Overeducation, Job Competition and Unemployment

The changing wage and employment structure in some OECD countries has beenattributed to increased levels of education and technical change in favour of skilledworkers. However, in the Netherlands and some other OECD countries the wages ofskilled workers did not rise, whereas investment in skills rose dramatically. This paperoffers a theory which is able to explain the dramatic increase in the level of education andskills without rising wages since the early 1980s. In this respect, we integrate the supplyside framework (human capital investments) and the demand side (containingendogenous skill upgrading as a result of job competition and screening) in a generalequilibrium model. In this way we provide a theory for the empirical observation ofrising unemployment levels among unskilled workers and rising employment levels ofskilled workers with relatively stable wages.economics of technology ;

The variability of corneal and anterior segment parameters in keratoconus

Purpose: To analyse, describe and test diverse corneal and anterior segment parameters in normal and keratoconic eyes to better understand the geometry of the keratoconic cornea. Method: 44 eyes from 44 keratoconic patients and 44 eyes from 44 healthy patients were included in the study. The Pentacam System was used for the analysis of the anterior segment parameters. New ad-hoc parameters were defined by measuring the distances on the Scheimpflug image at the horizontal diameter, with chamber depth now comprising of two distinctive distances: corneal sagittal depth and the distance from the endpoint of this segment to the anterior surface of the lens (DL). Results: Statistically significant differences (p<0.05) between normal and keratoconic eyes were found in all of the analysed corneal parameters. Anterior chamber depth presented statistical differences between normal and keratoconic eyes (3.06 ± 0.43 mm versus 3.34 ± 0.45 mm, respectively; p = 0.004). This difference was found to originate in an increase of the DL distance (0.40 ± 0.33 mm in normal eyes against 0.61 ± 0.45 mm in keratoconic eyes; p = 0.014), rather than in the changes in corneal sagittal depth. Conclusion: These findings indicate that keratoconus results in central and peripheral corneal manifestations, as well as changes in the shape of the scleral limbus. The DL parameter was useful in describing the forward elongation and advance of the scleral tissue in keratoconic eyes. This finding may help in the monitoring of disease progression and contact lens design and fitting.Preprin

Practical security considerations for IoT systems over satellite

Currently, the forecast for the European market for IoT is a yearly 19.8% increase up to reach $241 billion in 2025. Thisstrong growing will be concentrated in verticals from manufacturing, utilities, retail and transportation [1], [2]. However, in orderto monetize the potential services over IoT it is necessary to guarantee the security of the communications [3]. In this regardphysical-layer security methods may complement higher-layer encryption techniques by exploiting the characteristics of wirelesschannels. For this purpose, it is resorted to the secrecy-capacity metric to measure the security level. More specifically, it was shownin [4] that reliable information-theoretic security could be achieved, whenever the eavesdropper’s channel be a degraded versionof the legitimate user’s channel. In this case, if the secrecy rate is chosen below the secrecy-capacity, then reliable transmissionscan be achieved in perfect secrecy. However, the time-varying fading effect of wireless channels degrades the secrecy-capacity. Inthis situation, it is used the ergodic capacity to measure the secrecy-capacity [5]. In order to make the overhearing process of theeavesdroppers difficult, it is used the time-packing/faster than Nyquist strategy [6]- [7].Thus, the time-duration of the transmittedframes are reduced which: i) improves the interception probability of the packets, ii) augments the spectral efficiency of theM2M communications without increasing the transmission bandwidth, iii) diminishes the effect of Doppler spread in Non-GEOcommunications, and iv) permits to use the overlapping degree among the pulse shapes to boost the secrecy-capacity. On thecontrary, this overlapping degree introduces a multi-path channel that may difficult the synchronization process. However, thecoefficients of the multipath channel are known by the legitimate user but ignored by the eavesdropper. This strategy of securityis similar to that the Artificial Noise (AN) one pursues [5], [8]- [9], but without wasting energy for jamming the eavesdropper’schannel.Note that the satellite channel model has a large Line of Sight (LoS) component. So, it means that the channel of theeavesdropper and the legitimate user could be quite similar in the same beam of the satellite constellation. So it is necessary todistort the channel of the desired user in order to increase the security of the communications. The use of non-Nyquist pulses,permits to introduce an artificial multipath interference that degrades the eavesdropper’s channel. In this case, we have consideredtwo types of eavesdropper: i) without being able to estimate the time-packing multipath, and ii) equipped with an estimationblock of the time-packing interference. In the first case, all interference signals are considered as noise whereas in the secondone part of the interference is assumed as noise. In both cases, it is possible to obtain a secrecy-capacity. Finally, comment thatin satellite constellation there is a residual co-channel interference. This interference limits the resolution of the eavesdroppersalthough they be equipped with multiple antennas. We have considered that the eavesdropper does not have full knowledge of thetime-packed/faster than Nyquist multi-path interference. This pragmatic approach was also followed in [9]. However, there therain losses made difficult to obtain perfect channel estimations.Peer ReviewedPostprint (published version

Logistic Q-Learning

We propose a new reinforcement learning algorithm derived from a regularized linear-programming formulation of optimal control in MDPs. The method is closely related to the classic Relative Entropy Policy Search (REPS) algorithm of Peters et al. (2010), with the key difference that our method introduces a Q-function that enables efficient exact model-free implementation. The main feature of our algorithm (called QREPS) is a convex loss function for policy evaluation that serves as a theoretically sound alternative to the widely used squared Bellman error. We provide a practical saddle-point optimization method for minimizing this loss function and provide an error-propagation analysis that relates the quality of the individual updates to the performance of the output policy. Finally, we demonstrate the effectiveness of our method on a range of benchmark problems

Comparative analysis of peripheral corneal geometry in health and Keratoconus

OBJECTIVES:: To describe and compare corneal peripheral angles in normal and keratoconic eyes, to gain a better understanding of the topography of the periphery of the cornea in keratoconus and assist practitioners in the selection and fitting of large diameter contact lenses. METHODS:: Eighty-eight eyes were included in the study, divided into three groups: healthy (A0, 28 eyes), keratoconus at stage I according to the Amsler-Krumeich classification (AI, 33 eyes) and keratoconus at stages II to IV (AII, 27 eyes). The Pentacam Scheimpflug system was used to manually measure the corneal peripheral angles corresponding to a chord length range between 8.6 and 12.6 mm at 8 different peripheral locations. RESULTS:: The peripheral angle was influenced by ocular condition and by the peripheral location, with no interaction effect between both factors. Statistically significant differences were found in mean corneal peripheral angles between groups A0 (30.84°±2.33°) and AI (31.63°±2.02°) (P=0.001) and between A0 and AII (31.37°±2.11°) (P=0.030). The differences between AI and AII were not significant. In all eyes, the largest and smallest peripheral angles were found at the temporal inferior and temporal superior locations, respectively, with a mean difference between largest and smallest of 3.37°±1.42° in healthy eyes and 2.96°±1.54° in keratoconus (AI+AII). CONCLUSION:: Clinically insignificant differences were found in peripheral angles between keratoconus and healthy eyes, giving support to the use of large diameter, intralimbal contact lenses with peripheral designs, and resting on the same corneal region, as those fitted on normal corneas.Preprin

Anterior chamber parameters in early and advanced keratoconus. A meridian by meridian analysis

Purpose: To explore anterior segment changes with keratoconus onset and progression to determine whether structural changes are predominantly corneal, limbal or both. To investigate these changes in different corneal meridians. Method: Eighty-four eyes with keratoconus and 49 healthy eyes were included in the study. Eyes with keratoconus were divided in two groups according to the Amsler-Krumeich classification: stage I and stages II-IV. Scheimpflug images at three different meridians were used to evaluate the following parameters: anterior chamber depth from the endothelium (ACD_end) and corneal thickness (CT) (software provided), anterior chamber depth (ACD) and sagittal depth (SAGT) from the epithelium, and distance from the end point of SAGT to the anterior surface of the lens (DL) (measured manually), and [ACD – CT] and [SAGT – CT] (calculated). Changes in these parameters with ocular condition and meridian were analysed. Results: Statistically significant larger values were found of ACD (p=0.012) and DL (p=0.016) with keratoconus onset and progression, with no differences in SAGT values. Besides, [ACD – CT] and [SAGT – CT] were significantly larger in keratoconus eyes (p<0.001 and p=0.003, respectively). Significant differences (all p<0.001) were found in SAGT, [SAGT – CT] and DL among meridians. Changes in these parameters with keratoconus onset and progression were similar in all meridians. Conclusion: Considering the results from the three meridians under investigation, it may be concluded that keratoconus onset has an impact on the anterior segment as a whole and not only on corneal structures. The DL distance is a useful parameter to describe limbal changes in keratoconus.Postprint (author's final draft

Role of microfluctuations in accommodation: a novel approach to reduce non-accommodative noise

Accommodative response and its possible role in myopia development has been explored through the study of the microfluctuations of accommodation, which are commonly divided in high (1.0 to 2.3 Hz) and low (0.1 to 0.6 Hz) frequency components. Previous research efforts have evidenced that a certain percentage of the amplitude of microfluctuations seems not to originate in the accommodative response. We aimed to develop and test a new approach to reduce this non-accommodative noise. For this purpose, ten healthy participants were enrolled to determine the difference between the amplitude of microfluctuations at near and distance for each range of frequencies, which was defined as the relative amplitude of microfluctuations. The findings support the exploration of the relative rather than absolute values of the amplitude of microfluctuations to better understand the contribution of both accommodative and non-accommodative factors to microfluctuations.Postprint (author's final draft

Joint estimation of survival and dispersal effectively corrects the permanent emigration bias in mark‑recapture analyses

Robust and reliable estimates of demographic parameters are essential to understand population dynamics. Natal dispersal is a common process in monitored populations and can cause underestimations of survival and dispersal due to permanent emigration. Here, we present a multistate Bayesian capture-mark-recapture approach based on a joint estimation of natal dispersal kernel and detection probabilities to address biases in survival, dispersal, and related demographic parameters when dispersal information is limited. We implement this approach to long-term data of a threatened population: the Bonelli's eagle in Catalonia (SW Europe). To assess the method's performance, we compare demographic estimates structured by sex, age, and breeding status in cases of limited versus large data scales, with those of classical models where dispersal and detection probabilities are estimated separately. Results show substantial corrections of demographic estimates. Natal dispersal and permanent emigration probabilities were larger in females, and consequently, female non-breeder survival showed larger differences between separate and joint estimation models. Moreover, our results suggest that estimates are sensitive to the choice of the dispersal kernel, fat-tailed kernels providing larger values in cases of data limitation. This study provides a general multistate framework to model demographic parameters while correcting permanent emigration biases caused by natal dispersal

Study on the application of NOMA techniques for heterogeneous satellite terminals

This paper addresses the application of nonorthogonal multiple-access techniques (NOMA) to those satellite relayed communications for which a significant imbalance in the link quality of user terminals can be expected. The Signal-to-Interference and Noise Ratio (SINR) imbalance could be caused by the coexistence of different types of terminals, possibly with different antenna sizes, and offering different classes of service. This link SINR asymmetry can be exploited to outperform orthogonal access schemes under different rate metrics, paying special attention to fairness in the service provision. Both forward and asynchronous return link are addressed, with minimum signaling information and emphasis on some relevant implementation issues such as framing and synchronization

Experiència de portafoli docent i d’autoavaluació en les pràctiques de tecnologia òptica II

En les pràctiques de Tecnologia Òptica II hem implantat tècniques de seguiment basades en el portafoli de l’estudiant, i una metodologia automàtica d’autoavaluació amb criteris objectius que permetin a l’estudiant reflexionar sobre la qualitat dels seus propis resultats, i dels efectes que aquests poden tenir sobre un possible usuari d’ulleres. El portafoli de les pràctiques és un guió pautat on plasmar els resultats de cada muntatge d’ulleres que es realitza. A part d’anotar totes les dades necessàries relatives a l’usuari, la muntura i les lents que possibilitin l’execució del muntatge, l’estudiant ha de fer una comparació entre els resultats esperats i els obtinguts, reflexionant sobre les causes de possibles discrepàncies entre uns i altres. En cas de trobar diferències en el centrat de les lents o l’orientació de l’eix de l’astigmatisme haurà de valorar les repercussions en la binocularitat del pacient. De la comparació dels resultats obtinguts respecte els esperats sorgeix l’autoavaluació. Es valoren aspectes de centrat, de prescripció, mecànics i de presentació. Per cadascun dels aspectes l’alumne s’autoavalua amb una puntuació que va de 0 a 3. EL 3 s’utilitza pels muntatge perfectes. El 2 s’aplica als muntatges amb petits defectes que són tolerables segons el conveni establert. I les dues qualificacions signifiquen que el muntatge és entregable a l’usuari, sense produir-li cap mena d’alteració a la seva visió . L’1 s’utilitza quan el muntatge s’ha acabat amb errors que superen el límit tolerable, i en aquest cas les ulleres no es poden entregar al pacient perquè li produirien conseqüències indesitjades. El 0 es reserva per quan s’han realitzat errors greus en el muntatge, com per exemple muntar la lent de l’ull dret a l’ull esquerre, o canviar l’eix de l’astigmatisme. Tenint en compte això, l’estudiant s’atorga una nota global de l’1 al 9. Seguidament es reuneix amb el professor, que valorarà la qualitat del muntatge i la informació del portafoli, contrastant la seva avaluació amb l’autoavaluació de l’estudiant. En funció d’aquest procés, podrà modificar la nota del muntatge de -1 a +1