143 research outputs found
Constraint-Adaptive MPC for linear systems: A system-theoretic framework for speeding up MPC through online constraint removal
Reducing the computation time of model predictive control (MPC) is important,
especially for systems constrained by many state constraints. In this paper, we
propose a new online constraint removal framework for linear systems, for which
we coin the term constraint-adaptive MPC (ca-MPC). In so-called exact ca-MPC,
we adapt the imposed constraints by removing, at each time-step, a subset of
the state constraints in order to reduce the computational complexity of the
receding-horizon optimal control problem, while ensuring that the closed-loop
behavior is {\em identical} to that of the original MPC law. We also propose an
approximate ca-MPC scheme in which a further reduction of computation time can
be accomplished by a tradeoff with closed-loop performance, while still
preserving recursive feasibility, stability, and constraint satisfaction
properties. The online constraint removal exploits fast backward and forward
reachability computations combined with optimality properties
Size dependent exciton g-factor in self-assembled InAs/InP quantum dots
We have studied the size dependence of the exciton g-factor in self-assembled
InAs/InP quantum dots. Photoluminescence measurements on a large ensemble of
these dots indicate a multimodal height distribution. Cross-sectional Scanning
Tunneling Microscopy measurements have been performed and support the
interpretation of the macro photoluminescence spectra. More than 160 individual
quantum dots have systematically been investigated by analyzing single dot
magneto-luminescence between 1200nm and 1600 nm. We demonstrate a strong
dependence of the exciton g-factor on the height and diameter of the quantum
dots, which eventually gives rise to a sign change of the g-factor. The
observed correlation between exciton g-factor and the size of the dots is in
good agreement with calculations. Moreover, we find a size dependent anisotropy
splitting of the exciton emission in zero magnetic field.Comment: 15 pages, 7 figure
A Frequency-Domain Version of Willems' Fundamental Lemma
Willems' fundamental lemma has recently received an impressive amount of
attention in the (data-driven) control community. In this paper, we formulate a
frequency-domain equivalent of this lemma. In doing so, we bridge the gap
between recent developments in data-driven analysis and control and the
extensive knowledge on non-parametric frequency-domain identification that has
accumulated, particularly in industry, through decades of working with
classical (frequency-domain) control and identification techniques. Our
formulation also allows for the combination of multiple data sets in the sense
that, in the data, multiple input directions may be excited at the same
frequency. We also illustrate the usefulness of our results by demonstrating
how they can be applied to perform frequency-domain-data-driven simulation
The potential of time-multiplexed steering by temperature optimization in microwave hyperthermia
Introduction: In clinical practice at Erasmus MC, the target-to-hotspot-quotient (THQ) of the specific absorption rate (SAR) is used to optimize phases and amplitudes of the signals to be applied to the hyperthermia applicator [1]. Recent research showed that the ratio between tumor and healthy tissue temperatures can be increased when amplitudes and phases are time-multiplexed when applying SAR optimization [2]. However, direct temperature optimization achieves higher tumor temperatures when considering time-multiplexed antenna steering [3]. In this work, we investigated the benefit of time-multiplexed steering when applying temperature optimization in models of patients with tumors on the head and neck region. Methods: For five patients with a tumor in the head and neck region, a Sim4Life model was created and treatment planning was applied for the HyperCollar3D. A single distribution SAR based THQ optimization was performed for reference. A novel temperature optimization scheme was developed, which optimizes the tumor temperature for the first 15 minutes of the treatment. This results in higher tumor temperatures throughout the treatment by explicitly including the transient effects in the optimization. The evaluation was based on simulations of the full treatment time of 75 minutes, with the total power scaled to reach maximum 43°C in the tumor. Performance was evaluated by comparing T50 for both healthy and tumor tissue during treatment. Results: The ratio between T50 in the healthy and tumor tissue was improved when using the novel temperature-based optimization for time-multiplexed distributions (Figure 1C). The SAR THQ showed a lower ratio for the time-multiplexed solution, this is resolved in the temperature simulations (Figure 2).Conclusion/Discussion: The resulting T50 values, show that the temperatures during treatment might benefit from the temperature optimized with the multiplexed steering approach: either the temperature in the tumor tissue can be higher or the temperature in healthy tissue could remain lower. Although the approach seems beneficial, assessment of the impact of uncertainties in thermal parameters and inclusion of a larger dataset is still required to assess the significance of the improvement and the expected clinical benefit [4]. <br/
Adapting temperature predictions to MR imaging in treatment position to improve simulation-guided hyperthermia for cervical cancer
Hyperthermia treatment consists of elevating the temperature of the tumor to increase the effectiveness of radiotherapy and chemotherapy. Hyperthermia treatment planning (HTP) is an important tool to optimize treatment quality using pre-treatment temperature predictions. The accuracy of these predictions depends on modeling uncertainties such as tissue properties and positioning. In this study, we evaluated if HTP accuracy improves when the patient is imaged inside the applicator at the start of treatment. Because perfusion is a major uncertainty source, the importance of accurate treatment position and anatomy was evaluated using different perfusion values. Volunteers were scanned using MR imaging without (&#x201C;planning setup&#x201D;) and with the MR-compatible hyperthermia device (&#x201C;treatment setup&#x201D;). Temperature-based quality indicators were used to assess the differences between the standard, apparent and the optimized hyperthermia dose. We conclude that pre-treatment imaging can improve HTP predictions accuracy but also, that tissue perfusion modelling is crucial if temperature-based optimization is applied.</p
Rotterdam Aphasia Therapy Study (RATS) - 3: " The efficacy of intensive cognitive-linguistic therapy in the acute stage of aphasia"; design of a randomised controlled trial
Background: Aphasia is a severely disabling condition occurring in 20 to 25% of stroke patients. Most patients with aphasia due to stroke receive speech and language therapy. Methodologically sound randomised controlled trials investigating the effect of specific interventions for patients with aphasia following stroke are scarce.
Disease-specific, neurosphere-derived cells as models for brain disorders
There is a pressing need for patient-derived cell models of brain diseases that are relevant and robust enough to produce the large quantities of cells required for molecular and functional analyses. We describe here a new cell model based on patient-derived cells from the human olfactory mucosa, the organ of smell, which regenerates throughout life from neural stem cells. Olfactory mucosa biopsies were obtained from healthy controls and patients with either schizophrenia, a neurodevelopmental psychiatric disorder, or Parkinson's disease, a neurodegenerative disease. Biopsies were dissociated and grown as neurospheres in defined medium. Neurosphere-derived cell lines were grown in serum-containing medium as adherent monolayers and stored frozen. By comparing 42 patient and control cell lines we demonstrated significant disease-specific alterations in gene expression, protein expression and cell function, including dysregulated neurodevelopmental pathways in schizophrenia and dysregulated mitochondrial function, oxidative stress and xenobiotic metabolism in Parkinson's disease. The study has identified new candidate genes and cell pathways for future investigation. Fibroblasts from schizophrenia patients did not show these differences. Olfactory neurosphere-derived cells have many advantages over embryonic stem cells and induced pluripotent stem cells as models for brain diseases. They do not require genetic reprogramming and they can be obtained from adults with complex genetic diseases. They will be useful for understanding disease aetiology, for diagnostics and for drug discovery
Screening tests for aphasia in patients with stroke: a systematic review
Aphasia has a large impact on the quality of life and adds significantly to the costs of stroke care. Early recognition of aphasia in stroke patients is important for prognostication and well-timed treatment planning. We aimed to identify available screening tests for differentiating between aphasic and non-aphasic stroke patients, and to evaluate test accuracy, reliability, and feasibility. We searched PubMed, EMbase, Web of Science, and PsycINFO for published studies on screening tests aimed at assessing aphasia in stroke patients. The reference lists of the selected articles were scan
Enzymatic Depilation of Animal Hide: Identification of Elastase (LasB) from Pseudomonas aeruginosa MCM B-327 as a Depilating Protease
Conventional leather processing involving depilation of animal hide by lime and sulphide treatment generates considerable amounts of chemical waste causing severe environmental pollution. Enzymatic depilation is an environmentally friendly process and has been considered to be a viable alternative to the chemical depilation process. We isolated an extracellular protease from Pseudomonas aeruginosa strain MCM B-327 with high depilation activity using buffalo hide as a substrate. This 33 kDa protease generated a peptide mass fingerprint and de novo sequence that matched perfectly with LasB (elastase), of Pseudomonas aeruginosa. In support of this data a lasB mutant of MCM B-327 strain lacked depilatory activity and failed to produce LasB. LasB heterologously over-produced and purified from Escherichia coli also exhibited high depilating activity. Moreover, reintroduction of the lasB gene to the P. aeruginosa lasB mutant via a knock-in strategy also successfully restored depilation activity thus confirming the role of LasB as the depilating enzyme
The Evolution of Fangs, Venom, and Mimicry Systems in Blenny Fishes
Venom systems have evolved on multiple occasions
across the animal kingdom, and they can act as key
adaptations to protect animals from predators.
Consequently, venomous animals serve as models
for a rich source of mimicry types, as non-venomous
species benefit from reductions in predation risk by
mimicking the coloration, body shape, and/or movement
of toxic counterparts. The frequent evolution
of such deceitful imitations provides notable
examples of phenotypic convergence and are often
invoked as classic exemplars of evolution by natural
selection. Here, we investigate the evolution of fangs,
venom, and mimetic relationships in reef fishes from
the tribe Nemophini (fangblennies). Comparative
morphological analyses reveal that enlarged canine
teeth (fangs) originated at the base of the Nemophini
radiation and have enabled a micropredatory feeding
strategy in non-venomous Plagiotremus spp. Subsequently,
the evolution of deep anterior grooves and
their coupling to venom secretory tissue provide
Meiacanthus spp. with toxic venom that they effectively
employ for defense. We find that fangblenny
venom contains a number of toxic components that
have been independently recruited into other animal
venoms, some of which cause toxicity via interactions
with opioid receptors, and result in a multifunctional
biochemical phenotype that exerts potent hypotensive
effects. The evolution of fangblenny venom has
seemingly led to phenotypic convergence via the formation
of a diverse array of mimetic relationships that
provide protective (Batesian mimicry) and predatory
(aggressive mimicry) benefits to other fishes.
Our results further our understanding of how novel
morphological and biochemical adaptations stimulate
ecological interactions in the natural world
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