Applied physics: Gravity measurements on chips
Gravimeters have applications ranging from oil exploration to the detection of underground tunnels, but size and lack of portability have limited their field use. A device the size of a postage stamp promises fresh opportunities. See Letter p.614
 Gravimeters can measure tiny variations in the local gravitational acceleration, with sensitivity high enough to measure Earth's tides: the elastic deformation of the Earth's crust caused by the changing relative phases of the Sun, Earth and Moon. Existing gravimeters are bulky and costly, but now Giles Hammond and colleagues have developed a compact and inexpensive microelectromechanical gravimeter with a novel 'anti-spring' design. They use it to measure gravitational acceleration with sufficient sensitivity and stability to detect Earth's tides. The small size and low cost of the device mean it could be mounted on a drone for surveying and exploration roles, used to monitor volcanoes or built into multi-pixel density-contrast imaging arrays.
Gravity measurements as a calibration tool for geothermal reservoir modelling
Abstract Gravity measurements are sensitive to changes in mass due to subsurface fluid flow, which is vital to understand for sustainable management of production and reinjection at geothermal reservoirs. We here present a methodology to calculate changes in gravity from TOUGH2 numerical reservoir models, combining it with PEST analysis to create a semi-automated methodology for geothermal reservoir model calibration. This process can also provide statistical information about model parameter sensitivity. Comparing a simplified geothermal reservoir model with a real-world, high-temperature case study shows that gravity data is most sensitive to porosity, permeability, fracture volume and relative permeability. Refining several model parameters simultaneously in the real-world case study allows us to reduce the misfit between modelled and measured gravity changes by 20% compared to calibrating against well data alone. This process also highlights aspects of the reservoir model that may need refining conceptually.
A sustainable development indicator for NGOs and international organisations
The article offers an easy-to-use indicator for measuring whether NGOs, international organisations and government policies and projects meet the criteria for sustainable development that have been established by the Rio Declaration in 1992 and that are recognised by experts in the field. Use of this indicator reveals that most of the major actors in the field of development are actually failing to promote sustainable development and points to the specific areas where they need to improve in order to fulfil sustainability criteria. We also offer a sample test of the indicator using UNICEF as a case study.