166 research outputs found
Expected shortfall estimators and their use in asset allocation
No full textLa perdita attesa (Expected Shortfall - ES) è una misura di rischio che prende in considerazione le perdite maggiori del Valore al Rischio (Value at Risk - VaR). Siccome l’ES ha le proprietà di una misura di rischio coerente, il suo uso nell’allocazione del portafoglio è diventato rilevante. Nella prima sezione, proponiamo dei stimatori per ES, considerando il caso quando abbiamo a disposizione informazioni aggiuntive compresse in un set di variabile esogene. I stimatori sono costruiti partendo dalla rappresentazione equivalente del ES in termini di funzione di distribuzione e funzione quantilica. Nelle sezioni successive, partendo dalla rappresentazione del ES generalizzata tramite una funzione di pesi, il lavoro prosegue con il miglioramento delle proprietà statistiche e di predizione. Nel primo caso, ottimizziamo la funzione di pesi tale da minimizzare la varianza asintotica, mentre, nel secondo caso, la funzione di pesi minimizza l’errore di predizione dello stimatore. Inoltre, pensando al uso dei stimatori nelle applicazioni finanziarie, costruiamo un modello base di allocazione di portafoglio che massimizza il rendimento atteso con un vincolo sul ES.The Expected Shortfall (ES) is a risk measure that averages out all losses more severe than
the Value at Risk (VaR). As the ES shares the properties of coherent risk measures, its use
as risk constraint in asset allocation has became relevant. First of all, we propose estimators
for ES, considering the important case when additional information as some set of regressors
is available. The estimators are based on the equivalent representation of ES in terms of the
conditional distribution function and the conditional quantile function. Within the estimation
framework, departing from a generalized weighted representation of ES, we work on improving
the statistical and forecasting properties of the weighted estimators. In the first case, we
derive the weighting that minimizes the asymptotic variance of the estimators, while, in the
second case, the weighting minimizes some suitably defined forecast error. Nevertheless we
are concerned with the use of these estimators in financial applications and construct a simple
asset allocation model that maximizes expected return with a loss constraint on ES
Unified charge transport in disordered organic field-effect transistors and light-emitting diodes
No full textDe ontdekking dat plastics zich als halfgeleiders kunnen gedragen heeft hun toepassingsgebied verruimd van speelgoed, tassen of meubilair naar elektronische producten zoals flexibele beeldschermen, radiofrequentie identificatie labels, fotocellen and chemische sensoren. In dit proefschrift
bestuderen we de geleiding in wanorderlijke organische halfgeleiders. Deze materialen zijn bestudeerd onder de omstandigheden zoals ze in licht emitterende diodes (LEDs) en veldeffect transistoren (FETs) gebruikt worden.
Een belangrijke parameter voor de beschrijving van de prestatie van deze applicaties is de mobiliteit van de ladingsdragers, hetgeen een maat is voor de snelheid waarmee de ladingsdragers door de polymeerfilm bewegen. Wij
analyseren de mobiliteit van ladingsdragers als functie van temperatuur, elektrisch veld en ladingsdragerdichtheid. We laten zien dat een geunificeerd model voor zowel LEDs als FETs gebruikt kan worden, waarin de afhankelijkheid van de mobiliteit van de ladingsdragerdichtheid wordt meegenomen. Deze resultaten worden vervolgens gebruikt om de oorzaak van de sterke toename van de ruimteladingsbegrensde gatenstroom in poly(pphenylene vinylene) (PPV)-achtige polymeren bij hoge aangelegde spanningen te onderzoeken. We tonen aan dat de toename van de stroomdichtheid in ruimteladingsbegrensde diodes bij kamertemperatuur
gedomineerd wordt door de dichtheidsafhankelijkheid van de gatenmobiliteit. Dit is in tegenspraak met de in de literatuur algemeen geaccepteerde aanname dat de bijdrage van het elektrische veld overheerst.
Het ladingstransport van verschillende PPV derivaten zijn bestudeerd als functie van de chemische structuur en proces condities. Er wordt aangetoond dat d.m.v. chemische modificatie van asymmetrische naar volledig symmetrische gesubstitueerde PPVs de mobiliteit significant verbeterd kan
worden.
Een nieuw concept voor efficiente dubbellaag polymeren LEDs wordt gedemonstreerd. Een dergelijke LED bevat een polymeer met een hoge gatenmobiliteit, die de gaten efficient naar een sterk luminescerende laag transporteert.
Chronic postsurgical pain in Europe: An observational study.
No full textBACKGROUND
Chronic postsurgical pain (CPSP) is an important clinical problem. Prospective studies of the incidence, characteristics and risk factors of CPSP are needed.
OBJECTIVES
The objective of this study is to evaluate the incidence and risk factors of CPSP.
DESIGN
A multicentre, prospective, observational trial.
SETTING
Twenty-one hospitals in 11 European countries.
PATIENTS
Three thousand one hundred and twenty patients undergoing surgery and enrolled in the European registry PAIN OUT.
MAIN OUTCOME MEASURES
Pain-related outcome was evaluated on the first postoperative day (D1) using a standardised pain outcome questionnaire. Review at 6 and 12 months via e-mail or telephonic interview used the Brief Pain Inventory (BPI) and the DN4 (Douleur Neuropathique four questions). Primary endpoint was the incidence of moderate to severe CPSP (numeric rating scale, NRS ≥3/10) at 12 months.
RESULTS
For 1044 and 889 patients, complete data were available at 6 and 12 months. At 12 months, the incidence of moderate to severe CPSP was 11.8% (95% CI 9.7 to 13.9) and of severe pain (NRS ≥6) 2.2% (95% CI 1.2 to 3.3). Signs of neuropathic pain were recorded in 35.4% (95% CI 23.9 to 48.3) and 57.1% (95% CI 30.7 to 83.4) of patients with moderate and severe CPSP, respectively. Functional impairment (BPI) at 6 and 12 months increased with the severity of CPSP (P < 0.01) and presence of neuropathic characteristics (P < 0.001). Multivariate analysis identified orthopaedic surgery, preoperative chronic pain and percentage of time in severe pain on D1 as risk factors. A 10% increase in percentage of time in severe pain was associated with a 30% increase of CPSP incidence at 12 months.
CONCLUSION
The collection of data on CPSP was feasible within the European registry PAIN OUT. The incidence of moderate to severe CPSP at 12 months was 11.8%. Functional impairment was associated with CPSP severity and neuropathic characteristics. Risk factors for CPSP in the present study were chronic preoperative pain, orthopaedic surgery and percentage of time in severe pain on D1.
TRIAL REGISTRATION
Clinicaltrials.gov identifier: NCT01467102
Magnetic-based navigation system for endovascular interventions
No full textElectrical Engineering, Mathematics and Computer Scienc
On Bronislaw Malinowski(II)
No full textAs the theory of B. Malinowski (1884-1942) has been discussed widely in the academic circle of Japan, it is fairly well understood. Its method of field work also has been introduced and is put into practice. Even today, however, after ten years have passed since his death, the foundation of his theories is not yet analysed in Japan to the full. Therefore this paper tries to examine critically the significance of his theories in the history of science and the central point of the various problems in his theory of culture. First historical evolutionism and the Kulturkreis theory are analysed, and the author sees as highly important the method of the latter. But in the latter the relationship between cultural itemes in a cultural realm is only of co-existence and not seen in their connection in a chain. The author, in this point, recognises the excellency of observation of Malinowski, who has developed cultural anthropology as an analytical science, and the significance of his theory in the history of science. Then the author treats of the scope of his cultural or social anthropology and points out that he was a reformer in social science, but not a radical one. The author, then, tries to analize and criticize fully the theories of the integrated whole of culture, the correlation and concatenation in the whole, and the scientific treatment of the concept of integration. In connection with these problems, the author, treating of the concept of function and the problem of the biological basis of custom, in comparison with the theory of R. Radcliffe-Brown, recognises that Malinowski's theory of need is excellent for fundamental understanding of culture. However the author points out that he has no interest in the form of culture, the history and the geography of the world. In the last part, the author discusses the theory of Malinowski, in which culture means education, introducing its viewpoint for psychoanalysis. In a word, the paper analyses the fundamental standpoint of Malinowski's theory, without giving much attention to his topical auguments
Microsensors for Multiple-Parameter Medical Measurements
No full textOften in medical applications a single measurement does not give sufficient information to the clinicians. IC technology allows the combination of several sensors in a small volume for instantaneous multi-measurements at a single location. This paper presents two multi-parameter sensors for catheter applications, with initial experimental results, along with the packaging issue - an important aspect for biomedical sensors.Delft University of Technolog
Quality of Service in Large Scale Mobile Distributed Systems Based on Opportunistic Networks
No full textMagnetic-field navigation for catheters: Integrated chip for triple blood sampling
No full textCatheters are semi-rigid, hollow plastic tubes that are indispensable when it comes to local surgery inside the heart,brain,arms, legs, or lungs. But how can a surgeon tell whether the catheter is going the right way? Most hospitals still use x-ray methods to check the catheters progress. To navigate the catheters passage in real time, some ten to twenty x-ray images are made every second. Even though the radiation dose involved is very low, no radiation at all would be much healthier both for the patient and the medical staff who run the risk of being exposed to the radiation on a daily basis. Researchers of the TU Delft faculty of Electrical Engineering, Mathematics and Computer Science are currently developing a magnetic navigation system for medical instruments such as catheters and guide wires. A magnetic sensor on the tip of the medical instrument measures an external magnetic field and reports exactly where the tip of the instrument is located. In addition, the team is developing sensors that can measure a number of blood parameters simultaneously. Current systems allow the doctors to measure only a single parameter at a time so that a new catheter has to be inserted for each subsequent reading. A reduction in size of the sensors will bring this to an end.Delft University of Technolog
Microtubule organization in three-dimensional confined geometries: Evaluating the role of elasticity through a combined in vitro and modeling approach
No full textMicrotubules or microtubule bundles in cells often grow longer than the size of the cell, which causes their shape and organization to adapt to constraints imposed by the cell geometry. We test the reciprocal role of elasticity and confinement in the organization of growing microtubules in a confining box-like geometry, in the absence of other (active) microtubule organizing processes. This is inspired, for example, by the cortical microtubule array of elongating plant cells, where microtubules are typically organized in an aligned array transverse to the cell elongation axis. The method we adopt is a combination of analytical calculations, in which the polymers are modeled as inextensible filaments with bending elasticity confined to a two-dimensional surface that defines the limits of a three-dimensional space, and in vitro experiments, in which microtubules are polymerized from nucleation seeds in microfabricated chambers. We show that these features are sufficient to organize the polymers in aligned, coiling configurations as for example observed in plant cells. Though elasticity can account for the regularity of these arrays, it cannot account for a transverse orientation of microtubules to the cell's long axis. We therefore conclude that an additional active, force-generating process is necessary to create a coiling configuration perpendicular to the long axis of the cell
Potential Bioregulators for Rape (Brassica napus L.) Plants
No full textIt is known that polyphenols are a single group of phytochemicals which present in all plants. Their biological activity is based upon functional groups capable to participate in the plant metabolism influencing cell division and biosynthesis processes. In our experiments we have evaluated the effect of spruce bark polyphenolic extract and deuterium depleted water (DDW) as rapeseed plant bioregulators. After aqueous extraction of bark and quantification and identification of polyphenolic compounds by HPLC methods, we applied the extracts in the growth medium of rapeseed plants. Assessment the influence of extracts on rapeseed plants was achieved through determination of germination energy and capacity, biomass accumulation, assimilatory pigments accumulation and photosynthesis activity. The results has shown that it possible to establish the highest stimulating effect of polyphenols on germination energy and capacity. These, were registered in the presence of spruce bark polyphenolic extract (SBPE) with an equivalent content of 130 mg GAE/L. Rape plants treated with DDW+SBPE have accumulated the highest amount of biomass compared with other experimental variants. The photosynthesis activity was considerably intensified especially in the presence of SBPE
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