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Polarization anisotropy of luminescent properties of europium (III) ions in low-symmetry C2 sites is studied using monoclinic (sp. gr. C2/c) tungstate crystal KY(WO4)2. The 5D0 → 7FJ (where J = 0...6) transitions are characterized for the principal light polarizations. Polarization selection rules for the magnetic dipole 5D0 → 7F1 transition are presented. The stimulated-emission cross-sections for Eu3+ ions relevant for laser operation are determined.

With the increasing use of convolutional neural networks (CNNs) for computer vision and other artificial intelligence tasks, the need arises to interpret their predictions. In this work, we tackle the problem of explaining CNN misclassification of images. We propose to construct adversarial examples that allow identifying the regions of the input images that had the largest impact on the CNN wrong predictions. More specifically, for each image that was incorrectly classified by the CNN, we implemented an inverted adversarial attack consisting on modifying the input image as little as possible so that it becomes correctly classified. The changes made to the image to fix classification errors explain the causes of misclassification and allow adjusting the model and the data set to obtain more accurate models. We present two methods, of which the first one employs the gradients from the CNN itself to create the adversarial examples and is meant for model developers. However, end users only have access to the CNN model as a black box. Our second method is intended for end users and employs a surrogate model to estimate the gradients of the original CNN model, which are then used to create the adversarial examples. In our experiments, the first method achieved 99.67% success rate at finding the misclassification explanations and needed on average 1.96 queries per misclassified image to build the corresponding adversarial example. The second method achieved 73.08% success rate at finding the explanations with 8.73 queries per image on average.

© 2020 IOP Publishing Ltd. In this work, we report novel methods to produce SERS encoded nanoparticles (SEPs). Either as single nanoparticles (NPs) or as more complex core-satellites structures. Single NPs are produced in an easy and fast one-pot approach which, are further use as building blocks to produce the core-satellite SEPs. The presented protocols are very versatile allowing the NPs SERS codification with an extensive variety of Raman codes. Moreover, this protocol can be applied to different NPs materials and shapes. Furthermore, the core-satellite SEPs are designed to exhibit minimal interparticle distances (

© Published under licence by IOP Publishing Ltd. Transparent glass-ceramics of magnesium aluminum silicate system based on nanosized MgAl2O4 spinel crystals nucleated by TiO2 and doped with Fe2O3 were developed. Their structure and spectroscopic properties were studied. The glass-ceramics are important as reference samples in development of saturable absorbers in the short-wave infrared spectral range (2-3 μm).

© 2020 IOP Publishing Ltd. In this work, we report novel methods to produce SERS encoded nanoparticles (SEPs). Either as single nanoparticles (NPs) or as more complex core-satellites structures. Single NPs are produced in an easy and fast one-pot approach which, are further use as building blocks to produce the core-satellite SEPs. The presented protocols are very versatile allowing the NPs SERS codification with an extensive variety of Raman codes. Moreover, this protocol can be applied to different NPs materials and shapes. Furthermore, the core-satellite SEPs are designed to exhibit minimal interparticle distances (

© Published under licence by IOP Publishing Ltd. Transparent glass-ceramics of magnesium aluminum silicate system based on nanosized MgAl2O4 spinel crystals nucleated by TiO2 and doped with Fe2O3 were developed. Their structure and spectroscopic properties were studied. The glass-ceramics are important as reference samples in development of saturable absorbers in the short-wave infrared spectral range (2-3 μm).

© Springer Nature Switzerland AG 2019. In hospital intensive care units (ICU), patients are under continuous evaluation. One of the purposes of this evaluation is to determine the expected number of days to discharge. This value is important to manage ICUs. Some studies show that health care professionals are good at predicting short-term discharge times, but not as good at long-term predictions. Machine learning methods can achieve 1.79-day average prediction error. We performed a study on 3,787 patient-days in the ICU of the Hospital Joan XXIII (Spain) to obtain a data-driven model to predict the discharge time of ICU patients, in a daily basis. Our model, which is based on random forest technology, obtained an error of 1.34 days. We studied the progression of the model as more data are available and predicted that the number of instances required to reduce the error below one day is 4,745. When we trained the model with all the available data, we obtained a mean error of less than half a day with a coefficient of determination (R2) above 97% in their predictions on either ICU survivors and not survivors. Similar results were obtained differentiating by patients’ gender and age, confirming our approach as a good means to achieve optimal performance when more data will be available.

© Springer Nature Switzerland AG 2019. In hospital intensive care units (ICU), patients are under continuous evaluation. One of the purposes of this evaluation is to determine the expected number of days to discharge. This value is important to manage ICUs. Some studies show that health care professionals are good at predicting short-term discharge times, but not as good at long-term predictions. Machine learning methods can achieve 1.79-day average prediction error. We performed a study on 3,787 patient-days in the ICU of the Hospital Joan XXIII (Spain) to obtain a data-driven model to predict the discharge time of ICU patients, in a daily basis. Our model, which is based on random forest technology, obtained an error of 1.34 days. We studied the progression of the model as more data are available and predicted that the number of instances required to reduce the error below one day is 4,745. When we trained the model with all the available data, we obtained a mean error of less than half a day with a coefficient of determination (R2) above 97% in their predictions on either ICU survivors and not survivors. Similar results were obtained differentiating by patients’ gender and age, confirming our approach as a good means to achieve optimal performance when more data will be available.

© 2018 SPIE. The recent advances in the development of Holmium monoclinic double tungstate thin-disk lasers are reviewed. The thin-disk is based on a 250-μm-thick 3 at. % Ho:KY(WO4)2active layer grown on a (010)-oriented KY(WO4)2substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce pump geometry, the continuous-wave Ho:KY(WO4)2thin-disk laser generates an output power of 1.01 W at 2057 nm corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. The thin-disk laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. In this regime, it generates an average output power of 0.551 W at ∼2056 nm with η = 44%. The best pulse characteristics are 4.1 μJ/201 ns at a repetition rate of 135 kHz. The laser performance, beam quality and thermo-optic aberrations of such lasers are strongly affected by the Ho3+doping concentration. For the 3 at.% Ho3+-doped thin-disk, the thermal lens is negative (the sensitivity factors for the two principal meridional planes are-1.7 and-0.6 m-1/W) and astigmatic. The Ho:KY(WO4)2epitaxial structures are promising as active elements in mode-locked thin-disk lasers at ∼2060 nm.

Applied technologies to health systems have been noticed as a required tool to reduce the reappearance rate of certain illnesses, to identify groups of risk or to involve the patient in the care of his own health. Taking in consideration the fact that in the North Santander Department the occurrence of the outbreak of illnesses transmitted by the vector Aedes aegypti shows intense increase since its re-emergency in 2014, with the presence of several manifestations, one of the most likely solutions to prevent the illness, is the epidemiologic surveillance alongside the strategic prevention/control of the vector. In this context, this project was developed with the purpose of characterize patients by the building of a knowledge database for digital health that allows to create an architecture to integrate, analyze and structure the historical data according to the detected cases, in order to collect the information from the direct field, store it and process it, to present reports and knowledge models with the right indicators that allow to look out often the symptoms and to control the increase of such epidemies.

© 2018 SPIE. A buried depressed-index channel waveguide with a circular cladding and a core diameter of 40 ?m is fabricated in a bulk monoclinic 3 at.% Tm:KLu(WO 4 ) 2 crystal by femtosecond direct laser writing. In the continuous-wave regime, the Tm waveguide laser generates ?210 mW at 1849.6 nm with a slope efficiency ? of 40.8%. Passively Q-switched operation is achieved by inserting transmission-type 2D saturable absorbers (SAs) based on few-layer graphene and MoS 2 . Using the graphene-SA, a maximum average output power of ?25 mW is generated at 1844.8 nm. The pulse characteristics (duration/energy) are 88 ns/18 nJ at a repetition rate of 1.39 MHz.

Applied technologies to health systems have been noticed as a required tool to reduce the reappearance rate of certain illnesses, to identify groups of risk or to involve the patient in the care of his own health. Taking in consideration the fact that in the North Santander Department the occurrence of the outbreak of illnesses transmitted by the vector Aedes aegypti shows intense increase since its re-emergency in 2014, with the presence of several manifestations, one of the most likely solutions to prevent the illness, is the epidemiologic surveillance alongside the strategic prevention/ control of the vector. In this context, this project was developed with the purpose of characterize patients by the building of a knowledge database for digital health that allows to create an architecture to integrate, analyze and structure the historical data according to the detected cases, in order to collect the information from the direct field, store it and process it, to present reports and knowledge models with the right indicators that allow to look out often the symptoms and to control the increase of such epidemies.

© 2018 SPIE. High-resolution thermal sensing and bioimaging at the cellular level and in animal models is interesting for both early diagnosis and controlled treatment via photothermal conversion of several diseases. Despite excellent in vitro results have been obtained with visible emitting luminescent nanothermometers, their application for in vivo studies is very limited due to the reduced penetration depth of visible light in biological tissues. This can be overcome if materials with emitting in the so-called biological windows (650-1350 nm) are used. Despite all this work, the number of studies exploring the possibilities of longer emission wavelengths in luminescence thermometry are scarce. This includes those lying in the so called short-wavelength infrared (SWIR) that extends from 1.35 to 2.3 μm. SWIR light transmits more effectively (up to three times) through specific biological tissues (oxygenated blood and melanin-containing tumors), achieving higher penetrations depths. Due to the reduced tissue absorbance and scattering within this region. Here, we analyze the possibilities for temperature sensing purposes of emissions in the SWIR region generated by Er3+, Tm3+and Ho3+ions in KLu(WO4)2nanoparticles. The thermometric responses of these particles are compared with those shown by other Ln3+-doped nanoparticles of the same family of materials operating in the other biological windows, and demonstrate the potentiality of SWIR emitting nanoparticles for temperature measurements in biological tissues. The results indicate that SWIR emitting nanoparticles are good candidates for luminescent thermometry in biomedical applications.

© 2018 SPIE. Tetragonal calcium rare-earth aluminates, CaLnAlO 4 , are attractive laser host crystals. The emission of Nd 3+ ions at 1.3-1.4 ?m due to the 4 F 3/2 ? 4 I 13/2 transition is of interest for medicine, fiber optics, and light conversion. We report on compact Nd:CaLnAlO 4 lasers using a plane-plane cavity. With an a-cut 0.8 at.% Nd:CaYAlO 4 crystal diode-pumped at 802 nm, a maximum continuous-wave output power of 365 mW was achieved at 1.365 & 1.390 ?m corresponding to the ?-polarization. The 4 F 3/2 ? 4 I 13/2 laser performance of the Nd:CaLnAlO 4 crystals was compared to that from a monoclinic Nd:KGd(WO 4 ) 2 . At the 4 F 3/2 ? 4 I 11/2 transition (1.08 ?m), a Nd:CaYAlO 4 micro-laser generated multi-watt output ( > 4 W) with a slope efficiency of 39%.

© 2018 SPIE. We report on the first application of a topological insulator based on antimony telluride (Sb 2 Te 3 ) as a saturable absorber (SA) in a bulk microchip laser. The transmission-type SA consisted of a thin film of Sb 2 Te 3 (thickness: 3 nm) deposited on a glass substrate by pulsed magnetron sputtering. The saturable absorption of the Sb 2 Te 3 film was confirmed for ns-long pulses. The microchip laser was based on a Tm:GdVO 4 crystal diode-pumped at ?802 nm. In the continuous-wave regime, this laser generated 3.54 W at 1905-1921 nm with a slope efficiency ? of 37%. The Q-switched laser generated a maximum average output power of 0.70 W at 1913 nm. The pulse energy and duration were 3.5 ?J and 223 ns, respectively, at a repetition rate of 200 kHz. The Sb 2 Te 3 SAs are promising for passively Q-switched waveguide lasers at ?2 ?m.

© 2018 SPIE. We report on the first application of a topological insulator based on antimony telluride (Sb 2 Te 3 ) as a saturable absorber (SA) in a bulk microchip laser. The transmission-type SA consisted of a thin film of Sb 2 Te 3 (thickness: 3 nm) deposited on a glass substrate by pulsed magnetron sputtering. The saturable absorption of the Sb 2 Te 3 film was confirmed for ns-long pulses. The microchip laser was based on a Tm:GdVO 4 crystal diode-pumped at ?802 nm. In the continuous-wave regime, this laser generated 3.54 W at 1905-1921 nm with a slope efficiency ? of 37%. The Q-switched laser generated a maximum average output power of 0.70 W at 1913 nm. The pulse energy and duration were 3.5 ?J and 223 ns, respectively, at a repetition rate of 200 kHz. The Sb 2 Te 3 SAs are promising for passively Q-switched waveguide lasers at ?2 ?m.

© 2018 SPIE. The recent advances in the development of Holmium monoclinic double tungstate thin-disk lasers are reviewed. The thin-disk is based on a 250-μm-thick 3 at. % Ho:KY(WO4)2active layer grown on a (010)-oriented KY(WO4)2substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce pump geometry, the continuous-wave Ho:KY(WO4)2thin-disk laser generates an output power of 1.01 W at 2057 nm corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. The thin-disk laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. In this regime, it generates an average output power of 0.551 W at ∼2056 nm with η = 44%. The best pulse characteristics are 4.1 μJ/201 ns at a repetition rate of 135 kHz. The laser performance, beam quality and thermo-optic aberrations of such lasers are strongly affected by the Ho3+doping concentration. For the 3 at.% Ho3+-doped thin-disk, the thermal lens is negative (the sensitivity factors for the two principal meridional planes are-1.7 and-0.6 m-1/W) and astigmatic. The Ho:KY(WO4)2epitaxial structures are promising as active elements in mode-locked thin-disk lasers at ∼2060 nm.

© 2018 SPIE. A buried depressed-index channel waveguide with a circular cladding and a core diameter of 40 ?m is fabricated in a bulk monoclinic 3 at.% Tm:KLu(WO 4 ) 2 crystal by femtosecond direct laser writing. In the continuous-wave regime, the Tm waveguide laser generates ?210 mW at 1849.6 nm with a slope efficiency ? of 40.8%. Passively Q-switched operation is achieved by inserting transmission-type 2D saturable absorbers (SAs) based on few-layer graphene and MoS 2 . Using the graphene-SA, a maximum average output power of ?25 mW is generated at 1844.8 nm. The pulse characteristics (duration/energy) are 88 ns/18 nJ at a repetition rate of 1.39 MHz.

© 2018 SPIE. Tetragonal calcium rare-earth aluminates, CaLnAlO 4 , are attractive laser host crystals. The emission of Nd 3+ ions at 1.3-1.4 ?m due to the 4 F 3/2 ? 4 I 13/2 transition is of interest for medicine, fiber optics, and light conversion. We report on compact Nd:CaLnAlO 4 lasers using a plane-plane cavity. With an a-cut 0.8 at.% Nd:CaYAlO 4 crystal diode-pumped at 802 nm, a maximum continuous-wave output power of 365 mW was achieved at 1.365 & 1.390 ?m corresponding to the ?-polarization. The 4 F 3/2 ? 4 I 13/2 laser performance of the Nd:CaLnAlO 4 crystals was compared to that from a monoclinic Nd:KGd(WO 4 ) 2 . At the 4 F 3/2 ? 4 I 11/2 transition (1.08 ?m), a Nd:CaYAlO 4 micro-laser generated multi-watt output ( > 4 W) with a slope efficiency of 39%.

© 2018 SPIE. High-resolution thermal sensing and bioimaging at the cellular level and in animal models is interesting for both early diagnosis and controlled treatment via photothermal conversion of several diseases. Despite excellent in vitro results have been obtained with visible emitting luminescent nanothermometers, their application for in vivo studies is very limited due to the reduced penetration depth of visible light in biological tissues. This can be overcome if materials with emitting in the so-called biological windows (650-1350 nm) are used. Despite all this work, the number of studies exploring the possibilities of longer emission wavelengths in luminescence thermometry are scarce. This includes those lying in the so called short-wavelength infrared (SWIR) that extends from 1.35 to 2.3 μm. SWIR light transmits more effectively (up to three times) through specific biological tissues (oxygenated blood and melanin-containing tumors), achieving higher penetrations depths. Due to the reduced tissue absorbance and scattering within this region. Here, we analyze the possibilities for temperature sensing purposes of emissions in the SWIR region generated by Er3+, Tm3+and Ho3+ions in KLu(WO4)2nanoparticles. The thermometric responses of these particles are compared with those shown by other Ln3+-doped nanoparticles of the same family of materials operating in the other biological windows, and demonstrate the potentiality of SWIR emitting nanoparticles for temperature measurements in biological tissues. The results indicate that SWIR emitting nanoparticles are good candidates for luminescent thermometry in biomedical applications.

© Springer International Publishing AG 2016. Underwater sensor networks are an important field of research. Several applications require the use of this kind of networks like tsunami or oil spill alerts. The underwater medium is very harsh and only acoustic signals can be used for the transmission of information. The use of this kind of networks is still in a developing state far from reaching standard consensus on basic aspects like carrier frequency or modulation techniques. The use of these networks for real-time applications has not been analyzed previously. In this paper we present two solutions for the scheduling of real-time messages and we provide a time constraint analysis of the performance of the network.

© Springer International Publishing AG 2016. Underwater sensor networks are an important field of research. Several applications require the use of this kind of networks like tsunami or oil spill alerts. The underwater medium is very harsh and only acoustic signals can be used for the transmission of information. The use of this kind of networks is still in a developing state far from reaching standard consensus on basic aspects like carrier frequency or modulation techniques. The use of these networks for real-time applications has not been analyzed previously. In this paper we present two solutions for the scheduling of real-time messages and we provide a time constraint analysis of the performance of the network.

This investigation has studied the characterization of the thermomechanical behaviour of a TiNiCu shape memory alloy with different heat treatments. This characterization has been done by analyzing martensitic transformation at constant stress tests. The martensitic transformation was analyzed by measuring electrical resistance and strain. The results showed that orientation is reached at different stress levels during each heat treatment; low stress thermomechanical cycling does not affect transformation temperatures and thermomechanical cycling at upper stress levels produces different changes of behaviour depending on the stress level and/or heat treatment. © (2013) Trans Tech Publications, Switzerland.

The brightness constancy assumption has widely been used in variational optical flow approaches as their basic foundation. Unfortunately, this assumption does not hold when illumination changes or for objects that move into a part of the scene with different brightness conditions. This paper proposes a variation of the L1-norm dual total variational (TV-L1) optical flow model with a new illumination-robust data term defined from the histogram of oriented gradients computed from two consecutive frames. In addition, a weighted non-local term is utilized for denoising the resulting flow field. Experiments with complex textured images belonging to different scenarios show results comparable to state-of-the-art optical flow models, although being significantly more robust to illumination changes.

This investigation has studied the characterization of the thermomechanical behaviour of a TiNiCu shape memory alloy with different heat treatments. This characterization has been done by analyzing martensitic transformation at constant stress tests. The martensitic transformation was analyzed by measuring electrical resistance and strain. The results showed that orientation is reached at different stress levels during each heat treatment; low stress thermomechanical cycling does not affect transformation temperatures and thermomechanical cycling at upper stress levels produces different changes of behaviour depending on the stress level and/or heat treatment. © (2013) Trans Tech Publications, Switzerland.

In this paper PCM is added to three types of stabilized rammed. Mechanical and thermal characterization is carried out. To do so, the compressive strength is optimized and the final compositions obtained are used to formulate the materials which will be thermally characterized. The optimization process is done with a design of experiments (DoE) and a variance analysis (ANOVA). Finally, LCA is used to evaluate the environmental impact during the manufacturing phase, due to the addition of stabilizers and PCM in the rammed earth. © 2012 The Authors.

The sizes of certain types of lipoprotein particles have been associated with an increased risk of cardiovascular disease. However, there is currently no gold standard technique for the determination of this parameter. Here, we propose an analytical procedure to measure lipoprotein particles sizes using diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY). The method was tested on six lipoprotein fractions, VLDL, IDL, LDL1, LDL2, HDL2, and HDL3, which were obtained by sequential ultracentrifugation from four patients. We performed a pulsed-field gradient experiment on each fraction to obtain a mean diffusion coefficient, and then determined the apparent hydrodynamic radius using the Stokes–Einstein equation. To validate the hydrodynamic radii obtained, the particle size distribution of these lipoprotein fractions was also measured using transmission electron microscopy (TEM). The standard errors of duplicate measurements of diffusion coefficient ranged from 0.5% to 1.3%, confirming the repeatability of the technique. The coefficient of determination between the hydrodynamic radii and the TEM-derived mean particle size was r2 = 0.96, and the agreement between the two techniques was 85%. Thus, DOSY experiments have proved to be accurate and reliable for estimating lipoprotein particle sizes.

The sizes of certain types of lipoprotein particles have been associated with an increased risk of cardiovascular disease. However, there is currently no gold standard technique for the determination of this parameter. Here, we propose an analytical procedure to measure lipoprotein particles sizes using diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY). The method was tested on six lipoprotein fractions, VLDL, IDL, LDL1, LDL2, HDL2, and HDL3, which were obtained by sequential ultracentrifugation from four patients. We performed a pulsed-field gradient experiment on each fraction to obtain a mean diffusion coefficient, and then determined the apparent hydrodynamic radius using the Stokes–Einstein equation. To validate the hydrodynamic radii obtained, the particle size distribution of these lipoprotein fractions was also measured using transmission electron microscopy (TEM). The standard errors of duplicate measurements of diffusion coefficient ranged from 0.5% to 1.3%, confirming the repeatability of the technique. The coefficient of determination between the hydrodynamic radii and the TEM-derived mean particle size was r2 = 0.96, and the agreement between the two techniques was 85%. Thus, DOSY experiments have proved to be accurate and reliable for estimating lipoprotein particle sizes.

In this study we compare sensor responses to H2in air using two types of sensing materials: SnO2bulk doped with TiO2and mechanical mixtures of SnO2and TiO2. The materials were analyzed in the broad range of working temperatures and H2concentrations. Thermal stability of SnO2bulk doped with TiO2was studied by in-situ XRD at 700°C. © 2011 Published by Elsevier Ltd.

This paper presents an adaptation of the tensor voting framework for color image denoising, while preserving edges. Tensors are used in order to encode the CIELAB color channels, the uniformity and the edginess of image pixels. A specific voting process is proposed in order to propagate color from a pixel to its neighbors by considering the distance between pixels, the perceptual color difference (by using an optimized version of CIEDE2000), a uniformity measurement and the likelihood of the pixels being impulse noise. The original colors are corrected with those encoded by the tensors obtained after the voting process. Peak to noise ratios and visual inspection show that the proposed methodology has a better performance than state-of-the-art techniques.

The structure of real complex networks is often modular, with sets of nodes more connected between them than to the rest of the network. These communities are usually reflecting a topology-functionality interplay, whose discovery is basic for the understanding of the operation of the networks. Thus, much attention has been driven to the determination of the modular structure of complex networks. Recently it has been shown that this modular organization appears at several scales of description, which may be found by a synchronization process on top of these networks. Here we make use of it for a tentative uncovering of functional groups in the neural system of the nematode C. elegans. © 2008 Springer Berlin Heidelberg.

The structure of real complex networks is often modular, with sets of nodes more connected between them than to the rest of the network. These communities are usually reflecting a topology-functionality interplay, whose discovery is basic for the understanding of the operation of the networks. Thus, much attention has been driven to the determination of the modular structure of complex networks. Recently it has been shown that this modular organization appears at several scales of description, which may be found by a synchronization process on top of these networks. Here we make use of it for a tentative uncovering of functional groups in the neural system of the nematode C. elegans. © 2008 Springer Berlin Heidelberg.

Private information retrieval (PIR) is normally modeled as a game between two players: a user and a database. The user wants to retrieve some item from the database without the latter learning which item. Most current PIR protocols are ill-suited to provide PIR from a search engine or large database: i) their computational complexity is linear in the size of the database; ii) they assume active cooperation by the database server in the PIR protocol. If the database cannot be assumed to cooperate, a peer-to-peer user community is a natural alternative to achieve some query anonymity: a user submits a query on behalf of another user in the community. A peer-to-peer PIR system is described in this paper which relies on an underlying combinatorial structure to reduce the required key material and increase availability. © 2008 Springer-Verlag Berlin Heidelberg.

Private information retrieval (PIR) is normally modeled as a game between two players: a user and a database. The user wants to retrieve some item from the database without the latter learning which item. Most current PIR protocols are ill-suited to provide PIR from a search engine or large database: i) their computational complexity is linear in the size of the database; ii) they assume active cooperation by the database server in the PIR protocol. If the database cannot be assumed to cooperate, a peer-to-peer user community is a natural alternative to achieve some query anonymity: a user submits a query on behalf of another user in the community. A peer-to-peer PIR system is described in this paper which relies on an underlying combinatorial structure to reduce the required key material and increase availability. © 2008 Springer-Verlag Berlin Heidelberg.

Omnidirectional mirrors are multilayer periodic structures that reflect light in a wide range of wavelengths for all angles of incidence and for all polarizations of the incident light. These structures can be made using the porous silicon technology: the layers are electrochemically etched to have different porosities, corresponding to different refractive indices. Since the porosity depends on the current density of the electrochemical etching process, the layers may have any refractive index value from 1.2 to 2.7. In opposition to classical evaporated thin films where the refractive indices are fixed, this offers a new degree of freedom in the design of such structures. In this work, the four main parameters of a basic omnidirectional mirror (refractive index of the two kinds of layers and their optical thicknesses) are analyzed to find the condition to obtain the maximum width of the omnidirectional reflection band. The analysis is made using the framwork of the Photonic Band Gap materials and considering the omnidirectional mirrors as 1-D Photonic Crystals.

By using a voxel-based Monte Carlo simulation technique, we developed and validated a method to calculate radiation-absorbed dose in the computed tomography (CT) examinations from the images of phantoms and patients. The ionising radiation transport was simulated using the EGS4 code system. The geometry of the X-ray beam (focus-to-axis distance, field of view, collimation, and primary and beam-shaper filtration) and the X-ray spectral distribution (HiSpeed LX/i) were included in the simulation. Each axial CT image was reduced to a 256 x 256 matrix and stacked in a volume. The patient images were segmented before the simulation of radiation transport by using four categories of materials, such as air, lung, muscle and bone. To test the voxel-based method, the values of the radiation dose derived from a simulated CT exposure were calculated and compared with those obtained from the measurements performed within the dosimetry phantoms. To complete the scope of the work, series of CT scans of the trunk of an anthropomorphic phantom and patients were simulated to calculate the average dose in each 1-cm-wide transverse slice (ADS). The comparison between the simulated and measured dose data for the CT indices showed a difference of