Electrical and thermal transport properties of superconducting materials relevant for applications

2016 - 2017Superconducting materials are used in several applications among which the large-scale ones take advantage of the high energy transport capabilities of superconductors due to the low losses in electrical conduction. From a practical point of view, it is necessary to achieve the highest possible current density values without dissipation, thus the critical current density Jc has to be increased. Indeed, once the biasing current density increases above the critical value, the transition of the material to the normal state, referred also as a quench event, can be observed. Often this transition is not gradual. Thus, an important feature to consider is the voltage stability under current biasing in the dissipative regime. In particular, if the Flux-Flow Instability (FFI) phenomenon is triggered, the transition in the current-voltage (I-V) results in a sudden voltage jump. Electrical and thermal stability is strictly demanding in order to avoid quench phenomena or to adopt protection strategies. In a quench phenomenon, once a normal zone has started to grow, it will continue to expand under the combined actions of heat conduction and ohmic heating at a constant velocity referred as normal zone propagation velocity (NZPV). Thus, NZPV evaluation plays a key role in the protection strategies against quench-induced damages. NZPV depends mainly on electrical and thermal properties of the various components of the technical superconductor, which is made in composite form, containing both superconducting, conducting and insulating materials. Heat transfer through the conductor is the main channel for removing heat form the superconducting medium and, consequently, preventing a quench. In this work it is reported the study of the electrical transport properties of superconducting materials relevant for applications. In particular, it has been focused on pinning properties and voltage stability of superconducting materials and on electrical and thermal characterization of technical superconductors. Electrical characterization of Fe(Se,Te) thin films grown on CaF2 substrate has been performed in order to investigate the pinning properties and the voltage stability aspects in view of tapes manufacturing. Electrical and thermal properties of Bi-2212 technical superconductors have been investigated, in order to obtain information about the key factors for the quench analysis, i.e. electrical and thermal conductances. Regardless of the superconducting material, an accurate study based on avoiding quench by means of a deep investigation of electrical and thermal transport properties becomes relevant for applications. [edited by author]XXX n.s

Stability mechanisms of high current transport in iron-chalcogenides superconducting films

The improvement in the fabrication techniques of iron-based superconductors have made these materials real competitors of high temperature superconductors and MgB$_2$. In particular, iron-chalcogenides have proved to be the most promising for the realization of high current carrying tapes. But their use on a large scale cannot be achieved without the understanding of the current stability mechanisms in these compounds. Indeed, we have recently observed the presence of flux flow instabilities features in Fe(Se,Te) thin films grown on CaF$_2$. Here we present the results of current-voltage characterizations at different temperatures and applied magnetic fields on Fe(Se,Te) microbridges grown on CaF$_2$. These results will be analyzed from the point of view of the most validated models with the aim to identify the nature of the flux flow instabilities features (i.e., thermal or electronic), in order to give a further advance to the high current carrying capability of iron-chalcogenide superconductors.Comment: 4 pages, 3 figure

Enhancing Human Capital at Scale

A two-year randomized evaluation shows that the effectiveness of multi-tasking mentors on schooling outcomes crucially depends on their training. While a standard training modality in highly marginalized communities in Mexico generates null results, enhanced training yields sizable treatment effects on primary school children's cognitive, behavioral, and educational achievements. This difference cannot be explained by remedial educational activities or pedagogical support, but it can be reconciled with higher parental aspirations and investments. Evidence gathered on the subsequent national roll out of the intervention with enhanced training substantiates the external validity of our findings

Distance Estimation Algorithm for Wireless Localization Systems Based on Lyapunov Sensitivity Theory

The paper describes a novel distance evaluation algorithm based on the time-difference of arrival (TDOA) principle. The proposed method solves the distance estimation problem applying the Lyapunov theory. To perform this task, the distance evaluation problem is converted to a parameters identification process exploiting the sensing signal peculiarities. This latter combines the properties of the Frank-Zadoff-Chu (FZC) sequences with the Orthogonal Frequency-Division Multiplexing (OFDM) modulation scheme. The resulting signal can be used to improve accuracy and precision in distance estimation using a reduced signal bandwidth. The system was modeled considering either an additive white noise Gaussian channel and a moderate multipath model. The simulation results demonstrate that the system achieves an accuracy and a precision better than 10 cm considering SNR equal to 0 dB and signal bandwidths of only 125 MHz

Ten Years of Severe Vitreomacular Traction Syndrome without Functional Damage Demonstrated by Optical Coherence Tomography

Introduction. To describe anatomical and functional features in one patient with 10 years of severe vitreomacular traction syndrome (VTS) without functional damage demonstrated by optical coherence tomography (OCT). Patient and Methods. One patient with a history of 10 years VTS, with best-corrected visual acuity of 20/32, was followed up with OCT. Follow-up examinations, 3 months for the first year after diagnosis and every 6 months for the subsequent years, were performed. Results. Follow-up examinations showed no change anatomically and functionally. Far and near visual acuity was unchanged. OCT by Heidelberg Spectralis did not evidence differences from Stratus OCT images. Conclusion. VTS can be stable anatomically and functionally for 10 years. OCT is a valuable diagnostic tool in understanding the configuration of vitreomacular adhesion, followup, and eventually planning the surgical approach for operating on VTS

Prevalence and Antibiotic Resistance Patterns of Ocular Bacterial Strains Isolated from Pediatric Patients in University Hospital of Campania "Luigi Vanvitelli," Naples, Italy

Eye infections caused by bacteria are a serious public health problem among pediatric patients. These diseases, if not properly treated, can cause blindness and impaired vision. The study aimed to evaluate the antimicrobial resistance profiles of the main pathogens involved in eye infections. This study involved pediatric patients enrolled at the "Luigi Vanvitelli" University Hospital of Campania in Naples, Italy, between 2017 and 2019. Of a total of 228 pediatric patients, 73 (32%) tested positive for bacterial infection. In terms of strain distribution, 85% were Gram-positive bacteria, while 15% were Gram-negative bacteria. The most frequently isolated strains were coagulase-negative Staphylococci (60.4%), followed by Staphylococcus aureus (16.4%). The isolated bacteria showed a significant percentage of resistance to multiple antibiotics. Therefore, the identification of the causal bacteria and antimicrobial sensitivity tests are mandatory to select the effective drug for the treatment of eye infections and prevent the development of antibiotic-resistant bacteria

Mid-term safety and effectiveness of macular peeling one month after intravitreal dexamethasone implant for tractional diabetic macular edema

Macular peeling combined or followed by intravitreal dexamethasone implant (DEX-i) was recommended as an efficacy approach for tractional diabetic macular edema (tDME). Knowing the synergistic effect of cataract surgery and DEX-i one month earlier in eyes with DME, we compared Epiretinal Membrane/Inner Limiting Membrane (ERM/ILM) peeling preceded by DEX-i one month before versus ERM/ILM peeling alone for the treatment of tDME. A retrospective study on patients affected by tDME who underwent ERM/ILM peeling one month after DEX-i (n = 11; Group A) or ERM/ILM peeling alone (n = 10; Group B) was performed. Longitudinal comparison of best-correct visual acuity (BCVA), central retinal thickness (CRT), and intraocular pressure (IOP) between the time of surgery (T0) and each time point (months 1,3,5,6) within and among the groups were assessed. To evaluate the repeated measurements of BCVA, CRT, and IOP, a linear mixed-effects model was used. In Group A, DEX-i significantly improved mean BCVA and CRT (P < 0.001) just after 1 month (T0). After ERM/ILM peeling, mean BCVA and CRT significantly improved from month 1 in Group A and month 3 in Group B. Mixed model revealed a significant difference in BCVA (P ≤ 0.0001) and CRT (P ≤ 0.02) at different time-points among the groups with better results in Group A. Neither complications nor uncontrolled IOP increase was detected. ERM/ILM peeling confirmed its effectiveness in treating tDME. DEX-i performed one month before surgery seemed to be a safe approach and ensured a greater and faster recovery considering functional and tomographic parameters

Incidence and Risk Factors for Tractional Macular Detachment after Anti-Vascular Endothelial Growth Factor Agent Pretreatment before Vitrectomy for Complicated Proliferative Diabetic Retinopathy

The study's purpose was to determine the incidence, risk factors, and outcomes of tractional macular detachment after anti-vascular endothelial growth factor (VEGF) pretreatment before vitrectomy for complicated proliferative diabetic retinopathy. Patients who underwent primary vitrectomy for complicated proliferative diabetic retinopathy, from January 2012 to 31 December 2018, were enrolled. Ophthalmic and pre-operative data were extracted from electronic record systems. All eyes with a valuable Optical Coherence Tomography (OCT)performed within 5 days before injection of anti-VEGF and on the day of vitrectomy were included. Multivariable logistic regression showed that significant risk factors for developing tractional macular detachment included days between anti-VEGF and vitrectomy (OR, 0.71 [95% CI 0.65-0.76]; p < 0.001), vitreous hemorrhage (OR, 0.23 [95% CI 0.11-0.49]; p < 0.001), and age (OR, 1.05 [95% CI 1.02-1.08]; p < 0.001). Decision-tree analysis showed that the stronger predictors of tractional macular detachment were the time between anti-VEGF injection and vitrectomy (p < 0.001). Secondary predictors were the presence of vitreous hemorrhage (p = 0.012) in eyes that underwent vitrectomy between 6 and 10 days after anti-VEGF injection and younger age (p = 0.031) in eyes that underwent vitrectomy 10 days after anti-VEGF injection. Tractional macular detachment occurs in 10% of eyes after anti-VEGF injection, the main risk factors being days between anti-VEGF injection and vitrectomy, vitreous hemorrhage, and age