pulsed-Laser Deposition.

    PubMed

    Chakraverty, Suvankar; Ohtomo, Akira; Okude, Masaki; Ueno, Kazunori; Kawasaki, Masashi

    2010-04-01

    The epitaxial structures of SrFeO(2.5) films grown on SrTiO(3) (001) and (111) substrates by PLD are reported. A layer-by-layer growth mode was achieved in the initial stage on both substrates. The films were stabilized with a monoclinic structure, where we identified the in-plane domain structures and orientation relationship. Our study presents a guide to control the heteroepitaxy of (111)-oriented noncubic perovskites. PMID:20383295

  19. A psychological pulse train: how young children use this cognitive framework to structure simple rhythms.

    PubMed

    Drake, C; Gérard, C

    1989-01-01

    This paper examines the reproduction of both regular rhythms and irregular sequences by 5- and 7-year-old children, concentrating on the important role played by their organization around a pulse train. It is shown that: (a) the closer rhythms are to a regular beat the easier they are to reproduce and the greater are the improvements with age; (b) memory capacity is limited by the number of pulses around which the rhythm is organized rather than by the number of elements it contains; (c) all the children's productions contain two interval lengths that are in a ratio close to 1:2 and arranged in preferential sequences which we have called "stereotypes"; (d) arrhythmic sequences can only be reproduced if the intervals undergo a systematic distortion towards regularity. These results are interpreted in relation to a pulse-train hypothesis which states that on hearing a rhythm an "internal clock" or "time base" is evoked around which the rhythm is structured. PMID:2756070

  20. Investigating natural organic carbon removal and structural alteration induced by pulsed ultrasound.

    PubMed

    Al-Juboori, Raed A; Yusaf, Talal; Aravinthan, Vasantha; Bowtell, Leslie

    2016-01-15

    The application of pulsed ultrasound for DOC removal from natural water samples has been thoroughly investigated in this work. Natural water samples were treated with ultrasound at power levels of 48 and 84 W with treatment times of 5 and 15 min. Chemical fractionation was conducted for both untreated and treated samples to clearly identify the change in DOC structure caused by ultrasonic treatments. Statistical analyses applying 2(3) factorial design were performed to study the behaviour of the response (i.e. DOC removal) under different operating conditions. Overall, ultrasonic treatments resulted in DOC removal of 7-15% depending on the applied operating conditions. The treated water had high microbial loading that interfered with DOC removal due primarily to the release of microbial products when exposed to ultrasound. Pulse ultrasound was found to be more effective than the continuous mode for DOC removal at the same effective power level. A regression model was developed and tested for DOC removal prediction. The model was adequate in predicting DOC removal with a maximum deviation from the experimental data of <11%. Pulsed ultrasound at low power levels and short treatment times was found to be the most energy efficient treatment for DOC removal. PMID:26473704

  1. Laser pulse duration dependence of the low-energy structure in strong field ionization

    NASA Astrophysics Data System (ADS)

    Lai, Yu Hang; Zhang, Kaikai; Blaga, Cosmin; Xu, Junliang; Agostini, Pierre; Dimauro, Louis; Schmidt, Bruno; Légaré, François; The Ohio State University Team; Institut National de la Recherche Scientifique Team

    2015-05-01

    Low-energy structure (LES) in strong field ionization is a spike-like feature appearing in the low energy part (a few eV) of photoelectron spectra along the laser polarization. It has been observed in rare gas atoms and diatomic molecules. In the classical picture, the formation of LES is due to the Coulomb interaction between the ionized electron and its parent ion via the process of multiple forward scattering, which can happen only if the electron is ionized with a small drift momentum. We have studied the LES in rare gas atoms with few-cycle laser pulses centered at 1800nm. We observed that the LES peak shifts to lower energy as the pulse duration decreases from 5 down to 2 optical cycles, which is in qualitative agreement with classical-trajectory Monte Carlo simulations. Classically, the shift could be attributed to the dependence of the ratio between the field amplitude of the central cycle and the adjacent cycle on the pulse duration. Our data support the classical nature of the LES.

  2. Resistive pulse sensing of magnetic beads and supraparticle structures using tunable pores

    PubMed Central

    Willmott, Geoff R.; Platt, Mark; Lee, Gil U.

    2012-01-01

    Tunable pores (TPs) have been used for resistive pulse sensing of 1 μm superparamagnetic beads, both dispersed and within a magnetic field. Upon application of this field, magnetic supraparticle structures (SPSs) were observed. Onset of aggregation was most effectively indicated by an increase in the mean event magnitude, with data collected using an automated thresholding method. Simulations enabled discrimination between resistive pulses caused by dimers and individual particles. Distinct but time-correlated peaks were often observed, suggesting that SPSs became separated in pressure-driven flow focused at the pore constriction. The distinct properties of magnetophoretic and pressure-driven transport mechanisms can explain variations in the event rate when particles move through an asymmetric pore in either direction, with or without a magnetic field applied. Use of TPs for resistive pulse sensing holds potential for efficient, versatile analysis and measurement of nano- and microparticles, while magnetic beads and particle aggregation play important roles in many prospective biosensing applications. PMID:22662090

  3. Long-term signal of population disturbance after pulse exposure to an insecticide: rapid recovery of abundance, persistent alteration of structure.

    PubMed

    Liess, Matthias; Pieters, Barry Johan; Duquesne, Sabine

    2006-05-01

    Little is known about the effect of pulse exposure to toxicants on populations when density regulation is present. Yet, for a more realistic risk assessment, it is necessary to include effect and recovery at the population level. Here, we investigate the long-term and delayed effects as well as the subsequent recovery of populations of Daphnia magna. A 24-h pulse of the pyrethroid fenvalerate reduced the abundance at a concentration of 1.0 microg/L and higher. However, abundance recovered and reached control levels after one to two generation times (GTs) following reproduction of surviving individuals (GT = 8 d, from birth until first reproduction). At high concentrations above the acute median lethal concentration (3.2 micorg/L), abundance initially decreased even more strongly but was then elevated compared to control values for an extended period of time. Population structure (size distribution) was affected at lower concentrations than abundance (> 0.8 microg/L). In addition, the alteration of population structure lasted for a long time, so that control levels were approached only after approximately six or seven GTs. Our results show that pulse exposure to toxicants may lead to a long-term alteration of population structure even at sublethal concentrations. Possible mechanisms that sustain the effects of toxicants may be delayed life-history effects on the individual level and elevated competition because of altered population structure on the population level. PMID:16704065

  4. Structural properties and digestibility of pulsed electric field treated waxy rice starch.

    PubMed

    Zeng, Feng; Gao, Qun-Yu; Han, Zhong; Zeng, Xin-An; Yu, Shu-Juan

    2016-03-01

    Waxy rice starch was subjected to pulsed electric field (PEF) treatment at intensity of 30, 40 and 50kVcm(-1). The impact of PEF treatment on the granular morphology, molecular weight, semi-crystalline structure, thermal properties, and digestibility were investigated. The micrographs suggested that electric energy could act on the granule structure of starch granule, especially at high intensity of 50kVcm(-1). Gelatinization onset temperature, peak temperature, conclusion temperature and enthalpy value of PEF treated starches were lower than that of native starch. The 9nm lamellar peak of PEF treated starches decreased as revealed by small angle X-ray scattering. The relative crystallinity of treated starches decreased as the increase of electric field intensity. Increased rapidly digestible starch level and decreased slowly digestible starch level was found on PEF treated starches. These results would imply that PEF treatment induced structural changes in waxy rice starch significantly affected its digestibility. PMID:26471687

  5. Structural, optical, and electrical properties of pulsed laser deposition CIGSS thin films

    NASA Astrophysics Data System (ADS)

    Xu, Yan-Bin; Kang, Y. Zhen-Feng; Fan, Yue; Xiao, Ling-ling; Bo, Qing-Rui; Ding, Tie-Zhu

    2015-12-01

    High-quality CuIn0.75Ga0.25(Se0.75S0.25)2 (CIGSS) thin films were synthesized on the soda-lime glass (SLG) substrates by pulsed laser deposition. The structural and optical properties of CIGSS thin films were studied by experiments and theoretical calculations. XRD result reveals that the films are of chalcopyrite structure. The experiments and theory show that CIGSS is a semiconductor with a direct band gap. The direct band gap energy of the deposited CIGSS thin films are in the solar energy range. The band structure and density of states of the CIGSS crystals were studied by the first principles density functional theory. The experimental data and theoretical data have demonstrated good agreement.

  6. Process-structure-property correlations in pulsed dc reactive magnetron sputtered vanadium oxide thin films

    SciTech Connect

    Venkatasubramanian, Chandrasekaran; Cabarcos, Orlando M.; Drawl, William R.; Allara, David L.; Ashok, S.; Horn, Mark W.; Bharadwaja, S. S. N.

    2011-11-15

    Cathode hysteresis in the reactive pulsed dc sputtering of a vanadium metal target was investigated to correlate the structural and electrical properties of the resultant vanadium oxide thin films within the framework of Berg's model [Berg et al., J. Vac. Sci. Technol. A 5, 202 (1987)]. The process hysteresis during reactive pulsed dc sputtering of a vanadium metal target was monitored by measuring the cathode (target) current under different total gas flow rates and oxygen-to-argon ratios for a power density of {approx}6.6.W/cm{sup 2}. Approximately 20%-25% hysteretic change in the cathode current was noticed between the metallic and oxidized states of the V-metal target. The extent of the hysteresis varied with changes in the mass flow of oxygen as predicted by Berg's model. The corresponding microstructure of the films changed from columnar to equiaxed grain structure with increased oxygen flow rates. Micro-Raman spectroscopy indicates subtle changes in the film structure as a function of processing conditions. The resistivity, temperature coefficient of resistance, and charge transport mechanism, obeying the Meyer-Neldel relation [Meyer and Neldel, Z. Tech. Phys. (Leipzig) 12, 588 (1937)], were correlated with the cathode current hysteric behavior.

  7. Molecular Structure and Chirality Determination from Pulsed-Jet Fourier Transform Microwave Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lobsiger, Simon; Perez, Cristobal; Evangelisti, Luca; Seifert, Nathan A.; Pate, Brooks; Lehmann, Kevin

    2014-06-01

    Fourier transform microwave (FTMW) spectroscopy has been used for many years as one of the most accurate methods to determine gas-phase structures of molecules and small molecular clusters. In the last years two pioneering works ushered in a new era applications. First, by exploiting the reduced measurement time and the high sensitivity, the development of chirped-pulse CP-FTMW spectrometers enabled the full structural determination of molecules of increasing size as well as molecular clusters. Second, and more recently, Patterson et al. showed that rotational spectroscopy can also be used for enantiomer-specific detection. Here we present an experimental approach that combines both in a single spectrometer. This set-up is capable to rapidly obtain the full heavy-atom substitution structure using the CP-FTMW features. The inclusion of an extra set of broadband horns allows for a chirality-sensitive measurement of the sample. The measurement we implement is a three-wave mixing experiment that uses time-separated pulses to optimally create the chiral coherence - an approach that was proposed recently. Using samples of R-, S- and racemic Solketal, the physical properties of the three-wave mixing experiment were studied. This involved the measurement of the corresponding nutation curves (molecular signal intensity vs excitation pulse duration) to demonstrate the optimal pulse sequence. The phase stability of the chiral signal, required to assign the absolute stereochemistry, has been studied as a function of the measurement signal-to-noise ratio using a "phasogram" method. G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, B. H. Pate, Rev. Sci. Instrum. 2008, 79, 053103. D. Patterson, M. Schnell, J. M. Doyle, Nature 2013, 497, 475-477. D. Patterson, J. M. Doyle, Phys. Rev. Lett. 2013, 111, 023008. V. A. Shubert, D. Schmitz, D. Patterson, J. M. Doyle, M. Schnell, Angew. Chem. Int. Ed. 2014, 53, 1152-1155. J.-U. Grabow, Angew. Chem. 2013, 125, 11914

  8. Pulsed laser deposition to synthesize the bridge structure of artificial nacre: Comparison of nano- and femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Melaibari, Ammar A.; Molian, Pal

    2012-11-01

    Nature offers inspiration to new adaptive technologies that allow us to build amazing shapes and structures such as nacre using synthetic materials. Consequently, we have designed a pulsed laser ablation manufacturing process involving thin film deposition and micro-machining to create hard/soft layered "brick-bridge-mortar" nacre of AlMgB14 (hard phase) with Ti (soft phase). In this paper, we report pulsed laser deposition (PLD) to mimic brick and bridge structures of natural nacre in AlMgB14. Particulate formation inherent in PLD is exploited to develop the bridge structure. Mechanical behavior analysis of the AlMgB14/Ti system revealed that the brick is to be 250 nm thick, 9 μm lateral dimensions while the bridge (particle) is to have a diameter of 500 nm for a performance equivalent to natural nacre. Both nanosecond (ns) and femtosecond (fs) pulsed lasers were employed for PLD in an iterative approach that involves varying pulse energy, pulse repetition rate, and target-to-substrate distance to achieve the desired brick and bridge characteristics. Scanning electron microscopy, x-ray photoelectron spectroscopy, and optical profilometer were used to evaluate the film thickness, particle size and density, stoichiometry, and surface roughness of thin films. Results indicated that both ns-pulsed and fs-pulsed lasers produce the desired nacre features. However, each laser may be chosen for different reasons: fs-pulsed laser is preferred for much shorter deposition time, better stoichiometry, uniform-sized particles, and uniform film thickness, while ns-pulsed laser is favored for industrial acceptance, reliability, ease of handling, and low cost.

  9. Pulsed laser deposition to synthesize the bridge structure of artificial nacre: Comparison of nano- and femtosecond lasers

    SciTech Connect

    Melaibari, Ammar A.; Molian, Pal

    2012-11-15

    Nature offers inspiration to new adaptive technologies that allow us to build amazing shapes and structures such as nacre using synthetic materials. Consequently, we have designed a pulsed laser ablation manufacturing process involving thin film deposition and micro-machining to create hard/soft layered 'brick-bridge-mortar' nacre of AlMgB{sub 14} (hard phase) with Ti (soft phase). In this paper, we report pulsed laser deposition (PLD) to mimic brick and bridge structures of natural nacre in AlMgB{sub 14}. Particulate formation inherent in PLD is exploited to develop the bridge structure. Mechanical behavior analysis of the AlMgB{sub 14}/Ti system revealed that the brick is to be 250 nm thick, 9 {mu}m lateral dimensions while the bridge (particle) is to have a diameter of 500 nm for a performance equivalent to natural nacre. Both nanosecond (ns) and femtosecond (fs) pulsed lasers were employed for PLD in an iterative approach that involves varying pulse energy, pulse repetition rate, and target-to-substrate distance to achieve the desired brick and bridge characteristics. Scanning electron microscopy, x-ray photoelectron spectroscopy, and optical profilometer were used to evaluate the film thickness, particle size and density, stoichiometry, and surface roughness of thin films. Results indicated that both ns-pulsed and fs-pulsed lasers produce the desired nacre features. However, each laser may be chosen for different reasons: fs-pulsed laser is preferred for much shorter deposition time, better stoichiometry, uniform-sized particles, and uniform film thickness, while ns-pulsed laser is favored for industrial acceptance, reliability, ease of handling, and low cost.

  10. Pulse- and time-dependent observation of UV-laser-induced structures on polymer surfaces

    NASA Astrophysics Data System (ADS)

    Kesting, Wolfgang; Knittel, Dierk; Bahners, Thomas; Schollmeyer, Eckhard

    1992-01-01

    Irradiation of highly absorbing polymers with a pulsed excimer laser can change the surface topography under certain conditions. Fibres made of poly(ethylene terephthalate) and polyamide show a characteristic roll-like morphology after treatment with 193 or 248 nm laser irradiation, which promises interesting applications in industrial processing of textile fibres. For a systematic study of the influences of the various parameters monofilaments made of poly(ethylene terephthalate) and poly(propylene) were irradiated in place in a microscope. This allowed the observation of the evolution of the structure shot by shot. Quantitative data were taken by use of an image analysing system. The study was done with various laser fluences, wavelengths and in dependence on mechanical stress (draw) on the sample. With increasing number of shots the morphology gets more coarse due to a sort of "combining" of the rolls showing a logarithmic dependence of the mean roll-distance on the number of pulses applied. Characteristically, the fibre decomposes into ellipsoidal pieces after a sufficient number of shots. The polyolefinic material cannot be modified directly with 193 or 248 nm laser radiation due to the low absorption coefficient for these wavelenghts. By using a 157 nm F 2 laser certain surface modifications were observed on fibres and films. The structures were similar to the effects previously found on poly(ethylene terephthalate).

  11. Semiclassical modelling of finite-pulse effects on non-adiabatic photodynamics via initial condition filtering: The predissociation of NaI as a test case

    SciTech Connect

    Martínez-Mesa, Aliezer; Saalfrank, Peter

    2015-05-21

    Femtosecond-laser pulse driven non-adiabatic spectroscopy and dynamics in molecular and condensed phase systems continue to be a challenge for theoretical modelling. One of the main obstacles is the “curse of dimensionality” encountered in non-adiabatic, exact wavepacket propagation. A possible route towards treating complex molecular systems is via semiclassical surface-hopping schemes, in particular if they account not only for non-adiabatic post-excitation dynamics but also for the initial optical excitation. One such approach, based on initial condition filtering, will be put forward in what follows. As a simple test case which can be compared with exact wavepacket dynamics, we investigate the influence of the different parameters determining the shape of a laser pulse (e.g., its finite width and a possible chirp) on the predissociation dynamics of a NaI molecule, upon photoexcitation of the A(0{sup +}) state. The finite-pulse effects are mapped into the initial conditions for semiclassical surface-hopping simulations. The simulated surface-hopping diabatic populations are in qualitative agreement with the quantum mechanical results, especially concerning the subpicosend photoinduced dynamics, the main deviations being the relative delay of the non-adiabatic transitions in the semiclassical picture. Likewise, these differences in the time-dependent electronic populations calculated via the semiclassical and the quantum methods are found to have a mild influence on the overall probability density distribution. As a result, the branching ratios between the bound and the dissociative reaction channels and the time-evolution of the molecular wavepacket predicted by the semiclassical method agree with those computed using quantum wavepacket propagation. Implications for more challenging molecular systems are given.

  12. Structural and phase transformations in zinc and brass wires under heating with high-density current pulse

    NASA Astrophysics Data System (ADS)

    Pervikov, A. V.

    2016-06-01

    The work is focused on revealing the mechanism of structure and phase transformations in the metal wires under heating with a high-density current pulse (the electric explosion of wires, EEWs). It has been demonstrated on the example of brass and zinc wires that the transition of a current pulse with the density of j ≈ 3.3 × 107 A/cm2 results in homogeneous heating of the crystalline structure of the metal/alloy. It has been determined that under heating with a pulse of high-density current pulse, the electric resistance of the liquid phases of zinc and brass decreases as the temperature increases. The results obtained allow for a conclusion that the presence of the particles of the condensed phase in the expanding products of EEW is the result of overheating instabilities in the liquid metal.

  13. Influence of laser pulse duration on the electrochemical performance of laser structured LiFePO4 composite electrodes

    NASA Astrophysics Data System (ADS)

    Mangang, M.; Seifert, H. J.; Pfleging, W.

    2016-02-01

    Lithium iron phosphate is a promising cathode material for lithium-ion batteries, despite its low electrical conductivity and lithium-ion diffusion kinetic. To overcome the reduced rate performance, three dimensional (3D) architectures were generated in composite cathode layers. By using ultrashort laser radiation with pulse durations in the femtosecond regime the ablation depth per pulse is three times higher compared to nanosecond laser pulses. Due to the 3D structuring, the surface area of the active material which is in direct contact with liquid electrolyte, i.e. the active surface, is increased. As a result the capacity retention and the cycle stability were significantly improved, especially for high charging/discharging currents. Furthermore, a 3D structure leads to higher currents during cyclic voltammetry. Thus, the lithium-ion diffusion kinetic in the cell was improved. In addition, using ultrashort laser pulses results in a high aspect ratio and further improvement of the cell kinetic was achieved.

  14. A novel method for finding the initial structure parameters of optical systems via a genetic algorithm

    NASA Astrophysics Data System (ADS)

    Jun, LIU; Huang, Wei; Hongjie, Fan

    2016-02-01

    A novel method for finding the initial structure parameters of an optical system via the genetic algorithm (GA) is proposed in this research. Usually, optical designers start their designs from the commonly used structures from a patent database; however, it is time consuming to modify the patented structures to meet the specification. A high-performance design result largely depends on the choice of the starting point. Accordingly, it would be highly desirable to be able to calculate the initial structure parameters automatically. In this paper, a method that combines a genetic algorithm and aberration analysis is used to determine an appropriate initial structure of an optical system. We use a three-mirror system as an example to demonstrate the validity and reliability of this method. On-axis and off-axis telecentric three-mirror systems are obtained based on this method.

  15. Flame Structure and Emissions of Strongly-Pulsed Turbulent Diffusion Flames with Swirl

    NASA Astrophysics Data System (ADS)

    Liao, Ying-Hao

    This work studies the turbulent flame structure, the reaction-zone structure and the exhaust emissions of strongly-pulsed, non-premixed flames with co-flow swirl. The fuel injection is controlled by strongly-pulsing the fuel flow by a fast-response solenoid valve such that the fuel flow is completely shut off between pulses. This control strategy allows the fuel injection to be controlled over a wide range of operating conditions, allowing the flame structure to range from isolated fully-modulated puffs to interacting puffs to steady flames. The swirl level is controlled by varying the ratio of the volumetric flow rate of the tangential air to that of the axial air. For strongly-pulsed flames, both with and without swirl, the flame geometry is strongly impacted by the injection time. Flames appear to exhibit compact, puff-like structures for short injection times, while elongated flames, similar in behaviors to steady flames, occur for long injection times. The flames with swirl are found to be shorter for the same fuel injection conditions. The separation/interaction level between flame puffs in these flames is essentially governed by the jet-off time. The separation between flame puffs decreases as swirl is imposed, consistent with the decrease in flame puff celerity due to swirl. The decreased flame length and flame puff celerity are consistent with an increased rate of air entrainment due to swirl. The highest levels of CO emissions are generally found for compact, isolated flame puffs, consistent with the rapid quenching due to rapid dilution with excess air. The imposition of swirl generally results in a decrease in CO levels, suggesting more rapid and complete fuel/air mixing by imposing swirl in the co-flow stream. The levels of NO emissions for most cases are generally below the steady-flame value. The NO levels become comparable to the steady-flame value for sufficiently short jet-off time. The swirled co-flow air can, in some cases, increase the NO

  16. Effect of gel structure of matrix orientation in pulsed alternating electric fields

    SciTech Connect

    Stellwagen, N.C.; Stellwagen, J.

    1993-12-31

    Four polymeric gels with different structures, LE agarose, HEEO agarose, beta-carrageenan, and polyacrylamide, were studied by transient electric birefringence to determine the importance of various structural features on the orientation of the gels in pulsed alternating electric fields. The birefrigence relaxation times observed for agarose gels in low voltage electric fields suggest that long fibers and/or domains, ranging up to tens of microns in size, are oriented by the electric field. The sign of the birefringence reverses when the direction of the electric field is reversed, suggesting that the oriented domains change their direction of orientation from parallel to perpendicular (or vice versa) when the polarity of the electric field is reversed. These anamalous orientation effects are observed with both types of agarose gels, but not with beta-carrageenan or polyacrylamide gels, suggesting that the alternating D,L galactose residues in the agarose backbone are responsible for the anomalies.

  17. Superlattice CoCrPt/Ru/CoFe structure fabricated by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Hu, X. F.; Liang, Q.; Li, H. Q.; He, X. X.; Wang, Xiaoru; Zhang, W.

    2006-04-01

    The synthetic antiferromagnets (SAF) have been used in spin-valve sensor in data storage industry [1]. We report a new hard/Ru/soft sandwich structure (SHBL) fabricated by pulsed lased deposition to replace current single layer structure for information recording application. SHBL consists of two magnetic layers separated by thin nonmagnetic layers, typically with Ru layers of 0.7-1.2 nm, through which antiferromagnetic coupling is induced. Varying the relative thickness of the magnetic layers, the spacer layers, and the type of magnetic materials can alter magnetic properties of CoCrPt/Ru/CoFe superlattice. The coercivity Hc and grain size of magnetic layer is also dependent on the laser fluence. High laser fluence results in both small grain size and high Hc. The observed phenomena are related to high quenching and deposition rates during PLD at high fluence, resulting in more pronounced phase segregation.

  18. Propagation of the Ultra-Short Laser Pulses Through the Helical 1D Photonic Crystal Structure with Twist Defect

    NASA Astrophysics Data System (ADS)

    Antonov, Dmitrii V.; Iegorov, Roman

    2016-02-01

    The presence of the photonic band-gap is a featured property of the cholesteric liquid crystals (CLC). It can be practically realized for almost any reasonable wavelengths with very high degree of tunability. We have investigated theoretically the influence of the twist defect of the CLC helical structure onto the bandwidth-limited ultra-short laser pulse propagating inside the photonic band-gap. The changes of both pulse duration and peak power with defect angle were observed together with pulse acceleration and retardation for a case of normal incidence of the light.

  19. Production of Multi-Terawatt Time-Structured CO{sub 2} Laser Pulses for Ion Acceleration

    SciTech Connect

    Haberberger, Dan; Tochitsky, Sergei; Gong Chao; Joshi, Chan

    2010-11-04

    The UCLA Neptune Laboratory CO{sub 2} laser system has been recently upgraded to produce 3ps multi-terawatt 10{mu}m laser pulses. The laser energy is distributed over several 3 ps pulses separated by 18 ps. These temporally structured pulses are applied for laser driven ion acceleration in an H{sub 2} gas jet at a measured plasma density of 2x10{sup 19} cm{sup -3}. Protons in excess of 20 MeV have been observed in the forward direction and with energy spreads ({Delta}E/E{approx}10%).

  20. Efficient Cherenkov emission of broadband terahertz radiation from an ultrashort laser pulse in a sandwich structure with nonlinear core

    SciTech Connect

    Bodrov, S. B.; Bakunov, M. I.; Hangyo, M.

    2008-11-01

    A scheme for efficient generation of broadband terahertz radiation by a femtosecond laser pulse propagating in a planar sandwichlike structure is proposed. The structure consists of a thin nonlinear core cladded with prisms made of a material with low terahertz absorption. The focused into a line laser pulse propagates in the core as a leaky or waveguide mode and emits Cherenkov wedge of terahertz waves in the cladding. We developed a theory that describes terahertz generation in such a structure and calculated spatial distribution of the generated terahertz field, its energy spectrum and optical-to-terahertz conversion efficiency. The developed theory predicts the conversion efficiency of up to several percent in a 1 cm long and 1 cm wide Si-LiNbO{sub 3}-Si sandwich structure with a 20 {mu}m thick nonlinear layer pumped by 8.5 {mu}J Ti:sapphire laser with pulse duration of 100 fs.

  1. Structures of ribosome-bound initiation factor 2 reveal the mechanism of subunit association

    PubMed Central

    Sprink, Thiemo; Ramrath, David J. F.; Yamamoto, Hiroshi; Yamamoto, Kaori; Loerke, Justus; Ismer, Jochen; Hildebrand, Peter W.; Scheerer, Patrick; Bürger, Jörg; Mielke, Thorsten; Spahn, Christian M. T.

    2016-01-01

    Throughout the four phases of protein biosynthesis—initiation, elongation, termination, and recycling—the ribosome is controlled and regulated by at least one specified translational guanosine triphosphatase (trGTPase). Although the structural basis for trGTPase interaction with the ribosome has been solved for the last three steps of translation, the high-resolution structure for the key initiation trGTPase, initiation factor 2 (IF2), complexed with the ribosome, remains elusive. We determine the structure of IF2 complexed with a nonhydrolyzable guanosine triphosphate analog and initiator fMet-tRNAiMet in the context of the Escherichia coli ribosome to 3.7-Å resolution using cryo-electron microscopy. The structural analysis reveals previously unseen intrinsic conformational modes of the 70S initiation complex, establishing the mutual interplay of IF2 and initator transfer RNA (tRNA) with the ribsosome and providing the structural foundation for a mechanistic understanding of the final steps of translation initiation. PMID:26973877

  2. Structures of ribosome-bound initiation factor 2 reveal the mechanism of subunit association.

    PubMed

    Sprink, Thiemo; Ramrath, David J F; Yamamoto, Hiroshi; Yamamoto, Kaori; Loerke, Justus; Ismer, Jochen; Hildebrand, Peter W; Scheerer, Patrick; Bürger, Jörg; Mielke, Thorsten; Spahn, Christian M T

    2016-03-01

    Throughout the four phases of protein biosynthesis-initiation, elongation, termination, and recycling-the ribosome is controlled and regulated by at least one specified translational guanosine triphosphatase (trGTPase). Although the structural basis for trGTPase interaction with the ribosome has been solved for the last three steps of translation, the high-resolution structure for the key initiation trGTPase, initiation factor 2 (IF2), complexed with the ribosome, remains elusive. We determine the structure of IF2 complexed with a nonhydrolyzable guanosine triphosphate analog and initiator fMet-tRNAi (Met) in the context of the Escherichia coli ribosome to 3.7-Å resolution using cryo-electron microscopy. The structural analysis reveals previously unseen intrinsic conformational modes of the 70S initiation complex, establishing the mutual interplay of IF2 and initator transfer RNA (tRNA) with the ribsosome and providing the structural foundation for a mechanistic understanding of the final steps of translation initiation. PMID:26973877

  3. Super-hydrophobicity of PMMA and PDMS surfaces structured by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Jeong, Hong-Myeong; Lee, Woon-Young; Lee, Jin-Ho; Yang, Deok-Cho; Lim, Ki-Soo

    2013-03-01

    Surface wettability depends on both physical surface structure and chemical material. In this report, we demonstrate super-hydrophobic surface of cast polymethyl methacrylate (PMMA) sheet by femtosecond laser fabrication. Twodimensional micro-array structures of square-typed pillars with various heights, widths, and intervals were fabricated on the PMMA surface by femtosecond laser irradiation and chemical etching. The Yb:KGW femtosecond laser processing system (λ=1030 nm) delivering 250 fs pulses at a repetition rate 100 kHz was employed for fabrication. The contact angle of PMMA changed 64° (hydrophilic plane) to 150° (super-hydrophobic structure). We also improved superhydrophobicity up to 170° contact angle by spin-coating PMMA surface with PDMS and fabricating regular microstructures including irregular nano-structures. We also coated the structured PMMA surface with a car ash spray material to use another combination of surface morphology and chemistry. All the experimental results were compared with those expected values by Cassie-Baxter model.

  4. Initiation of Translation in Bacteria by a Structured Eukaryotic IRES RNA

    PubMed Central

    Colussi, Timothy M.; Costantino, David A.; Zhu, Jianyu; Donohue, John Paul; Korostelev, Andrei A.; Jaafar, Zane A.; Plank, Terra-Dawn M.; Noller, Harry F.; Kieft, Jeffrey S.

    2015-01-01

    The central dogma of gene expression (DNA→RNA→protein) is universal, but in different domains of life there are fundamental mechanistic differences within this pathway. For example, the canonical molecular signals used to initiate protein synthesis in bacteria and eukaryotes are mutually exclusive1,2. However, the core structures and conformational dynamics of ribosomes that are responsible for the steps of translation following initiation are ancient and conserved across the domains of life3,4. We asked whether an undiscovered RNA-based signal might be able to use these conserved features, bypassing mechanisms specific to each domain of life, and initiate protein synthesis in both bacteria and eukaryotes. Although structured internal ribosome entry site (IRES) RNAs can manipulate ribosomes to initiate translation in eukaryotic cells, an analogous RNA structure-based mechanism has not been observed in bacteria. Here, we report our discovery that a eukaryotic viral IRES can initiate translation in live bacteria. We solved the crystal structure of this IRES bound to a bacterial ribosome to 3.8 Å resolution, revealing that despite differences between bacterial and eukaryotic ribosomes this IRES binds directly to both and occupies the space normally used by tRNAs. Initiation in both bacteria and eukaryotes depends on the structure of the IRES RNA but in bacteria this RNA uses a different mechanism that includes a form of ribosome repositioning after initial recruitment. This IRES RNA bridges billions of years of evolutionary divergence as an example of an RNA structure-based translation initiation signal capable of operating in two domains of life. PMID:25652826

  5. Initiation of translation in bacteria by a structured eukaryotic IRES RNA.

    PubMed

    Colussi, Timothy M; Costantino, David A; Zhu, Jianyu; Donohue, John Paul; Korostelev, Andrei A; Jaafar, Zane A; Plank, Terra-Dawn M; Noller, Harry F; Kieft, Jeffrey S

    2015-03-01

    The central dogma of gene expression (DNA to RNA to protein) is universal, but in different domains of life there are fundamental mechanistic differences within this pathway. For example, the canonical molecular signals used to initiate protein synthesis in bacteria and eukaryotes are mutually exclusive. However, the core structures and conformational dynamics of ribosomes that are responsible for the translation steps that take place after initiation are ancient and conserved across the domains of life. We wanted to explore whether an undiscovered RNA-based signal might be able to use these conserved features, bypassing mechanisms specific to each domain of life, and initiate protein synthesis in both bacteria and eukaryotes. Although structured internal ribosome entry site (IRES) RNAs can manipulate ribosomes to initiate translation in eukaryotic cells, an analogous RNA structure-based mechanism has not been observed in bacteria. Here we report our discovery that a eukaryotic viral IRES can initiate translation in live bacteria. We solved the crystal structure of this IRES bound to a bacterial ribosome to 3.8 Å resolution, revealing that despite differences between bacterial and eukaryotic ribosomes this IRES binds directly to both and occupies the space normally used by transfer RNAs. Initiation in both bacteria and eukaryotes depends on the structure of the IRES RNA, but in bacteria this RNA uses a different mechanism that includes a form of ribosome repositioning after initial recruitment. This IRES RNA bridges billions of years of evolutionary divergence and provides an example of an RNA structure-based translation initiation signal capable of operating in two domains of life. PMID:25652826

  6. Temporal structure of attosecond pulses from intense laser-atom interactions.

    PubMed

    Pukhov, A; Gordienko, S; Baeva, T

    2003-10-24

    We find that the high harmonics have a power-law spectrum I(omega) approximately omega(-3.3+/-0.25) in a wide frequency domain starting at the ionization potential I(p) and down to the plateau beginning. Our spectrotemporal analysis of the emitted radiation displays clear bowlike structures in the (t,omega) plane. These "bows" correspond to Corkum's reencounters of the freed electron with the atom. We find that the bows are not filled and thus cannot be due to any bremsstrahlung. Rather, it is a resonant process that we call stimulated recombination (SR). It occurs when an electron with momentum p reencounters the incompletely ionized atom, and interferes with itself still remaining in the ground state. The SR leads to a highly efficient resonant emission at Planck's over 2pi omega=p(2)/2m+I(p) in the form of attosecond pulses. The SR relies on a low level of ionization and strongly benefits from the use of few-cycle laser pulses. PMID:14611340

  7. Structural Engineering of Nanoporous Anodic Alumina Photonic Crystals by Sawtooth-like Pulse Anodization.

    PubMed

    Law, Cheryl Suwen; Santos, Abel; Nemati, Mahdieh; Losic, Dusan

    2016-06-01

    This study presents a sawtooth-like pulse anodization approach aiming to create a new type of photonic crystal structure based on nanoporous anodic alumina. This nanofabrication approach enables the engineering of the effective medium of nanoporous anodic alumina in a sawtooth-like manner with precision. The manipulation of various anodization parameters such as anodization period, anodization amplitude, number of anodization pulses, ramp ratio and pore widening time allows a precise control and fine-tuning of the optical properties (i.e., characteristic transmission peaks and interferometric colors) exhibited by nanoporous anodic alumina photonic crystals (NAA-PCs). The effect of these anodization parameters on the photonic properties of NAA-PCs is systematically evaluated for the establishment of a fabrication methodology toward NAA-PCs with tunable optical properties. The effective medium of the resulting NAA-PCs is demonstrated to be optimal for the development of optical sensing platforms in combination with reflectometric interference spectroscopy (RIfS). This application is demonstrated by monitoring in real-time the formation of monolayers of thiol molecules (11-mercaptoundecanoic acid) on the surface of gold-coated NAA-PCs. The obtained results reveal that the adsorption mechanism between thiol molecules and gold-coated NAA-PCs follows a Langmuir isotherm model, indicating a monolayer sorption mechanism. PMID:27171214

  8. Mechanism of DNA Trapping in Nanoporous Structures during Asymmetric Pulsed-Field Electrophoresis

    NASA Astrophysics Data System (ADS)

    Zhou, Ya; Harrison, D. Jed

    2014-03-01

    DNA molecules (>100kbp) are trapped in separation sieves when high electric fields are applied in pulsed field electrophoresis, seriously limiting the speed of separation. Using crystalline particle arrays, to generate interstitial pores for molecular sieving, allows higher electric fields than in gels, (e.g 40 vs 5 V/cm), however trapping still limits the field strength. Using reverse pulses, which release DNA from being fully-stretched, allows higher fields (140 V/cm). We investigate the trapping mechanism of individual DNA molecules in ordered nanoporous structures. Two prerequisites for trapping are revealed by the dynamics of single trapped DNA, hernia formation and fully-stretched U/J shapes. Fully stretched DNA has longer unhooking times than expected by simple models. We propose a dielectrophoretic (DEP) force reduces the mobility of segments at the apex of the U or J, where field gradients are highest, based on simulations. A modified model for unhooking time is obtained after the DEP force is introduced. The new model explains the unhooking time data by predicting an infinite trapping time when the ratio of arm length differences (of the U or J) to molecule length Δx / L < β . β is a DEP parameter that is found to strongly increase with electric field. The work was supported by grant from Natural Sciences and Engineering Research Council of Canada (NSERC) and the National Institute for Nanotechnology (NINT).

  9. Particle Generation by Pulsed Excimer Laser Ablation in Liquid: Hollow Structures and Laser-Induced Reactions

    NASA Astrophysics Data System (ADS)

    Yan, Zijie

    2011-12-01

    Pulsed laser ablation of solid targets in liquid media is a powerful method to fabricate micro-/nanoparticles, which has attracted much interest in the past decade. It represents a combinatorial library of constituents and interactions, and one can explore disparate regions of parameter space with outcomes that are impossible to envision a priori. In this work, a pulsed excimer laser (wavelength 248 nm, pulse width 30 ns) has been used to ablate targets in liquid media with varying laser fluences, frequencies, ablation times and surfactants. It is observed that hollow particles could be fabricated by excimer laser ablation of Al, Pt, Zn, Mg, Ag, Si, TiO2, and Nb2O5 in water or aqueous solutions. The hollow particles, with sizes from tens of nanometers to micrometers, may have smooth and continuous shells or have morphologies demonstrating that they were assembled from nanoparticles. A new mechanism has been proposed to explain the formation of these novel particle geometries. They were formed on laser-produced bubbles through bubble interface pinning by laser-produced solid species. Considering the bubble dynamics, thermodynamic and kinetic requirements have been discussed in the mechanism that can explain some phenomena associated with the formation of hollow particles, especially (1) larger particles are more likely to be hollow particles; (2) Mg and Al targets have stronger tendency to generate hollow particles; and (3) the 248 nm excimer laser is more beneficial to fabricate hollow particles in water than other lasers with longer wavelengths. The work has also demonstrated the possiblities to fabricate novel nanostructures through laser-induced reactions. Zn(OH)2/dodecyl sulfate flower-like nanostructures, AgCl cubes, and Ag2O cubes, pyramids, triangular plates, pentagonal rods and bars have been obtained via reactions between laser-produced species with water, electrolyes, or surfactant molecules. The underlying mechanisms of forming these structures have been

  10. Dynamic adjustment of echolocation pulse structure of big-footed myotis (Myotis macrodactylus) in response to different habitats.

    PubMed

    Wang, Lei; Luo, Jinhong; Wang, Hongna; Ou, Wei; Jiang, Tinglei; Liu, Ying; Lyle, Dennis; Feng, Jiang

    2014-02-01

    Studying relationships between characteristics of sonar pulses and habitat clutter level is important for the understanding of signal design in bat echolocation. However, most studies have focused on overall spectral and temporal parameters of such vocalizations, with focus less on potential variation in frequency modulation rates (MRs) occurring within each pulse. In the current study, frequency modulation (FM) characteristics were examined in echolocation pulses recorded from big-footed myotis (Myotis macrodactylus) bats as these animals searched for prey in five habitats differing in relative clutter level. Pulses were analyzed using ten parameters, including four structure-related characters which were derived by dividing each pulse into three elements based on two knees in the FM sweep. Results showed that overall frequency, pulse duration, and MR all varied across habitat. The strongest effects were found for MR in the body of the pulse, implying that this particular component plays a major role as M. macrodactylus, and potentially other bat species, adjust to varying clutter levels in their foraging habitats. PMID:25234900

  11. Simultaneous observation of ultrafast structural dynamics and transient electrical field by picosecond electron pulses

    NASA Astrophysics Data System (ADS)

    Li, Run-Ze; Zhu, Pengfei; Chen, Long; Chen, Jie; Cao, Jianming; Sheng, Zheng-Ming; Zhang, Jie

    2014-03-01

    Ultrafast electron diffraction and microscopy are very promising methods to study transient structural dynamics with atomic spatial-temporal resolution. However, in these laser-pump electron-probe studies of structural dynamics, a transient electric field induced by laser excitation of the sample could deflect probing electrons, which may eventually leads to a misinterpretation of the diffraction data. Here, picosecond structural dynamics and transient surface electric field evolution, excited by femtosecond laser interaction with a metallic thin film, have been observed simultaneously in real time by ultrashort electron pulses in a transmission configuration. By tracing time dependent changes of electron diffraction and deflection angles, these two processes are found to be significantly different and distinguishable in their temporal behavior. This observation provides an effective approach to extract the otherwise obscured ultrafast structural dynamics and may help to improve the spatiotemporal resolution in ultrafast electron diffraction and microscopy studies. This work was supported by the National Basic Research Program of China and the National Natural Science Foundation of China.

  12. Origin of double-line structure in nonsequential double ionization by few-cycle laser pulses.

    PubMed

    Huang, Cheng; Zhong, Mingmin; Wu, Zhengmao

    2016-07-28

    We investigate nonsequential double ionization (NSDI) of molecules by few-cycle laser pulses at the laser intensity of 1.2-1.5 × 10(14) W/cm(2) using the classical ensemble model. The same double-line structure as the lower intensity (1.0 × 10(14) W/cm(2)) is also observed in the correlated electron momentum spectra for 1.2-1.4 × 10(14) W/cm(2). However, in contrast to the lower intensity where NSDI proceeds only through the recollision-induced double excitation with subsequent ionization (RDESI) mechanism, here, the recollision-induced excitation with subsequent ionization (RESI) mechanism has a more significant contribution to NSDI. This indicates that RDESI is not necessary for the formation of the double-line structure and RESI can give rise to the same type of structure independently. Furthermore, we explore the ultrafast dynamics underlying the formation of the double-line structure in RESI. PMID:27475356

  13. An Improved Chirped Pulse Ftmw Analysis of the Structures of Phenol Dimer and Trimer

    NASA Astrophysics Data System (ADS)

    Seifert, Nathan A.; Perez, Cristobal; Steber, Amanda L.; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Lesarri, Alberto

    2013-06-01

    With the recent improvements for chirped pulse FTMW (CP-FTMW) spectroscopy between 2-18 GHz, substitution structures of molecules and clusters with more than 10 heavy atoms are becoming routine. While previous CP-FTMW results for phenol dimer reported at this conference by Steber et al. necessitated reduced-band measurements in order to achieve the sensitivity to detect the carbon isotopologues, the latest improvements for the 2-8 GHz arrangement have enabled full band detection of all 12 ^{13}C and 2 ^{18}O isotopologues of phenol dimer in natural abundance, with improved fits for all detected species. In addition, the added sensitivity of this new 2-8 GHz configuration has enabled a full carbon substitution structure of phenol trimer. The experimental structure of phenol trimer, in agreement with the M06-2X/6-311++g(d,p) ab initio structure, is a C_{3} oblate symmetric top with 21 heavy atoms; however, all possible isotopic substitutions are off-symmetry axis, so the resulting detected isotopologues have been fit as c-type prolate asymmetric tops. Use of Kraitchman's equations for structural determination of a symmetric top molecule require some assumptions from the ab initio structure for the complete r_{s} structure of the trimer. A detailed summary of these methods, as well as the microwave results for both species, will be presented. A. L. Steber, J. L. Neill, D. P. Zaleski, B. H. Pate, A. Lesarri. 67th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2012, MH13.

  14. Surface pressure profiles, vortex structure and initialization for hurricane prediction. Part I: analysis of observed and synthetic structures

    NASA Astrophysics Data System (ADS)

    Ma, Yimin; Kafatos, Menas; Davidson, Noel E.

    2012-07-01

    Without detailed reconnaissance, consistent representation of hurricane-like vortices in initial conditions for operational prediction and research simulations still remains elusive. It is thus often necessary, particularly for high-resolution intensity forecasting, to use synthetic tropical cyclone circulations to initialize forecast models. Variants on three commonly used surface pressure profiles are evaluated for possible use. Enhancements to the original profiles are proposed that allows definition of both the inner-core and outer circulation. The latter improvement creates a vortex more consistent with the estimated outer structure which sometimes appears to be crucial to the evolving intensity of the storm. It also allows smoother merging of the synthetic vortex with the environment. Comparisons of the profiles against (a) structure estimates, (b) each other, (c) structures obtained via conservation of angular momentum, and (d) observed vorticity structures, suggest that a new enhanced Fujita profile best represents real TC structures. Student- t tests indicate that improved fitting to the observations is statistically significant.

  15. On study fine atmospheric structure by using of the method of decomposition of infrasonic signals from pulsed sources

    NASA Astrophysics Data System (ADS)

    Kulichkov, Sergey; Chunchuzov, Igor; Demin, Dmitry

    2016-04-01

    The proposed method are based on the decomposition of infrasonic signals from pulse sources. In this method, the recorded infrasonic signal is modeled by the sequence of single acoustic pulse having the form of a U and N waves. Each pulse U and N wave corresponds to the reflection of sound from atmospheric inhomogeneities at different altitudes in the atmosphere. By determining time intervals between such pulses U and N waves it is possible to determine vertical gradients of the effective sound speed at the different altitudes in the atmosphere. The method to determine the vertical profiles of the vertical gradients of effective sound velocity in the atmosphere by using data from infrasound monitoring are proposed. The obtained data are corresponds to the theory of the fine structure in the upper atmosphere.

  16. A comparative study of experimental and simulated ultrasonic pulse-echo signals from multilayered structures

    NASA Technical Reports Server (NTRS)

    Abedin, M. N.; Prabhu, D. R.; Winfree, W. P.; Johnston, P. H.

    1992-01-01

    The effect on the system acoustic response of variations in the adhesive thickness, coupling thickness, and paint thickness is considered. Both simulations and experimental measurements are used to characterize and classify A-scans from test regions, and to study the effects of various parameters such as paint thickness and epoxy thickness on the variations in the reflected signals. A 1D model of sound propagation in multilayered structures is used to verify the validity of the measured signals, and is also used to computationally generate signals for a class of test locations with gradually varying parameters. This approach exploits the ability of numerical simulations to provide a good understanding of the ultrasonic pulses reflected at disbonds.

  17. Photonic bandgap amorphous chalcogenide thin films with multilayered structure grown by pulsed laser deposition method

    NASA Astrophysics Data System (ADS)

    Zhang, Shao-qian; Němec, Petre; Nazabal, Virginie; Jin, Yu-qi

    2016-05-01

    Amorphous chalcogenide thin films were fabricated by the pulsed laser deposition technique. Thereafter, the stacks of multilayered thin films for reflectors and microcavity were designed for telecommunication wavelength. The prepared multilayered thin films for reflectors show good compatibility. The microcavity structure consists of Ge25Ga5Sb10S65 (doped with Er3+) spacer layer surrounded by two 5-layer As40Se60/Ge25Sb5S70 reflectors. Scanning/transmission electron microscopy results show good periodicity, great adherence and smooth interfaces between the alternating dielectric layers, which confirms a suitable compatibility between different materials. The results demonstrate that the chalcogenides can be used for preparing vertical Bragg reflectors and microcavity with high quality.

  18. Compositional and structural properties of pulsed laser-deposited ZnS:Cr films

    NASA Astrophysics Data System (ADS)

    Nematollahi, Mohammadreza; Yang, Xiaodong; Seim, Eivind; Vullum, Per Erik; Holmestad, Randi; Gibson, Ursula J.; Reenaas, Turid W.

    2016-02-01

    We present the properties of Cr-doped zinc sulfide (ZnS:Cr) films deposited on Si(100) by pulsed laser deposition. The films are studied for solar cell applications, and to obtain a high absorption, a high Cr content (2.0-5.0 at.%) is used. It is determined by energy-dispersive X-ray spectroscopy that Cr is relatively uniformly distributed, and that local Cr increases correspond to Zn decreases. The results indicate that most Cr atoms substitute Zn sites. Consistently, electron energy loss and X-ray photoelectron spectroscopy showed that the films contain mainly Cr2+ ions. Structural analysis showed that the films are polycrystalline and textured. The films with ~4 % Cr are mainly grown along the hexagonal [001] direction in wurtzite phase. The average lateral grain size decreases with increasing Cr content, and at a given Cr content, increases with increasing growth temperature.

  19. Structural analysis of infinite layer superlattices grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Del Vecchio, A.; Tapfer, L.; Aruta, C.; Balestrino, G.; Petrocelli, G.

    1996-07-01

    In this work we investigate the structural properties of SrCuO2/CaCuO2 infinite layer superlattices by high-resolution x-ray diffraction and x-ray specular reflectivity measurements. The infinite layer superlattices are grown by pulsed laser deposition on slightly misoriented (001) SrTiO3 substrates. We demonstrate that good quality superlattices with few monolayers thick constituent SrCuO2 and CaCuO2 layers can be grown having an interface roughness of less than 3-4 Å. A strain analysis of the epitaxial film shows that the SrCuO2 layers are completely relaxed with respect to the substrate. However, the CaCuO2 layers are elastically strained with respect to the SrCuO2 layer. The Poisson ratio of the CaCuO2 is estimated to be 0.40±0.08.

  20. Structural and morphological properties of metallic thin films grown by pulsed laser deposition for photocathode application

    NASA Astrophysics Data System (ADS)

    Lorusso, A.; Gontad, F.; Caricato, A. P.; Chiadroni, E.; Broitman, E.; Perrone, A.

    2016-03-01

    In this work yttrium and lead thin films have been deposited by pulsed laser deposition technique and characterized by ex situ different diagnostic methods. All the films were adherent to the substrates and revealed a polycrystalline structure. Y films were uniform with a very low roughness and droplet density, while Pb thin films were characterized by a grain morphology with a relatively high roughness and droplet density. Such metallic materials are studied because they are proposed as a good alternative to copper and niobium photocathodes which are generally used in radiofrequency and superconducting radiofrequency guns, respectively. The photoemission performances of the photocathodes based on Y and Pb thin films have been also studied and discussed.

  1. Robust integral variable structure controller and pulse-width pulse-frequency modulated input shaper design for flexible spacecraft with mismatched uncertainty/disturbance.

    PubMed

    Hu, Qinglei

    2007-10-01

    This paper presents a dual-stage control system design method for the flexible spacecraft attitude maneuvering control by use of on-off thrusters and active vibration control by input shaper. In this design approach, attitude control system and vibration suppression were designed separately using lower order model. As a stepping stone, an integral variable structure controller with the assumption of knowing the upper bounds of the mismatched lumped perturbation has been designed which ensures exponential convergence of attitude angle and angular velocity in the presence of bounded uncertainty/disturbances. To reconstruct estimates of the system states for use in a full information variable structure control law, an asymptotic variable structure observer is also employed. In addition, the thruster output is modulated in pulse-width pulse-frequency so that the output profile is similar to the continuous control histories. For actively suppressing the induced vibration, the input shaping technique is used to modify the existing command so that less vibration will be caused by the command itself, which only requires information about the vibration frequency and damping of the closed-loop system. The rationale behind this hybrid control scheme is that the integral variable structure controller can achieve good precision pointing, even in the presence of uncertainties/disturbances, whereas the shaped input attenuator is applied to actively suppress the undesirable vibrations excited by the rapid maneuvers. Simulation results for the spacecraft model show precise attitude control and vibration suppression. PMID:17706218

  2. Multistage plasma initiation process by pulsed CO2 laser irradiation of a Ti sample in an ambient gas (He, Ar, or N2)

    NASA Astrophysics Data System (ADS)

    Hermann, J.; Boulmer-Leborgne, C.; Mihailescu, I. N.; Dubreuil, B.

    1993-02-01

    New experimental results are reported on plasma initiation in front of a titanium sample irradiated by ir (λ=10.6 μm) laser pulses in an ambient gas (He, Ar, and N2) at pressures ranging from several Torr up to the atmosphere. The plasma is studied by space- and time-resolved emission spectroscopy, while sample vaporization is probed by laser-induced fluorescence spectroscopy. Threshold laser intensities leading to the formation of a plasma in the vapor and in the ambient gases are determined. Experimental results support the model of a vaporization mechanism for the plasma initiation (vaporization-initiated plasma breakdown). The plasma initiation is described by simple numerical criteria based on a two-stage process. Theoretical predictions are found to be in a reasonable agreement with the experiment. This study provides also a clear explanation of the influence of the ambient gas on the laser beam-metal surface energy transfer. Laser irradiation always causes an important vaporization when performed in He, while in the case of Ar or N2, the interaction is reduced in heating and vaporization of some surface defects and impurities.

  3. Silicon structuring by etching with liquid chlorine and fluorine precursors using femtosecond laser pulses

    SciTech Connect

    Radu, C.; Simion, S.; Zamfirescu, M.; Ulmeanu, M.; Enculescu, M.; Radoiu, M.

    2011-08-01

    The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl{sub 4}) and fluorine (C{sub 2}Cl{sub 3}F{sub 3}) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm{sup 2} laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 {mu}m, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 {mu}m in height and with a full width at half maximum of 2.3 {mu}m with irradiation of 700 pulses at 560 mJ/cm{sup 2} laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D

  4. Advances in Protein NMR Impacting Drug Discovery Provided by the NIGMS Protein Structure Initiative

    PubMed Central

    Montelione, Gaetano T.; Szyperski, Thomas

    2014-01-01

    Rational drug design relies on three-dimensional structures of biological macromolecules, especially proteins. Structural genomics high-throughput (HTP) structure determination platforms established by the NIH Protein Structure Initiative are uniquely suited to provide these structures. NMR plays a critical role since (i) many important protein targets do not form single crystals required for X-ray diffraction and (ii) NMR can provide valuable structural and dynamic information on proteins and their drug complexes that cannot be obtained with X-ray crystallography. In this article, recent advances of NMR driven by structural genomics projects are reviewed. These advances promise that future pharmaceutical discovery and design of drugs can increasingly rely on protocols for rapid and accurate NMR structure determination. PMID:20443167

  5. Maternal, Infant Characteristics, Breastfeeding Techniques, and Initiation: Structural Equation Modeling Approaches

    PubMed Central

    Htun, Tha Pyai; Lim, Peng Im; Ho-Lim, Sarah

    2015-01-01

    Objectives The aim of this study was to examine the relationships among maternal and infant characteristics, breastfeeding techniques, and exclusive breastfeeding initiation in different modes of birth using structural equation modeling approaches. Methods We examined a hypothetical model based on integrating concepts of a breastfeeding decision-making model, a breastfeeding initiation model, and a social cognitive theory among 952 mother-infant dyads. The LATCH breastfeeding assessment tool was used to evaluate breastfeeding techniques and two infant feeding categories were used (exclusive and non-exclusive breastfeeding). Results Structural equation models (SEM) showed that multiparity was significantly positively associated with breastfeeding techniques and the jaundice of an infant was significantly negatively related to exclusive breastfeeding initiation. A multigroup analysis in the SEM showed no difference between the caesarean section and vaginal delivery groups estimates of breastfeeding techniques on exclusive breastfeeding initiation. Breastfeeding techniques were significantly positively associated with exclusive breastfeeding initiation in the entire sample and in the vaginal deliveries group. However, breastfeeding techniques were not significantly associated with exclusive breastfeeding initiation in the cesarean section group. Maternal age, maternal race, gestations, birth weight of infant, and postnatal complications had no significant impacts on breastfeeding techniques or exclusive breastfeeding initiation in our study. Overall, the models fitted the data satisfactorily (GFI = 0.979–0.987; AGFI = 0.951–0.962; IFI = 0.958–0.962; CFI = 0.955–0.960, and RMSEA = 0.029–0.034). Conclusions Multiparity and jaundice of an infant were found to affect breastfeeding technique and exclusive breastfeeding initiation respectively. Breastfeeding technique was related to exclusive breastfeeding initiation according to the mode of birth. This

  6. Bi-stable states of initially stressed elastic cylindrical shell structures with two piezoelectric surface layers

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Nie, Guo-Hua

    2015-10-01

    A theoretical model is proposed in this paper to predict the bi-stable states of initially stressed cylindrical shell structures attached by surface anisotropic piezoelectric layers. The condition for existence of bi-stability of the shell structural system is presented and analytical expressions for corresponding rolled-up radii of the stable shell are given based on the principle of minimum strain energy. The resulting solution indicates that the shell system may have two stable configurations besides its initial state under a combined action of the actuating electric field and initial stresses characterized by the bending moment. If the piezoelectric layer materials act as only sensor materials without the actuating electric field, initial stresses may produce the bi-stable states, but one corresponding to its initial state. For the shell without initial stresses, the magnitude in the actuating electric field determines the number of the stable states, one or two stable configurations besides the initial state. The theoretical prediction for the bi-stable states is verified by finite element method (FEM) simulation by using the ABAQUS code.

  7. Feedbacks between structures and processes during initial ecosystem development in an artificial catchment

    NASA Astrophysics Data System (ADS)

    Schaaf, Wolfgang; Elemer, Michael; Gerwin, Werner; Fischer, Anton; Zaplata, Markus; Neneov, Rossen

    2013-04-01

    We studied the role of strutures and processes and their feedbacks during initial ecosystem development in the artificial catchment Chicken Creek. During the first seven years, considerable changes within the catchment were observed. Both internal and external factors could be identified as driving forces for the formation of structures and patterns in the artificial catchment. Initial structures formed by the construction process and initial substrate characteristics were decisive for the distribution and flow of water. External factors like episodic events triggered erosion and dissection during this initial phase, promoted by the low vegetation cover and the unconsolidated sandy substrate. The transformation of the initial geo-system into areas with evolving terrestrial or aquatic characteristics and from a very episodic to a more permanent stream network and discharge, together with the observed vegetation dynamics increased site diversity and heterogeneity with respect to water and nutrient availability and transformation processes compared to the more homogenous conditions at point zero. The processes and feedback mechanisms in the initial development of a new landscape may deviate in rates, intensity and dominance from those known from mature ecosystems. It is therefore crucial to understand these early phases of ecosystem development and to disentangle the increasingly complex interactions between the evolving terrestrial and aquatic, biotic and abiotic compartments of the system. Artificially created catchments could be a suitable tool to study these initial developments at the landscape scale under known, designed and defined boundary conditions.

  8. Dielectric structure pyrotechnic initiator realized by integrating Ti/CuO-based reactive multilayer films

    NASA Astrophysics Data System (ADS)

    Zhu, Peng; Shen, Ruiqi; Fiadosenka, N. N.; Ye, Yinghua; Hu, Yan

    2011-04-01

    A dielectric structure pyrotechnic initiator was proposed and the initiator samples were designed and realized by integrating Ti/CuO-based reactive multilayer films on ceramic substrate. The dielectric structure consists of essentially two titanium films separated by a copper oxide (CuO) film, which is just like as a capacitor guaranteeing the initiator will not be discharged until the external voltage has exceeded the breakdown strength of the CuO film. Results of the electrical explosion experiment show that the breakdown strength of 1-μm-thick CuO film is 60 V, and the initiator has "late time discharge" characteristics, which will improve the conversion ratio of the electricity greatly, and there is a nanoscale exothermic reaction in the electrical explosion process. A systematic temperature measurement model based on the "double-line atomic emission spectroscopy of copper element" was presented and used to test the explosion temperature and duration. The ejected explosion flame was seen clearly with a potential temperature exceeding 4500 K for 0.1 ms, 4250 K for 0.35 ms, and 4000 K for 0.5 ms. Besides, electric energy and exothermic reaction create high-temperature products, which discharge to a distance of 1 cm or more. The high temperature and ejected products may be able to ignite the attached energetic materials even if the initiator makes no physical contact. These characteristics of the initiator may open a door to the preparation of the highly efficient and insensitive initiating explosive device.

  9. Investigating the Structural Properties of Integral Membrane Proteins with Pulsed EPR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lorigan, Gary

    2013-03-01

    Very limited structural and dynamic information on proteins embedded inside a membrane currently exist, because they are difficulty to crystalize. New biophysical/structural biology methods are needed to probe these systems in a lipid bilayer. The Lorigan lab is applying unique hybrid NMR and spin-label EPR spectroscopic techniques to study membrane proteins. Magnetic resonance spectroscopic data of 15N-, 2H-labeled and/or spin-labeled membrane proteins incorporated into vesicles and bicelles will be presented. State-of-the-art pulsed EPR techniques such as Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy, and Double Electron-Electron Resonance (DEER) spectroscopy will be used. The ESEEM technique can determine short to medium range distances (out to about 8 Å) between a site-specific nitroxide spin label and a nearby NMR-active isotopic labeled residue for a variety of different peptides and proteins which ultimately can be used to determine the difference between an α-helical and β-sheet secondary structure. DEER can be used to measure distances between 2 spin labels out to about 70 Å. We have shown a huge improvement is sensitivity with DEER measurements at Q-band when compared to X-band.

  10. Fundamental studies on initiation and evolution of multi-channel discharges and their application to next generation pulsed power machines.

    SciTech Connect

    Schwarz, Jens; Savage, Mark E.; Lucero, Diego Jose; Jaramillo, Deanna M.; Seals, Kelly Gene; Pitts, Todd Alan; Hautzenroeder, Brenna M.; Laine, Mark Richard; Karelitz, David B.; Porter, John L.

    2014-09-01

    Future pulsed power systems may rely on linear transformer driver (LTD) technology. The LTD's will be the building blocks for a driver that can deliver higher current than the Z-Machine. The LTD's would require tens of thousands of low inductance ( %3C 85nH), high voltage (200 kV DC) switches with high reliability and long lifetime ( 10 4 shots). Sandia's Z-Machine employs 36 megavolt class switches that are laser triggered by a single channel discharge. This is feasible for tens of switches but the high inductance and short switch life- time associated with the single channel discharge are undesirable for future machines. Thus the fundamental problem is how to lower inductance and losses while increasing switch life- time and reliability. These goals can be achieved by increasing the number of current-carrying channels. The rail gap switch is ideal for this purpose. Although those switches have been extensively studied during the past decades, each effort has only characterized a particular switch. There is no comprehensive understanding of the underlying physics that would allow predictive capability for arbitrary switch geometry. We have studied rail gap switches via an extensive suite of advanced diagnostics in synergy with theoretical physics and advanced modeling capability. Design and topology of multichannel switches as they relate to discharge dynamics are investigated. This involves electrically and optically triggered rail gaps, as well as discrete multi-site switch concepts.

  11. Effect of the light spectrum of various substrates for inkjet printed conductive structures sintered with intense pulsed light

    NASA Astrophysics Data System (ADS)

    Weise, Dana; Mitra, Kalyan Yoti; Ueberfuhr, Peter; Baumann, Reinhard R.

    2015-02-01

    In this work, the novel method of intense pulsed light (IPL) sintering of a nanoparticle silver ink is presented. Various patterns are printed with the Inkjet technology on two flexible foils with different light spectra. One is a clear Polyethylenterephthalat [PET] foil and the second is a light brownish Polyimide [PI] foil. The samples are flashed with different parameters regarding to pulse intensity and pulse length. Microscopic images are indicating the impact of the flashing parameters and the different light spectra of the substrates on the sintered structures. Sheet and line resistance are measured and the conductivity is calculated. A high influence of the property of the substrate with respect to light absorption and thermal conductivity on the functionality of printed conductive structures could be presented. With this new method of IPL sintering, highly conductive inkjet printed silver patterns could be manufactured within milliseconds on flexible polymeric foils without damaging the substrate.

  12. Effect of the light spectrum of various substrates for inkjet printed conductive structures sintered with intense pulsed light

    SciTech Connect

    Weise, Dana Mitra, Kalyan Yoti Ueberfuhr, Peter; Baumann, Reinhard R.

    2015-02-17

    In this work, the novel method of intense pulsed light (IPL) sintering of a nanoparticle silver ink is presented. Various patterns are printed with the Inkjet technology on two flexible foils with different light spectra. One is a clear Polyethylenterephthalat [PET] foil and the second is a light brownish Polyimide [PI] foil. The samples are flashed with different parameters regarding to pulse intensity and pulse length. Microscopic images are indicating the impact of the flashing parameters and the different light spectra of the substrates on the sintered structures. Sheet and line resistance are measured and the conductivity is calculated. A high influence of the property of the substrate with respect to light absorption and thermal conductivity on the functionality of printed conductive structures could be presented. With this new method of IPL sintering, highly conductive inkjet printed silver patterns could be manufactured within milliseconds on flexible polymeric foils without damaging the substrate.

  13. Using Data on Vegetation Structure to Initialize and Test Ecosystem Models (Invited)

    NASA Astrophysics Data System (ADS)

    Hurtt, G. C.; Dubayah, R.; Fisk, J.; Dolan, K. A.; Shugart, H. H.

    2010-12-01

    Scientists have long recognized the importance of vegetation structure in forest dynamics, but relevant data and models have generally not been available for large-scale applications. Now future satellite missions utilizing lidar and radar technologies have the potential to provide globally consistent data on vegetation structure, and new models are being developed to track the dynamics of vegetation 3-D structure over large scales. Used together, these advances have the potential to revolutionize the initialization and testing of terrestrial models, and thereby reduce key uncertainties and improve model predictions of carbon cycle dynamics. Here, using both theoretical models and an advanced mechanistic ecosystem model, we investigate the use, and potential use, of data on various forest structural metrics for initializing and testing terrestrial models. Focus is on quantifying the potential utility of various metrics, and the resolution and accuracy with which these measurements need to be made.

  14. Structure and composition of oligohaline marsh plant communities exposed to salinity pulses

    USGS Publications Warehouse

    Howard, R.J.; Mendelssohn, I.A.

    2000-01-01

    The response of two oligohaline marsh macrophyte communities to pulses of increased salinity was studied over a single growing season in a greenhouse experiment. The plant communities were allowed a recovery period in freshwater following the pulse events. The experimental treatments included: (1) salinity influx rate (rate of salinity increase from 0 to 12 gl-1); (2) duration of exposure to elevated salinity; and (3) water depth. The communities both included Sagittaria lancifolia L.; the codominant species were Eleocharis palustris (L.) Roemer and J.A. Schultes in community 1 and Schoenoplectus americanus (Pers.) Volk. ex Schinz and R. Keller in community 2. Effects of the treatments on sediment chemical characteristics (salinity, pH, redox potential, and sulfide and ammonium concentrations) and plant community attributes (aboveground and belowground biomass, stem density, leaf tissue nutrients, and species richness) were examined. The treatment effects often interacted to influence sediment and plant communities characteristics following recovery in fresh water. Salinity influx rate per se, however, had little effect on the abiotic or biotic response variables; significant influx effects were found when the 0 gl-1 (zero influx) treatment was compared to the 12 gl-1 treatments, regardless of the rate salinity was raised. A salinity level of 12 gl-1 had negative effects on plant community structure and composition; these effects were usually associated with 3 months of salinity exposure. Water depth often interacted with exposure duration, but increased water depth did independently decrease the values of some community response measures. Community 1 was affected more than community 2 in the most extreme salinity treatment (3 months exposure/15-cm water depth). Although species richness in both communities was reduced, structural changes were more dramatic in community 1. Biomass and stem density were reduced in community 1 overall and in both dominant species

  15. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing.

    PubMed

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-24

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities. PMID:25815515

  16. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

    NASA Astrophysics Data System (ADS)

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-01

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm-2, the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm-1 at 300.7 cm-1, which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

  17. Structural, morphological and Raman studies of pulse electrosynthesised indium antimonide thin films

    NASA Astrophysics Data System (ADS)

    Singh, Joginder; Chandel, Tarun; Rajaram, P.

    2015-08-01

    InSb films deposited on fluorine doped tin oxide (FTO) substrates by a pulse elctrodeposition technique. The deposition was carried out at an applied potential -1.3V versus Ag/AgCl electrode. Structural, morphological and optical studies were performed on the electrodeposited InSb. X-ray diffraction (XRD) studies show that the deposited InSb films are polycrystalline in nature having the zinc blend structure. The crystallite size (D), dislocation density (δ) and strain (ɛ) were calculated using XRD results. The EDAX analysis shows that chemical composition of In3+ and Sb3+ ions is close to the required stoichiometry. The surface morphology of the deposited films was examined using scanning electron scanning electron microscopy (SEM). SEM studies reveal that the surface of the films is uniformly covered with submicron sized spherical particles. However, the crystallite size determined by the Scherrer method shows a size close to 30 nm. Surface morphology studies of the InSb films were also performed using atomic force microscopy (AFM). The average surface roughness as measured by AFM is around 40 nm. Hot probe studies show that all the electrodeposited thin films have n type conductivity and the thickness of the films is calculated using electrochemical formula.

  18. Structural, morphological and Raman studies of pulse electrosynthesised indium antimonide thin films

    SciTech Connect

    Singh, Joginder Chandel, Tarun; Rajaram, P.

    2015-08-28

    InSb films deposited on fluorine doped tin oxide (FTO) substrates by a pulse elctrodeposition technique. The deposition was carried out at an applied potential −1.3V versus Ag/AgCl electrode. Structural, morphological and optical studies were performed on the electrodeposited InSb. X-ray diffraction (XRD) studies show that the deposited InSb films are polycrystalline in nature having the zinc blend structure. The crystallite size (D), dislocation density (δ) and strain (ε) were calculated using XRD results. The EDAX analysis shows that chemical composition of In{sup 3+} and Sb{sup 3+} ions is close to the required stoichiometry. The surface morphology of the deposited films was examined using scanning electron microscopy (SEM). SEM studies reveal that the surface of the films is uniformly covered with submicron sized spherical particles. However, the crystallite size determined by the Scherrer method shows a size close to 30 nm. Surface morphology studies of the InSb films were also performed using atomic force microscopy (AFM). The average surface roughness as measured by AFM is around 40 nm. Hot probe studies show that all the electrodeposited thin films have n type conductivity and the thickness of the films is calculated using electrochemical formula.

  19. Applications of pulsed EPR spectroscopy to structural studies of sulfite oxidizing enzymes

    SciTech Connect

    Klein, Eric L.; Astashkin, Andrei V.; Raitsimring, Arnold M.; Enemark, John H.

    2013-01-01

    Sulfite oxidizing enzymes (SOEs), including sulfite oxidase (SO) and bacterial sulfite dehydrogenase (SDH), catalyze the oxidation of sulfite (SO32-) to sulfate (SO42-). The active sites of SO and SDH are nearly identical, each having a 5-coordinate, pseudo-square-pyramidal Mo with an axial oxo ligand and three equatorial sulfur donor atoms. One sulfur is from a conserved Cys residue and two are from a pyranopterindithiolene (molybdopterin, MPT) cofactor. The identity of the remaining equatorial ligand, which is solvent-exposed, varies during the catalytic cycle. Numerous in vitro studies, particularly those involving electron paramagnetic resonance (EPR) spectroscopy of the Mo(V) states of SOEs, have shown that the identity and orientation of this exchangeable equatorial ligand depends on the buffer pH, the presence and concentration of certain anions in the buffer, as well as specific point mutations in the protein. Until very recently, however, EPR has not been a practical technique for directly probing specific structures in which the solvent-exposed, exchangeable ligand is an O, OH-, H2O, SO32-, or SO42- group, because the primary O and S isotopes (16O and 32S) are magnetically silent (I = 0). This review focuses on the recent advances in the use of isotopic labeling, variable-frequency high resolution pulsed EPR spectroscopy, synthetic model compounds, and DFT calculations to elucidate the roles of various anions, point mutations, and steric factors in the formation, stabilization, and transformation of SOE active site structures.

  20. Dual polarized receiving steering antenna array for measurement of ultrawideband pulse polarization structure.

    PubMed

    Balzovsky, E V; Buyanov, Yu I; Koshelev, V I; Nekrasov, E S

    2016-03-01

    To measure simultaneously two orthogonal components of the electromagnetic field of nano- and subnano-second duration, an antenna array has been developed. The antenna elements of the array are the crossed dipoles of dimension 5 × 5 cm. The arms of the dipoles are connected to the active four-pole devices to compensate the frequency response variations of a short dipole in the frequency band ranging from 0.4 to 4 GHz. The dipoles have superimposed phase centers allowing measuring the polarization structure of the field in different directions. The developed antenna array is the linear one containing four elements. The pattern maximum position is controlled by means of the switched ultrawideband true time delay lines. Discrete steering in seven directions in the range from -40° to +40° has been realized. The error at setting the pattern maximum position is less than 4°. The isolation of the polarization exceeds 29 dB in the direction orthogonal to the array axis and in the whole steering range it exceeds 23 dB. Measurement results of the polarization structure of radiated and scattered pulses with different polarization are presented as well. PMID:27036799

  1. Dual polarized receiving steering antenna array for measurement of ultrawideband pulse polarization structure

    NASA Astrophysics Data System (ADS)

    Balzovsky, E. V.; Buyanov, Yu. I.; Koshelev, V. I.; Nekrasov, E. S.

    2016-03-01

    To measure simultaneously two orthogonal components of the electromagnetic field of nano- and subnano-second duration, an antenna array has been developed. The antenna elements of the array are the crossed dipoles of dimension 5 × 5 cm. The arms of the dipoles are connected to the active four-pole devices to compensate the frequency response variations of a short dipole in the frequency band ranging from 0.4 to 4 GHz. The dipoles have superimposed phase centers allowing measuring the polarization structure of the field in different directions. The developed antenna array is the linear one containing four elements. The pattern maximum position is controlled by means of the switched ultrawideband true time delay lines. Discrete steering in seven directions in the range from -40° to +40° has been realized. The error at setting the pattern maximum position is less than 4°. The isolation of the polarization exceeds 29 dB in the direction orthogonal to the array axis and in the whole steering range it exceeds 23 dB. Measurement results of the polarization structure of radiated and scattered pulses with different polarization are presented as well.

  2. The Clause-Initial Position in L2 German Declaratives: Transfer of Information Structure

    ERIC Educational Resources Information Center

    Bohnacker, Ute; Rosen, Christina

    2008-01-01

    This article investigates the information structure of verb-second (V2) declaratives in Swedish, German, and nonnative German. Even though almost any type of element can occur in the so-called prefield, the clause-initial preverbal position of V2 declaratives, we have found language-specific patterns in native-speaker corpora: The frequencies of…

  3. Mitochondrial iron supply is required for the developmental pulse of ecdysone biosynthesis that initiates metamorphosis in Drosophila melanogaster.

    PubMed

    Llorens, Jose V; Metzendorf, Christoph; Missirlis, Fanis; Lind, Maria I

    2015-12-01

    Synthesis of ecdysone, the key hormone that signals the termination of larval growth and the initiation of metamorphosis in insects, is carried out in the prothoracic gland by an array of iron-containing cytochrome P450s, encoded by the halloween genes. Interference, either with iron-sulfur cluster biogenesis in the prothoracic gland or with the ferredoxins that supply electrons for steroidogenesis, causes a block in ecdysone synthesis and developmental arrest in the third instar larval stage. Here we show that mutants in Drosophila mitoferrin (dmfrn), the gene encoding a mitochondrial carrier protein implicated in mitochondrial iron import, fail to grow and initiate metamorphosis under dietary iron depletion or when ferritin function is partially compromised. In mutant dmfrn larvae reared under iron replete conditions, the expression of halloween genes is increased and 20-hydroxyecdysone (20E), the active form of ecdysone, is synthesized. In contrast, addition of an iron chelator to the diet of mutant dmfrn larvae disrupts 20E synthesis. Dietary addition of 20E has little effect on the growth defects, but enables approximately one-third of the iron-deprived dmfrn larvae to successfully turn into pupae and, in a smaller percentage, into adults. This partial rescue is not observed with dietary supply of ecdysone's precursor 7-dehydrocholesterol, a precursor in the ecdysone biosynthetic pathway. The findings reported here support the notion that a physiological supply of mitochondrial iron for the synthesis of iron-sulfur clusters and heme is required in the prothoracic glands of insect larvae for steroidogenesis. Furthermore, mitochondrial iron is also essential for normal larval growth. PMID:26468126

  4. Radiography of magnetically-driven implosions of initially solid beryllium cylindrical shells for equation-of-state studies at the Z pulsed-power facility

    NASA Astrophysics Data System (ADS)

    McBride, Ryan

    2011-06-01

    The Z accelerator delivers approximately 4-MV, 26-MA electrical pulses with adjustable current rise times of 100--600 ns, as well as adjustable pulse waveforms. The magnetic pressure produced is used for various applications, including magnetically-driven implosions. The Z-Beamlet Laser (ZBL) is a pulsed (0.3-1.5 ns), multi-kJ, TW-class Nd:glass laser system that provides x-ray radiography capabilities for Z experiments. This talk focuses primarily on the radiography diagnostic used to study the magnetically-driven implosions of initially solid cylindrical shells (also referred to as ``liners''). Specifically, we discuss the 6.151-keV monochromatic backlighting system and its use in obtaining radiographs of imploding beryllium (Be) liners. The high transmission efficiency of 6.151-keV photons in Be allowed us to obtain radiographs with finite transmission throughout the radial extent of the imploding liners. Abel inverting these data, we have obtained time-resolved measurements of the imploding liner's density as a function of both axial and radial location throughout the field of view. These data are allowing us to study magneto-Rayleigh-Taylor (MRT) growth for inertial-confinement-fusion applications, as well as compression-wave propagation for equation-of-state studies (see talks by R.L. Lemke and M.R. Martin). Additionally, Z's pulse-shaping capabilities have enabled us to obtain data for both shock- and quasi-isentropically-compressed Be. Example data from MRT, shock-compression, and quasi-isentropic-compression experiments will be shown. We will also discuss planned upgrades to 25-keV radiography that will allow us to study materials with opacities beyond that of beryllium. This work was done in collaboration with R.W. Lemke, M.R. Martin, J.-P. Davis, M.D. Knudson, D.B. Sinars, S.A. Slutz, C.A. Jennings, M.E. Cuneo, D.G. Flicker, and M.C. Herrmann. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin company, for the US

  5. Redistribution of Kv1 and Kv7 enhances neuronal excitability during structural axon initial segment plasticity

    PubMed Central

    Kuba, Hiroshi; Yamada, Rei; Ishiguro, Go; Adachi, Ryota

    2015-01-01

    Structural plasticity of the axon initial segment (AIS), the trigger zone of neurons, is a powerful means for regulating neuronal activity. Here, we show that AIS plasticity is not limited to structural changes; it also occurs as changes in ion-channel expression, which substantially augments the efficacy of regulation. In the avian cochlear nucleus, depriving afferent inputs by removing cochlea elongated the AIS, and simultaneously switched the dominant Kv channels at the AIS from Kv1.1 to Kv7.2. Due to the slow activation kinetics of Kv7.2, the redistribution of the Kv channels reduced the shunting conductance at the elongated AIS during the initiation of action potentials and effectively enhanced the excitability of the deprived neurons. The results indicate that the functional plasticity of the AIS works cooperatively with the structural plasticity and compensates for the loss of afferent inputs to maintain the homeostasis of auditory circuits after hearing loss by cochlea removal. PMID:26581625

  6. Startup and initial operation of a DFGD and pulse jet fabric filter system on Cokenergy's Indiana Harbor coke oven off gas system

    SciTech Connect

    Morris, W.J.; Gansley, R.R.; Schaddell, J.G.

    1999-07-01

    This paper describes the design, initial operation and performance testing of a Dry Flue Gas Desulfurization (DFGD) and Modular Pulse Jet Fabric Filter (MPJFF) system installed at Cokenergy's site in East Chicago, Indiana. The combined flue gas from the sixteen (16) waste heat recovery boilers is processed by the system to control emissions of sulfur dioxide and particulates. These boilers recover energy from coke oven off gas from Indiana Harbor Coke Company's coke batteries. The DFGD system consists of two 100% capacity absorbers. Each absorber vessel uses a single direct drive rotary atomizer to disperse the lime slurry for SO{sub 2} control. The MPJFF consists of thirty two (32) modules arranged in twin sixteen-compartment (16) units. The initial start up of the DFGD/MPJFF posed special operational issues due to the low initial gas flows through the system as the four coke oven batteries were cured and put in service for the first time. This occurred at approximately monthly intervals beginning in March 1998. A plan was implemented to perform a staged startup of the DFGD and MPJFF to coincide with the staged start up of the coke batteries and waste heat boilers. Operational issues that are currently being addressed include reliability of byproduct removal. Performance testing was conducted in August and September 1998 at the inlet of the system and the outlet stack. During these tests, particulate, SO{sub 2}, SO{sub 3}, and HCI emissions were measured simultaneously at the common DFGD inlet duct and the outlet stack. Measurements were also taken for average lime, water, and power consumption during the tests as well as system pressure losses. These results showed that all guarantee parameters were achieved during the test periods. The initial operation and performance testing are described in this paper.

  7. Interactions between surface structures, runoff and erosion in an artificial watershed during the initial ecosystem development

    NASA Astrophysics Data System (ADS)

    Gerwin, W.; Raab, T.; Dimitrov, M.

    2009-04-01

    In its initial phase an ecosystem can be characterized as a Geo-(Hydro-)System since biotic compartments are still missing to a large extent. In this very first stage of the ecosystem development the hydrological processes forming the first surface structures are mainly controlled by runoff patterns and by the physical properties of the surface and the substrate. Based on that, it can be hypothesized that the initially formed structures are responsible for the future development of the ecosystem and define later structures. However, initial structures are very dynamic, and few alterations of surface properties may initiate the development of completely new patches and patterns which again control surface processes like erosion and sedimentation. Loose sand and other fine particles are transported directly by wind and water from the upper initial soil surface and a first physical soil crust is formed very quickly. This new surface exhibits clearly different properties compared with the original initial surface. For example, infiltration can be minimized and surface runoff is promoted by this crusting. In contrast, sandy or silty substrate that has been relocated by erosion processes into small hollows of the surface changes the soil physical properties of these parts of the landscape as well but into another direction. In these parts of the system the sedimentation may create small patches with higher infiltration rates and eventually better water storage capacities. This may result into the formation of initial vegetation patches and patterns which in turn influence the further quality and quantity as well as the location of soil surface processes. Against this background this paper presents a recently launched research project using an artificially created water catchment of 6 ha in size. This site called ‘Chicken Creek' (‘Hühnerwasser') was established in 2005 in Lusatia (Germany) and is the central research site of a German-Swiss Collaborative Research

  8. Chirped Pulse Adiabatic Passage in CARS for Imaging of Biological Structure and Dynamics

    SciTech Connect

    Malinovskaya, Svetlana A.

    2007-12-26

    We propose the adiabatic passage control scheme implementing chirped femtosecond laser pulses to maximize coherence in a predetermined molecular vibrational mode using two-photon Raman transitions. We investigate vibrational energy relaxation and collisional dephasing as factors of coherence loss, and demonstrate the possibility for preventing decoherence by the chirped pulse train. The proposed method may be used to advance noninvasive biological imaging techniques.

  9. Growth of nanolaminate structure of tetragonal zirconia by pulsed laser deposition

    PubMed Central

    2013-01-01

    Alumina/zirconia (Al2O3/ZrO2) multilayer thin films were deposited on Si (100) substrates at an optimized oxygen partial pressure of 3 Pa at room temperature by pulsed laser deposition. The Al2O3/ZrO2 multilayers of 10:10, 5:10, 5:5, and 4:4 nm with 40 bilayers were deposited alternately in order to stabilize a high-temperature phase of zirconia at room temperature. All these films were characterized by X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. The XRD studies of all the multilayer films showed only a tetragonal structure of zirconia and amorphous alumina. The high-temperature XRD studies of a typical 5:5-nm film indicated the formation of tetragonal zirconia at room temperature and high thermal stability. It was found that the critical layer thickness of zirconia is ≤10 nm, below which tetragonal zirconia is formed at room temperature. The XTEM studies on the as-deposited (Al2O3/ZrO2) 5:10-nm multilayer film showed distinct formation of multilayers with sharp interface and consists of mainly tetragonal phase and amorphous alumina, whereas the annealed film (5:10 nm) showed the inter-diffusion of layers at the interface. PMID:23413942

  10. Pulsed photothermal radiometry as a method for investigating blood vessel-like structures.

    PubMed

    Schmitz, C H; Oberheide, U; Lohmann, S; Lubatschowski, H; Ertmer, W

    2001-04-01

    Pulsed photothermal radiometry (PPTR) is known to be suitable for in vivo investigations of tissue optical properties. As a noncontact, nondestructive method it is a very attractive candidate for on-line dosimetry of laser treatments that rely on thermal laser-tissue interaction. In this article, we extend the one-dimensional (1D) analytical formalism that has widely been used to describe PPTR signals to a two-dimensional treatment of a simplified model of a blood vessel. This approach leads to quantitative description of a PPTR signal that, unlike in an 1D treatment, not only shows changes in time, but also varies in space. Using this approach, we are able to gain instructive understanding on how target characteristics of a blood vessel-like structure influence such a spatiotemporal PPTR signal. Likewise, the ability of extracting target features from those measurements is evaluated. Subsequently, we present experimental realization of the idealized model of a blood vessel as used in our theory. Comparison of actual PPTR measurements with theoretical predictions allow vessel localization laterally and in depth. Using our setup, we furthermore demonstrate the influence of flow inside the vessel on the measured signal. PMID:11375732

  11. Analysis of pulsed eddy current data using regression models for steam generator tube support structure inspection

    NASA Astrophysics Data System (ADS)

    Buck, J. A.; Underhill, P. R.; Morelli, J.; Krause, T. W.

    2016-02-01

    Nuclear steam generators (SGs) are a critical component for ensuring safe and efficient operation of a reactor. Life management strategies are implemented in which SG tubes are regularly inspected by conventional eddy current testing (ECT) and ultrasonic testing (UT) technologies to size flaws, and safe operating life of SGs is predicted based on growth models. ECT, the more commonly used technique, due to the rapidity with which full SG tube wall inspection can be performed, is challenged when inspecting ferromagnetic support structure materials in the presence of magnetite sludge and multiple overlapping degradation modes. In this work, an emerging inspection method, pulsed eddy current (PEC), is being investigated to address some of these particular inspection conditions. Time-domain signals were collected by an 8 coil array PEC probe in which ferromagnetic drilled support hole diameter, depth of rectangular tube frets and 2D tube off-centering were varied. Data sets were analyzed with a modified principal components analysis (MPCA) to extract dominant signal features. Multiple linear regression models were applied to MPCA scores to size hole diameter as well as size rectangular outer diameter tube frets. Models were improved through exploratory factor analysis, which was applied to MPCA scores to refine selection for regression models inputs by removing nonessential information.

  12. Enhancing pulsed eddy current for inspection of P-3 Orion lap-joint structures

    NASA Astrophysics Data System (ADS)

    Butt, D. M.; Underhill, P. R.; Krause, T. W.

    2016-02-01

    During flight, aircraft are subjected to cyclic loading. In the Lockheed P-3 Orion airframe, this cyclic loading can lead to development of fatigue cracks at steel fastener locations in the top and second layers of aluminum wing skin lap-joints. An inspection method that is capable of detecting these cracks, without fastener removal, is desirable as this can minimize aircraft downtime, while subsequently reducing the risk of collateral damage. The ability to detect second layer cracks has been demonstrated using a Pulsed Eddy Current (PEC) probe design that utilizes the ferrous fastener as a flux conduit. This allows for deeper penetration of flux into the lap-joint second layer and consequently, sensitivity to the presence of cracks. Differential pick-up coil pairs are used to sense the eddy current response due to the presence of a crack. The differential signal obtained from pick-up coils on opposing sides of the fastener is analyzed using a Modified Principal Components Analysis (MPCA). This is followed by a cluster analysis of the resulting MPCA scores to separate fastener locations with cracks from those without. Probe design features, data acquisition system parameters and signal post-processing can each have a strong impact on crack detection. Physical probe configurations and signal analysis processes, used to enhance the PEC system for detection of cracks in P-3 Orion lap-joint structures, are investigated and an enhanced probe design is identified.

  13. Plasma structures observed in gas breakdown using a 1.5 MW, 110 GHz pulsed gyrotron

    SciTech Connect

    Hidaka, Yoshiteru; Choi, E. M.; Mastovsky, I.; Shapiro, M. A.; Sirigiri, J. R.; Temkin, R. J.; Edmiston, G. F.; Neuber, A. A.; Oda, Y.

    2009-05-15

    Regular two-dimensional plasma filamentary arrays have been observed in gas breakdown experiments using a pulsed 1.5 MW, 110 GHz gyrotron. The gyrotron Gaussian output beam is focused to an intensity of up to 4 MW/cm{sup 2}. The plasma filaments develop in an array with a spacing of about one quarter wavelength, elongated in the electric field direction. The array was imaged using photodiodes, a slow camera, which captures the entire breakdown event, and a fast camera with a 6 ns window. These diagnostics demonstrate the sequential development of the array propagating back toward the source. Gases studied included air, nitrogen, SF{sub 6}, and helium at various pressures. A discrete plasma array structure is observed at high pressure, while a diffuse plasma is observed at lower pressure. The propagation speed of the ionization front for air and nitrogen at atmospheric pressure for 3 MW/cm{sup 2} was found to be of the order of 10 km/s.

  14. Structure of an RNA polymerase II-TFIIB complex and the transcription initiation mechanism.

    PubMed

    Liu, Xin; Bushnell, David A; Wang, Dong; Calero, Guillermo; Kornberg, Roger D

    2010-01-01

    Previous x-ray crystal structures have given insight into the mechanism of transcription and the role of general transcription factors in the initiation of the process. A structure of an RNA polymerase II-general transcription factor TFIIB complex at 4.5 angstrom resolution revealed the amino-terminal region of TFIIB, including a loop termed the "B finger," reaching into the active center of the polymerase where it may interact with both DNA and RNA, but this structure showed little of the carboxyl-terminal region. A new crystal structure of the same complex at 3.8 angstrom resolution obtained under different solution conditions is complementary with the previous one, revealing the carboxyl-terminal region of TFIIB, located above the polymerase active center cleft, but showing none of the B finger. In the new structure, the linker between the amino- and carboxyl-terminal regions can also be seen, snaking down from above the cleft toward the active center. The two structures, taken together with others previously obtained, dispel long-standing mysteries of the transcription initiation process. PMID:19965383

  15. Structure of an RNA Polymerase II-TFIIB Complex and the Transcription Initiation Mechanism

    SciTech Connect

    Liu, Xin; Bushnell, David A; Wang, Dong; Calero, Guillermo; Kornberg, Roger D

    2010-01-14

    Previous x-ray crystal structures have given insight into the mechanism of transcription and the role of general transcription factors in the initiation of the process. A structure of an RNA polymerase II-general transcription factor TFIIB complex at 4.5 angstrom resolution revealed the amino-terminal region of TFIIB, including a loop termed the 'B finger,' reaching into the active center of the polymerase where it may interact with both DNA and RNA, but this structure showed little of the carboxyl-terminal region. A new crystal structure of the same complex at 3.8 angstrom resolution obtained under different solution conditions is complementary with the previous one, revealing the carboxyl-terminal region of TFIIB, located above the polymerase active center cleft, but showing none of the B finger. In the new structure, the linker between the amino- and carboxyl-terminal regions can also be seen, snaking down from above the cleft toward the active center. The two structures, taken together with others previously obtained, dispel long-standing mysteries of the transcription initiation process.

  16. Highly doped p-ZnTe films and quantum well structures grown by nonequilibrium pulsed laser ablation

    SciTech Connect

    Lowndes, D.H.; Rouleau, C.M.; Budai, J.D.; Geohegan, D.B.; McCamy, J.W.

    1995-06-01

    Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) and unintentionally doped (p-type) GaSb (001) substrates by pulsed KrF (248 nm) excimer laser ablation of a ZnTe target through an N{sub 2} ambient, without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range have been obtained. This appears to be the first time that any wide band gap (E{sub g} {ge} 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by pulsed-laser ablation (PLA). The maximum carrier concentrations also may be the highest obtained for ZnTe by any method thus far. Because pulsed laser deposition is inherently digital, attractive deposition rates can be combined with precise control of layer thickness in epitaxial multilayered structures. Typical deposition conditions are < 0.5 {angstrom} per laser pulse, with crystalline quality governed by tradeoffs between substrate temperature, pulse repetition rate, and the focused pulsed laser energy density. PLA`s capability for growth of very thin epitaxial layers is being exploited and studied through growth of doped heteroepitaxial quantum well structures in the nearly lattice-matched ZnTe/CdSe//GaSb(substrate) system. Results obtained from growth and characterization of heterostructures in this system will be presented.

  17. Formation of the domain structure in CLN under the pyroelectric field induced by pulse infrared laser heating

    SciTech Connect

    Shur, V. Ya.; Kosobokov, M. S.; Mingaliev, E. A.; Karpov, V. R.

    2015-10-15

    The evolution of the self-assembled quasi-regular micro- and nanodomain structures after pulse infrared laser irradiation in congruent lithium niobate crystal was studied by in situ optical observation. Several scenarios of domain kinetics represented covering of the irradiated zone by nets of the separated domain chains and rays have been revealed. The time dependence of the total domain length was analyzed in terms of modified Kolmogorov-Avrami theory. The domain structure evolution was attributed to the action of pyroelectric field appeared during cooling. The time dependence of the spatial distribution of the pyroelectric field during pulse laser heating and subsequent cooling was calculated by finite element method. The results of computer simulation allowed us to explain the experimental results and can be used for creation of tailored domain structures thus opening the new abilities of the submicron-scale domain engineering in ferroelectrics.

  18. Formation of the domain structure in CLN under the pyroelectric field induced by pulse infrared laser heating

    NASA Astrophysics Data System (ADS)

    Shur, V. Ya.; Kosobokov, M. S.; Mingaliev, E. A.; Karpov, V. R.

    2015-10-01

    The evolution of the self-assembled quasi-regular micro- and nanodomain structures after pulse infrared laser irradiation in congruent lithium niobate crystal was studied by in situ optical observation. Several scenarios of domain kinetics represented covering of the irradiated zone by nets of the separated domain chains and rays have been revealed. The time dependence of the total domain length was analyzed in terms of modified Kolmogorov-Avrami theory. The domain structure evolution was attributed to the action of pyroelectric field appeared during cooling. The time dependence of the spatial distribution of the pyroelectric field during pulse laser heating and subsequent cooling was calculated by finite element method. The results of computer simulation allowed us to explain the experimental results and can be used for creation of tailored domain structures thus opening the new abilities of the submicron-scale domain engineering in ferroelectrics.

  19. Effects of pulsed nutrient inputs on phytoplankton assemblage structure and blooms in an enclosed coastal area

    NASA Astrophysics Data System (ADS)

    Spatharis, Sofie; Tsirtsis, George; Danielidis, Daniel B.; Chi, Thang Do; Mouillot, David

    2007-07-01

    The response of phytoplankton assemblage structure to terrestrial nutrient inputs was examined for the Gulf of Kalloni in the Northern Aegean Sea, a productive semi-enclosed coastal marine ecosystem. The study was focused on a typical annual cycle, and emphasis was placed on the comparative analysis between blooms developing after significant nutrient inputs from the watershed, and naturally occurring blooms. Baseline information was collected on a monthly basis from a network of stations located in the oligotrophic open sea and the interior and more productive part of the embayment. Intensive sampling was also carried out along a gradient in the vicinity of a river which was the most important source of freshwater and nutrient input for the Gulf. Phytoplankton assemblage structure was analyzed from 188 samples using diversity indices (Shannon and Average Taxonomic Distinctness), multivariate plotting methods (NMDS), multivariate statistics (PERMANOVA), and canonical correspondence analysis (CCA). Three characteristic assemblages were recognized: (1) an autumn assemblage developed under nutrient depleted conditions, having low diversity due to the dominance of two small diatoms, (2) a winter bloom of the potentially toxic species Pseudo-nitzschia calliantha occurring immediately after a nutrient peak and characterized by very low diversity, and (3) a naturally occurring early summer bloom of centric diatoms with relatively high diversity. The results of the study support the view that moderate nutrient inputs may have a beneficial effect on the functioning of coastal ecosystems, stimulating the taxonomic diversity through the growth of different taxonomic groups and taxa. On the other hand, a sudden pulse of high nutrient concentrations may greatly affect the natural succession of organisms, have a negative effect on the diversity through the dominance of a single species, and can increase the possibility of a harmful algal bloom development.

  20. Study on the Structures of Two Booster Pellets Having High Initiation Capacity

    NASA Astrophysics Data System (ADS)

    Shuang-Qi, Hu; Hong-Rong, Liu; Li-shuang, Hu; Xiong, Cao; Xiang-Chao, Mi; Hai-Xia, Zhao

    2014-05-01

    Insensitive munitions (IM) improve the survivability of both weapons and their associated platforms, which can lead to a reduction in casualties, mission losses, and whole life costs. All weapon systems contain an explosive train that needs to meet IM criteria but reliably initiate a main charge explosive. To ensure that these diametrically opposed requirements can be achieved, new highly effective booster charge structures were designed. The initiation capacity of the two booster pellets was studied using varied composition and axial-steel-dent methods. The results showed that the two new booster pellets can initiate standard main charge pellets with less explosive mass than the ordinary cylindrical booster pellet. The numerical simulation results were in good agreement with the experiment results.

  1. X-ray Crystal Structures Elucidate the Nucleotidyl Transfer Reaction of Transcript Initiation Using Two Nucleotides

    SciTech Connect

    M Gleghorn; E Davydova; R Basu; L Rothman-Denes; K Murakami

    2011-12-31

    We have determined the X-ray crystal structures of the pre- and postcatalytic forms of the initiation complex of bacteriophage N4 RNA polymerase that provide the complete set of atomic images depicting the process of transcript initiation by a single-subunit RNA polymerase. As observed during T7 RNA polymerase transcript elongation, substrate loading for the initiation process also drives a conformational change of the O helix, but only the correct base pairing between the +2 substrate and DNA base is able to complete the O-helix conformational transition. Substrate binding also facilitates catalytic metal binding that leads to alignment of the reactive groups of substrates for the nucleotidyl transfer reaction. Although all nucleic acid polymerases use two divalent metals for catalysis, they differ in the requirements and the timing of binding of each metal. In the case of bacteriophage RNA polymerase, we propose that catalytic metal binding is the last step before the nucleotidyl transfer reaction.

  2. Crystal structure of translation initiation factor 5B from the crenarchaeon Aeropyrum pernix.

    PubMed

    Murakami, Ryo; Miyoshi, Tomohiro; Uchiumi, Toshio; Ito, Kosuke

    2016-05-01

    Initiation factor 5B (IF5B) is a universally conserved translational GTPase that catalyzes ribosomal subunit joining. In eukaryotes, IF5B directly interacts via a groove in its domain IV with initiation factor 1A (IF1A), another universally conserved initiation factor, to accomplish efficient subunit joining. Here, we have determined the first structure of a crenarchaeal IF5B, which revealed that the archaea-specific region of IF5B (helix α15) binds and occludes the groove of domain IV. Therefore, archaeal IF5B cannot access IF1A in the same manner as eukaryotic IF5B. This fact suggests that different relationships between IF5B and IF1A exist in archaea and eukaryotes. Proteins 2016; 84:712-717. © 2016 Wiley Periodicals, Inc. PMID:26868175

  3. The design and solving for initial structure of dual field of view IR system

    NASA Astrophysics Data System (ADS)

    Wang, Xue-xin; Jiao, Ming-yin; Yang, Bin

    2009-07-01

    In this paper, the zoom theory of IR dual field-of-view zoom optical lens (FOVs) is introduced. The process of how to solve the focal length and spaces of every group element by using performance parameters of infrared dual FOV optical system is described and the solving method for initial structure of single lens and double separate lens used as group is presented in detail. Particularly, great emphasis is give to discuss how to solve the initial structure for every group with PW method. Finally, the design results for 8μm~12μm dual field-of-view zoom infrared systems using the method mentioned above is presented and evaluated for each field by diffraction modulation transfer function(MTF), which shows that the design makes a good system with high image quality.

  4. Spanwise Spacing Effects on the Initial Structure and Decay of Axial Vortices

    NASA Technical Reports Server (NTRS)

    Wendt, B. J.; Reichert, B. A.

    1996-01-01

    The initial structure and axial decay of an array of streamwise vortices embedded in a turbulent pipe boundary layer is experimentally investigated. The vortices are shed in counter-rotating fashion from an array of equally-spaced symmetric airfoil vortex generators. Vortex structure is quantified in terms of crossplane circulation and peak streamwise vorticity. Flow conditions are subsonic and incompressible. The focus of this study is on the effect of the initial spacing between the parent vortex generators. Arrays with vortex generators spaced at 15 and 30 degrees apart are considered. When the spacing between vortex generators is decreased the circulation and peak vorticity of the shed vortices increases. Analysis indicates this strengthening results from regions of fluid acceleration in the vicinity of the vortex generator array. Decreased spacing between the constituent vortices also produces increased rates of circulation and peak vorticity decay.

  5. Importance of Granular Structure in the Initial Conditions for the Elliptic Flow

    SciTech Connect

    Andrade, R. P. G.; Grassi, F.; Hama, Y.; Qian, W. L.; Kodama, T.

    2008-09-12

    We show the effects of the granular structure of the initial conditions of a hydrodynamic description of high-energy nucleus-nucleus collisions on some observables, especially on the elliptic-flow parameter v{sub 2}. Such a structure enhances production of isotropically distributed high-p{sub T} particles, making v{sub 2} smaller there. Also, it reduces v{sub 2} in the forward and backward regions where the global matter density is smaller and, therefore, where such effects become more efficacious.

  6. Structure of a Complete Mediator-RNA Polymerase II Pre-Initiation Complex.

    PubMed

    Robinson, Philip J; Trnka, Michael J; Bushnell, David A; Davis, Ralph E; Mattei, Pierre-Jean; Burlingame, Alma L; Kornberg, Roger D

    2016-09-01

    A complete, 52-protein, 2.5 million dalton, Mediator-RNA polymerase II pre-initiation complex (Med-PIC) was assembled and analyzed by cryo-electron microscopy and by chemical cross-linking and mass spectrometry. The resulting complete Med-PIC structure reveals two components of functional significance, absent from previous structures, a protein kinase complex and the Mediator-activator interaction region. It thereby shows how the kinase and its target, the C-terminal domain of the polymerase, control Med-PIC interaction and transcription. PMID:27610567

  7. Three-dimensional structure of Escherichia coli initiator tRNA/f//Met/

    NASA Technical Reports Server (NTRS)

    Woo, N. H.; Rich, A.; Roe, B. A.

    1980-01-01

    The crystal structure of Escherichia coli tRNA(f)(Met), an initiator transfer RNA, has been determined. While grossly similar to that of the chain-elongating yeast tRNA(Phe), there are three major differences. One involves the folding of the anticodon loop; in particular, the position of the constant uridine, U33. This difference was unexpected and may be of functional significance.

  8. Initial condition effects on large scale structure in numerical simulations of plane mixing layers

    NASA Astrophysics Data System (ADS)

    McMullan, W. A.; Garrett, S. J.

    2016-01-01

    In this paper, Large Eddy Simulations are performed on the spatially developing plane turbulent mixing layer. The simulated mixing layers originate from initially laminar conditions. The focus of this research is on the effect of the nature of the imposed fluctuations on the large-scale spanwise and streamwise structures in the flow. Two simulations are performed; one with low-level three-dimensional inflow fluctuations obtained from pseudo-random numbers, the other with physically correlated fluctuations of the same magnitude obtained from an inflow generation technique. Where white-noise fluctuations provide the inflow disturbances, no spatially stationary streamwise vortex structure is observed, and the large-scale spanwise turbulent vortical structures grow continuously and linearly. These structures are observed to have a three-dimensional internal geometry with branches and dislocations. Where physically correlated provide the inflow disturbances a "streaky" streamwise structure that is spatially stationary is observed, with the large-scale turbulent vortical structures growing with the square-root of time. These large-scale structures are quasi-two-dimensional, on top of which the secondary structure rides. The simulation results are discussed in the context of the varying interpretations of mixing layer growth that have been postulated. Recommendations are made concerning the data required from experiments in order to produce accurate numerical simulation recreations of real flows.

  9. The Cryo-EM Structure of a Complete 30S Translation Initiation Complex from Escherichia coli

    PubMed Central

    Julián, Patricia; Milon, Pohl; Agirrezabala, Xabier; Lasso, Gorka; Gil, David; Rodnina, Marina V.; Valle, Mikel

    2011-01-01

    Formation of the 30S initiation complex (30S IC) is an important checkpoint in regulation of gene expression. The selection of mRNA, correct start codon, and the initiator fMet-tRNAfMet requires the presence of three initiation factors (IF1, IF2, IF3) of which IF3 and IF1 control the fidelity of the process, while IF2 recruits fMet-tRNAfMet. Here we present a cryo-EM reconstruction of the complete 30S IC, containing mRNA, fMet-tRNAfMet, IF1, IF2, and IF3. In the 30S IC, IF2 contacts IF1, the 30S subunit shoulder, and the CCA end of fMet-tRNAfMet, which occupies a novel P/I position (P/I1). The N-terminal domain of IF3 contacts the tRNA, whereas the C-terminal domain is bound to the platform of the 30S subunit. Binding of initiation factors and fMet-tRNAfMet induces a rotation of the head relative to the body of the 30S subunit, which is likely to prevail through 50S subunit joining until GTP hydrolysis and dissociation of IF2 take place. The structure provides insights into the mechanism of mRNA selection during translation initiation. PMID:21750663

  10. Structure of the initiation-competent RNA polymerase I and its implication for transcription

    NASA Astrophysics Data System (ADS)

    Pilsl, Michael; Crucifix, Corinne; Papai, Gabor; Krupp, Ferdinand; Steinbauer, Robert; Griesenbeck, Joachim; Milkereit, Philipp; Tschochner, Herbert; Schultz, Patrick

    2016-07-01

    Eukaryotic RNA polymerase I (Pol I) is specialized in rRNA gene transcription synthesizing up to 60% of cellular RNA. High level rRNA production relies on efficient binding of initiation factors to the rRNA gene promoter and recruitment of Pol I complexes containing initiation factor Rrn3. Here, we determine the cryo-EM structure of the Pol I-Rrn3 complex at 7.5 Å resolution, and compare it with Rrn3-free monomeric and dimeric Pol I. We observe that Rrn3 contacts the Pol I A43/A14 stalk and subunits A190 and AC40, that association re-organizes the Rrn3 interaction interface, thereby preventing Pol I dimerization; and Rrn3-bound and monomeric Pol I differ from the dimeric enzyme in cleft opening, and localization of the A12.2 C-terminus in the active centre. Our findings thus support a dual role for Rrn3 in transcription initiation to stabilize a monomeric initiation competent Pol I and to drive pre-initiation complex formation.

  11. The Cryo-EM structure of a complete 30S translation initiation complex from Escherichia coli.

    PubMed

    Julián, Patricia; Milon, Pohl; Agirrezabala, Xabier; Lasso, Gorka; Gil, David; Rodnina, Marina V; Valle, Mikel

    2011-07-01

    Formation of the 30S initiation complex (30S IC) is an important checkpoint in regulation of gene expression. The selection of mRNA, correct start codon, and the initiator fMet-tRNA(fMet) requires the presence of three initiation factors (IF1, IF2, IF3) of which IF3 and IF1 control the fidelity of the process, while IF2 recruits fMet-tRNA(fMet). Here we present a cryo-EM reconstruction of the complete 30S IC, containing mRNA, fMet-tRNA(fMet), IF1, IF2, and IF3. In the 30S IC, IF2 contacts IF1, the 30S subunit shoulder, and the CCA end of fMet-tRNA(fMet), which occupies a novel P/I position (P/I1). The N-terminal domain of IF3 contacts the tRNA, whereas the C-terminal domain is bound to the platform of the 30S subunit. Binding of initiation factors and fMet-tRNA(fMet) induces a rotation of the head relative to the body of the 30S subunit, which is likely to prevail through 50S subunit joining until GTP hydrolysis and dissociation of IF2 take place. The structure provides insights into the mechanism of mRNA selection during translation initiation. PMID:21750663

  12. Structure of the initiation-competent RNA polymerase I and its implication for transcription

    PubMed Central

    Pilsl, Michael; Crucifix, Corinne; Papai, Gabor; Krupp, Ferdinand; Steinbauer, Robert; Griesenbeck, Joachim; Milkereit, Philipp; Tschochner, Herbert; Schultz, Patrick

    2016-01-01

    Eukaryotic RNA polymerase I (Pol I) is specialized in rRNA gene transcription synthesizing up to 60% of cellular RNA. High level rRNA production relies on efficient binding of initiation factors to the rRNA gene promoter and recruitment of Pol I complexes containing initiation factor Rrn3. Here, we determine the cryo-EM structure of the Pol I-Rrn3 complex at 7.5 Å resolution, and compare it with Rrn3-free monomeric and dimeric Pol I. We observe that Rrn3 contacts the Pol I A43/A14 stalk and subunits A190 and AC40, that association re-organizes the Rrn3 interaction interface, thereby preventing Pol I dimerization; and Rrn3-bound and monomeric Pol I differ from the dimeric enzyme in cleft opening, and localization of the A12.2 C-terminus in the active centre. Our findings thus support a dual role for Rrn3 in transcription initiation to stabilize a monomeric initiation competent Pol I and to drive pre-initiation complex formation. PMID:27418187

  13. Structure of the initiation-competent RNA polymerase I and its implication for transcription.

    PubMed

    Pilsl, Michael; Crucifix, Corinne; Papai, Gabor; Krupp, Ferdinand; Steinbauer, Robert; Griesenbeck, Joachim; Milkereit, Philipp; Tschochner, Herbert; Schultz, Patrick

    2016-01-01

    Eukaryotic RNA polymerase I (Pol I) is specialized in rRNA gene transcription synthesizing up to 60% of cellular RNA. High level rRNA production relies on efficient binding of initiation factors to the rRNA gene promoter and recruitment of Pol I complexes containing initiation factor Rrn3. Here, we determine the cryo-EM structure of the Pol I-Rrn3 complex at 7.5 Å resolution, and compare it with Rrn3-free monomeric and dimeric Pol I. We observe that Rrn3 contacts the Pol I A43/A14 stalk and subunits A190 and AC40, that association re-organizes the Rrn3 interaction interface, thereby preventing Pol I dimerization; and Rrn3-bound and monomeric Pol I differ from the dimeric enzyme in cleft opening, and localization of the A12.2 C-terminus in the active centre. Our findings thus support a dual role for Rrn3 in transcription initiation to stabilize a monomeric initiation competent Pol I and to drive pre-initiation complex formation. PMID:27418187

  14. Structural barriers to timely initiation of antiretroviral treatment in Vietnam: findings from six outpatient clinics.

    PubMed

    Tran, Dam Anh; Shakeshaft, Anthony; Ngo, Anh Duc; Rule, John; Wilson, David P; Zhang, Lei; Doran, Christopher

    2012-01-01

    In Vietnam, premature mortality due to AIDS-related conditions is commonly associated with late initiation to antiretroviral therapy (ART). This study explores reasons for late ART initiation among people living with HIV (PLHIV) from the perspectives of health care providers and PLHIV. The study was undertaken in six clinics from five provinces in Vietnam. Baseline CD4 counts were collected from patient records and grouped into three categories: very late initiators (≤100 cells/mm(3) CD4), late initiators (100-200 cells/mm(3)) and timely initiators (200-350 cells/mm(3)). Thirty in-depth interviews with patients who started ART and 15 focus group discussions with HIV service providers were conducted and thematic analysis of the content performed. Of 934 patients, 62% started ART very late and 11% initiated timely treatment. The proportion of patients for whom a CD4 count was obtained within six months of their HIV diagnosis ranged from 22% to 72%. The proportion of patients referred to ART clinics by voluntary testing and counselling centres ranged from 1% to 35%. Structural barriers to timely ART initiation were poor linkage between HIV testing and HIV care and treatment services, lack of patient confidentiality and a shortage of HIV/AIDS specialists. If Vietnam's treatment practice is to align with WHO recommendations then the connection between voluntary counselling and testing service and ART clinics must be improved. Expansion and decentralization of HIV/AIDS services to allow implementation at the community level increased task sharing between doctors and nurses to overcome limited human resources, and improved patient confidentiality are likely to increase timely access to HIV treatment services for more patients. PMID:23240013

  15. The structure and properties of boron carbide ceramics modified by high-current pulsed electron-beam

    NASA Astrophysics Data System (ADS)

    Ivanov, Yuri; Tolkachev, Oleg; Petyukevich, Maria; Teresov, Anton; Ivanova, Olga; Ikonnikova, Irina; Polisadova, Valentina

    2016-01-01

    The present work is devoted to numerical simulation of temperature fields and the analysis of structural and strength properties of the samples surface layer of boron carbide ceramics treated by the high-current pulsed electron-beam of the submillisecond duration. The samples made of sintered boron carbide ceramics are used in these investigations. The problem of calculating the temperature field is reduced to solving the thermal conductivity equation. The electron beam density ranges between 8…30 J/cm2, while the pulse durations are 100…200 μs in numerical modelling. The results of modelling the temperature field allowed ascertaining the threshold parameters of the electron beam, such as energy density and pulse duration. The electron beam irradiation is accompanied by the structural modification of the surface layer of boron carbide ceramics either in the single-phase (liquid or solid) or two-phase (solid-liquid) states. The sample surface of boron carbide ceramics is treated under the two-phase state (solid-liquid) conditions of the structural modification. The surface layer is modified by the high-current pulsed electron-beam produced by SOLO installation at the Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia. The elemental composition and the defect structure of the modified surface layer are analyzed by the optical instrument, scanning electron and transmission electron microscopes. Mechanical properties of the modified layer are determined measuring its hardness and crack resistance. Research results show that the melting and subsequent rapid solidification of the surface layer lead to such phenomena as fragmentation due to a crack network, grain size reduction, formation of the sub-grained structure due to mechanical twinning, and increase of hardness and crack resistance.

  16. Effects of pulsed atrazine exposures on autotrophic community structure, biomass, and production in field-based stream mesocosms.

    PubMed

    King, Ryan S; Brain, Richard A; Back, Jeffrey A; Becker, Christopher; Wright, Moncie V; Toteu Djomte, Valerie; Scott, W Casan; Virgil, Steven R; Brooks, Bryan W; Hosmer, Alan J; Chambliss, C Kevin

    2016-03-01

    The authors performed a multiple-pulsed atrazine experiment to measure responses of autotrophic endpoints in outdoor stream mesocosms. The experiment was designed to synthetically simulate worst-case atrazine chemographs from streams in agricultural catchments to achieve 60-d mean concentrations of 0 μg/L (control), 10 μg/L, 20 μg/L, and 30 μg/L. The authors dosed triplicate streams with pulses of 0 μg/L, 50 μg/L, 100 μg/L, and 150 μg/L atrazine for 4 d, followed by 7 d without dosing. This 11-d cycle occurred 3 times, followed by a recovery (untreated) period from day 34 to day 60. Mean ± standard error 60-d atrazine concentrations were 0.07 ± 0.03 μg/L, 10.7 ± 0.05 μg/L, 20.9 ± 0.24 μg/L, and 31.0 ± 0.17 μg/L for the control, 10-μg/L, 20-μg/L, and 30-μg/L treatments, respectively. Multivariate analyses revealed that periphyton and phytoplankton community structure did not differ among treatments on any day of the experiment, including during the atrazine pulses. Control periphyton biomass in riffles was higher immediately following the peak of the first atrazine pulse and remained slightly higher than some of the atrazine treatments on most days through the peak of the last pulse. However, periphyton biomass was not different among treatments at the end of the present study. Phytoplankton biomass was not affected by atrazine. Metaphyton biomass in pools was higher in the controls near the midpoint of the present study and remained higher on most days for the remainder of the study. Ceratophyllum demersum, a submersed macrophyte, biomass was higher in controls than in 20-μg/L and 30-μg/L treatments before pulse 3 but was not different subsequent to pulse 3 through the end of the present study. Maximum daily dissolved oxygen (DO, percentage of saturation) declined during each pulse in approximate proportion to magnitude of dose but rapidly converged among treatments after the third pulse. However

  17. Effect of initial structure on recrystallization of the {alpha} matrix in an ({alpha} + {gamma}) microduplex stainless steel

    SciTech Connect

    Huang Xiaoxu; Tsuzaki, K.; Maki, T.

    1995-08-01

    The high temperature annealing behavior at 1,273K after 80% cold-rolling of the {alpha} matrix in ({alpha} + {gamma}) microduplex structures in a Fe-26Cr-7Ni alloy has been studied with particular attention to the effects of the size of initial structure and the initial orientation of {alpha}. The main results obtained are as follows: (1) No recrystallization of the {alpha} matrix takes place when the initial structure before rolling is fine; the {gamma} particle size is smaller than 9 {micro}m and the {alpha} subgrain size is not larger than 10 {micro}m. This result deduces the conclusion that the {alpha} matrix in ({alpha} + {gamma}) microduplex structures is very hard to recrystallize. (2) Recrystallization occurs in the {alpha} matrix with the {l_brace}111{r_brace}<{bar 1}10> initial orientation when the initial structure is coarse; the {gamma} particle size is 13.8 {micro}m and the {alpha}subgrain size is 15.6 {micro}m. The {l_brace}001{r_brace}<110>initially-oriented regions, by contrast, do not recrystallize even in the coarse initial structure. These results indicate that they recrystallization of the {alpha} matrix in ({alpha} + {gamma}) microduplex structures strongly depends on the initial orientation of {alpha} as well as the size of initial structure.

  18. Structure and properties of uranium oxide thin films deposited by pulsed dc magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Lin, Jianliang; Dahan, Isaac; Valderrama, Billy; Manuel, Michele V.

    2014-05-01

    Crystalline uranium oxide thin films were deposited in an unbalanced magnetron sputtering system by sputtering from a depleted uranium target in an Ar + O2 mixture using middle frequency pulsed dc magnetron sputtering. The substrate temperature was constantly maintained at 500 °C. Different uranium oxide phases (including UO2-x, UO2, U3O7 and U3O8) were obtained by controlling the percentage of the O2 flow rate to the total gas flow rate (f) in the chamber. The crystal structure of the films was characterized using X-ray diffraction and the microstructure of the films was studied using transmission electron microscopy and atom probe tomography. When the f was below 10%, the film contains a mixture of metallic uranium and UO2-x phases. As the f was controlled in the range of 10-13%, UO2 films with a (2 2 0) preferential orientation were obtained. The oxide phase rapidly changed to a mixture of U3O7 and U3O8 as the f was increased to the range of 15-18%. Further increasing the f to 20% and above, polycrystalline U3O8 thin films with a (0 0 1) preferential orientation were formed. The hardness and Young's modulus of the uranium oxide films were evaluated using nanoindentation. The film containing a single UO2 phase exhibited the maximum hardness of 14.3 GPa and a Young's modulus of 195 GPa. The UO2 thin film also exhibited good thermal stability in that no phase change was observed after annealing at 600 °C in vacuum for 104 h.

  19. Structure and optical properties of TiO2 thin films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Białous, Anna; Gazda, Maria; Śliwiński, Gerard

    2013-03-01

    Thin TiO2 films prepared by pulsed laser deposition (PLD) in the O2 gas ambient using the bulk metal Ti or pressed TiO2 powder targets were characterized using spectroscopic methods. Films were deposited on SiO2 (001) and SiO2 glass substrates heated up to 300 °C. The deposition process was investigated at laser fluencies from the range of 1 - 3 J/cm2 and at oxygen pressure of 0.1 - 3.2 Pa. The μ-Raman and X-ray diffraction (XRD) spectra of the TiO2 films revealed consistently both the anatase and rutile crystalline phases and a strong dependence of the phase content ratio on target material and deposition conditions. The range of crystallite size determined from XRD bandwidths was between (2-30) nm and (6-14) nm for anatase and rutile, respectively. The film thickness values between 0.74 and 1.65 μm depending on the deposition time were obtained from the transmittance and ellipsometric measurements. Values of the band gap of 3.5-4.1 eV derived from absorption spectra were higher than that of 3.2 eV corresponding to anatase and this difference was ascribed to the relatively small size of the anatase crystallites and presence of rutile, too. The SEM images of films produced under similar conditions from Ti and TiO2 targets revealed porous structures. The highest anatase content was observed for films deposited by ablation of the TiO2 target at moderate laser fluencies below 2 J/cm2 and at oxygen pressure around 1.9 Pa.

  20. Ultra-short-pulsed laser-machined nanogratings of laser-induced periodic surface structures on thin molybdenum layers

    NASA Astrophysics Data System (ADS)

    Scorticati, Davide; Römer, Gert-Willem; de Lange, Dirk Frederik; Huis in't Veld, Bert

    2012-01-01

    Large areas of regular diffraction nanogratings were produced consisting of so-called laser-induced periodic surface structures (LIPSS) on thin molybdenum layers (<400 nm) deposited on a borosilicate glass substrate. The aim was to produce these structures without ablating nor cracking the molybdenum layer. Ultra short laser pulses were applied using a focused Gaussian beam profile. Processing parameters such as laser fluence, pulse overlap, number of overscans, repetition frequency, wavelength and polarization were varied to study the effect on periodicity, height, and especially regularity of the obtained LIPSS. It was found that a careful choice of the correct laser parameters is required to avoid detrimental mechanical stresses, cracking, and delamination during the laser processing of the layer in order to remain in its correct range of ductility as well as to ensure regular LIPSS. A possible photovoltaic application of these nanogratings could be found in texturing of thin film cells to enhance light trapping mechanisms.

  1. Structural design considerations for stretched-membrane heliostat reflector modules with stability and initial imperfection considerations

    SciTech Connect

    Murphy, L.M.; Simms, D.; Sallis, D.V.

    1986-10-01

    This report extends the work of several previous reports that present the background leading to the development of stretched-membrane modules and analysis methods to study the structural response of the stretched-membrane module. Specifically, this report presents and discusses the design implications based on our analysis of single- or double-membrane concepts, and the amplification of initial imperfections and deflections caused by loading, which results from stability considerations. In this document, we present analysis results for both single- and double-membrane concepts corresponding to a range of design and loading conditions. Further, we show that stretched-membrane/frame combinations respond quite differently to external loads than can be inferred by studying the decoupled frame and membrane independently. Thus the coupled membrane/frame problem should be considered to assure an accurate description of its response. For idealized configurations and loadings, we discuss the relative merits of various design features for both of these designs. In addition, we studied the structural stability (i.e., the tendency of structural deformation to grow with little increase in applied load) of the tensioned-membrane, compressed-frame combination. Moreover, we demonstrate how stability considerations are important in determining the amplification of both initial displacement imperfection and the deformations caused by wind and weight loading on the structure.

  2. DOE EPSCoR Initiative in Structural and computational Biology/Bioinformatics

    SciTech Connect

    Wallace, Susan S.

    2008-02-21

    The overall goal of the DOE EPSCoR Initiative in Structural and Computational Biology was to enhance the competiveness of Vermont research in these scientific areas. To develop self-sustaining infrastructure, we increased the critical mass of faculty, developed shared resources that made junior researchers more competitive for federal research grants, implemented programs to train graduate and undergraduate students who participated in these research areas and provided seed money for research projects. During the time period funded by this DOE initiative: (1) four new faculty were recruited to the University of Vermont using DOE resources, three in Computational Biology and one in Structural Biology; (2) technical support was provided for the Computational and Structural Biology facilities; (3) twenty-two graduate students were directly funded by fellowships; (4) fifteen undergraduate students were supported during the summer; and (5) twenty-eight pilot projects were supported. Taken together these dollars resulted in a plethora of published papers, many in high profile journals in the fields and directly impacted competitive extramural funding based on structural or computational biology resulting in 49 million dollars awarded in grants (Appendix I), a 600% return on investment by DOE, the State and University.

  3. Effect of structural defects on corrosion initiation of TiN nanocrystalline films

    NASA Astrophysics Data System (ADS)

    He, Chunlin; Zhang, Jinlin; Wang, Jianming; Ma, Guofeng; Zhao, Dongliang; Cai, Qingkui

    2013-07-01

    TiN thin films were deposited on AISI304 stainless steel using a DC reactive magnetron sputtering process. An in situ observation is carried out in order to investigate the relationship between the corrosion initiation and the structural defects such as pores and pinholes by using atomic force microscopy (AFM). It is found that the corrosion initiates at some larger structural pores in the form of the detachment of the particles which will plug the transport path for the corrosion products, whereas the small enough pinholes are easily filled in by corrosion products at the beginning of corrosion. Also, the surface roughness of the corroded film is improved with increasing the corrosion time. The corrosion morphology after polarization test shows that fewer and large pits appear on the TiN-coated substrates probably associated with large structural defects such as high density area of through film pores or pinholes present in the films, which is in accord with those results obtained by in situ AFM observation. Additionally, the effect of bias voltages on corrosion resistance of the films is also involved because the structural defects are strongly associated with the bias voltages.

  4. A structure-based approach for targeting the HIV-1 genomic RNA dimerization initiation site.

    PubMed

    Ennifar, Eric; Paillart, Jean-Christophe; Bernacchi, Serena; Walter, Philippe; Pale, Patrick; Decout, Jean-Luc; Marquet, Roland; Dumas, Philippe

    2007-10-01

    Dimerization of the genomic RNA is an important step of the HIV-1 replication cycle. The Dimerization Initiation Site (DIS) promotes dimerization of the viral genome by forming a loop-loop complex between two DIS hairpins. Crystal structures of the DIS loop-loop complex revealed an unexpected and strong similitude with the bacterial 16S ribosomal aminoacyl-tRNA site (A site), which is the target of aminoglycoside antibiotics. As a consequence of these structural and sequence similarities, the HIV-1 DIS also binds some aminoglycosides, not only in vitro, but also ex vivo, in lymphoid cells and in viral particles. Crystal structures of the DIS loop-loop in complex with several aminoglycoside antibiotics provide a detailed-view of the DIS/drug interaction and reveal some hints about possible modifications to increase the drug affinity and/or specificity. PMID:17434658

  5. Initial Droplet Size Impacts pH-Induced Structural Changes in Phase-Separated Polymer Dispersions.

    PubMed

    Thongkaew, Chutima; Zeeb, Benjamin; Gibis, Monika; Hinrichs, Jörg; Weiss, Jochen

    2016-05-01

    The effect of pH change on the morphology of whey protein isolate (WPI)-pectin dispersions obtained from phase-separated systems after mild shear was studied. The purpose of this study was to examine the impact of mixing speed on the initial particle size of biopolymer complexes and their structure morphology after sequentially changing the pH. Therefore, solutions of WPI and pectin were combined at pH 6.1, allowed to phase separate and were then mildly homogenized at 50, 100, and 150 rpm, respectively, to form a dispersion containing differently sized WPI droplets in a surrounding pectin-rich phase. Each dispersion was then subjected to a pH change, such as 6.1 to 5.2 and 3.2, by slowly adding hydrochloric acid. The systems morphology, size, appearance, rheology, and storage stability was then characterized by optical microscopy, static light scattering, visual inspections, and steady shear rheometry to gain insights into the structural rearrangements. Results indicated substantial changes in the structure of the dispersion when the pH was changed. Formation of core-shell structures from the WPI droplets was observed at an intermediate pH. There, initial droplet size was found to affect structures formed, that is, core-shell type particles would only form if droplets were large (>1.5 μm) prior to pH change. Insights gained may be of importance to food manufacturers intending to create new structures from mixtures of proteins and carbohydrates. PMID:27061600

  6. Structure of promoter-bound TFIID and model of human pre-initiation complex assembly.

    PubMed

    Louder, Robert K; He, Yuan; López-Blanco, José Ramón; Fang, Jie; Chacón, Pablo; Nogales, Eva

    2016-03-31

    The general transcription factor IID (TFIID) plays a central role in the initiation of RNA polymerase II (Pol II)-dependent transcription by nucleating pre-initiation complex (PIC) assembly at the core promoter. TFIID comprises the TATA-binding protein (TBP) and 13 TBP-associated factors (TAF1-13), which specifically interact with a variety of core promoter DNA sequences. Here we present the structure of human TFIID in complex with TFIIA and core promoter DNA, determined by single-particle cryo-electron microscopy at sub-nanometre resolution. All core promoter elements are contacted by subunits of TFIID, with TAF1 and TAF2 mediating major interactions with the downstream promoter. TFIIA bridges the TBP-TATA complex with lobe B of TFIID. We also present the cryo-electron microscopy reconstruction of a fully assembled human TAF-less PIC. Superposition of common elements between the two structures provides novel insights into the general role of TFIID in promoter recognition, PIC assembly, and transcription initiation. PMID:27007846

  7. Structural Changes Enable Start Codon Recognition by the Eukaryotic Translation Initiation Complex

    PubMed Central

    Hussain, Tanweer; Llácer, Jose L.; Fernández, Israel S.; Munoz, Antonio; Martin-Marcos, Pilar; Savva, Christos G.; Lorsch, Jon R.; Hinnebusch, Alan G.; Ramakrishnan, V.

    2014-01-01

    Summary During eukaryotic translation initiation, initiator tRNA does not insert fully into the P decoding site on the 40S ribosomal subunit. This conformation (POUT) is compatible with scanning mRNA for the AUG start codon. Base pairing with AUG is thought to promote isomerization to a more stable conformation (PIN) that arrests scanning and promotes dissociation of eIF1 from the 40S subunit. Here, we present a cryoEM reconstruction of a yeast preinitiation complex at 4.0 Å resolution with initiator tRNA in the PIN state, prior to eIF1 release. The structure reveals stabilization of the codon-anticodon duplex by the N-terminal tail of eIF1A, changes in the structure of eIF1 likely instrumental in its subsequent release, and changes in the conformation of eIF2. The mRNA traverses the entire mRNA cleft and makes connections to the regulatory domain of eIF2α, eIF1A, and ribosomal elements that allow recognition of context nucleotides surrounding the AUG codon. PMID:25417110

  8. Crystal structures of two intermediates in the assembly of the papillomavirus replication initiation complex.

    PubMed

    Enemark, Eric J; Stenlund, Arne; Joshua-Tor, Leemor

    2002-03-15

    Initiation of DNA replication of the papillomavirus genome is a multi-step process involving the sequential loading of viral E1 protein subunits onto the origin of replication. Here we have captured structural snapshots of two sequential steps in the assembly process. Initially, an E1 dimer binds to adjacent major grooves on one face of the double helix; a second dimer then binds to another face of the helix. Each E1 monomer has two DNA-binding modules: a DNA-binding loop, which binds to one DNA strand and a DNA-binding helix, which binds to the opposite strand. The nature of DNA binding suggests a mechanism for the transition between double- and single-stranded DNA binding that is implicit in the progression to a functional helicase. PMID:11889054

  9. Noncrystalline structure of Ni-P nanoparticles prepared by liquid pulse discharge.

    PubMed

    Tan, Yuanyuan; Yu, Hongying; Wu, Zhonghua; Yang, Bin; Gong, Yu; Yan, Shi; Du, Rong; Chen, Zhongjun; Sun, Dongbai

    2015-03-01

    Noncrystalline nickel phosphide (Ni-P) nanoparticles have drawn great attention due to their high potential as catalysts. However, the structure of noncrystalline Ni-P nanoparticles is still unknown, which may shed light on explaining the catalysis mechanism of the Ni-P nanoparticles. In this paper, noncrystalline Ni-P nanoparticles were synthesized. Their morphology, particle size, element contents, local atomic structures, as well as the catalysis in the thermal decomposition of ammonium perchlorate were studied. The results demonstrate that the as-prepared Ni-P nanoparticles are spherical with an average diameter of about 13.5 nm. The Ni and P contents are, respectively, 78.15% and 21.85%. The noncrystalline nature of the as-prepared Ni-P nanoparticles can be attributed to cross-linkage between P-doping f.c.c.-like Ni centers and Ni3P-like P centers. The locally ordered Ni centers and P centers are the nuclei sites, which can explain well the origin of initial nuclei to form the crystalline phases after high-temperature annealing. The starting temperature of high-temperature decomposition of ammonium perchlorate was found having a significant decrease in the presence of the noncrystalline Ni-P nanoparticles. Therefore, the as-prepared noncrystalline Ni-P nanoparticles can be used as a potential catalyst in the thermal decomposition of ammonium perchlorate. PMID:25723939

  10. Difference-frequency generation in the field of a few-cycle laser pulse propagating in a GaAs crystal with a domain structure

    SciTech Connect

    Oganesyan, David L; Vardanyan, Aleksandr O; Oganesyan, G D

    2013-06-30

    Difference-frequency generation in a GaAs crystal with a periodic domain structure in the field of a few-cycle laser pulse is considered for the case of weakly pronounced material dispersion. The straight-line method is used to solve numerically the system of coupled nonlinear partial differential equations describing the evolution of the electric field of this laser pulse in GaAs crystals with periodic and chirped domain structures. It is shown that application of a GaAs crystal with a chirped domain structure makes it possible to control the frequency-modulation law for a broadband differencefrequency pulse. (nonlinear optical phenomena)

  11. The Structure of a Transcribing T7 RNA Polymerase in Transition from Initiation to Elongation

    SciTech Connect

    Durniak, K.; Bailey, S; Steitz, T

    2008-01-01

    Structural studies of the T7 bacteriophage DNA-dependent RNA polymerase (T7 RNAP) have shown that the conformation of the amino-terminal domain changes substantially between the initiation and elongation phases of transcription, but how this transition is achieved remains unclear. We report crystal structures of T7 RNAP bound to promoter DNA containing either a 7- or an 8-nucleotide (nt) RNA transcript that illuminate intermediate states along the transition pathway. The amino-terminal domain comprises the C-helix subdomain and the promoter binding domain (PBD), which consists of two segments separated by subdomain H. The structures of the intermediate complex reveal that the PBD and the bound promoter rotate by 45 degrees upon synthesis of an 8-nt RNA transcript. This allows the promoter contacts to be maintained while the active site is expanded to accommodate a growing heteroduplex. The C-helix subdomain moves modestly toward its elongation conformation, whereas subdomain H remains in its initiation- rather than its elongation-phase location, more than 70 angstroms away.

  12. Brain Genomics Superstruct Project initial data release with structural, functional, and behavioral measures

    PubMed Central

    Holmes, Avram J.; Hollinshead, Marisa O.; O’Keefe, Timothy M.; Petrov, Victor I.; Fariello, Gabriele R.; Wald, Lawrence L.; Fischl, Bruce; Rosen, Bruce R.; Mair, Ross W.; Roffman, Joshua L.; Smoller, Jordan W.; Buckner, Randy L.

    2015-01-01

    The goal of the Brain Genomics Superstruct Project (GSP) is to enable large-scale exploration of the links between brain function, behavior, and ultimately genetic variation. To provide the broader scientific community data to probe these associations, a repository of structural and functional magnetic resonance imaging (MRI) scans linked to genetic information was constructed from a sample of healthy individuals. The initial release, detailed in the present manuscript, encompasses quality screened cross-sectional data from 1,570 participants ages 18 to 35 years who were scanned with MRI and completed demographic and health questionnaires. Personality and cognitive measures were obtained on a subset of participants. Each dataset contains a T1-weighted structural MRI scan and either one (n=1,570) or two (n=1,139) resting state functional MRI scans. Test-retest reliability datasets are included from 69 participants scanned within six months of their initial visit. For the majority of participants self-report behavioral and cognitive measures are included (n=926 and n=892 respectively). Analyses of data quality, structure, function, personality, and cognition are presented to demonstrate the dataset’s utility. PMID:26175908

  13. Effect of Initial Microstructure on Impact Toughness of 1200 MPa-Class High Strength Steel with Ultrafine Elongated Grain Structure

    NASA Astrophysics Data System (ADS)

    Jafari, Meysam; Garrison, Warren M.; Tsuzaki, Kaneaki

    2014-02-01

    A medium-carbon low-alloy steel was prepared with initial structures of either martensite or bainite. For both initial structures, warm caliber-rolling was conducted at 773 K (500 °C) to obtain ultrafine elongated grain (UFEG) structures with strong <110>//rolling direction (RD) fiber deformation textures. The UFEG structures consisted of spheroidal cementite particles distributed uniformly in a ferrite matrix of a transverse grain size of about 331 and 311 nm in samples with initial martensite and bainite structures, respectively. For both initial structures, the UFEG materials had similar tensile properties, upper shelf energy (145 J), and ductile-to-brittle transition temperatures 98 K (500 °C). Obtaining the martensitic structure requires more rapid cooling than is needed to obtain the bainitic structure and this more rapid cooling promote cracking. As the UFEG structures obtained from initial martensitic and bainitic structures have almost identical properties, but obtaining the bainitic structure does not require a rapid cooling which promotes cracking suggests the use of a bainitic structure in obtaining UFEG structures should be examined further.

  14. Field-Programmable Gate Array Computer in Structural Analysis: An Initial Exploration

    NASA Technical Reports Server (NTRS)

    Singleterry, Robert C., Jr.; Sobieszczanski-Sobieski, Jaroslaw; Brown, Samuel

    2002-01-01

    This paper reports on an initial assessment of using a Field-Programmable Gate Array (FPGA) computational device as a new tool for solving structural mechanics problems. A FPGA is an assemblage of binary gates arranged in logical blocks that are interconnected via software in a manner dependent on the algorithm being implemented and can be reprogrammed thousands of times per second. In effect, this creates a computer specialized for the problem that automatically exploits all the potential for parallel computing intrinsic in an algorithm. This inherent parallelism is the most important feature of the FPGA computational environment. It is therefore important that if a problem offers a choice of different solution algorithms, an algorithm of a higher degree of inherent parallelism should be selected. It is found that in structural analysis, an 'analog computer' style of programming, which solves problems by direct simulation of the terms in the governing differential equations, yields a more favorable solution algorithm than current solution methods. This style of programming is facilitated by a 'drag-and-drop' graphic programming language that is supplied with the particular type of FPGA computer reported in this paper. Simple examples in structural dynamics and statics illustrate the solution approach used. The FPGA system also allows linear scalability in computing capability. As the problem grows, the number of FPGA chips can be increased with no loss of computing efficiency due to data flow or algorithmic latency that occurs when a single problem is distributed among many conventional processors that operate in parallel. This initial assessment finds the FPGA hardware and software to be in their infancy in regard to the user conveniences; however, they have enormous potential for shrinking the elapsed time of structural analysis solutions if programmed with algorithms that exhibit inherent parallelism and linear scalability. This potential warrants further

  15. Crystal Structure of pi Initiator Protein-iteron Complex of Plasmid R6K: Implications for Initiation of Plasmid DNA Replication

    SciTech Connect

    Swan,M.; Bastia, D.; Davies, C.

    2006-01-01

    We have determined the crystal structure of a monomeric biologically active form of the {pi} initiator protein of plasmid R6K as a complex with a single copy of its cognate DNA-binding site (iteron) at 3.1-{angstrom} resolution. The initiator belongs to the family of winged helix type of proteins. The structure reveals that the protein contacts the iteron DNA at two primary recognition helices, namely the C-terminal {alpha}4' and the N-terminal {alpha}4 helices, that recognize the 5' half and the 3' half of the 22-bp iteron, respectively. The base-amino acid contacts are all located in {alpha}4', whereas the {alpha}4 helix and its vicinity mainly contact the phosphate groups of the iteron. Mutational analyses show that the contacts of both recognition helices with DNA are necessary for iteron binding and replication initiation. Considerations of a large number of site-directed mutations reveal that two distinct regions, namely {alpha}2 and {alpha}5 and its vicinity, are required for DNA looping and initiator dimerization, respectively. Further analysis of mutant forms of {pi} revealed the possible domain that interacts with the DnaB helicase. Thus, the structure-function analysis presented illuminates aspects of initiation mechanism of R6K and its control.

  16. Initiation factor 2 crystal structure reveals a different domain organization from eukaryotic initiation factor 5B and mechanism among translational GTPases.

    PubMed

    Eiler, Daniel; Lin, Jinzhong; Simonetti, Angelita; Klaholz, Bruno P; Steitz, Thomas A

    2013-09-24

    The initiation of protein synthesis uses initiation factor 2 (IF2) in prokaryotes and a related protein named eukaryotic initiation factor 5B (eIF5B) in eukaryotes. IF2 is a GTPase that positions the initiator tRNA on the 30S ribosomal initiation complex and stimulates its assembly to the 50S ribosomal subunit to make the 70S ribosome. The 3.1-Å resolution X-ray crystal structures of the full-length Thermus thermophilus apo IF2 and its complex with GDP presented here exhibit two different conformations (all of its domains except C2 domain are visible). Unlike all other translational GTPases, IF2 does not have an effecter domain that stably contacts the switch II region of the GTPase domain. The domain organization of IF2 is inconsistent with the "articulated lever" mechanism of communication between the GTPase and initiator tRNA binding domains that has been proposed for eIF5B. Previous cryo-electron microscopy reconstructions, NMR experiments, and this structure show that IF2 transitions from being flexible in solution to an extended conformation when interacting with ribosomal complexes. PMID:24029018

  17. Simulations of terahertz pulse emission from thin-film semiconductor structures

    NASA Astrophysics Data System (ADS)

    Semichaevsky, Andrey

    The photo-Dember effect is the formation of transient electric dipoles due to the interaction of semiconductors with ultrashort optical pulses. Typically the optically-induced dipole moments vary on the ns- or ps- scales, leading to the emission of electromagnetic pulses with terahertz (THz) bandwidths. One of the applications of the photo-Dember effect is a photoconductive dipole antenna (PDA). This work presents a computational model of a PDA based on Maxwell's equations coupled to the Boltzmann transport equation. The latter is solved semiclassically for the doped GaAs using a continuum approach. The emphasis is on the accurate prediction of the emitted THz pulse shape and bandwidth, particularly when materials are doped with a rare-earth metal such as erbium or terbium that serve as carrier recombination centers. Field-dependent carrier mobility is determined from particle-based simulations. Some of the previous experimental results are used as a basis for comparison with our model.

  18. CdTe-Cd1 - xMnxTe multiple quantum well structures grown by pulsed laser evaporation and epitaxy

    NASA Astrophysics Data System (ADS)

    Dubowski, J. J.; Roth, A. P.; Wasilewski, Z. R.; Rolfe, S. J.

    1991-09-01

    Structural and optical properties of (001) CdTe-Cd1-xMnxTe (x=0.10) multiple quantum well structures grown by pulsed laser evaporation and epitaxy (PLEE) are investigated. The layers are grown on (001) CdZnTe wafers held at a temperature in the range of 210-230 °C. Secondary-ion mass spectroscopy in-depth profiles reveal that highly uniform structures are grown. Numerical analysis of double crystal x-ray diffraction results demonstrates high structural quality of the layers and indicates partial relaxation of the strain in these structures. Low-temperature photoluminescence exhibits excitonic recombinations in the CdTe wells whereas photoluminescence from the Cd1-xMnxTe barriers is not observed. The chemical composition of the barriers deduced from photoluminescence is in excellent agreement with the intended chemical composition set during growth.

  19. Structure of the Sevoflurane-Benzene Complex as Determined by Chirped-Pulse Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Seifert, Nathan A.; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Lesarri, Alberto; Vallejo, Montserrat; Cocinero, Emilio J.; Castano, Fernando

    2012-06-01

    Following previous microwave studies on sevoflurane monomer by Suenram {et al.} and Vega-Toribio et al. we report the broadband rotational spectrum of sevoflurane clustered with benzene. The structure assigned is consistent with a C-H...π interaction between the benzene ring and the (CF_3)_2C-H hydrogen on sevoflurane. The spectrum of this species is complicated by the six-fold internal rotation of the benzene ring over the C_1 framework of sevoflurane. The six-fold tunneling falls into a high effective barrier case where there are several bound torsional levels. The tunneling spectrum has been successfully analyzed using the BELGI internal rotation program and a barrier to internal rotation of the benzene against sevoflurane of 32.5 cm-1 has been determined. Structural information about the complex has been obtained by studying the complex of sevoflurane with benzene-{d_1}. For this complex, six unique isomers are observed making it possible to determine the positions of the benzene H-atoms in the complex. Combination of these hydrogen r_s positions with the sevoflurane monomer r_s coordinates reported by Lesarri {et al.} results in a substitution structure in excellent agreement with the ab initio results. Finally, initial microwave results on two sevoflurane dimer species will also be presented. R. D. Suenram, D. J. Brugh, F. J. Lovas and C. Chu, 51st OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 1999, RB07. A. Vega-Toribio, A. Lesarri, R.D. Suenram, J. Grabow, 64th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2009, MH07. A. Lesarri, A. Vega-Toribio, R. D. Suenram, D. J. Brugh, J.-U. Grabow, Phys. Chem. Chem. Phys., 12, 9624-9631 (2010).

  20. Structures of E. coli σS-transcription initiation complexes provide new insights into polymerase mechanism.

    PubMed

    Liu, Bin; Zuo, Yuhong; Steitz, Thomas A

    2016-04-12

    In bacteria, multiple σ factors compete to associate with the RNA polymerase (RNAP) core enzyme to form a holoenzyme that is required for promoter recognition. During transcription initiation RNAP remains associated with the upstream promoter DNA via sequence-specific interactions between the σ factor and the promoter DNA while moving downstream for RNA synthesis. As RNA polymerase repetitively adds nucleotides to the 3'-end of the RNA, a pyrophosphate ion is generated after each nucleotide incorporation. It is currently unknown how the release of pyrophosphate affects transcription. Here we report the crystal structures of E coli transcription initiation complexes (TICs) containing the stress-responsive σ(S) factor, a de novo synthesized RNA oligonucleotide, and a complete transcription bubble (σ(S)-TIC) at about 3.9-Å resolution. The structures show the 3D topology of the σ(S) factor and how it recognizes the promoter DNA, including likely specific interactions with the template-strand residues of the -10 element. In addition, σ(S)-TIC structures display a highly stressed pretranslocated initiation complex that traps a pyrophosphate at the active site that remains closed. The position of the pyrophosphate and the unusual phosphodiester linkage between the two terminal RNA residues suggest an unfinished nucleotide-addition reaction that is likely at equilibrium between nucleotide addition and pyrophosphorolysis. Although these σ(S)-TIC crystals are enzymatically active, they are slow in nucleotide addition, as suggested by an NTP soaking experiment. Pyrophosphate release completes the nucleotide addition reaction and is associated with extensive conformational changes around the secondary channel but causes neither active site opening nor transcript translocation. PMID:27035955

  1. Structures of E. coli σS-transcription initiation complexes provide new insights into polymerase mechanism

    PubMed Central

    Liu, Bin; Zuo, Yuhong; Steitz, Thomas A.

    2016-01-01

    In bacteria, multiple σ factors compete to associate with the RNA polymerase (RNAP) core enzyme to form a holoenzyme that is required for promoter recognition. During transcription initiation RNAP remains associated with the upstream promoter DNA via sequence-specific interactions between the σ factor and the promoter DNA while moving downstream for RNA synthesis. As RNA polymerase repetitively adds nucleotides to the 3′-end of the RNA, a pyrophosphate ion is generated after each nucleotide incorporation. It is currently unknown how the release of pyrophosphate affects transcription. Here we report the crystal structures of E. coli transcription initiation complexes (TICs) containing the stress-responsive σS factor, a de novo synthesized RNA oligonucleotide, and a complete transcription bubble (σS-TIC) at about 3.9-Å resolution. The structures show the 3D topology of the σS factor and how it recognizes the promoter DNA, including likely specific interactions with the template-strand residues of the −10 element. In addition, σS-TIC structures display a highly stressed pretranslocated initiation complex that traps a pyrophosphate at the active site that remains closed. The position of the pyrophosphate and the unusual phosphodiester linkage between the two terminal RNA residues suggest an unfinished nucleotide-addition reaction that is likely at equilibrium between nucleotide addition and pyrophosphorolysis. Although these σS-TIC crystals are enzymatically active, they are slow in nucleotide addition, as suggested by an NTP soaking experiment. Pyrophosphate release completes the nucleotide addition reaction and is associated with extensive conformational changes around the secondary channel but causes neither active site opening nor transcript translocation. PMID:27035955

  2. Evolution of morphology and structure of Pb thin films grown by pulsed laser deposition at different substrate temperatures

    SciTech Connect

    Lorusso, Antonella Maiolo, Berlinda; Perrone, Alessio; Gontad, Francisco; Maruccio, Giuseppe; Tasco, Vittorianna

    2014-03-15

    Pb thin films were prepared by pulsed laser deposition on a Si (100) substrate at different growth temperatures to investigate their morphology and structure. The morphological analysis of the thin metal films showed the formation of spherical submicrometer grains whose average size decreased with temperature. X-ray diffraction measurements confirmed that growth temperature influences the Pb polycrystalline film structure. A preferred orientation of Pb (111) normal to the substrate was achieved at 30 °C and became increasingly pronounced along the Pb (200) plane as the substrate temperature increased. These thin films could be used to synthesize innovative materials, such as metallic photocathodes, with improved photoemission performances.

  3. Modification of film structure by plasma potential control using triode high power pulsed magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Nakano, Takeo; Umahashi, Takuya; Baba, Shigeru

    2014-02-01

    We have designed a new triode configuration in a magnetron sputtering apparatus to control the plasma potential of the discharge. An additional chimney electrode was introduced above the conventional sputter gun to apply a positive voltage. The discharge power was provided by a pulse power source to achieve high power pulsed magnetron sputtering operation. We confirmed that the plasma potential increased with increasing positive electrode voltage. Copper films with substantially flatter surfaces could be obtained on a water-cooled and electrically grounded substrate at an Ar gas pressure of 5 Pa.

  4. Temporal Structure of Attosecond Pulses from Laser-Driven Coherent Synchrotron Emission

    NASA Astrophysics Data System (ADS)

    Cousens, S.; Reville, B.; Dromey, B.; Zepf, M.

    2016-02-01

    The microscopic dynamics of laser-driven coherent synchrotron emission transmitted through thin foils are investigated using particle-in-cell simulations. For normal incidence interactions, we identify the formation of two distinct electron nanobunches from which emission takes place each half-cycle of the driving laser pulse. These emissions are separated temporally by 130 as and are dominant in different frequency ranges, which is a direct consequence of the distinct characteristics of each electron nanobunch. This may be exploited through spectral filtering to isolate these emissions, generating electromagnetic pulses of duration ˜70 as .

  5. Temporal Structure of Attosecond Pulses from Laser-Driven Coherent Synchrotron Emission.

    PubMed

    Cousens, S; Reville, B; Dromey, B; Zepf, M

    2016-02-26

    The microscopic dynamics of laser-driven coherent synchrotron emission transmitted through thin foils are investigated using particle-in-cell simulations. For normal incidence interactions, we identify the formation of two distinct electron nanobunches from which emission takes place each half-cycle of the driving laser pulse. These emissions are separated temporally by 130 as and are dominant in different frequency ranges, which is a direct consequence of the distinct characteristics of each electron nanobunch. This may be exploited through spectral filtering to isolate these emissions, generating electromagnetic pulses of duration ∼70  as. PMID:26967416

  6. Influence of an optical pulsed discharge on the structure of a supersonic air flow

    SciTech Connect

    Malov, A N; Orishich, A M

    2014-01-31

    We present the results of investigation of the parameters of an optical pulsed discharge (OPD) and their relation with gasdynamic parameters of a supersonic flow and with characteristics of laser radiation. For the first time the discrete objects are detected in the OPD by an optical method, namely, low-density caverns moving along with the flow. The propagation velocity of the thermal track arising in a supersonic flow under the action of the OPD is measured. It is found that at a pulse repetition rate of 90 – 120 kHz the caverns unite into a single plasma jet. (laser applications and other topics in quantum electronics)

  7. Structural Plasticity within the Barrel Cortex during Initial Phases of Whisker-Dependent Learning

    PubMed Central

    O'Connor, Daniel H.; Fox, Kevin; Svoboda, Karel

    2014-01-01

    We report learning-related structural plasticity in layer 1 branches of pyramidal neurons in the barrel cortex, a known site of sensorimotor integration. In mice learning an active, whisker-dependent object localization task, layer 2/3 neurons showed enhanced spine growth during initial skill acquisition that both preceded and predicted expert performance. Preexisting spines were stabilized and new persistent spines were formed. These findings suggest rapid changes in connectivity between motor centers and sensory cortex guide subsequent sensorimotor learning. PMID:24760867

  8. Study of deep level characteristics in the neutrons irradiated Si structures by combining pulsed and steady-state spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Kalendra, V.; Ceponis, T.; Uleckas, A.; Tekorius, A.; Vaitkus, J.; Velicka, A.

    2012-11-01

    The standard methods, such as capacitance deep level transient spectroscopy (C-DLTS) and thermally stimulated current (TSC) techniques are unsuitable for the analysis of heavily irradiated devices. In this work, therefore, several steady-state and pulsed techniques have been combined to comprehensively evaluate parameters of radiation defects and functional characteristics of the irradiated Si pin detectors. In order to understand defects created by radiation and evaluate their evolution with fluence, C-DLTS and TSC techniques have been employed to make a baseline identification of the radiation induced traps after irradiation with a rather small neutron fluence of 1012 cm-2. The steady-state photo-ionization spectroscopy (PIS) technique has been involved to correlate thermal- and photo- activation energies for definite radiation defects. A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels based on microwave probed pulsed photo-conductivity (MW-PC) spectroscopy has been applied to correlate carrier capture cross-sections and densities of the identified different radiation defects. A technique for spectroscopy of deep levels in junction structures (BELIV) based on measurements of barrier capacitance charging current transient changes due to additional spectrally resolved pulsed illumination has been applied to evaluate the functional characteristics of the irradiated diodes. Pulsed spectroscopic measurements were implemented by combining the analysis of generation current and of barrier capacitance charging transients modified by a single fs pulse of illumination generated by an optical parametric oscillator of varied wavelength in the range from 0.5 to 10 μm. Several deep levels with activation energy in the range of 0.18-0.8 eV have been resolved from spectral analysis in the samples of Si grown by magnetic field applied Czochralski (MCz) technology.

  9. Single-shot three-dimensional structure determination of nanocrystals with femtosecond X-ray free-electron laser pulses

    NASA Astrophysics Data System (ADS)

    Xu, Rui; Jiang, Huaidong; Song, Changyong; Rodriguez, Jose A.; Huang, Zhifeng; Chen, Chien-Chun; Nam, Daewoong; Park, Jaehyun; Gallagher-Jones, Marcus; Kim, Sangsoo; Kim, Sunam; Suzuki, Akihiro; Takayama, Yuki; Oroguchi, Tomotaka; Takahashi, Yukio; Fan, Jiadong; Zou, Yunfei; Hatsui, Takaki; Inubushi, Yuichi; Kameshima, Takashi; Yonekura, Koji; Tono, Kensuke; Togashi, Tadashi; Sato, Takahiro; Yamamoto, Masaki; Nakasako, Masayoshi; Yabashi, Makina; Ishikawa, Tetsuya; Miao, Jianwei

    2014-06-01

    Conventional three-dimensional (3D) structure determination methods require either multiple measurements at different sample orientations or a collection of serial sections through a sample. Here we report the experimental demonstration of single-shot 3D structure determination of an object; in this case, individual gold nanocrystals at ~5.5 nm resolution using ~10 fs X-ray free-electron laser pulses. Coherent diffraction patterns are collected from high-index-faceted nanocrystals, each struck by an X-ray free-electron laser pulse. Taking advantage of the symmetry of the nanocrystal and the curvature of the Ewald sphere, we reconstruct the 3D structure of each nanocrystal from a single-shot diffraction pattern. By averaging a sufficient number of identical nanocrystals, this method may be used to determine the 3D structure of nanocrystals at atomic resolution. As symmetry exists in many virus particles, this method may also be applied to 3D structure studies of such particles at nanometer resolution on femtosecond time scales.

  10. The formation of nanodimensional structures on the surface of Tin exposed to femtosecond laser pulses in the ambient environment of ethanol

    NASA Astrophysics Data System (ADS)

    Bashir, Shazia; Rafique, M. Shahid; Nathala, Chandra S.; Husinsky, Wolfgang

    2014-01-01

    The formation of nanodimensional structures on the surface of Tin (Sn) has been explored as a function of the laser fluence and pulse duration. The targets were exposed by employing femtosecond pulses of a Ti: Sapphire laser (wavelength of 800 nm, pulse length of 25 fs and pulse repetition rate of 1 kHz) in ethanol. In order to investigate the effect of fluence, the targets were exposed to 1000 succeeding pulses for four various fluences ranging from 4.7 to 11.8 J cm-2 with the pulse duration of 25 fs. To probe the effect of pulse duration, targets were exposed for various pulse durations ranging from 25 fs to 100 fs at a constant fluence of 11.8 J cm-2 (i.e. maximum). Nano sized structures including globules, droplets, craters and grooves were observed by SEM analysis. The dependence of structure formation on the laser fluence and pulse duration has been explored both for central as well as peripheral ablated areas. For increasing fluences, the more energy deposition is responsible for the growth of distinct features. For increasing fluence, the size distribution of nanostructures reduces and their number density increases after fragmentation. As the pulse width increases, the size distribution of structures increases significantly due to enhanced thermal effects. The development of nanostructures has been correlated with structural analysis carried out by micro-Raman spectroscopy. The formation of various bands e.g. SnO, SnO2, C2H5 Sn, Sn-CO complexes after laser irradiation of Sn in a liquid-confined environment (ethanol) has been observed. For higher fluences more energy deposition takes place which enhances the chemical reactivity and is responsible for an appearance of additional and strong bands. However, with increasing pulse width more thermal effects are responsible for bond breaking and disappearance of those peaks which are identified for the shortest pulse duration. It is found first time that both the pulse duration as well as laser fluence are

  11. Crystal structure of yeast initiation factor 4A, a DEAD-box RNA helicase

    PubMed Central

    Caruthers, Jonathan M.; Johnson, Eric R.; McKay, David B.

    2000-01-01

    The eukaryotic translation initiation factor 4A (eIF4A) is a member of the DEA(D/H)-box RNA helicase family, a diverse group of proteins that couples an ATPase activity to RNA binding and unwinding. Previous work has provided the structure of the amino-terminal, ATP-binding domain of eIF4A. Extending those results, we have solved the structure of the carboxyl-terminal domain of eIF4A with data to 1.75 Å resolution; it has a parallel α-β topology that superimposes, with minor variations, on the structures and conserved motifs of the equivalent domain in other, distantly related helicases. Using data to 2.8 Å resolution and molecular replacement with the refined model of the carboxyl-terminal domain, we have completed the structure of full-length eIF4A; it is a “dumbbell” structure consisting of two compact domains connected by an extended linker. By using the structures of other helicases as a template, compact structures can be modeled for eIF4A that suggest (i) helicase motif IV binds RNA; (ii) Arg-298, which is conserved in the DEA(D/H)-box RNA helicase family but is absent from many other helicases, also binds RNA; and (iii) motifs V and VI “link” the carboxyl-terminal domain to the amino-terminal domain through interactions with ATP and the DEA(D/H) motif, providing a mechanism for coupling ATP binding and hydrolysis with conformational changes that modulate RNA binding. PMID:11087862

  12. Micro pulse laser radar

    NASA Technical Reports Server (NTRS)

    Spinhirne, James D. (Inventor)

    1993-01-01

    An eye safe, compact, solid state lidar for profiling atmospheric cloud and aerosol scattering is disclosed. The transmitter of the micro pulse lidar is a diode pumped micro-J pulse energy, high repetition rate Nd:YLF laser. Eye safety is obtained through beam expansion. The receiver employs a photon counting solid state Geiger mode avalanche photodiode detector. Data acquisition is by a single card multichannel scaler. Daytime background induced quantum noise is controlled by a narrow receiver field-of-view and a narrow bandwidth temperature controlled interference filter. Dynamic range of the signal is limited to optical geometric signal compression. Signal simulations and initial atmospheric measurements indicate that micropulse lider systems are capable of detecting and profiling all significant cloud and aerosol scattering through the troposphere and into the stratosphere. The intended applications are scientific studies and environmental monitoring which require full time, unattended measurements of the cloud and aerosol height structure.

  13. Dynamic analysis of offshore structures with non-zero initial conditions in the frequency domain

    NASA Astrophysics Data System (ADS)

    Liu, Fushun; Lu, Hongchao; Li, Huajun

    2016-03-01

    The state of non-zero conditions is typically treated as fact when considering the dynamic analysis of offshore structures. This article extends a newly proposed method [1] to manage the non-zero initial conditions of offshore structures in the frequency domain, including new studies on original environmental loads reconstruction, response comparisons with the commercial software ANSYS, and a demonstration using an experimental cantilever beam. The original environmental loads, such as waves, currents, and winds, that act on a structure are decomposed into multiple complex exponential components are represented by a series of poles and corresponding residues. Counter to the traditional frequency-domain method, the non-zero initial conditions of offshore structures could be solved in the frequency domain. Compared with reference [1], an improvement reported in this article is that practical issues, including the choice of model order and central-processing-unit (CPU) time consumption, are further studied when applying this new method to offshore structures. To investigate the feasibility of the representation of initial environmental loads by their poles and corresponding residues, a measured random wave force collected from a column experiment at the Lab of Ocean University of China is used, decomposed, reconstructed and then compared with the original wave force; then, a numerical offshore platform is used to study the performance of the proposed method in detail. The numerical results of this study indicate that (1) a short duration of environmental loads are required to obtain their constitutive poles and residues, which implies good computational efficiency; and (2) the proposed method has a similar computational efficiency to traditional methods due to the use of the inverse Fourier transform technique. To better understand the performance, of time consumption and accuracy of the proposed method, the commercial software ANSYS is used to determine responses

  14. Effect of initial vortex core size on the coherent structures in the swirling jet near field

    NASA Astrophysics Data System (ADS)

    Rukes, Lothar; Sieber, Moritz; Paschereit, C. Oliver; Oberleithner, Kilian

    2015-10-01

    This study investigates the sensitivity to initial conditions of swirling jets undergoing vortex breakdown. Emphasis is placed on the recirculation bubble and on the helical coherent structures that evolve in its periphery. It is proposed that the vortex core size of the incoming swirling jet is the critical parameter that determines the dynamics of these coherent structures. This proposition is assessed with Stereo Particle-Image-Velocimetry (PIV) measurements of the breakdown region of two swirling jet configurations with different vortex core sizes at very similar overall swirl intensities. The swirling jets were generated by radial vanes entering a mixing tube, and the vortex core size was adjusted by using different center-body geometries. The time-averaged flow fields in the breakdown region reveal substantial differences in the jet spreading and the size of the recirculation bubble. Proper Ortogonal Decomposition (POD) was applied to the anti-axisymmetric and axisymmetric velocity fluctuations, to reconstruct the dynamics of the helical instability and the breakdown bubble, respectively. We find that the mode shape of the helical instability is not affected by the vortex core size. The frequency is found to coincide with the vortex core rotation rate, which relates inversely to the core size. The shape and dynamics of the non-periodic breakdown bubble are significantly affected by a change in vortex core size. The POD reveals that the energy content of the dominant non-periodic structure is changed markedly with the vortex core size. The bubble dynamics are further investigated by tracking the upstream stagnation point from the PIV snapshots. It is shown that a larger vortex core promotes smooth fluctuations of the recirculation bubble, while a small initial vortex core is linked to bimodal fluctuations of the recirculation bubble. The conclusions drawn from this study are relevant for fundamental swirling jet studies, as well as for the design of swirl

  15. Fast fabrication of super-hydrophobic surfaces on polypropylene by replication of short-pulse laser structured molds

    NASA Astrophysics Data System (ADS)

    Bekesi, J.; Kaakkunen, J. J. J.; Michaeli, W.; Klaiber, F.; Schoengart, M.; Ihlemann, J.; Simon, P.

    2010-06-01

    A new two-step method, facilitating the rapid generation of super-hydrophobic surface structures via parallel laser processing followed by a replica generation by injection molding is reported. A self-made fused silica-based diffractive optical element (DOE) is applied to distribute the laser energy into a 25×25 dot matrix. This DOE is used as a transmission mask for surface ablation of metal molds, applying short-pulse UV laser pulses. In a subsequent process step, replicas of the processed stamp are produced by variothermal injection molding, enabling the mass production of the surface pattern on plastics parts. The resulting topography facilitates a super-hydrophobic behavior of the fabricated components.

  16. Electrical Pulse Modification and Reversal of the Exchange-Bias in Magnetic Tunnel Junction Structures

    NASA Astrophysics Data System (ADS)

    Li, Yun; Tseng, Hsin-Wei; Ralph, Dan; Buhrman, Robert

    2010-03-01

    The use of antiferromagnetic layers to exchange-bias (EB) the reference layer is common in spin-torque (ST) experiments. Previous work has shown that the EB in both MTJs and spin valves can be degraded or reversed by electrical pulses, with the effect being attributed to heating or possibly to ST effects in the spin valve case. We have studied EB modification due to individual electrical pulses in the presence of a small external field (<50Oe) in FeCoB/MgO/FeCoB/IrMn MTJs as a function of MgO thickness. For MgO thickness = 1.7 nm, RA = 5 x 10^3φμm^2, pulses with Jc = 4 x 10^4A/cm^2 and V = 1.8 V, can repeatedly and reliably reverse the EB. For 1.3 nm barriers, RA =150φμm^2, much higher power pulses, Jc = 6 x 10^5A/cm^2 and V = 0.9 V, are required for reversal. Such results indicate that a combination of heating and ST, with the latter possibly involving the field-like spin torque component at high bias, is responsible for EB reversal in our MTJs. We will discuss the details of the EB reversal behavior and report the phase diagram for reversal as function of electrical and field bias.

  17. Comprehensive modeling of structural modification induced by a femtosecond laser pulse inside fused silica glass

    NASA Astrophysics Data System (ADS)

    Najafi, Somayeh; Sadat Arabanian, Atoosa; Massudi, Reza

    2016-06-01

    A comprehensive theoretical model is proposed based on equations describing the nonlinear propagation of an ultrashort pulse inside transparent material, electron density evolution, non-Fourier heat conduction, and thermo-elasto plastic displacement which are respectively solved by various methods. These methods include the split-step finite difference technique and alternating-direction implicit algorithm, fourth-order Range–Kutta algorithm, hybrid finite-element method/finite-difference method, and finite-element method in both space and time to achieve refractive index changes. The whole chain of processes occurring in the interaction of a focused ultrashort laser pulse with fused silica glass in prevalent conditions of micromachining applications is numerically investigated. By optimizing the numerical method and by using an adaptive mesh approach, the execution time of the program is significantly reduced so that the calculations are done at each time step in a fraction of a second. Simulation results show that the energy and duration of the input pulse are very important parameters in induced changes, but the chirp of the input pulse is not an effective parameter. Consequently, by appropriate setting of those parameters one can design a desired refractive index profile.

  18. Internal translation initiation from HIV-1 transcripts is conferred by a common RNA structure

    PubMed Central

    Plank, Terra-Dawn M; Whitehurst, James T; Cencic, Regina; Pelletier, Jerry; Kieft, Jeffrey S

    2014-01-01

    Alternative splicing of the human immunodeficiency virus 1 (HIV-1) RNA transcripts produces mRNAs encoding nine different viral proteins. The leader of each contains a common non-coding exon at the 5' end. Previous studies showed that the leaders from the common exon-containing transcripts gag, nef, vif, vpr and vpu can direct protein synthesis through internal ribosome entry sites (IRESs) with varying efficiencies. Here we explored whether the common exon acts as an IRES element in the context of all the 5' leaders or if each harbors a distinct IRES. We also explored the relationship between the IRESs and initiation codon selection. We find that the common exon adopts a similar conformation in every leader we explored and that the sequence and structure is required for IRES activity. We also find that each leader uses a scanning mechanism for start codon identification. Together, our data point to a model in which the common exon on HIV-1 transcripts acts as the ribosome landing pad, recruiting preinitiation complexes upstream of the initiation codon, followed by scanning to each transcript's initiator AUG. PMID:26779399

  19. Internal translation initiation from HIV-1 transcripts is conferred by a common RNA structure.

    PubMed

    Plank, Terra-Dawn M; Whitehurst, James T; Cencic, Regina; Pelletier, Jerry; Kieft, Jeffrey S

    2014-01-01

    Alternative splicing of the human immunodeficiency virus 1 (HIV-1) RNA transcripts produces mRNAs encoding nine different viral proteins. The leader of each contains a common non-coding exon at the 5' end. Previous studies showed that the leaders from the common exon-containing transcripts gag, nef, vif, vpr and vpu can direct protein synthesis through internal ribosome entry sites (IRESs) with varying efficiencies. Here we explored whether the common exon acts as an IRES element in the context of all the 5' leaders or if each harbors a distinct IRES. We also explored the relationship between the IRESs and initiation codon selection. We find that the common exon adopts a similar conformation in every leader we explored and that the sequence and structure is required for IRES activity. We also find that each leader uses a scanning mechanism for start codon identification. Together, our data point to a model in which the common exon on HIV-1 transcripts acts as the ribosome landing pad, recruiting preinitiation complexes upstream of the initiation codon, followed by scanning to each transcript's initiator AUG. PMID:26779399

  20. Structural insights into the initiating complex of the lectin pathway of complement activation.

    PubMed

    Kjaer, Troels R; Le, Le T M; Pedersen, Jan Skov; Sander, Bjoern; Golas, Monika M; Jensenius, Jens Christian; Andersen, Gregers R; Thiel, Steffen

    2015-02-01

    The proteolytic cascade of the complement system is initiated when pattern-recognition molecules (PRMs) bind to ligands, resulting in the activation of associated proteases. In the lectin pathway of complement, the complex of mannan-binding lectin (MBL) and MBL-associated serine protease-1 (MASP-1) initiates the pathway by activating a second protease, MASP-2. Here we present a structural study of a PRM/MASP complex and derive the overall architecture of the 450 kDa MBL/MASP-1 complex using small-angle X-ray scattering and electron microscopy. The serine protease (SP) domains from the zymogen MASP-1 dimer protrude from the cone-like MBL tetramer and are separated by at least 20 nm. This suggests that intracomplex activation within a single MASP-1 dimer is unlikely and instead supports intercomplex activation, whereby the MASP SP domains are accessible to nearby PRM-bound MASPs. This activation mechanism differs fundamentally from the intracomplex initiation models previously proposed for both the lectin and the classical pathway. PMID:25579818

  1. Initiation and growth of gypsum piercement structures in the Zechstein Basin

    USGS Publications Warehouse

    Williams-Stroud, S. C.; Paul, J.

    1997-01-01

    The importance of tectonic processes in initiating halite diapirs has become much better understood in recent years. Less well understood is the development of diapiric structures involving rocks composed predominantly of gypsum. Below about 1000 m, gypsum dehydrates to anhydrite, which often obscures primary sedimentary textures. If the strain associated with diapiric rise in the rock induces the transition to anhydrite, obliteration of primary features in the gypsum can be expected. In our study, we infer that the diapiric movement in the Werra Anhydrite member of cycle 1 of the Zechstein Formation of Europe occurred before the initial transition of gypsum to anhydrite based on the presence of pseudomorphs of bedded primary gypsum crystals, the overburden lithologies and depositional environment, and the mechanical properties of gypsum, anhydrite and carbonate rocks. Faulting and differential loading of a shallow overburden were the key components in initiating the gypsum diapirism. The transition to anhydrite occurred after burial and after cessation of diapirism. In comparison, the diapirism of calcium sulfate of the Leine Anhydrite into the Leine Halite members of cycle 3 of the Zechstein Formation probably occurred much later after burial and appears to have been triggered by halite diapirism, which in turn triggered the dehydration reaction, causing the calcium sulfate to become the incompetent phase relative to the halite. Published by Elsevier Science Ltd.

  2. Structure and dimerization of translation initiation factor aIF5B in solution

    SciTech Connect

    Rasmussen, Louise Caroe Vohlander; Oliveira, Cristiano Luis Pinto; Byron, Olwyn; Jensen, Janni Mosgaard; Pedersen, Jan Skov; Sperling-Petersen, Hans Uffe; Mortensen, Kim Kusk

    2011-12-09

    Highlights: Black-Right-Pointing-Pointer aIF5B forms maximum 5.0-6.8% irreversible dimers in solution. Black-Right-Pointing-Pointer Sedimentation coefficients for monomer and dimer are 3.64 and 5.51 {+-} 0.29 S. Black-Right-Pointing-Pointer Adding only 2% glycerol prevents dimerization. Black-Right-Pointing-Pointer SAXS on aIF5B monomer gave an R{sub g} of 37.5 {+-} 0.2 A and a D{sub max} of {approx}130 A. Black-Right-Pointing-Pointer There are universal structural differences between aIF5B and Escherichia coli IF2. -- Abstract: Translation initiation factor 5B (IF5B) is required for initiation of protein synthesis. The solution structure of archaeal IF5B (aIF5B) was analysed by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) and was indicated to be in both monomeric and dimeric form. Sedimentation equilibrium (SE) analytical ultracentrifugation (AUC) of aIF5B indicated that aIF5B forms irreversible dimers in solution but only to a maximum of 5.0-6.8% dimer. Sedimentation velocity (SV) AUC at higher speed also indicated the presence of two species, and the sedimentation coefficients s{sub 20,w}{sup 0} were determined to be 3.64 and 5.51 {+-} 0.29 S for monomer and dimer, respectively. The atomic resolution (crystallographic) structure of aIF5B (Roll-Mecak et al. ) was used to model monomer and dimer, and theoretical sedimentation coefficients for these models were computed (3.89 and 5.63 S, respectively) in good agreement with the sedimentation coefficients obtained from SV analysis. Thus, the structure of aIF5B in solution must be very similar to the atomic resolution structure of aIF5B. SAXS data were acquired in the same buffer with the addition of 2% glycerol to inhibit dimerization, and the resultant monomeric aIF5B in solution did indeed adopt a structure very similar to the one reported earlier for the protein in crystalline form. The p(r) function indicated an elongated conformation supported by a radius of gyration of 37.5 {+-} 0.2 A

  3. Structural, mechanical and optical properties of nitrogen-implanted titanium at different pulse frequency

    NASA Astrophysics Data System (ADS)

    Raaif, Mohamed; Mohamed, Sodky H.; Abd El-Rahman, Ahmed M.; Kolitsch, Andreas

    2013-04-01

    Plasma-immersion ion implantation (PIII) is a potent method to obtain hard and wear-resistant surface on Ti by nitrogen implantation. This presentation is one part of a sequence of experiments to optimize the microstructure and physical properties of TiN through adapting the plasma-processing parameters. In this work, nitrogen ions were implanted into samples of pure Ti at different nitrogen pulse frequency without using any external source of heating. The nitrogen-implanted surfaces were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES), optical microscope, nano-indentation technique, ball-on-disk type tribometer, surface profilemeter, Tafel polarization technique for corrosion performance and ellipsometry. The outcomes show that, nitrogen PIII is an effectual method for nitriding titanium and nitrogen pulse frequency affected the microstructure and physical properties of the treated Ti. X-ray diffraction depicted the formation of α-Ti (N) and the cubic TiN after implanting titanium by nitrogen and the thickness of the nitrided layer increased as the nitrogen pulse frequency increased. The wear and corrosion resistance of the nitrogen-implanted titanium are improved and the friction coefficient decreased from nearly 0.8 for the un-implanted titanium to 0.3 for the implanted titanium, this ascribed to the formation of the titanium nitrided phases. Ellipsometric measurements were carried out on the PIII titanium samples at different nitrogen pulse frequency. The ellipsometric measurements show that, the thickness of the nitrided layer and surface roughness increased while the refractive index decreased with increasing nitrogen pulse frequency.

  4. Structure of the apoptosome: mechanistic insights into activation of an initiator caspase from Drosophila

    PubMed Central

    Pang, Yuxuan; Bai, Xiao-chen; Yan, Chuangye; Hao, Qi; Chen, Zheqin; Wang, Jia-Wei

    2015-01-01

    Apoptosis is executed by a cascade of caspase activation. The autocatalytic activation of an initiator caspase, exemplified by caspase-9 in mammals or its ortholog, Dronc, in fruit flies, is facilitated by a multimeric adaptor complex known as the apoptosome. The underlying mechanism by which caspase-9 or Dronc is activated by the apoptosome remains unknown. Here we report the electron cryomicroscopic (cryo-EM) structure of the intact apoptosome from Drosophila melanogaster at 4.0 Å resolution. Analysis of the Drosophila apoptosome, which comprises 16 molecules of the Dark protein (Apaf-1 ortholog), reveals molecular determinants that support the assembly of the 2.5-MDa complex. In the absence of dATP or ATP, Dronc zymogen potently induces formation of the Dark apoptosome, within which Dronc is efficiently activated. At 4.1 Å resolution, the cryo-EM structure of the Dark apoptosome bound to the caspase recruitment domain (CARD) of Dronc (Dronc-CARD) reveals two stacked rings of Dronc-CARD that are sandwiched between two octameric rings of the Dark protein. The specific interactions between Dronc-CARD and both the CARD and the WD40 repeats of a nearby Dark protomer are indispensable for Dronc activation. These findings reveal important mechanistic insights into the activation of initiator caspase by the apoptosome. PMID:25644603

  5. NMR structure of the N-terminal domain of the replication initiator protein DnaA

    SciTech Connect

    Wemmer, David E.; Lowery, Thomas J.; Pelton, Jeffrey G.; Chandonia, John-Marc; Kim, Rosalind; Yokota, Hisao; Wemmer, David E.

    2007-08-07

    DnaA is an essential component in the initiation of bacterial chromosomal replication. DnaA binds to a series of 9 base pair repeats leading to oligomerization, recruitment of the DnaBC helicase, and the assembly of the replication fork machinery. The structure of the N-terminal domain (residues 1-100) of DnaA from Mycoplasma genitalium was determined by NMR spectroscopy. The backbone r.m.s.d. for the first 86 residues was 0.6 +/- 0.2 Angstrom based on 742 NOE, 50 hydrogen bond, 46 backbone angle, and 88 residual dipolar coupling restraints. Ultracentrifugation studies revealed that the domain is monomeric in solution. Features on the protein surface include a hydrophobic cleft flanked by several negative residues on one side, and positive residues on the other. A negatively charged ridge is present on the opposite face of the protein. These surfaces may be important sites of interaction with other proteins involved in the replication process. Together, the structure and NMR assignments should facilitate the design of new experiments to probe the protein-protein interactions essential for the initiation of DNA replication.

  6. Inverted initial conditions: Exploring the growth of cosmic structure and voids

    NASA Astrophysics Data System (ADS)

    Pontzen, Andrew; Slosar, Anže; Roth, Nina; Peiris, Hiranya V.

    2016-05-01

    We introduce and explore "paired" cosmological simulations. A pair consists of an A and B simulation with initial conditions related by the inversion δA(x ,tinitial)=-δB(x ,tinitial) (underdensities substituted for overdensities and vice versa). We argue that the technique is valuable for improving our understanding of cosmic structure formation. The A and B fields are by definition equally likely draws from Λ CDM initial conditions, and in the linear regime evolve identically up to the overall sign. As nonlinear evolution takes hold, a region that collapses to form a halo in simulation A will tend to expand to create a void in simulation B. Applications include (i) contrasting the growth of A-halos and B-voids to test excursion-set theories of structure formation, (ii) cross-correlating the density field of the A and B universes as a novel test for perturbation theory, and (iii) canceling error terms by averaging power spectra between the two boxes. Generalizations of the method to more elaborate field transformations are suggested.

  7. Inverted initial conditions: Exploring the growth of cosmic structure and voids

    DOE PAGESBeta

    Pontzen, Andrew; Roth, Nina; Peiris, Hiranya V.; Slosar, Anze

    2016-05-18

    We introduce and explore “paired” cosmological simulations. A pair consists of an A and B simulation with initial conditions related by the inversion δA(x,tinitial) = –δB(x,tinitial) (underdensities substituted for overdensities and vice versa). We argue that the technique is valuable for improving our understanding of cosmic structure formation. The A and B fields are by definition equally likely draws from ΛCDM initial conditions, and in the linear regime evolve identically up to the overall sign. As nonlinear evolution takes hold, a region that collapses to form a halo in simulation A will tend to expand to create a void inmore » simulation B. Applications include (i) contrasting the growth of A-halos and B-voids to test excursion-set theories of structure formation, (ii) cross-correlating the density field of the A and B universes as a novel test for perturbation theory, and (iii) canceling error terms by averaging power spectra between the two boxes. Furthermore, generalizations of the method to more elaborate field transformations are suggested.« less

  8. Professional identity acquisition process model in interprofessional education using structural equation modelling: 10-year initiative survey.

    PubMed

    Kururi, Nana; Tozato, Fusae; Lee, Bumsuk; Kazama, Hiroko; Katsuyama, Shiori; Takahashi, Maiko; Abe, Yumiko; Matsui, Hiroki; Tokita, Yoshiharu; Saitoh, Takayuki; Kanaizumi, Shiomi; Makino, Takatoshi; Shinozaki, Hiromitsu; Yamaji, Takehiko; Watanabe, Hideomi

    2016-01-01

    The mandatory interprofessional education (IPE) programme at Gunma University, Japan, was initiated in 1999. A questionnaire of 10 items to assess the students' understanding of the IPE training programme has been distributed since then, and the factor analysis of the responses revealed that it was categorised into four subscales, i.e. "professional identity", "structure and function of training facilities", "teamwork and collaboration", and "role and responsibilities", and suggested that these may take into account the development of IPE programme with clinical training. The purpose of this study was to examine the professional identity acquisition process (PIAP) model in IPE using structural equation modelling (SEM). Overall, 1,581 respondents of a possible 1,809 students from the departments of nursing, laboratory sciences, physical therapy, and occupational therapy completed the questionnaire. The SEM technique was utilised to construct a PIAP model on the relationships among four factors. The original PIAP model showed that "professional identity" was predicted by two factors, namely "role and responsibilities" and "teamwork and collaboration". These two factors were predicted by the factor "structure and function of training facilities". The same structure was observed in nursing and physical therapy students' PIAP models, but it was not completely the same in laboratory sciences and occupational therapy students' PIAP models. A parallel but not isolated curriculum on expertise unique to the profession, which may help to understand their professional identity in combination with learning the collaboration, may be necessary. PMID:26930464

  9. C9orf72 nucleotide repeat structures initiate molecular cascades of disease.

    PubMed

    Haeusler, Aaron R; Donnelly, Christopher J; Periz, Goran; Simko, Eric A J; Shaw, Patrick G; Kim, Min-Sik; Maragakis, Nicholas J; Troncoso, Juan C; Pandey, Akhilesh; Sattler, Rita; Rothstein, Jeffrey D; Wang, Jiou

    2014-03-13

    A hexanucleotide repeat expansion (HRE), (GGGGCC)n, in C9orf72 is the most common genetic cause of the neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we identify a molecular mechanism by which structural polymorphism of the HRE leads to ALS/FTD pathology and defects. The HRE forms DNA and RNA G-quadruplexes with distinct structures and promotes RNA•DNA hybrids (R-loops). The structural polymorphism causes a repeat-length-dependent accumulation of transcripts aborted in the HRE region. These transcribed repeats bind to ribonucleoproteins in a conformation-dependent manner. Specifically, nucleolin, an essential nucleolar protein, preferentially binds the HRE G-quadruplex, and patient cells show evidence of nucleolar stress. Our results demonstrate that distinct C9orf72 HRE structural polymorphism at both DNA and RNA levels initiates molecular cascades leading to ALS/FTD pathologies, and provide the basis for a mechanistic model for repeat-associated neurodegenerative diseases. PMID:24598541

  10. Structural remodeling of bacteriophage T4 and host membranes during infection initiation.

    PubMed

    Hu, Bo; Margolin, William; Molineux, Ian J; Liu, Jun

    2015-09-01

    The first stages of productive bacteriophage infections of bacterial host cells require efficient adsorption to the cell surface followed by ejection of phage DNA into the host cytoplasm. To achieve this goal, a phage virion must undergo significant structural remodeling. For phage T4, the most obvious change is the contraction of its tail. Here, we use skinny E. coli minicells as a host, along with cryo-electron tomography and mutant phage virions, to visualize key structural intermediates during initiation of T4 infection. We show for the first time that most long tail fibers are folded back against the tail sheath until irreversible adsorption, a feature compatible with the virion randomly walking across the cell surface to find an optimal site for infection. Our data confirm that tail contraction is triggered by structural changes in the baseplate, as intermediates were found with remodeled baseplates and extended tails. After contraction, the tail tube penetrates the host cell periplasm, pausing while it degrades the peptidoglycan layer. Penetration into the host cytoplasm is accompanied by a dramatic local outward curvature of the cytoplasmic membrane as it fuses with the phage tail tip. The baseplate hub protein gp27 and/or the ejected tape measure protein gp29 likely form the transmembrane channel for viral DNA passage into the cell cytoplasm. Building on the wealth of prior biochemical and structural information, this work provides new molecular insights into the mechanistic pathway of T4 phage infection. PMID:26283379

  11. Laboratory information management system for membrane protein structure initiative--from gene to crystal.

    PubMed

    Troshin, Petr V; Morris, Chris; Prince, Stephen M; Papiz, Miroslav Z

    2008-12-01

    Membrane Protein Structure Initiative (MPSI) exploits laboratory competencies to work collaboratively and distribute work among the different sites. This is possible as protein structure determination requires a series of steps, starting with target selection, through cloning, expression, purification, crystallization and finally structure determination. Distributed sites create a unique set of challenges for integrating and passing on information on the progress of targets. This role is played by the Protein Information Management System (PIMS), which is a laboratory information management system (LIMS), serving as a hub for MPSI, allowing collaborative structural proteomics to be carried out in a distributed fashion. It holds key information on the progress of cloning, expression, purification and crystallization of proteins. PIMS is employed to track the status of protein targets and to manage constructs, primers, experiments, protocols, sample locations and their detailed histories: thus playing a key role in MPSI data exchange. It also serves as the centre of a federation of interoperable information resources such as local laboratory information systems and international archival resources, like PDB or NCBI. During the challenging task of PIMS integration, within the MPSI, we discovered a number of prerequisites for successful PIMS integration. In this article we share our experiences and provide invaluable insights into the process of LIMS adaptation. This information should be of interest to partners who are thinking about using LIMS as a data centre for their collaborative efforts. PMID:18991141

  12. Structural remodeling of bacteriophage T4 and host membranes during infection initiation

    PubMed Central

    Hu, Bo; Margolin, William; Molineux, Ian J.; Liu, Jun

    2015-01-01

    The first stages of productive bacteriophage infections of bacterial host cells require efficient adsorption to the cell surface followed by ejection of phage DNA into the host cytoplasm. To achieve this goal, a phage virion must undergo significant structural remodeling. For phage T4, the most obvious change is the contraction of its tail. Here, we use skinny E. coli minicells as a host, along with cryo-electron tomography and mutant phage virions, to visualize key structural intermediates during initiation of T4 infection. We show for the first time that most long tail fibers are folded back against the tail sheath until irreversible adsorption, a feature compatible with the virion randomly walking across the cell surface to find an optimal site for infection. Our data confirm that tail contraction is triggered by structural changes in the baseplate, as intermediates were found with remodeled baseplates and extended tails. After contraction, the tail tube penetrates the host cell periplasm, pausing while it degrades the peptidoglycan layer. Penetration into the host cytoplasm is accompanied by a dramatic local outward curvature of the cytoplasmic membrane as it fuses with the phage tail tip. The baseplate hub protein gp27 and/or the ejected tape measure protein gp29 likely form the transmembrane channel for viral DNA passage into the cell cytoplasm. Building on the wealth of prior biochemical and structural information, this work provides new molecular insights into the mechanistic pathway of T4 phage infection. PMID:26283379

  13. New York-Structural GenomiX Research Consortium (NYXGXRC): a Large Scale Center for the Protein Structure Initiative

    SciTech Connect

    Bonanno,J.; Almo, S.; Bresnick, A.; Chance, M.; Fiser, A.; Swaminathan, S.; Jiang, J.; Studier, F.; Shapiro, L.; et al.

    2005-01-01

    Structural GenomiX, Inc. (SGX), four New York area institutions, and two University of California schools have formed the New York Structural GenomiX Research Consortium (NYSGXRC), an industrial/academic Research Consortium that exploits individual core competencies to support all aspects of the NIH-NIGMS funded Protein Structure Initiative (PSI), including protein family classification and target selection, generation of protein for biophysical analyses, sample preparation for structural studies, structure determination and analyses, and dissemination of results. At the end of the PSI Pilot Study Phase (PSI-1), the NYSGXRC will be capable of producing 100-200 experimentally determined protein structures annually. All Consortium activities can be scaled to increase production capacity significantly during the Production Phase of the PSI (PSI-2). The Consortium utilizes both centralized and de-centralized production teams with clearly defined deliverables and hand-off procedures that are supported by a web-based target/sample tracking system (SGX Laboratory Information Data Management System, LIMS, and NYSGXRC Internal Consortium Experimental Database, ICE-DB). Consortium management is provided by an Executive Committee, which is composed of the PI and all Co-PIs. Progress to date is tracked on a publicly available Consortium web site (http://www.nysgxrc.org) and all DNA/protein reagents and experimental protocols are distributed freely from the New York City Area institutions. In addition to meeting the requirements of the Pilot Study Phase and preparing for the Production Phase of the PSI, the NYSGXRC aims to develop modular technologies that are transferable to structural biology laboratories in both academe and industry. The NYSGXRC PI and Co-PIs intend the PSI to have a transforming effect on the disciplines of X-ray crystallography and NMR spectroscopy of biological macromolecules. Working with other PSI-funded Centers, the NYSGXRC seeks to create the

  14. Structural engineering masters level education framework of knowledge for the needs of initial professional practice

    NASA Astrophysics Data System (ADS)

    Balogh, Zsuzsa Enriko

    For at least the last decade, engineering, civil engineering, along with structural engineering as a profession within civil engineering, have and continue to face an emerging need for "Raising the Bar" of preparedness of young engineers seeking to become practicing professional engineers. The present consensus of the civil engineering profession is that the increasing need for broad and in-depth knowledge should require the young structural engineers to have at least a Masters-Level education. This study focuses on the Masters-Level preparedness in the structural engineering area within the civil engineering field. It follows much of the methodology used in the American Society of Civil Engineers (ASCE) Body of Knowledge determination for civil engineering and extends this type of study to better define the portion of the young engineers preparation beyond the undergraduate program for one specialty area of civil engineering. The objective of this research was to create a Framework of Knowledge for the young engineer which identifies and recognizes the needs of the profession, along with the profession's expectations of how those needs can be achieved in the graduate-level academic setting, in the practice environment, and through lifelong learning opportunities with an emphasis on the initial five years experience past completion of a Masters program in structural engineering. This study applied a modified Delphi method to obtain the critical information from members of the structural engineering profession. The results provide a Framework of Knowledge which will be useful to several groups seeking to better ensure the preparedness of the future young structural engineers at the Masters-Level.

  15. Does complex absorption behavior leading to conditioning and damage in KDP/DKDP reflect the electronic structure of initiators?

    SciTech Connect

    Feit, M D; DeMange, P P; Negres, R A; Rubenchik, A M; Demos, S G

    2007-10-24

    Currently, most of our thinking about the defects responsible for initiating laser damage considers them as featureless absorbers. However, an increasing body of evidence, particularly involving multi-wavelength irradiation, suggests electronic structure of damage initiators is important in determining both initiation and conditioning behaviors in KDP. The effective absorption coefficient of energy under multi-wavelength irradiation cannot be accounted for by a structureless absorber, but is consistent with an initiator with a multi-level structure. We outline the evidence and assess the ability of such a simple multi-level model to explain these and other experimentally observed behaviors.

  16. Structure and dimerization of translation initiation factor aIF5B in solution

    SciTech Connect

    Carø VohlanderRasmussen, Louise; Oliveira, Cristiano Luis Pinto; Byron, Olwyn; Jensen, Janni Mosgaard; Pedersen, Jan Skov; Sperling-Petersen, Hans Uffe; Mortensen, Kim Kusk

    2012-02-07

    Translation initiation factor 5B (IF5B) is required for initiation of protein synthesis. The solution structure of archaeal IF5B (aIF5B) was analysed by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) and was indicated to be in both monomeric and dimeric form. Sedimentation equilibrium (SE) analytical ultracentrifugation (AUC) of aIF5B indicated that aIF5B forms irreversible dimers in solution but only to a maximum of 5.0-6.8% dimer. Sedimentation velocity (SV) AUC at higher speed also indicated the presence of two species, and the sedimentation coefficients s{sub 20,w}{sup 0} were determined to be 3.64 and 5.51 {+-} 0.29 S for monomer and dimer, respectively. The atomic resolution (crystallographic) structure of aIF5B (Roll-Mecak et al. [6]) was used to model monomer and dimer, and theoretical sedimentation coefficients for these models were computed (3.89 and 5.63 S, respectively) in good agreement with the sedimentation coefficients obtained from SV analysis. Thus, the structure of aIF5B in solution must be very similar to the atomic resolution structure of aIF5B. SAXS data were acquired in the same buffer with the addition of 2% glycerol to inhibit dimerization, and the resultant monomeric aIF5B in solution did indeed adopt a structure very similar to the one reported earlier for the protein in crystalline form. The p(r) function indicated an elongated conformation supported by a radius of gyration of 37.5 {+-} 0.2 {angstrom} and a maximum dimension of {approx}130 {angstrom}. The effects of glycerol on the formation of dimers are discussed. This new model of aIF5B in solution shows that there are universal structural differences between aIF5B and the homologous protein IF2 from Escherichia coli.

  17. Effect of pulsed electric field (PEF) on structures and antioxidant activity of soybean source peptides-SHCMN.

    PubMed

    Lin, Songyi; Liang, Rong; Li, Xingfang; Xing, Jie; Yuan, Yuan

    2016-12-15

    Recently, high-intensity pulsed electric field (PEF) has successfully used in improvement of antioxidant activity. Ser-His-Cys-Met-Asn (SHCMN) obtained from soybean protein was chosen to investigate the phenomenon of antioxidant activity improvement. Effects of PEF treatment on antioxidant activity of SHCMN were evaluated by DPPH radical inhibition. Nuclear magnetic resonance (NMR), mid-infrared (MIR), circular dichroism (CD) were used to analyze structures of SHCMN. Two-factor-at-a-time results show that DPPH radical inhibition of SHCMN is significantly (P<0.05) increased to 94.35±0.03% at conditions of electric field intensity of 5kV/cm, pulse frequency of 2400Hz, and retention time of 2h. In addition, MIR and NMR spectra show that the basic structure of peptides SHCMN is stable by PEF treatment. But the secondary structures (α-helix, β-turn, and random coil) can be affected and zeta potential of PEF-treated SHCNM was reduced to 0.59±0.03mV. The antioxidant activity improvement of SHCMN might result from the changes of secondary structures and zeta potential. PMID:27451222

  18. The Structured Operational Research and Training Initiative for public health programmes.

    PubMed

    Ramsay, A; Harries, A D; Zachariah, R; Bissell, K; Hinderaker, S G; Edginton, M; Enarson, D A; Satyanarayana, S; Kumar, A M V; Hoa, N B; Tweya, H; Reid, A J; Van den Bergh, R; Tayler-Smith, K; Manzi, M; Khogali, M; Kizito, W; Ali, E; Delaunois, P; Reeder, J C

    2014-06-21

    In 2009, the International Union Against Tuberculosis and Lung Disease (The Union) and Médecins sans Frontières Brussels-Luxembourg (MSF) began developing an outcome-oriented model for operational research training. In January 2013, The Union and MSF joined with the Special Programme for Research and Training in Tropical Diseases (TDR) at the World Health Organization (WHO) to form an initiative called the Structured Operational Research and Training Initiative (SORT IT). This integrates the training of public health programme staff with the conduct of operational research prioritised by their programme. SORT IT programmes consist of three one-week workshops over 9 months, with clearly-defined milestones and expected output. This paper describes the vision, objectives and structure of SORT IT programmes, including selection criteria for applicants, the research projects that can be undertaken within the time frame, the programme structure and milestones, mentorship, the monitoring and evaluation of the programmes and what happens beyond the programme in terms of further research, publications and the setting up of additional training programmes. There is a growing national and international need for operational research and related capacity building in public health. SORT IT aims to meet this need by advocating for the output-based model of operational research training for public health programme staff described here. It also aims to secure sustainable funding to expand training at a global and national level. Finally, it could act as an observatory to monitor and evaluate operational research in public health. Criteria for prospective partners wishing to join SORT IT have been drawn up. PMID:26399203

  19. Ultrafast pulsed laser deposition of carbon nanostructures: Structural and optical characterization

    NASA Astrophysics Data System (ADS)

    Pervolaraki, M.; Komninou, Ph.; Kioseoglou, J.; Othonos, A.; Giapintzakis, J.

    2013-08-01

    Carbon nanostructured materials were obtained by high-repetition rate pulsed laser ablation of a graphite target using a train of 10-ps duration pulses at 1064 nm in different pressures of high-purity Ar gas. It is demonstrated that their microstructure and optical properties vary as a function of the argon pressure. High-resolution transmission electron microscopy revealed the existence of onion-like carbon nanostructures embedded in a matrix of amorphous carbon nanofoam for samples prepared at 300 Pa. In comparison samples prepared at 30 Pa show evidence of both onion-like and turbostratic carbon coexisting in a matrix of amorphous carbon nanofoam whereas samples prepared in vacuum are continuous films of amorphous carbon. Transient transmission spectroscopy measurements suggested that free carrier absorption is the dominant effect following photo-excitation for probing wavelengths in the range of 550-1000 nm and its magnitude varies among the materials investigated due to their different microstructures.

  20. Femtosecond Pulse Characterization as Applied to One-Dimensional Photonic Band Edge Structures

    NASA Technical Reports Server (NTRS)

    Fork, Richard L.; Gamble, Lisa J.; Diffey, William M.

    1999-01-01

    The ability to control the group velocity and phase of an optical pulse is important to many current active areas of research. Electronically addressable one-dimensional photonic crystals are an attractive candidate to achieve this control. This report details work done toward the characterization of photonic crystals and improvement of the characterization technique. As part of the work, the spectral dependence of the group delay imparted by a GaAs/AlAs photonic crystal was characterized. Also, a first generation an electrically addressable photonic crystal was tested for the ability to electronically control the group delay. The measurement technique, using 100 femtosecond continuum pulses was improved to yield high spectral resolution (1.7 nanometers) and concurrently with high temporal resolution (tens of femtoseconds). Conclusions and recommendations based upon the work done are also presented.

  1. Selective ablation of atherosclerotic lesions with less thermal damage by controlling the pulse structure of a quantum cascade laser in the 5.7-µm wavelength range

    NASA Astrophysics Data System (ADS)

    Hashimura, Keisuke; Ishii, Katsunori; Awazu, Kunio

    2016-04-01

    Cholesteryl esters are the main components of atherosclerotic plaques, and they have an absorption peak at the wavelength of 5.75 µm. To realize less-invasive ablation of the atherosclerotic plaques using a quasi-continuous wave (quasi-CW) quantum cascade laser (QCL), the thermal effects on normal vessels must be reduced. In this study, we attempted to reduce the thermal effects by controlling the pulse structure. The irradiation effects on rabbit atherosclerotic aortas using macro pulse irradiation (irradiation of pulses at intervals) and conventional quasi-CW irradiation were compared. The macro pulse width and the macro pulse interval were determined based on the thermal relaxation time of atherosclerotic and normal aortas in the oscillation wavelength of the QCL. The ablation depth increased and the coagulation width decreased using macro pulse irradiation. Moreover, difference in ablation depth between the atherosclerotic and normal rabbit aortas using macro pulse irradiation was confirmed. Therefore, the QCL in the 5.7-µm wavelength range with controlling the pulse structure was effective for less-invasive laser angioplasty.

  2. A structure generator for modelling the initial sediment distribution of an artificial hydrologic catchment

    NASA Astrophysics Data System (ADS)

    Maurer, T.; Schneider, A.; Gerke, H. H.

    2011-05-01

    Artificially-created hydrological catchments are characterized by sediment structures from technological construction processes that can potentially be important for modelling of flow and transport and for understanding initial soil and ecosystem development. The subsurface spatial structures of such catchments have not yet been sufficiently explored and described. Our objective was to develop a structure generator programme for modelling the 3-D spatial sediment distribution patterns depending on the technical earth-moving and deposition processes. For the development, the artificially-constructed hydrological catchment "Chicken Creek" located in Lower Lusatia, Germany, served as an example. The structure generator describes 3-D technological sediment distributions at two scales: (i) for a 2-D-vertical cross-section, texture and bulk density distributions are generated within individual spoil cones that result from mass dumping, particle segregation, and compaction and (ii) for the whole catchment area, the spoil cones are horizontally arranged along trajectories of mass dumping controlled by the belt stacker-machine relative to the catchment's clay layer topography. The generated 3-D texture and bulk density distributions are interpolated and visualized as a gridded 3-D-volume body using 3-D computer-aided design software. The generated subsurface sediment distribution for the Chicken Creek catchment was found to correspond to observed patterns although still without any calibration. Spatial aggregation and interpolation in the gridded volume body modified the generated distributions towards more uniform (unimodal) distributions and lower values of the standard deviations. After incorporating variations and pedotransfer approaches, generated sediment distributions can be used for deriving realizations of the 3-D hydraulic catchment structure.

  3. A structure generator for modelling the initial sediment distribution of an artificial hydrologic catchment

    NASA Astrophysics Data System (ADS)

    Maurer, T.; Schneider, A.; Gerke, H. H.

    2011-12-01

    Artificially-created hydrological catchments are characterised by sediment structures from technological construction processes that can potentially be important for modelling of flow and transport and for understanding initial soil and ecosystem development. The subsurface spatial structures of such catchments have not yet been sufficiently explored and described. Our objective was to develop a structure generator programme for modelling the 3-D spatial distribution patterns of dumped sediments depending on the technical earth-moving and deposition processes. We are focussing in a first step on integrating sediment dumping, particle size, and bulk density modification processes on the catchment scale. For the model development, the artificially-constructed hydrological catchment "Chicken Creek" located in Lower Lusatia, Germany, served as an example. The structure generator describes 3-D technological sediment distributions at two scales: (i) for a 2-D-vertical cross-section, texture and bulk density distributions are generated within individual spoil cones that result from mass dumping, particle segregation, and compaction and (ii) for the whole catchment, the spoil cones are horizontally arranged along trajectories of mass dumping controlled by the belt stacker-machine relative to the catchment's clay layer topography. The generated 3-D texture and bulk density distributions are interpolated and visualised as a gridded 3-D-volume body using 3-D computer-aided design software. The generated subsurface sediment distribution for the Chicken Creek catchment was found to correspond to observed patterns already without calibration. Spatial aggregation and interpolation in the gridded volume body modified the generated distributions towards more uniform (unimodal) distributions and lower values of the standard deviations. The modelling approach is generally applicable to all situations where large masses of unconsolidated sediment are moved and dumped thereby allowing

  4. Enhanced temperature and emission from a standoff 266 nm laser initiated LIBS plasma using a simultaneous 10.6 microm CO2 laser pulse.

    PubMed

    Pal, Avishekh; Waterbury, Robert D; Dottery, Edwin L; Killinger, Dennis K

    2009-05-25

    A deep UV 266 nm laser induced LIBS plasma has been enhanced by using a simultaneous 10.6 microm CO(2) laser pulse at standoff ranges up to 55 m for several targets including metals, ceramics and plastics. The LIBS plasma emission was produced, for the first time, by a 266 nm laser and was enhanced by several orders of magnitude using the CO(2) laser pulse. The temperature of the enhanced LIBS plasma was measured, for the first time, and was observed to increase by about 3000K due to the addition of the CO(2) laser pulse. PMID:19466135

  5. Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Nicolodelli, Gustavo; de Fátima Zanirato Lizarelli, Rosane; Salvador Bagnato, Vanderlei

    2012-04-01

    Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788+/-0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses.

  6. Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation.

    PubMed

    Nicolodelli, Gustavo; Lizarelli, Rosane de Fátima Zanirato; Bagnato, Vanderlei Salvador

    2012-04-01

    Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788±0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses. PMID:22559697

  7. Three-dimensional EM Structure of an Intact Activator-dependent Transcription Initiation Complex

    SciTech Connect

    Hudson, B.; Quispe, J; Lara-González, S; Kim, Y; Berman, H; Arnold, E; Ebright, R; Lawson, C

    2009-01-01

    We present the experimentally determined 3D structure of an intact activator-dependent transcription initiation complex comprising the Escherichia coli catabolite activator protein (CAP), RNA polymerase holoenzyme (RNAP), and a DNA fragment containing positions -78 to +20 of a Class I CAP-dependent promoter with a CAP site at position -61.5 and a premelted transcription bubble. A 20-{angstrom} electron microscopy reconstruction was obtained by iterative projection-based matching of single particles visualized in carbon-sandwich negative stain and was fitted using atomic coordinate sets for CAP, RNAP, and DNA. The structure defines the organization of a Class I CAP-RNAP-promoter complex and supports previously proposed interactions of CAP with RNAP {alpha} subunit C-terminal domain ({alpha}CTD), interactions of {alpha}CTD with {sigma}70 region 4, interactions of CAP and RNAP with promoter DNA, and phased-DNA-bend-dependent partial wrapping of DNA around the complex. The structure also reveals the positions and shapes of species-specific domains within the RNAP {beta}{prime}, {beta}, and {sigma}70 subunits.

  8. Studies in electron phenomena in MOS structures: The pulsed C-V method. M.S. Thesis. Abstract Only

    NASA Technical Reports Server (NTRS)

    Kaplan, G.

    1983-01-01

    The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

  9. Structured Benefit-risk assessment: a review of key publications and initiatives on frameworks and methodologies.

    PubMed

    Mt-Isa, Shahrul; Ouwens, Mario; Robert, Veronique; Gebel, Martin; Schacht, Alexander; Hirsch, Ian

    2016-07-01

    Introduction The conduct of structured benefit-risk assessment (BRA) of pharmaceutical products is a key area of interest for regulatory agencies and the pharmaceutical industry. However, the acceptance of a standardized approach and implementation are slow. Statisticians play major roles in these organizations, and have a great opportunity to be involved and drive the shaping of future BRA. Method We performed a literature search of recent reviews and initiatives assessing BRA methodologies, and grouped them to assist those new to BRA in learning, understanding, and choosing methodologies. We summarized the key points and discussed the impact of this emerging field on various stakeholders, particularly statisticians in the pharmaceutical industry. Results We provide introductory, essential, special interest, and further information and initiatives materials that direct readers to the most relevant materials, which were published between 2000 and 2013.  Based on recommendations in these materials we supply a toolkit of advocated BRA methodologies. Discussion Despite initiatives promoting these methodologies, there are still barriers, one of which being the lack of a consensus on the most appropriate methodologies among stakeholders. However, this opens up opportunities, for statisticians in the pharmaceutical industry especially, to champion appropriate BRA methodology use throughout the pharmaceutical product lifecycle. Conclusions This article may serve as a starting point for discussions and to reach a mutual consensus for methodology selection in a particular situation. Regulators and pharmaceutical industry should continue to collaborate to develop and take forward BRA methodologies, and by clear communication develop a mutual understanding of the key issues. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25981683

  10. Crystal structure of the DNA binding domain of the replication initiation protein E1 from papillomavirus.

    PubMed

    Enemark, E J; Chen, G; Vaughn, D E; Stenlund, A; Joshua-Tor, L

    2000-07-01

    Papillomaviral infection causes both benign and malignant lesions and is a necessary cause of cervical carcinoma. Replication of this virus requires the replication initiation proteins E1 and E2, which bind cooperatively at the origin of replication (ori) as an (E1)2-(E2)2-DNA complex. This is a precursor to larger E1 complexes that distort and unwind the ori. We present the crystal structure of the E1 DNA binding domain refined to 1.9 A resolution. Residues critical for DNA binding are located on an extended loop and an alpha helix. We identify the E1 dimerization surface by selective mutations at an E1/E1 interface observed in the crystal and propose a model for the (E1)2-DNA complex. These and other observations suggest how the E1 DNA binding domain orchestrates assembly of the hexameric helicase on the ori. PMID:10949036

  11. AEG-1/MTDH/LYRIC, the Beginning: Initial Cloning, Structure, Expression Profile, and Regulation of Expression

    PubMed Central

    DeSalle, Rob; Sarkar, Devanand; Fisher, Paul B.

    2014-01-01

    Since its initial identification as a HIV-1-inducible gene in 2002, astrocyte elevated gene-1 (AEG-1), subsequently cloned as metadherin (MTDH) and lysine-rich CEACAM1 coisolated (LYRIC), has emerged over the past 10 years as an important oncogene providing a valuable prognostic marker in patients with various cancers. Recent studies demonstrate that AEG-1/MTDH/LYRIC is a pleiotropic protein that can localize in the cell membrane, cytoplasm, endoplasmic reticulum (ER), nucleus, and nucleolus, and contributes to diverse signaling pathways such as PI3K–AKT, NF-κB, MAPK, and Wnt. In addition to tumorigenesis, this multifunctional protein is implicated in various physiological and pathological processes including development, neurodegeneration, and inflammation. The present review focuses on the discovery of AEG-1/MTDH/LYRIC and conceptualizes areas of future direction for this intriguing gene. We begin by describing how AEG-1, MTDH, and LYRIC were initially identified by different research groups and then discuss AEG-1 structure, functions, localization, and evolution. We conclude with a discussion of the expression profile of AEG-1/MTDH/LYRIC in the context of cancer, neurological disorders, inflammation, and embryogenesis, and discuss how AEG-1/MTDH/LYRIC is regulated. This introductory discussion of AEG-1/MTDH/LYRIC will serve as the basis for the detailed discussions in other chapters of the unique properties of this intriguing molecule. PMID:23889986

  12. Initial studies of Bremsstrahlung energy deposition in small-bore superconducting undulator structures in linac environments

    SciTech Connect

    Cremer, T.; Tatchyn, R.

    1995-12-31

    One of the more promising technologies for developing minimal-length insertion devices for linac-driven, single-pass Free Electron Lasers (FELs) operating in the x-ray range is based on the use of superconducting (SC) materials. In recent FEL simulations, for example, a bifilar helical SC device with a 2 cm period and 1.8 T field was found to require a 30 m saturation length for operation at 1.5{Angstrom} on a 15 GeV linac, more than 40% shorter than an alternative hybrid/permanent magnet (hybrid/PM) undulator. AT the same time, however, SC technology is known to present characteristic difficulties for insertion device design, both in engineering detail and in operation. Perhaps the most critical problem, as observed, e.g., by Madey and co-workers in their initial FEL experiments, was the frequent quenching induced by scattered electrons upstream of their (bifilar) device. Postulating that this quenching was precipitated by directly-scattered or bremsstrahlung-induced particle energy deposited into the SC material or into material contiguous with it, the importance of numerical and experimental characterizations of this phenomenon for linac-based, user-facility SC undulator design becomes evident. In this paper we discuss selected prior experimental results and report on initial EGS4 code studies of scattered and bremsstrahlung induced particle energy deposition into SC structures with geometries comparable to a small-bore bifilar helical undulator.

  13. Structural controls on Tertiary orogenic gold mineralization during initiation of a mountain belt, New Zealand

    NASA Astrophysics Data System (ADS)

    Craw, D.; Begbie, M.; MacKenzie, D.

    2006-10-01

    Two types of structurally controlled hydrothermal mineralization have occurred during folding of fissile schist in southern New Zealand: fold-related mineralization and normal fault-related mineralization. Both types have the same mineralogy and textures, and are dominated by quartz-ankerite veins and silicified breccias with ankeritic alteration. Most mineralized zones are thin (centimetre scale), although host schist is commonly impregnated with ankerite up to 20 m away. Thick (up to 5 m wide) mineralized zones are generally gold-bearing and contain pyrite and arsenopyrite with stibnite pods locally. Some of these auriferous zones have been extensively mined historically despite rugged topography and difficult access. Mineralization occurred during regional tectonic compression in the initial stages of development of the Southern Alps mountain belt at the Pacific-Australian plate boundary in the Miocene. Most of the gold-bearing deposits occur in east to south-east, striking normal faults that cut across mesoscopic folds in a belt that coincides with the southern termination of a regional-scale north trending antiform. Mineralized zones have similar structural control and relative timing to a nearby swarm of Miocene lamprophyre dykes and carbonatites. Limited stable isotopic data (C and O) and trace element geochemistry suggest that there was probably no genetic link between the igneous activity and gold mineralization. However, these two types of fluid flow have been controlled by the same tectonically created crustal plumbing system. This Miocene hydrothermal activity and gold deposition demonstrates that orogenic (mesothermal) mineralization can occur during the inception of an orogenic belt, not just in the latter stages as is commonly believed. These Miocene structures have been preserved in the orogen because the locus of uplift has moved northwards, so the early-formed gold deposits have not yet been structurally overprinted or eroded.

  14. Chicxulub central crater structure: Initial results from physical property measurements and combined velocity and gravity modeling

    NASA Astrophysics Data System (ADS)

    Vermeesch, P. M.; Morgan, J. V.

    2004-07-01

    The Chicxulub crater in Mexico is a nearly pristine example of a large impact crater. Its slow burial has left the central impact basin intact, within which there is an apparently uneroded topographic peak ring. Its burial, however, means that we must rely on drill holes and geophysical data to interpret the crater form. Interpretations of crater structures using geophysical data are often guided by numerical modeling and observations at other large terrestrial craters. However, such endeavors are hindered by uncertainties in current numerical models and the lack of any obvious progressive change in structure with increasing crater size. For this reason, proposed structural models across Chicxulub remain divergent, particularly within the central crater region, where the deepest well is only ~1.6 km deep. The shape and precise location of the stratigraphic uplift are disputed. The spatial extent and distribution of the allogenic impact breccias and melt rocks remain unknown, as do the lithological nature of the peak ring and the mechanism for its formation. The objective of our research is to provide a well-constrained 3D structural and lithological model across the central region of the Chicxulub crater that is consistent with combined geophysical data sets and drill core samples. With this in mind, we present initial physical property measurements made on 18 core samples from the Yaxcopoil-1 (Yax-1) drill hole between 400 and 1500 m deep and present a new density model that is in agreement with both the 3D velocity and gravity data. Future collation of petrophysical and geochemical data from Yax-1 core, as well as further seismic surveys and drilling, will allow us to calibrate our geophysical models-assigning a suite of physical properties to each lithology. An accurate 3D model of Chicxulub is critical to our understanding of large craters and to the constraining of the environmental effects of this impact.

  15. Effect of Heat Input Pulse on the Structure and Properties of Welded Joints of Steels Ferritic-Pearlitic Class, Operating Under Low-Frequency Temperature-Force Loading

    NASA Astrophysics Data System (ADS)

    Saraev, Y. N.; Bezborodov, V. P.; Putilova, E. A.

    2015-09-01

    We have investigated the influence of the modes of adaptive pulse-arc welding and surfacing on the structure and physical-mechanical properties of welded joints of steel 09Mn2Si and the surfaced composition of this steel coated with modified powder material of chromium carbide with the submicrocrystalline structure. It is shown that the pulsed mode of welding and surfacing can improve the homogeneity of the structure of the welded joint of steel and surfaced coating and reduce the grain size of metals in both of them. Structural changes lead to the increase in ductility and toughness of the weld metal.

  16. Protein Structure Initiative Material Repository: an open shared public resource of structural genomics plasmids for the biological community

    PubMed Central

    Cormier, Catherine Y.; Mohr, Stephanie E.; Zuo, Dongmei; Hu, Yanhui; Rolfs, Andreas; Kramer, Jason; Taycher, Elena; Kelley, Fontina; Fiacco, Michael; Turnbull, Greggory; LaBaer, Joshua

    2010-01-01

    The Protein Structure Initiative Material Repository (PSI-MR; http://psimr.asu.edu) provides centralized storage and distribution for the protein expression plasmids created by PSI researchers. These plasmids are a resource that allows the research community to dissect the biological function of proteins whose structures have been identified by the PSI. The plasmid annotation, which includes the full length sequence, vector information and associated publications, is stored in a freely available, searchable database called DNASU (http://dnasu.asu.edu). Each PSI plasmid is also linked to a variety of additional resources, which facilitates cross-referencing of a particular plasmid to protein annotations and experimental data. Plasmid samples can be requested directly through the website. We have also developed a novel strategy to avoid the most common concern encountered when distributing plasmids namely, the complexity of material transfer agreement (MTA) processing and the resulting delays this causes. The Expedited Process MTA, in which we created a network of institutions that agree to the terms of transfer in advance of a material request, eliminates these delays. Our hope is that by creating a repository of expression-ready plasmids and expediting the process for receiving these plasmids, we will help accelerate the accessibility and pace of scientific discovery. PMID:19906724

  17. Material instabilities and their role for the initiation of boudinage and folding structures

    NASA Astrophysics Data System (ADS)

    Veveakis, Manolis; Peters, Max; Poulet, Thomas; Karrech, Ali; Herwegh, Marco; Regenauer-Lieb, Klaus

    2015-04-01

    Localized phenomena, such as pinch-and-swell boudinage or localized folds, are usually interpreted to arise from viscosity contrasts. These are caused by structural heterogeneities, such as geometric or material imperfections. An alternative possibility for strain localization exists in material science, where dynamic localization emerges out of a steady state for a given critical set of material parameters and loading rates (Montési and Zuber, 2002). In our contribution, we will investigate the conditions under which this type of instabilities triggers localized deformation. Moreover, we discuss whether geological materials necessarily require structural heterogeneities, such as weak seeds, in order to generate aforementioned localized structures. We set up a random distribution of grain sizes in a layer embedded in a matrix with a diffusion creep rheology. Deformation within the layer is accommodated by dislocation and diffusion creep as end member deformation mechanism. The grain size evolution follows the paleowattmeter scaling relationship for calcite creep (Austin and Evans, 2007), which is controlled by thermo-mechanical feedbacks (Herwegh et al., 2014). During the first strain increments in the numerical simulation, the layer establishes a viscous steady state, which is the systems' response to optimize energy following the paleowattmeter (Herwegh et al., 2014). With further loading, localization interestingly arises out of a homogeneous state. We will demonstrate the robustness of this numerical solution by identifying the natural mode shapes and frequencies of the simulated structure and material parameters, including geometric imperfections (Rudnicki and Rice, 1975). This technique aims at the determination of the spatial manifestation of the instability pattern (Peters et al., in review). The eigenvalues are thought to represent the nodal points, where the onset of (visco)-elasto-plastic localization can initiate in the structure (Rudnicki and Rice

  18. Renal function and structure in a rat model of arterial calcification and increased pulse pressure.

    PubMed

    Gaillard, Virginie; Jover, Bernard; Casellas, Daniel; Cordaillat, Magali; Atkinson, Jeffrey; Lartaud, Isabelle

    2008-10-01

    Clinical studies suggest a strong link between tissue calcification and pressure hyperpulsatility in end stage renal disease patients. Using a Wistar rat model of arterial elastocalcinosis and hyperpulsatility [vitamin D and nicotine (VDN) treatment], we evaluated the relative importance of tissue calcification and hyperpulsatility in the etiology of renal failure. VDN rats showed significant increases in aortic wall calcium content (50 times; 992+/-171 vs. control 19+/-1 micromol/g dry wt) and pulse pressure (1.5 times; 61+/-4 vs. control 40+/-2 mmHg). Significant renal calcification (16 times; 124+/-27 vs. control 8.1+/-0.7 micromol/g dry wt) occurred mainly within the media of the preglomerular vasculature and in the areas of interstitial fibrosis in VDN. Extensive renal damages (5 times; 26+/-5% of collapsed-atrophic or sclerotic glomeruli, or glomerular cysts vs. control 5.2+/-0.3%; 28 times; 61+/-12% areas of focal, cortical areas exhibiting interstitial fibrosis per section vs. control 2.2+/-0.6%) were observed histologically. The glomerular filtration rate significantly decreased (880+/-40 vs. control 1,058+/-44 microl.min(-1).g kidney wt(-1)). Albuminuria increased six times (1.6+/-0.4 vs. control 0.27+/-0.04 mg/24 h). There were significant linear relationships between albuminuria and pulse pressure (r2=0.408; n=24) or renal calcium content (r2=0.328; n=24; P<0.05) and between glomerular filtration rate and pulse pressure (r2=0.168; n=27). To our knowledge, this study provides the first evidence of links between both 1) hyperpulsatility and renal dysfunction, and 2) renal calcification and renal dysfunction. Given the increasing frequency of end-stage renal disease, this model could prove useful for preclinical evaluation of drugs that prevent or attenuate hyperpulsatility and/or tissue calcification. PMID:18715942

  19. A method for localized computation of Pulse Wave Velocity in carotid structure.

    PubMed

    Patil, Ravindra B; Krishnamoorthy, P; Sethuraman, Shriram

    2015-08-01

    Pulse Wave Velocity (PWV) promises to be a useful clinical marker for noninvasive diagnosis of atherosclerosis. This work demonstrates the ability to perform localized carotid PWV measurements from the distention waveform derived from the Radio Frequency (RF) ultrasound signal using a carotid phantom setup. The proposed system consists of low cost custom-built ultrasound probe and algorithms for envelope detection, arterial wall identification, echo tracking, distension waveform computation and PWV estimation. The method is proposed on a phantom data acquired using custom-built prototype non-imaging probe. The proposed approach is non-image based and can be seamlessly integrated into existing clinical ultrasound scanners. PMID:26736653

  20. Changes in chromatin structure at recombination initiation sites during yeast meiosis.

    PubMed Central

    Ohta, K; Shibata, T; Nicolas, A

    1994-01-01

    Transient double-strand breaks (DSBs) occur during Saccharomyces cerevisiae meiosis at recombination hot spots and are thought to initiate most, if not all, homologous recombination between chromosomes. To uncover the regulatory mechanisms active in DSB formation, we have monitored the change in local chromatin structure at the ARG4 and CYS3 recombination hot spots over the course of meiosis. Micrococcal nuclease (MNase) digestion of isolated meiotic chromatin followed by indirect end-labeling revealed that the DSB sites in both loci are hypersensitive to MNase and that their sensitivity increases 2- to 4-fold prior to the appearance of meiotic DSBs and recombination products. Other sensitive sites are not significantly altered. The study of hyper- and hypo-recombinogenic constructs at the ARG4 locus, also revealed that the MNase sensitivity at the DSB site correlates with both the extent of DSBs and the rate of gene conversion. These results suggest that the local chromatin structure and its modification in early meiosis play an important role in the positioning and frequency of meiotic DSBs, leading to meiotic recombination. Images PMID:7988571

  1. Ordered YBCO sub-micron array structures induced by pulsed femtosecond laser irradiation.

    PubMed

    Luo, C W; Lee, C C; Li, C H; Shih, H C; Chen, Y-J; Hsieh, C C; Su, C H; Tzeng, W Y; Wu, K H; Juang, J Y; Uen, T M; Chen, S P; Lin, J-Y; Kobayashi, T

    2008-12-01

    We report on the formation of organized sub-micron YBa(2)Cu(3)O(7) (YBCO) dots induced by irradiating femtosecond laser pulses on YBCO films prepared by pulse laser deposition with fluence in the range of 0.21 approximately 0.53 J/cm(2). The morphology of the YBCO film surface depends strongly on the laser fluences irradiated. At lower laser fluence (approximately 0.21 J/cm(2)) the morphology was pattern of periodic ripples with sub-micrometer spacing. Slightly increasing the laser fluence to 0.26 J/cm(2) changes the pattern into organized sub-micron dots with diameters ranging from 100 nm to 800 nm and height of 150 nm. Further increase of the laser fluence to over 0.32 J/cm(2), however, appeared to result in massive melting and led to irregular morphology. The mechanism and the implications of the current findings will be discussed. Arrays of YBCO sub-micron dots with T(c) = 89.7 K were obtained. PMID:19065200

  2. A long-term soil structure observatory for post-compaction soil structure evolution: design and initial soil structure recovery observations

    NASA Astrophysics Data System (ADS)

    Keller, Thomas; Colombi, Tino; Ruiz, Siul; Grahm, Lina; Reiser, René; Rek, Jan; Oberholzer, Hans-Rudolf; Schymanski, Stanislaus; Walter, Achim; Or, Dani

    2016-04-01

    Soil compaction due to agricultural vehicular traffic alters the geometrical arrangement of soil constituents, thereby modifying mechanical properties and pore spaces that affect a range of soil hydro-ecological functions. The ecological and economic costs of soil compaction are dependent on the immediate impact on soil functions during the compaction event, and a function of the recovery time. In contrast to a wealth of soil compaction information, mechanisms and rates of soil structure recovery remain largely unknown. A long-term (>10-yr) soil structure observatory (SSO) was established in 2014 on a loamy soil in Zurich, Switzerland, to quantify rates and mechanisms of structure recovery of compacted arable soil under different post-compaction management treatments. We implemented three initial compaction treatments (using a two-axle agricultural vehicle with 8 Mg wheel load): compaction of the entire plot area (i.e. track-by-track), compaction in wheel tracks, and no compaction. After compaction, we implemented four post-compaction soil management systems: bare soil (BS), permanent grass (PG), crop rotation without mechanical loosening (NT), and crop rotation under conventional tillage (CT). BS and PG provide insights into uninterrupted natural processes of soil structure regeneration under reduced (BS) and normal biological activity (PG). The two cropping systems (NT and CT) enable insights into soil structure recovery under common agricultural practices with minimal (NT) and conventional mechanical soil disturbance (CT). Observations include periodic sampling and measurements of soil physical properties, earthworm abundance, crop measures, electrical resistivity and ground penetrating radar imaging, and continuous monitoring of state variables - soil moisture, temperature, CO2 and O2 concentrations, redox potential and oxygen diffusion rates - for which a network of sensors was installed at various depths (0-1 m). Initial compaction increased soil bulk density

  3. Annealing effects on the structural and electrical properties of pulsed laser deposited BaPbO3 thin films

    NASA Astrophysics Data System (ADS)

    Satish, B.; Jayaraj, M. K.

    2014-01-01

    Conductive pervoskite BaPbO3 (BPO) films as potential electrodes for ferroelectric / tuneable applications were prepared by pulsed laser deposition technique at 600°C and at 0.1 mbar oxygen partial pressure on fused silica substrates. The structural and electrical properties of the films showed a dependence on annealing temperatures and the high oxygen ambient. XRD and standard four probe method with Hall setup were employed to investigate the dependence of growth conditions on crystal structure, resistivity and the carrier concentration on annealing the BPO thin films. The surface topography was analysed by AFM. The unannealed as deposited films showed the least resistivity of 1.6 × 10-2 ohm cm and a bandgap of 4.1eV.

  4. Structural Evolution and Li Dynamics in Nanophase Li3PS4 by Solid-State and Pulsed Field Gradient NMR

    SciTech Connect

    Gobet, Mallory; Greenbaum, Steve; Sahu, Gayatri; Liang, Chengdu

    2014-01-01

    The ceramic lithium ion conductor -Li3PS4 has a disordered and nanoporous structure that leads to an enhancement in ionic conductivity by some three orders of magnitude compared to the crystalline phase. The phase is prepared by thermal treatment of an inorganic-organic complex based on Li3PS4 and THF. Multinuclear (1H, 6,7Li, 31P) solid state NMR spectroscopy is used to characterize the structural phase evolution of the starting material at various steps in the thermal treatment. The phase formed after high temperature treatment is recognized as spectroscopically distinct from the bulk -Li3PS4 compound. Also formed is an amorphous lithium thiophosphate phase that is metastable as verified by annealing over an extended period. Lithium ion self-diffusion coefficients are measurable by standard pulsed gradient NMR methods at 100oC and with values consistent with the high ionic conductivity previously reported for this material.

  5. Pulsed ion beam source

    DOEpatents

    Greenly, John B.

    1997-01-01

    An improved pulsed ion beam source having a new biasing circuit for the fast magnetic field. This circuit provides for an initial negative bias for the field created by the fast coils in the ion beam source which pre-ionize the gas in the source, ionize the gas and deliver the gas to the proper position in the accelerating gap between the anode and cathode assemblies in the ion beam source. The initial negative bias improves the interaction between the location of the nulls in the composite magnetic field in the ion beam source and the position of the gas for pre-ionization and ionization into the plasma as well as final positioning of the plasma in the accelerating gap. Improvements to the construction of the flux excluders in the anode assembly are also accomplished by fabricating them as layered structures with a high melting point, low conductivity material on the outsides with a high conductivity material in the center.

  6. Parametric Geometry, Structured Grid Generation, and Initial Design Study for REST-Class Hypersonic Inlets

    NASA Technical Reports Server (NTRS)

    Ferlemann, Paul G.; Gollan, Rowan J.

    2010-01-01

    Computational design and analysis of three-dimensional hypersonic inlets with shape transition has been a significant challenge due to the complex geometry and grid required for three-dimensional viscous flow calculations. Currently, the design process utilizes an inviscid design tool to produce initial inlet shapes by streamline tracing through an axisymmetric compression field. However, the shape is defined by a large number of points rather than a continuous surface and lacks important features such as blunt leading edges. Therefore, a design system has been developed to parametrically construct true CAD geometry and link the topology of a structured grid to the geometry. The Adaptive Modeling Language (AML) constitutes the underlying framework that is used to build the geometry and grid topology. Parameterization of the CAD geometry allows the inlet shapes produced by the inviscid design tool to be generated, but also allows a great deal of flexibility to modify the shape to account for three-dimensional viscous effects. By linking the grid topology to the parametric geometry, the GridPro grid generation software can be used efficiently to produce a smooth hexahedral multiblock grid. To demonstrate the new capability, a matrix of inlets were designed by varying four geometry parameters in the inviscid design tool. The goals of the initial design study were to explore inviscid design tool geometry variations with a three-dimensional analysis approach, demonstrate a solution rate which would enable the use of high-fidelity viscous three-dimensional CFD in future design efforts, process the results for important performance parameters, and perform a sample optimization.

  7. In-situ structural integrity evaluation for high-power pulsed spallation neutron source - Effects of cavitation damage on structural vibration

    NASA Astrophysics Data System (ADS)

    Wan, Tao; Naoe, Takashi; Futakawa, Masatoshi

    2016-01-01

    A double-wall structure mercury target will be installed at the high-power pulsed spallation neutron source in the Japan Proton Accelerator Research Complex (J-PARC). Cavitation damage on the inner wall is an important factor governing the lifetime of the target-vessel. To monitor the structural integrity of the target vessel, displacement velocity at a point on the outer surface of the target vessel is measured using a laser Doppler vibrometer (LDV). The measured signals can be used for evaluating the damage inside the target vessel because of cyclic loading and cavitation bubble collapse caused by pulsed-beam induced pressure waves. The wavelet differential analysis (WDA) was applied to reveal the effects of the damage on vibrational cycling. To reduce the effects of noise superimposed on the vibration signals on the WDA results, analysis of variance (ANOVA) and analysis of covariance (ANCOVA), statistical methods were applied. Results from laboratory experiments, numerical simulation results with random noise added, and target vessel field data were analyzed by the WDA and the statistical methods. The analyses demonstrated that the established in-situ diagnostic technique can be used to effectively evaluate the structural response of the target vessel.

  8. The Structure of Eukaryotic Translation Initiation Factor-4E from Wheat Reveals a Novel Disulfide Bond

    SciTech Connect

    Monzingo,A.; Dhaliwal, S.; Dutt-Chaudhuri, A.; Lyon, A.; Sadow, J.; Hoffman, D.; Robertus, J.; Browning, K.

    2007-01-01

    Eukaryotic translation initiation factor-4E (eIF4E) recognizes and binds the m{sup 7} guanosine nucleotide at the 5' end of eukaryotic messenger RNAs; this protein-RNA interaction is an essential step in the initiation of protein synthesis. The structure of eIF4E from wheat (Triticum aestivum) was investigated using a combination of x-ray crystallography and nuclear magnetic resonance (NMR) methods. The overall fold of the crystallized protein was similar to eIF4E from other species, with eight {beta}-strands, three {alpha}-helices, and three extended loops. Surprisingly, the wild-type protein did not crystallize with m{sup 7}GTP in its binding site, despite the ligand being present in solution; conformational changes in the cap-binding loops created a large cavity at the usual cap-binding site. The eIF4E crystallized in a dimeric form with one of the cap-binding loops of one monomer inserted into the cavity of the other. The protein also contained an intramolecular disulfide bridge between two cysteines (Cys) that are conserved only in plants. A Cys-to-serine mutant of wheat eIF4E, which lacked the ability to form the disulfide, crystallized with m{sup 7}GDP in its binding pocket, with a structure similar to that of the eIF4E-cap complex of other species. NMR spectroscopy was used to show that the Cys that form the disulfide in the crystal are reduced in solution but can be induced to form the disulfide under oxidizing conditions. The observation that the disulfide-forming Cys are conserved in plants raises the possibility that their oxidation state may have a role in regulating protein function. NMR provided evidence that in oxidized eIF4E, the loop that is open in the ligand-free crystal dimer is relatively flexible in solution. An NMR-based binding assay showed that the reduced wheat eIF4E, the oxidized form with the disulfide, and the Cys-to-serine mutant protein each bind m{sup 7}GTP in a similar and labile manner, with dissociation rates in the range of 20

  9. Short-Pulse Laser Sintering of Multilayer Hard Metal Coatings: Structure and Wear Behavior

    NASA Astrophysics Data System (ADS)

    Kharanzhevskiy, Evgeny; Ipatov, Alexey; Nikolaeva, Irina; Zakirova, Raushaniya

    2015-06-01

    This paper reports on the phase composition and properties of multilayer hard metal coatings deposited on steel by a process variant of Selective laser melting (SLM). The process is based on layer-wise short-pulse laser sintering of high-dispersive WC-Co powder on a steel substrate. High temperature in the molten zone and chemical interaction with the substrate explain high level of adhesion strength between the coating and the substrate. The technique allows obtaining both high quality hard-metal multilayer gradient coatings with thickness up to 200 μm, density near to the theoretical density (TD), hardness up to 21 GPa and complex 3D objects by layer-wise powder based process such as SLM.

  10. Effect of pulsed ion irradiation on the electronic structure of multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Bolotov, V. V.; Korusenko, P. M.; Nesov, S. N.; Povoroznyuk, S. N.

    2014-04-01

    The effect of pulsed ion irradiation and vacuum annealing on the ratio of sp 2- and sp 3-hybridized orbitals of carbon atoms in the layers of oriented multi-walled carbon nanotubes has been studied by analyzing the photoemission spectra of the C1 s core level and the valence band of carbon, which were obtained using the equipment of the BESSY II Russian-German beamline of synchrotron radiation and a Riber analytical system. It has been shown that the ion irradiation leads to a significant decrease in the fraction of atoms with the sp 3 hybridization of electrons. On the contrary, the annealing reduces the fraction of the sp 3-component in the spectra of carbon. Typical features of the valence band of multi-walled carbon nanotubes in the annealed and irradiated states have been established.

  11. Local Structure and Electrical Performance of Pulsed Laser Deposited CdTe/CdS Thin-Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Nabizadeh, Arya; Lesinski, Darren; Cerqueira, Luis; Sahiner, Mehmet; Sahiner-Amscl Team

    2015-03-01

    The photovoltaic thin films of CdS/CdTe were prepared by pulsed laser deposition (PLD) on indium tin oxide (ITO) coated glass. The local structural variations in the thin films around Cd atom upon variations in the thin film growth parameters were investigated by X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS) and x-ray diffraction. X-ray absorption spectroscopy measurements were performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The effect of the thicknesses of the CdS and CdTe layers, laser energy and the substrate temperature on the local crystal structure and coordination around the Cd atoms were investigated through quantitative multiple scattering analysis and modeling of the x-ray absorption spectroscopy data. The induced local structural modifications upon varying synthesis conditions are correlated with the electrical performance of these photovoltaic thin-films. The quantitative multiple scattering analyses and modeling of X-ray absorption spectroscopy data revealed the local environment around the Cd atoms are highly sensitive to thin film deposition parameters and the variations of the Cd local structure influences interface quality consequently, affect the electrical performance of these photovoltaic thin films. This work is supported by NSF Award #:DMI-0420952 and Research Corporation Award #:CC6405 and New Jersey Space Grant Consortium.

  12. ELECTRICAL PULSE COUNTER APPARATUS

    DOEpatents

    Kaufman, W.M.; Jeeves, T.A.

    1962-09-01

    A progressive electrical pulse counter circuit rs designed for the counting of a chain of input pulses. The circuit employs a series of direct connected bistable counting stages simultaneously pulsed by each input pulse and a delay means connected between each of the stages. Each bistable stage has two d-c operative states, which stage, when in its initial state, prevents the next succeeding stage from changing its condition when the latter stage is pulsed. Since the delay circuits between the stages prevents the immediate decay of the d-c state of each stage when the stages are pulsed, only one stage will change its state for each input pulse, thereby providing progressive stage-by-stage counting. (AEC)

  13. Effect of bow-type initial imperfection on reliability of minimum-weight, stiffened structural panels

    NASA Technical Reports Server (NTRS)

    Stroud, W. Jefferson; Krishnamurthy, Thiagaraja; Sykes, Nancy P.; Elishakoff, Isaac

    1993-01-01

    Computations were performed to determine the effect of an overall bow-type imperfection on the reliability of structural panels under combined compression and shear loadings. A panel's reliability is the probability that it will perform the intended function - in this case, carry a given load without buckling or exceeding in-plane strain allowables. For a panel loaded in compression, a small initial bow can cause large bending stresses that reduce both the buckling load and the load at which strain allowables are exceeded; hence, the bow reduces the reliability of the panel. In this report, analytical studies on two stiffened panels quantified that effect. The bow is in the shape of a half-sine wave along the length of the panel. The size e of the bow at panel midlength is taken to be the single random variable. Several probability density distributions for e are examined to determine the sensitivity of the reliability to details of the bow statistics. In addition, the effects of quality control are explored with truncated distributions.

  14. Structural health and prognostics management for offshore wind turbines : an initial roadmap.

    SciTech Connect

    Griffith, Daniel Todd; Resor, Brian Ray; White, Jonathan Randall; Paquette, Joshua A.; Yoder, Nathanael C.

    2012-12-01

    Operations and maintenance costs for offshore wind plants are expected to be significantly higher than the current costs for onshore plants. One way in which these costs may be able to be reduced is through the use of a structural health and prognostic management system as part of a condition based maintenance paradigm with smart load management. To facilitate the creation of such a system a multiscale modeling approach has been developed to identify how the underlying physics of the system are affected by the presence of damage and how these changes manifest themselves in the operational response of a full turbine. The developed methodology was used to investigate the effects of a candidate blade damage feature, a trailing edge disbond, on a 5-MW offshore wind turbine and the measurements that demonstrated the highest sensitivity to the damage were the local pitching moments around the disbond. The multiscale method demonstrated that these changes were caused by a local decrease in the blade's torsional stiffness due to the disbond, which also resulted in changes in the blade's local strain field. Full turbine simulations were also used to demonstrate that derating the turbine power by as little as 5% could extend the fatigue life of a blade by as much as a factor of 3. The integration of the health monitoring information, conceptual repair cost versus damage size information, and this load management methodology provides an initial roadmap for reducing operations and maintenance costs for offshore wind farms while increasing turbine availability and overall profit.

  15. Development and initial validation of the Structured Interview for Self-Destructive Behaviors.

    PubMed

    Carlson, Eve B; McDade-Montez, Elizabeth; Armstrong, Judith; Dalenberg, Constance; Loewenstein, Richard J

    2013-01-01

    This article describes the initial validation of the Structured Interview for Self-Destructive Behaviors (SI-SDB), a brief interview assessing suicidality, self-injury, substance abuse, disordered eating, and risky sexual behaviors. Self-destructive behaviors present clinical and practical challenges for mental health treatment providers. Participants were 217 psychiatric inpatients with a wide variety of diagnoses who completed the SI-SDB and other measures of psychiatric symptoms, trauma exposure, and other childhood experiences. Internal validity analyses revealed an internally consistent measure with 2 major factors. External validity analyses indicated that the Substance Abuse and Disordered Eating scales were predictive of related psychiatric diagnoses. All scales except Substance Abuse were significantly correlated with psychiatric symptoms and childhood abuse. These findings indicate that the SI-SDB is a valid means of assessing 5 significant domains of dangerous behaviors in clinical and research settings. Further research on the reliability of reports over time, interrater consistency, and convergent validity with longer measures of the SI-SDB domains is needed. PMID:23627480

  16. Structured Analysis Tool interface to the Strategic Defense Initiative architecture dataflow modeling technique. Master's thesis

    SciTech Connect

    Austin, K.A.

    1989-12-01

    A software interface was designed and implemented that extends the use of Structured Analysis (SA) Tool (SAtool) as a graphical front-end to the Strategic Defense Initiative Architecture Dataflow Modeling Technique (SADMT). SAtool is a computer-aided software engineering tool developed at the Air Force Institute of Technology that automates the requirements analysis phase of software development using a graphics editor. The tool automates two approaches for documenting software requirements analysis: SA diagrams and data dictionaries. SADMT is an Ada based simulation framework that enables users to model real-world architectures for simulation purposes. This research was accomplished in three phases. During the first phase, entity-relationship (E-R) models of each software package were developed. From these E-R models, relationships between the two software packages were identified and used to develop a mapping from SAtool to SADMT. The next phase of the research was the development of a software interface in Ada based on the mapping developed in the first phase. A combination of a top-down and a bottom-up approach was used in developing the software.

  17. Development and Initial Validation of the Structured Interview for Self-Destructive Behaviors

    PubMed Central

    Carlson, Eve B.; McDade-Montez, Elizabeth; Armstrong, Judith; Dalenberg, Constance; Loewenstein, Richard J.

    2013-01-01

    This article describes initial validation of the Structured Interview for Self-Destructive Behaviors (SI-SDB), a brief interview assessing suicidality, self-injury, substance abuse, disordered eating and risky sexual behaviors. Self-destructive behaviors present clinical and practical challenges for mental health treatment providers. Participants were 217 psychiatric inpatients with a wide variety of diagnoses who completed the SI-SDB and other measures of psychiatric symptoms, trauma exposure, and other childhood experiences. Internal validity analyses revealed an internally consistent measure with two major factors. External validity analyses indicated that Substance Abuse and Disordered Eating scales were predictive of related psychiatric diagnoses. All scales except Substance Abuse were significantly correlated with psychiatric symptoms and childhood abuse. These findings indicate that the SI-SDB is a valid means to assess five significant domains of dangerous behaviors in clinical and research settings. Further research on the reliability of reports over time, interrater consistency, and convergent validity with longer measures of the SI-SDB domains are needed. PMID:23627480

  18. QUEST: QUantitative estimation of Earth's seismic sources and STructure: a European Initial Training Network

    NASA Astrophysics Data System (ADS)

    Igel, Heiner

    2010-05-01

    The Marie-Curie Initial Training Network QUEST joins scientists from 15 European partner institutions in the fields of exploration seismics, seismology, applied mathematics, high-performance computing, earthquake physics, physical inverse problems, geodynamics, from Departments of Mathematics, Physics, Earth and Computational Sciences, Oceanography and Exploration Geophysics. The main goal of QUEST is research and training in the development of strategies for seismic imaging using the increasing power of 3-D simulation technology. Existing methodologies are currently subject to a revolutionary change: While so far the observed information was severely reduced and approximate methods (e.g., ray theory) were used to determine Earth's structure, the massive increase in available computational resources allows us now to make use of the complete information contained in the observations. The QUEST objective is to integrate the various elements (wave propagation, high-performance computing, inverse problems) exploiting the synergies of the network expertise and develop the next generation of imaging tools for use on all spatial scales. The consortium is complemented by the formal partnership of one of the leading suppliers of geophysical technology to the oil and gas industry (Schlumberger Research) and Spectraseis AG (Zurich) exploiting passive imaging for industrial problems. The project offers funding for a substantial number of PhD and postdoc positons. More info at www.quest-itn.org.

  19. Constraining the initial conditions of the Universe using large scale structure

    SciTech Connect

    Agarwal, Nishant; Ho, Shirley; Shandera, Sarah E-mail: shirleyh@andrew.cmu.edu

    2014-02-01

    Primordial non-Gaussianity induces a scale-dependent bias in large scale structure (LSS) data, proportional to f{sub NL}/k{sup 2} for the exact local ansatz. Recent work has shown that models of inflation that predict a large squeezed limit bispectrum, such as multi-field models and single field inflation with a modified initial state, typically give rise to a generalized local ansatz, with the scale-dependent bias now proportional to A{sub NL}/k{sup α}. We use photometric measurements of the angular power spectrum of luminous red galaxies and quasars in the Sloan Digital Sky Survey Data Release Eight (SDSS DR8) with the above parameterization to constrain the amplitude A{sub NL} and scale-dependence α. We find that the marginalized upper limit on α is 2.0 at the 95% confidence level, consistent with the local ansatz. We also present Fisher forecasts for a survey of the same size as DR8 to assess the role of systematics in current photometric LSS data. Moreover, we present analytic results on the expected mass dependence of A{sub NL} for different inflationary models, which can be an important observable for future surveys, if primordial non-Gaussianity is non-zero.

  20. Spectroscopic detection and analysis of atomic emissions during industrial pulsed laser-drilling of structural aerospace alloys

    NASA Astrophysics Data System (ADS)

    Bright, Robin Michael

    The ability to adequately cool internal gas-turbine engine components in next-generation commercial and military aircraft is of extreme importance to the aerospace industry as the demand for high-efficiency engines continues to push operating temperatures higher. Pulsed laser-drilling is rapidly becoming the preferred method of creating cooling holes in high temperature components due a variety of manufacturing advantages of laser-drilling over conventional hole-drilling techniques. As cooling requirements become more demanding, the impact of drilling conditions on material removal behavior and subsequent effects on hole quality becomes critical. In this work, the development of emission spectroscopy as a method to probe the laser-drilling process is presented and subsequently applied to the study of material behavior of various structural aerospace materials during drilling. Specifically, emitted photons associated with energy level transitions within excited neutral atoms in material ejected during drilling were detected and analyzed. Systematic spectroscopic studies indicated that electron energy level populations and calculated electron temperatures within ejected material are dependent on both laser pulse energy and duration. Local thermal conditions detected by the developed method were related to the characteristics of ejected material during drilling and to final hole quality. Finally, methods of utilizing the observed relationships for spectroscopic process monitoring and control were demonstrated.

  1. Measuring the temporal structure of few-femtosecond free-electron laser X-ray pulses directly in the time domain

    NASA Astrophysics Data System (ADS)

    Helml, W.; Maier, A. R.; Schweinberger, W.; Grguraš, I.; Radcliffe, P.; Doumy, G.; Roedig, C.; Gagnon, J.; Messerschmidt, M.; Schorb, S.; Bostedt, C.; Grüner, F.; Dimauro, L. F.; Cubaynes, D.; Bozek, J. D.; Tschentscher, Th.; Costello, J. T.; Meyer, M.; Coffee, R.; Düsterer, S.; Cavalieri, A. L.; Kienberger, R.

    2014-12-01

    Short-wavelength free-electron lasers are now well established as essential and unrivalled sources of ultrabright coherent X-ray radiation. One of the key characteristics of these intense X-ray pulses is their expected few-femtosecond duration. No measurement has succeeded so far in directly determining the temporal structure or even the duration of these ultrashort pulses in the few-femtosecond range. Here, by deploying the so-called streaking spectroscopy technique at the Linac Coherent Light Source, we demonstrate a non-invasive scheme for temporal characterization of X-ray pulses with sub-femtosecond resolution. This method is independent of photon energy, decoupled from machine parameters, and provides an upper bound on the X-ray pulse duration. We measured the duration of the shortest X-ray pulses currently available to be on average no longer than 4.4 fs. Analysing the pulse substructure indicates a small percentage of the free-electron laser pulses consisting of individual high-intensity spikes to be on the order of hundreds of attoseconds.

  2. Ultrasonic damage detection of concrete structures by using pulse-echo sensor arrays and SAFT

    NASA Astrophysics Data System (ADS)

    Shi, Li-hua; Shao, Zhi-xue; Shao, Zhe

    2009-07-01

    In ultrasonic nondestructive testing (NDT) of concrete structures, the synthetic aperture focusing technique (SAFT) can improve the resolution of target and therefore gives a better image display of the B-scan data. In traditional B-scan of concrete structures the ultrasonic transducers are usually moved manually to detect the whole structure, the detection speed and the consistency in different test points are greatly affected. A PZT sensor array is designed in this paper to perform B-scan on large concrete structures more efficiently. The excitation of the sensor array and the data processing techniques for the array data are discussed. A signal processing approach is proposed to improve the consistency between different test channels in the array. Experiments on real structures show the embedded objects can be located accurately by using the array sensor and SAFT method.

  3. Advances in transient (pulsed) eddy current for inspection of multi-layer aluminum structures in the presence of ferrous fasteners

    NASA Astrophysics Data System (ADS)

    Desjardins, D. R.; Vallières, G.; Whalen, P. P.; Krause, T. W.

    2012-05-01

    An experimental investigation of the electromagnetic processes underlying transient (pulsed) eddy current inspection of aircraft wing structures in the vicinity of ferrous fasteners is performed. The separate effects of transient excitation of ferrous fastener and eddy currents induced in the surrounding aluminum structure are explored using a transmit-receive configuration with transient excitation of a steel rod, an aluminum plate with a bore hole and a steel rod through the bore hole. Observations are used to interpret results from a coupled driving and differential coil sensing unit applied to detect fatigue cracks emanating from bolt holes in aluminum structures with ferrous fasteners present. In particular, it is noted that abrupt magnetization of the fastener, by the probe's central driving unit, can transfer flux and consequently, induce strong eddy current responses deep within the aluminum structure in the vicinity of the bore hole. Rotation of the probe, centered over the fastener, permits detection of subsurface discontinuities, such as cracks, by the pair of differentially connected pickup coils.

  4. Structure of the protein core of translation initiation factor 2 in apo, GTP-bound and GDP-bound forms

    SciTech Connect

    Simonetti, Angelita; Fabbretti, Attilio; Hazemann, Isabelle; Jenner, Lasse; Gualerzi, Claudio O.; Klaholz, Bruno P.

    2013-06-01

    The crystal structures of the eubacterial translation initiation factor 2 in apo form and with bound GDP and GTP reveal conformational changes upon nucleotide binding and hydrolysis, notably of the catalytically important histidine in the switch II region. Translation initiation factor 2 (IF2) is involved in the early steps of bacterial protein synthesis. It promotes the stabilization of the initiator tRNA on the 30S initiation complex (IC) and triggers GTP hydrolysis upon ribosomal subunit joining. While the structure of an archaeal homologue (a/eIF5B) is known, there are significant sequence and functional differences in eubacterial IF2, while the trimeric eukaryotic IF2 is completely unrelated. Here, the crystal structure of the apo IF2 protein core from Thermus thermophilus has been determined by MAD phasing and the structures of GTP and GDP complexes were also obtained. The IF2–GTP complex was trapped by soaking with GTP in the cryoprotectant. The structures revealed conformational changes of the protein upon nucleotide binding, in particular in the P-loop region, which extend to the functionally relevant switch II region. The latter carries a catalytically important and conserved histidine residue which is observed in different conformations in the GTP and GDP complexes. Overall, this work provides the first crystal structure of a eubacterial IF2 and suggests that activation of GTP hydrolysis may occur by a conformational repositioning of the histidine residue.

  5. Effect of pulsed electric fields assisted acetylation on morphological, structural and functional characteristics of potato starch.

    PubMed

    Hong, Jing; Chen, Rujiao; Zeng, Xin-An; Han, Zhong

    2016-02-01

    Pulsed electric fields (PEF)-assisted acetylation of potato starch with different degree of substitution (DS) was prepared and effects of PEF strength, reaction time, starch concentration on DS were studied by response surface methodology. Results showed DS was increased from 0.054 (reaction time of 15 min) to 0.130 (reaction time of 60 min) as PEF strength increased from 3 to 5 kV/cm. External morphology revealed that acetylated starch with higher DS was aggravated more bulges and asperities. Fourier-transformed infrared spectroscopy confirmed the introduction of acetyl group through a band at 1730 cm(-1). The optimum sample (DS =0 .13) had lower retrogradation (39.1%), breakdown (155 BU) and setback value (149BU), while pasting temperature (62.2 °C) was slightly higher than non-PEF-assisted samples. These results demonstrated PEF treatment can be a potential and beneficial method for acetylation and achieve higher DS with shorter reaction time. PMID:26304315

  6. Investigation of pulsed eddy current probes for detection of defects in riveted structures

    NASA Astrophysics Data System (ADS)

    Yang, Binfeng; Zhang, Hui; Kang, Zhibin; Wang, Xiaofeng

    2013-09-01

    The fatigue crack is the threat to integrity and safety of fuselage lap-joints. Quantification of fatigue cracks by designing and utilisation of an optimised electromagnetic nondestructive evaluation probe can insure the flight safety of aircrafts. In this paper, pulsed eddy current (PEC) for detection and characterisation of fatigue cracks is investigated. The principle of PEC is analysed first, from which four different models of PEC probes are simulated in ANSYS. The signal features, namely zero-crossing time, zero-crossing frequency and peak value are extracted from the time and frequency domains in an effort to qualitatively compare the crack detectability of the four models. The sensitivities of the different probes to cracks are analysed quantitatively. The difference in detectability among the probes is investigated based on the working principle. Simulation results show that the probe consisting of two horizontal detecting coils along with a magnetic field shield focusing the flux has the highest detectability. The conclusions derived from the simulation study are also validated by experiments.

  7. Silicon and zinc telluride nanoparticles synthesized by pulsed laser ablation: Size distributions and nanoscale structure

    SciTech Connect

    Lowndes, D.H.; Rouleau, C.M.; Duscher, G.

    1997-08-01

    Size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure and target-substrate separation, D{sub ts}, using atomic force microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). For low energy density (Ed = 1.04 J/cm{sup 2}) ablation of Si into He at pressures of 0.5, 1.5, 4 and 10 torr, large nanoparticles were most numerous at D{sub ts} = 10 mm, with smaller nanoparticles found at 20 mm and 40 mm. For each D{sub ts} value a maximum of the mean nanoparticle diameter occurred for a He pressure near 6 torr, in contrast to other recent measurements in which the size of Si nanoparticles increased monotonically with the He pressure. High resolution Z-contrast transmission electron microscopy (HRZTEM) and electron energy loss spectroscopy (EELS) revealed that ZnTe nanoparticles formed by ablation into nitrogen at E{sub d} = 0.74 J/cm{sup 2} consisted of a crystalline ZnTe core surrounded by an amorphous ZnO shell. Growth defects and surface steps were clearly visible in the ZnTe crystalline core. The dependences of the mean diameter of ZnTe nanocrystals on nitrogen pressure and D{sub ts}, were qualitatively similar to those found for Si in He.

  8. Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films.

    PubMed

    Goyal, Rajendra N; Kaur, Davinder; Pandey, Ashish K

    2010-12-01

    Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode. PMID:21121292

  9. Structures of the Lowest Energy Nonamer and Decamer Water Clusters from Chirped-Pulse Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Perez, Cristobal; Pate, Brooks H.; Kisiel, Zbigniew; Temelso, Berhane; Shields, George C.

    2013-06-01

    In the breakthrough paper reporting observation and analysis of pure rotational spectra of the hexamer, heptamer and nonamer water clusters only one nonamer species was identified. The advances in this experiment, as described in the previous talk, allowed identification, among others, of five different nonamer, (H_2O)_9, conformers and of four different decamer, (H_2O)_{10}, conformers. Analysis of ^{18}O enriched spectra resulted in determination of oxygen framework geometries for three of the water nonamers and two of the water decamers. Determination of experimental geometries proved considerably more challenging than for the lighter clusters since isotopic changes to moments of inertia are proportionally smaller, and there are multiple instances of near-zero principal coordinates. There are also more indications of the effect of internal motions. These problems have been overcome by careful application of r_s and least-squares r_m techniques in concert with ab initio calculations so that it was possible to match the experimental and theoretical geometries unambiguously. The precise oxygen framework geometries obtained from chirped-pulse spectroscopy for water clusters ranging in size from the hexamer to the decamer allow, for the first time, to identify some common features of the underlying hydrogen bonding from direct experimental evidence. C. Perez, M. T. Muckle, D. P. Zaleski, N. A. Seifert, B. Temelso, G. C. Shields, Z. Kisiel, and B. H. Pate, Science {336}, 897 (2012).

  10. Skewness in large-scale structure and non-Gaussian initial conditions

    NASA Technical Reports Server (NTRS)

    Fry, J. N.; Scherrer, Robert J.

    1994-01-01

    We compute the skewness of the galaxy distribution arising from the nonlinear evolution of arbitrary non-Gaussian intial conditions to second order in perturbation theory including the effects of nonlinear biasing. The result contains a term identical to that for a Gaussian initial distribution plus terms which depend on the skewness and kurtosis of the initial conditions. The results are model dependent; we present calculations for several toy models. At late times, the leading contribution from the initial skewness decays away relative to the other terms and becomes increasingly unimportant, but the contribution from initial kurtosis, previously overlooked, has the same time dependence as the Gaussian terms. Observations of a linear dependence of the normalized skewness on the rms density fluctuation therefore do not necessarily rule out initially non-Gaussian models. We also show that with non-Gaussian initial conditions the first correction to linear theory for the mean square density fluctuation is larger than for Gaussian models.

  11. Differently Structured Advance Organizers Lead to Different Initial Schemata and Learning Outcomes

    ERIC Educational Resources Information Center

    Gurlitt, Johannes; Dummel, Sebastian; Schuster, Silvia; Nuckles, Matthias

    2012-01-01

    Does the specific structure of advance organizers influence learning outcomes? In the first experiment, 48 psychology students were randomly assigned to three differently structured advance organizers: a well-structured, a well-structured and key-concept emphasizing, and a less structured advance organizer. These were followed by a sorting task, a…

  12. Comparison of High Rate Laser Ablation and Resulting Structures Using Continuous and Pulsed Single Mode Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Knebel, T.; Streek, A.; Exner, H.

    This paper compares high rate laser ablation and resulting structures of aluminum by using both a continuous wave and a ns-pulsed single mode fiber laser of high average laser power. Two different scan technologies were applied for fast deflection of the laser beams. In this work, 2.5D laser processing was studied by using a high aperture galvanometer scanner with a maximum scan speed of 18 m/s. By contrast, considerably higher scan speeds up to 1,000 m/s were achieved by using the in-house developed polygon scanner system. The ablation rates and the processing rates per unit area were analyzed by means of the depths of line-scan ablation tracks and laser processed cavities. In addition, SEM photograph of the machining samples will be presented in order to evaluate the machining quality. Finally the feasibility of this high rate technology for industrial application is demonstrated by machining examples.

  13. Chirped-Pulsed Ftmw Spectrum of 4-FLUOROBENZYL Alcohol. Structure and Torsional Motions in the Ground Electronic State Phase

    NASA Astrophysics Data System (ADS)

    Bird, Ryan G.; Pratt, David W.; Neill, Justin L.; Pate, Brooks H.

    2010-06-01

    Previous studies of 4-fluorobenzyl alcohol (4FBA) in the gas phase have revealed the existence of tunneling splittings in its high resolution electronic spectrum. These could be attributed either to the ground S0 state, or the excited S1 state, or both. Motivated by this finding, we report here a study of the CP-FTMW spectrum of 4FBA. Its pure rotational spectrum was collected using a series of 250 MHz chirped pulses, over the frequency range of 6.5-18 GHz. Analysis of this data shows that 4FBA has a gauche structure and yields the V2 barrier for CH2OH torsion, from which the predicted tunneling splittings in the ground state have been extracted.

  14. Picosecond-pulse-induced two-photon fluorescence enhancement in biological material by application of grating waveguide structures

    NASA Astrophysics Data System (ADS)

    Selle, André; Kappel, Christoph; Bader, Mark Andreas; Marowsky, Gerd; Winkler, Kathrin; Alexiev, Ulrike

    2005-07-01

    We report enhancement of two-photon fluorescence (TPF) excitation in fluorescent dyes and fluorescently labeled biomolecules by exploiting the optical properties of double grating waveguide structures (DGWSs). Picosecond laser pulses generate a large evanescent field based on the guided mode phenomenon in the resonant DGWSs, which induces strong TPF signals from fluorescent dyes at the waveguide surface. By recording enhanced TPF signals of Rhodamine B and Lucifer Yellow under resonance conditions, a detection sensitivity of concentrations of approximately one dye molecule per 0.1 μm2 was achieved. For the first time to our knowledge, enhanced TPF signals of a Lucifer Yellow-labeled biomolecule (human self-peptide) in an aqueous environment are demonstrated. These results strongly encourage the use of DGWSs as enhancement platforms in modern biophysics and biotechnology for investigations of biological membranes and cells.

  15. Broadband Chirped-Pulse Fourier Transform Microwave Spectroscopy and Molecular Structure of the ARGON-{ {(Z)}}-1-CHLORO-2-FLUOROETHYLENE Complex

    NASA Astrophysics Data System (ADS)

    Marshall, Mark D.; Leung, Helen O.

    2012-06-01

    A chirped-pulse Fourier transform microwave spectrometer is used to obtain the 6--18 GHz rotational spectrum of the gas-phase complex formed between argon and (Z)-1-chloro-2-fluoroethylene. Both the 35Cl and 37Cl isotopologues are observed in natural abundance, and analysis of these spectra provides predictions for both singly-substituted 13C species with sufficient precision to allow their observation with minimal searching using the more sensitive narrow band Balle-Flygare cavity technique. The non-planar structure of the complex is similar to previously observed argon-fluoroethylene complexes with the argon atom closer to the fluorine than to the chlorine. In contrast to the argon-vinyl chloride and argon-cis-1,2-difluoroethylene complexes, tunneling of the argon atom between the two equivalent, non-planar geometries is not observed.

  16. Broadband Chirped-Pulse Fourier Transform Microwave Spectroscopy and Molecular Structure of the ARGON-1-CHLORO-1-FLUOROETHYLENE Complex

    NASA Astrophysics Data System (ADS)

    Marshall, Mark D.; Leung, Helen O.

    2013-06-01

    Previous studies of argon complexes with fluoroethylenes have revealed a preference for a geometry that maximizes the contact of the argon atom with heavy atoms on the fluoroethylene. We have observed a continuation of this trend when one of the fluorine atoms is replaced by chlorine. As part of a systematic study of the effect of chlorine substitution on intermolecular interactions, we have examined the argon-1-chloro-1-fluoroethylene complex, and obtained the 5.6 - 18.1 GHz chirped-pulse Fourier transform microwave spectrum of this species. Transitions for both the ^{35}Cl and ^{37}Cl isotopologues are observed and analyzed to provide geometric parameters for this non-planar complex. The structure is found to be similar to those of analogous complexes and agrees well with ab initio predictions. Z. Kisiel, P.W. Fowler, and A.C. Legon, J. Chem. Phys. {95,} 2283 (1991).

  17. Pulse-based non-thermal plasma (NTP) disrupts the structural characteristics of bacterial biofilms.

    PubMed

    Ferrell, James R; Shen, Fan; Grey, Scott F; Woolverton, Christopher J

    2013-01-01

    Bacterial biofilms were constructed in vitro with two pathogenic strains of Pseudomonas aeruginosa and Staphylococcus aureus using a modified, novel sequential bioreactor system. The structure and stability of bacterial biofilms were evaluated following exposure to non-thermal plasma (NTP) discharge. Mathematical software was used to determine structural changes as biofilms grew over the course of 7 days. Statistical modeling was also performed to assess the ability of NTP to affect the development of the biofilms over different periods of time. Several structural characteristics were significantly affected by NTP discharge whereas others were unaffected. Changes in the three-dimensional structure of the biofilm following introduction of NTP was not limited to one period of development. The mechanism for this phenomenon is not understood but is likely to be a dual, synergistic effect due to the composition of the reactive species and other plasma-associated molecules isolated previously in the NTP discharge used in this study. PMID:23682750

  18. Structuring by field enhancement of glass, Ag, Au, and Co thin films using short pulse laser ablation

    NASA Astrophysics Data System (ADS)

    Ulmeanu, M.; Zamfirescu, M.; Rusen, L.; Luculescu, C.; Moldovan, A.; Stratan, A.; Dabu, R.

    2009-12-01

    Single pulse laser ablation of glass, Ag, Au, and Co thin films was experimentally investigated with a laser pulse width of 400 ps at a wavelength of 532 nm both in the far and near fields. In the far-field regime, the electromagnetic field results from a focused laser beam, while the near-field regime is realized by a combination of the focused laser beam incident on a spherical colloidal particle. For the near-field experiments we have used polystyrene colloidal particles of 700 nm diameter self-assembled or spin coated on top of the surfaces. Laser fluences applied are in the range of 0.01-10 J/cm2. The diameter and the morphologies of the ablated holes were investigated by optical microscopy, profilometry, scanning electron microscopy, and atomic force microscopy. The dependence of the shape of the holes reflects the fluence regime and the thermophysical properties, i.e., melting temperature and thermal diffusivity of the surfaces involved in the experiments. We give quantitative data about the fluence threshold, diameter, and depth ablation dependence for the far and near fields and discuss their values with respect to the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain method by using the RSOFT software. The application of near fields allows structuring of the surfaces with structure dimension in the order of 100 nm and even below.

  19. Structuring by field enhancement of glass, Ag, Au, and Co thin films using short pulse laser ablation

    SciTech Connect

    Ulmeanu, M.; Zamfirescu, M.; Rusen, L.; Luculescu, C.; Moldovan, A.; Stratan, A.; Dabu, R.

    2009-12-01

    Single pulse laser ablation of glass, Ag, Au, and Co thin films was experimentally investigated with a laser pulse width of 400 ps at a wavelength of 532 nm both in the far and near fields. In the far-field regime, the electromagnetic field results from a focused laser beam, while the near-field regime is realized by a combination of the focused laser beam incident on a spherical colloidal particle. For the near-field experiments we have used polystyrene colloidal particles of 700 nm diameter self-assembled or spin coated on top of the surfaces. Laser fluences applied are in the range of 0.01-10 J/cm{sup 2}. The diameter and the morphologies of the ablated holes were investigated by optical microscopy, profilometry, scanning electron microscopy, and atomic force microscopy. The dependence of the shape of the holes reflects the fluence regime and the thermophysical properties, i.e., melting temperature and thermal diffusivity of the surfaces involved in the experiments. We give quantitative data about the fluence threshold, diameter, and depth ablation dependence for the far and near fields and discuss their values with respect to the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain method by using the RSOFT software. The application of near fields allows structuring of the surfaces with structure dimension in the order of 100 nm and even below.

  20. A period of structural plasticity at the axon initial segment in developing visual cortex

    PubMed Central

    Gutzmann, Annika; Ergül, Nursah; Grossmann, Rebecca; Schultz, Christian; Wahle, Petra; Engelhardt, Maren

    2014-01-01

    Cortical networks are shaped by sensory experience and are most susceptible to modifications during critical periods characterized by enhanced plasticity at the structural and functional level. A system particularly well-studied in this context is the mammalian visual system. Plasticity has been documented for the somatodendritic compartment of neurons in detail. A neuronal microdomain not yet studied in this context is the axon initial segment (AIS) located at the proximal axon segment. It is a specific electrogenic axonal domain and the site of action potential (AP) generation. Recent studies showed that structure and function of the AIS can be dynamically regulated. Here we hypothesize that the AIS shows a dynamic regulation during maturation of the visual cortex. We therefore analyzed AIS length development from embryonic day (E) 12.5 to adulthood in mice. A tri-phasic time course of AIS length remodeling during development was observed. AIS first appeared at E14.5 and increased in length throughout the postnatal period to a peak between postnatal day (P) 10 to P15 (eyes open P13–14). Then, AIS length was reduced significantly around the beginning of the critical period for ocular dominance plasticity (CP, P21). Shortest AIS were observed at the peak of the CP (P28), followed by a moderate elongation toward the end of the CP (P35). To test if the dynamic maturation of the AIS is influenced by eye opening (onset of activity), animals were deprived of visual input before and during the CP. Deprivation for 1 week prior to eye opening did not affect AIS length development. However, deprivation from P0 to 28 and P14 to 28 resulted in AIS length distribution similar to the peak at P15. In other words, deprivation from birth prevents the transient shortening of the AIS and maintains an immature AIS length. These results are the first to suggest a dynamic maturation of the AIS in cortical neurons and point to novel mechanisms in the development of neuronal

  1. Structure and Rotation of the Solar Interior: Initial Results from the MDI Medium-L Program

    NASA Technical Reports Server (NTRS)

    Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; DeForest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard J.; Daeppen W.; Duvall, T. L., Jr.

    1997-01-01

    The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to approximately 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle.

  2. QUEST: QUantitative estimation of Earth's sources and STructure: A European Initial Training Network

    NASA Astrophysics Data System (ADS)

    Igel, H.

    2009-04-01

    This Marie-Curie Initial Training Network joins lead scientists in the fields of exploration seismics, seismology, applied mathematics and high-performance computing, volcanic and seismic hazard, earthquake physics, physical inverse problems, geodynamics, from Departments of Mathematics, Physics, Earth and Computational Sciences, Oceanography and Exploration Geophysics. The main goal of QUEST is research and training in the development of strategies for automated seismic imaging using the increasing power of 3-D simulation technology. Existing methodologies are currently subject to a revolutionary change: While so far the observed information was severely reduced and approximate methods (e.g., ray theory) were used to determine Earth's structure, the massive increase in available computational resources allows us now to make use of the complete information contained in the observations. The QUEST objective is to integrate the various elements (wave propagation, high-performance computing, inverse problems) exploiting the synergies of the network expertise and develop the next generation of imaging tools for use on all spatial scales. The consortium is complemented by the formal partnership of the leading supplier of geophysical technology to the oil and gas industry (Schlumberger Research) and an expanding new company (Spectraseis AG, Zurich) exploiting passive imaging - the latest development in seismological imaging - for industrial problems. This is the first EU-wide project of its kind focusing on the scientific and technical challenges of the seismic imaging problem in the PetaFlop age employing 3-D high-performance computing methodologies. The project commencing in 2009 offers funding for a substantial number of PhD and postdoc positons. More info at www.quest-itn.org.

  3. APPLICATIONS OF LASERS AND OTHER TOPICS IN LASER PHYSICS AND TECHNOLOGY: Switching of a pulsed ionic diode through the bulk of an ion source with laser plasma initiation

    NASA Astrophysics Data System (ADS)

    Pleshakova, R. P.; Shikanov, A. E.

    1987-10-01

    An analysis was made of the results of an investigation of switching of a pulsed ionic diode through the bulk of an ion source with a laser plasma and a vacuum arc. The dependences of the neutron yield on the electrical energy of the diode were recorded and analyzed. The results indicated a possible way of simple construction of an acceleration tube with switching via a laser-plasma source.

  4. Investigation of internal magnetic structures and comparison with two-fluid equilibrium configurations in the multi-pulsing CHI on HIST

    NASA Astrophysics Data System (ADS)

    Nakayama, T.; Hanao, T.; Hirono, H.; Hyobu, T.; Ito, K.; Matsumoto, K.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.; Kanki, T.

    2012-10-01

    Spherical torus (ST) plasmas have been successfully maintained by Muti-pulsing Coaxial Helicity Injection (M-CHI) on HIST. This research object is to clarify relations between plasma characteristics and magnetic flux amplifications, and to compare magnetic field structures measured in the plasma interior to a flowing equilibrium calculation. Two-dimensional magnetic probe array has been newly introduced nearby the gun muzzle. The initial result shows that the diverter configuration with a single X-point can be formed after a bubble burst process of the plasma. The closed magnetic flux is surrounded by the open magnetic field lines intersecting with the gun electrodes. To evaluate the sustained configurations, we use the two-fluid equilibrium code containing generalized Bernoulli and Grad-Shafranov equations which was developed by L.C. Steinhauer. The radial profiles of plasma flow, density and magnetic fields measured on the midplane of the FC are consistent to the calculation. We also found that the poloidal shear flow generation is attributed to ExB drift and ion diamagnetic drift. In addition, we will study temporal behaviors of impurity lines such as OV and OVI during the flux amplification by VUV spectroscopic measurements.

  5. Structural Minimality, CP and the Initial State in Second Language Acquisition.

    ERIC Educational Resources Information Center

    Bhatt, Rakesh M.; Hancin-Bhatt, Barbara

    2002-01-01

    Considers the current debate on the initial state of second language (L2) acquisition and presents critical empirical evidence from Hindi learners of English-as-a-Second-Language that supports the claim that the complementizer phase (CP) is initially absent from the grammar of L2 speakers.(Author/VWL)

  6. Structural Studies of Pyrrole-Benzene Complexes by Chirped-Pulse Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lobsiger, Simon; Perez, Cristobal; Zaleski, Daniel P.; Seifert, Nathan A.; Pate, Brooks H.; Pfaffen, Chantal; Trachsel, Maria A.; Leutwyler, Samuel

    2013-06-01

    Non-covalent intermolecular interactions are important in structural biology. The N-H \\cdots π hydrogen bond between amino acid side chains is an important structural determinant and highly affects the secondary structure of proteins. The pyrrole-benzene complex can be viewed as a model system for studying these fundamental interactions. Previous IR and UV spectroscopic studies of the pyrrole-benzene complex by Dauster et al. support a T-shaped structure with an N-H \\cdots π hydrogen bond to the benzene ring. In order to obtain accurate structural information we have investigated the broadband rotational spectrum of the supersonic-jet cooled complexes of pyrrole with benzene and benzene-d_{1} in the 2-18 GHz frequency range. In addition to the hetero dimer we have also observed the two cyclic mixed trimers (pyrrole)_{2}-benzene and pyrrole-(benzene)_{2}. I. Dauster, C. A. Rice, P. Zielke, and M. A. Suhm Phys. Chem. Chem. Phys. {10}, 2827 (2008) C. Pfaffen, D. Infanger, P. Ottiger, H. M. Frey, and S. Leutwyler Phys. Chem. Chem. Phys. {13}, 14110 (2011)

  7. [The structural basis for fatigue failure initiation in glassy polymers]. Progress report, July 1991--October 1993

    SciTech Connect

    Yee, A.F.

    1993-12-31

    In this period efforts were devoted to studying the microstructural elements characterizing fatigue failure initiation, their evolution as a function of fatigue history, and role of external variables. Materials studied include polycarbonate (PC) and its derivatives with different relaxation behaviors, and epoxies with different cross-link densities. The majority of the studies were devoted to PC. Techniques used included mechanical testing, volumetry, density, DSC, x-ray scattering, positron annihilation, TEM, etc. Results suggest that craze initiation starts with expansion of ``elementary`` voids; that fatigue failure initiation in bulk, amorphous PC is generation of stable voids or ``proto-crazes``; that sizes of initial voids are generally in the range of tens of nanometers; that growth of proto- crazes into mature crazes occurs through expansion of voids and generation of new ones perpendicular to fatigue stress; and that fatigue craze initiation in bulk, amorphous PC even at below T{sub g} may involve disentanglement of polymer chains.

  8. Phase and Structural States Formed in Titanium Nickelide Subsurface Layers Exposed to High-Current Pulsed Electron Beams

    NASA Astrophysics Data System (ADS)

    Neyman, A. A.; Meisner, L. L.; Lotkov, A. I.; Semin, V. O.

    2015-06-01

    The behavior of the non-equilibrium states formed in the subsurface layers of a titanium nickelide-based alloy exposed to electron beams operated in the pulsed surface layer melting mode is investigated experimentally. Using methods of an x-ray diffraction analysis, and optical, scanning, and transmission electron microscopies, an 8-10 μm thick surface layer is shown to exhibit В2 phase-based structure undergoing inhomogeneous lattice microstrain. The core layer located at a depth of 10-20 μm below the irradiated surface contains a small amount (up to 5 vol.%) of a phase with В19' martensite structure along with a slightly distorted lattice and unmelted Ti2Ni phase particles. Electron beam treatment brings about changes in the chemical composition of the surface-modified layer which becomes enriched in titanium owing to the dissolution of the Ti2Ni phase particles therein. Transmission electron microscopy has not revealed martensite phases in the modified layer. The electron beam exposure of the titanium nickelide surface is assumed to give rise to nonequilibrium highly distorted bcc structure.

  9. Investigating dynamical information transfer in the brain following a TMS pulse: Insights from structural architecture.

    PubMed

    Amico, Enrico; Van Mierlo, Pieter; Marinazzo, Daniele; Laureys, Steven

    2015-01-01

    Transcranial magnetic stimulation (TMS) has been used for more than 20 years to investigate connectivity and plasticity in the human cortex. By combining TMS with high-density electroencephalography (hd-EEG), one can stimulate any cortical area and measure the effects produced by this perturbation in the rest of the cerebral cortex. The purpose of this paper is to investigate changes of information flow in the brain after TMS from a functional and structural perspective, using multimodal modeling of source reconstructed TMS/hd-EEG recordings and DTI tractography. We prove how brain dynamics induced by TMS is constrained and driven by its structure, at different spatial and temporal scales, especially when considering cross-frequency interactions. These results shed light on the function-structure organization of the brain network at the global level, and on the huge variety of information contained in it. PMID:26737511

  10. Reasonable structure for the discharge type plasma source. [In Pulsed Plasma Thruster

    SciTech Connect

    An, S.M.

    1987-01-01

    Experiments conducted with a magnetoplasma thruster in which plasma production and acceleration were treated separately indicate that different plasma source geometries have the most direct effect on energy conversion efficiency. An analysis of cup and tube type constraining structures shows the cup type to incur the greatest losses. It is noted that a parallel rail-type open structure such as that employed by the Chinese MDT-2A thruster leads to substantial discharge process dispersion. It is emphasized that the type and performance characteristics of a plasma source have a critical influence on thruster behavior. 5 references.

  11. Control of structural inheritance on thrust initiation and material transfer in accretionary wedges

    NASA Astrophysics Data System (ADS)

    Leever, Karen; Geersen, Jacob; Ritter, Malte; Lieser, Kathrin; Behrmann, Jan

    2016-04-01

    Faults in the incoming sediment layer are commonly observed in subduction zone settings and well developed in the incoming plate off Sumatra. To investigate how they affect the structural development of the accretionary wedge, we conducted a series of 2D analogue tectonic experiments in which a 2 cm thick quartz sand layer on top of a thin detachment layer of glass beads was pulled against a rigid backstop by a basal conveyor belt in a 20cm wide box with glass walls. A gap at the base of the back wall avoids entrainment of the glass beads. At regular spacing of either 2.3, 5.5 or 7.8 cm (fractions of the thrust sheet length in the reference model), conjugate pairs of weakness zones dipping 60deg were created by cutting the sand layer with a thin (1 mm) metal blade. Both the undisturbed sand and the pre-cuts have an angle of internal friction of ~29o, but their cohesion is different by 50 Pa (110 Pa for the undisturbed material, 60 Pa along the pre-cuts). Friction of the glass beads is ~24deg. The experiments are monitored with high resolution digital cameras; displacement fields derived from digital image correlation are used to constrain fault activity. In all experiments, a critically tapered wedge developed with a surface slope of 7.5deg. In the reference model (no weakness zones in the input section), the position of new thrust faults is controlled by the frontal slope break. The average length of the thrust sheets is 11 cm and the individual thrusts accommodate on average 8 cm displacement each. The presence of weakness zones causes thrust initiation at a position different from the reference case, and affects their dip. For a fault spacing of 7.8 cm (or 75% of the reference thrust sheet length), every single incoming weakness zone causes the formation of a new thrust, thus resulting in thrust sheets shorter than the equilibrium case. In addition, less displacement is accommodated on each thrust. As a consequence, the frontal taper is smaller than expected

  12. BLOCKING OSCILLATOR DOUBLE PULSE GENERATOR CIRCUIT

    DOEpatents

    Haase, J.A.

    1961-01-24

    A double-pulse generator, particuiarly a double-pulse generator comprising a blocking oscillator utilizing a feedback circuit to provide means for producing a second pulse within the recovery time of the blocking oscillator, is described. The invention utilized a passive network which permits adjustment of the spacing between the original pulses derived from the blocking oscillator and further utilizes the original pulses to trigger a circuit from which other pulses are initiated. These other pulses are delayed and then applied to the input of the blocking oscillator, with the result that the output from the oscillator circuit contains twice the number of pulses originally initiated by the blocking oscillator itself.

  13. Structure Study of the Chiral Lactide Molecules by Chirped-Pulse Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Bialkowska-Jaworska, Ewa; Kisiel, Zbigniew

    2011-06-01

    Lactide is a six member cyclic diester with two chiral centers that forms from lactic acid in the presence of heat and an acid catalyst. It can form either a homo-chiral (RR) structure with both methyl groups equatorial or a hetero-chiral (RS) structure where one methyl group is equatorial and the other methyl group is axial. Structurally lactide is similar to lactic acid dimer; however, the kinked ring is covalently bonded and two waters are lost. And unlike lactic acid dimer, which has a very small dipole moment, the dipole moment of lactide is on the order of 3 Debye. Here the microwave spectra of the highly rigid homo- and hetero-chiral lactides are presented, which were first assigned in a heated lactic acid spectrum where the chemistry took place in the reservoir nozzles. Further isotopic information from a commercial sample of predominately homo-chiral lactide was obtained leading to a Kraitchman substitution structure of the homo-chiral lactide. Preliminary results of the cluster of homo-chiral lactide with one water molecule attached are also presented.

  14. An Improved Analysis of the Sevoflurane-Benzene Structure by Chirped Pulse Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Seifert, Nathan A.; Perez, Cristobal; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Lesarri, Alberto; Vallejo, Montserrat; Cocinero, Emilio J.; Castano, Fernando; Kleiner, Isabelle

    2013-06-01

    Recent improvements to the 2-8 GHz CP-FTMW spectrometer at University of Virginia have improved the structural and spectroscopic analysis of the sevoflurane-benzene cluster. Previously reported results, although robust, were limited to a fit of the a-type transitions of the normal species in the determination of the six-fold barrier to benzene internal rotation. Structural analysis was limited to the benzene hydrogen atom positions using benzene-d_{1}. The increased sensitivity of the new 2-8 GHz setup allows for a full internal rotation analysis of the a- and c-type transitions of the normal species, which was performed with BELGI. A fit value for V_{6} of 32.868(11) cm^{-1} is determined. Additionally, a full substitution structure of the benzene carbon atom positions was determined in natural abundance. Also, new measurements of a sevoflurane/benzene-d_{1} mixture enabled detection of 33 of the 60 possible ^{2}D / ^{13}C double isotopologues. This abundance of isotopic data, a total of 45 isotopologues, enabled a full heavy atom least-squares r_{0} structure fit for the complex, including positions for all seven fluorines in sevoflurane. N. A. Seifert, D. P. Zaleski, J. L. Neill, B. H. Pate, A. Lesarri, M. Vallejo, E. J. Cocinero, F. Castańo. 67th OSU Int. Symp. On Mol. Spectrosc., Columbus, OH, 2012, MH13.

  15. Broadband Chirped-Pulse Fourier-Transform Microwave Spectroscopic Investigation of the Structures of Three Diethylsilane Conformers

    NASA Astrophysics Data System (ADS)

    Steber, Amanda L.; Obenchain, Daniel A.; Peebles, Rebecca A.; Peebles, Sean A.; Neill, Justin L.; Muckle, Matt T.; Pate, Brooks H.; Guirgis, Gamil A.

    2009-06-01

    The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Previously, Fourier-transform microwave rotational spectra were observed using a Balle-Flygare type instrument for the ^{28}Si isotopologues of the gauche-gauche, trans-gauche, and trans-trans conformers. In the present study, a broadband microwave spectrum was obtained at the University of Virginia, taking advantage of the ability to perform deep signal averaging to increase the measurement sensitivity. To obtain a full structural determination of the conformers of this molecule, spectra for the ^{29}Si, ^{30}Si, and single ^{13}C substitutions for the gauche-gauche, the trans-gauche, and the trans-trans species were assigned. Substitution (r_s) structures and inertial fit (r_0) structures were determined and a comparison between the experimental and ab initio structures will be presented. For the ^{28}Si isotopologues, the percent differences between the experimental and ab initio rotational constants are less than 1.5% for the trans-trans and trans-gauche and are between 2.0 and 5.0% for the gauche-gauche conformer. The structural parameters will be compared between this molecule, diethylgermane and other silicon containing molecules and the relative abundances of the three conformers will be discussed. S.A. Peebles, M.M. Serafin, R.A. Peebles, G.A. Guirgis, and H.D. Stidham J. Phys. Chem. A, (2009), DOI: 10.1021/jp811049n.

  16. Structure of correlated initial states that guarantee completely positive reduced dynamics

    NASA Astrophysics Data System (ADS)

    Lu, Xiao-Ming

    2016-04-01

    We use the Koashi-Imoto decomposition of the degrees of freedom of joint system-environment initial states to investigate the reduced dynamics. We show that a subset of joint system-environment initial states guarantees completely positive reduced dynamics if and only if the system privately owns all quantum degrees of freedom and can locally access the classical degrees of freedom, without disturbing all joint initial states in the given subset. Furthermore, we show that the quantum mutual information for such kinds of states must be independent of the quantum degrees of freedom.

  17. The conjugate passive margins of the eastern gulf of Aden : structure and oceanic initiation

    NASA Astrophysics Data System (ADS)

    D'Acremont, E.; Leroy, S.; Beslier, M. O.; Fournier, M.; Bellahsen, N.; Patriat, P.; Maia, M.

    2003-04-01

    The geophysical data set of the Encens-Sheba cruise in the eastern gulf of Aden allows us to define and compare the structure of the conjugate passive margins and to locate the continental ocean transition zone (COT). Between the Alula-Fartak and Socotra transform faults, the non-volcanic margins are segmented by two transfer fault zones trending N027°E. These transfer zones with left-lateral offsets define three N110°E trending segments. The two margins display titled blocks, horsts and grabens bounded by landward and seaward dipping faults, responsible for two syn-rift antithetic sequences observed on the seismic profile. Normal faulting prevails on the northern margin, with prominent basement rises and basins, and is less important on the southern margin. The latter being characterised by a deep basin at the toe of the continental slope in the vicinity of the continent-ocean transition. Moreover, the offsets along the transfer zones are greater on the northern margin than on the southern one. The conjugate margins are asymmetrical: the southern rifted domain is about twice as large as the northern one. This asymmetry could be due to reactivation of inherited faults. Indeed, the Jurassic rifting has affected the southern margin and not the northern one. The segmentation of the first oceanic spreading centre which is dated at least at 17.6 Ma by the magnetic anomaly An-5d identification seems to be directly related to the segmentation of the margins. The segmentation of the oceanic crust between the Alula-Fartak and Socotra transform faults evolves from three segments (an5d to an5) to two segments (an5 to an1). At the onset of the accretion process, the western segment propagated eastward at the expense of the eastern segment. Reconstruction of the oceanisation process suggests a complex non-uniform opening along the COT by punctiform initiation of seafloor spreading. Several arguments lead to propose a rifting model by mantle exhumation in the COT. The gravity

  18. Laser-induced periodic surface structures on 6H-SiC single crystals using temporally delayed femtosecond laser double-pulse trains

    NASA Astrophysics Data System (ADS)

    Song, Juan; Tao, Wenjun; Song, Hui; Gong, Min; Ma, Guohong; Dai, Ye; Zhao, Quanzhong; Qiu, Jianrong

    2016-04-01

    In this paper, a time-delay-adjustable double-pulse train with 800-nm wavelength, 200-fs pulse duration and a repetition rate of 1 kHz, produced by a collinear two-beam optical system like a Mach-Zehnder interferometer, was employed for irradiation of 6H-SiC crystal. The dependence of the induced structures on time delay of double-pulse train for parallel-polarization configuration was studied. The results show that as the time delay of collinear parallel-polarization dual-pulse train increased, the induced near-subwavelength ripples (NSWRs) turn from irregular rippled pattern to regularly periodic pattern and have their grooves much deepened. The characteristics timescale for this transition is about 6.24 ps. Besides, the areas of NSWR were found to decay exponentially for time delay from 0 to 1.24 ps and then slowly increase for time delay from 1.24 to 14.24 ps. Analysis shows that multiphoton ionization effect, grating-assisted surface plasmon coupling effect, and timely intervene of second pulse in a certain physical stage experienced by 6H-SiC excited upon first pulse irradiation may contribute to the transition of morphology details.

  19. Tribological and structural properties of titanium nitride and titanium aluminum nitride coatings deposited with modulated pulsed power magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ward, Logan

    The demand for economical high-performance materials has brought attention to the development of advanced coatings. Recent advances in high power magnetron sputtering (HPPMS) have shown to improve tribological properties of coatings. These coatings offer increased wear and oxidation resistance, which may facilitate the use of more economical materials in harsh applications. This study demonstrates the use of novel forms of HPPMS, namely modulated pulsed-power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS), for depositing TiN and Ti1-xAlxN tribological coatings on commonly used alloys, such as Ti-6Al-4V and Inconel 718. Both technologies have been shown to offer unique plasma characteristics in the physical vapor deposition (PVD) process. High power pulses lead to a high degree of ionization compared to traditional direct-current magnetron sputtering (DCMS) and pulsed magnetron sputtering (PMS). Such a high degree of ionization was previously only achievable by cathodic arc deposition (CAD); however, CAD can lead to increased macroparticles that are unfavorable in high friction and corrosive environments. MPPMS, DOMS, and other HPPMS techniques offer unique plasma characteristics and have been shown to produce coatings with refined grain structure, improved density, hardness, adhesion, and wear resistance. Using DOMS and MPPMS, TiN and Ti1-xAlxN coatings were deposited using PMS to compare microstructures and tribological performance. For Ti1-xAlxN, two sputtering target compositions, Ti 0.5Al0.5 and Ti0.3Al0.7, were used to evaluate the effects of MPPMS on the coating's composition and tribological properties. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize microstructure and crystallographic texture. Several tribological properties were evaluated including: wear rate, coefficient of friction, adhesion, and nanohardness. Results show that substrate

  20. Keratin film ablation for the fabrication of brick and mortar skin structure using femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Haq, Bibi Safia; Khan, Hidayat Ullah; Dou, Yuehua; Alam, Khan; Attaullah, Shehnaz; Zari, Islam

    2015-09-01

    The patterning of thin keratin films has been explored to manufacture model skin surfaces based on the "bricks and mortar" view of the relationship between keratin and lipids. It has been demonstrated that laser light is capable of preparing keratin-based "bricks and mortar" wall structure as in epidermis, the outermost layer of the human skin. "Bricks and mortar" pattern in keratin films has been fabricated using an ArF excimer laser (193 nm wavelength) and femtosecond laser (800 and 400 nm wavelength). Due to the very low ablation threshold of keratin, femtosecond laser systems are practical for laser processing of proteins. These model skin structures are fabricated for the first time that will help to produce potentially effective moisturizing products for the protection of skin from dryness, diseases and wrinkles.

  1. Regulatory focus as a mediator of the influence of initiating structure and servant leadership on employee behavior.

    PubMed

    Neubert, Mitchell J; Kacmar, K Michele; Carlson, Dawn S; Chonko, Lawrence B; Roberts, James A

    2008-11-01

    In this research, the authors test a model in which the regulatory focus of employees at work mediates the influence of leadership on employee behavior. In a nationally representative sample of 250 workers who responded over 2 time periods, prevention focus mediated the relationship of initiating structure to in-role performance and deviant behavior, whereas promotion focus mediated the relationship of servant leadership to helping and creative behavior. The results indicate that even though initiating structure and servant leadership share some variance in explaining other variables, each leadership style incrementally predicts disparate outcomes after controlling for the other style and dispositional tendencies. A new regulatory focus scale, the Work Regulatory Focus (WRF) Scale, also was developed and initially validated for this study. Implications for the results and the WRF Scale are discussed. PMID:19025244

  2. Regulatory Focus as a Mediator of the Influence of Initiating Structure and Servant Leadership on Employee Behavior

    ERIC Educational Resources Information Center

    Neubert, Mitchell J.; Kacmar, K. Michele; Carlson, Dawn S.; Chonko, Lawrence B.; Roberts, James A.

    2008-01-01

    In this research, the authors test a model in which the regulatory focus of employees at work mediates the influence of leadership on employee behavior. In a nationally representative sample of 250 workers who responded over 2 time periods, prevention focus mediated the relationship of initiating structure to in-role performance and deviant…

  3. Teachers' Perceptions of Principals' Use of Consideration and Initiating Structure and the Relationships to Student Achievement and Teacher Turnover

    ERIC Educational Resources Information Center

    Adams, Edgar D.

    2008-01-01

    The purpose of this study was to determine if there was a significant difference between teachers' perceptions of principals' use of consideration and initiating structure and elementary school student achievement as measured by academic growth according to the results of North Carolina End of Grade tests for reading and math during the school…

  4. Describing small-scale structure in random media using pulse-echo ultrasound

    PubMed Central

    Insana, Michael F.; Wagner, Robert F.; Brown, David G.; Hall, Timothy J.

    2009-01-01

    A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J. J. Faran, J. Acoust. Soc. Am. 23, 405–418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed. PMID:2299033

  5. Study of hydrogenated silicene: The initialization model of hydrogenation on planar, low buckled and high buckled structures of silicene

    SciTech Connect

    Syaputra, Marhamni Wella, Sasfan Arman; Wungu, Triati Dewi Kencana; Purqon, Acep; Suprijadi

    2015-09-30

    We study the hydrogenation structures possessed by silicene i.e. planar (PL), low buckled (LB) and high buckled (HB). On those structures we found the hydrogenation process occurs with some particular notes. Hydrogen stable position on the silicene surface is determined by its initial configuration. We only considered the fully hydrogenated case with the formula unit (SiH){sub n} for all of these structures. Physical and electronic structure shift after the process are compared with hydrogenated graphene. Moreover, we observed a chemical process in the presence of hydrogen on the PL structure by nudged elastic band (NEB) which illustrates how hydrogen has a significant impact to the force barrier of the PL that changing it from its original structure.

  6. PULSE AMPLITUDE ANALYZER

    DOEpatents

    Gray, G.W.; Jensen, A.S.

    1957-10-22

    A pulse-height analyzer system of improved design for sorting and counting a series of pulses, such as provided by a scintillation detector in nuclear radiation measurements, is described. The analyzer comprises a main transmission line, a cathode-ray tube for each section of the line with its deflection plates acting as the line capacitance; means to bias the respective cathode ray tubes so that the beam strikes a target only when a prearranged pulse amplitude is applied, with each tube progressively biased to respond to smaller amplitudes; pulse generating and counting means associated with each tube to respond when the beam is deflected; a control transmission line having the same time constant as the first line per section with pulse generating means for each tube for initiating a pulse on the second transmission line when a pulse triggers the tube of corresponding amplitude response, the former pulse acting to prevent successive tubes from responding to the pulse under test. This arrangement permits greater deflection sensitivity in the cathode ray tube and overcomes many of the disadvantages of prior art pulse-height analyzer circuits.

  7. The Structure and Properties of Pulsed dc Sputtered Nanocrystalline NbN Coatings for Proton Exchange Membrane Fuel Cell.

    PubMed

    Chun, Sung-Yong

    2016-02-01

    Niobium nitride coatings for the surface modified proton exchange membrane fuel cells with various pulse parameters have been prepared using dc (direct current) and asymmetric-bipolar pulsed dc magnetron sputtering. The pulse frequency and the duty cycle were varied from 5 to 50 kHz and 50 to 95%, respectively. The deposition rate, grain size and resistivity of pulsed dc sputtered films were decreased when the pulse frequency increased, while the nano hardness of niobium nitride films increased. We present in detail coatings (e.g., deposition rate, grain size, prefer-orientation, resistivity and hardness). Our studies show that niobium nitride coatings with superior properties can be prepared using asymmetric-bipolar pulsed dc sputtering. PMID:27433732

  8. Structure of the fMet-tRNAfMet-binding domain of B.stearothermophilus initiation factor IF2

    PubMed Central

    Meunier, Sylvie; Spurio, Roberto; Czisch, Michael; Wechselberger, Rainer; Guenneugues, Marc; Gualerzi, Claudio O.; Boelens, Rolf

    2000-01-01

    The three-dimensional structure of the fMet-tRNAfMet -binding domain of translation initiation factor IF2 from Bacillus stearothermophilus has been determined by heteronuclear NMR spectroscopy. Its structure consists of six antiparallel β-strands, connected via loops, and forms a closed β-barrel similar to domain II of elongation factors EF-Tu and EF-G, despite low sequence homology. Two structures of the ternary complexes of the EF-Tu⋅aminoacyl-tRNA⋅ GDP analogue have been reported and were used to propose and discuss the possible fMet-tRNAfMet-binding site of IF2. PMID:10775275

  9. Influence of cloth structure on operational characteristics of pulse-jet cleaned filter bags

    SciTech Connect

    Hindy, K.T.; Sievert, J.; Loeffler, F.

    1987-01-01

    An investigation on the effect of the surface properties and the cloth structure of a filter medium on the operation of a filter bag was conducted using a pilot-scale testing device. The collection properties and the increase in the residual drop, as well as the mass of the residual dust embedded within the filter medium, were measured. Three filter media were investigated: a singed filter medium, a calendered filter medium, and one with a membrane-laminated surface. The experimental results obtained show that the operational characteristics of a filter bag is greatly influenced by the surface properties and the cloth structure of the filter medium. The calendered filter bag has an unfavorable operational quality concerning both the collection properties and the residual pressure drop. The hard thickening of the filter medium drives to the rapid clogging of the filter bag. In contrast, the other two filter media have favorable characteristics concerning the above two criteria. At the same time, it was found that after tests conducted for about 70 h each, the singed filter bag, compared with the membrane-laminated one, exhibits a lower residual pressure drop, although more particles are deposited inside. The lowest filtration cycle duration was recorded by the calendered medium, whereas the cleaning frequency by the other two media was nearly in the same range.

  10. Controlling Chaos Via Knowledge of Initial Condition for a Curved Structure

    NASA Technical Reports Server (NTRS)

    Maestrello, L.

    2000-01-01

    Nonlinear response of a flexible curved panel exhibiting bifurcation to fully developed chaos is demonstrated along with the sensitivity to small perturbation from the initial conditions. The response is determined from the measured time series at two fixed points. The panel is forced by an external nonharmonic multifrequency and monofrequency sound field. Using a low power time-continuous feedback control, carefully tuned at each initial condition, produces large long-term effects on the dynamics toward taming chaos. Without the knowledge of the initial conditions, control may be achieved by destructive interference. In this case, the control power is proportional to the loading power. Calculation of the correlation dimension and the estimation of positive Lyapunov exponents, in practice, are the proof of chaotic response.

  11. Formation of low-frequency periodic structures in a pulsed magnetron discharge

    NASA Astrophysics Data System (ADS)

    Kaziev, A. V.; Khodachenko, G. V.; Kharkov, M. M.

    2016-01-01

    Periodic plasma structures are observed in non-sputtering magnetron discharge (NSMD) that is the transient quasi-stationary low-voltage regime between the high-current magnetron discharge (HCIMD) and an arc. The fast camera imaging synchronized with the magnetic probe diagnostics reveals the correlation between the observed rotation of the plasma inhomogeneities and the magnetic field perturbation behaviour. The frequencies of the periodic processes fall into kHz-range. A simple analytical model of the ionization instability in crossed electric and magnetic fields is suggested for the low-pressure discharge case. Using the model, the possible ranges of wavelengths and frequencies for the plasma inhomogeneities are evaluated. The results show good agreement between the experimental data and theory.

  12. Micro pulse lidar

    NASA Technical Reports Server (NTRS)

    Spinhirne, James D.

    1993-01-01

    An eye safe, compact, solid state lidar for profiling atmospheric cloud and aerosol scattering has been demonstrated. The transmitter of the micropulse lidar is a diode pumped micro-J pulse energy, high repetition rate Nd:YLF laser. Eye safety is obtained through beam expansion. The receiver employs a photon counting solid state Geiger mode avalanche photodiode detector. Data acquisition is by a single card multichannel scaler. Daytime background induced quantum noise is controlled by a narrow receiver field-of-view and a narrow bandwidth temperature controlled interference filter. Dynamic range of the signal is limited by optical geometric signal compression. Signal simulations and initial atmospheric measurements indicate that systems built on the micropulse lidar concept are capable of detecting and profiling all significant cloud and aerosol scattering through the troposphere and into the stratosphere. The intended applications are scientific studies and environmental monitoring which require full time, unattended measurements of the cloud and aerosol height structure.

  13. Secondary RNA structure and nucleotide specificity contribute to internal initiation mediated by the human tau 5′ leader

    PubMed Central

    Veo, Bethany L.; Krushel, Leslie A.

    2012-01-01

    Mechanisms by which eukaryotic internal ribosomal entry sites (IRESs) initiate translation have not been well described. Viral IRESs utilize a combination of secondary/tertiary structure concomitant with sequence specific elements to initiate translation. Eukaryotic IRESs are proposed to utilize the same components, although it appears that short sequence specific elements are more common. In this report we perform an extensive analysis of the IRES in the human tau mRNA. We demonstrate that the tau IRES exhibits characteristics similar to viral IRESs. It contains two main structural domains that exhibit secondary interactions, which are essential for internal initiation. Moreover, the tau IRES is extremely sensitive to small nucleotide substitutions. Our data also indicates that the 40S ribosome is recruited to the middle of the IRES, but whether it scans to the initiation codon in a linear fashion is questioned. Overall, these results identify structural and sequence elements critical for tau IRES activity and consequently, provide a novel target to regulate tau protein expression in disease states including Alzheimer disease and other tauopathies. PMID:22995835

  14. Microsecond Rearrangements of Hydrophobic Clusters in an Initially Collapsed Globule Prime Structure Formation during the Folding of a Small Protein.

    PubMed

    Goluguri, Rama Reddy; Udgaonkar, Jayant B

    2016-07-31

    Determining how polypeptide chain collapse initiates structure formation during protein folding is a long standing goal. It has been challenging to characterize experimentally the dynamics of the polypeptide chain, which lead to the formation of a compact kinetic molten globule (MG) in about a millisecond. In this study, the sub-millisecond events that occur early during the folding of monellin from the guanidine hydrochloride-unfolded state have been characterized using multiple fluorescence and fluorescence resonance energy transfer probes. The kinetic MG is shown to form in a noncooperative manner from the unfolded (U) state as a result of at least three different processes happening during the first millisecond of folding. Initial chain compaction completes within the first 37μs, and further compaction occurs only after structure formation commences at a few milliseconds of folding. The transient nonnative and native-like hydrophobic clusters with side chains of certain residues buried form during the initial chain collapse and the nonnative clusters quickly disassemble. Subsequently, partial chain desolvation occurs, leading to the formation of a kinetic MG. The initial chain compaction and subsequent chain rearrangement appear to be barrierless processes. The two structural rearrangements within the collapsed globule appear to prime the protein for the actual folding transition. PMID:27370109

  15. The International Permafrost Association: new structure and initiatives for cryospheric research

    NASA Astrophysics Data System (ADS)

    May, I.; Lewkowicz, A. G.; Christiansen, H.; Romanovsky, V. E.; Lantuit, H.; Schrott, L.; Sergeev, D.; Wei, M.

    2012-12-01

    within Global Climate Models and promote the study of the carbon cycle and other biogeochemical cycles in permafrost regions that contribute to atmospheric greenhouse gas concentrations. Within the discussion of climate change and the organic carbon stored in the frozen ground, the IPA also fosters and supports the activities of the Global Terrestrial Network on Permafrost (GTN-P) sponsored by the Global Terrestrial Observing System, GTOS, and the Global Climate Observing System, GCOS, whose long-term goal is to obtain a comprehensive view of the spatial structure, trends, and variability of changes in the active layer thickness and permafrost temperature. A further important initiative of the IPA is the new Standing Committee on Outreach and Education that is responsible for the development and implementation of new outreach products and projects on permafrost for schools, universities, and the general public. In all of these activities, the IPA emphasizes the involvement of young researchers (especially through the Permafrost Young Researchers Network) as well as its international partner organizations.

  16. Composition, structure and properties of SiN x films fabricated by pulsed reactive closed-field unbalanced magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Yao, Zh. Q.; Yang, P.; Huang, N.; Sun, H.; Wan, G. J.; Leng, Y. X.; Chen, J. Y.

    2005-11-01

    Silicon nitride (SiNx) thin films are of special interest in both scientific research and industrial applications due to their remarkable properties such as high thermal stability, chemical inertness, high hardness and good dielectric properties. In this work, SiNx films were fabricated by pulsed reactive closed-field unbalanced magnetron sputtering of high purity single crystal silicon targets in an Ar-N2 mixture. The effect of N2 partial pressure on the film composition, chemical bonding configurations, surface morphology, surface free energy, optical and mechanical properties were investigated. We showed that with increased N2 partial pressure, the N to Si ratio (N/Si) in the film increased and N atoms are preferentially incorporated in the NSi3 stoichiometric configuration. It leads the Si-N network a tendency to chemical order. Films deposited at a high N2 fraction were consistently N-rich. The film surface transformed from a loose granular structure with microporosity to a homogeneous, continuous, smooth and dense structure. A progressive densification of the film microstructure occurs as the N2 fraction is increased. The reduced surface roughness and the increased N incorporation in the film give rise to the increased contact angle with double-distilled water from 24° to 49.6°. To some extent, the SiNx films deposited by pulsed magnetron sputtering are hydrophilic in nature. The as-deposited SiNx films exhibit good optical transparency in the visible region and the optical band gap Eopt can be varied from 1.68 eV for a-Si to 3.62 eV for SiNx films, depending on the synthesis parameters. With the increase of the N/Si atomic ratio, wear resistance of the SiNx films was improved, a consequence of increased hardness and elastic modulus. The SiNx films have lower friction coefficient and better wear resistance than 316L stainless steel under dry sliding friction, where the SiNx films experienced only fatigue wear.

  17. [Impact of an |A|B|S|-training initiative on |A|B|S|-structural quality of participating hospitals].

    PubMed

    Christoph, Anna; Ehm, Christine; de With, Katja

    2015-01-01

    The "ABS-training initiative" was funded by the German Ministry of Health as part of the German Antimicrobial Resistance Strategy (Deutsche Antibiotika-Resistenz-Strategie, DART) from 2009 until early 2014. The initiative was designed for clinicians and clinical pharmacists and contains several training units covering antiinfectives, infectious diseases and ABS strategies including the conduction of a research project at the participants' hospital. Participants who complete the four-weeks training initiative will become a certified "ABS Expert". 281 ABS Experts were asked to take part in a survey (staff for ABS, surveillance data about agents and consumption, ABS activity) to estimate the influence of the ABS-training initiative on the ABS-structural quality. The evaluation was performed using GrafStat (V 4.255), statistical software package for the evaluation of surveys. Ninety-two ABS Experts representing 92 hospitals participated in a questionnaire-based survey before and after completing the training initiative. Forty (44 %) hospitals appointed an ABS representative (+22 %) after completing the training initiative. Antibiotic surveillance data available as a report increased from 34 (40 %) to 54 (60 %) and correct data presentation (DDD or RDD/100 days) from 7 (8 %) to 40 (43 %). Proactive auditing of antiinfective prescribing improved from 54 (60 %) to 71 (78 %) in intensive care units, and from 28 (31 %) to 53 (58 %) on normal wards. Availability of local guidelines increased from 36 (39 %) to 52 (57 %). The "ABS Training Initiative" had a positive impact on ABS-structural quality regarding nomination of ABS-teams, surveillance data of antibiotic consumption, implementation of proactive auditing of antiinfective prescribing and availability of local guidelines. However, there is optimization potential in many sectors. The short time period between pre- and post-assessment and the ongoing personnel or time constraints need to be taken into account. PMID

  18. Initial Conditions Effects in the Population Dynamics of a Driven Semiconductor Quantum Well Structure

    SciTech Connect

    Voutsinas, Evangelos; Boviatsis, John

    2007-12-26

    We study Rabi oscillations between two subbands of a symmetric double quantum well that is coupled by a strong electromagnetic field. We use the effective nonlinear Bloch equations for the description of the system dynamics and present numerical results for different initial conditions of the system.

  19. Initial Development and Factor Structure of the Educator Test Stress Inventory

    ERIC Educational Resources Information Center

    von der Embse, Nathaniel P.; Kilgus, Stephen P.; Solomon, Hadley J.; Bowler, Mark; Curtiss, Caroline

    2015-01-01

    With the proliferation of test-based accountability policies, educators and students alike are under pressure to improve test performance. However, little is known regarding the stress experienced by educators in response to these policies. The purpose of this article is to describe the initial development and validation of a new measure of stress…

  20. Structures of minute virus of mice replication initiator protein N-terminal domain: Insights into DNA nicking and origin binding

    SciTech Connect

    Tewary, Sunil K.; Liang, Lingfei; Lin, Zihan; Lynn, Annie; Cotmore, Susan F.; Tattersall, Peter; Zhao, Haiyan; Tang, Liang

    2015-02-15

    Members of the Parvoviridae family all encode a non-structural protein 1 (NS1) that directs replication of single-stranded viral DNA, packages viral DNA into capsid, and serves as a potent transcriptional activator. Here we report the X-ray structure of the minute virus of mice (MVM) NS1 N-terminal domain at 1.45 Å resolution, showing that sites for dsDNA binding, ssDNA binding and cleavage, nuclear localization, and other functions are integrated on a canonical fold of the histidine-hydrophobic-histidine superfamily of nucleases, including elements specific for this Protoparvovirus but distinct from its Bocaparvovirus or Dependoparvovirus orthologs. High resolution structural analysis reveals a nickase active site with an architecture that allows highly versatile metal ligand binding. The structures support a unified mechanism of replication origin recognition for homotelomeric and heterotelomeric parvoviruses, mediated by a basic-residue-rich hairpin and an adjacent helix in the initiator proteins and by tandem tetranucleotide motifs in the replication origins. - Highlights: • The structure of a parvovirus replication initiator protein has been determined; • The structure sheds light on mechanisms of ssDNA binding and cleavage; • The nickase active site is preconfigured for versatile metal ligand binding; • The binding site for the double-stranded replication origin DNA is identified; • A single domain integrates multiple functions in virus replication.

  1. Design Features and Initial RF Performance of a Gradient Hardened 17 GHz TW Linac Structure

    SciTech Connect

    Haimson, J.; Mecklenburg, B.

    2009-01-22

    To avoid surface erosion damage and to assist in studying RF breakdown thresholds in 17 GHz TW linac structures, a gradient hardened structure has been fabricated with high temperature brazed and machined stainless steel surfaces located in the peak E-field region of the beam apertures and the peak H-field regions of the input coupler cavity. The microwave design parameters and physical dimensions of this 22 cavity, 120 degree phase advance structure were chosen to allow the high gradient performance to be compared against a similar design all-copper structure that has been tested in a dual ring, power recirculating amplifier system. The final design parameters of the gradient hardened structure are discussed; the influence of stainless steel RF losses on the power buildup of the resonant ring and on the structure gradient distribution are described; waveforms are shown of the unique ability of the power amplifier to rapidly quench RF breakdown discharges in the linac structure by automatically sensing and redirecting the RF source power to a matched load; and preliminary test results during high power RF processing of the gradient hardened linac structure are presented.

  2. Design Features and Initial RF Performance of a Gradient Hardened 17 GHz TW Linac Structure

    NASA Astrophysics Data System (ADS)

    Haimson, J.; Mecklenburg, B.

    2009-01-01

    To avoid surface erosion damage and to assist in studying RF breakdown thresholds in 17 GHz TW linac structures, a gradient hardened structure has been fabricated with high temperature brazed and machined stainless steel surfaces located in the peak E-field region of the beam apertures and the peak H-field regions of the input coupler cavity. The microwave design parameters and physical dimensions of this 22 cavity, 120 degree phase advance structure were chosen to allow the high gradient performance to be compared against a similar design all-copper structure that has been tested in a dual ring, power recirculating amplifier system. The final design parameters of the gradient hardened structure are discussed; the influence of stainless steel RF losses on the power buildup of the resonant ring and on the structure gradient distribution are described; waveforms are shown of the unique ability of the power amplifier to rapidly quench RF breakdown discharges in the linac structure by automatically sensing and redirecting the RF source power to a matched load; and preliminary test results during high power RF processing of the gradient hardened linac structure are presented.

  3. Investigation of variation of energy of laser beam on structural, electrical and optical properties of pulsed laser deposited CuO thin films

    SciTech Connect

    Dahiya, V. Kumar, A.; Kaur, G.; Mitra, A.

    2014-04-24

    In this paper, copper oxide (CuO) thin films have been deposited successfully by pulsed laser deposition technique using copper metal as target material. Thin films have been prepared under different energy of laser pulses ranging from 100mJ/pulse to 250 mJ/pulse. These films have been characterized for their structural, electrical and optical properties by using X-Ray Diffractometer (XRD), Four probe method and UV spectroscopy. Morphological and structural studies show that there is increase in crystallite size with the increase in energy of laser beam. Thus resulting in improved crystallinity and degree of orientation of the CuO thin films. Optoelectrical properties show direct relation between conductivity and energy of laser beam. Optical analysis of CuO thin films prepared under different energy of laser beam shows good agreement with structural analysis. The prepared CuO thin films show high absorbance in the UV and visible range and thus are suitable candidate for thin films solar cell application.

  4. The origin of changes in the electronic structure of oriented multi-walled carbon nanotubes under the influence of pulsed ion radiation

    NASA Astrophysics Data System (ADS)

    Bolotov, V. V.; Korusenko, P. M.; Nesov, S. N.; Povoroznyuk, S. N.; Knyazev, E. V.

    2014-10-01

    On the basis of spectra obtained through the X-ray Auger-electron spectroscopy (XAES) of carbon (C KVV) and X-ray photoelectron spectroscopy (XPS) of the carbon valence band using the equipment of the Russian-German beam line of the synchrotron radiation facility BESSY II and a Kratos Axis Ultra DLD analytical system, the influence of pulsed ion radiation on the ratio of sp2/sp3-hybridized orbitals of carbon atoms in layers of oriented multi-walled carbon nanotubes (MWCNTs) is investigated. It is shown that when the MWCNTs are subjected to ten pulses, a substantial increase in the proportion of carbon atoms in the sp3 hybridization state occurs compared with MWCNTs subjected to a single pulse. This increase is associated with the formation of thin (<10 nm) nanotubes and onion-like carbon, inside which masses of nanodiamond structures are observed in some cases.

  5. Numerical simulation of deformation and fracture of space protective shell structures from concrete and fiber concrete under pulse loading

    NASA Astrophysics Data System (ADS)

    Radchenko, P. A.; Batuev, S. P.; Radchenko, A. V.; Plevkov, V. S.

    2015-11-01

    This paper presents results of numerical simulation of interaction between aircraft Boeing 747-400 and protective shell of nuclear power plant. The shell is presented as complex multilayered cellular structure comprising layers of concrete and fiber concrete bonded with steel trusses. Numerical simulation was held three-dimensionally using the author's algorithm and software taking into account algorithms for building grids of complex geometric objects and parallel computations. The dynamics of stress-strain state and fracture of structure were studied. Destruction is described using two-stage model that allows taking into account anisotropy of elastic and strength properties of concrete and fiber concrete. It is shown that wave processes initiate destruction of shell cellular structure—cells start to destruct in unloading wave, originating after output of compression wave to the free surfaces of cells.

  6. Probing the Structure of the Mechanosensitive Channel of Small Conductance in Lipid Bilayers with Pulsed Electron-Electron Double Resonance

    PubMed Central

    Ward, Richard; Pliotas, Christos; Branigan, Emma; Hacker, Christian; Rasmussen, Akiko; Hagelueken, Gregor; Booth, Ian R.; Miller, Samantha; Lucocq, John; Naismith, James H.; Schiemann, Olav

    2014-01-01

    Mechanosensitive channel proteins are important safety valves against osmotic shock in bacteria, and are involved in sensing touch and sound waves in higher organisms. The mechanosensitive channel of small conductance (MscS) has been extensively studied. Pulsed electron-electron double resonance (PELDOR or DEER) of detergent-solubilized protein confirms that as seen in the crystal structure, the outer ring of transmembrane helices do not pack against the pore-forming helices, creating an apparent void. The relevance of this void to the functional form of MscS in the bilayer is the subject of debate. Here, we report PELDOR measurements of MscS reconstituted into two lipid bilayer systems: nanodiscs and bicelles. The distance measurements from multiple mutants derived from the PELDOR data are consistent with the detergent-solution arrangement of the protein. We conclude, therefore, that the relative positioning of the transmembrane helices is preserved in mimics of the cell bilayer, and that the apparent voids are not an artifact of detergent solution but a property of the protein that will have to be accounted for in any molecular mechanism of gating. PMID:24559986

  7. Probing local and electronic structure in Warm Dense Matter: single pulse synchrotron x-ray absorption spectroscopy on shocked Fe

    PubMed Central

    Torchio, Raffaella; Occelli, Florent; Mathon, Olivier; Sollier, Arnaud; Lescoute, Emilien; Videau, Laurent; Vinci, Tommaso; Benuzzi-Mounaix, Alessandra; Headspith, Jon; Helsby, William; Bland, Simon; Eakins, Daniel; Chapman, David; Pascarelli, Sakura; Loubeyre, Paul

    2016-01-01

    Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models. PMID:27246145

  8. Structural and electrical properties of different vanadium oxide phases in thin film form synthesized using pulsed laser deposition

    SciTech Connect

    Majid, S. S. Rahman, F.; Shukla, D. K.; Choudhary, R. J.; Phase, D. M.

    2015-06-24

    We present here the structural and electrical properties of the thin films of V{sub 2}O{sub 3} (Vanadium sesquioxide) and V{sub 5}O{sub 9}. Both these oxide phases, V{sub 2}O{sub 3} and V{sub 5}O{sub 9}, have beenachieved on (001) orientedSi substrate using the V{sub 2}O{sub 5} target by optimizing the deposition parameters using pulsed laser deposition technique (PLD).Deposited films were characterized by X-ray diffraction(XRD)and four probe temperature dependent resistivity measurements. XRD studies reveal the V{sub 2}O{sub 3} and V{sub 5}O{sub 9} phases and the amount of strain present in both these films. The temperature dependency of electrical resistivity confirmed the characteristic metal-insulator transitions (MIT) for both the films, V{sub 2}O{sub 3} and V{sub 5}O{sub 9}.

  9. Micro-structural, electrical and spectroscopic investigations of pulsed laser ablated palladium incorporated nanostructured tungsten oxide films.

    PubMed

    Lethy, K J; Beena, D; Pillai, V P Mahadevan; Suresh, K A

    2009-09-01

    Pure and Pd incorporated (0.5, 1 and 5 wt%) WO3 films are prepared on quartz substrates using pulsed laser ablation (PLD) technique in an oxygen ambient of 0.12 mbar, at a substrate temperature (Ts) of 873 K. Palladium incorporation effects on the microstructure, optical and electrical properties of tungsten oxide films are systematically investigated using techniques like X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), micro-Raman spectroscopy, UV-Vis absorption spectroscopy and temperature dependent electrical resistivity measurements. The micro-structural analysis by XRD and micro-Raman indicates that Pd addition can perturb the tungsten oxide lattice and suppress the grain growth. Optical band gap values of the films increases from 3.17 eV for pure WO3 to 3.29 eV for 5 wt% Pd incorporated WO3 films. All the films present high transparency in the visible spectral range. The electrical resistivity studies of the pure and Pd incorporated films done at room temperature and for the range of temperature; 170-450 K reveal that Pd addition can lower the resistivity of the WO3 thin films. Room temperature resistivity as well as activation energy of the film decreases exponentially with Pd incorporation concentration. Highly transparent, nanocrystalline and semiconducting WO3 films with low resistivity obtained by Pd incorporation can make WO3 suitable for microelectronics industry and for gas sensing applications. PMID:19928224

  10. Probing local and electronic structure in Warm Dense Matter: single pulse synchrotron x-ray absorption spectroscopy on shocked Fe

    NASA Astrophysics Data System (ADS)

    Torchio, Raffaella; Occelli, Florent; Mathon, Olivier; Sollier, Arnaud; Lescoute, Emilien; Videau, Laurent; Vinci, Tommaso; Benuzzi-Mounaix, Alessandra; Headspith, Jon; Helsby, William; Bland, Simon; Eakins, Daniel; Chapman, David; Pascarelli, Sakura; Loubeyre, Paul

    2016-06-01

    Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models.

  11. Probing local and electronic structure in Warm Dense Matter: single pulse synchrotron x-ray absorption spectroscopy on shocked Fe.

    PubMed

    Torchio, Raffaella; Occelli, Florent; Mathon, Olivier; Sollier, Arnaud; Lescoute, Emilien; Videau, Laurent; Vinci, Tommaso; Benuzzi-Mounaix, Alessandra; Headspith, Jon; Helsby, William; Bland, Simon; Eakins, Daniel; Chapman, David; Pascarelli, Sakura; Loubeyre, Paul

    2016-01-01

    Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models. PMID:27246145

  12. Structure and properties of the (HCl)2H2O cluster observed by chirped-pulse Fourier transform microwave spectroscopy.

    PubMed

    Kisiel, Zbigniew; Lesarri, Alberto; Neill, Justin L; Muckle, Matt T; Pate, Brooks H

    2011-08-21

    The rotational spectrum of the cyclic (HCl)(2)H(2)O cluster has been identified for the first time in the chirped pulse, Fourier transform microwave spectrum of a supersonically expanded HCl/H(2)O/Ar mixture. The spectrum was measured at frequencies 6-18.5 GHz, and transitions in two inversion-tunneling states, at close to 1 : 3 relative intensity, have been assigned for the parent species. The two single (37)Cl isotopic species, and the double (37)Cl species have been assigned in the natural abundance sample, and the (18)O and HDO species of the cluster were identified in isotopically enriched samples. The rich nuclear quadrupole hyperfine structure due to the presence of two chlorine nuclei has been satisfactorily fitted and provided useful information on the nonlinearity of intermolecular bonds in the cluster. The r(s) heavy atom geometry of the cluster was determined and the strongest bond in the intermolecular cycle r(O···HCl) = 3.126(3) Å, is found to be intermediate in length between the values in H(2)O···HCl and (H(2)O)(2)HCl. The fitted spectroscopic constants and derived molecular properties are compared with ab initio predictions, and a discussion of complexation effects in these three clusters is made. PMID:21743896

  13. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    NASA Astrophysics Data System (ADS)

    Sokolov, N. S.; Fedorov, V. V.; Korovin, A. M.; Suturin, S. M.; Baranov, D. A.; Gastev, S. V.; Krichevtsov, B. B.; Maksimova, K. Yu.; Grunin, A. I.; Bursian, V. E.; Lutsev, L. V.; Tabuchi, M.

    2016-01-01

    Pulsed laser deposition has been used to grow thin (10-84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (YIG) on (111)-oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

  14. Probing the structure of the mechanosensitive channel of small conductance in lipid bilayers with pulsed electron-electron double resonance.

    PubMed

    Ward, Richard; Pliotas, Christos; Branigan, Emma; Hacker, Christian; Rasmussen, Akiko; Hagelueken, Gregor; Booth, Ian R; Miller, Samantha; Lucocq, John; Naismith, James H; Schiemann, Olav

    2014-02-18

    Mechanosensitive channel proteins are important safety valves against osmotic shock in bacteria, and are involved in sensing touch and sound waves in higher organisms. The mechanosensitive channel of small conductance (MscS) has been extensively studied. Pulsed electron-electron double resonance (PELDOR or DEER) of detergent-solubilized protein confirms that as seen in the crystal structure, the outer ring of transmembrane helices do not pack against the pore-forming helices, creating an apparent void. The relevance of this void to the functional form of MscS in the bilayer is the subject of debate. Here, we report PELDOR measurements of MscS reconstituted into two lipid bilayer systems: nanodiscs and bicelles. The distance measurements from multiple mutants derived from the PELDOR data are consistent with the detergent-solution arrangement of the protein. We conclude, therefore, that the relative positioning of the transmembrane helices is preserved in mimics of the cell bilayer, and that the apparent voids are not an artifact of detergent solution but a property of the protein that will have to be accounted for in any molecular mechanism of gating. PMID:24559986

  15. Morphological and structural effects on tungsten targets produced by fusion plasma pulses from a table top plasma focus

    NASA Astrophysics Data System (ADS)

    Inestrosa-Izurieta, M. J.; Ramos-Moore, E.; Soto, L.

    2015-09-01

    A table top plasma focus device operating at hundreds of joules was used to simulate an equivalent damage factor than the obtained on the divertor in tokamak experiments. Using the ejected plasma produced after the pinch disruptions, the effects on tungsten targets from 50 cumulative plasma shocks with power fluxes per shot between 2.6 and 9200 kW cm-2 and with a duration time in the order of tens of nanoseconds (damage factor in the order of 100-103 (W cm-2)s1/2) were studied. Morphological analysis shows an increasing appearance of cracked surfaces with holes, fissures and defects, suggesting a potential progression of stress effects and a fast heat load that melts the surface, ending in thermal contractions that recrystallize the surface of the target. A structural analysis demonstrates a compressive stress development and suggests that part of the energy is released in the melting of the surface in case of a plasma shock with a power flux of 9.2 MW cm-2, 75 ns duration pulse, 2.5   ×   103 (W cm-2)s1/2 damage factor. How to increase the damage factor by one order of magnitude up to the expected value from type I ELMs on the ITER divertor, i.e. 104 (W cm-2)s1/2 is discussed.

  16. Structure of an archaeal heterotrimeric initiation factor 2 reveals a nucleotide state between the GTP and the GDP states

    PubMed Central

    Yatime, Laure; Mechulam, Yves; Blanquet, Sylvain; Schmitt, Emmanuelle

    2007-01-01

    Initiation of translation in eukaryotes and in archaea involves eukaryotic/archaeal initiation factor (e/aIF)1 and the heterotrimeric initiation factor e/aIF2. In its GTP-bound form, e/aIF2 provides the initiation complex with Met–tRNAiMet. After recognition of the start codon by initiator tRNA, e/aIF1 leaves the complex. Finally, e/aIF2, now in a GDP-bound form, loses affinity for Met–tRNAiMet and dissociates from the ribosome. Here, we report a 3D structure of an aIF2 heterotrimer from the archeon Sulfolobus solfataricus obtained in the presence of GDP. Our report highlights how the two-switch regions involved in formation of the tRNA-binding site on subunit γ exchange conformational information with α and β. The zinc-binding domain of β lies close to the guanine nucleotide and directly contacts the switch 1 region. As a result, switch 1 adopts a not yet described conformation. Moreover, unexpectedly for a GDP-bound state, switch 2 has the “ON” conformation. The stability of these conformations is accounted for by a ligand, most probably a phosphate ion, bound near the nucleotide binding site. The structure suggests that this GDP–inorganic phosphate (Pi) bound state of aIF2 may be proficient for tRNA binding. Recently, it has been proposed that dissociation of eIF2 from the initiation complex is closely coupled to that of Pi from eIF2γ upon start codon recognition. The nucleotide state of aIF2 shown here is indicative of a similar mechanism in archaea. Finally, we consider the possibility that release of Pi takes place after e/aIF2γ has been informed of e/aIF1 dissociation by e/aIF2β. PMID:18000047

  17. Electrical control of quantum-dot fine-structure splitting for high-fidelity hole spin initialization

    NASA Astrophysics Data System (ADS)

    Mar, J. D.; Baumberg, J. J.; Xu, X. L.; Irvine, A. C.; Williams, D. A.

    2016-01-01

    We demonstrate electrical control of the neutral exciton fine-structure splitting in a single InAs/GaAs self-assembled quantum dot by significantly reducing the splitting to near zero through the application of a vertical electric field in the fast electron tunneling regime. This is verified by performing high-resolution photocurrent spectroscopy of the two fine-structure split exciton eigenstates as a function of reverse bias voltage. Using the qubit initialization scheme for a quantum-dot hole spin based on rapid electric-field ionization of a spin-polarized exciton, our results suggest a practical approach towards achieving qubit initialization with near-unity fidelity in the absence of magnetic fields.

  18. Modelling the initial structure dynamics of soil and sediment exemplified for a constructed hydrological catchment

    NASA Astrophysics Data System (ADS)

    Maurer, Thomas; Schneider, Anna; Gerke, Horst H.

    2016-04-01

    The structure of a hydrological catchment is determined by the geometry of the boundaries and the spatial distribution of soil and sediment properties. Models of the 3D subsurface structure and the soil heterogeneity have often been built based on geostatistical approaches and conditional simulations for spatial interpolation between measurements. Here, an alternative model was proposed that generated 3D subsurface structures by imitating basic structures resulting from mass distribution processes. Instead of directly assuming stochastic variations of the subsurface structure, the present approach assumed stochastic variations in parameters of the process-based algorithms of the generator models. The constructed hydrological catchment "Hühnerwasser" located in the Lower Lusatia region of Brandenburg, Germany, was used as an example for the development of such a 3D structure generator model. Boundary geometries and changes in the surface topography due to erosion and sedimentation processes were quantified on the basis of digital elevation models (DEMs) derived from aerial photographs and terrestrial laser scanning information. Basic sediment properties came i) from a geological model of the parent material at the outcrop site, ii) from actual soil sample measurements on-site, and iii) based on stochastic texture variations. Sediment distributions were generated according to construction processes such as sediment dumping, particle segregation, and soil compaction. The resulting internal structures reflect the formation of spoil cones and surface compaction by machinery. The simulated 3D model scenarios of soil texture and bulk density distributions were incorporated in a gridded 3D volume model using the 3D software tool GoCAD (Paradigm Ltd.). This 3D distributed solid phase structure of the catchment allowed for a more direct comparison with observations using minimal invasive methods. By including structural changes over time (e.g., derived from DEM

  19. Early efforts to initiate the field of fiber optic smart structures at McDonnell Douglas

    NASA Astrophysics Data System (ADS)

    Udd, Eric

    1998-07-01

    McDonnell Douglas began efforts on fiber optic sensor technology in 1977 that resulted directly in the development of a technology base that was used in the mid 1980s to implement fiber optic nervous systems that later would be termed fiber optic smart structures. This paper overviews some of the early history associated with this program as well as a story of how the field of fiber optic smart structures got its name.

  20. PulseSoar

    SciTech Connect

    Carter, P.; Peglow, S.

    1992-07-21

    This paper is an introduction to the PulseSoar concept. PulseSoar is a hypervelocity airplane that uses existing airport facilities and current technologies to fly at the very edge of space. It will be shown that PulseSoar can fly between any two points on the globe in less than two hours with fuel efficiency exceeding current state of the art commercial airliners. In addition, it will be shown that PulseSoar avoids environmental issues concerning the ozone layer and sonic booms because of its unique flight profile. All of this can be achieved with current technology. PulseSoar does not require the development of enabling technology. It is a concept which can be demonstrated today. The importance of this idea goes beyond the technical significance`s of PulseSoar in terms of feasibility and performance. PulseSoar could provide a crucial economic advantage to America`s largest export market: commercial aircraft. PulseSoar is a breakthrough concept for addressing the emerging markets of long range and high speed aircraft. Application of PulseSoar to commercial transport could provide the US Aerospace industry a substantial lead in offering high speed/long range aircraft to the world`s airlines. The rapid emergence of a US developed high speed aircraft could also be important to our competitiveness in the Pacific Rim and South American economies. A quick and inexpensive demonstration vehicle is proposed to bang the concept to reality within two years. This discussion will address all the major technical subjects encompassed by PulseSoar and identifies several near-term, and low risk, applications which may be further explored with the initial demonstration vehicle. What is PulseSoar? PulseSoar could enable high speed, high altitude and long range flight without many of the difficulties encountered by traditional hypersonic vehicles.

  1. STRUTEX: A prototype knowledge-based system for initially configuring a structure to support point loads in two dimensions

    NASA Technical Reports Server (NTRS)

    Rogers, James L.; Feyock, Stefan; Sobieszczanski-Sobieski, Jaroslaw

    1988-01-01

    The purpose of this research effort is to investigate the benefits that might be derived from applying artificial intelligence tools in the area of conceptual design. Therefore, the emphasis is on the artificial intelligence aspects of conceptual design rather than structural and optimization aspects. A prototype knowledge-based system, called STRUTEX, was developed to initially configure a structure to support point loads in two dimensions. This system combines numerical and symbolic processing by the computer with interactive problem solving aided by the vision of the user by integrating a knowledge base interface and inference engine, a data base interface, and graphics while keeping the knowledge base and data base files separate. The system writes a file which can be input into a structural synthesis system, which combines structural analysis and optimization.

  2. The structure of the translational initiation factor IF1 from E.coli contains an oligomer-binding motif.

    PubMed Central

    Sette, M; van Tilborg, P; Spurio, R; Kaptein, R; Paci, M; Gualerzi, C O; Boelens, R

    1997-01-01

    The structure of the translational initiation factor IF1 from Escherichia coli has been determined with multidimensional NMR spectroscopy. Using 1041 distance and 78 dihedral constraints, 40 distance geometry structures were calculated, which were refined by restrained molecular dynamics. From this set, 19 structures were selected, having low constraint energy and few constraint violations. The ensemble of 19 structures displays a root-mean-square deviation versus the average of 0.49 A for the backbone atoms and 1.12 A for all atoms for residues 6-36 and 46-67. The structure of IF1 is characterized by a five-stranded beta-barrel. The loop connecting strands three and four contains a short 3(10) helix but this region shows considerably higher flexibility than the beta-barrel. The fold of IF1 is very similar to that found in the bacterial cold shock proteins CspA and CspB, the N-terminal domain of aspartyl-tRNA synthetase and the staphylococcal nuclease, and can be identified as the oligomer-binding motif. Several proteins of this family are nucleic acid-binding proteins. This suggests that IF1 plays its role in the initiation of protein synthesis by nucleic acid interactions. Specific changes of NMR signals of IF1 upon titration with 30S ribosomal subunit identifies several residues that are involved in the interaction with ribosomes. PMID:9135158

  3. Magnetic Properties and Structure of Iron-Nickel Nanoparticles and Thin Films Synthesized by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Ibrahim, Sally Ahmed

    The study of new combinations of self-assembled magnetic materials in nanoparticle and thin film form is becoming increasingly important with the continuous shrinking of data storage device size with higher densities. The work presented in this dissertation is focused towards synthesis, structural characterizations, and magnetic properties of an L10 iron-nickel (Fe50Ni50) phase that has a potential to replace noble metals based L10 magnetic materials, such as Ni-Pt, Fe-Pt, being used as recording media. Fe50Ni50 was fabricated using a pulsed laser disposition (PLD) method under various deposition conditions, the most important among which was the substrate temperature. The substrate temperature was varied all the way from liquid nitrogen boiling temperature of 77K (-196 ºC) to high temperatures up to 600 ºC. In order to understand and optimize the formation of L10 phase, the PLD method was used to fabricate FeNi in three distinct ways: (i) FeNi films were prepared using a FeNi composite (alloy) target, (ii) FeNi films were fabricated in a multilayered structure using sequential ablation of Fe and Ni targets, and (iii) FeNi thin films were fabricated in alumina (Al2O3)/FeNi/Al2O 3 sandwich structures. To promote the stabilization of L10 FeNi phase, a thin film layer of gold catalyst was deposited prior to the deposition of FeNi films. FeNi films deposited in the presence or absence of gold catalyst were annealed at 600°C for 1 hour to study effect of annealing that has been found to bring about significant alterations in structural and magnetic properties. The substrate materials such as silicon and sapphire were also found to play a significant role in the microstructural and magnetic properties of the FeNi films. The FeNi samples deposited at liquid nitrogen temperature were found to be completely glassy (amorphous), and they exhibited a perfect superparamagnetic behavior, making them good candidates for magnetic biomedical devices.

  4. Forgotten but not gone: an examination of fit between leader consideration and initiating structure needed and received.

    PubMed

    Lambert, Lisa Schurer; Tepper, Bennett J; Carr, Jon C; Holt, Daniel T; Barelka, Alex J

    2012-09-01

    We examined the effects of fit between leader consideration and initiating structure needed and received on employees' work-related attitudes (i.e., trust in the supervisor, job satisfaction, and affective commitment to the organization). Consistent with predictions that derive from the person-environment fit research tradition, results from Study 1 suggested that deficient amounts of both leadership behaviors were associated with unfavorable attitudinal outcomes. However, while excess levels of consideration were associated with favorable attitudinal outcomes, excess levels of initiating structure were associated with unfavorable attitudes, and for both forms of leadership, higher levels of absolute fit were associated with more favorable outcomes. Results from Study 2 suggested that attitudes generated by the fit between leadership needed and received influence employees' organizational citizenship behavior as reported by their supervisors. The relationship between consideration needed and received and subordinates' organizational citizenship behavior relating to individuals (OCBI) and organizational citizenship behavior relating to the organization itself (OCBO) was partially mediated by employees' trust in the supervisor, while the relationship between initiating structure needed and received and OCBI was fully mediated by trust in the supervisor, and for OCBO was partially mediated. PMID:22708919

  5. Characteristics of a pulsed chemical laser utilizing an H2-F2 mixture and initiated by radiation from an XeCl excimer laser

    NASA Astrophysics Data System (ADS)

    Gordon, E. B.; Matiushenko, V. I.; Sizov, V. D.

    1982-11-01

    Using He, Kr, Xe, N2 and SF6 as diluents, a study was undertaken of the influence of active mixture composition on the energy and temporal characteristics of an HF laser. A 1500 percent efficiency was obtained by an F2:O2:H2:SF6 = 7.5:0.75:2.5:3.5 mixture at a pressure of 110 Torr. Specific output energy was found to increase in proportion to both the initiation energy and the fuel mixture concentration for a given initiation energy. In the case of an F2:O2:H2:SF6 = 25:2.5:2.5:20 mixture at a pressure of 0.5 atm, an output energy of 38 J/liter was reached, with a concentration of atoms created by the UV radiation of F(zero) of approximately 2 x 10 to the 16th/cu cm.

  6. Investigation of pulsed electromagnetic field as a novel organic pre-sowing method on germination and initial growth stages of cotton.

    PubMed

    Bilalis, Dimitrios J; Katsenios, Nikolaos; Efthimiadou, Aspasia; Karkanis, Anestis; Efthimiadis, Panagiotis

    2012-06-01

    Two different pre-sowing techniques have been investigated for their influence in an important industrial plant, namely cotton. Priming methods are very useful for agricultural practices because they improve crop seedling establishment, especially when environmental conditions are not optimum. Pulsed electromagnetic fields have been found to promote germination and improve early growth characteristics of cotton seedlings. Such priming techniques are especially valuable in organic cultivation, where chemical compounds are prohibited. PEG treatment showed an enhancement in some measurements, however in some cases the results were not statistically different compared to control plants. In addition, PEG treatment is a sophisticated method that is far from agricultural practices and farmers. In this research, two different ages of seeds were used (1- and 2-year-old) in order to investigate the promotory effects of priming techniques. Magnetic field treatment of 15 min was found to stimulate germination percentage and to promote seeds, resulting in 85% higher values than control seeds under real field conditions. Furthermore, seeds that were treated with magnetic field performed better in terms of early-stage measurements and root characteristics. PMID:22268861

  7. Modeling and design of lossy waveguide structures for generation of broadband terahertz pulses through difference frequency mixing

    NASA Astrophysics Data System (ADS)

    Vallejo Monsalve, Felipe Antonio

    We present an integral coupled mode theory (CMT), suited to account for high optical losses, to model ultra-broadband terahertz (THz) waveguide emitters (0.1- 20 THz) based on difference frequency generation (DFG) pumped by femtosecond infrared (IR) optical pulses. This integral model works even in the situation where the DFG occurs between several IR and THz modes. We also present a simplified CMT approximation that reproduces the results of the rigorous integral CMT for situations where the THz generation is mediated through single-IR-mode to single-THz-mode interactions. Using the simplified approach we derive a new expression that incorporates loss effects into the coherence length for optical rectification (OR). The expression that we derived for the coherence length can be adapted to describe other second order nonlinear processes such as second harmonic generation. We apply both models to study waveguide emitters whose nonlinear cores are composed of poled guest-host electro-optic (EO) polymer composites, which belong to the 1mm symmetry class and have high nonlinearities. We apply the models to a generic, symmetric, five-layer, metal/cladding/core waveguide structure and provide design strategies for efficient ultra-broadband THz emitters. Two different design strategies are analyzed, one in which the waveguides are designed to have a single-IR-mode and a single-THz-mode guided within the structure, and other where the waveguide is made with a single-THz-mode but admits several IR guided modes. In both strategies the waveguide geometric parameters are optimized to obtain the highest THz conversion efficiencies and broader output bandwidth. The simplified CMT approach is much faster to implement than the integral CMT. Thus, we use the simplified approach to perform a parametric study for different waveguide parameters and pumping wavelengths, in the telecom and short wavelength infrared region, to establish under what conditions the five-layered structure

  8. Evolution of crystal structure during the initial stages of ZnO atomic layer deposition

    DOE PAGESBeta

    Boichot, R.; Tian, L.; Richard, M. -I.; Crisci, A.; Chaker, A.; Cantelli, V.; Coindeau, S.; Lay, S.; Ouled, T.; Guichet, C.; et al

    2016-01-05

    In this study, a complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films depend strongly on the nature of the interfacial bonds.

  9. What the Myddosome structure tells us about the initiation of innate immunity.

    PubMed

    Gay, Nicholas J; Gangloff, Monique; O'Neill, Luke A J

    2011-03-01

    Signaling by the toll-like receptor (TLR) and interleukin-1 receptor superfamily requires the adapter protein myeloid differentiation primary response protein 88 (MyD88). The recent determination of the structure of the so-called Myddosome provides us with new insights into the structural basis for innate immune signaling. Other information on the biochemistry and genetics of MyD88 and other adapters, such as MyDD adapter-like and TRIF-related adapter molecule, allows us to describe in some detail the signaling process activated by TLRs and provides new insights into the role these important proteins play in innate immunity. PMID:21269878

  10. Bayesian large-scale structure inference: initial conditions and the cosmic web

    NASA Astrophysics Data System (ADS)

    Leclercq, Florent; Wandelt, Benjamin

    2014-05-01

    We describe an innovative statistical approach for the ab initio simultaneous analysis of the formation history and morphology of the large-scale structure of the inhomogeneous Universe. Our algorithm explores the joint posterior distribution of the many millions of parameters involved via efficient Hamiltonian Markov Chain Monte Carlo sampling. We describe its application to the Sloan Digital Sky Survey data release 7 and an additional non-linear filtering step. We illustrate the use of our findings for cosmic web analysis: identification of structures via tidal shear analysis and inference of dark matter voids.

  11. Experimental Evaluation of Fatigue Crack Initiation from Corroded Hemispherical Notches in Aerospace Structural Materials

    NASA Technical Reports Server (NTRS)

    Garcia, Daniel B.; Forman, Royce; Shindo, David

    2010-01-01

    A test program was developed and executed to evaluate the influence of corroded hemispherical notches on the fatigue crack initiation and propagation in aluminum 7075-T7351, 4340 steel, and D6AC steel. Surface enhancements such as shot peening and laser shock peening were also incorporated as part of the test effort with the intent of improving fatigue performance. In addition to the testing, fracture mechanics and endurance limit based analysis methods were evaluated to characterize the results with the objective of challenging typical assumptions used in modeling fatigue cracks from corrosion pits. The results specifically demonstrate that the aluminum and steel alloys behave differently with respect to fatigue crack initiation from hemispherical corrosion pits. The aluminum test results were bounded by the fracture mechanics and endurance limit models while exhibiting a general insensitivity to the residual stress field generated by shot peening. The steel specimens were better characterized by the endurance limit fatigue properties and did exhibit sensitivities to residual stresses from the shot peening and laser shock peening

  12. The Model Parameter Estimation Experiment (MOPEX): Its structure, connection to other international initiatives and future directions

    SciTech Connect

    Wagener, T; Hogue, T; Schaake, J; Duan, Q; Gupta, H; Andreassian, V; Hall, A; Leavesley, G

    2006-05-08

    The Model Parameter Estimation Experiment (MOPEX) is an international project aimed at developing enhanced techniques for the a priori estimation of parameters in hydrologic models and in land surface parameterization schemes connected to atmospheric models. The MOPEX science strategy involves: database creation, a priori parameter estimation methodology development, parameter refinement or calibration, and the demonstration of parameter transferability. A comprehensive MOPEX database has been developed that contains historical hydrometeorological data and land surface characteristics data for many hydrologic basins in the United States (US) and in other countries. This database is being continuously expanded to include basins from various hydroclimatic regimes throughout the world. MOPEX research has largely been driven by a series of international workshops that have brought interested hydrologists and land surface modelers together to exchange knowledge and experience in developing and applying parameter estimation techniques. With its focus on parameter estimation, MOPEX plays an important role in the international context of other initiatives such as GEWEX, PUB and PILPS. This paper outlines the MOPEX initiative, discusses its role in the scientific community and briefly states future directions.

  13. Prosodic domain-initial effects on the acoustic structure of vowels

    NASA Astrophysics Data System (ADS)

    Fox, Robert Allen; Jacewicz, Ewa; Salmons, Joseph

    2003-10-01

    In the process of language change, vowels tend to shift in ``chains,'' leading to reorganizations of entire vowel systems over time. A long research tradition has described such patterns, but little is understood about what factors motivate such shifts. Drawing data from changes in progress in American English dialects, the broad hypothesis is tested that changes in vowel systems are related to prosodic organization and stress patterns. Changes in vowels under greater prosodic prominence correlate directly with, and likely underlie, historical patterns of shift. This study examines acoustic characteristics of vowels at initial edges of prosodic domains [Fougeron and Keating, J. Acoust. Soc. Am. 101, 3728-3740 (1997)]. The investigation is restricted to three distinct prosodic levels: utterance (sentence-initial), phonological phrase (strong branch of a foot), and syllable (weak branch of a foot). The predicted changes in vowels /e/ and /ɛ/ in two American English dialects (from Ohio and Wisconsin) are examined along a set of acoustic parameters: duration, formant frequencies (including dynamic changes over time), and fundamental frequency (F0). In addition to traditional methodology which elicits list-like intonation, a design is adapted to examine prosodic patterns in more typical sentence intonations. [Work partially supported by NIDCD R03 DC005560-01.

  14. The Model Parameter Estimation Experiment (MOPEX): Its structure, connection to other international initiatives and future directions

    USGS Publications Warehouse

    Wagener, T.; Hogue, T.; Schaake, J.; Duan, Q.; Gupta, H.; Andreassian, V.; Hall, A.; Leavesley, G.

    2006-01-01

    The Model Parameter Estimation Experiment (MOPEX) is an international project aimed at developing enhanced techniques for the a priori estimation of parameters in hydrological models and in land surface parameterization schemes connected to atmospheric models. The MOPEX science strategy involves: database creation, a priori parameter estimation methodology development, parameter refinement or calibration, and the demonstration of parameter transferability. A comprehensive MOPEX database has been developed that contains historical hydrometeorological data and land surface characteristics data for many hydrological basins in the United States (US) and in other countries. This database is being continuously expanded to include basins from various hydroclimatic regimes throughout the world. MOPEX research has largely been driven by a series of international workshops that have brought interested hydrologists and land surface modellers together to exchange knowledge and experience in developing and applying parameter estimation techniques. With its focus on parameter estimation, MOPEX plays an important role in the international context of other initiatives such as GEWEX, HEPEX, PUB and PILPS. This paper outlines the MOPEX initiative, discusses its role in the scientific community, and briefly states future directions.

  15. Using Molecular Initiating Events to Develop a Structural Alert Based Screening Workflow for Nuclear Receptor Ligands Associated with Hepatic Steatosis.

    PubMed

    Mellor, Claire L; Steinmetz, Fabian P; Cronin, Mark T D

    2016-02-15

    In silico models are essential for the development of integrated alternative methods to identify organ level toxicity and lead toward the replacement of animal testing. These models include (quantitative) structure-activity relationships ((Q)SARs) and, importantly, the identification of structural alerts associated with defined toxicological end points. Structural alerts are able both to predict toxicity directly and assist in the formation of categories to facilitate read-across. They are particularly important to decipher the myriad mechanisms of action that result in organ level toxicity. The aim of this study was to develop novel structural alerts for nuclear receptor (NR) ligands that are associated with inducing hepatic steatosis and to show the vast number of existing data that are available. Current knowledge on NR agonists was extended with data from the ChEMBL database (12,713 chemicals in total) of bioactive molecules and from studying NR ligand-binding interactions within the protein database (PDB, 624 human NR structure files). A computational structural alert based workflow was developed using KNIME from these data using molecular fragments and other relevant chemical features. In total, 214 structural features were recorded computationally as SMARTS strings, and therefore, they can be used for grouping and screening during drug development and hazard assessment and provide knowledge to anchor adverse outcome pathways (AOPs) via their molecular initiating events (MIEs). PMID:26787004

  16. Development and Initial Testing of a Structured Clinical Observation Tool to Assess Pharmacotherapy Competence

    ERIC Educational Resources Information Center

    Young, John Q.; Lieu, Sandra; O'Sullivan, Patricia; Tong, Lowell

    2011-01-01

    Objective: The authors developed and tested the feasibility and utility of a new direct-observation instrument to assess trainee performance of a medication management session. Methods: The Psychopharmacotherapy-Structured Clinical Observation (P-SCO) instrument was developed based on multiple sources of expertise and then implemented in 4…

  17. Mid-follicular phase pulses of inhibin B are absent in polycystic ovarian syndrome and are initiated by successful laparoscopic ovarian diathermy: a possible mechanism regulating emergence of the dominant follicle.

    PubMed

    Lockwood, G M; Muttukrishna, S; Groome, N P; Matthews, D R; Ledger, W L

    1998-05-01

    . Four women with PCOS whose anovulation was successfully treated with laparoscopic ovarian diathermy (LOD) underwent repeat venous sampling following LOD. Their serum inhibin B levels fell to the upper limit of the normal range (160 +/- 38.5) pg/mL, and pulsatility was initiated. It is possible that inhibin B pulses are being generated directly by the ovary in response to pulses of GnRH in the peripheral circulation, or indirectly in response to FSH pulses arising in the pituitary. The function of inhibin B pulses in the mid-follicular phase of the normal cycle remains to be elucidated, but the absence of the normal pulsatile pattern in women with PCOS, in conjunction with high basal levels of inhibin B arising from the multiple small follicles characteristic of the PCOS ovary, appears to reinforce the development of a large cohort of small, developmentally arrested, and ultimately atretic follicles in these patients. Initiation of normal inhibin B pulsatility by LOD in patients with polycystic ovaries appears to correlate with the post-operative onset of ovular cycles. PMID:9589683

  18. Tertiary structure and function of an RNA motif required for plant vascular entry to initiate systemic trafficking.

    PubMed

    Zhong, Xuehua; Tao, Xiaorong; Stombaugh, Jesse; Leontis, Neocles; Ding, Biao

    2007-08-22

    Vascular entry is a decisive step for the initiation of long-distance movement of infectious and endogenous RNAs, silencing signals and developmental/defense signals in plants. However, the mechanisms remain poorly understood. We used Potato spindle tuber viroid (PSTVd) as a model to investigate the direct role of the RNA itself in vascular entry. We report here the identification of an RNA motif that is required for PSTVd to traffic from nonvascular into the vascular tissue phloem to initiate systemic infection. This motif consists of nucleotides U/C that form a water-inserted cis Watson-Crick/Watson-Crick base pair flanked by short helices that comprise canonical Watson-Crick/Watson-Crick base pairs. This tertiary structural model was inferred by comparison with X-ray crystal structures of similar motifs in rRNAs and is supported by combined mutagenesis and covariation analyses. Hydration pattern analysis suggests that water insertion induces a widened minor groove conducive to protein and/or RNA interactions. Our model and approaches have broad implications to investigate the RNA structural motifs in other RNAs for vascular entry and to study the basic principles of RNA structure-function relationships. PMID:17660743

  19. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, Jr., C G; Throop, A; Eder, D; Kimbrough, J

    2007-08-28

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dots and D-dots, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetic codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a corresponding broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  20. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, C G; Throop, A; Eder, D; Kimbrough, J

    2008-02-04

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dot and D-dot probes, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from several hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetics codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a correspondingly broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  1. Pulse Oximetry

    MedlinePlus

    ... www.thoracic.org amount of gases (oxygen and carbon dioxide) that are in your blood. To get an ... Also, a pulse oximeter does not measure your carbon dioxide level. How accurate is the pulse oximeter? The ...

  2. Initial-boundary value problems for solid-fluid composite structures

    NASA Astrophysics Data System (ADS)

    Chinchaladze, N.; Gilbert, R. P.; Jaiani, G.; Kharibegashvili, S.; Natroshvili, D.

    2012-08-01

    We investigate a three-dimensional mixed initial-boundary value problem arising in the dynamical solid-fluid interaction theory. A 3D domain occupied by an incompressible and viscous Stokes fluid may be bounded or unbounded, while a domain occupied by an elastic body immersed in the fluid is assumed to be bounded. On the basis of the results obtained for an elastic inclusion of an arbitrary geometrical shape, we derive a special model and analyze in detail the case when an elastic inclusion is a thin prismatic shell, in particular a plate of variable thickness. Here, we apply I. Vekua's dimension reduction method in the elastic part which reduces 3D solid-3D fluid interaction problems to the 2D solid-3D fluid interaction problems and which is important from the practical point of view since it takes into account intrinsic differences of the dimensions of solid and fluids part. The main goal of the paper was to study the strain-stress state of the elastic part under the action of the Stokes flow. The corresponding mechanical model is described mathematically as a transmission problem for the linear Stokes system and the dynamical Lamé equations in the corresponding domains with appropriate initial conditions along with the boundary and interface conditions. For 3D solid-3D fluid dynamical interaction problems, we prove the uniqueness and existence theorem. Further, considering the case when the elastic inclusion is a thin prismatic shell of variable thickness, we apply the N = 0 approximation of Vekua's hierarchical model for the elastic field in the solid part. In contrast to the usual classical streamline conditions, in the case under consideration, on the cut surface, there appear non-local boundary conditions. We prove unique solvability of the non-classical boundary value problem that leads to the existence results for the solid-fluid interaction problem with a thin elastic inclusion.

  3. Development of a facility for probing the structural dynamics of materials with femtosecond X-ray pulses

    NASA Astrophysics Data System (ADS)

    Faatz, B.; Fateev, A. A.; Feldhaus, J.; Floettmann, K.; Tschentscher, T.; Krzywinski, J.; Pflueger, J.; Rossbach, J.; Saldin, E. L.; Schneidmiller, E. A.; Yurkov, M. V.

    2001-08-01

    We propose to use Thomson backscattering of far-infrared (FIR) pulses (100-300 μm wavelength range) by a 500 MeV electron beam to generate femtosecond X-rays at the TESLA Test Facility (TTF) at DESY. Using the parameters of the photocathode rf gun and the magnetic bunch compressors of the TESLA Test Facility (TTF), it is shown that electron pulses of 100-fs (FWHM) duration can be generated. Passing the short electron bunches through an undulator (after the conversion point) can provide a FIR high-power source with laser-like characteristics. On the basis of the TTF parameters we expect to produce X-ray pulses with 100-fs duration, an average brilliance of nearly 1013photons s-1 mrad-2 mm-2 per 0.1% BW at a photon energy 50 keV. The total number of Thomson backscattered photons, produced by a single passage of the electron bunch through the mirror focus, can exceed 107 photons/pulse. We also describe the basic ideas for an upgrade to shorter X-ray pulse duration. It is demonstrated that the TTF has the capability of reaching the 1012photons s-1 mrad-2 mm-2 per 0.1% BW brilliance at a ten femtosecond scale pulse duration.

  4. PULSE AMPLITUDE DISTRIBUTION RECORDER

    DOEpatents

    Cowper, G.

    1958-08-12

    A device is described for automatica1ly recording pulse annplitude distribution received from a counter. The novelty of the device consists of the over-all arrangement of conventional circuit elements to provide an easy to read permanent record of the pulse amplitude distribution during a certain time period. In the device a pulse analyzer separates the pulses according to annplitude into several channels. A scaler in each channel counts the pulses and operates a pen marker positioned over a drivable recorder sheet. Since the scalers in each channel have the sanne capacity, the control circuitry permits counting of the incoming pulses until one scaler reaches capacity, whereupon the input is removed and an internal oscillator supplies the necessary pulses to fill up the other scalers. Movement of the chart sheet is initiated wben the first scaler reaches capacity to thereby give a series of marks at spacings proportional to the time required to fill the remaining scalers, and accessory equipment marks calibration points on the recorder sheet to facilitate direct reading of the number of external pulses supplied to each scaler.

  5. STRUTEX: A prototype knowledge-based system for initially configuring a structure to support point loads in two dimensions

    NASA Technical Reports Server (NTRS)

    Robers, James L.; Sobieszczanski-Sobieski, Jaroslaw

    1989-01-01

    Only recently have engineers begun making use of Artificial Intelligence (AI) tools in the area of conceptual design. To continue filling this void in the design process, a prototype knowledge-based system, called STRUTEX has been developed to initially configure a structure to support point loads in two dimensions. This prototype was developed for testing the application of AI tools to conceptual design as opposed to being a testbed for new methods for improving structural analysis and optimization. This system combines numerical and symbolic processing by the computer with interactive problem solving aided by the vision of the user. How the system is constructed to interact with the user is described. Of special interest is the information flow between the knowledge base and the data base under control of the algorithmic main program. Examples of computed and refined structures are presented during the explanation of the system.

  6. Structure of the fMet-tRNA(fMet)-binding domain of B. stearothermophilus initiation factor IF2.

    PubMed

    Meunier, S; Spurio, R; Czisch, M; Wechselberger, R; Guenneugues, M; Gualerzi, C O; Boelens, R

    2000-04-17

    The three-dimensional structure of the fMet-tRNA(fMet) -binding domain of translation initiation factor IF2 from Bacillus stearothermophilus has been determined by heteronuclear NMR spectroscopy. Its structure consists of six antiparallel beta-strands, connected via loops, and forms a closed beta-barrel similar to domain II of elongation factors EF-Tu and EF-G, despite low sequence homology. Two structures of the ternary complexes of the EF-Tu small middle dotaminoacyl-tRNA small middle dot GDP analogue have been reported and were used to propose and discuss the possible fMet-tRNA(fMet)-binding site of IF2. PMID:10775275

  7. Nano/Micro-Structured Si/C Anodes with High Initial Coulombic Efficiency in Li-Ion Batteries.

    PubMed

    Xu, Quan; Li, Jin-Yi; Yin, Ya-Xia; Kong, Yi-Ming; Guo, Yu-Guo; Wan, Li-Jun

    2016-04-20

    One of the major challenges for designing high-capacity anode materials is to combine both Coulombic efficiency and cycling stability. Herein, nano/micro-structured Si/C composites are designed and synthesized to address this challenge by decreasing the specific surface area and improving the tap density of Si/C materials. An ultrahigh initial Coulombic efficiency of 91.2 % could be achieved due to a proper particle size, low specific surface area, and optimized structure. The nano/micro-structured Si/C anodes exhibit excellent cycling stability with 96.5 % capacity retention after 100 cycles under a current density of 0.2 A g(-1) . PMID:26853080

  8. [The structure of the initial inputs into the metasympathetic nervous system of the rat uterus].

    PubMed

    Kucheriavykh, L E; Skopichev, V G; Nozdrachev, A D

    1999-01-01

    Different populations of sympathetic neurons exerting modulating influence on neurons of nervous plexuses of proper metasympathetic nervous system of the uterus in albino laboratory rats were detected using the method on retrograde transport of fluorescent marker primulin. Following the injection of the marker into uterovaginal plexus, labelled neurons were found as aggregations in caudal mesenterial sympathetic ganglia, ganglia of coeliac plexus, renal ganglia and ganglia of coeliac trunk. The structure of nervous paths of external control of uterus functioning was analysed. PMID:10709194

  9. Large scale prop-fan structural design study. Volume 1: Initial concepts

    NASA Technical Reports Server (NTRS)

    Billman, L. C.; Gruska, C. J.; Ladden, R. M.; Leishman, D. K.; Turnberg, J. E.

    1988-01-01

    In recent years, considerable attention has been directed toward improving aircraft fuel consumption. Studies have shown that the inherent efficiency advantage that turboprop propulsion systems have demonstrated at lower cruise speeds may now be extended to the higher speeds of today's turbofan and turbojet-powered aircraft. To achieve this goal, new propeller designs will require features such as thin, high speed airfoils and aerodynamic sweep, features currently found only in wing designs for high speed aircraft. This is Volume 1 of a 2 volume study to establish structural concepts for such advanced propeller blades, to define their structural properties, to identify any new design, analysis, or fabrication techniques which were required, and to determine the structural tradeoffs involved with several blade shapes selected primarily on the basis of aero/acoustic design considerations. The feasibility of fabricating and testing dynamically scaled models of these blades for aeroelastic testing was also established. The preliminary design of a blade suitable for flight use in a testbed advanced turboprop was conducted and is described in Volume 2.

  10. Molecular Mechanisms of Transcription Initiation-Structure, Function, and Evolution of TFE/TFIIE-Like Factors and Open Complex Formation.

    PubMed

    Blombach, Fabian; Smollett, Katherine L; Grohmann, Dina; Werner, Finn

    2016-06-19

    Transcription initiation requires that the promoter DNA is melted and the template strand is loaded into the active site of the RNA polymerase (RNAP), forming the open complex (OC). The archaeal initiation factor TFE and its eukaryotic counterpart TFIIE facilitate this process. Recent structural and biophysical studies have revealed the position of TFE/TFIIE within the pre-initiation complex (PIC) and illuminated its role in OC formation. TFE operates via allosteric and direct mechanisms. Firstly, it interacts with the RNAP and induces the opening of the flexible RNAP clamp domain, concomitant with DNA melting and template loading. Secondly, TFE binds physically to single-stranded DNA in the transcription bubble of the OC and increases its stability. The identification of the β-subunit of archaeal TFE enabled us to reconstruct the evolutionary history of TFE/TFIIE-like factors, which is characterised by winged helix (WH) domain expansion in eukaryotes and loss of metal centres including iron-sulfur clusters and Zinc ribbons. OC formation is an important target for the regulation of transcription in all domains of life. We propose that TFE and the bacterial general transcription factor CarD, although structurally and evolutionary unrelated, show interesting parallels in their mechanism to enhance OC formation. We argue that OC formation is used as a way to regulate transcription in all domains of life, and these regulatory mechanisms coevolved with the basal transcription machinery. PMID:27107643

  11. On the interferometric coherent structures in femtosecond supercontinuum generation

    NASA Astrophysics Data System (ADS)

    Dinda, Sirshendu; Bandyopadhyay, Soumendra Nath; Goswami, Debabrata

    2016-05-01

    We report structured interferometric features in femtosecond supercontinuum generation (FSG) with incident laser powers that are near threshold for FSG. We argue that near threshold, these structures arise from the coherent superposition of pulses that are split initially into two daughter pulses during FSG process. Increase in the input pulse energy generates multiple daughter fragments in the temporal domain to an extent that correlated interference structures are not measurable.

  12. An accurately preorganized IRES RNA structure enables eIF4G capture for initiation of viral translation.

    PubMed

    Imai, Shunsuke; Kumar, Parimal; Hellen, Christopher U T; D'Souza, Victoria M; Wagner, Gerhard

    2016-09-01

    Many viruses bypass canonical cap-dependent translation in host cells by using internal ribosomal entry sites (IRESs) in their transcripts; IRESs hijack initiation factors for the assembly of initiation complexes. However, it is currently unknown how IRES RNAs recognize initiation factors that have no endogenous RNA binding partners; in a prominent example, the IRES of encephalomyocarditis virus (EMCV) interacts with the HEAT-1 domain of eukaryotic initiation factor 4G (eIF4G). Here we report the solution structure of the J-K region of this IRES and show that its stems are precisely organized to position protein-recognition bulges. This multisite interaction mechanism operates on an all-or-nothing principle in which all domains are required. This preorganization is accomplished by an 'adjuster module': a pentaloop motif that acts as a dual-sided docking station for base-pair receptors. Because subtle changes in the orientation abrogate protein capture, our study highlights how a viral RNA acquires affinity for a target protein. PMID:27525590

  13. Initiation of ignition of a combustible gas mixture in a closed volume by the radiation of a high-power pulsed CO{sub 2} laser

    SciTech Connect

    Kazantsev, S Yu; Kononov, I G; Kossyi, I A; Popov, N A; Tarasova, N M; Firsov, K N

    2012-01-31

    The results of experiments on initiating the ignition of a CH{sub 4} - O{sub 2} - SF{sub 6} triple gas mixture in a closed volume by the radiation of a high-power CO{sub 2} laser are presented. It is shown that spatially nonuniform (in the direction of the laser beam) gas heating by the laser radiation leads to formation of a fast combustion wave, propagating along the chamber axis and giving rise to 'instantaneous' ignition. At the threshold value 16.5 J of the laser radiation energy the fast combustion wave is transformed into a detonation wave, which causes an explosion and destruction of the reaction chamber.

  14. The Kinetic Scale Structure of the Low Latitude Boundary Layer: Initial MMS Results

    NASA Astrophysics Data System (ADS)

    Dorelli, John; Gershman, Dan; Avanov, Levon; Pollock, Craig; Giles, Barbara; Gliese, Ulrik; Barrie, Alexander; Holland, Matthew; Salo, Chad; Dickson, Charles; Coffey, Victoria; Chandler, Michael; Sato, Yoshifumi; Strangeway, Robert; Russell, Christopher; Baumjohann, Wolfgang; Khotyainstev, Yuri; Torbert, Roy; Burch, James

    2016-04-01

    Since its launch in March of 2015, NASA's Magnetospheric Multiscale (MMS) mission has captured thousands of high resolution magnetopause crossings, routinely resolving the sub-Larmor radius structure of the magnetopause boundary layer for the first time. The primary goal of MMS is to understand the microphysics of magnetic reconnection, and it is well on its way to achieving this objective. However, MMS is also making routine measurements of the electron and ion gyroviscous and heat flux tensors with unprecedented resolution and accuracy. This opens up the possibility of directly observing the physical processes that facilitate momentum and energy transport across the magnetopause boundary layer under arbitrary conditions (e.g., magnetic field geometry and flow shear) far from the reconnection X line. Currently, our global magnetosphere fluid models (e.g., resistive or Hall MHD) do not include accurate descriptions of viscosity and heat flow, both of which are known to be critical players at the magnetopause (not just at the reconnection sites), and several groups are attempting to make progress on this difficult fluid closure problem. In this talk, we will address the fluid closure problem in the context of MMS observations of the Low Latitude Boundary Layer (LLBL), focusing on high resolution particle observations by the Fast Plasma Investigation (FPI). FPI electron bulk velocities are accurate enough to compute current density in both the high density magnetosheath and low density magnetosphere and have already revealed that the LLBL has a complex parallel current structure on the proton Larmor radius scale. We discuss the relationship between these parallel currents and the Hall electric field structures predicted by kinetic models. We also present first observations of the ion and electron gyroviscous and heat flux tensors in the LLBL and discuss implications for the fluid closure problem at Earth's magnetopause.

  15. Electromagnetic and muonic structure of showers initiated by gamma-rays and by hadrons

    NASA Technical Reports Server (NTRS)

    Hillas, A. M.

    1985-01-01

    If photon cascades develop by the usual mechanisms, there should indeed be notable differences between the structure of showers due to photon and hadron primaries, as regards muon densities and lateral distributions of some detector signals. The muon content of showers from Cygnus X-3, observed at Kiel, cannot be understood in this way. One remedy is to postulate arbitrarily a strong hadronic interaction of photons in the TeV region. This would utterly change the nature of electromagnetic cascades, but surprisingly does not at first sight seem to be in conflict with air shower observations.

  16. Toward structured macroporous hydrogel composites: electron beam-initiated polymerization of layered cryogels.

    PubMed

    Golunova, Anna; Chvátil, David; Krist, Pavel; Jaroš, Josef; Jurtíková, Veronika; Pospíšil, Jakub; Kotelnikov, Ilya; Abelová, Lucie; Kotek, Jiří; Sedlačík, Tomáš; Kučka, Jan; Koubková, Jana; Studenovská, Hana; Streit, Libor; Hampl, Aleš; Rypáček, František; Proks, Vladimír

    2015-04-13

    The ability to tailor mechanical properties and architecture is crucial in creating macroporous hydrogel scaffolds for tissue engineering. In the present work, a technique for the modification of the pore size and stiffness of acrylamide-based cryogels is demonstrated via the regulation of an electron beam irradiation dose. The samples were characterized by equilibrium swelling measurements, light and scanning electron microscopy, mercury porosimetry, Brunauer-Emmett-Teller surface area analysis, and stiffness measurements. Their properties were compared to cryogels prepared by a standard redox-initiated radical polymerization. A (125)I radiolabeled azidopentanoyl-GGGRGDSGGGY-NH2 peptide was bound to the surface to determine the concentration of the adhesive sites available for biomimetic modification. The functionality of the prepared substrates was evaluated by in vitro cultivation of adipose-derived stem cells. Moreover, the feasibility of preparing layered cryogels was demonstrated. This may be the key to the future preparation of complex hydrogel-based scaffolds to mimic the extracellular microenvironment in a wide range of applications. PMID:25728457

  17. 3D Visualization of Monte-Carlo Simulation's of HZE Track Structure and Initial Chemical Species

    NASA Technical Reports Server (NTRS)

    Plante, Ianik; Cucinotta, Francis A.

    2009-01-01

    Heavy ions biophysics is important for space radiation risk assessment [1] and hadron-therapy [2]. The characteristic of heavy ions tracks include a very high energy deposition region close to the track (<20 nm) denoted as the track core, and an outer penumbra region consisting of individual secondary electrons (6-rays). A still open question is the radiobiological effects of 6- rays relative to the track core. Of importance is the induction of double-strand breaks (DSB) [3] and oxidative damage to the biomolecules and the tissue matrix, considered the most important lesions for acute and long term effects of radiation. In this work, we have simulated a 56Fe26+ ion track of 1 GeV/amu with our Monte-Carlo code RITRACKS [4]. The simulation results have been used to calculate the energy depiction and initial chemical species in a "voxelized" space, which is then visualized in 3D. Several voxels with dose >1000 Gy are found in the penumbra, some located 0.1 mm from the track core. In computational models, the DSB induction probability is calculated with radial dose [6], which may not take into account the higher RBE of electron track ends for DSB induction. Therefore, these simulations should help improve models of DSB induction and our understanding of heavy ions biophysics.

  18. Population Genetic Structure of Listeria monocytogenes Strains as Determined by Pulsed-Field Gel Electrophoresis and Multilocus Sequence Typing

    PubMed Central

    Henri, Clémentine; Félix, Benjamin; Guillier, Laurent; Leekitcharoenphon, Pimlapas; Michelon, Damien; Mariet, Jean-François; Aarestrup, Frank M.; Mistou, Michel-Yves; Hendriksen, René S.

    2016-01-01

    ABSTRACT Listeria monocytogenes is a ubiquitous bacterium that may cause the foodborne illness listeriosis. Only a small amount of data about the population genetic structure of strains isolated from food is available. This study aimed to provide an accurate view of the L. monocytogenes food strain population in France. From 1999 to 2014, 1,894 L. monocytogenes strains were isolated from food at the French National Reference Laboratory for L. monocytogenes and classified according to the five risk food matrices defined by the European Food Safety Authority (EFSA). A total of 396 strains were selected on the basis of different pulsed-field gel electrophoresis (PFGE) clusters, serotypes, and strain origins and typed by multilocus sequence typing (MLST), and the MLST results were supplemented with MLST data available from Institut Pasteur, representing human and additional food strains from France. The distribution of sequence types (STs) was compared between food and clinical strains on a panel of 675 strains. High congruence between PFGE and MLST was found. Out of 73 PFGE clusters, the two most prevalent corresponded to ST9 and ST121. Using original statistical analysis, we demonstrated that (i) there was not a clear association between ST9 and ST121 and the food matrices, (ii) serotype IIc, ST8, and ST4 were associated with meat products, and (iii) ST13 was associated with dairy products. Of the two major STs, ST121 was the ST that included the fewest clinical strains, which might indicate lower virulence. This observation may be directly relevant for refining risk analysis models for the better management of food safety. IMPORTANCE This study showed a very useful backward compatibility between PFGE and MLST for surveillance. The results enabled better understanding of the population structure of L. monocytogenes strains isolated from food and management of the health risks associated with L. monocytogenes food strains. Moreover, this work provided an accurate view

  19. Initial operational capability of the ASTREX large space structures test bed

    NASA Technical Reports Server (NTRS)

    Norris, G. A.

    1989-01-01

    Future DOD, NASA, and SDI space systems will be larger than any spacecraft flown before. The economics of placing these large space systems (LSS) into orbit dictates that they be as low in mass as possible. The combination of very large size and relatively low mass produces systems which possess little structural rigidity. This flexibility causes severe technical problems when combined with the precise shape and pointing requirements associated with many future LSS missions. Development of new control technologies which can solve these problems and enable future LSS missions is under way, but a test bed is needed for demonstration and evaluation of the emerging control hardware (sensors and actuators) and methodologies. In particular, the need exists for a facility which enables both large angle slewing and subsequent pointing/shape control of a variety of flexible bodies. The Air Force Astronautics Laboratory (AFAL) has conceived the Advanced Space Structures Technology Research Experiments (ASTREX) facility to fill this need. An overview of the ASTREX facility is given.

  20. Plectin from bovine lenses. Chemical properties, structural analysis and initial identification of interaction partners.

    PubMed

    Weitzer, G; Wiche, G

    1987-11-16

    Plectin was purified to near homogeneity from epithelial and cortical cell layers of bovine lenses using a simple and fast purification scheme that included as last step, gel permeation chromatography in the presence of 0.25% sodium N-lauroyl sarcosinate. Lens cell plectin showed extensive structural homology to plectin from cultured cells as revealed by immunoblotting experiments and amino acid analysis. Further characterization included solubility in various buffer solutions, codistribution with vimentin in repeated rounds of intermediate filament disassembly and assembly, and hydrodynamic behaviour in high-performance gel permeation chromatography. Electron microscopy of negatively stained and rotary shadowed plectin molecules revealed a dumb-bell-like structure with an estimated relative molecular mass of 1.16 X 10(6). Specific head-to-head self-interaction of plectin molecules at low salt concentrations and formation of large aggregates under high-salt and physiological conditions was also demonstrated. Isolation, as well as reconstitution of soluble protein complexes containing plectin, vimentin and other cytoskeletal and membrane skeleton proteins, provided first hints to plectin's role as an interlinking component of the cytoskeleton and the membrane skeleton of lens tissue. PMID:3678232