4,845 research outputs found
Proportional-integral-plus (PIP) control of the ALSTOM gasifier problem
Although it is able to exploit the full power of optimal state variable feedback within a non-minimum state-space (NMSS) setting, the proportional-integral-plus (PIP) controller is simple to implement and provides a logical extension of conventional proportional-integral and proportional-integral-derivative (PI/PID) controllers, with additional dynamic feedback and input compensators introduced automatically by the NMSS formulation of the problem when the process is of greater than first order or has appreciable pure time delays. The present paper applies the PIP methodology to the ALSTOM benchmark challenge, which takes the form of a highly coupled multi-variable linear model, representing the gasifier system of an integrated gasification combined cycle (IGCC) power plant. In particular, a straightforwardly tuned discrete-time PIP control system based on a reduced-order backward-shift model of the gasifier is found to yield good control of the benchmark, meeting most of the specified performance requirements at three different operating points
Excitation Spectrum at the Yang-Lee Edge Singularity of 2D Ising Model on the Strip
At the Yang-Lee edge singularity, finite-size scaling behavior is used to
measure the low-lying excitation spectrum of the Ising quantum spin chain for
free boundary conditions. The measured spectrum is used to identify the CFT
that describes the Yang-Lee edge singularity of the 2D Ising model for free
boundary conditions.Comment: 7 pages, 1 figur
Estimating population cardinal health state valuation models from individual ordinal (rank) health state preference data
Ranking exercises have routinely been used as warm-up exercises within health state valuation surveys. Very little use has been made of the information obtained in this process. Instead, research has focussed upon the analysis of health state valuation data obtained using the visual analogue scale, standard gamble and time trade off methods.
Thurstone’s law of comparative judgement postulates a stable relationship between ordinal and cardinal preferences, based upon the information provided by pairwise choices. McFadden proposed that this relationship could be modelled by estimating conditional logistic regression models where alternatives had been ranked. In this paper we report the estimation of such models for the Health Utilities Index Mark 2 and the SF-6D. The results are compared to the conventional regression models estimated from standard gamble data, and to the observed mean standard gamble health state valuations.
For both the HUI2 and the SF-6D, the models estimated using rank data are broadly comparable to the models estimated on standard gamble data and the predictive performance of these models is close to that of the standard gamble models. Our research indicates that rank data has the potential to provide useful insights into community health state preferences. However, important questions remain
Modelling the cost effectiveness of interferon beta and glatiramer acetate in the management of multiple sclerosis
OBJECTIVE: To evaluate the cost effectiveness of four disease modifying treatments (interferon betas and glatiramer acetate) for relapsing remitting and secondary progressive multiple sclerosis in the United Kingdom. DESIGN: Modelling cost effectiveness. SETTING: UK NHS. PARTICIPANTS: Patients with relapsing remitting multiple sclerosis and secondary progressive multiple sclerosis. MAIN OUTCOME MEASURES: Cost per quality adjusted life year gained. RESULTS: The base case cost per quality adjusted life year gained by using any of the four treatments ranged from £42 000 ($66 469; 61 630) to £98 000 based on efficacy information in the public domain. Uncertainty analysis suggests that the probability of any of these treatments having a cost effectiveness better than £20 000 at 20 years is below 20%. The key determinants of cost effectiveness were the time horizon, the progression of patients after stopping treatment, differential discount rates, and the price of the treatments. CONCLUSIONS: Cost effectiveness varied markedly between the interventions. Uncertainty around point estimates was substantial. This uncertainty could be reduced by conducting research on the true magnitude of the effect of these drugs, the progression of patients after stopping treatment, the costs of care, and the quality of life of the patients. Price was the key modifiable determinant of the cost effectiveness of these treatments
The relaxation of OH (v = 1) and OD (v = 1) by H2O and D2O at temperatures from 251 to 390 K
We report rate coefficients for the relaxation of OH(v = 1) and OD(v = 1) by H2O and D2O as a function of temperature between 251 and 390 K. All four rate coefficients exhibit a negative dependence on temperature. In Arrhenius form, the rate coefficients for relaxation (in units of 10–12 cm3 molecule–1 s–1) can be expressed as: for OH(v = 1) + H2O between 263 and 390 K: k = (2.4 ± 0.9) exp((460 ± 115)/T); for OH(v = 1) + D2O between 256 and 371 K: k = (0.49 ± 0.16) exp((610 ± 90)/T); for OD(v = 1) + H2O between 251 and 371 K: k = (0.92 ± 0.16) exp((485 ± 48)/T); for OD(v = 1) + D2O between 253 and 366 K: k = (2.57 ± 0.09) exp((342 ± 10)/T). Rate coefficients at (297 ± 1 K) are also reported for the relaxation of OH(v = 2) by D2O and the relaxation of OD(v = 2) by H2O and D2O. The results are discussed in terms of a mechanism involving the formation of hydrogen-bonded complexes in which intramolecular vibrational energy redistribution can occur at rates competitive with re-dissociation to the initial collision partners in their original vibrational states. New ab initio calculations on the H2O–HO system have been performed which, inter alia, yield vibrational frequencies for all four complexes: H2O–HO, D2O–HO, H2O–DO and D2O–DO. These data are then employed, adapting a formalism due to Troe (J. Troe, J. Chem. Phys., 1977, 66, 4758), in order to estimate the rates of intramolecular energy transfer from the OH (OD) vibration to other modes in the complexes in order to explain the measured relaxation rates—assuming that relaxation proceeds via the hydrogen-bonded complexes
Critical Excitation Spectrum of Quantum Chain With A Local 3-Spin Coupling
This article reports a measurement of the low-energy excitation spectrum
along the critical line for a quantum spin chain having a local interaction
between three Ising spins and longitudinal and transverse magnetic fields. The
measured excitation spectrum agrees with that predicted by the (D, A)
conformal minimal model under a nontrivial correspondence between translations
at the critical line and discrete lattice translations. Under this
correspondence, the measurements confirm a prediction that the critical line of
this quantum spin chain and the critical point of the 2D 3-state Potts model
are in the same universality class.Comment: 7 pages, 2 figure
Estimating population cardinal health state valuation models from individual ordinal (rank) health state preference data
Ranking exercises have routinely been used as warm-up exercises within health state valuation surveys. Very little use has been made of the information obtained in this process. Instead, research has focussed upon the analysis of health state valuation data obtained using the visual analogue scale, standard gamble and time trade off methods. Thurstone’s law of comparative judgement postulates a stable relationship between ordinal and cardinal preferences, based upon the information provided by pairwise choices. McFadden proposed that this relationship could be modelled by estimating conditional logistic regression models where alternatives had been ranked. In this paper we report the estimation of such models for the Health Utilities Index Mark 2 and the SF-6D. The results are compared to the conventional regression models estimated from standard gamble data, and to the observed mean standard gamble health state valuations. For both the HUI2 and the SF-6D, the models estimated using rank data are broadly comparable to the models estimated on standard gamble data and the predictive performance of these models is close to that of the standard gamble models. Our research indicates that rank data has the potential to provide useful insights into community health state preferences. However, important questions remain.health state valuation; HUI-2; SF-6D
Estimating population cardinal health state valuation models from individual ordinal (rank) health state preference data
Ranking exercises have routinely been used as warm-up exercises within health state valuation surveys. Very little use has been made of the information obtained in this process. Instead, research has focussed upon the analysis of health state valuation data obtained using the visual analogue scale, standard gamble and time trade off methods.
Thurstone’s law of comparative judgement postulates a stable relationship between ordinal and cardinal preferences, based upon the information provided by pairwise choices. McFadden proposed that this relationship could be modelled by estimating conditional logistic regression models where alternatives had been ranked. In this paper we report the estimation of such models for the Health Utilities Index Mark 2 and the SF-6D. The results are compared to the conventional regression models estimated from standard gamble data, and to the observed mean standard gamble health state valuations.
For both the HUI2 and the SF-6D, the models estimated using rank data are broadly comparable to the models estimated on standard gamble data and the predictive performance of these models is close to that of the standard gamble models. Our research indicates that rank data has the potential to provide useful insights into community health state preferences. However, important questions remain
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Enhanced neural response to anticipation, effort and consummation of reward and aversion during Bupropion treatment
Background
We have previously shown that the selective serotonergic re-uptake inhibitor, citalopram, reduces the neural
response to reward and aversion in healthy volunteers. We suggest that this inhibitory effect might underlie
the emotional blunting reported by patients on these medications. Bupropion is a dopaminergic and
noradrenergic re-uptake inhibitor and has been suggested to have more therapeutic effects on reward-related
deficits. However, how bupropion affects the neural responses to reward and aversion is unclear.
Methods
17 healthy volunteers (9 female, 8 male) received 7 days of bupropion (150 mg/day) and 7 days of placebo
treatment, in a double-blind crossover design. Our functional Magnetic Resonance Imaging task consisted of
3 phases; an anticipatory phase (pleasant or unpleasant cue), an effort phase (button presses to achieve a
pleasant taste or to avoid an unpleasant taste) and a consummatory phase (pleasant or unpleasant tastes).
Volunteers also rated wanting, pleasantness and intensity of the tastes.
Results
Relative to placebo, bupropion increased activity during the anticipation phase in the ventral medial
prefrontal cortex (vmPFC) and caudate. During the effort phase, bupropion increased activity in the vmPFC,
striatum, dorsal anterior cingulate cortex and primary motor cortex. Bupropion also increased medial
orbitofrontal cortex, amygdala and ventral striatum activity during the consummatory phase.
Conclusions
Our results are the first to show that bupropion can increase neural responses during the anticipation, effort
and consummation of rewarding and aversive stimuli. This supports the notion that bupropion might be
beneficial for depressed patients with reward-related deficits and blunted affect
Effect of selenium supplementation on adiponectin concentration as a marker of type-2 diabetes risk in UK pregnant women
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