869 research outputs found
First-Order Transition in XY Fully Frustrated Simple Cubic Lattice
We study the nature of the phase transition in the fully frustrated simple
cubic lattice with the XY spin model. This system is the Villain's model
generalized in three dimensions. The ground state is very particular with a
12-fold degeneracy. Previous studies have shown unusual critical properties.
With the powerful Wang-Landau flat-histogram Monte Carlo method, we carry out
in this work intensive simulations with very large lattice sizes. We show that
the phase transition is clearly of first order, putting an end to the
uncertainty which has lasted for more than twenty years
Phase Transition in Heisenberg Fully Frustrated Simple Cubic Lattice
The phase transition in frustrated spin systems is a fascinated subject in
statistical physics. We show the result obtained by the Wang-Landau flat
histogram Monte Carlo simulation on the phase transition in the fully
frustrated simple cubic lattice with the Heisenberg spin model. The degeneracy
of the ground state of this system is infinite with two continuous parameters.
We find a clear first-order transition in contradiction with previous studies
which have shown a second-order transition with unusual critical properties.
The robustness of our calculations allows us to conclude this issue putting an
end to the 20-year long uncertainty.Comment: submitted for publicatio
Competitive Facility Location under Random Utilities and Routing Constraints
In this paper, we study a facility location problem within a competitive
market context, where customer demand is predicted by a random utility choice
model. Unlike prior research, which primarily focuses on simple constraints
such as a cardinality constraint on the number of selected locations, we
introduce routing constraints that necessitate the selection of locations in a
manner that guarantees the existence of a tour visiting all chosen locations
while adhering to a specified tour length upper bound. Such routing constraints
find crucial applications in various real-world scenarios. The problem at hand
features a non-linear objective function, resulting from the utilization of
random utilities, together with complex routing constraints, making it
computationally challenging. To tackle this problem, we explore three types of
valid cuts, namely, outer-approximation and submodular cuts to handle the
nonlinear objective function, as well as sub-tour elimination cuts to address
the complex routing constraints. These lead to the development of two exact
solution methods: a nested cutting plane and nested branch-and-cut algorithms,
where these valid cuts are iteratively added to a master problem through two
nested loops. We also prove that our nested cutting plane method always
converges to optimality after a finite number of iterations. Furthermore, we
develop a local search-based metaheuristic tailored for solving large-scale
instances and show its pros and cons compared to exact methods. Extensive
experiments are conducted on problem instances of varying sizes, demonstrating
that our approach excels in terms of solution quality and computation time when
compared to other baseline approaches
Effect of Disorder in the Frustrated Ising FCC Antiferromagnet: Phase Diagram and Stretched Exponential Relaxation
We study the phase transition in a face-centered-cubic antiferromagnet with
Ising spins as a function of the concentration of ferromagnetic bonds
randomly introduced into the system. Such a model describes the spin-glass
phase at strong bond disorder. Using the standard Monte Carlo simulation and
the powerful Wang-Landau flat-histogram method, we carry out in this work
intensive simulations over the whole range of . We show that the first-order
transition disappears with a tiny amount of ferromagnetic bonds, namely , in agreement with theories and simulations on other 3D models. The
antiferromagnetic long-range order is also destroyed with a very small
(). With increasing , the system changes into a spin glass and
then to a ferromagnetic phase when . The phase diagram in the space
() shows an asymmetry, unlike the case of the Ising spin glass
on the simple cubic lattice. We calculate the relaxation time around the
spin-glass transition temperature and we show that the spin autocorrelation
follows a stretched exponential relaxation law where the factor is equal to
at the transition as suggested by the percolation-based theory.
This value is in agreement with experiments performed on various spin glasses
and with Monte Carlo simulations on different SG models
Domain-specific queries and Web search personalization: some investigations
Major search engines deploy personalized Web results to enhance users'
experience, by showing them data supposed to be relevant to their interests.
Even if this process may bring benefits to users while browsing, it also raises
concerns on the selection of the search results. In particular, users may be
unknowingly trapped by search engines in protective information bubbles, called
"filter bubbles", which can have the undesired effect of separating users from
information that does not fit their preferences. This paper moves from early
results on quantification of personalization over Google search query results.
Inspired by previous works, we have carried out some experiments consisting of
search queries performed by a battery of Google accounts with differently
prepared profiles. Matching query results, we quantify the level of
personalization, according to topics of the queries and the profile of the
accounts. This work reports initial results and it is a first step a for more
extensive investigation to measure Web search personalization.Comment: In Proceedings WWV 2015, arXiv:1508.0338
The Impacts of Internal Audit Practices on the Quality of Internal Control in Vietnamese Smes
Purpose: This study examines the impacts of internal audit practices on internal control in Vietnamese SMEs.
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Theoretical framework: This paper employs the three lines of defense model framework to study the impact of internal audit practices on internal control in Vietnamese SMEs. Internal auditing practices were measured by the items listed in the attribute standards and performance standards of the International Professional Practices Framework (IPPF). Internal control quality includes control environment, risk assessment, control activities, information and communication, and monitoring which are provided by the Committee of Sponsoring Organizations of the Treadway Commission (COSO) Framework.
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Design/methodology/approach: We collect primary data using questionnaire. Data collected from the questionnaire is divided into two groups (1) the measurement of the internal auditing practices and (2) the measurement of the quality of internal control system. We then use the Structural Equation Modelling (SEM) to test for the hypotheses related to the relationship between internal audit practices and internal control.
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Findings: Our results suggest that both attribute standards and performance standards have positive impacts on the control environment, risk assessment, control activities, and monitoring aspects of internal control. Meanwhile, internal audit seems to not influence the information and communication.
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Research, Practical & Social implications: The study contributes to the literature by shedding light on the impacts of internal audit practices on the quality of internal control in Vietnamese SMEs.
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Originality/value: This study examines the unique context of Vietnamese SMEs. Ultimately, the framework aims to provide a comprehensive understanding of how internal audit practices impact internal control quality in this specific context
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