10,263 research outputs found
Searching for quantum optimal controls in the presence of singular critical points
Quantum optimal control has enjoyed wide success for a variety of theoretical
and experimental objectives. These favorable results have been attributed to
advantageous properties of the corresponding control landscapes, which are free
from local optima if three conditions are met: (1) the quantum system is
controllable, (2) the Jacobian of the map from the control field to the
evolution operator is full rank, and (3) the control field is not constrained.
This paper explores how gradient searches for globally optimal control fields
are affected by deviations from assumption (2). In some quantum control
problems, so-called singular critical points, at which the Jacobian is
rank-deficient, may exist on the landscape. Using optimal control simulations,
we show that search failure is only observed when a singular critical point is
also a second-order trap, which occurs if the control problem meets additional
conditions involving the system Hamiltonian and/or the control objective. All
known second-order traps occur at constant control fields, and we also show
that they only affect searches that originate very close to them. As a result,
even when such traps exist on the control landscape, they are unlikely to
affect well-designed gradient optimizations under realistic searching
conditions.Comment: 14 pages, 2 figure
Searching for quantum optimal controls under severe constraints
The success of quantum optimal control for both experimental and theoretical
objectives is connected to the topology of the corresponding control
landscapes, which are free from local traps if three conditions are met: (1)
the quantum system is controllable, (2) the Jacobian of the map from the
control field to the evolution operator is of full rank, and (3) there are no
constraints on the control field. This paper investigates how the violation of
assumption (3) affects gradient searches for globally optimal control fields.
The satisfaction of assumptions (1) and (2) ensures that the control landscape
lacks fundamental traps, but certain control constraints can still introduce
artificial traps. Proper management of these constraints is an issue of great
practical importance for numerical simulations as well as optimization in the
laboratory. Using optimal control simulations, we show that constraints on
quantities such as the number of control variables, the control duration, and
the field strength are potentially severe enough to prevent successful
optimization of the objective. For each such constraint, we show that exceeding
quantifiable limits can prevent gradient searches from reaching a globally
optimal solution. These results demonstrate that careful choice of relevant
control parameters helps to eliminate artificial traps and facilitate
successful optimization.Comment: 16 pages, 7 figure
Stress at Work: Factors Associated with Cognitive Disorganisation among private sector professionals
This study explores psychological and psychological variables associated with perceived stress at work. A total of 100 international participants consented to donating a hair sample and completing a work-related stress survey. Logistic regression was used to investigate associations with low/high cognitive disorganisation using data collected from hair cortisol analysis and self-report questionnaires. High cognitive disorganisation scores were associated with high cardiopulmonary and anger scores. Low perceived self-efficacy was associated with high cognitive disorganisation. An association was found between low cortisol and low perceived self-efficacy. The relationship between high cognitive disorganisation and low self-efficacy endorses previous claims linking performance to perceived high self-efficacy
Definitions of relapse in trials comparing antipsychotic maintenance with discontinuation or reduction for schizophrenia spectrum disorders: A systematic review
INTRODUCTION: Avoidance of relapse is the main aim of long-term antipsychotic treatment in schizophrenia, yet how 'relapse' is defined in trials is not well-known. METHODS: We conducted a systematic review of definitions of relapse in trials of continuous antipsychotic treatment compared with discontinuation, intermittent treatment or dose reduction for people with schizophrenia spectrum disorders. Trials were identified from previous Cochrane reviews and a new search. The quality of relapse definitions was rated in terms of reliability and clinical relevance and associations between quality of definitions and trial characteristics and outcome were explored. RESULTS: We identified 82 reports of 81 trials which employed 54 different definitions of relapse. There were 33 definitions in the 35 trials published since 1990, with recent trials employing complex definitions often involving alternative criteria. Only ten primary definitions of relapse required the presence of psychotic symptoms in all cases, and only three specified this in combination with a measure of overall severity or functional decline. Only two definitions specified a duration longer than two days. Relapse definitions were rated as showing good reliability in 37 trials, but only seven showed good clinical relevance. Six trials with definitions that were both reliable and clinically relevant were slightly longer, but did not differ from remaining trials in other characteristics or overall or relative risk of relapse. CONCLUSIONS: Antipsychotic trials define relapse in numerous different ways, and few definitions consistently reflect suggested indications of a clinically significant relapse
Missense Mutation R338W in ARHGEF9 in a Family with X-linked Intellectual Disability with Variable Macrocephaly and Macro-Orchidism
Non-syndromal X-linked intellectual disability (NS-XLID) represents a broad group of clinical disorders in which ID is the only clinically consistent manifestation. Although in many cases either chromosomal linkage data or knowledge of the >100 existing XLID genes has assisted mutation discovery, the underlying cause of disease remains unresolved in many families. We report the resolution of a large family (K8010) with NS-XLID, with variable macrocephaly and macro-orchidism. Although a previous linkage study had mapped the locus to Xq12-q21, this region contained too many candidate genes to be analyzed using conventional approaches. However, X-chromosome exome sequencing, bioinformatics analysis and segregation analysis revealed a novel missense mutation (c.1012C>T; p.R338W) in ARHGEF9. This gene encodes collybistin (CB), a neuronal GDP-GTP exchange factor previously implicated in several cases of XLID, as well as clustering of gephyrin and GABAA receptors at inhibitory synapses. Molecular modeling of the CB R338W substitution revealed that this change results in the substitution of a long electropositive side-chain with a large non-charged hydrophobic side-chain. The R338W change is predicted to result in clashes with adjacent amino acids (K363 and N335) and disruption of electrostatic potential and local folding of the PH domain, which is known to bind phosphatidylinositol-3-phosphate (PI3P/PtdIns-3-P). Consistent with this finding, functional assays revealed that recombinant CB CB2SH3- (R338W) was deficient in PI3P binding and was not able to translocate EGFP-gephyrin to submembrane microaggregates in an in vitro clustering assay. Taken together, these results suggest that the R338W mutation in ARHGEF9 is the underlying cause of NS-XLID in this family
Using the theory of planned behaviour as a process evaluation tool in randomised trials of knowledge translation strategies : A case study from UK primary care
Peer reviewedPublisher PD
“It’s hard to tell”. The challenges of scoring patients on standardised outcome measures by multidisciplinary teams: a case study of Neurorehabilitation
Background
Interest is increasing in the application of standardised outcome measures in clinical practice. Measures designed for use in research may not be sufficiently precise to be used in monitoring individual patients. However, little is known about how clinicians and in particular, multidisciplinary teams, score patients using these measures. This paper explores the challenges faced by multidisciplinary teams in allocating scores on standardised outcome measures in clinical practice.
Methods
Qualitative case study of an inpatient neurorehabilitation team who routinely collected standardised outcome measures on their patients. Data were collected using non participant observation, fieldnotes and tape recordings of 16 multidisciplinary team meetings during which the measures were recited and scored. Eleven clinicians from a range of different professions were also interviewed. Data were analysed used grounded theory techniques.
Results
We identified a number of instances where scoring the patient was 'problematic'. In 'problematic' scoring, the scores were uncertain and subject to revision and adjustment. They sometimes required negotiation to agree on a shared understanding of concepts to be measured and the guidelines for scoring. Several factors gave rise to this problematic scoring. Team members' knowledge about patients' problems changed over time so that initial scores had to be revised or dismissed, creating an impression of deterioration when none had occurred. Patients had complex problems which could not easily be distinguished from each other and patients themselves varied in their ability to perform tasks over time and across different settings. Team members from different professions worked with patients in different ways and had different perspectives on patients' problems. This was particularly an issue in the scoring of concepts such as anxiety, depression, orientation, social integration and cognitive problems.
Conclusion
From a psychometric perspective these problems would raise questions about the validity, reliability and responsiveness of the scores. However, from a clinical perspective, such characteristics are an inherent part of clinical judgement and reasoning. It is important to highlight the challenges faced by multidisciplinary teams in scoring patients on standardised outcome measures but it would be unwarranted to conclude that such challenges imply that these measures should not be used in clinical practice for decision making about individual patients. However, our findings do raise some concerns about the use of such measures for performance management
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