651 research outputs found
Applying Psychological Theory to in-game moral behaviors through the development of a purpose-made game
A number of video games involve moral narratives or require the players to make
moral decisions. Research from psychologists has helped to understand the effects that video
game content can have on how individuals think, feel and behave. Recent research has
examined the role of morality in video games, yet there are many inconsistencies in the
findings that could be due to the use of commercial video games for research purposes, which
contain biases such as familiarity with the game and favorite characters. By developing a
bespoke game designed specifically for the purpose of exploring morality, these potential
biases can be reduced. Before designing the game, morality in existing video games is
critically analyzed, using theories from moral psychology. From this, a game was developed
to measure behavioral outcomes through which moral decisions are made; with the aim to
address biases that are inherent in commercial games. Then, the resultant game was used to
investigate how participants make moral choices in video games
A new method for the estimation of variance matrix with prescribed zeros in nonlinear mixed effects models
We propose a new method for the Maximum Likelihood Estimator (MLE) of
nonlinear mixed effects models when the variance matrix of Gaussian random
effects has a prescribed pattern of zeros (PPZ). The method consists in
coupling the recently developed Iterative Conditional Fitting (ICF) algorithm
with the Expectation Maximization (EM) algorithm. It provides positive definite
estimates for any sample size, and does not rely on any structural assumption
on the PPZ. It can be easily adapted to many versions of EM.Comment: Accepted for publication in Statistics and Computin
Landau Expansion for the Kugel-Khomskii Hamiltonian
The Kugel-Khomskii (KK) Hamiltonian for the titanates describes spin and
orbital superexchange interactions between ions in an ideal perovskite
structure in which the three orbitals are degenerate in energy and
electron hopping is constrained by cubic site symmetry. In this paper we
implement a variational approach to mean-field theory in which each site, ,
has its own single-site density matrix \rhov(i), where , the
number of allowed single-particle states, is 6 (3 orbital times 2 spin states).
The variational free energy from this 35 parameter density matrix is shown to
exhibit the unusual symmetries noted previously which lead to a
wavevector-dependent susceptibility for spins in orbitals which is
dispersionless in the -direction. Thus, for the cubic KK model
itself, mean-field theory does not provide wavevector `selection', in agreement
with rigorous symmetry arguments. We consider the effect of including various
perturbations. When spin-orbit interactions are introduced, the susceptibility
has dispersion in all directions in -space, but the resulting
antiferromagnetic mean-field state is degenerate with respect to global
rotation of the staggered spin, implying that the spin-wave spectrum is
gapless. This possibly surprising conclusion is also consistent with rigorous
symmetry arguments. When next-nearest-neighbor hopping is included, staggered
moments of all orbitals appear, but the sum of these moments is zero, yielding
an exotic state with long-range order without long-range spin order. The effect
of a Hund's rule coupling of sufficient strength is to produce a state with
orbital order.Comment: 20 pages, 5 figures, submitted to Phys. Rev. B (2003
Water wave propagation and scattering over topographical bottoms
Here I present a general formulation of water wave propagation and scattering
over topographical bottoms. A simple equation is found and is compared with
existing theories. As an application, the theory is extended to the case of
water waves in a column with many cylindrical steps
Metal insulator transition in TlSr2CoO5 from orbital degeneracy and spin disproportionation
To describe the metal insulator transition in the new oxide TlSr2CoO5 we
investigate its electronic structure by LDA and model Hartree-Fock
calculations. Within LDA we find a homogeneous metallic and ferromagnetic
ground state, but when including the Coulomb interaction more explicitly within
the Hartree-Fock approximation, we find an insulating state of lower energy
with both spin and orbital order. We also interpret our results in terms of a
simple model.Comment: 8 pages, 9 figure
Green's function approach to the magnetic properties of the kagome antiferromagnet
The Heisenberg antiferromagnet is studied on the kagom\'e lattice by
using a Green's function method based on an appropriate decoupling of the
equations of motion. Thermodynamic properties as well as spin-spin correlation
functions are obtained and characterize this system as a two-dimensional
quantum spin liquid. Spin-spin correlation functions decay exponentially with
distance down to low temperature and the calculated missing entropy at T=0 is
found to be . Within the present scheme, the specific heat exhibits
a single peak structure and a dependence at low temperature.Comment: 6 (two-column revtex4) pages, 5 ps figures. Submitted to Phys. Rev.
Differentiating normal and problem gambling: a grounded theory approach.
A previous study (Ricketts & Macaskill, 2003) delineated a theory of problem gambling based on the experiences of treatment seeking male gamblers and allowed predictions to be made regarding the processes that differentiate between normal and problem gamblers. These predictions are the focus of the present study, which also utilised a grounded theory approach, but with a sample of male high frequency normal gamblers. The findings suggest that there are common aspects of gambling associated with arousal and a sense of achievement. The use of gambling to manage negative emotional states differentiated normal and problem gambling. Perceived self-efficacy , emotion management skills and perceived likelihood of winning money back were intervening variables differentiating problem and normal gamblers.</p
Weak antiferromagnetism due to Dzyaloshinskii-Moriya interaction in BaCuOCl
The antiferromagnetic insulating cuprate BaCuOCl contains
folded CuO chains with four magnetic copper ions () per unit cell.
An underlying multiorbital Hubbard model is formulated and the superexchange
theory is developed to derive an effective spin Hamiltonian for this cuprate.
The resulting spin Hamiltonian involves a Dzyaloshinskii-Moriya term and a more
weak symmetric anisotropic exchange term besides the isotropic exchange
interaction. The corresponding Dzyaloshinskii-Moriya vectors of each magnetic
Cu-Cu bond in the chain reveal a well defined spatial order. Both, the
superexchange theory and the complementary group theoretical consideration,
lead to the same conclusion on the character of this order. The analysis of the
ground-state magnetic properties of the derived model leads to the prediction
of an additional noncollinear modulation of the antiferromagnetic structure.
This weak antiferromagnetism is restricted to one of the Cu sublattices.Comment: 13 pages, 1 table, 4 figure
Modified gravity without dark matter
On an empirical level, the most successful alternative to dark matter in
bound gravitational systems is the modified Newtonian dynamics, or MOND,
proposed by Milgrom. Here I discuss the attempts to formulate MOND as a
modification of General Relativity. I begin with a summary of the
phenomenological successes of MOND and then discuss the various covariant
theories that have been proposed as a basis for the idea. I show why these
proposals have led inevitably to a multi-field theory. I describe in some
detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and
discuss its successes and shortcomings. This lecture is primarily pedagogical
and directed to those with some, but not a deep, background in General
RelativityComment: 28 pages, 10 figures, lecture given at Third Aegean Summer School,
The Invisible Universe: Dark Matter and Dark Energy, minor errors corrected,
references update
Bond order from disorder in the planar pyrochlore magnet
We study magnetic order in the Heisenberg antiferromagnet on the checkerboard
lattice, a two-dimensional version of the pyrochlore network with strong
geometric frustration. By employing the semiclassical (1/S) expansion we find
that quantum fluctuations of spins induce a long-range order that breaks the
four-fold rotational symmetry of the lattice. The ordered phase is a
valence-bond crystal. We discuss similarities and differences with the extreme
quantum case S = 1/2 and find a useful phenomenology to describe the
bond-ordered phases.Comment: Minor clarifications + reference to an informal introduction
cond-mat/030809
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