Search

Since the development of the original specifications in the '90s the PDF document format has become the de-facto standard for the distribution and archival of documents in electronic form because of its ability to preserve the original layout of the documents, independently of the hardware, operating system and application software used to visualize them.Unfortunately the PDF format does not contain explicit structural and semantic information, making it very difficult to extract structured information from them, in particular data presented in tabular form. The automatic extraction of tabular data is a difficult and challenging task because tables can have extremely different formats and layouts, and involves several complex steps, from the proper recognition and conversion of printed text into machine-encoded characters, to the identification of logically coherent table constructs (headers, columns, rows, spanning elements), and to the breaking down of the data constructs into elemental objects.Several tools have been developed to support the extraction process. In this work we survey the most interesting tools for the automatic detection and extraction of tabular data, analyzing their respective advantages and limitations. A particular emphasis is given on programmable open source tools because of their flexibility and long-term availability, together with the possibility to easily tweak them to meet the peculiar needs of the problem at hand.As a practical application, we also present a workflow based on a set of R and AWK scripts that can automatically extract daily temperature and precipitation data from the official PDF documents made available each year by Regione Puglia, in Italy. The lessons learned from the development of this workflow and the possibility to generalize the approach to different kinds of PDF documents are also discussed.

The risk of wildfires has risen significantly in recent years, not just in Europe but around the world. In Italy alone, hundreds of thousands of hectares are burned each year, resulting in deaths, the destruction of forests and loss of biodiversity, and damage to infrastructure and farms. One way to address this issue is through satellite remote sensing, which is a valuable tool for monitoring and managing fires, assessing risks, surveying and evaluating the damage caused by fires and preparing recovery actions.The objective that the Alta Murgia National Park is pursuing with this project is to gather information on fires that have occurred within the Park area, in order to quickly identify affected areas and aid in their perimeter, characterization and control, and to support the preliminary and timely design of forest restoration efforts, as well as the updating of AIB plans according to legal requirements.The project aims to develop automated satellite monitoring procedures using Landsat and Sentinel2 imagery to assess the health of forested areas and identify and characterize degradation caused by negative events such as forest fires, illegal logging, conversion of forest land to agriculture, and improper use of areas historically affected by fire. A module based on difference in the Normalized Burn Ratio (NBR) index would allow to define the effective perimeter of damage caused by a fire within the larger perimeter defined by firefighting crews. Additionally, a module using various vegetation indices, such as those related to chlorophyll and carotenoids, will be employed to compare vegetation changes across the landscape and over time.The project also involves using a time series analysis to retrospectively monitor the recovery of vegetation following a critical event, and a Bayesian approach previously developed by the group will be used to estimate expected phenological statistics with associated error. To further understand the recovery process, a single forested site burned in 2020 will be closely monitored with an eddy covariance tower and through repeated floristic surveys.Lastly, the project aims to establish a pilot low-cost ground-based monitoring and video surveillance system to supplement the existing video surveillance network. This system will focus on monitoring remote or less frequented areas of the park, where installing high-end monitoring stations would not be cost-effective. The system proposed is self-sufficient in terms of power and is capable of performing real-time image analysis over the study area. In the event of a fire or the emission of harmful gases, the system will immediately alert relevant law enforcement agencies.The current work summarizes the current state of the project and the scientific results obtained so far.

The efficient and reliable monitoring of the flow of water in open channels provides useful information for preventing water slow-downs due to the deposition of materials within the bed of the channel, which might lead to critical floods. A reliable monitoring system can thus help to protect properties and, in the most critical cases, save lives. A sensing system capable of monitoring the flow conditions and the possible geo-environmental constraints within a channel can operate using still images or video imaging. The latter approach better supports the above two features, but the acquisition of still images can display a better accuracy. To increase the accuracy of the video imaging approach, we propose an improved particle tracking algorithm for flow hydrodynamics supported by a machine learning approach based on a convolutional neural network-evolutionary fuzzy integral (CNN-EFI), with a sub-comparison performed by multi-layer perceptron (MLP). Both algorithms have been applied to process the video signals captured from a CMOS camera, which monitors the water flow of a channel that collects rain water from an upstream area to discharge it into the sea. The channel plays a key role in avoiding upstream floods that might pose a serious threat to the neighboring infrastructures and population. This combined approach displays reliable results in the field of environmental and hydrodynamic safety.

Replication

Monitoring networks are essential tools for the effective management of vulnerable or limited environmental resources. Cost and logistics constraints often suggest to reduce the number of monitoring sites while minimizing the loss of information determined by these changes. The problem can be rigorously addressed through the optimization of one or more objective functions that represent the managerial goals associated to the network. However, the use of objective functions is based on assumptions that in practical cases can be inaccurate. To overcome this problem, we have developed a retrospective analysis procedure that validates the degree of acceptability of the optimal reduced configuration at a local and global level. The procedure has been applied to a case study in Apulia, Italy, finding that the optimal reduced network was unable to recover the measured values of the monitored parameter of two discarded locations, making it unable to accomplish its monitoring goals.

Flow slow-down in rivers and artificial canals is a basic aspect to be monitored and kept strictly under control. Flow slow-downs can become a major concern in the event of extreme phenomena. The paper illustrates an advanced image processing method that uses particle tracking velocimetry in conjunction with a monadic approach to better characterize water flow in the presence of waste or debris that block normal water flow within a river. An high-speed camera installed beneath a bridge takes periodic images of the water flow. The measured water level and the images taken by the camera are sent to a central system in real-time. Results demonstrate the capability of the proposed method to accurately detect the presence of debris from the measured water flow.

Bioclimatic indices combine atmospheric parameters to provide analytical indication of climatic features and their evolution in space and time that can directly relate with natural resource availability, distribution, and related bio-physical processes. The availability of bioclimatic information can provide natural resource managers with analytical means to assess the magnitude and temporal evolution of drought and climate change parameters that could affect the availability, demand and use of natural resources for various sectors. This paper presents a methodology to process bioclimatic data in the space and time domains for assessing the moisture/dryness level and water requirements of a region, and inform water resource planning and management decisions related to drought, climate variability and change. The methodology relies on a modular assembly of statistical tests and methods, and utilizes point scale measurements of meteorological data to perform the analysis of the spatial behavior of derived bioclimatic indicators at the continuous regional scale, and evaluate the significance of the temporal trends. Also, the article presents an application of the proposed methodology to a coastal area of southern Italy (the Apulia Region) that is characterized by recurring water supply limitations, involving the use of the popular De Martonne bioclimatic aridity index. The methodology allowed to obtain qualitative and quantitative information about the aridity level of the Apulia region, the identification of main bioclimatic zones, and the evaluation of spatial pattern and time evolution of aridity. The determination of bioclimatic zones showed that nearly 40% of the regional territory is characterized by dry sub-humid (Mediterranean) climate, about 30% by sub-humid climate, while nearly 10% and 20% are characterized by semi-arid and humid climates, respectively. The temporal analysis revealed that the Salento and the Ionian coastal zone are areas at risk of increasing aridity, with resulting impacts on the water supply and demand for irrigated agriculture. (C) 2019 Elsevier B.V. All rights reserved.

The Caribbean coast is characterized by the presence of mud volcanoes, a secondary phenomenon of volcanism similar to mud diapirs for its development and evolution, but different in terms of geological features and forms. These mud volcanoes are often located close to tectonic faults and oil and gas deposits. Their geological context is dominated by the presence of clay sediments and brackish water, that favors the decomposition of organic material and the formation of methane. Mud volcanoes can thus be an important reservoir of hydrocarbons. This paper aims to fill the existing gap in the knowledge of mud volcanoes (MVs) of Colombia. We analyze the physical and geochemical characteristics of nine onshore mud volcanoes located in the Departments of Atlántico (La Laguna), Bolívar (Las Palomas, La Bonga, Santa Catalina, Yerbabuena, Clemencia, and Membrillal), Cordóba (Los Olivos), and Magdalena (Cañaveral). These structures present a kaolinitic composition, except for La Laguna mud volcano in which smectite is predominant. Apart from tectonic processes, this influences the shape and size of MVs and, also, the type and frequency of eruptions. The abundance of methane in all sites confirms the thermogenic origin of these structures. MVs are often considered landscape attractions as well as a therapeutic resources, but unfortunately they also represent a serious risk for the local communities, due to the frequent unexpected, eruptions, sometimes accompanied by the release of toxic gases or by landslides, that can damage the infrastructures and hurt the population living in the area. The MVs are classified into five vulnerability classes using a novel synthetic index which could improve the understanding of risks associated with the presence of MVs in proximity to towns and infrastructures.

We have fabricated microstrips of Nb thin films by dc magnetron sputtering and lift-off. Focused ion beam (FIB) has been used to mill the surface of the films in a nanometer-sized region across the width of the strip. FIB has the side effect of implanting Ga+ ions on the exposed surface of Nb, damaging the film and modifying its superconducting properties. To overcome this problem, the surface of the FIB-milled Nb films has been passivated by anodization, including the damaged region of the strip into the oxidized layer. Anodization also allows for finely tuning the thickness of the nanoconstrictions after the milling process. We report here the effect of FIB exposure and anodization voltage on the superconducting transition temperature and on the temperature dependence of the resistance of the Nb nanoconstric- tions. We also show some preliminary results suggesting that these devices behave as overdamped SNS-like Josephson junctions.

This paper presents a software package for the automatic processing of bioclimatic data in the space and time domains whose final goal is to provide land and water management authorities with reliable information about the moisture/dryness level of a region and its water requirements. The current state of development of package is reported, presenting an example of application of the program to a specific case study.

The measurement of ultra-weak magnetic fields with nanometer-scale spatial resolution is a powerful tool for investigating several biological, chemical and physical systems. Among the available detectors, SQUIDs are the most sensitive magnetic field and flux detectors and are rapidly approaching the quantum sensitivity limit. To reach such sensing capability, technological advances in the fabrication of nanoscale SQUIDs with submicrometric loops are needed. In this work we present a novel process for the fabrication of nanoscale SQUIDs, based on superconducting vertical Nb nanoconstrictions. The fabrication process uses laser lithogra- phy to define the device geometry, focused ion beam to mill the top surface of the Nb in a nanometer-sized region across the width of the film and anodization to define the final thickness of the nanoconstriction and at the same time to embed the ion- implanted amorphous layer produced by the FIB milling step. A preliminary electrical characterization of nano-sized single Josephson junctions and SQUIDs fabricated with this process is also reported.

A research study was conducted on a coastal irrigated agricultural area of southern Italy to assess the risks of aquifer degradation likely resulting from the intensive groundwater pumping from individual farm wells and reduced aquifer recharge. Information were collected both from farmers and delivery system's operators during a survey conducted in 2012 revealing that farmers depend mainly on groundwater with the aim to achieve flexible irrigation management as opposed to the rigid rotational delivery service of surface water supply provided by the local water management agency. The study area is intensively farmed by small land-holding growers with high-value micro-irrigated horticultural crops. Our team appraised the soil and aquifer degradation hazards using a simplified procedure for environmental risk assessment that allowed identifying the risk-generating processes, evaluating the magnitude of impacts, and estimating the overall risks significance. We also collected the stakeholders' perceptions on agricultural water management and use through field interviews, whereas parallel investigations revealed significant aquifer salinity increase during the recent years. As a final step, some preliminary risk mitigation options were appraised by exploring the growers' response to possible changes of irrigation deliveries by the water management agency. The present study integrated multi-annual observations, data interpretation, and modelling efforts, which jointly enabled the analysis of complex water management scenarios and the development of informed decisions.

Atmospheric deposition of pollutants is a major challenge for the environmental governance and management of cities. Different depositions could be harmful especially on ground and roads. In particular, in areas were industrial activities are located and/or significant car traffics occur, depositions on roads are harmful for all people especially for pregnant women who will be attacked as well as other people. The main effects are risks of breathing pathologies and possible cancer as a long-term consequence. The main objective of this research is to illustrate the latest achievements in terms of the use of titanium dioxide to be spread on a road as a cover film to neutralize pollutants as NOx, SO x , NH 3 , CO, dusts and aromatic substances. The removal is performed by means of a photocatalytic reaction. The nanoparticles play a key role in this process. The paper show some experimental and interesting results.

In the last century, the International System of Units (SI) changed its perspectives, evolving from an artifact-based system to a system mainly based on physical processes at the atomic level and fundamental constants. In particular, the discovery of the Josephson effect made available a quantum voltage standard. As an consequence, in the last decade the worldwide consistency of the representation and maintenance of the electrical units and the electrical measurements based on it has improved a hundredfold. The Josephson effect, together with the quantum Hall effect for the definition of a modern resistance standard, will certainly play a major role in the next modernization of the SI, when the kilogram, the last base unit still based on a physical artifact, will be linked to fundamental constants. Furthermore, the definition of a new SI is strictly linked to the technological issues for the realisation of new devices capable to reproduce the electrical units with quantum accuracy. The challenges faced by modern metrology, sensing and quantum electronics are directing the new generations of devices towards smaller dimensions and higher levels of integration. Taking into account this requirement, at INRIM we fabricate and characterize superconducting quantum devices for a wide range of applications. The devices are based on the overdamped Nb/Al-AlOx/Nb SNIS (Superconductor-Normal metal-Insulator-Superconductor) Josephson junctions and exploiting thin film technology to guarantee a good control of electrical parameters of junctions, a higher reproducibility of their currentvoltage response, and increasingly an accurate dimension control. The main objective of the current experimental activity is addressed on downscaling the junction size from the micro to the nanoscale, exploiting three different lithographic techniques: optical lithography to realize SNISs with a size resolution of the order of the microme- ter, electron beam lithography (EBL) at the submicrometer range and, lastly, a recently proposed mesoscopic tunnel junction nano-fabrication technique, based on focused ion beam (FIB). We report the fabrication process and the electrical characterisation of a 1 Volt binary-divider array based on 8192 overdamped SNIS Josephson junctions for the programmable Josephson Voltage Standard (PJVS) [1] and of a 3D nano-SQUID (Super- conducting Quantum Interference Device) [2] as a sensor for the detection of magnetic nanoparticles. Preliminary results on Nb-based nano-constrictions fabricated by FIB and anodisation will also be presented [3]. The effect of FIB exposure and anodization voltage on the superconducting transition temperature and on the temperature dependence of the resistance of the nano-constrictions has been investigated, as well as the behaviour of these constrictions as overdamped SNS-like Josephson junctions. [1] V. Lacquaniti, N. De Leo, M. Fretto, A. Sosso, F. Mueller, J. Kohlmann, Superconductor Sci. Technol. 24 (2011). [2] C. Granata, A. Vettoliere, R. Russo, M. Fretto, N. De Leo, V. Lacquaniti, Appl. Phys. Lett. 103 (2013). [3] N. De Leo, M. Fretto, V. Lacquaniti, C. Cassiago, L. D'Ortenzi, L. Boarino, S. Maggi, accepted for publication in IEEE Trans. Appl. Supercond. (2016).

A novel and convenient approach to functionalized pyrroles is presented, based on Pd-catalyzed oxidative heterocyclization-alkoxycarbonylation of readily available N-Boc-1-amino-3-yn-2-ols. Reactions were carried out in alcoholic solvents at 80-100 °C and under 20 atm (at 25 °C) of a 4:1 mixture of CO-air, in the presence of the PdI(2)-KI catalytic system (2-5 mol % of PdI(2), KI/PdI(2) molar ratio = 10). In the case of N-Boc-1-amino-3-yn-2-ols 3, bearing alkyl or aryl substituents, the carbonylation reaction led to a mixture of Boc-protected and N-unsubstituted pyrrole-3-carboxylic esters 4 and 5, respectively. This mixture could be conveniently and quantitatively converted into deprotected pyrrole-3-carboxylic esters 5 by a simple basic treatment. In the case of diastereomeric (3RS,4RS)- and (3RS,4SR)-N-Boc-3-amino-2-methyldec-5-yn-4-ol (syn-3f and anti-3f, respectively, whose relative configuration was determined by X-ray crystallographic analysis), no particular difference was observed in the reactivity of the two diastereomers between them and with respect to the diastereomeric mixture (3S,4S) + (3S,4R). Interestingly, N-Boc-2-alkynyl-1-amino-3-yn-2-ols 6, bearing an additional alkynyl substituent α to the hydroxyl group, spontaneously underwent N-deprotection under the reaction conditions and regioselective water addition to the alkynyl group at C-3 of the corresponding pyrrole-3-carboxylic ester derivative, thus directly affording highly functionalized pyrrole derivatives 7 in one step. In a similar manner, a novel functionalized dihydropyrrolizine derivative 9 was directly synthesized starting from (S)-7-(pyrrolidin-2-yl)trideca-5,8-diyn-7-ol 8.

Calcium hydroxyapatite (CaHAp) was prepared in the presence of two alkylphosphonates, the tert-butylphosphonic acid TBPOH and the 2-carboxyletylphosphonic acid 2-CEPA, by hydrothermal method at120 ◦ C for 15h. The modification of hydroxyapatite by grafting organic moieties is confirmed by IR andNMR MAS ( 1 H and 31 P) spectroscopy and chemical analysis. X-ray powder diffraction patterns show thatthe incorporation of organic moieties induces a significant loss of the material crystallinity and a clearincrease of the unit cell lattice parameter a as function of 2-CEPA grafting rate. The specific surface area(SSA) increases with increasing phosphonate amount especially for 2-CEPA. All techniques show thelower reactivity of TBPOH due to the steric effects of tert-butyl, whereas the 2-CEPA with a linear chainand double acidic functions is more reactive and can replace the OH − groups of the apatitic structure.© 2010 Elsevier B.V. All rights reserved. 1. IntroductionCalciumhydroxyapatiteCa

The temperature stability is one of the most important factors determining the successful application of the Josephson effect to the ac voltage standard or to analog and digital electronics. Whereas SIS hysteretic junctions with an Ambegaokar-Baratoff (A&B) IC(T) behavior exhibit a reduced drift around the working temperature of the liquid helium, metallic-barrier SNS junctions follow a Kulik-Omelianchuck (K&O) behavior with a sharp temperature dependence of Ic in this region. The objective of our research is to study this aspect for overdamped Nb/Al-AlOx/Nb heterostructures with current densities of 10-75 kA/cm2 and characteristic voltages from 100 to more than 500 muV, that have been fabricated at INRiM. The IC(T) characteristics, measured for Josephson heterostructures with different thickness, s, and exposure, E, essentially deviate from A&B and K&O curves, because of proximity effect caused by the comparatively high value of s (up to 100 nm). We study theoretically two extreme limits: the clean and the dirty limit for the interlayer between the superconducting electrodes and discuss the temperature stability of the junctions characterizing it with the temperature derivative dIC/dT. The combined experimental and theoretical analysis of the problem provides a way for understanding, controlling and improving the design of the Nb/Al-AlOx/Nb junctions in order to enhance their reliability.

Overdamped Nb/Al–AlOx/Nb Josephson junctions are an intermediate state between the SIS and SNS Josephson junctions. Stable and reproducible non-hysteretic current–voltage characteristics have been obtained with a proper choice of the fabrication parameters, featuring critical current densities Jc up to 25 kA/cm2 and characteristic voltages up to 450 μV. While these values make the junctions interesting for RSFQ electronic circuits, their response to an RF signal at 70 GHz has demonstrated their suitability for both programmable and ac voltage standard. In these work we analyse the temperature behavior of these junctions up to T/Tc = 1, Tc being the niobium critical temperature, which gives relevant information on the junction structure and, especially, on the oxide insulator/metallic film barrier, which is the key for the reproducible transition from an hysteretic to a non-hysteretic behavior. The results are also compared with other data of hysteretic and overdamped junctions.

Josephson devices for superconducting electronic applications, such as RSFQ logic circuits and programmable voltage standards, require nonhysteretic junctions with a high speed or a high voltage resolution and hence with characteristic voltages spanning over several orders of magnitude. We present here our recent results on Nb/Al/Nb junctions where, by changing some fabrication parameters such as the thickness and deposition rate of the Al barrier, it is possible to obtain junctions with very different electrical properties. These junctions have characteristic voltages varying from a few tens of /spl mu/V up to more than 1 mV, with critical current densities from 10/sup 3/ up to 10/sup 6/ A/cm/sup 2/.

Overdamped Josephson junctions are gaining interest in many fields of superconducting electronics. The characteristic voltage ICRN is the parameter limiting the highest possible speed and voltage resolution of the junctions. Nb/Al/Nb technology is a good candidate for these devices because of its wide range of characteristic voltages. In our laboratory we have so far fabricated Nb/Al/Nb SNS junctions having (a) high critical currents and smooth interfaces, (b) low critical currents and smooth interfaces, (c) low critical currents and rough interfaces. However, further improvements to this technology are still needed.

Superconductor–normal metal–superconductor (SNS) Josephson junctions are gaining interest in many fields, related to superconducting electronics. Their main advantages are the high critical current density and non-hysteretic I – V characteristic. We have studied Nb/Al/Nb SNS junctions, where the combined effects of the thickness and deposition rate of the Al barrier play a relevant role in determining the electrical behaviour of the junction. The increase of the Al deposition rate from 0.5 to 5 nm/s increases the surface roughness of the junction by a factor of two, with a corresponding variation of the current density and of the I C R N product from 10 6 to 10 3 A/cm 2 and from 100 μV to 1 mV, respectively.

The water retention curve has a key role for the hydraulic characterization of porous media. Its experimental determination requires the accurate and detailed measurement of the matric potential and water content from saturation to oven dryness. The experimental data are fitted with a parametric model to calculate the analytic curve describing the hydraulic properties of the sample. We present a new method, based on differential evolution, for the determination of the characteristic parameters of the water retention models. This method allows to reduce the number of measurements necessary for obtaining accurate model parameters, decreasing the time needed to adequately characterize the sample. The method is applied to the calculation of water retention curves of sedimentary carbonatic rock of marine origin.

Nei Paesi più sviluppati - USA, Giappone e Germania su tutti - la ricerca viene considerata un settore strategico per lo sviluppo del Paese: qui non a caso il numero dei ricercatori e i fondi destinati alla ricerca sono cresciuti costantemente anche negli ultimi anni di crisi economica mondiale. In Italia si deve finalmente sviluppare una visione positiva che veda la ricerca come una occasione strategica per aumentare la competitività del Paese e rafforzarne l'economia, considerando i fondi destinati alla ricerca come un investimento e non un costo. Del resto siamo circondati da prodotti o servizi originati direttamente dalla ricerca, spesso in modo del tutto inaspettato. Esempi lampante sono internet e il world wide web che, nati per scopi militari o di pura e semplice comunicazione fra scienziati, sono diventati parte integrante ed inscindibile della nostra vita. Ma non serve andare così lontano: in realtà la maggior parte delle attività di ricerca scientifica possono avere ricadute più o meno immediate in termini di prodotti o di servizi, spesso basta solo trovare lo spunto o il partner industriale giusto. Ecco perché una maggiore interazione fra i due mondi si rivela assolutamente preziosa.

We report the current status of our SNS technology aimed at the development of programmable voltage standard devices. Using the simple Nb/Al/Nb trilayer process, with an Al barrier thickness of the order of 100 nm, we have fabricated SNS Josephson junctions whose electrical properties can be changed by varying the morphology of the Al film. The major role in determining the electrical behavior of the junctions is played by the roughness of the thick Al barrier. AFM analysis shows that the Al roughness is strongly reduced by increasing its deposition rate. The critical current density varies by two orders of magnitude, from 10/sup 3/ A/cm/sup 2/ up to 10/sup 5/ A/cm/sup 2/, with correspondingly normal resistances from 1 /spl Omega/ down to few m/spl Omega/. The magnetic field dependence of the critical current is also affected by the barrier structure, while all the junctions show regular Shapiro-like rf-induced steps at 70 GHz.

Single and multijunctions thermal converters are devices widely utilized for AC measurements at room temperature. However, low sensitivity and high noise of these devices limits their applications at voltage level above 10 mV. A cryogenic thermal transfer sensor has been developed to realise AC measurements at 1 mV voltage level. This device consists of a superconducting-resistive-transition Nb thin film, which detects the AC power, dissipated on a Cr film resistor. To improve the sensitivity, the sensor has been fabricated on a 500 nm thick square silicon nitride membrane with size ranging from 1 × 1 mm 2 to 3.5 × 3.5 mm 2. The device has been tested at liquid helium and a thermal conductance lower than 10-6 W/K has been measured. From these data we expect an increasing of responsivity higher than three order of magnitude and a noise limited by intrinsic thermal noise.

We have fabricated superconducting Nb/Al microstrip detectors. The low sensitivity to radiation damage and aging and the high energy resolution make these devices very attractive. The samples are fabricated by superposing a 2 mm × 2 mm Al area on a 5 μm wide, 100 μm long Nb strip. The thickness of each film is between 50 and 200 nm. We present the results both of steady and dynamical tests on Nb/Al bilayers, after irradiation with a 241 Am alpha-source (T = 5.47 MeV ). These devices can operate both in the on-off and in the auto-recovery regimes. We show that the performance of Nb/Al bilayers is better than single Nb strip devices.

We report here our results on the development of Nb/Al/Nb Josephson junctions for a programmable voltage standard. The Al barrier is 5–120 nm thick. Its properties are quite different with respect to the single Al films because of diffusion between Al and the Nb counter-electrode. The resistivity of the Al barrier ranges from hundreds of microhm centimetres to a few milliohm centimetres, probably depending on the surface roughness of the Al layer, measured by atomie force microscopy (AFM). The junctions, with areas between 25 and 200 μm2, have critical currents I C in the milliampere range, associated with normal resistances R N of about 1 Ω. The very high I C R N product of these junctions allows us to use a microwave source of 70 GHz and above, as in present dc voltage standards. Preliminary rf measurements on these devices are reported. Structural investigations by AFM and X-ray diffraction were also carried out to relate the electrical properties of the junctions to the Nb-Al interfaces.

We studied electron localization effects in superconducting Nb/Al bilayers. These effects are characterized by a decrease in resistivity with increasing temperature typical of a semiconductor and by an enhancement of the critical temperature Tc. The samples, made by superposition of Nb and Al films, each 50–200 nm thick, show a sharp superconducting transition between 8 and 9K. The electron localization effects are detectable only when the resistivity at 10 K is larger than about 100μΩcm. We discuss the fabrication conditions leading to the observed electron localization. We also present some measurements of the current-voItage characteristics in localized and metallic Nb/Al bilayers and we analyse them in terms of a simple thermal picture.

Superconducting thin "lm particle detectors can be very attractive due to the low sensitivity to radiation damage. We describe the fabrication procedure and the characterization of Nb/Al bilayers as particle detectors. First steady and dynamical results are reported from tests of 5 MeV alpha-particle detection. ( 2000 Elsevier Science B.V. All rights reserved.

We have measured the temperature dependence of resistivity in relatively thick Nb/Al bilayers fabricated at room temperature, observing the decrease of ρ for increasing T typical of Anderson localization in disordered systems. We report the experimental conditions which determine this behavior and compare it to theoretical models for localization in 3D systems.

We report results achieved in the fabrication of two different Nb-based SNS devices which can be used for the development of a programmable Josephson voltage standard. Junctions with an Al metal barrier, 5 to 100 nm thick, have been fabricated obtaining devices with I/sub C/R/sub N//spl ap/0.5 mV. A second kind of junction has been fabricated using 10 nm thick non-stabilized TaO/sub x/ as a barrier, deposited by bias sputtering. For these devices, using the bias voltage as the main process parameter, I/sub C/R/sub N//spl ap/0.1 mV was obtained. Measurements of the electrical properties of the Nb/Al/Nb and the Nb/TaO/sub x//Nb junctions are reported.

We report recent results on the development of two different kinds of SNS Josephson junctions which can be used as quantum D/A converters. We have fabricated these devices using as a barrier either a thick 50-100 aluminum layer or a not-stabilized tantalum oxide layer. For both technologies we have determined the dependence of the main electrical properties of the junctions on the fabrication process. Measurements of the rf properties for the Nb/Al/Nb junctions and of the magnetical properties for the Nb/TaO x/ Nb junctions are also reported.

We report here the experimental evidence of semiconductor-superconductor transitions in relatively thick Nb/Al structures. The temperature dependence of resistivity ρ(T) shows a sharp superconducting transition followed by either a normal metallic behavior in low-resistivity samples, or a semiconducting behavior when the sample resistivity at 10 K is above 100 μΩ cm. We discuss here the fabrication conditions and the electron localization regime associated with the measured ρ(T) dependence.

We have investigated the effect of a combined lateral and longitudinal idle region on the magnetic field dependence of the critical current of both single and vertically stacked Josephson junctions. An excellent agreement has been found with numerical calculations made using a simple model of junction with idle region. The magnetic field response of the single junction after a proper trimming of the idle region has also been analyzed.

The surface properties of vertical stacks of Nb/(Al-AlO/sub x//Nb)/sub n/ Josephson junctions have been investigated by Atomic Force Microscopy (AFM). The results indicate that the roughness of the AlO/sub x/ layers is nearly constant and independent of the surface features of the underlaying Nb films. The superposition of several Nb and Al-AlO/sub x/ films has an overall smoothing effect on their surfaces, as indicated by the strong reduction of the rms roughness in a stack of junctions with respect to that of the base Nb film. The height-height correlation function shows that the rms roughness increases on small sampling lengths l(l

The constant voltage steps generated by a slightly damped Josephson junction driven by short rectangular current pulses are studied within the RSJ model for a broad range of dc and rf bias. The height of the rf-induced steps strongly depends on model parameters but always largely exceeds that of a sinusoidally driven junction. The dynamical response of the junction is also briefly analyzed.

We have experimentally investigated the effect of a combined lateral and longitudinal idle region on the magnetic field dependence of the critical current of Nb/Al−AlOx/Nb Josephson junctions. All the samples were high quality devices with a good uniformity and reproducibility of the electrical parameters. An excellent agreement has been found with calculations of the magnetic field patterns made using a simple model of junction with idle region. A comparison with the magnetic field response of the same devices after a proper trimming of the idle region has also been done.

A new type of nonhysteretic Josephson junction suitable for applications in voltage metrology has been developed. These junctions derive from the Nb/Al-AlO/sub x//Nb SIS junctions using a relatively thick Al layer oxidized at a low value of oxygen exposure. This produces junctions with reproducible and spatially homogeneous I-V characteristics, having current densities ranging from 10/sup 3/ to more than 2/spl times/10/sup 4/ A/cm/sup 2/ and characteristic voltages up to 0.40 mV. The authors report here the rf response of these junctions at 70 GHz. The authors have measured the dependence of the rf-induced steps on the microwave power and the stability of the steps, in view of a future application of these junctions to an AC Josephson voltage standard.

The response of an overdamped current biased Josephson junction to a pulsed rf drive has been investigated by both numerical and analog simulations. The rf signal was a periodic rectangular pulse of varying amplitude and duration. A considerable increase of the width of the rf‐induced steps with respect to those of an equivalent junction driven by a sinusoidal signal has been obtained. In the limiting case of a pulse repetition frequency much lower than the junction RC cutoff frequency, all steps have a maximum width which is independent of the step order n and increases with decreasing pulse duration.

A detailed analysis of the properties of Nb/Al-AlO/sub x//Nb Josephson tunnel junctions fabricated with a modified SNAP process is presented. Selective niobium anodization has been used not only as on-line monitoring of the junction quality, through depth profiling anodization spectroscopy, but also to achieve a controlled reduction of the junction area at micrometer level by a proper choice of the anodization current. The dependence of the most relevant junction electrical parameters on fabrication variables has been investigated. With this fabrication process, junctions with V/sub m/ as high as 60 mV and current densities J/sub c//spl les/2000 A/cm/sup 2/ at 4.2 K are routinely obtained, thus demonstrating its feasibility for high frequency mixer and voltage standard applications.

Nb thin films 10 to 1000 nm thick, deposited by rf sputtering on Corning glass substrates, are widely characterized both from the electrical and structural points of view by measuring resistivity, grain size, lattice parameter, and surface roughness. The strong dependence of these properties, especially resistivity, on film thickness is evidenced, and the effect of sputter etching of the substrate before deposition is also evaluated. Size effects alone are unable to account for the observed thickness dependence. In this paper, it is shown that electron scattering at the grain boundaries, analyzed through the Reiss conduction model, can be considered to be the main reason of the nonbulk-like behaviour of these films. A comparison between theoretical and experimental data suggests, however, that the transmission coefficient at the grain boundaries is not constant at all thicknesses. Impurities diffusion and stress at the grain boundaries modifying intragrain potential may be the reasons of this inhomogeneity.

A new and convenient method to prepare a number of pyrrole-3-carboxylic esters is reported.

C27H36ClN2O9PS, monoclinic, C12/c1 (no. 15), a = 36.495(3) A?, b = 8.5574(4) A?, c = 20.487(4) A?, b = 101.18(2)°, V = 6276.8 A?3, Z = 8, Rgt(F) = 0.052, wRref(F2) = 0.125, T = 295 K.