Quantum halo states in two-dimensional dipolar clusters

A halo is an intrinsically quantum object defined as a bound state of a spatial size which extends deeply into the classically forbidden region. Previously, halos have been observed in bound states of two and less frequently of three atoms. Here, we propose a realization of halo states containing as many as six atoms. We report the binding energies, pair correlation functions, spatial distributions, and sizes of few-body clusters composed by bosonic dipolar atoms in a bilayer geometry. We find two very distinct halo structures, for large interlayer separation the halo structure is roughly symmetric and we discover an unusual highly anisotropic shape of halo states close to the unbinding threshold. Our results open avenues of using ultracold gases for the experimental realization of halos composed by atoms with dipolar interactions and containing as many as six atoms.

Aharonov–Bohm effect in a Coulomb-type potential under the influence of a cutoff point

We analyze the influence of a cutoff point on a Coulomb-type potential that stems from the interaction of an electron with electric fields. This cutoff point establishes a forbidden region for the electron. Then, we search for bound state solutions to the Schrödinger equation. In addition, we consider a rotating reference frame. We show that the effects of rotation break the degeneracy of the energy levels. Further, we discuss the Aharonov–Bohm effect for bound states.

AGN-driven galactic outflows: comparing models to observations

ABSTRACT The actual mechanism(s) powering galactic outflows in active galactic nuclei (AGNs) is still a matter of debate. At least two physical models have been considered in the literature: wind shocks and radiation pressure on dust. Here, we provide a first quantitative comparison of the AGN radiative feedback scenario with observations of galactic outflows. We directly compare our radiation pressure-driven shell models with the observational data from the most recent compilation of molecular outflows on galactic scales. We show that the observed dynamics and energetics of galactic outflows can be reproduced by AGN radiative feedback, with the inclusion of radiation trapping and/or luminosity evolution. The predicted scalings of the outflow energetics with AGN luminosity can also quantitatively account for the observational scaling relations. Furthermore, sources with both ultrafast and molecular outflow detections are found to be located in the ‘forbidden’ region of the NH–λ plane. Overall, an encouraging agreement is obtained over a wide range of AGN and host galaxy parameters. We discuss our results in the context of recent observational findings and numerical simulations. In conclusion, AGN radiative feedback is a promising mechanism for driving galactic outflows that should be considered, alongside wind feedback, in the interpretation of future observational data.

Virtual Fixture Generation for Task Planning with Complex Geometries

Many robotic processes require the system to maintain a tool's orientation and distance from a surface. To do so, researchers often use Virtual Fixtures (VFs) to either guide the robot along a path or forbid it from leaving the workspace. Previous efforts relied on volumetric primitives (planes, cylinders, etc.) or raw sensor data to define VFs. However, those approaches only work for a small subset of real-world objects. Extending this approach is complicated not only by VF generation but also generalizing user traversal of the VF to command a robot trajectory remotely. In this work, we present the concept of Task VFs, which convert layers of point cloud based Guidance VF into a bidirectional graph structure and pair it with a Forbidden Region VF. These VFs are hardware-agnostic and can be generated from virtually any source data, including from parametric objects (superellipsoids, supertoroids, etc.), meshes (including from CAD), and real-time sensor data for open-world scenarios. We address surface convexity and concavity since these and distance to the task surface determine the size and resolution of VF layers. This paper then presents the Manipulator-to-Task Transform Tool for Task VF visualization and to limit human-robot interaction ambiguities. Testing confirmed generation success, and users performed spatially discrete experiments to evaluate Task VF usability complex geometries, which showed their interpretability. The Manipulator-to-Task Transform Tool applies many robotic applications, including collision avoidance, process design, training, task definition, etc. for virtually any geometry.

Case Study on Safety Assessment of Rockfall and Splash Stone Protective Structures for Secondary Excavation of Highway Slope

Rockfall occurs on the excavation of the slope of highway resulting from excavated rock pieces. In order to solve the problem of rockfall protection during the disturbance of high slope secondary excavation, rockfall analysis program RocFall was used to perform inverse calculation for rockfall path of excavation disturbed rock. Based on a case study of a reconstruction and expansion project, two rockfall movement models were proposed under excavation disturbance. Moreover, the safety of protective structures under five protection schemes and different initial rockfall movement points is evaluated according to the rockfall interceptions rate. The evaluation results were further verified by long-term field observation. The results show that the protective structure at the slope top has a better interception effect to rockfall. It was difficult to intercept the splash stone, which threats to the traffic safety of the existing roads. According to different construction points of mechanical excavation and the interception rate of splash stone by the protective structure, the forbidden region and safety region of mechanical excavation were proposed.

Specific entropy as a clock for the evolutionary quantization of the isotropic Universe

In this paper, we analyze the dynamics of an isotropic closed Universe in presence of a cosmological constant term and we compare its behavior in the standard Wheeler–DeWitt equation approach with the one when a Lagrangian fluid is considered in the spirit of the Kuchar–Brown paradigm. In particular, we compare the tunnelling of the Universe from the classically forbidden region to the allowed one, showing that considering a time evolution deeply influences the nature of the model. In fact, we show that in the presence of the Lagrangian fluid, the cosmological singularity is restored both in the classical and the quantum regime. However, in the quantum regime the singularity is probabilistically suppressed for some energy eigenvalues and in the case the latter is equal to zero one recovers the standard WDW case. Finally, we introduce a cut-off physics feature in the Minisuperspace by considering a Polymer quantum mechanical approach limiting our attention to the semi-classical dynamics mainly (the quantum treatment is inhibited by the non-local nature of the Hamiltonian operator). We show that the singularity is again removed, like in the fluid-free model, and a bouncing cosmology emerges so that the present model could mimic a cyclic cosmology.

Condensates beyond the horizons

In this work we continue our previous studies concerning the possibility of the existence of a Bose–Einstein condensate in the interior of a static black hole, a possibility first advocated by Dvali and Gómez. We find that the phenomenon seems to be rather generic and it is associated to the presence of a horizon, acting as a confining potential. We extend the previous considerations to a Reissner–Nordström black hole and to the de Sitter cosmological horizon. In the latter case the use of static coordinates is essential to understand the physical picture. In order to see whether a BEC is preferred, we use the Brown–York quasilocal energy, finding that a condensate is energetically favorable in all cases in the classically forbidden region. The Brown–York quasilocal energy also allows us to derive a quasilocal potential, whose consequences we explore. Assuming the validity of this quasilocal potential allows us to suggest a possible mechanism to generate a graviton condensate in black holes. However, this mechanism appears not to be feasible in order to generate a quantum condensate behind the cosmological de Sitter horizon.

Lower and upper bounds for the continuous single facility location problem in the presence of a forbidden region and travel barrier

In this paper, we investigate FRB, which is the single facility Euclidean location problem in the presence of a (non-)convex polygonal forbidden region where travel and location are not permitted. We search for a new facility’s location that minimizes the weighted Euclidean distances to existing ones. To overcome the non-convexity and non-differentiability of the problem’s objective function, we propose an equivalent reformulation (RFRB) whose objective is linear. Using RFRB, we limit the search space to regions of a set of non-overlapping candidate domains that may contain the optimum; thus we reduce RFRB to a finite series of tight mixed integer convex programming sub-problems. Each sub-problem has a linear objective function and both linear and quadratic constraints that are defined on a candidate domain. Based on these sub-problems, we propose an efficient bounding-based algorithm (BA) that converges to a (near-)optimum. Within BA, we use two lower and four upper bounds for the solution value of FRB. The two lower and two upper bounds are solution values of relaxations of the restricted problem. The third upper bound is the near-optimum of a nested partitioning heuristic. The fourth upper bound is the outcome of a divide and conquer technique that solves a smooth sub-problem for each sub-region. We reveal via our computational investigation that BA matches an existing upper bound and improves two more.