Tuning porosity with electric fields: Many metal-organic framework (MOF) compounds exhibit soft porosity—i.e., their lattices can undergo considerable deformation. Knebel et al. formed membrane layers of the MOF ZIF-8 and found that it was converted into a polar polymorph with a stiffer lattice in response to an applied electric field (see the Perspective by Gascon). This change reduced gas transport but, for certain gas mixtures such as propane and propene, also improved their separation factor. Science , this issue p. 347 ; see also p. 303

Various energy harvesting systems have been proposed in the last years. The use of ambient energy, such as vibration energy, has evoked great interests. Most vibration-based converters generate the maximum power only when the generator is excited at its resonance frequency. To overcome this limitation, researchers focus on strategies for increasing the working bandwidth of an energy harvester. Due to the amount of different approaches for broadband energy harvesting, we suggest a categorization. This review presents a classification of the current techniques. Every technique has its own benefits and drawbacks and is suitable for different applications. This review presents the categorization and describes each conversion technique. Typical research approaches are shown to get a better understanding of the energy harvesting techniques. The advantages and drawbacks are presented, and the suitability is shown for each category.

Ultrasonic turning has time variant parameters due to temperature effects and changing load conditions during the process. This results in a change of the resonance frequency and vibration amplitude. To realize constant vibration amplitudes it is necessary to control the ultrasonic transducer by a suitable feedback controller. One approach to drive such a system is to use the resonance frequency as operating point in connection with an amplitude feedback controller. The advantages of resonant driven low damped systems are low voltages and high values of effective power. This paper presents a digital system used for parameter identification and model-based feedback control of the ultrasonic turning tool. During the turning process the system load depends on several factors like chip formation, material inhomogeneity, warming and tool wear. To achieve a stable process and a uniform surface of the work piece the feedback controller has to guarantee constant vibration amplitudes of the ultrasonic tool. The controller used in this paper consists of a digital resonance controller and a current amplitude controller with a frequency of 500Hz. The current amplitude and phase between the excitation voltage and current are determined by phase sensitive demodulation (PSD). To determine the feedback parameters a model-based approach is used