1,388 research outputs found
Formulation, existence, and computation of boundedly rational dynamic user equilibrium with fixed or endogenous user tolerance
This paper analyzes dynamic user equilibrium (DUE) that incorporates the notion of boundedly rational (BR) user behavior in the selection of departure times and routes. Intrinsically, the boundedly rational dynamic user equilibrium (BR-DUE) model we present assumes that travelers do not always seek the least costly route-and-departure-time choice. Rather, their perception of travel cost is affected by an indifference band describing travelers’ tolerance of the difference between their experienced travel costs and the minimum travel cost. An extension of the BR-DUE problem is the so-called variable tolerance dynamic user equilibrium (VT-BR-DUE) wherein endogenously determined tolerances may depend not only on paths, but also on the established path departure rates. This paper presents a unified approach for modeling both BR-DUE and VT-BR-DUE, which makes significant contributions to the model formulation, analysis of existence, solution characterization, and numerical computation of such problems. The VT-BR-DUE problem, together with the BR-DUE problem as a special case, is formulated as a variational inequality. We provide a very general existence result for VT-BR-DUE and BR-DUE that relies on assumptions weaker than those required for normal DUE models. Moreover, a characterization of the solution set is provided based on rigorous topological analysis. Finally, three computational algorithms with convergence results are proposed based on the VI and DVI formulations. Numerical studies are conducted to assess the proposed algorithms in terms of solution quality, convergence, and computational efficiency
Policing Diversity with Diversity: Exploring Organizational Rhetoric, Myth, and Minority Police Officers\u27 Perceptions and Experiences
Police services are responding to the current realities of diversity. Specifically, police services attempt to adopt diversity policies, initiatives, and practices as a way to reflect community representation. The present study examines how minority police officers’ perceive and experience organizational diversity. While diversity is a broad term encompassing such variables as race, sex and sexual orientation, the present study focuses primarily on racial diversity. Through in-depth interviews with 12 Canadian police officers and 1 diversity trainer, as well as descriptive statistical data pertaining to the last 15 years of recruitment trends, the perceptions held by participants suggest that police services attempt to provide an image of embracing diversity philosophies. Although the image of diversity is portrayed by the organization, intrinsic challenges, barriers, and tensions within the organization are concealed in a window dressing effect (Cashmore, 2002). This study uncovers how minority officers\u27 perceptions of organizational diversity identify a rationalized institutional myth (Meyer & Rowan, 1977). That is, minority officers\u27 perceive a discrepancy between the adoption of diversity philosophies and the realities with respect to their implementation within the organization. While external legitimacy and appearance is maintained, the myth remains untouched in the organization
Asymptotic analysis of first passage time in complex networks
The first passage time (FPT) distribution for random walk in complex networks
is calculated through an asymptotic analysis. For network with size and
short relaxation time , the computed mean first passage time (MFPT),
which is inverse of the decay rate of FPT distribution, is inversely
proportional to the degree of the destination. These results are verified
numerically for the paradigmatic networks with excellent agreement. We show
that the range of validity of the analytical results covers networks that have
short relaxation time and high mean degree, which turn out to be valid to many
real networks.Comment: 6 pages, 4 figures, 1 tabl
Electronic Structure in Gapped Graphene with Coulomb Potential
In this paper, we numerically study the bound electron states induced by long
range Coulomb impurity in gapped graphene and the quasi-bound states in
supercritical region based on the lattice model. We present a detailed
comparison between our numerical simulations and the prediction of the
continuum model which is described by the Dirac equation in (2+1)-dimensional
Quantum Electrodynamics (QED). We also use the Fano's formalism to investigate
the quasi-bound state development and design an accessible experiments to test
the decay of the supercritical vacuum in the gapped graphene.Comment: 5 page, 4 figure
Elastic demand dynamic network user equilibrium: Formulation, existence and computation
This paper is concerned with dynamic user equilibrium with elastic travel demand (E-DUE) when the trip demand matrix is determined endogenously. We present an infinite-dimensional variational inequality (VI) formulation that is equivalent to the conditions defining a continuous-time E-DUE problem. An existence result for this VI is established by applying a fixed-point existence theorem (Browder, 1968) in an extended Hilbert space. We present three computational algorithms based on the aforementioned VI and its re-expression as a differential variational inequality (DVI): a projection method, a self-adaptive projection method, and a proximal point method. Rigorous convergence results are provided for these methods, which rely on increasingly relaxed notions of generalized monotonicity, namely mixed strongly-weakly monotonicity for the projection method; pseudomonotonicity for the self-adaptive projection method, and quasimonotonicity for the proximal point method. These three algorithms are tested and their solution quality, convergence, and computational efficiency are compared. Our convergence results, which transcend the transportation applications studied here, apply to a broad family of VIs and DVIs, and are the weakest reported to date
Students\u27 use of personal technology in the classroom: analyzing the perceptions of the digital generation
Faculty frequently express concerns about students’ personal use of information
and communication technologies in today’s university classrooms. As a requirement
of a graduate research methodology course in a university in Ontario,
Canada, the authors conducted qualitative research to gain an in-depth understanding
of students’ perceptions of this issue. Their findings reveal students’
complex considerations about the acceptability of technology use. Their analysis
of the broader contexts of students’ use reveals that despite a technological revolution,
university teaching practices have remained largely the same, resulting in
‘cultural lag’ within the classroom. While faculty are technically ‘in charge’, students
wield power through course evaluations, surveillance technologies and
Internet postings. Neoliberalism and the corporatisation of the university have
engendered an ‘entrepreneurial student’ customer who sees education as a means
to a career. Understanding students’ perceptions and their technological, social
and political contexts offers insights into the tensions within today’s classrooms
Resolved stellar population of distant galaxies in the ELT era
The expected imaging capabilities of future Extremely Large Telescopes (ELTs)
will offer the unique possibility to investigate the stellar population of
distant galaxies from the photometry of the stars in very crowded fields. Using
simulated images and photometric analysis we explore here two representative
science cases aimed at recovering the characteristics of the stellar
populations in the inner regions of distant galaxies. Specifically: case A) at
the center of the disk of a giant spiral in the Centaurus Group, (mu B~21,
distance of 4.6 Mpc); and, case B) at half of the effective radius of a giant
elliptical in the Virgo Cluster (mu~19.5, distance of 18 Mpc). We generate
synthetic frames by distributing model stellar populations and adopting a
representative instrumental set up, i.e. a 42 m Telescope operating close to
the diffraction limit. The effect of crowding is discussed in detail showing
how stars are measured preferentially brighter than they are as the confusion
limit is approached. We find that (i) accurate photometry (sigma~0.1,
completeness >90%) can be obtained for case B) down to I~28.5, J~27.5 allowing
us to recover the stellar metallicity distribution in the inner regions of
ellipticals in Virgo to within ~0.1 dex; (ii) the same photometric accuracy
holds for the science case A) down to J~28.0, K~27.0, enabling to reconstruct
of the star formation history up to the Hubble time via simple star counts in
diagnostic boxes. For this latter case we discuss the possibility of deriving
more detailed information on the star formation history from the analysis of
their Horizontal Branch stars. We show that the combined features of high
sensitivity and angular resolution of ELTs may open a new era for our knowledge
of the stellar content of galaxies of different morphological type up to the
distance of the Virgo cluster.Comment: 21 pages, 17 figures, PASP accepted in pubblicatio
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