Hollow MEMS:An Integrated Sensor for Combined Density, Viscosity, Buoyant Mass and IR Absorption Spectrometry

Miniaturization of electro mechanical sensor systems to the micro range and beyond has shown impressive sensitivities measuring sample properties like mass, viscosity, acceleration, pressure and force just to name a few applications. In order to enable these kinds of measurements on liquid samples a hollow MEMS sensor has been designed, fabricated and tested. Combined density, viscosity, buoyant mass spectrometry and IR absorption spectroscopy are possible on liquid samples and micron sized suspended particles (e.g. single cells). Measurements are based on changes in the resonant behavior of these sensors.Optimization of the microfabrication process has led to a process yield of almost 100% .This is achieved despite the fact, that the process still offers a high degree of flexibility. By simple modifications the Sensor shape can be optimized for different size ranges and sensitivities.Microfluidic interfacing has been realized using high throughput and low cost technologies such as injection molding and ultra-sonic welding. Standard fluidic LUER connections were used that are widely applied in other micro fluidic projects at DTU Nanotech to enable future interfacing of the system with other technologies and pre-concentration approaches.A thorough theoretical analysis of the expected sensor responsivity and sensitivity is performed. Predictions made are confirmed by finite element simulations. Using these tools the sensor geometry is optimized for ideal performance in both mass density and IR spectroscopy measurements of samples, the size of single yeast cells (≈ 5 μm). A relative frequency shift of 69 ppm/single cell buoyant mass in case of the mass spectroscopy measurements and 40 ppm/μW in case of the IR absorption spectroscopy measurements are calculated and confirmed by FE simulations for the sensor geometry fabricated.In order to verify sufficient frequency stability, Allan Deviation measurements are performed on the fabricated sensors. In combination with the calculated responsivities these measurements confirm that the sensor sensitivity will enable single cell measurements. Initial experiments confirming the calculated responsivities are performed. Experiments filling the sensor with liquids of different densities confirmed the predicted mass responsivity. The resonance frequency shifts 29% when filled with water compared to air. By irradiating the sensor with a tunable IR laser source and tracking the resonance frequency the capability of the sensor to perform spectroscopic measurements is tested. Experiments with both an empty and a paraffin wax filled channel confirm the predicted heating responsivity. A resonance shiftof &gt;8000 ppm at the absorption peak of paraffin is observed. Individual absorption peaks can be resolved with a wavenumber resolution below 1 cm-1.<br/

The topology of fullerenes

Fullerenes are carbon molecules that form polyhedral cages. Their bond structures are exactly the planar cubic graphs that have only pentagon and hexagon faces. Strikingly, a number of chemical properties of a fullerene can be derived from its graph structure. A rich mathematics of cubic planar graphs and fullerene graphs has grown since they were studied by Goldberg, Coxeter, and others in the early 20th century, and many mathematical properties of fullerenes have found simple and beautiful solutions. Yet many interesting chemical and mathematical problems in the field remain open. In this paper, we present a general overview of recent topological and graph theoretical developments in fullerene research over the past two decades, describing both solved and open problems. WIREs Comput Mol Sci 2015, 5:96–145. doi: 10.1002/wcms.1207 Conflict of interest: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website

Rethinking the political economy of place: challenges of productivity and inclusion

The global financial crisis of just over a decade ago exposed longer-term systemic problems in global capitalism of which two of the most prominent are the slowdown in the underlying trend rate of productivity growth, alongside a rise in economic and spatial inequalities in many advanced economies. The Covid-19 pandemic looks set to further amplify these problems. This Editorial begins by discussing the scale of the productivity slowdown and of the widening inequalities that have emerged, particularly with regard to their spatial dimension: That is how the uneven and slow development of productivity and rise in inequalities have played out across and within regions and cities. It then briefly considers underlying factors that lie behind these trends, including financialisation/financial globalization, the diminishing role of organised labour, segmentation of the labour market favouring workers who play a key role in financialisation, together with the increasing polarisation within societies according to skill and, crucially, the impact of changing industrial composition particularly as it relates to the rise of the high-tech sectors. The Editorial then examines in what ways the slowdown of productivity and widening of economic and spatial inequalities, may be interrelated, and questions the notion of any efficiency-equity trade-off. Lastly, it considers whether the 'inclusive growth' agenda can potentially reconcile the two ambitions of improving productivity performance and lessening inequalities, reflecting on what inclusive growth could mean, and what it could imply in terms of policy. Thus far, it appears that an inclusive growth agenda has only gained some traction at the subnational level, which seems to reflect- A t least in part- A ttempts by cities and regions to address gaps in policy left by national governments