Superconductivity of Bi-III phase of elemental Bismuth: insights from Muon-Spin Rotation and Density Functional Theory

Using muon-spin rotation the pressure-induced superconductivity in the Bi-III phase of elemental Bismuth (transition temperature $T_{\rm c}\simeq7.05$ K) was investigated. The Ginzburg-Landau parameter $\kappa=\lambda/\xi=30(6)$ ($\lambda$ is the magnetic penetration depth, $\xi$ is the coherence length) was estimated which is the highest among single element superconductors. The temperature dependence of the superconducting energy gap [$\Delta(T)$] reconstructed from $\lambda^{-2}(T)$ deviates from the weak-coupled BCS prediction. The coupling strength $2\Delta/k_{\rm B}T_{\rm c}\simeq 4.34$ was estimated thus implying that Bi-III stays within the strong coupling regime. The Density Functional Theory calculations suggest that superconductivity in Bi-III could be described within the Eliashberg approach with the characteristic phonon frequency $\omega_{\rm ln}\simeq 5.5$ meV. An alternative pairing mechanism to the electron-phonon coupling involves the possibility of Cooper pairing induced by the Fermi surface nesting.Comment: 5 pages, 4 figure

On the superconducting nature of the Bi-II phase of elemental Bismuth

The superconductivity in the Bi-II phase of elemental Bismuth (transition temperature $T_{\rm c}\simeq3.92$ K at pressure $p\simeq 2.80$ GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with Density Functional Theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field $B_{\rm c}(0)\simeq31.97$~mT. The Eliashberg theory approach provides a good agreement with the experimental $T_{\rm c}$ and the temperature evolution of $B_{\rm c}$. The estimated value for the retardation (coupling) parameter $k_{\rm B}T_{\rm c}/\omega_{\rm ln} \approx 0.07$ ($\omega_{\rm ln}$ is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately-coupled superconductor.Comment: 6 pages, 2 figure

High-throughput design of all-d-metal Heusler alloys for magnetocaloric applications

Due to their versatile composition and customizable properties, A$_2$BC Heusler alloys have found applications in magnetic refrigeration, magnetic shape memory effects, permanent magnets, and spintronic devices. The discovery of all-$d$-metal Heusler alloys with improved mechanical properties compared to those containing main group elements, presents an opportunity to engineer Heuslers alloys for energy-related applications. Using high-throughput density functional theory calculations, we screened magnetic all-$d$-metal Heusler compounds and identified 686 (meta)stable compounds. Our detailed analysis revealed that the inverse Heusler structure is preferred when the electronegativity difference between the A and B/C atoms is small, contrary to conventional Heusler alloys. Additionally, our calculations of Pugh ratios and Cauchy pressures demonstrated that ductile and metallic bonding are widespread in all-$d$-metal Heuslers, supporting their enhanced mechanical behaviour. We identified 49 compounds with a double-well energy surface based on Bain path calculations and magnetic ground states, indicating their potential as candidates for magnetocaloric and shape memory applications. Furthermore, by calculating the free energies, we propose that 11 compounds exhibit structural phase transitions, and propose isostructural substitution to enhance the magnetocaloric effect

Axisymmetric Stokes flow due to a point-force singularity acting between two coaxially positioned rigid no-slip disks

We investigate theoretically on the basis of the steady Stokes equations for a viscous incompressible fluid the flow induced by a Stokeslet located on the centre axis of two coaxially positioned rigid disks. The Stokeslet is directed along the centre axis. No-slip boundary conditions are assumed to hold at the surfaces of the disks. We perform the calculation of the associated Green's function in large parts analytically, reducing the spatial evaluation of the flow field to one-dimensional integrations amenable to numerical treatment. To this end, we formulate the solution of the hydrodynamic problem for the viscous flow surrounding the two disks as a mixed-boundary-value problem, which we then reduce into a system of four dual integral equations. We show the existence of viscous toroidal eddies arising in the fluid domain bounded by the two disks, manifested in the plane containing the centre axis through adjacent counterrotating eddies. Additionally, we probe the effect of the confining disks on the slow dynamics of a point-like particle by evaluating the hydrodynamic mobility function associated with axial motion. Thereupon, we assess the appropriateness of the commonly-employed superposition approximation and discuss its validity and applicability as a function of the geometrical properties of the system. Additionally, we complement our semi-analytical approach by finite-element computer simulations, which reveals a good agreement. Our results may find applications in guiding the design of microparticle-based sensing devices and electrokinetic transport in small scale capacitors

Design-Prinzipien und Umsetzung personalisierter Assistenzsysteme unter Berücksichtigung des Datenschutzes

Digitale Assistenzsysteme stellen Beschäftigten aufgabenbezogene Informationen in ihren Arbeitsprozessen über tragbare Endgeräte wie beispielsweise Datenbrillen bereit. Durch eine Personalisierung können diese Systeme dazu befähigt werden, sich an den individuellen Arbeitsfortschritt und Wissensstand der Beschäftigten anzupassen. Die technischen Komponenten eines Assistenzsystems stellen hierzu dann nicht nur die Assistenz bereit, sondern sammeln auch personenbezogene Daten, um die Personalisierung zu ermöglichen. Die Personalisierung erfordert jedoch auch einen adäquaten Umgang mit diesen sensiblen Daten, um die Akzeptanz der Assistenzsysteme durch die Beschäftigten sowie einen rechtskonformen Einsatz der Assistenzsysteme überhaupt zu gewährleisten. Um die Akzeptanz und Rechtskonformität sicherzustellen, wurden im PersonA-Projekt insgesamt 19 Design-Prinzipien entwickelt und evaluiert, die bei der Entwicklung von personalisierten Assistenzsystemen in Produktion und Service berücksichtigt werden sollten. Diese gliedern sich in Design-Prinzipien zu generellen Funktionen von Assistenzsystemen, zur Personalisierung von Assistenzsystemen und zur Datenerhebung und -verwendung von Assistenzsystemen. Ausgehend von diesen Design-Prinzipien wurden Funktionen für ein Privatsphäre-Management für das bestehende Lösungsportfolio von TeamViewer Germany GmbH entwickelt und in Pilotprojekten bei den Anwendungspartnern Kemper GmbH und WS System GmbH zum Einsatz gebracht. Vorher-Nachher-Betrachtungen der Prozesse und Kennzahlen bei den Anwendungspartnern zeigen bemerkenswerte Verbesserungen. Darüber hinaus wurden organisationskulturelle Aspekte bei der Einführung und Nutzung der technischen Lösungen bei den Anwendungspartnern durch die nextpractice GmbH untersucht. Aus den Pilotprojekten ergaben sich praktische Handlungsempfehlungen, die auch für weitere Unternehmen eine Orientierung für ihre eigenen Projekte zur Einführung von personalisierten Assistenzsystemen bieten können

Additive value of [18F]PI-2620 perfusion imaging in progressive supranuclear palsy and corticobasal syndrome

Purpose: Early after [18F]PI-2620 PET tracer administration, perfusion imaging has potential for regional assessment of neuronal injury in neurodegenerative diseases. This is while standard late-phase [18F]PI-2620 tau-PET is able to discriminate the 4-repeat tauopathies progressive supranuclear palsy and corticobasal syndrome (4RTs) from disease controls and healthy controls. Here, we investigated whether early-phase [18F]PI-2620 PET has an additive value for biomarker based evaluation of 4RTs. Methods: Seventy-eight patients with 4RTs (71 ± 7 years, 39 female), 79 patients with other neurodegenerative diseases (67 ± 12 years, 35 female) and twelve age-matched controls (69 ± 8 years, 8 female) underwent dynamic (0-60 min) [18F]PI-2620 PET imaging. Regional perfusion (0.5-2.5 min p.i.) and tau load (20-40 min p.i.) were measured in 246 predefined brain regions [standardized-uptake-value ratios (SUVr), cerebellar reference]. Regional SUVr were compared between 4RTs and controls by an ANOVA including false-discovery-rate (FDR, p < 0.01) correction. Hypoperfusion in resulting 4RT target regions was evaluated at the patient level in all patients (mean value - 2SD threshold). Additionally, perfusion and tau pattern expression levels were explored regarding their potential discriminatory value of 4RTs against other neurodegenerative disorders, including validation in an independent external dataset (n = 37), and correlated with clinical severity in 4RTs (PSP rating scale, MoCA, activities of daily living). Results: Patients with 4RTs had significant hypoperfusion in 21/246 brain regions, most dominant in thalamus, caudate nucleus, and anterior cingulate cortex, fitting to the topology of the 4RT disease spectrum. However, single region hypoperfusion was not specific regarding the discrimination of patients with 4RTs against patients with other neurodegenerative diseases. In contrast, perfusion pattern expression showed promise for discrimination of patients with 4RTs from other neurodegenerative diseases (AUC: 0.850). Discrimination by the combined perfusion-tau pattern expression (AUC: 0.903) exceeded that of the sole tau pattern expression (AUC: 0.864) and the discriminatory power of the combined perfusion-tau pattern expression was replicated in the external dataset (AUC: 0.917). Perfusion but not tau pattern expression was associated with PSP rating scale (R = 0.402; p = 0.0012) and activities of daily living (R = - 0.431; p = 0.0005). Conclusion: [18F]PI-2620 perfusion imaging mirrors known topology of regional hypoperfusion in 4RTs. Single region hypoperfusion is not specific for 4RTs, but perfusion pattern expression may provide an additive value for the discrimination of 4RTs from other neurodegenerative diseases and correlates closer with clinical severity than tau pattern expression

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation

This paper reports the development of a two-dimensional thick film lead zirconate titanate (PZT) ultrasonic transducer array, operating at frequency approximately 7.5 MHz, to demonstrate the potential of this fabrication technique for microparticle manipulation. All layers of the array are screen-printed then sintered on an alumina substrate without any subsequent patterning processes. The thickness of the thick film PZT is 139 ± 2 μm, the element pitch of the array is 2.3 mm, and the dimension of each individual PZT element is 2 × 2 mm2 with top electrode 1.7 × 1.7 mm2. The measured relative dielectric constant of the PZT is 2250 ± 100 and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis was used to predict the behaviour of the array and to optimise its configuration. Electrical impedance spectroscopy and laser vibrometry were used to characterise the array experimentally. The measured surface motion of a single element is on the order of tens of nanometres with a 10 Vpeak continuous sinusoidal excitation. Particle manipulation experiments have been demonstrated with the array by manipulating Ø10 μm polystyrene microspheres in degassed water. The simplified array fabrication process and the bulk production capability of screen-printing suggest potential for the commercialisation of multilayer planar resonant devices for ultrasonic particle manipulation

Effective poling of hard PZT ceramics for high-power ultrasound applications

For high power ultrasound transducers, the poling condition of the piezoceramic is crucial for stable and continuous operation. In this investigation, poling during the temperature-timepaths heating and cooling in addition to poling at constant temperatures were investigated and evaluated regarding the achieved poling result.The planar coupling factor and large signal loss factor are used for characterization. From the results, poling process parameters can be derived, minimizing losses while maximizing the electromechanical coupling

Effect of temperature path on the poling of commercial hard PZT ceramics and its implication for mass production

In order to identify process parameters for the efficient poling of hard piezoelectrics in mass production, the effect of temperature modification during poling is investigated for a commercial hard PZT in the temperature range from 25 °C to 150 °C. While an electric field is applied, the temperature of the specimens was kept constant or the specimens were heated or cooled. The resulting piezoelectric performance was evaluated on the basis of the planar coupling factor at room temperature. An optimal poling temperature associated with maximum piezoelectric performance was found for poling with constant temperature. However, for poling while cooling, even higher performance is attained if the starting temperature is high enough. If poling becomes necessary after fabrication at high temperature, the cooling period could be exploited. The observed correlation between permittivity and the coupling factor could be exploited in quality control

Basisprojekt: Smart Tools for Smart Design: Schlussbericht

Ziel des Basisvorhabens „Smart Tools for Smart Design“ war es, Design als Mehrwert zu Beginn eines Entwicklungszyklus zu integrieren, um so Produkte mit neuen auf Smart Materials basierenden Alleinstellungsmerkmalen zu entwickeln. Dafür sollten auf Grundlage einer zu erstellenden Werkstoff-Datenbank für die drei Smart Materials Formgedächtnislegierungen (FGL), Piezokeramiken (Piezo) und dielektrische Elastomere (DE) Vorgehensweisen, Formate und Werkzeuge, sog. Tools, konzipiert, umgesetzt und getestet werden. Die entworfenen Tools sollen Designer für die Potentiale der Smart Materials sensibilisieren, um diese in ihre Produktideen einzubringen ohne zunächst die Hürde des komplexen technischen Know-hows meistern zu müssen. Möglichkeiten, aber auch momentane Einsatzgrenzen derartiger Materialien können so ad hoc abgeschätzt werden, was die Konzeption und Umsetzung von zukunftsweisenden, nicht stereotypen Ideen für konkrete Anwendungen erst ermöglicht. In visionären Pilotprojekten und Studien wurden die entwickelten Werkzeuge sowie Vorgehensweisen von Gestaltern erprobt. Dabei sollte iterativ sowohl die technische Umsetzung der Tools optimiert, als auch die Intuitivität der Handhabung auf die Bedürfnisse der Anwender angepasst werden, um die Akzeptanz u.a. bei Designern zu maximieren. Das Basisvorhaben hat zum Zweck, eine innovative Zusammenarbeit von Designern und Wissenschaftlern zu ermöglichen, um mit dieser Grundlage umsetzbare Konzepte und Prototypen für neue und verbesserte Produkte mit Smart Materials zu gestalten