Rotational dynamics of CO solvated in small He clusters: a quantum Monte Carlo study

The rotational dynamics of CO single molecules solvated in small He clusters (CO@He_N) has been studied using Reptation Quantum Monte Carlo for cluster sizes up to N=30. Our results are in good agreement with the roto-vibrational features of the infrared spectrum recently determined for this system, and provide a deep insight into the relation between the structure of the cluster and its dynamics. Simulations for large N also provide a prediction of the effective moment of inertia of CO in the He nano-droplet regime, which has not been measured so far

The itinerant ferromagnetic phase of the Hubbard model

Using a newly developed quantum Monte Carlo technique, we provide strong evidence for the stability of a saturated ferromagnetic phase in the high-density regime of the two-dimensional infinite-U Hubbard model. By decreasing the electron density, a discontinuous transition to a paramagnetic phase is observed, accompanied by a divergence of the susceptibility on the paramagnetic side. This behavior, resulting from a high degeneracy among different spin sectors, is consistent with an infinite-order phase transition. The remarkable stability of itinerant ferromagnetism renews the hope to describe this phenomenon within a purely kinetic mechanism and will facilitate the validation of experimental quantum simulators with cold atoms loaded in optical lattices

Reptation quantum Monte Carlo for lattice Hamiltonians with a directed-update scheme

We provide an extension to lattice systems of the reptation quantum Monte Carlo algorithm, originally devised for continuous Hamiltonians. For systems affected by the sign problem, a method to systematically improve upon the so-called fixed-node approximation is also proposed. The generality of the method, which also takes advantage of a canonical worm algorithm scheme to measure off-diagonal observables, makes it applicable to a vast variety of quantum systems and eases the study of their ground-state and excited-states properties. As a case study, we investigate the quantum dynamics of the one-dimensional Heisenberg model and we provide accurate estimates of the ground-state energy of the two-dimensional fermionic Hubbard model

Structure, rotational dynamics, and superfluidity of small OCS-doped He clusters

The structural and dynamical properties of OCS molecules solvated in Helium clusters are studied using reptation quantum Monte Carlo, for cluster sizes n=3-20 He atoms. Computer simulations allow us to establish a relation between the rotational spectrum of the solvated molecule and the structure of the He solvent, and of both with the onset of superfluidity. Our results agree with a recent spectroscopic study of this system, and provide a more complex and detailed microscopic picture of this system than inferred from experiments.Comment: 4 pages. TeX (requires revtex4) + 3 ps figures (1 color

Impact of the Threshold on the Performance Verification of Computerized Tomography Scanners

Computerized tomography is an emerging technology for geometric inspection. Its capability of easily scanning internal and undercut surfaces, as well as micro components, makes it the only possible choice for several measurement tasks. However, traceability is still a relevant issue, due to the lack of well-established procedures for testing CT scanners: several international standards about the application of computerized tomography for geometric inspection are still under development. In this work, we will propose the results we obtained in the application of the VDI/VDE 2617 part 13 standard on two computerized tomography scanners. In particular, we will show the impact of the choice of the threshold on the results of the test

Optimal inspection strategy planning for geometric tolerance verification

"Two features characterize a good inspection system: it is accurate, and compared to the manufacturing cost, it is not expensive. Unfortunately, few measuring systems posses both these characteristics, i.e. low uncertainty comes with a cost. But also high uncertainty comes with a cost, because measuring systems with high uncertainty tend to generate more inspection errors, which come with a cost. In the case of geometric inspection, the geometric deviation is evaluated from a cloud of points sampled on a part. Therefore, not only the measuring device has to be selected, but also the sampling strategy has to be planned, i.e. the sampling point cloud size and where points should be located on the feature to inspect have to be decided. When the measuring device is already available, as it often happens in geometric measurement, where most instruments are flexible, an unwise strategy planning can be the largest uncertainty contributor. In this work, a model for the evaluation of the overall inspection cost is proposed. The optimization of the model can lead to an optimal inspection strategy in economic sense. However, the model itself is based on uncertainty evaluation, in order to assess the impact of measurement error on inspection cost. Therefore, two methodologies for evaluating the uncertainty will be proposed. These methodologies will be focused on the evaluation of the contribution of the sampling strategy to the uncertainty. Finally, few case studies dealing with the inspection planning for a Coordinate Measuring Machine will be proposed

Distributed energy production in a polycentric scenario: policy reforms and community management

Any discussion of distributed energy systems inevitably centres on how they compare with the large energy systems, i.e. the traditional centralised model of energy production, and on the viability of local energy systems as alternatives in terms of efficiency and sustainability. At present, the debate on local energy systems and distributed energy production hinges mainly on questions of technology and engineering; at most, some reflections on economy are thrown in. What we believe is essential is to cast the net wider and include other dimensions. In particular, we also need to consider in greater depth the organisational and institutional issues involved \u2013 until now, less considered and discussed. In this perspective, the main question addressed by the present article is if and how new forms of local organisations can provide the crucial catalyst for a new polycentric distributed energy scenario. Copyright \ua9 2018 Informa UK Limite

Effect of filters on segmentation-free geometric verification by X-ray CT

A method has been proposed to verify geometric tolerances by X-ray computed tomography (XCT) without the need for image segmentation The method is based on the direct comparison of a part XCT image to a volumetric representation of its geometric tolerance. In previous works the method was directly applied to raw images. However, filters are commonly applied to XCT images. Usually, they mitigate noise or enhance details. In this work, we study if the segmentation-free verification benefits from the application of filters to XCT images. Standard filters a considered, e.g. Gaussian and non-local means

Experimenting in urban self-organization. Framework-rules and emerging orders in Oosterwold (Almere, The Netherlands)

Thee intent of this article is to explore the scope and working of “framework-rules” in relation to self-organization in urban development, both theoretically and empirically. It explores the strategies promoted in Oosterwold (Almere, e Netherland), and the framework-rules that discipline its emergent development, without wanting to suggest that Oosterwold is a “best practice”. It is an extreme case that helps us to broaden our thinking about governing urban development