927 research outputs found

    Computational fluid dynamic analysis of underwater rubble mound leveling equipment against tidal current loading

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    Underwater rubble mound leveling works usually have been carried out as a preliminary process prior to\ud the installation of caissons and blocks onto the seabed in a harbor and wave energy structures. So far, underwater\ud construction works are mostly depended on divers. These divers are confronted with many difficulties, such as working\ud time limitation due to depth, poor visibility in a working field and so on. These problems can be overcome using\ud machineries in the underwater construction. The practical unmanned underwater equipment for port constructions was\ud newly developed. The equipment can be applicable in underwater leveling works of rubble mound by using its blade\ud and bucket with automatic arms. Also, it can monitor the working environment using sonars and optical devices. The\ud safety analysis considering harsh circumstances such as strong currents is necessary because the equipment is usually\ud mobilized on the seabed. In this paper, the effect of tidal current forces on the behavior of the equipment was\ud investigated by using the Computational Fluid Dynamics (CFD), which is mainly used in investigating the relative\ud movements of fluid and structure. The numerical results reveal that the possibility of overturning and sliding of the\ud equipment can be negligible and the structural stability can be assured under a given current velocity of 1m/s

    Single gluino production in the R-parity lepton number violating MSSM at the LHC

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    We examine the RpR_{p}-violating signal of single gluino production associated with a charged lepton or neutrino at the large hadron collider (LHC), in the model of R-parity relaxed supersymmetric model. If the parameters in the /Rp{\rlap/R}_p supersymmetric interactions are not too small, and the mass of gluino is considered in the range from several GeV (as the Lightest Supersymmetric Particle) to 800 GeV, the cross section of the single gluino production via Drell-Yan processes can be in the order of 10210310^2 \sim 10^3 femto barn, and that via gluon fusion in the order of 10110310^{-1} \sim 10^3 femto barn. If the gluino decay can be well detected in the CERN LHC, this process provides a prospective way to probe supersymmetry and RpR_p violation.Comment: LaTex, 22 pages, 5 EPS file

    Discrete Ambiguities in the Measurement of the Weak Phase Gamma

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    Several time-independent methods have been devised for measuring the phase gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is shown that such measurements generally suffer from discrete ambiguity which is at least 8-fold, not 4-fold as commonly stated. This has serious experimental implications, which are explored in methods involving B->DK decays. The measurement sensitivity and new physics discovery potential are estimated using a full Monte Carlo detector simulation with realistic background estimates.Comment: 15 pages, 2 figures, fixed typ

    Microstructure modelling of hot deformation of Al–1%Mg alloy

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    This study presents the application of the finite elementmethod and intelligent systems techniques to the prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element is defined using a hybrid model. The hybrid model is based on neuro-fuzzy and physically based components and it has been combined with the finite element technique. The model simulates the evolution of the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation) and their effect on the recrystallisation behaviour of the stock. This paper presents the theory behind the model development, the integration between the numerical techniques, and the application of the technique to a hot rolling operation using aluminium, 1 wt% magnesium alloy. Furthermore, experimental data from plane strain compression (PSC) tests and rolling are used to validate the modelling outcome. The results show that the recrystallisation kinetics agree well with the experimental results for different annealing times. This hybrid approach has proved to be more accurate than conventional methods using empirical equations

    Segmentation of Loops from Coronal EUV Images

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    We present a procedure which extracts bright loop features from solar EUV images. In terms of image intensities, these features are elongated ridge-like intensity maxima. To discriminate the maxima, we need information about the spatial derivatives of the image intensity. Commonly, the derivative estimates are strongly affected by image noise. We therefore use a regularized estimation of the derivative which is then used to interpolate a discrete vector field of ridge points ``ridgels'' which are positioned on the ridge center and have the intrinsic orientation of the local ridge direction. A scheme is proposed to connect ridgels to smooth, spline-represented curves which fit the observed loops. Finally, a half-automated user interface allows one to merge or split, eliminate or select loop fits obtained form the above procedure. In this paper we apply our tool to one of the first EUV images observed by the SECCHI instrument onboard the recently launched STEREO spacecraft. We compare the extracted loops with projected field lines computed from almost-simultaneously-taken magnetograms measured by the SOHO/MDI Doppler imager. The field lines were calculated using a linear force-free field model. This comparison allows one to verify faint and spurious loop connections produced by our segmentation tool and it also helps to prove the quality of the magnetic-field model where well-identified loop structures comply with field-line projections. We also discuss further potential applications of our tool such as loop oscillations and stereoscopy.Comment: 13 pages, 9 figures, Solar Physics, online firs

    Direct visualization of coexisting channels of interaction in CeSb

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    Our understanding of correlated electron systems is vexed by the complexity of their interactions. Heavy fermion compounds are archetypal examples of this physics, leading to exotic properties that weave magnetism, superconductivity and strange metal behavior together. The Kondo semimetal CeSb is an unusual example where different channels of interaction not only coexist, but have coincident physical signatures, leading to decades of debate about the microscopic picture describing the interactions between the f moments and the itinerant electron sea. Using angle-resolved photoemission spectroscopy, we resonantly enhance the response of the Ce f electrons across the magnetic transitions of CeSb and find there are two distinct modes of interaction that are simultaneously active, but on different kinds of carriers. This study reveals how correlated systems can reconcile the coexistence of different modes on interaction-by separating their action in momentum space, they allow their coexistence in real space.11Ysciescopu

    Growth of vertically aligned arrays of carbon nanotubes for high field emission

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    International audienceVertically aligned multi-walled carbon nanotubes have been grown on Ni-coated silicon substrates, by using either direct current diode or triode plasma-enhanced chemical vapor deposition at low temperature (around 620 °C). Acetylene gas has been used as the carbon source while ammonia and hydrogen have been used for etching. However densely packed (∼ 109 cm− 2) CNTs were obtained when the pressure was ∼ 100 Pa. The alignment of nanotubes is a necessary, but not a sufficient condition in order to get an efficient electron emission: the growth of nanotubes should be controlled along regular arrays, in order to minimize the electrostatic interactions between them. So a three dimensional numerical simulation has been developed to calculate the local electric field in the vicinity of the tips for a finite square array of nanotubes and thus to calculate the maximum of the electron emission current density as a function of the spacing between nanotubes. Finally the triode plasma- enhanced process combined with pre-patterned catalyst films (using different lithography techniques) has been chosen in order to grow regular arrays of aligned CNTs with different pitches in the micrometer range. The comparison between the experimental and the simulation data permits to define the most efficient CNT-based electron field emitter

    Measuring γ\gamma in B±K±(KK)DB^\pm \to K^\pm (K K^*)_D decays

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    We develop a method to measure the CKM angle γ\gamma without hadronic uncertainties from the analysis of B±K±D0B^\pm \to K^\pm D^0 and K^\pm \D0bar followed by singly Cabibbo-suppressed DD decays to non CP-eigenstates, such as K±KK^\pm K^{*\mp}. This method utilizes the interference between bcuˉsb\to c\bar u s and bucˉsb\to u\bar c s decays, and we point out several attractive features of it. All the modes that need to be measured for this method are accessible in the present data.Comment: 8 page

    Profiling translatomes of discrete cell populations resolves altered cellular priorities during hypoxia in Arabidopsis

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    Multicellular organs are composed of distinct cell types with unique assemblages of translated mRNAs. Here, ribosome-associated mRNAs were immunopurified from specific cell populations of intact seedlings using Arabidopsis thaliana lines expressing a FLAG-epitope tagged ribosomal protein L18 (FLAG-RPL18) via developmentally regulated promoters. The profiling of mRNAs in ribosome complexes, referred to as the translatome, identified differentially expressed mRNAs in 21 cell populations defined by cell-specific expression of FLAG-RPL18. Phloem companion cells of the root and shoot had the most distinctive translatomes. When seedlings were exposed to a brief period of hypoxia, a pronounced reprioritization of mRNA enrichment in the cell-specific translatomes occurred, including a ubiquitous rise in 49 mRNAs encoding transcription factors, signaling proteins, anaerobic metabolism enzymes, and uncharacterized proteins. Translatome profiling also exposed an intricate molecular signature of transcription factor (TF) family member mRNAs that was markedly reconfigured by hypoxia at global and cell-specific levels. In addition to the demonstration of the complexity and plasticity of cell-specific populations of ribosome-associated mRNAs, this study provides an in silico dataset for recognition of differentially expressed genes at the cell-, region-, and organ-specific levels.Instituto de Biotecnologia y Biologia Molecula

    Stabilized electron emission from silicon coated carbon nanotubes for a high-performance electron source

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    The authors show that carbon nanotubes (CNTs) coated with an amorphous silicon layer around their periphery show enhanced and stable electron emission. The CNT-field emitter array was grown on silicon substrate through a resist-assisted patterning process. The CNTs become coated with silicon from the substrate, which is etched and redeposited onto the CNTs. The authors obtained enhanced and stabilized electron emission from the silicon coated CNTs with a turn-on field of 2 V/μm at an emission current density of 1 μA/ cm 2. The structure and electron emission properties of the functionalized emitters are discussed
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