1,582 research outputs found

    Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles

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    Low-frequency Raman scattering experiments have been performed on thin films consisting of nickel-silver composite nanoparticles embedded in alumina matrix. It is observed that the Raman scattering by the quadrupolar modes, strongly enhanced when the light excitation is resonant with the surface dipolar excitation, is mainly governed by the silver electron contribution to the plasmon excitation. The Raman results are in agreement with a core-shell structure of the nanoparticles, the silver shell being loosely bonded to the nickel core.Comment: 3 figures. To be published in Phys. Rev.

    Perceptions of Parents’ Attitudes towards Activism and its Impacts on the Political Behavior of Undergraduate Student Activists

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    This paper seeks to study student activism by focusing on how parents\u27 perception of their activism affects their political actions and decisions. Six students from three undergraduate student activist organizations across Metro Manila were purposely sampled to participate individually in a semi-structured interview developed around the concept of attitudes categorized into three components: the behavioral, the cognitive, and the affective. Thematic analysis reveals that parents generally tend to negatively perceive activism, which does not necessarily affect students\u27 decision to continue activism despite accompanying emotional burdens. The findings ascertain that parents employ various parenting styles from rational to authoritarian and emotions such as worry and rage in reaction to their child’s activism. Moreover, the participants were found to apply values such as tireless persuasion and discretion to negotiate conflicting perceptions of their activism with their parents

    MEME-ChIP: motif analysis of large DNA datasets

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    Motivation: Advances in high-throughput sequencing have resulted in rapid growth in large, high-quality datasets including those arising from transcription factor (TF) ChIP-seq experiments. While there are many existing tools for discovering TF binding site motifs in such datasets, most web-based tools cannot directly process such large datasets

    Continuum limit of amorphous elastic bodies: A finite-size study of low frequency harmonic vibrations

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    The approach of the elastic continuum limit in small amorphous bodies formed by weakly polydisperse Lennard-Jones beads is investigated in a systematic finite-size study. We show that classical continuum elasticity breaks down when the wavelength of the sollicitation is smaller than a characteristic length of approximately 30 molecular sizes. Due to this surprisingly large effect ensembles containing up to N=40,000 particles have been required in two dimensions to yield a convincing match with the classical continuum predictions for the eigenfrequency spectrum of disk-shaped aggregates and periodic bulk systems. The existence of an effective length scale \xi is confirmed by the analysis of the (non-gaussian) noisy part of the low frequency vibrational eigenmodes. Moreover, we relate it to the {\em non-affine} part of the displacement fields under imposed elongation and shear. Similar correlations (vortices) are indeed observed on distances up to \xi~30 particle sizes.Comment: 28 pages, 13 figures, 3 table

    PROBABLES IMPACTOS AMBIENTALES GENERADOS POR LAS DISTINTAS ACTIVIDADES ECONÓMICAS EN LA ISLA DE MARGARITA, VENEZUELA

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    En el entorno de la Isla de Margarita existe una gran actividad pesquera donde interactúan la pesqueria industrial y artesanal por la captura de recursos comunes, generándose algunos conflictos Asimismo, el desarrollo del turismo también interfiere con las actividades de la pesca artesanal. Para identificar los impactos ambientales probables generados por la pesca de arrastre y por la actividad del turismo, se utilizó el «Enfoque de Planificación Ambiental Estratégica», y con base al contexto fisico-químico, biológico, pesquero, económico, tecnológico, político, social y legal, se identificaron veintiséis (26) elementos con los cuales se construyó una Matriz APR (MAPR) (Acción- Proceso- Receptor) del tipo simétrica. De un total de 676 interacciones, se seleccionaron aquellas que afectaban a la población, a la economía regional y/o a los recursos pesqueros. Se concluye que las pesquerías artesanales que desarrollan las comunidades pesqueras litorales ubicadas al norte y este de la Isla de Margarita son las más afectadas por la acción de la pesca de arrastre, así como por el desarrollo de la industria de la construcción que contribuye a la degradación del medio marino-costero. Por otra parte, estas comunidades interfieren entre sí al competir por zonas y modalidades de pesca.   PALABRAS CLAVES: Ambiente. Pesca Artesanal e Industrial. Actividad Turística. Margarita. Venezuela.   SUMMARY Around Margarita lsland there is a great fishing activity where interact both the artisanal and industrial fisheries oríginating severa! conflicts. In addition to this, tourist development interferes with artisanal fishery activities. To identity probable environmental impacts by trawling fishing and tourísm activity "Strategic Environmental Planning Approach" was used, and twenty six (26) elements associated to the physico-chemical, social, biological, fishing, economic, technological and legal contexts, were identified in order to build an APR MATRIX (APRM) (ACTION- PROCESS- RECEIVER) ofsymmetric type. From a total of 676 interactions, those affecting people, local economy and 1 or fishery resources were selected. It was concluded that the activit ies most affected by trawling fishing, as well as the development ofthe building industry which deteriorates offshore marine environment, are those carried out fishing communities located North and East of Margarita Island. Moreover, these communities interfere with one another due to the competition of space, zone and because ofthe different fishing methods used.   KEY WORDS: Environment. Artisanal and Industrial Fishery. Tourism Activity. Margarita. Venezuela

    Spatters and Spills: Spreading Dynamics for Partially Wetting Droplets

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    We present a solvable model inspired by dimensional analysis for the time-dependent spreading of droplets that partially wet a substrate, where the spreading eventually stops and the contact angle reaches a nonzero equilibrium value. We separately consider small droplets driven by capillarity and large droplets driven by gravity. To explore both regimes, we first measure the equilibrium radius vs a comprehensive range of droplet volumes for four household fluids, and we compare the results with predictions based on minimizing the sum of gravitational and interfacial energies. The agreement is good and gives a reliable measurement of an equilibrium contact angle that is consistent in both small and large droplet regimes. Next, we use energy considerations to develop equations of motion for the time dependence of the spreading, in both regimes, where the driving forces are balanced against viscous drag in the bulk of the droplet and by friction at the moving contact line. Our approach leads to explicit prediction of the functional form of the spreading dynamics. It successfully describes prior data for a small capillary-driven droplet, and it fits well to new data we obtain for large gravity-driven droplets with a wide range of volumes. While our prediction for the dynamics of small capillary-driven droplets assumes the case of thin nearly wetting droplets, with a small contact angle, this restriction is not otherwise invoked

    Spatters and Spills: Spreading Dynamics for Partially Wetting Droplets

    Get PDF
    We present a solvable model inspired by dimensional analysis for the time-dependent spreading of droplets that partially wet a substrate, where the spreading eventually stops and the contact angle reaches a nonzero equilibrium value. We separately consider small droplets driven by capillarity and large droplets driven by gravity. To explore both regimes, we first measure the equilibrium radius vs a comprehensive range of droplet volumes for four household fluids, and we compare the results with predictions based on minimizing the sum of gravitational and interfacial energies. The agreement is good and gives a reliable measurement of an equilibrium contact angle that is consistent in both small and large droplet regimes. Next, we use energy considerations to develop equations of motion for the time dependence of the spreading, in both regimes, where the driving forces are balanced against viscous drag in the bulk of the droplet and by friction at the moving contact line. Our approach leads to explicit prediction of the functional form of the spreading dynamics. It successfully describes prior data for a small capillary-driven droplet, and it fits well to new data we obtain for large gravity-driven droplets with a wide range of volumes. While our prediction for the dynamics of small capillary-driven droplets assumes the case of thin nearly wetting droplets, with a small contact angle, this restriction is not otherwise invoked

    Scissors modes in triaxial metal clusters

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    We study the scissors mode (orbital M1 excitations) in small Na clusters, triaxial metal clusters Na12{\rm Na}_{12} and Na16{\rm Na}_{16} and the close-to-spherical Na9+{{\rm Na}_9}^+, all described in DFT with detailed ionic background. The scissors modes built on spin-saturated ground and spin-polarized isomeric states are analyzed in virtue of both macroscopic collective and microscopic shell-model treatments. It is shown that the mutual destruction of Coulomb and the exchange-correlation parts of the residual interaction makes the collective shift small and the net effect can depend on details of the actual excited state. The crosstalk with dipole and spin-dipole modes is studied in detail. In particular, a strong crosstalk with spin-dipole negative-parity mode is found in the case of spin-polarized states. Triaxiality and ionic structure considerably complicate the scissors response, mainly at expense of stronger fragmentation of the strength. Nevertheless, even in these complicated cases the scissors mode is mainly determined by the global deformation. The detailed ionic structure destroys the spherical symmetry and can cause finite M1 response (transverse optical mode) even in clusters with zero global deformation. But its strength turns out to be much smaller than for the genuine scissors modes in deformed systems.Comment: 17 pages, 5 figure

    UniPROBE: an online database of protein binding microarray data on protein–DNA interactions

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    The UniPROBE (Universal PBM Resource for Oligonucleotide Binding Evaluation) database hosts data generated by universal protein binding microarray (PBM) technology on the in vitro DNA-binding specificities of proteins. This initial release of the UniPROBE database provides a centralized resource for accessing comprehensive PBM data on the preferences of proteins for all possible sequence variants (‘words’) of length k (‘k-mers’), as well as position weight matrix (PWM) and graphical sequence logo representations of the k-mer data. In total, the database hosts DNA-binding data for over 175 nonredundant proteins from a diverse collection of organisms, including the prokaryote Vibrio harveyi, the eukaryotic malarial parasite Plasmodium falciparum, the parasitic Apicomplexan Cryptosporidium parvum, the yeast Saccharomyces cerevisiae, the worm Caenorhabditis elegans, mouse and human. Current web tools include a text-based search, a function for assessing motif similarity between user-entered data and database PWMs, and a function for locating putative binding sites along user-entered nucleotide sequences. The UniPROBE database is available at http://thebrain.bwh.harvard.edu/uniprobe/
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