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Search Results: 1 - 10 of 307031 matches for " Brian J. Rodriguez "
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The Impact of Hyper-components Design on Web Usefulness and Ease of Use
Dae R. Kim,Brian J. Reithel,Carlos M. Rodriguez
International Journal of Electronic Business Management , 2006,
Abstract: The structure and formal organization of a hypermedia design are critical to the effectiveness of the navigation process. Both nodes and hyperlinks often referred, as “hyper-components” are basic building blocks of hypermedia. Effective use of these components facilitates appropriate organization of data and efficient navigation. This study explores the impact of the number of hyperlinks and node size on user’s perceived ease of use and perceived usefulness of websites. Results suggest that websites designed with many hyperlinks and small node size yield the highest positive users' perceptions. Theories of reasoned action and self-efficacy are the framework for the proposed model. Implications for navigation processes and web designs are discussed.
Dissatisfaction with Democracy: Evidence from the Latinobarómetro 2005 Insatisfacción con la Democracia: Evidencia de Latinobarómetro 2005
Brian J. L. Berry,Osvaldo S. Tello Rodriguez
Journal of Politics in Latin America , 2010,
Abstract: Data for 17 Latin American countries collected by Latinobarómetro 2005 reveal that dissatisfaction with democracy is a sign of progress. Political stability and increased governmental effectiveness enable the better-educated leftish young to express their feelings without fear of repression and violence, which is particularly notable in countries least connected into the global economy, where inequality remains high. Dissatisfaction is thus an indicator of political modernization running ahead of progress in the economic sphere. Datos de 17 países Latinoamericanos recolectados por Latinobarómetro 2005 revelan que la insatisfacción con la democracia es un signo de progreso. La estabilidad política y la mejor efectividad gubernamental permite a los jovenes de izquierda mejor educados a expresar sus sentimientos sin el temor de represión y violencia, que es particularmente notable en países que están menos conectados en la economía global, donde la desigualdad permanece alta. La insatisfacción es por tanto un indicador de la modernización política que va adelante del progreso en la esfera económica.
Nanoscale polarization manipulation and imaging in ferroelectric Langmuir-Blodgett polymer films
Brian J. Rodriguez,Stephen Jesse,Sergei V. Kalinin,Jihee Kim,Stephen Ducharme,V. M. Fridkin
Physics , 2006, DOI: 10.1063/1.2715102
Abstract: The behavior of ferroelectricity at the nanoscale is the focus of increasing research activity because of intense interest in the fundamental nature of spontaneous order in condensed-matter systems and because of the many practical applications of ferroelectric thin films to, for example, electromechanical transducers, infrared imaging sensors, and nonvolatile random-access memories. Ferroelectricity, in analogy with its namesake ferromagnetism, is the property of some crystalline systems to maintain a permanent, but reversible, electrical polarization in the absence of an external electric field. The imaging and dynamics of the piezoelectric response at the nanoscale is perhaps the most direct means of probing polarization, as has been demonstrated in a number of thin films and nanostructures . Here we report the use of piezoresponse force microscopy (PFM) and switching spectroscopy PFM (SSPFM) to image the ferroelectric properties, domain structure, and polarization switching of ultrathin ferroelectric Langmuir-Blodgett films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymers. PFM imaging of P(VDF-TrFE) thin films reveals ferroelectric domain sizes on the order of 25-50 nm and an imaging resolution below 5 nm. The feature sizes in topography and PFM images are comparable and the boundaries of uniformly polarized regions coincide with topographic features. Arbitrary polarization patterns could be repeatedly written and erased, with writing resolution limited by the grain size. Hysteresis loops from individual domains show clear coercive voltage, but are not well saturated at +/-10 V amplitude.
The Relationship Between X-ray Luminosity and Major Flare Launching in GRS 1915+105
Brian Punsly,Jerome Rodriguez
Physics , 2012, DOI: 10.1088/0004-637X/764/2/173
Abstract: We perform the most detailed analysis to date of the X-ray state of the Galactic black hole candidate GRS 1915+105 just prior to (0 to 4 hours) and during the brief (1 to 7 hour) ejection of major (superluminal) radio flares. A very strong model independent correlation is found between the 1.2 keV - 12 keV X-ray flux 0 to 4 hours before flare ejections with the peak optically thin 2.3 GHz emission of the flares. This suggests a direct physical connection between the energy in the ejection and the luminosity of the accretion flow preceding the ejection. In order to quantify this concept, we develop techniques to estimate the intrinsic (unabsorbed) X-ray luminosity, $L_{\mathrm{intrinsic}}$, from RXTE ASM data and to implement known methods to estimate the time averaged power required to launch the radio emitting plasmoids, $Q$ (sometimes called jet power). We find that the distribution of intrinsic luminosity from 1.2 keV - 50 keV, $L_{\mathrm{intrinsic}}(1.2 - 50)$, is systematically elevated just before ejections compared to arbitrary times when there are no major ejections. The estimated $Q$ is strongly correlated with $L_{\mathrm{intrinsic}}(1.2 - 50)$ 0 to 4 hours before the ejection, the increase in $L_{\mathrm{intrinsic}}(1.2 - 50)$ in the hours preceding the ejection and the time averaged $L_{\mathrm{intrinsic}}(1.2 - 50)$ during the flare rise. Furthermore, the total time averaged power during the ejection ($Q$ + the time average of $L_{\mathrm{intrinsic}}(1.2 - 50)$ during ejection) is strongly correlated with $L_{\mathrm{intrinsic}}(1.2 - 50)$ just before launch with near equality if the distance to the source is $ \approx 10.5$ kpc.
GRS 1915+105 as a Galactic Analog of a Fanaroff-Riley II Quasar
Brian Punsly,Jerome Rodriguez
Physics , 2013, DOI: 10.1088/0004-637X/770/2/99
Abstract: We study the long term time averaged kinetic luminosity, $\bar{Q}$, of the major flares of the Galactic microquasar GRS 1915+105 and the relationship to the intrinsic X-ray (bolometric) luminosity, $L_{\mathrm{bol}}$, and scale it to that of a complete sample of SDSS/FIRST FR II quasars. If the scale invariance hypothesis for black holes (BHs) holds then we show that the expected distribution in the $\bar{Q}$ - $L_{\mathrm{bol}}$ scatter plane of GRS 1915+105 is consistent with FR II quasars for distances D = 10.7 - 11 kpc. We compare the specific values of kinetic luminosity and $L_{\mathrm{bol}}$ during flares of GRS 1915+105 to that predicted by several 3-D MHD simulations of BH accretion flows with relativistic ejections. If FR II quasars are a scaled up version of GRS 1915+105, the data are consistent with numerical models when they contain an ergospheric disk jet and the BH spin is $a/M= 0.99$ or $a/M=0.998$ (we estimate $a/M>0.984$). In the framework of scale invariance of BHs, our results may imply that FR II quasars also hold rapidly rotating BHs.
Calibrated Estimates of the Energy in Major Flares of GRS 1915+105
Brian Punsly,Jerome Rodriguez
Physics , 2013, DOI: 10.1093/mnras/stt1455
Abstract: We analyze the energetics of the major radio flare of October 8 2005 in GRS 1915+105. The flare is of particular interest because it is one of the most luminous and energetic radio flares from a Galactic black hole that has ever been observed. The motivation is two-fold. One, to learn more about the energetics of this most extreme phenomenon and its relationship to the accretion state. The second is to verify if the calibrated estimates of the energy of major radio flares (based on the peak low frequency optically thin flux) derived from flares in the period 1996-2001 in Punsly & Rodriguez (2013), PR13 hereafter, can be used to estimate plasmoid energy beyond this time period. We find evidence that the calibrated curves are still accurate for this strong flare. Furthermore, the physically important findings of PR13 are supported by the inclusion of this flare: the flare energy is correlated with both the intrinsic bolometric X-ray luminosity, $L_{\mathrm{bol}}$, $\sim 1$ hour before ejection and $L_{\mathrm{bol}}$ averaged over the duration of the ejection of the plasmoid and $L_{\mathrm{bol}}$ is highly elevated relative to historic levels just before and during the ejection episode. A search of the data archives reveal that only the October 8 2005 flare and those in PR13 have adequate data sampling to allow estimates of both the energy of the flare and the X-ray luminosity before and during flare launch.
Misregulated E-Cadherin Expression Associated with an Aggressive Brain Tumor Phenotype
Laura J. Lewis-Tuffin,Fausto Rodriguez,Caterina Giannini,Bernd Scheithauer,Brian M. Necela,Jann N. Sarkaria,Panos Z. Anastasiadis
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013665
Abstract: Cadherins are essential components of the adherens junction complexes that mediate cell-cell adhesion and regulate cell motility. During tissue morphogenesis, changes in cadherin expression (known as cadherin switching) are a common mechanism for altering cell fate. Cadherin switching is also common during epithelial tumor progression, where it is thought to promote tumor invasion and metastasis. E-cadherin is the predominant cadherin expressed in epithelial tissues, but its expression is very limited in normal brain.
Local Polarization Switching in the Presence of Surface Charged Defects: Microscopic Mechanisms and Piezoresponse Force Spectroscopy Observations
Anna N. Morozovska,Sergei V. Svechnikov,Eugene A. Eliseev,Brian J. Rodriguez,Stephen Jesse,Sergei V. Kalinin
Physics , 2007, DOI: 10.1103/PhysRevB.78.054101
Abstract: The thermodynamics and kinetics of tip-induced polarization switching in Piezoresponse Force Microscopy in the presence of surface charge defects is studied using the combination of analytical and numerical techniques. The signature of the defects in hysteresis loop fine structure and Switching Spectroscopy PFM images is identified and compared to experimental observations. An approach for the deconvolution of PFM spectroscopy measurements to extract relevant defect parameters is derived. This methodology is universal and can be extended to switching in other ferroics and in reversible electrochemical processes, establishing a pathway for the understanding of the thermodynamics and kinetics of phase transitions at a single defect level.
Imaging Mechanism of Piezoresponse Force Microscopy in Capacitor Structures
Sergei V. Kalinin,Brian J. Rodriguez,Seung-Hyun Kim,S-K. Hong,Alexei Gruverman,Eugene A. Eliseev
Physics , 2008, DOI: 10.1063/1.2905266
Abstract: The image formation mechanism in Piezoresponse Force Microscopy (PFM) of capacitor structures is analyzed. We demonstrate that the spatial resolution is a bilinear function of film and top electrode thicknesses, and derive the corresponding analytical expressions. For many perovskites, the opposite contributions of d31 and d33 components can result in anomalous domain wall profiles. This analysis establishes the applicability limits of PFM for polarization dynamics studies in capacitors, and applies to other structural probes, including focused X-ray studies of capacitor structures.
Piezoresponse Force Spectroscopy of Ferroelectric Materials
Anna N. Morozovska,Sergei V. Svechnikov,Eugene A. Eliseev,Stephen Jesse,Brian J. Rodriguez,Sergei V. Kalinin
Physics , 2006, DOI: 10.1063/1.2818370
Abstract: Piezoresponse Force Spectroscopy (PFS) has emerged as a powerful technique for probing highly localized switching behavior and the role of microstructure and defects on switching. The application of a dc bias to a scanning probe microscope tip in contact with a ferroelectric surface results in the nucleation and growth of a ferroelectric domain below the tip, resulting in changes in local electromechanical response. Resulting hysteresis loops contains information on local ferroelectric switching behavior. The signal in PFS is the convolution of the volume of the nascent domain and the probing volume of the tip. Here, we analyze the signal formation mechanism in PFS by deriving the main parameters of domain nucleation in a semi-infinite material and establishing the relationships between domain parameters and PFM signal using a linear Greens function theory. The effect of surface screening and finite Debye length on the switching behavior is established. In particular, we predict that the critical nucleus size in PFM is controlled by the surface screening mechanism and in the absence of screening, tip-induced switching is impossible. Future prospects of PFS to study domain nucleation in the vicinity of defects, local switching centers in ferroelectrics, and unusual polarization states in low-dimensional ferroelectrics are discussed.
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