The biharmonic homotopy problem for unit vector fields on 2-tori

The bienergy of smooth maps between Riemannian manifolds, when restricted to unit vector fields, yields two different variational problems depending on whether one takes the full functional or just the vertical contribution. Their critical points, called biharmonic unit vector fields and biharmonic unit sections, form different sets. Working with surfaces, we first obtain general characterizations of biharmonic unit vector fields and biharmonic unit sections under conformal change of the metric. In the case of a 2-dimensional torus, this leads to a proof that biharmonic unit sections are always harmonic and a general existence theorem, in each homotopy class, for biharmonic unit vector fields

Does the weather affect stock market volatility?

This paper investigates the empirical association between stock market volatility and investor mood-proxies related to the weather (cloudiness, temperature and precipitation) and the environment (nighttime length). Overall, our results suggest that cloudiness and length of nighttime are inversely related to historical, implied and realized measures of volatility. The strength of association seems to vary with the location of an exchange on Earth with respect to the equator. Weather deviations from seasonal norms and dummies representing extreme weather conditions do not offer additional explanatory power in our datasets.Stock market anomalies; Volatility; Sunshine effect; SAD effect; Behavioral Finance

Electricity futures prices in an emissions constrained economy: Evidence from European power markets

We investigate the economic factors that drive electricity risk premia in the European emissions constrained economy. Our analysis is undertaken for monthly baseload electricity futures for delivery in the Nordic, French and British power markets. We find that electricity risk premia are significantly related to the volatility of electricity spot prices, demand and revenues, and the price volatility of the carbon dioxide (CO2) futures traded under the EU Emissions Trading Scheme (EU ETS). This finding has significant implications for the pricing of electricity futures since it highlights for the first time the role of carbon market uncertainties as a main determinant of the relationship between spot and futures electricity prices in Europe. Our results also suggest that for the electricity markets under scrutiny futures prices are determined rationally by risk-averse economic agents

Printed temperature sensor based on PEDOT: PSS-graphene oxide composite

Temperature sensing is an important parameter needed to be measured by the eSkin during the physical interaction of robots with real-world objects. Yet, most of the work on sensors in eSkin has focused on pressure sensing. Here we present a skin conformable printed temperature sensor with poly(3,4-ethylenedioxythiophene): poly (styr-enesulfonate) (PEDOT:PSS)-graphene oxide (GO) as a temperature sensitive layer and silver (Ag) as contact electrodes. The demonstration of PEDOT:PSS/GO as a highly temperature sensitive layer is the distinct feature of the work. The response of presented sensor observed over ~25 °C (room temperature (RT)) to 100°C, by measuring the variation in resistance across the GO/PEDOT:PSS layer showed ~80% decrease in resistance. The sensitivity of the sensor was found to be 1.09% per °C. The sensor's response was also observed under static and dynamic bending (for 1000 cycles) conditions. The stable and repeatable response of sensor, in both cases, signifies strong adhesion of the layers with negligible delamination or debonding. In comparison to the commercial thermistor, the printed GO/PEDOT:PSS sensor is faster (~73% superior) with response and recovery times of 18 s and 32 s respectively. Finally, the sensor was attached to a robotic hand to allow the robot to act by using temperature feedback

Covariance forecasting in equity markets

We compare the performance of popular covariance forecasting models in the context of a portfolio of major European equity indices. We find that models based on high-frequency data offer a clear advantage in terms of statistical accuracy. They also yield more theoretically consistent predictions from an empirical asset pricing perspective, and, lead to superior out-of-sample portfolio performance. Overall, a parsimonious Vector Heterogeneous Autoregressive (VHAR) model that involves lagged daily, weekly and monthly realised covariances achieves the best performance out of the competing models. A promising new simple hybrid covariance estimator is developed that exploits option-implied information and high-frequency data while adjusting for the volatility riskpremium. Relative model performance does not change during the global financial crisis, or, if a different forecast horizon, or, intraday sampling frequency is employed. Finally, our evidence remains robust when we consider an alternative sample of U.S. stocks

Olive oil and cancer risk: Case 1

ΥΠΟΒΑΘΡΟ: Διάφορες επιδημιολογικές μελέτες υποστηρίζουν ότι το ελαιόλαδο θα μπορούσε να συμβάλλει στη μείωση του κινδύνου εμφάνισης καρκίνου. Για το σκοπό της παρούσας εργασίας πραγματοποιήσαμε μια συστηματική ανασκόπηση και μετα-ανάλυση με στόχο τη διερεύνηση της συσχέτισης μεταξύ της κατανάλωσης ελαιολάδου και της επίπτωσης καρκίνου του γαστρεντερικού και ουρογεννητικού συστήματος. ΜΕΘΟΔΟΙ: Μια συστηματική αναζήτηση πραγματοποιήθηκε στις βάσεις δεδομένων PubMed, EMBASE και Google Scholar (καταληκτική ημερομηνία αναζήτησης: 10 Μαΐου 2020). Εκτιμήθηκε ο συγκεντρωτικός σχετικός κίνδυνος (RR) και τα διαστήματα εμπιστοσύνης 95% (95% CIs) με μοντέλα τυχαίων επιδράσεων (DerSimonian-Laird). Πραγματοποιήθηκαν επίσης αναλύσεις υποομάδων, ανάλυση ευαισθησίας και ανάλυση μετα-παλινδρόμησης. ΑΠΟΤΕΛΕΣΜΑΤΑ: 15 μελέτες για γαστρεντερικό καρκίνο συμπεριλήφθηκαν στη μετα-ανάλυση: 13 ήταν ασθενών-μαρτύρων και 2 ήταν κοόρτης. Υψηλότερη κατανάλωση ελαιολάδου συσχετίστηκε με 23% μικρότερη πιθανότητα ανάπτυξης καρκίνου του μαστού (RR=0.77, 95%CI: 0.66-0.89). Αναφορικά με το ουρογεννητικό σύστημα, συνθετική ανάλυση 6 μελετών ασθενών-μαρτύρων έδειξε μείωση κινδύνου κατά 54% (RR=0.46, 95%CI: 0.29-0.72). Σημαντικές προστατευτικές επιδράσεις παρατηρήθηκαν τόσο σε υποομάδες ανάλογα με τη θέση της κακοήθειας, σε Μεσογειακούς όσο και μη Μεσογειακούς πλυθησμούς, μελέτες με μόνο- και πολυμεταβλητή ανάλυση και σε όλες τις υποομάδες βάσει της ποιότητας της μελέτης. ΣΥΜΠΕΡΑΣΜΑΤΑ: Η κατανάλωση ελαιολάδου φαίνεται να έχει ευεγερτικές επιδράσεις στην πρόληψη του καρκίνου του γαστρεντερικού και του ουρογεννητικού συστήματος. Επιπρόσθετες προοπτικές μελέτες κοόρτης, όπως και ελεγχόμενες τυχαιοποιημένες κλινικές δοκιμές, είναι ωστόσο επιθυμητές.BACKGROUND: Various epidemiological studies have suggested that olive oil component could play a role in decreasing cancer risk. For the scope of the present thesis we conducted a systematic review and meta-analysis aiming at investigating the association between olive oil consumption and incidence of gastrointestinal and urogenital cancer. METHODS: A systematic search was conducted in PubMed, EMBASE and Google Scholar databases (end-of-search: May 10, 2020). Pooled relative risk (RR) and 95% confidence intervals (95% CIs) were estimated with random-effects (DerSimonian-Laird) models. Subgroup analyses, sensitivity analysis and meta-regression analysis were also performed. RESULTS: 15 studies on gastrointestinal cancer were included in the meta-analysis; 13 were case-control and 2 were cohort studies. Highest olive oil consumption was associated with 23% lower likelihood of developing breast cancer (RR=0.77, 95%CI: 0.66-0.89).Concerning the urogenital cancers, pooled analysis of 6 case-control studies showed a cancer risk reduction of 54% (RR=0.46, 95%CI: 0.29-0.72). Effect remained significant in subanalysis on different tumour sites, Mediterranean and non-Mediterranean participants, studies presenting a multivariate and a univariate analysis and subgroups by study quality. CONCLUSIONS: Olive oil consumption seems to exert favourable actions in terms of gastrointestinal and urogenital cancer prevention. Additional prospective cohort studies, as well as large randomized trials, seem desirable

Dynamic interaction between markets for leasing and selling automobiles

We develop a model of dynamic interactions between price variations in leasing and selling markets for automobiles. Our framework assumes a differential game between multiple Bertrand-type competing firms which offer differentiated products to forward-looking agents. Empirical analysis of our model using monthly US data from 2002 to 2011 shows that variations in selling (cash) market prices lead rapidly dissipating changes of leasing market prices in the opposite direction. We discuss the practical implications of these results by augmenting a standard leasing valuation formula. The additional terms represent the leased asset value changes that can be expected on the basis of past variations in automobile selling market prices