Calibration of the torsional and lateral spring constants of cantilever sensors

Financial support from the EPSRC (EP/K000411/1) and the University of St. Andrews under an Impact Acceleration Account (EP/K503940/1) are gratefully acknowledged.A method suitable for the calibration of the spring constants of all torsional and lateral eigenmodes of micro- and nanocantilever sensors is described. Such sensors enable nanomechanical measurements and the characterization of nanomaterials, for example with atomic force microscopy. The method presented involves the interaction of a flow of fluid from a microchannel with the cantilever beam. Forces imparted by the flow cause the cantilever to bend and induce a measurable change of the torsional and lateral resonance frequencies. From the frequency shifts the cantilever spring constants can be determined. The method does not involve physical contact between the cantilever or its tip and a hard surface. As such it is non-invasive and does not risk damage to the cantilever. Experimental data is presented for two rectangular microcantilevers with fundamental flexural spring constants of 0.046 and 0.154 N/m. The experimentally determined torsional stiffness values are compared with those obtained by the Sader method. We demonstrate that the torsional spring constants can be readily calibrated using the method with an accuracy of around 15%.PostprintPeer reviewe

Uwagi dotyczące tworzenia w NRD kolektywnych form korzystania z techniki EPD

Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę

Business perception of contextual changes: sources and impediments to organizational learning

A firm's ability to shape its policies to meet societal demands depends on how it perceives the opportunities and risks in its environment. We hypothesized that corporate culture plays a significant role in shaping organizational perceptions. This paper summarizes the findings of a study on how the organizational culture of a chemical firm headquartered in West Germany affected the evolution of its social and personnel policy from 1950 to 1989 given the changes in its sociopolitical environment during this period. The study shows that the culture of a company, by shaping its perceptions, plays a central role in determining the areas in which the organization is likely to be able to learn easily and those in which it is likely to resist changing its policies. -- Die Fähigkeit von Unternehmen, geeignete Strategien für den Umgang mit Veränderungen in ihren Rahmenbedingungen zu entwickeln, hängt oft davon ab, wie in diesem Unternehmen Möglichkeiten und Risiken im gesellschaftlichen, politischen und ökonomischen Umfeld wahrgenommen werden. Dieser Untersuchung liegt die Hypothese zugrunde, daß die Organisationskultur eine wichtige Rolle bei diesen Wahrnehmungsprozessen spielt. Am Beispiel einer Studie über einen Chemiekonzern wird in diesem Aufsatz aufgezeigt, wie die Sozial- und Personalpolitik des Unternehmens durch den gesellschaftlichen Wandel, im Zeitraum von 1950-1989, beeinflußt wurde. Durch ihre Auswirkung auf die Perzeption legt die Unternehmenskultur auch im wesentlichen die Bereiche im Unternehmen fest, in denen die Lernbereitschaft hoch ist und diejenigen, die eher zögerlich auf Veränderungen reagieren.

Nanoindentation of ferritic‐martensitic steels – a comparative study of static and dynamic measurements

Nano- and micromechanical test techniques offer important advantages for the assessment of neutron irradiation damage (minimized volume of activated material) and ion irradiation damage (limited penetration depth) which is of interest for the emulation of neutron irradiation damage. This paper presents a comparative study of different nanoindentation methods as applied to two ferritic-martensitic steels (T91 and Eurofer97), here investigated in the unirradiated reference state, but envisaged as structural materials for nuclear applications. Depth-controlled single cycle (DSC) measurements at various final indentation depths, force-controlled single cycle (FSC), force-controlled progressive multi-cycle (PMC) measurements, and continuous stiffness measurements (CSM) using a Berkovich tip at room temperature have been combined to determine the indentation hardness and elastic modulus, and assess the robustness of the different methods together with their statistical properties. The Nix-Gao model is applied to analyse the indentation size effects observed with static and dynamic measurement methods. The breakdown of the scaling regime at large inverse indentation depths is sensitive to the dynamic testing parameters. The work has been performed in the framework of nine laboratories engaged in a more comprehensive round robin exercise within the European Energy Research Alliance – Joint Programme on Nuclear Materials (EERA JPNM), the results of which will be presented elsewhere. Nano- and micromechanical test techniques offer important advantages for the assessment of neutron irradiation damage (minimized volume of activated material) and ion irradiation damage (limited penetration depth) which is of interest for the emulation of neutron irradiation damage. This paper presents a comparative study of different nanoindentation methods as applied to two ferritic-martensitic steels (T91 and Eurofer97), here investigated in the unirradiated reference state, but envisaged as structural materials for nuclear applications. Depth-controlled single cycle (DSC) measurements at various final indentation depths, force-controlled single cycle (FSC), force-controlled progressive multi-cycle (PMC) measurements, and continuous stiffness measurements (CSM) using a Berkovich tip at room temperature have been combined to determine the indentation hardness and elastic modulus, and assess the robustness of the different methods together with their statistical properties. The Nix-Gao model is applied to analyse the indentation size effects observed with static and dynamic measurement methods. The breakdown of the scaling regime at large inverse indentation depths is sensitive to the dynamic testing parameters. The work has been performed in the framework of nine laboratories engaged in a more comprehensive round robin exercise within the European Energy Research Alliance – Joint Programme on Nuclear Materials (EERA JPNM), the results of which will be presented elsewhere. Please click Additional Files below to see the full abstract

Contact-free experimental determination of the static flexural spring constant of cantilever sensors using a microfluidic force tool

Financial support from the EPSRC (EP/K000411/1 and EP/L017008/1) and the University of St. Andrews under an Impact Acceleration Account (EP/K503940/1) are gratefully acknowledged.Micro- and nanocantilevers are employed in atomic force microscopy (AFM) and in micro- and nanoelectromechanical systems (MEMS and NEMS) as sensing elements. They enable nanomechanical measurements, are essential for the characterization of nanomaterials, and form an integral part of many nanoscale devices. Despite the fact that numerous methods described in the literature can be applied to determine the static flexural spring constant of micro- and nanocantilever sensors, experimental techniques that do not require contact between the sensor and a surface at some point during the calibration process are still the exception rather than the rule. We describe a noncontact method using a microfluidic force tool that produces accurate forces and demonstrate that this, in combination with a thermal noise spectrum, can provide the static flexural spring constant for cantilever sensors of different geometric shapes over a wide range of spring constant values (≈0.8–160 N/m).Publisher PDFPeer reviewe

An Adaptive Flow-Aware Packet Scheduling Algorithm for Multipath Tunnelling

This paper proposes AFMT, a packet scheduling algorithm to achieve adaptive flow-aware multipath tunnelling. AFMT has two unique properties. Firstly, it implements robust adaptive traffic splitting for the subtunnels. Secondly, it detects and schedules bursts of packets cohesively, a scheme that already enabled traffic splitting for load balancing with little to no packet reordering. Several NS-3 experiments over different network topologies show that AFMT successfully deals with changing path characteristics due to background traffic while increasing throughput and reliability.Comment: submitted and accepted on IEEE LCN 2019, 4 pages, 5 figure

Refining mutation variants in Cartesian genetic programming

In this work, we improve upon two frequently used mutation algorithms and therefore introduce three refined mutation strategies for Cartesian Genetic Programming. At first, we take the probabilistic concept of a mutation rate and split it into two mutation rates, one for active and inactive nodes respectively. Afterwards, the mutation method Single is taken and extended. Single mutates nodes until an active node is hit. Here, our extension mutates nodes until more than one but still predefined number n of active nodes are hit. At last, this concept is taken and a decay rate for n is introduced. Thus, we decrease the required number of active nodes hit per mutation step during CGP’s training process. We show empirically on different classification, regression and boolean regression benchmarks that all methods lead to better fitness values. This is then further supported by probabilistic comparison methods such as the Bayesian comparison of classifiers and the Mann-Whitney-U-Test. However, these improvements come with the cost of more mutation steps needed which in turn lengthens the training time. The third variant, in which n is decreased, does not differ from the second mutation strategy listed

SupRB: A Supervised Rule-based Learning System for Continuous Problems

We propose the SupRB learning system, a new Pittsburgh-style learning classifier system (LCS) for supervised learning on multi-dimensional continuous decision problems. SupRB learns an approximation of a quality function from examples (consisting of situations, choices and associated qualities) and is then able to make an optimal choice as well as predict the quality of a choice in a given situation. One area of application for SupRB is parametrization of industrial machinery. In this field, acceptance of the recommendations of machine learning systems is highly reliant on operators' trust. While an essential and much-researched ingredient for that trust is prediction quality, it seems that this alone is not enough. At least as important is a human-understandable explanation of the reasoning behind a recommendation. While many state-of-the-art methods such as artificial neural networks fall short of this, LCSs such as SupRB provide human-readable rules that can be understood very easily. The prevalent LCSs are not directly applicable to this problem as they lack support for continuous choices. This paper lays the foundations for SupRB and shows its general applicability on a simplified model of an additive manufacturing problem.Comment: Submitted to the Genetic and Evolutionary Computation Conference 2020 (GECCO 2020