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O artigo discute as contribuições do feminismo negro para a crítica da injustiça epistêmica – aqui entendida como uma das faces da injustiça social global. Particularmente, são analisadas as abordagens da filósofa brasileira Sueli Carneiro e da socióloga estadunidense Patricia Hill Collins. Cada qual em seu contexto pós-colonial, as duas autoras (a) teorizam a respeito dos mecanismos de opressão/sujeição das mulheres negras e suas lutas por emancipação; (b) formulam sua crítica tendo em vista as matrizes teóricas e epistemológicas do conhecimento hegemônico; (c) apresentam horizontes alternativos existentes, que emergem a partir do feminismo negro. O artigo conclui positivamente quanto ao vigor e a importância da crítica social formulada por ambas e argumenta quanto à relevância de enquadrar o debate sob os termos das reivindicações por justiça social

O texto discute as convergências e divergências entre duas caracterizações da modernidade que apontam para sua dimensão mítica: a crítica formulada por Adorno e Horkheimer na Dialética do esclarecimento e a concepção de Enrique Dussel, sobretudo conforme se apresenta em seu livro 1492: o encobrimento do outro. Essa proposta de interlocução teórica almeja enriquecer o projeto de descolonização da Teoria Crítica e melhor explorar seu potencial de crítica sociopolítica – sobretudo no que tange a estruturas, processos e relações sociais nas sociedades periféricas do capitalismo mundial. Para tal, o artigo é desenvolvido em três passos: inicia com a apresentação dos argumentos clássicos da Teoria Crítica quanto à narrativa mítica da modernidade; em seguida, discorre sobre as possibilidades de ampliação e revisão crítica dessa perspectiva com base nos trabalhos de Dussel; e, por fim, realiza um balanço da discussão e traça considerações sobre a pertinência e a necessidade desse diálogo.

Partindo da polêmica entre Axel Honneth e Nancy Fraser sobre a teoria do reconhecimento, o artigo tem como objeto a abordagem da autora estadunidense para a Economia Política. Após discutir o tratamento conferido ao tema em seus artigos que compõem a coletânea Redistribution or recognition, bem como as objeções a ele levantadas, busca-se investigar em que medida as revisões ulteriores propostas por Fraser foram suficientes e satisfatórias para superar as principais limitações e questões não-respondidas de seu modelo

The development and calibration of a measurement system designed for assessing the performance of the avalanche photodiodes (APDs) used in the Compton scattering polarimeter of the CUSP project is discussed in this work. The designed system is able to characterize the APD gain G A P D and energy resolution across a wide range of temperatures T (from −20 °C to +60 °C) and bias voltages V b i a s (from 260 V to 410 V). The primary goal was to experimentally determine the G A P D dependence on the T and V b i a s in order to establish a strategy for stabilizing G A P D by compensating for T fluctuations, acting on V b i a s . The results demonstrate the system capability to accurately characterize APD behavior and develop feedback mechanisms to ensure its stable operation. This work provides a robust framework for calibrating APDs for space environments. It is essential for the successful implementation of spaceborne polarimeters such as the Compton scattering polarimeter foreseen aboard the CUbeSat Solar Polarimeter (CUSP) mission under development to perform solar flare X-ray polarimetry. [ABSTRACT FROM AUTHOR]

In this work, a detailed parametric study assessing the impact of low-conductivity coatings on the radio-frequency accelerating cavity quality factor and resonance frequency shift is presented. In particular, this study is aimed at proving the feasibility of molybdenum oxides deposited on copper to reduce the dark current in high-gradient applications due to its intrinsically high work function. In order to compute the effective surface impedance of the resulting layered structure, a transmission line-based approach is adopted. The present analysis demonstrates the potential effectiveness of molybdenum thin-films, which only slightly affects the accelerating cavity quality factor, with very low sensitivity to thickness and resistivity inhomogeneities. [ABSTRACT FROM AUTHOR]

Microwave transducers are widely used for sensing applications in areas such as gas sensing and microfluidics. Inkjet printing technology has been proposed as a promising method for fabricating such devices due to its capability to produce complex patterns and geometries with high precision. In this work, the temperature-dependent electrical properties of an inkjet-printed single-port interdigitated capacitor (IDC) were investigated at cryogenic temperatures down to 20 K. The IDC was designed and fabricated using inkjet printing technology, while its reflection coefficient was measured using a vector network analyzer in a cryogenic measurement setup and then transformed into the corresponding admittance. The resonant frequency and quality factor (Q-factor) of the IDC were extracted as functions of the temperature and their sensitivity was evaluated. The results showed that the resonant frequency shifted to higher frequencies as the temperature was reduced, while the Q-factor increased as the temperature decreased. The trends and observations in the temperature-dependent electrical properties of the IDC are discussed and analyzed in this paper, and are expected to be useful in future advancement of the design and optimization of inkjet-printed microwave transducers for sensing applications and cryogenic electronics. [ABSTRACT FROM AUTHOR]

We report on the characterization of NbTi films at ∼ 11 GHz and in DC magnetic fields up to 4 T, performed by means of the coplanar waveguide resonator technique, providing quantitative information about the penetration depth, the complex impedance, and the vortex-motion-induced complex resistivity. This kind of characterization is essential for the development of radiofrequency cavity technology. To access the vortex-pinning parameters, the complex impedance was analyzed within the formalism of the Campbell penetration depth. Measurements in this frequency range allowed us to determine the complete set of vortex-pinning parameters and the flux flow resistivity, both analyzed and discussed in the framework of high-frequency vortex dynamics models. The analysis also benefits from the comparison with results obtained by a dielectric-loaded resonator technique on similar samples and by other ancillary structural and electromagnetic characterization techniques that provide us with a comprehensive picture of the material. It turns out that the normalized flux flow resistivity follows remarkably well the trend predicted by the time dependent Ginzburg-Landau theory, while the pinning constant exhibits a decreasing trend with the field which points to a collective pinning regime. [ABSTRACT FROM AUTHOR]

We present the multifrequency measurements of the surface resistance of spark-plasma-sintered MgB 2 performed through a dielectric loaded resonator operating at 16.5 and 26.7 GHz. By normally applying magnetic fields ≤1.2 T to the sample surface, we drove it in the mixed state. By means of data-rooted analysis, we found that the sample vortex dynamics could be fully described within a single-component approach. Pinning phenomena were present and characterized by a depinning frequency smaller than the measurement ones. The multiband nature of the superconductor emerged in the flux-flow resistivity, whose field dependence could be interpreted well within theoretical models. By exploiting them, the upper critical field was extracted in the low-temperature range, which exhibited a consistent temperature trend with the values obtained at the onset of the resistive transition near T c , and was well in line with literature data on other polycrystalline samples. [ABSTRACT FROM AUTHOR]

The spread of additive manufacturing techniques in the prototyping and realization of high-frequency applications renewed the interest in the characterization of the electromagnetic properties of both dielectric and conductive materials, as well as the design of new versatile measurement techniques. In this framework, a new configuration of a dielectric-loaded resonator is presented. Its optimization, realization, and use are presented. A measurement repeatability of about one order of magnitude lower than the commonly found values ( 10 − 3 on the Q-factor and 15 × 10 − 6 on the resonance frequency, given in terms of the relative standard deviations of repeated measurements) was reached thanks to the design of a closed resonator in which the samples can be loaded without disassembling the whole measurement fixture. The uncertainty levels, the ease of use, and the versatility of the realized system make its use of potential interest in numerous scenarios. [ABSTRACT FROM AUTHOR]

The root mean square surface roughness R q of metals is detrimental in several microwave applications. R q characterization methods are thus largely used and of great interest. In this work, a new dielectric loaded resonator (DR) design is proposed to evaluate the surface resistance variations of samples with different R q . The new design is thought to make the measurement accuracy, usually strongly affected by the measurement repeatability, suitable for this study. We analyze the measurement method's sensitivity and accuracy in order to assess the possibility of using this new DR design for highly accurate surface resistance measurements sensitive to R q variations. [ABSTRACT FROM AUTHOR]

Axions, hypothetical particles theorised to solve the strong CP problem, are presently being considered as strong candidates for cold dark matter constituents. The signal power of resonant-based axion detectors, known as haloscopes, is directly proportional to their quality factor Q. In this paper, the impact of the use of superconductors on the performances of haloscopes is studied by evaluating the obtainable Q. In particular, the surface resistance R s of NbTi, Nb 3 Sn, YBa 2 Cu 3 O 7 − δ , and FeSe 0.5 Te 0.5 is computed in the frequency, magnetic field, and temperature ranges of interest, starting from the measured vortex motion complex resistivity and the screening lengths of these materials. From R s , the quality factor Q of a cylindrical haloscope with copper conical bases and a superconductive lateral wall, operating with the TM 010 mode, is evaluated and used to perform a comparison of the performances of the different materials. Both YBa 2 Cu 3 O 7 − δ and FeSe 0.5 Te 0.5 are shown to improve the measurement sensitivity by almost an order of magnitude, with respect to a whole Cu cavity, while NbTi is shown to be suitable only at lower frequencies (<10 GHz). Nb 3 Sn can provide an intermediate improvement of the whole spectrum of interest. [ABSTRACT FROM AUTHOR]

Particle physics and radio-frequency (RF) superconductivity have driven each other on since the 1970s. The unique properties of superconductors (SC) have been the enabling keys for the realization of accelerators with always increased performances thanks to the realization of all-superconducting cavities. The use of increasingly pure superconducting coatings for accelerating cavities, with lower and lower RF losses, determined such high-quality factors [1] that the need to operate at low temperatures (below the superconducting transition temperature $T_{c}$) was well paid for. Recently, with respect to the path followed by the high frequency superconductivity [2], a new field opened since SCs are being considered for GHz operation in high dc magnetic fields, and measurements (and optimization) of totally different quantities are needed. The possibility of successfully using SCs in high magnetic fields for these purposes is far from obvious and it depends on the outcome of accurate measurements of usually overlooked quantities. [ABSTRACT FROM AUTHOR]

We report on the anisotropy of the vortex motion surface impedance of a FeSex Te1-x thin film grown on a CaF2 substrate. The dependence on the magnetic field intensity up to 1.2 T and direction, both parallel and perpendicular to the sample c-axis, was explored at fixed temperature at two distinct frequencies, ~ 16  GHz and ~ 27 GHz, by means of a bitonal dielectric resonator. The free flux flow resistivity ρff was obtained by exploiting standard models for the high frequency dynamics, whereas the angle dependence was studied in the framework of the well known and widely used Blatter-Geshkenbein-Larkin (BGL) scaling theory for anistropic superconductors. Excellent agreement with the scaling law prescription by the fluxon flux flow resistivity was obtained. From the scaling analysis, a low-field mass anisotropy ~ 1.8 was obtained, well within the value ranges reported in literature. The angular dependence of the pinning constant suggests that pinning is dominated by random, isotropic point pins, consistently with critical current density measurements. [ABSTRACT FROM AUTHOR]

The 1144 family of Iron Based Superconductors (IBSCs) is characterized by critical currents among the highest for single crystalline IBSCs. The synthesis of polycrystalline compounds is usually carried out through high temperature (T > 900 °C) processes. These methods, justified by a supposed thermodynamic instability of the 1144 phase at low temperature, are complicated by the presence of highly volatile elements and require fast heating and cooling steps. Here, it is shown how a High Energy Ball Milling (HEBM) treatment is effective to promote the reaction among the starting elements, thus favoring the synthesis of the 1144 phase at lower temperature. The evolution of the powders has been assessed for different milling times, observing the consumption of the starting reactants and the formation of crystalline pnictide phases. Different thermal treatments have been coupled to the HEBM treatment, allowing the study of the effect of time and temperature of the thermal step on the materials properties. It has been observed how the formation of the superconducting phase occurs on the HEBM samples at 500 °C and 600 °C. Critical temperatures comparable with data reported in the literature were obtained. Granularity phenomena and critical current density of sintered samples are highly dependent on the processing variables. [ABSTRACT FROM AUTHOR]

The high frequency vortex motion in Nb3Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance Z of a Nb3Sn bulk sample (24.8 at.%Sn). From the field induced variation of Z, the high frequency vortex parameters (the pinning constant kp, the depinning frequency νp and the flux flow resistivity ρff) were obtained over a large temperature and field range; their field and temperature dependencies were analyzed. Comparison with other superconducting materials shows that high frequency applications in strong magnetic fields are also feasible with Nb3Sn. In the present work, we report the first measurements about the microwave response in Nb3Sn in strong magnetic fields. [ABSTRACT FROM AUTHOR]

Superconducting properties of the Fe(Se,Te) system are directly related to its microstructure. However, in the framework of a not well assessed phase diagram, a large spread of chemico-physical and functional properties is reported for compounds characterized by similar overall chemical compositions. This is in particular observed in materials produced by melting routes, where chemical inhomogeneities and multiple phases are commonly obtained. Both composition and morphology of these inhomogeneities seem to play a role in the behaviour of the superconducting phases, pointing out the need to assess the dependence of phase composition and therefore of the material performance on the sample thermal history. In this work, the effect of different post-synthesis annealing treatments is studied. A melting route has been adopted to synthesize polycrystalline samples, subsequently subjected to thermal treatments at different temperatures. Morphology and microstructure were characterized by means of x-ray diffraction and microscopy techniques. The superconducting properties have been evaluated by means of electrical and magnetic measurements. It is observed how microstructure, chemical composition and morphology of the obtained products strictly depend on the annealing temperature. Moreover, a crucial role of the cooling step is evidenced: in fact, a rapid cooling procedure from high temperature leads to the formation of high temperature (Tconset > 19 K) superconducting phases, but the overall bulk superconducting performance is negatively affected. Other annealing treatments can promote instead an enhancement in the critical current at high fields with respect to pristine sample, suggesting that a careful engineering of a post-synthesis thermal step can represent a useful tool to optimize the material properties. [ABSTRACT FROM AUTHOR]

Based on Axel Honneth and Nancy Fraser's controversy about the theory of recognition, the article focuses on the North-American author's approach to Political Economy. After discussing the given treatment to the issue in her articles that compose Redistribution or recognition, as well as the objections to it, this work seeks to investigate if the subsequent revisions achieved by Fraser were enough and satisfactory to overcome the main limitations and unanswered questions of her critical model. [ABSTRACT FROM AUTHOR]

The transport and vortex pinning properties of nanocomposite YBa2Cu3O7-x (YBCO) film grown by pulsed laser deposition with addition of Ba2 Y(Nb/Ta)O6 (BYNTO) were compared with BaZrO3 added YBCO by DC (long-range vortex motion) and microwave (small-displacement vortex motion) measurement techniques. A high efficiency of BYNTO was observed in the field dependence and in the angular dependence of the critical current density Jc at 77 K, as well as in the field dependence of the complex surface impedance ΔZ. Based on the field dependence of the pinning parameters, such as the pinning parameter r and the pinning constant kp, the vortex pinning regimes were discussed. [ABSTRACT FROM AUTHOR]

The search for continuous improvement of the magnetic properties of coated conductors requires in-depth knowledge of vortex pinning. Microwave measurements of the superconductor complex resistivity are a very effective tool in obtaining complementary information on vortex pinning, in addition to conventional critical current density Jc measurements. The microwave characterization suffers, however, from geometrical effects when the superconducting films are not thick with respect to the penetration depth, as the high-frequency field leaks through the superconductor and also probes the underlying substrate structure. Whilst the resulting electromagnetic problem has largely been addressed in the case of insulating or semiconducting substrates, metal substrates in coated conductors require further consideration. In this paper, we address the issue of obtaining the microwave resistivity of thin superconducting films grown on metal substrates, with particular emphasis on the correct determination of the vortex parameters. We finally illustrate the extraction procedure on a real sample measurements performed on a YBCO film deposited on metal tape. [ABSTRACT FROM AUTHOR]

In the effort to unveil the relations between synthesis conditions, morpho-structural features and superconducting properties of (11)-type iron-based superconductors, this study is focused on FeSe0.5 Te0.5 materials obtained from high-temperature melts and different cooling rates. Crystalline and chemical composition are evaluated by means of XRD and SEManalyses, highlighting the formation of complex multiphase structures: the obtained results suggest that high-temperature nucleating phases may play a key role in the observed phase separation. Superconducting properties, evaluated by magnetization measurement and dc electrical resistance in different magnetic field conditions up to 18 T, highlight the low homogeneity of the superconducting phases, reflecting the microstructural observation. [ABSTRACT FROM AUTHOR]

Measurements of the high-frequency complex resistivity in superconductors are a tool often used to obtain the vortex parameters, such as the vortex viscosity, the pinning constant, and the depinning frequency. In anisotropic superconductors, the extraction of these quantities from the measurements faces new difficulties due to the tensor nature of the electromagnetic problem. The problem is specifically intricate when the magnetic field is tilted with respect to the crystallographic axes. Partial solutions exist in the free-flux-flow(no pinning) and Campbell (pinning dominated) regimes. In this paper, we develop a full tensor model for the vortex motion complex resistivity, including flux-flow, pinning, and creep. We give explicit expressions for the tensors involved. We obtain that, despite the complexity of the physics, some parameters remain scalar in nature. We show that under specific circumstances the directly measured quantities do not reflect the true vortex parameters, and we give procedures to derive the true vortex parameters from measurements taken with arbitrary field orientations. Finally, we discuss the applicability of the angular scaling properties to the measured and transformed vortex parameters and we exploit these properties as a tool to unveil the existence of directional pinning. [ABSTRACT FROM AUTHOR]

We discuss calibration issues in wideband (2–20 GHz) surface impedance measurements in a cryogenic and high magnetic field environment. We show that, in the case of measurements taken on superconducting thin films, the substantial impossibility of a full, three-standard calibration can be partially overcome by exploiting appropriate approximations and the basic properties of superconductors. We discuss a modification of the so-called short-only calibration, in order to increase the accuracy of the measurements. We relate the material properties of a sample under study to the measured surface impedance, which is affected by the geometry of the measurement, and we discuss the effects on the proposed approximate calibration procedure. We experimentally check the applicability of the approximations at the ground of the method, and we thoroughly discuss the uncertainties related to the approximations employed. Finally, we report the sample measurements of the surface impedance of two MgB2 superconducting films. [ABSTRACT FROM AUTHOR]

A detailed study on YBa2Cu3O7-δ (YBCO) films with BaZrO3(BZO) inclusions (YBCO-BZO) deposited on SrTiO3 substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (Ta) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed Tc values close to that of pure YBCO indicating that the Tc reduction which is usually observed on YBCO-BZO films can be successfully recovered by changing the deposition conditions. All YBCO-BZO films showed an improved critical current density (Jc) dependence on magnetic field if compared to the typical Jc(H) of YBCO, resulting in higher irreversibility fields up to 9 T at 77 K. SEM observation on etched samples suggests a direct link between the defect density measured in YBCO-BZO samples and that calculated from the observed in field performances. The analysis of Jc(B) as a function of applied magnetic field direction revealed that the pinning due to isotropic pinning centers typical for YBCO is coupled with a c-axis correlated pinning in YBCO-BZO which can be ascribed to BZO induced columnar defects. Jc(B) recorded at several temperatures down to 10 K revealed matching effect features. [ABSTRACT FROM AUTHOR]

We perform measurements of high-frequency (∼48 GHz) microwave surface impedance with an applied magnetic field in YBa2Cu3O7-δ (YBCO) laser-ablated films with various amounts of BaZrO3 (BZO) sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusions are very effective in the reduction of the field-induced surface resistance in our experimentally accessible field range [0, 0.8] T. At temperatures low enough, the application of a moderate (∼0.2 T) field makes the YBCO/BZO films markedly less dissipative than pure YBCO. This result, examined in the light of the very high measuring frequency (very small vortex oscillation amplitude) shows that BZO inclusions are even more effective pinning centers than columnar defects. We study the dependence of the vortex parameters (vortex viscosity, pinning constant) on the BZO concentration. We examine the correlation between the reduction of the microwave dissipation and the areal density of BZO-induced defects. We argue that the very improved performances in a magnetic field are due to individual pinning of vortices on BZO inclusions. [ABSTRACT FROM AUTHOR]

Evaluates a microwave broadband technique to measure the complex electric resistivity of high temperature superconductor thin films. Extraction of film resistivity from measured reflection coefficients; Electromagnetic analysis of the coaxial circular transition structure; Coaxial line calibration.

In the present study, the local atomic structure of a Nb3Sn superconductor sample has been probed by X-ray absorption fine structure (XAFS) as a function of hydrostatic pressure (from ambient up to 26 GPa) using a diamond anvil cell set-up. The analysis of the Nb-K edge extended X-ray absorption fine structure (EXAFS) data was carried out combining standard multi shell structural refinement and reverse Monte Carlo method to provide detailed in situ characterization of the pressure-induced evolution of the Nb local structure in Nb3Sn. The results highlight a complex evolution of Nb chains at the local atomic scale, with a peculiar correlated displacement of Nb–Nb and Nb–Nb–Nb configurations. Such a local effect appears related to anomalies evidenced by X-ray diffraction in other superconductors belonging to the same A15 crystallographic structure. [ABSTRACT FROM AUTHOR]