Direct Observation of Propagating Gigahertz Coherent Guided Acoustic Phonons in Free Standing Single Copper Nanowires

We report on gigahertz acoustic phonon waveguiding in free-standing single copper nanowires studied by femtosecond transient reflectivity measurements. The results are discussed on the basis of the semianalytical resolution of the Pochhammer and Chree equation. The spreading of the generated Gaussian wave packet of two different modes is derived analytically and compared with the observed oscillations of the sample reflectivity. These experiments provide a unique way to independently obtain geometrical and material characterization. This direct observation of coherent guided acoustic phonons in a single nano-object is also the first step toward nanolateral size acoustic transducer and comprehensive studies of the thermal properties of nanowires

Tackling barriers to COVID-19 vaccine uptake in London: a mixed-methods evaluation

BACKGROUND: In response to the COVID-19 pandemic, the first vaccine was administered in December 2020 in England. However, vaccination uptake has historically been lower in London than in other English regions. METHODS: Mixed-methods: This comprised an analysis of cumulative percentage uptake across London between 8 December 2020 and 6 June 2021 by vaccine priority cohorts and ethnicity. We also undertook thematic analyses of uptake barriers, interventions to tackle these and key learning from a qualitative survey of 27 London local authority representatives, vaccine plans from London's five Integrated Care Systems and interviews with 38 London system representatives. RESULTS: Vaccine uptake was lower in Black ethnic (57-65% uptake) compared with the White British group (90% uptake). Trust was a critical issue, including mistrust in the vaccine itself and in authorities administering or promoting it. The balance between putative costs and benefits of vaccination created uptake barriers for zero-hour and shift workers. Intensive, targeted and 'hyper-local' initiatives, which sustained community relationships and were not constrained by administrative boundaries, helped tackle these barriers. CONCLUSIONS: The success of the national vaccination programme depended on conceding local autonomy, investing in responsive and long-term partnerships to engender trust through in-depth understanding of communities' beliefs

Tackling barriers to COVID-19 vaccine uptake in London: a mixed-methods evaluation.

BACKGROUND: In response to the COVID-19 pandemic, the first vaccine was administered in December 2020 in England. However, vaccination uptake has historically been lower in London than in other English regions. METHODS: Mixed-methods: This comprised an analysis of cumulative percentage uptake across London between 8 December 2020 and 6 June 2021 by vaccine priority cohorts and ethnicity. We also undertook thematic analyses of uptake barriers, interventions to tackle these and key learning from a qualitative survey of 27 London local authority representatives, vaccine plans from London's five Integrated Care Systems and interviews with 38 London system representatives. RESULTS: Vaccine uptake was lower in Black ethnic (57-65% uptake) compared with the White British group (90% uptake). Trust was a critical issue, including mistrust in the vaccine itself and in authorities administering or promoting it. The balance between putative costs and benefits of vaccination created uptake barriers for zero-hour and shift workers. Intensive, targeted and 'hyper-local' initiatives, which sustained community relationships and were not constrained by administrative boundaries, helped tackle these barriers. CONCLUSIONS: The success of the national vaccination programme depended on conceding local autonomy, investing in responsive and long-term partnerships to engender trust through in-depth understanding of communities' beliefs

A model-based approach for robustness testing

Abstract. Robustness testing is a part of the validation process which consists in testing the behavior of a system implementation under exceptional execution conditions in order to check if it still fulfills some robustness requirements. We propose a theoretical framework for modelbased robustness testing together with an implementation within the If validation environment. Robustness test cases are generated from both a (partial) operational specification and an abstract fault model. This generation technique is inspired from the ones used in (classical) conformance testing -already implemented in several tools. This framework is illustrated on a small example

Data-Driven Predesign Tool for Small-Scale Centrifugal Compressor in Refrigeration

Domestic scale heat pumps and air conditioners are mainly driven by volumetric com-pressors. Yet the use of reduced scale centrifugal compressors is reconsidered due to their high efficiency and power density. The design procedure of centrifugal compressors starts with predesign tools based on the Cordier line. However, the optimality of the obtained predesign, which is the starting point of a complex and iterative process, is not guaranteed, especially for small-scale compressors operating with refrigerants. This paper proposes a data-driven predesign tool tailored for small-scale centrifugal com-pressors used in refrigeration applications. The predesign model is generated using an experimentally validated one-dimensional (1D) code which evaluates the compressor performance as a function of its detailed geometry and operating conditions. Using a symbolic regression tool, a reduced order model that predicts the performance of a given compressor geometry has been built. The proposed predesign model offers an alternative to the existing tools by providing a higher level of detail and flexibility. Particularly, the model includes the effect of the pressure ratio, the blade height ratio, and the shroud to tip radius ratio. The analysis of the centrifugal compressor losses allows identifying the underlying phenomena that shape the new isentropic efficiency contours. Compared to the validated 1D code, the new predesign model yields deviations below 4%on the isen-tropic efficiency, while running 1500 times faster. The new predesign model is, therefore, of significant interest when the compressor is part of an integrated system design process

A model-based approach for robustness testing

Abstract. Robustness testing is a part of the validation process which consists in testing the behavior of a system implementation under exceptional execution conditions in order to check if it still fulfills some robustness requirements. We propose a theoretical framework for modelbased robustness testing together with an implementation within the If validation environment. Robustness test cases are generated from both a (partial) operational specification and an abstract fault model. This generation technique is inspired from the ones used in (classical) conformance testing -already implemented in several tools. This framework is illustrated on a small example

Dynamics analysis of a drillstring model

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