3,006 research outputs found
Users’ Continued Usage of Online Healthcare Virtual Communities: An Empirical Investigation in the Context of HIV Support Communities
This study uses data from an online HIV/AIDS health support virtual community to examine whether users’ emotional states and the social support they receive influence their continued usage. We adopt grief theory to conceptualize the negative emotions that people living with HIV/AIDS could experience. Linguistic analysis is used to measure the emotional states of the users and the informational and emotional support that they receive. Results show that users showing a higher level of disbelief and yearning are more likely to leave the community while those with a high level of anger and depression are more likely to stay on. Users who receive more informational support are more likely to leave once they have obtained the information they sought, but those who receive more emotional support are more likely to stay on. The findings of this study can help us better understand users’ support seeking behavior in online support VCs
Performance characteristics of an adaptive controller based on least-mean-square filters
A closed loop, adaptive control scheme that uses a least mean square filter as the controller model is presented, along with simulation results that demonstrate the excellent robustness of this scheme. It is shown that the scheme adapts very well to unknown plants, even those that are marginally stable, responds appropriately to changes in plant parameters, and is not unduly affected by additive noise. A heuristic argument for the conditions necessary for convergence is presented. Potential applications and extensions of the scheme are also discussed
Inside Money, Procyclical Leverage, and Banking Catastrophes
We explore a model of the interaction between banks and outside investors in
which the ability of banks to issue inside money (short-term liabilities
believed to be convertible into currency at par) can generate a collapse in
asset prices and widespread bank insolvency. The banks and investors share a
common belief about the future value of certain long-term assets, but they have
different objective functions; changes to this common belief result in
portfolio adjustments and trade. Positive belief shocks induce banks to buy
risky assets from investors, and the banks finance those purchases by issuing
new short-term liabilities. Negative belief shocks induce banks to sell assets
in order to reduce their chance of insolvency to a tolerably low level, and
they supply more assets at lower prices, which can result in multiple
market-clearing prices. A sufficiently severe negative shock causes the set of
equilibrium prices to contract (in a manner given by a cusp catastrophe),
causing prices to plummet discontinuously and banks to become insolvent.
Successive positive and negative shocks of equal magnitude do not cancel;
rather, a banking catastrophe can occur even if beliefs simply return to their
initial state. Capital requirements can prevent crises by curtailing the
expansion of balance sheets when beliefs become more optimistic, but they can
also force larger price declines. Emergency asset price supports can be
understood as attempts by a central bank to coordinate expectations on an
equilibrium with solvency.Comment: 31 pages, 10 figure
Expedient and Monotone Learning Rules
This paper considers learning rules for environments in which little prior and feedback information is available to the decision-maker. Two properties of such learning rules, absolute expediency and monotonicity, are studied. The paper provides some necessary and some sufficient conditions for these properties. A number of examples show that there is quite a large variety of learning rules which have these properties. It is also shown that all learning rules that have these properties are, in some sense, related to replicator dynamics of evolutionary game theory.Absolute expediency, monotonicity, learning rule, decision making
Ground State of the Kagome Lattice Heisenberg Antiferromagnet
Using series expansions around the dimer limit, we show that the ground state
of the Heisenberg Antiferromagnet on the Kagome Lattice appears to be a Valence
Bond Crystal (VBC) with a 36-site unit cell, and an energy per site of
. It is a honeycomb lattice of `perfect hexagons' as
discussed by Nikolic and Senthil. The energy difference between the ground
state and other ordered states with the maximum number of `perfect hexagons',
such as a stripe-ordered state, is of order . The energy of the
36-site system with periodic boundary conditions is further lowered by an
amount of , consistent with Exact Diagonalization. Every unit
cell of the VBC has two singlet states whose degeneracy is not lifted to
order in the expansion. We estimate this energy difference to be smaller than
. Two leading orders of perturbation theory find the lowest-energy
triplet excitations to be dispersionless and confined to the `perfect
hexagons'
How did the Welsh government manage to reform council tax in 2005?
Repeated calls have been made for council tax (CT) in the UK to be reformed. A ‘tyranny of the status quo’ suggests that politicians will avoid this because they fear a backlash from the losers of reform. This paper claims that the tyranny of the status quo is not a fixed law. The Welsh government revalued CT in 2005 but did not communicate the complexity of reform sufficiently. Reform requires greater efforts to communicate the complexity of winning and losing
Vorticity-transport and unstructured RANS investigation of rotor-fuselage interactions
The prediction capabilities of unstructured primitive-variable and vorticity-transport-based Navier-Stokes solvers have been compared for rotorcraft-fuselage interaction. Their accuracies have been assessed using the NASA Langley ROBIN series of experiments. Correlation of steady pressure on the isolated fuselage delineates the differences between the viscous and inviscid solvers. The influence of the individual blade passage, model supports, and viscous effects on the unsteady pressure loading has been studied. Smoke visualization from the ROBIN experiment has been used to determine the ability of the codes to predict the wake geometry. The two computational methods are observed to provide similar results within the context of their physical assumptions and simplifications in the test configuration
Fluctuations, strangeness and quasi-quarks in heavy-ion collisions from lattice QCD
We report measurements of diagonal susceptibilities for the baryon number,
chi_B, electrical charge, chi_Q, third component of isospin, chi_I,
strangeness, chi_S, and hypercharge, chi_Y, as well as the off-diagonal chi_BQ,
chi_BY, chi_BS, etc. We show that the ratios of susceptibilities in the high
temperature phase are robust variables, independent of lattice spacing, and
therefore give predictions for experiments. We also investigate strangeness
production and flavour symmetry breaking matrix elements at finite temperature.
Finally, we present evidence that in the high temperature phase of QCD the
different flavour quantum numbers are excited in linkages which are exactly the
same as one expects from quarks. We present some investigations of these
quark-like quasi particles
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