Página 1 dos resultados de 5877 itens digitais encontrados em 0.027 segundos

Determinants of online travel purchase intentions: a holistic approach; Determinantes das intenções de compra de viagens online: uma abordagem holística

Amaro, Suzanne Fonseca
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
46.925107%
Online travel shopping has attracted researchers due to its significant growth and there is a growing body of literature in this field. However, research on what drives consumers to purchase travel online has typically been fragmented. In fact, existing studies have largely concentrated on examining consumers’ online travel purchases either grounded on Davis’s Technology Acceptance Model, on the Theory of Reasoned Action and its extension, the Theory of Planned Behaviour or on Roger’s model of perceived innovation attributes, the Innovation Diffusion Theory. A thorough literature review has revealed that there is a lack of studies that integrate all theories to better understand online travel shopping. Therefore, based on relevant literature in tourism and consumer behaviour, this study proposes and tests an integrated model to explore which factors affect intentions to purchase travel online. Furthermore, it proposes a new construct, termed social media involvement, defined as a person’s level of interest or emotional attachment with social media, and examines its relationship with intentions to purchase travel online. To test the 18 hypotheses, a quantitative approach was followed by first collecting data through an online survey. With a sample of 1...

Determinants of intentions to purchase travel online: A holistic approach

Amaro, Suzanne
Fonte: Instituto Politécnico de Viseu Publicador: Instituto Politécnico de Viseu
Tipo: Tese de Doutorado
Publicado em 08/01/2014 ENG
Relevância na Pesquisa
46.925107%
Online travel shopping has attracted researchers due to its significant growth and there is a growing body of literature in this field. However, research on what drives consumers to purchase travel online has typically been fragmented. In fact, existing studies have largely concentrated on examining consumers’ online travel purchases either grounded on Davis’s Technology Acceptance Model, on the Theory of Reasoned Action and its extension, the Theory of Planned Behaviour or on Roger’s model of perceived innovation attributes, the Innovation Diffusion Theory. A thorough literature review has revealed that there is a lack of studies that integrate all theories to better understand online travel shopping. Therefore, based on relevant literature in tourism and consumer behaviour, this study proposes and tests an integrated model to explore which factors affect intentions to purchase travel online. Furthermore, it proposes a new construct, termed social media involvement, defined as a person’s level of interest or emotional attachment with social media, and examines its relationship with intentions to purchase travel online. To test the 18 hypotheses, a quantitative approach was followed by first collecting data through an online survey. With a sample of 1...

Mobile Banking : factores influenciadores da utilização de APPS bancárias

Domingos, Clara Rita Rodrigues
Fonte: Instituto Superior de Economia e Gestão Publicador: Instituto Superior de Economia e Gestão
Tipo: Dissertação de Mestrado
Publicado em /09/2012 POR
Relevância na Pesquisa
46.571177%
Mestrado em Marketing; Os canais electrónicos, fruto do desenvolvimento tecnológico, vieram transformar por completo o relacionamento dos Bancos com os seus clientes, nos últimos anos. O canal de mobile banking, é a mais recente aposta dos Bancos em termos de canais electrónicos apresentando como principais vantagens a redução de custos e a ubiquidade, permitindo aos clientes aceder ao banco em qualquer hora e/ou local, a partir de um smartphone ou tablet com ligação à internet. No entanto, apesar das vantagens de utilização, a taxa de adopção das Apps bancárias fica muito aquém das expectactivas, pelo que se torna crucial conhecer os factores que influenciam o processo de decisão. É nesta perspectiva que surge esta investigação. Construiu-se um modelo de pesquisa resultante da combinação da Teoria da Difusão da Inovação, Risco Percebido, Confiança e características sócio demográficas. As hipóteses formuladas foram testadas, no âmbito de uma análise quantitiva, tendo por base 439 questionários recolhidos online, durante a primeira semana de Setembro de 2012. Concluiu-se que a Compatibilidade e a Complexidade são factores que influenciam directa e positivamente a adopção, de acordo com a literatura existente. Contrariamente às evidências empíricas mais consensuais...

Modeling Buffered Ca2+ Diffusion Near the Membrane: Implications for Secretion in Neuroendocrine Cells

Klingauf, Jürgen; Neher, Erwin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1997 EN
Relevância na Pesquisa
46.712686%
Secretion of catecholamines from neuroendocrine cells is relatively slow and it is likely that redistribution and buffering of Ca2+ is a major factor for delaying the response after a stimulus. In fact, in a recent study (Chow, R. H., J. Klingauf, and E. Neher. 1994. Time course of Ca2+ concentration triggering exocytosis in neuroendocrine cells. Proc. Natl. Acad. Sci. U.S.A. 91:12765-12769) Chow et al. concluded that the concentration of free calcium ([Ca2+]i) at a release site peaks at <10 μM during short-step depolarizations, and then decays to baseline over tens of milliseconds. To check whether such a time course is consistent with diffusion theory, we modeled buffered diffusion in the vicinity of a Ca2+ channel pore. Peak [Ca2+]i and the slow decay were well simulated when release-ready granules were randomly distributed within a regular grid of Ca2+ channels with mean interchannel distances of 300-600 nm. For such large spacings, however, the initial rise in [Ca2+]i was underestimated, suggesting that a small fraction of the release-ready pool (∼10%) experiences much higher [Ca2+]i, and thus might be collocalized with Ca2+ channels. A model that accommodates these findings then correctly predicts many recent observations...

Lookup-table method for imaging optical properties with structured illumination beyond the diffusion theory regime

Erickson, Tim A.; Mazhar, Amaan; Cuccia, David; Durkin, Anthony J.; Tunnell, James W.
Fonte: Society of Photo-Optical Instrumentation Engineers Publicador: Society of Photo-Optical Instrumentation Engineers
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.571177%
Sinusoidally structured illumination is used in concert with a phantom-based lookup-table (LUT) to map wide-field optical properties in turbid media with reduced albedos as low as 0.44. A key advantage of the lookup-table approach is the ability to measure the absorption (μa) and reduced scattering coefficients (μs′) over a much broader range of values than permitted by current diffusion theory methods. Through calibration with a single reflectance standard, the LUT can extract μs′ from 0.8 to 2.4 mm−1 with an average root-mean-square (rms) error of 7% and extract μa from 0 to 1.0 mm−1 with an average rms error of 6%. The LUT is based solely on measurements of two parameters, reflectance R and modulation M at an illumination period of 10 mm. A single set of three phase-shifted images is sufficient to measure both M and R, which are then used to generate maps of absorption and scattering by referencing the LUT. We establish empirically that each pair (M,R) maps uniquely to only one pair of (μs′,μa) and report that the phase function (i.e., size) of the scatterers can influence the accuracy of optical property extraction.

18.175 Theory of Probability, Spring 2005; Theory of Probability

Panchenko, Dmitry A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
EN-US
Relevância na Pesquisa
56.705166%
Laws of large numbers and central limit theorems for sums of independent random variables, conditioning and martingales, Brownian motion and elements of diffusion theory.

Spectroscopy and characterization of turbid media within the diffusion and P3 approximations

Hull, Edward L. (1967 - ); Foster, Thomas H.
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xxii, 231 leaves
ENG
Relevância na Pesquisa
57.01652%
Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 1999.; Noninvasive measurement of tissue optical properties has become an area of increasing interest in recent years. Because such measurements have the potential to provide a wide range of clinically useful information, techniques for determining tissue optical properties from straightforward measurements are of considerable importance. In this thesis, the diffusion approximation to the radiative transport equation is applied to radially-resolved measurements of the reflectance emitted from highly scattering media interrogated by a normally-incident pencil beam. Solutions to the photo-diffusion equation are considered which express the reflectance as a function of the tissue absorption and transport scattering coefficients. The expressions are then fitted to measured reflectance data in order to extract these optical properties as fitting Parameters. The expressions am evaluated through a series of Monte Carlo experiments. The design and testing of a steady-state reflectance spectrometer is described, and it is demonstrated that the diffusion-theory solutions can be used to determine absorption and scattering coefficients of turbid media from experimental reflectance data to accuracies of 10% or better when medium optical properties are within the regime of validity of the diffusion approximation. These techniques are applied to studies of tissue-simulating phantoms containing human red blood cells and to measurements of the hemoglobin oxygenation status of subcutaneous rodent mammary tumors. Optical diffusion theory is only valid when the tissue transport scattering coefficient is much greater than the absorption coefficient. In cases where absorption and scattering are comparable in magnitude...

A quantitative approach on the diffusion of neoliberal tax policies un the post communist new-EU member states

TODOR, Arpad
Fonte: Acad Organisation Environmental Engineering & Sustainable Dev Publicador: Acad Organisation Environmental Engineering & Sustainable Dev
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.700405%
Within this paper I employ the OLS PCSE analysis to investigate the relationships between the CIT (Corporate Income Tax) and various potential independent variables testing for competing theories within the 10 post communist New EU Member States. Reforms in the area of CIT reforms, events were triggered immediately after the fall of the communist regimes. I test the degree to which four theories of policy diffusion explain the observed patterns. The OLS PCSE analysis reveals that while FDI represented an important variable in triggering CIT cuts, its directionality does not confirm the competitive diffusion theory.

Understanding the Adoption and Diffusion of Information Technology Related Curricula: Multiple Theoretical Perspectives

Chiu, Shu-Chuan
Fonte: Indiana University Publicador: Indiana University
Formato: 1168245 bytes; application/pdf
EN_US
Relevância na Pesquisa
47.145996%
Doctor of Philosophy in the School of Public and Environmental Affairs Indiana University; This dissertation conducts two complementary empirical studies to explain why curricular components related to information technology (IT) show different rates of adoption and diffusion in Master of Public Administration (MPA) programs. The first study uses a large-N sample and probit and Tobit regression analyses to explain the variations in core curriculum and concentration offerings related to IT management (ITM). The second study relies on narratives from in-depth interviews to provide a more detailed and nuanced analysis of IT-related curricular decision-making. To interpret the results, these studies draw on four theoretical perspectives: resource dependence theory, institutional theory, garbage can theory, and diffusion theory.These two studies produce the following findings: 1) faculty size and program ranking are positively associated with ITM concentration offerings; 2) accredited programs and programs with greater faculty size have higher expected ratios of required ITM credits to total degree hours; 3) faculty influence or advocacy; the perception of faculty's core competencies; program development strategies; and responses to broader IT trends in society are the major reasons behind the adoption of IT-related curricular components; 4) programs show different degrees to which they respond to potential sources of pressure to conform to external expectations...

The emergence of diffusion theory in latin america: a restropect analysis

Jesús Arroyave Cabrera; Universidad del Norte
Fonte: Universidad del Norte Publicador: Universidad del Norte
Tipo: article; publishedVersion Formato: application/pdf
SPA
Relevância na Pesquisa
56.968335%
ResumenLa difusión de innovaciones es una de las teorías más ampliamente estudiadas y aplicadas en diferentes contextos en todo el mundo. Sin embargo, no ha sido así en América Latina. La mayoría de la literatura relacionada con la difusión de innovaciones en el continente mantiene un enfoque crítico. El presente artículo analiza cómo los primeros estudios de difusión de innovaciones fueron conducidos y aplicados en América Latina. Cuatro tradiciones intelectuales que fueron muy importantes en la Academia Norteamericana (el paradigma dominante, la conceptualización linear de comunicación, la teoría de la modernización y la noción de los efectos poderosos) dejaron una huella en la teoría difusionista que guiaron su aplicación en una dirección muy particular en la región. No obstante, la aplicación de esta teoría en el continente parece haber dejado cierto estigma que ha mantenido alejado a los nuevos académicos de esta práctica y popular teoría.AbstractDiffusion of Innovation is one of the most widely studied and applied theories in different contexts all over the world. However, this is not the case in Latin American countries. Most of the literature that deals with Diffusion of Innovation maintains a critical approach. This paper reviews the way that earlier diffusionist studies were carried out and applied in Latin America. Four intellectual constructions that were pervasive in the mainstream American academy (the dominant paradigm...

Kramers' diffusion theory applied to gating kinetics of voltage-dependent ion channels.

Sigg, D; Qian, H; Bezanilla, F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1999 EN
Relevância na Pesquisa
46.941704%
Kramers' diffusion theory of reaction rates in the condensed phase is considered as an alternative to the traditional discrete-state Markov (DSM) model in describing ion channel gating current kinetics. Diffusion theory can be expected to be particularly relevant in describing high-frequency (>100 kHz) events in channel activation. The generalized voltage sensor of a voltage-dependent ion channel is treated as a Brownian motion particle undergoing spatial diffusion along a one-dimensional energy landscape. Two classes of energy landscapes are considered. The first class contains large barriers, which give rise to gating currents with two distinct time scales: the usual low-frequency decay, which can modeled with a DSM scheme, and a high-frequency component arising from intrastate relaxation. Large depolarizations reduce potential barriers to such a degree that activation rates are diffusion limited, causing the two time scales to merge. Landscapes of the second class are either featureless or contain barriers that are small compared to kT; these are termed "drift landscapes." These landscapes require a larger friction coefficient to generate slow gating kinetics. The high-frequency component that appears with barrier models is not present in pure drift motion. The presence of a high-frequency component can be tested experimentally with large-bandwidth recordings of gating currents. Topics such as frequency domain analysis...

Power spectra of black holes and neutron stars as a probe of hydrodynamical structure of the source. Diffusion theory and its application to Cyg X-1 and Cyg X-2 X-ray observations

Titarchuk, Lev; Shaposhnikov, Nikolai; Arefiev, Vadim
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/12/2006
Relevância na Pesquisa
46.712686%
We present a model of Fourier Power Density Spectrum (PDS) formation in accretion powered X-ray binary systems derived from the first principles of the diffusion theory. Timing properties of X-ray emission are considered to be a result of diffusive propagation of the driving perturbations in a bounded medium. We prove that the integrated power P_x of the resulting PDS is only a small fraction of the integrated power P_dr of the driving oscillations, which is distributed over the disk. The resulting PDS continuum is a sum of two components, a low frequency (LF) component which presumably originates in an extended accretion disk and a high frequency (HF) component which originates in the innermost part of the source (Compton cloud or corona). The LF PDS component has a power-law shape with index of 1.0-1.5 at higher frequencies (``red'' noise) and a flat spectrum below a characteristic (break) frequency (``white'' noise). This white-red noise (WRN) continuum spectrum holds information about the physical parameters of the bounded extended medium, diffusion time scale and the dependence law of viscosity vs radius. We apply our model of the PDS to a sample of RXTE and EXOSAT timing data from Cyg X-1 and Cyg X-2 which describes adequately the spectral transitions in these sources.; Comment: 45 pages...

Wave-diffusion theory of spin transport in metals after ultrashort-pulse excitation

Kaltenborn, Steffen; Zhu, Yao-Hui; Schneider, Hans Christian
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/11/2011
Relevância na Pesquisa
46.712686%
Spin and charge-current dynamics after ultrafast spin-polarized excitation in a normal metal are studied theoretically using a wave-diffusion theory. It is shown analytically how this macroscopic approach correctly describes the ballistic and diffusive properties of spin and charge transport, but also applies to the intermediate regime between these two limits. Using the wave-diffusion equations we numerically analyze spin and charge dynamics after ultrafast excitation of spin polarized carriers in thin gold films. Assuming slightly spin-dependent momentum relaxation times, we find that a unified treatment of diffusive and ballistic transport yields robust signatures in the spin and charge dynamics, which are in qualitative agreement with recent experimental results [Phys. Rev. Lett 107, 076601 (2011)]. The influence of boundary effects on the temporal signatures of spin transport is also studied.; Comment: 8 pages, 8 figures

An asteroseismic test of diffusion theory in white dwarfs

Metcalfe, T. S.; Nather, R. E.; Watson, T. K.; Kim, S. -L.; Park, B. -G.; Handler, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/02/2005
Relevância na Pesquisa
46.846675%
The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. We have obtained dual-site observations of the pulsating DB star CBS114, to complement existing observations of the slightly cooler star GD358. We recover the 7 independent pulsation modes that were previously known, and we discover 4 new ones to provide additional constraints on the models. We perform objective global fitting of our updated double-layered envelope models to both sets of observations, leading to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG1159 stars.; Comment: 7 pages, 3 figures, 3 tables, accepted for publication in A&A

Recent OH Zeeman Observations: Do they Really Contradict the Ambipolar-Diffusion Theory of Star Formation?

Mouschovias, Telemachos Ch.; Tassis, Konstantinos
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/07/2008
Relevância na Pesquisa
46.993306%
Until recently, many of the dozens of quantitative predictions of the ambipolar-diffusion theory of gravitational fragmentation (or core formation) of molecular clouds have been confirmed by observations and, just as importantly, no prediction has been contradicted by any observation. A recent paper, however, claims that measurements of the variation of the mass-to-flux ratio from envelopes to cores in four clouds {\it de}creases, in direct contrast to a prediction of the theory but in agreement with turbulent fragmentation (in the absence of gravity) and, therefore, the ambipolar-diffusion theory is invalid (Crutcher et al 2008). The paper treats magnetic-field nondetections as if they were detections. We show that the analysis of the data is fundamentally flawed and, moreover, the comparison with the theoretical prediction ignores major geometrical effects, suggested by the data themselves if taken at face value. The magnetic fluxes of the envelopes are also miscalculated. We carry out a proper error analysis and treatment of the nondetections and we show that the claimed measurement of the variation of the mass-to-flux ratio from envelopes to cores is not valid, no contradiction with the ambipolar-diffusion theory can be concluded...

An Asteroseismic Test of Diffusion Theory

Metcalfe, Travis S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/09/2005
Relevância na Pesquisa
46.846675%
The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG 1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. Objective global fitting of our updated double-layered envelope models to recent observations of the pulsating DB star CBS 114, and to existing observations of the slightly cooler star GD 358, lead to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG 1159 stars.; Comment: 4 pages, Workshop on Stellar Pulsation & Evolution 2005 (Rome)

Interacting drift-diffusion theory for photoexcited electron-hole gratings in semiconductor quantum wells

Shen, Ka; Vignale, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/12/2012
Relevância na Pesquisa
46.65412%
Phase-resolved transient grating spectroscopy in semiconductor quantum wells has been shown to be a powerful technique for measuring the electron-hole drag resistivity $\rho_{eh}$, which depends on the Coulomb interaction between the carriers. In this paper we develop the interacting drift-diffusion theory, from which $\rho_{eh}$ can be determined, given the measured mobility of an electron-hole grating. From this theory we predict a cross-over from a high-excitation-density regime, in which the mobility has the "normal" positive value, to a low-density regime, in which Coulomb-drag dominates and the mobility becomes negative. At the crossover point, the mobility of the grating vanishes.; Comment: 5 pages, 5 figures

Molecular dynamics of C-peptide of ribonuclease A studied by replica-exchange Monte Carlo method and diffusion theory

La Penna, Giovanni; Mitsutake, Ayori; Masuya, Masato; Okamoto, Yuko
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/09/2003
Relevância na Pesquisa
46.712686%
Generalized-ensemble algorithm and diffusion theory have been combined in order to compute the dynamical properties monitored by nuclear magnetic resonance experiments from efficient and reliable evaluation of statistical averages. Replica-exchange Monte Carlo simulations have been performed with a C-peptide analogue of ribonuclease A, and Smoluchowski diffusion equations have been applied. A fairly good agreement between the calculated and measured $^1$H-NOESY NMR cross peaks has been obtained. The combination of these advanced and continuously improving statistical tools allows the calculation of a wide variety of dynamical properties routinely obtained by experiments.; Comment: 17 pages, 5 figures, (LaTeX); Chemical Physics Letters, in press

Diffusion theory of spin injection through resistive contacts

Rashba, Emmanuel I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.571177%
Insertion of a resistive contact between a ferromagnetic metal and a semiconductor microstructure is of critical importance for achieving efficient spin injection into a semiconductor. However, the equations of the diffusion theory are rather cumbersome for the junctions including such contacts. A technique based on deriving a system of self-consistent equations for the coefficients of spin injection, "gamma", through different contacts are developed. These equations are concise when written in the proper notations. Moreover, the resistance of a two-contact junction can be expressed in terms of "gamma"'s of both contacts. This equation makes calculating the spin valve effect straightforward, allows to find an explicit expression for the junction resistance and to prove that its nonequilibrium part is positive. Relation of these parameters to different phenomena like spin-e.m.f. and the junction transients is established. Comparative effect of the Coulomb screening on different parameters is clarified. It is also shown that the spin non-conservation in a contact can have a dramatic effect on the non-equilibrium resistance of the junction.; Comment: 16 pages, 2 column REVTeX format, minor editorial changes, references to recent papers added...

Analysis and modelling of flood risk assessment using information diffusion and artificial neural network

Li,Qiong; Jiang,Xingwen; Liu,Donghan
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 EN
Relevância na Pesquisa
46.641416%
Floods are a serious hazard to life and property. The traditional probability statistical method is acceptable in analysing the flood risk but requires a large sample size of hydrological data. This paper puts forward a composite method based on artificial neural network (ANN) and information diffusion method (IDM) for flood analysis. Information diffusion theory helps to extract as much useful information as possible from the sample and thus improves the accuracy of system recognition. Meanwhile, an artificial neural network model, back-propagation (BP) neural network, is used to map the multidimensional space of a disaster situation to a one-dimensional disaster space and to enable resolution of the grade of flood disaster loss. These techniques all contribute to a reasonable prediction of natural disaster risk. As an example, application of the method is verified in a flood risk analysis in China, and the risks of different flood grades are determined. Our model yielded very good results and suggests that the methodology is effective and practical, with the potentiality to be used to forecast flood risk for use in flood risk management. It is also hoped that by conducting such analyses lessons can be learned so that the impact of natural disasters such as floods can be mitigated in the future.