On the nature of self-field critical current in superconductors and its use as a probe of the superfluid density

<p>Superconductors are used in many applications where large electrical currents are needed. This is due to their ability to transport an electric current without resistance. There is however a limit to the magnitude of current that can be conducted before dissipation starts to occur. This is known as the critical current and is a topic of great interest in applied superconductivity. For type II superconductors, it is well known that vortex motion plays a role in the determination of the in-field critical current. This has led great effort in engineering the microstructure of these superconductors to hinder the motion of vortices and enhance their critical currents. However the self-field critical current (when there is no applied external field) generally does not see any enhancement due to efforts to pin vortex motion. The work here examines the behaviour of the self-field critical current in thin-film and cylindrical wire superconductors of many different superconductor types and sizes. It is found that a critical state is reached when the current density at the surface of the sample reaches the magnitude of Bc/μ₀λ for type I and Bc₁/μ₀λ for type II superconductors regardless of the size and material type. This finding shows that there is a fundamental limit to the self-field current density that cannot be enhanced by engineering the microstructure and is essentially of thermodynamic origin. The result also sets up the self-field critical current density as a probe of the superfluid density. This was explored in many different superconductor types by considering the temperature dependence of the self-field critical current. The ground-state magnetic penetration depth, groundstate energy gap and specific heat jump at the critical temperature were key thermodynamic parameters extracted from the critical current data. For a very large number of superconductors the extracted parameters in general matched well with literature values measured using conventional but much more complex techniques. A result inferred from the critical state was that the current distribution across the width of a rectangular superconductor would be uniform, contrary to expectations of the Meissner state. This was tested by measuring the perpendicular magnetic field resulting from a transport current in a superconducting tape as it reached the critical state. It was indeed found that the current distribution is uniform across the width. The self-field critical current was also measured in YBa₂Cu₃Oy samples with Zn impurities to measure the superfluid density and further test the self-field critical current as a measure of superfluid density and in particular explore whether it follows the canonical dependence on the transition temperature observed for superconductors with d-wave symmetry. Here the critical current was found to reduce as more impurities were added and indeed this matched its expected canonical reduction, following the superfluid density as Jc(sf) ∝p³/². These results taken together support the unexpected existence of a fundamental limit in the self-field critical current, which is thermodynamic in origin.</p>

On the nature of self-field critical current in superconductors and its use as a probe of the superfluid density

<p>Superconductors are used in many applications where large electrical currents are needed. This is due to their ability to transport an electric current without resistance. There is however a limit to the magnitude of current that can be conducted before dissipation starts to occur. This is known as the critical current and is a topic of great interest in applied superconductivity. For type II superconductors, it is well known that vortex motion plays a role in the determination of the in-field critical current. This has led great effort in engineering the microstructure of these superconductors to hinder the motion of vortices and enhance their critical currents. However the self-field critical current (when there is no applied external field) generally does not see any enhancement due to efforts to pin vortex motion. The work here examines the behaviour of the self-field critical current in thin-film and cylindrical wire superconductors of many different superconductor types and sizes. It is found that a critical state is reached when the current density at the surface of the sample reaches the magnitude of Bc/μ₀λ for type I and Bc₁/μ₀λ for type II superconductors regardless of the size and material type. This finding shows that there is a fundamental limit to the self-field current density that cannot be enhanced by engineering the microstructure and is essentially of thermodynamic origin. The result also sets up the self-field critical current density as a probe of the superfluid density. This was explored in many different superconductor types by considering the temperature dependence of the self-field critical current. The ground-state magnetic penetration depth, groundstate energy gap and specific heat jump at the critical temperature were key thermodynamic parameters extracted from the critical current data. For a very large number of superconductors the extracted parameters in general matched well with literature values measured using conventional but much more complex techniques. A result inferred from the critical state was that the current distribution across the width of a rectangular superconductor would be uniform, contrary to expectations of the Meissner state. This was tested by measuring the perpendicular magnetic field resulting from a transport current in a superconducting tape as it reached the critical state. It was indeed found that the current distribution is uniform across the width. The self-field critical current was also measured in YBa₂Cu₃Oy samples with Zn impurities to measure the superfluid density and further test the self-field critical current as a measure of superfluid density and in particular explore whether it follows the canonical dependence on the transition temperature observed for superconductors with d-wave symmetry. Here the critical current was found to reduce as more impurities were added and indeed this matched its expected canonical reduction, following the superfluid density as Jc(sf) ∝p³/². These results taken together support the unexpected existence of a fundamental limit in the self-field critical current, which is thermodynamic in origin.</p>

Expectation values of minimum-length Ricci scalar

In this paper, we consider a specific model, implementing the existence of a fundamental limit distance [Formula: see text] between (space or time separated) points in spacetime, which in the recent past has exhibited the intriguing feature of having a minimum-length Ricci scalar [Formula: see text] that does not approach the ordinary Ricci scalar [Formula: see text] in the limit of vanishing [Formula: see text]. [Formula: see text] at a point has been found to depend on the direction along which the existence of minimum distance is implemented. Here, we point out that the convergence [Formula: see text] in the [Formula: see text] limit is anyway recovered in a relaxed or generalized sense, which is when we average over directions, this suggesting we might be taking the expectation value of [Formula: see text] promoted to be a quantum variable. It remains as intriguing as before the fact that we cannot identify (meaning this is much more than simply equating in the generalized sense above) [Formula: see text] with [Formula: see text] in the [Formula: see text] limit, namely, when we get ordinary spacetime. Thing is like if, even when [Formula: see text] (read here the Planck length) is far too small to have any direct detection of it feasible, the intrinsic quantum nature of spacetime might anyway be experimentally at reach, witnessed by the mentioned special feature of Ricci, not fading away with [Formula: see text] (i.e. persisting when taking the [Formula: see text] limit).

An eight-state molecular sequential switch featuring a dual single-bond rotation photoreaction

Typical photowitches interconvert between two different states by simple isomerization reactions, which represents a fundamental limit for applications. To expand the switching capacity usually different photoswitches have to be linked together leading to strong increase in molecular weight, diminished switching function, and less precision and selectivity of switching events. Herein we present an approach for solving this essential problem with a different photoswitching concept. A basic molecular switch architecture provides precision photoswitching between eight different states via controlled rotations around three adjacent covalent bonds. All eight states can be populated one after another in an eight-step cycle by alternating between photochemical Hula-Twist isomerizations and thermal single bond rotations. By simply changing solvent and temperature the same switch can also undergo a different cycle instead interconverting just five isomers in a selective sequence. This behavior is enabled through the discovery of an unprecedented photoreaction, a one photon dual single bond rotation.

The Posthumanist Concepts of Life and Death, From the Viewpoint of Paul Ricoeur’s Hermeneutics of the Self. A Critical Analysis

How can the human self face the paradigm shifts that posthumanism mobilizes? We intend to answer this question setting out from the concept of Paul Ricoeur’s hermeneutics of the self. According to this hermeneutics, the self is capable of action, self-reflection, called by Ricoeur “attestation”, and of the fact that it can be accompanied by the moral values acquired. We will notice that Ricoeur’s hermeneutics of the self can be reduced to an ontology of the self deeply engraved by three dialectics, self-reflection, identity, and the relationship between the self-as-another and anothers-as-self. We will subsequently infer that the self holds ontologically the condition of being a self constrained by the manner of being as orientation. This condition represents the fundamental limit of consciousness which, consequently, contributes significantly to an epistemlogy of the consciousness that sketches out the project of a hermeneutics which places both language and consciousness at the centre of the process of differentiation between the posthumanist narratives about life and death.

HUBUNGAN INDEKS MASSA TUBUH (IMT) DENGAN RASIO VOLUME EKSPIRASI PAKSA SATU DETIK PERTAMA PER KAPASITAS VITAL PAKSA (VEP1/KVP) PADA PASIEN ASMA STABIL DI RSUD KOTA MATARAM 2019

Saat ini asma masih menjadi salah satu masalah kesehatan utama baik di negara maju maupun di negara berkembang. Diperkirakan terdapat 300 juta penduduk di dunia menderita asma. Prevalensi asma di Indonesia sendiri pada tahun 2018 sebesar 2,4%. Provinsi Nusa Tenggara Barat (NTB) berada di peringkat ke 7 dengan angka kejadian mencapai 2,5%. Asma adalah penyakit heterogen dengan berbagai proses penyebab yang mendasarinya. Salah satu penyebab asma yang telah diidentifkasi adalah asma dengan obesitas. Gold standart dalam pemeriksaan penyakit asma adalah spirometri. Parameter yang dinilai dalam pemeriksaan spirometri untuk menilai derajat obstruksi pasien asma adalah VEP1/KVP. Perubahan pada IMT baik overweight maupun underweight akan menyebabkan perubahan mekanik dan kimiawi sistem pernapasan yang nantinya berperan sebagai faktor yang berpengaruh dan memperberat nilai VE1/KVP pada pasien asma. Tujuan dalam penelitian ini mengetahui hubungan indek massa tubuh dengan rasio volume ekspirasi paksa satu detik pertama per kapasital vital paksa pada pasien asma stabil di RSUD Kota Mataram 2019. Penelitian ini merupakan analitik observasional, dengan rancangan cross sectional. Sumber data yang digunakan dalam penelitian ini berupa data sekunder dari rekam medik pasien asma yang menjalani rawat jalan di RSUD Kota Mataram 2019 berupa data berat badan dan tinggi badan serta nilai VEP1/KVP. Sampel pada penelitian ini berjumlah 118 orang. Analisis data menggunakan rank spearman dengan bantuan software SPSS versi 25. Hasil analisis didapatkan nilai p-value 0,000 (p-value ≤0,05), yang berarti terdapat hubungan antara IMT dan VEP1/KVP pada pasien asma stabil. Terdapat hubungan antara Indeks Massa Tubuh dengan rasio VEP1/KVP pada pasien asma stabil di RSUD Kota Mataram 2019.Kata Kunci: Asma, indeks massa tubuh, VEP1/KVP.ABSTRACTRight now, asthma is as yet one of the principle medical issues in both created and non-industrial nations. The highest quality level in inspecting asthma is spirometry. The boundary evaluated in the spirometry assessment to survey the level of impediment in asthma patients was FEV1/FVC. Changes in BMI both overweight and underweight will cause mechanical and synthetic changes in the respiratory framework which will later go about as an impacting factor and bother the VE1/KVP esteem in asthma patients. The reason for this examination to decide the connection between weight file and the proportion of constrained expiratory volume of the first second per constrained fundamental limit in stable asthma patients at Mataram City Clinic 2019. This examination was an observational scientific contemplated, with a cross sectional plan. This examination utilizing optional information from clinical records of asthma patients as weight and tallness information just as VEP1/KVP esteems. The patients are going through outpatient at the Mataram City Medical clinic in 2019. The example in this investigation added up to 118 individuals. Information examination utilized position spearman with the assistance of SPSS form 25 programming The aftereffects of the investigation utilizing Rank Spearmen acquired a p-value of 0.000 (p-value ≤0.05), which implies that there is a connection among BMI and FEV1/FVC in stable asthma patients at Mataram City Clinic 2019.Keywords: Asthma, body mass index, FEV1/FVC.