Electric field sensing with a scanning fiber-coupled quantum dot

We demonstrate the application of a fiber-coupled quantum-dot-in-a-tip as a probe for scanning electric field microscopy. We map the out-of-plane component of the electric field induced by a pair of electrodes by measurement of the quantum-confined Stark effect induced on a quantum dot spectral line. Our results are in agreement with finite element simulations of the experiment. Furthermore, we present results from analytic calculations and simulations which are relevant to any electric field sensor embedded in a dielectric tip. In particular, we highlight the impact of the tip geometry on both the resolution and sensitivity.Comment: 10 pages, 4 figure

The diet problem, a mathematical approach

Background and aim: Differential equations have always been used to modelize physical phenomena from other branches of science: physics, biology, chemistry, engineering, computer science etc. The aim of this paper is to find a simple mathematical model that can describe the variation of weight depending on time and calories intake. The idea is simple and is based on the so-called Malthus mathematical model, an ordinary differential equation associated to an initial condition, which studies the growth of a population with respect to a certain phenomenon or under the influence of external/internal factors. Methods: The most basic and intuitive Malthus model is formalized as follows: given P=P(t) the function that describes the size of a population, the ordinary differential equation P’(t)=rP expresses the fact that the rate of change of the size of the population (i.e. the derivative P’(t) with respect to the time t) depends directly on the size of the population itself multiplied by a factor r that represents the population growth rate, sometimes called Malthusian parameter. The equation needs to be associated to an initial condition, say P0 = P(0), which represents the size of the population at the time t=0. The solution of this problem can be calculated explicitly and this allows to precisely link the weight loss (or gain) according to calories intake, expected time, gender, kind of physical activity etc. Results: Our model considers age, gender and physical activity and allows us to discuss how to calculate a reasonable diet plan depending on different variables. Morever, it can give an idea, by studying the asymptotic behaviour of the solution, why the so-called miracle-diets can’t work, why long diet plans usually fail and how to deal with severe obesity. Conclusions: The results obtained by means of this mathematical model shed new light on how to approach the creation of a reasonable diet plan. These results can be improved by introducing numerical simulations, which is the aim of a subsequent paper

Boundary between the thermal and statistical polarization regimes in a nuclear spin ensemble

As the number of spins in an ensemble is reduced, the statistical uctuations in its polarization eventually exceed the mean thermal polarization. This transition has now been surpassed in a number of recent nuclear magnetic resonance experiments, which achieve nanometer-scale detection volumes. Here, we measure nanometer- scale ensembles of nuclear spins in a KPF6 sample using magnetic resonance force microscopy. In particular, we investigate the transition between regimes dominated by thermal and statistical nuclear polarization. The ratio between the two types of polarization provides a measure of the number of spins in the detected ensemble

Low-mass dark matter search with the DarkSide-50 experiment

We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below 20 GeV=c2using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at 0.1 keVee. The observed rate in the detector at 0.5 keVee is about 1.5 event=keVee=kg=d and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above 1.8 GeV=c2for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range 1.8-6 GeV=c2

Dark Matter search with directional sensitivity

The perspectives of an argon Dark Matter detector with directional information located at Laboratori Nazionali del Gran Sasso are discussed. Columnar recombination combined with a dual-phase Liquid Argon Time Projection Chamber looks a promising approach in view of a directional detector. Even for a minimal angular resolution, a very clear WIMP signature is expected

DarkSide new results and prospects

New results on the scattering cross-section between dark matter particles and nuclei and electrons are presented. They are obtained using a livedays exposure of 532.4 days from the DarkSide-50 experiment, which is a dual-phase liquid-argon time projection chamber (LAr TPC) installed at Laboratori Nazionali del Gran Sasso (LNGS). In this paper, the DarkSide-20k experiment, a LAr TPC with an active (fiducial) mass of 23 t (20 t) to be built at LNGS, is also reviewed. Thanks to its exceptionally low instrumental background, DarkSide-20k will be able to exclude cross sections between weakly interacting massive particles (WIMPs) and nuclei at 90% confidence level down to 2.8×10−48 cm2 (1.2×10−47 cm2) for a WIMP mass of 100GeV/c2 (1TeV/c2)

On the validation of rainfall retrieval algorithms for satellite microwave data

The Algorithm Intercomparison Project utilises rainfall estimates derived from radar data to validate the algorithms developed for rainfall retrievals from satellite microwave data. Since seven minutes are needed in order to have a complete radar scan, while the acquisition of the corresponding satellite microwave image needs only a few seconds, the same pixel can be sensed by radar as much as seven minutes later. Within this time delay the raining cells can be displaced and the consequent mismatch can cause a decrease in the correlation coefficient of the comparison. A method to reveal this time-lag effect is presented and a possible approach to take it into account in the validation process for future missions is suggested

On the validation of rainfall retrieval algorithms for satellite microwave data

The Algorithm Intercomparison Project utilises rainfall estimates derived from radar data to validate the algorithms developed for rainfall retrievals from satellite microwave data. Since seven minutes are needed in order to have a complete radar scan, while the acquisition of the corresponding satellite microwave image needs only a few seconds, the same pixel can be sensed by radar as much as seven minutes later. Within this time delay the raining cells can be displaced and the consequent mismatch can cause a decrease in the correlation coefficient of the comparison. A method to reveal this time-lag effect is presented and a possible approach to take it into account in the validation process for future missions is suggested