1,721,264 research outputs found
Charge transport modelling in organic semiconductors: From diodes to transistors, memories and energy harvesters
Full text linkOrganic semiconductors are playing an increasingly important role for the fabrication of many electronic and optoelectronic devices such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs) [2], organic thinfilm transistors (OTFTs) [3] and organic memories [4].
Amorphous and/or regular assembly of polymers/small molecules can form such materials which typically exhibit complex electronic properties. Thus, a unified, comprehensive and transferable model of charge transport and injection in organic semiconductors is highly desired to help the understanding, development and optimization of organic devices. In this work, we will present the efforts made to identify a consistent scheme for charge transport in organic semiconductors and applications of this model to the description of diodes, resistive memories, OTFTs and OPVs
Sapienza S5Lab student driven small-scale space missions and experiments
No full textThe rising number of concepts for small size space payloads, e.g. space station experiments, nano- or pico-satellites and stratospheric experiments, is widening the users number for such payloads to virtually all the people in the world, as per the so-called “New Space Economy”. In this framework, the involvement of students at the early stages of their academic careers into development of space payloads is beneficial on multiple points of view. As an example, students have the chance to face and solve “reallife” problems and to gain their soft skills (e.g. team working skills or basic manufacturing and coding capabilities). Moreover, students learn how to face success and failure of their small missions and how to improve processes for their future. At Sapienza Space Systems and Space Surveillance Laboratory (S5Lab), a group of around 50 students is developing small-scale missions since 2014. Four CubeSats have been launched with the support of ASI and other institutions, while a fifth CubeSat will be launched in mid-2022 on the maiden Vega-C launch. Three stratospheric payloads manufactured by S5Lab have been successfully launched from the Esrange Space Center in Sweden, through the REXUS/BEXUS and HEMERA international programmes. The new perspectives of payload development, besides continuing to manufacture CubeSats (through the selection of a new 2-Unit mission to be launched in 2023) and stratospheric experiments (through a new participation in REXUS/BEXUS) include the possibility of developing a student-led analog mission simulating lunar lava tube operations, and the chance to study and develop prototypes for innovative launcher navigation systems and suborbital experiments. The main lessons learned obtained by the years of development with students deals with reaching a certain continuity of payload manufacturing, from a “one-shot” concept in the early years to a better knowledge management for launch opportunities potentially obtainable every year. Other lessons learned are dealing with the correct time and year of involvement of the students, and with manpower management when the involved students are volunteering for joining the teams. This paper will deal with the experience in payload and missions development at Sapienza S5Lab. After an introduction over the present, past and future space missions, the main lessons learned from how to turn these projects into success stories of students involvement will be presented. The future perspectives for reaching a more stable continuity of launch opportunities and payloads development with a wider knowledge management among students will be discussed
Accurate in-operando study of molten carbonate fuel cell degradation processes -part I: Physiochemical processes individuation
No full textThis work has the difficult task to deeply study the electrochemical processes that occur inside a 100 cm2 of Molten Carbonate Fuel Cells (MCFC) impedance spectra using the high resolution of Distribution of Relaxation Time (DRT) method. Using this method, it is possible to shed light on the different physicochemical processes occurring within these cells, identifying the characteristic relaxation times by means of an appropriate experimental campaign where temperature and gas compositions in anode and cathode were varied one at a time. The quality of the recorded spectra was verified by Kramers-Kronig relation before applying DRT calculations. In this work, five distinct and separated peaks with different time constants ranging from 0.01 to 500 Hz were identified and associated with physiochemical processes of the cell. Three peaks at high frequency represent the charge transfer processes in anode and cathode active sites. The other two, located at low frequency, are associated with the gas diffusion in the electrodes and to the gas conversion process. This study represents the first application of the DRT approach to this technology allowing to understand the physicochemical origin of the individual polarization processes controlling the cell performance and the degradation. The analysis of degradation processes using the DRT method and the physiochemical processes identification presented in this paper will be shown in part II of this work. © 2018 Elsevier Lt
Optical road-ice detector operating in the near infrared
No full text"Introduced is an optical approach for the assessment of the road conditions due to various atmospheric perturbations, such as the presence of ice and rain. The technique is based on measuring the polarisation contrast in reflection, in conjunction with the intensity of the diffused light, in the near infrared.
Lightcurve inversion for attitude determination
No full textThe interest in determining the attitude of an orbiting object has grown significantly in recent years. Besides being one of the key parameters needed to obtain a precise orbital determination, the attitude is also crucial in the perspective of planning a space debris removing mission. In this paper, we present a method to retrieve the attitude of an orbiting object, based on a virtual reality simulation together with a global optimization. The attitude will be determined using the object's lightcurve derived information, i.e. the total reflected light variation in time. This technique, derived from the asteroids attitude and trajectory reconstruction techniques, has recently been introduced in the uncooperative satellite optical attitude determination. The idea behind the proposed method is to generate, for a selected target, different synthetic lightcurves to be compared with the observed one; the synthetic lightcurve most similar to the experimental one will be chosen as the presumable object attitude. In such a context, the crucial procedure tool is the synthetic lightcurve generator, that needs to be as realistic as possible in terms of optical and physical properties. To satisfy these requirements, the orbital position of the object will be recovered by propagating its orbit from the known TLE (Two-Line Element) through an SGP-4 (Simplified General Perturbations) routine. At the same time, the real positions of the observer and the Sun will be used to derive a precise value of the phase angle Sun-object-observer, aimed at obtaining an estimate of the light reflected by each object part. A realistic image of the object will be then produced at each instant of time using an advanced rendering algorithm, that takes into account parameters such as the atmospheric extinction, the object shape and materials, and the direction of the sunlight. A particular effort is made to accurately reproduce the shadow areas cast by the different object's components. Finally, to find the best attitude parameters, an evolutive algorithm that minimizes the residual between the real and the simulated lightcurves is employed. The results obtained on very heterogeneous datasets show a very promising potential in terms of applicability of the developed method. In this paper, this method developed for the attitude reconstruction is discussed: first, the used lightcurve analysis tools are described, and then the simulation environment able to generate artificial lightcurves is presented. The achieved results (on synthetic and on real data, acquired during in January and February 2018), and future perspectives will be found in the conclusions
Evaluation of time difference of arrival (Tdoa) networks performance for launcher vehicles and spacecraft tracking
Full text linkTime Difference of Arrival (TDOA) networks could support spacecraft orbit determination or near-space (launcher and suborbital) vehicle tracking for an increased number of satellite launches and space missions in the near future. The evaluation of the geometry of TDOA networks could involve the dilution of precision (DOP), but this parameter is related to a single position of the target, while the positioning accuracy of the network with targets in the whole celestial vault should be evaluated. The paper presents the derivation of the MDOP (minimum dilution of precision), a parameter that can be used for evaluating the performance of TDOA networks for spacecraft tracking and orbit determination. The MDOP trend with respect to distance, number of stations and target altitude is reported in the paper, as well as examples of applications for network performance evaluation or time precision requirement definitions. The results show how an increase in the baseline enables the inclusion of more impactive improvements on the MDOP and the mean error than an increase in the number of stations. The target altitude is demonstrated as noninfluential for the MDOP trend, making the networks uniformly applicable to lower altitude (launchers and suborbital vehicles) and higher altitude (Low and Medium Earth Orbits satellites) spacecraft
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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