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In this work we analyze the existence of electrically charged scalar clouds which are bound states of a complex-valued massive scalar field in the background of subextremal and extremal Kerr-Newman black holes (BH). In particular, we reanalyze neutral (uncharged) clouds in extremal Kerr BH's. For the extremal scenarios we have implemented a novel technique which allows us to obtain regular clouds at the BH horizon ${\cal H}^+$ which turn out to be connected ``continuously'' with the cloud solutions in the subextremal case even if some derivatives of the scalar field are unbounded at the horizon. In particular, for subextremal BH's we have established regularity conditions at ${\cal H}^+$, by demanding that the field and its radial derivatives are bounded there, but in the extremal scenarios we relax this last condition while demanding that some scalar invariants are well behaved at ${\cal H}^+$. Furthermore we have implemented an integral technique to understand and justify in a simple and heuristic way the existence of such cloud configurations in those BH backgrounds., Comment: 25 pages, 19 Figures

We analyze numerically the existence of regular stationary rotating hairy black holes within the framework of general relativity, which are the result of solving the Einstein-Klein-Gordon system for a complex-valued scalar field under suitable boundary (regularity and asymptotically flat) conditions. To that aim we solve the corresponding system of elliptic partial differential equations using spectral methods which are specially suited for such a numerical task. In order to obtain such system of equations we employ a parametrization for the metric that corresponds to quasi-isotropic coordinates (QIC) that have been used in the past for analyzing different kinds of stationary rotating relativistic systems. Our findings are in agreement with those reported originally by Herdeiro \& Radu ite{Herdeiro2014,Herdeiro2015}. The method is submitted to several analytic and numerical tests, which include the recovery of the Kerr solution in QIC and the cloud solutions in the Kerr background. We report different global quantities that allow us to determine the contribution of the boson hair to the spacetime, as well as relevant quantities at the horizon, like the surface gravity. The latter indicates to what extent the hairy solutions approach the extremal limit, noting that for this kind of solutions the ratio of the angular momentum per squared mass $J_\infty/M^2_{\rm ADM}$ can be larger than unity due to the contribution of the scalar hair, a situation which differs from the Kerr metric where this parameter is bounded according to $0\leq |J/M^2| \leq 1$ with the upper bound corresponding to the extremal case., Comment: 28 pages, 36 figures

The design of Microprocessors Computer Architectures remains as a fundamental course in Computer Science and Computer Engineering. The technology and organization inside microprocessors have changed quite fast in the last twenty years. That change has increased the information handled in class, difficulting the teaching/learning process among students. Although there are tools, mainly simulators, available to exemplify abstract concepts during the course, these tools have not come along with the technology. The computer architecture group of the Centro de Investigaci\'on en Computaci\'on at the IPN Mexico is working on a project called Lagarto to create an open computing platform for research and education to simplify the understanding of fundamental concepts involved in computer architecture and operating systems. This paper introduces Lagarto, our soft-core-processor micro-architecture. It has a scalar pipeline structure and executes a full MIPS 32 R6 ISA [9] [10] and includes an MMU to support modern Operative Systems. The complete design has been described using Verilog HDL and is fully synthesizable in an FPGA. Additionally, this work shows different ways to use and test the microprocessor with codes written in either assembly language or C language. We show that the Lagarto project allows students to incorporate during the course not only the traditional model of visualizing theoretical knowledge in a practical exercise through simulators but also integrate into the teaching process the RTL design to build the Microprocessor Architecture., Comment: in Spanish. Research in Computing Science. https://www.rcs.cic.ipn.mx/2017_137/Lagarto%20I%20-%20Una%20plataforma%20hardware_software%20de%20arquitectura%20de%20computadoras%20para%20la%20academia.pdf

Chiral transition-metal complexes are of interest in many fields ranging from asymmetric catalysis and molecular materials science to optoelectronic applications or fundamental physics including parity violation effects. We present here a combined theoretical and experimental investigation of gas-phase valence-shell photoelectron circular dichroism (PECD) on the challenging open-shell ruthenium(iii)-tris-(acetylacetonato) complex, Ru(acac)$_3$. Enantiomerically pure $\Delta$- or $\Lambda$-Ru(acac)$_3$, characterized by electronic circular dichroism (ECD), were vaporized and adiabatically expanded to produce a supersonic beam and photoionized by circularly-polarized VUV light from the DESIRS beamline at Synchrotron SOLEIL. Photoelectron spectroscopy (PES) and PECD experiments were conducted using a double imaging electron/ion coincidence spectrometer, and compared to density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The open-shell character of Ru(acac)$_3$, which is not taken into account in our DFT approach, is expected to give rise to a wide multiplet structure, which is not resolved in our PES signals but whose presence might be inferred from the additional striking features observed in the PECD curves. Nevertheless, the DFT-based assignment of the electronic bands leads to the characterisation of the ionized orbitals. In line with other recent works, the results confirm that PECD persists independently on the localization and/or on the achiral or chiral nature of the initial orbital, but is rather a probe of the molecular potential as a whole. Overall, the measured PECD signals on Ru(acac)$_3$, a system exhibiting D$_3$ propeller-type chirality, are of similar magnitude compared to those on asymmetric-carbon-based chiral organic molecules which constitute the vast majority of species investigated so far, thus suggesting that PECD is a universal mechanism, inherent to any type of chirality.

In this work we reanalyze the possibility of finding bound states (scalar clouds) of a test, charged and complex-valued scalar field with mass and charge q in the background of a Reissner-Nordstrom black hole (RNBH). In order to determine the existence of such scalar clouds we impose suitable regularity conditions for the scalar field at the event horizon. We find numerical evidence for the absence of such clouds in the subextremal and extremal RNBH when the field is massive but not self-interacting. More importantly, we put forward a theorem that proves that such clouds cannot exist. On the other hand, when a suitable self-interacting potential is included, the theorem no longer applies, providing a heuristic justification behind the existence of charged clouds (Q-clouds) that were reported recently., Comment: 14 pages, 14 figures

We review experimental and theoretical cross sections for electron transport in $\alpha$-tetrahydrofurfuryl alcohol (THFA) and, in doing so, propose a plausible complete set. To assess the accuracy and self-consistency of our proposed set, we use the pulsed-Townsend technique to measure drift velocities, longitudinal diffusion coefficients and effective Townsend first ionisation coefficients for electron swarms in admixtures of THFA in argon, across a range of density-reduced electric fields from 1 Td to 450 Td. These measurements are then compared to simulated values derived from our proposed set using a multi-term solution of Boltzmann's equation. We observe discrepancies between the simulation and experiment, which we attempt to address by employing a neural network model that is trained to solve the inverse swarm problem of unfolding the cross sections underpinning our experimental swarm measurements. What results from our neural network-based analysis is a refined set of electron-THFA cross sections, which we confirm is of higher consistency with our swarm measurements than that we initially proposed. We also use our data base to calculate electron transport coefficients in pure THFA, across a range of reduced electric fields from 0.001 Td to 10,000 Td., Comment: 37 pages, 19 figures, submitted to The Journal of Chemical Physics

A new instrument dedicated to the kinetic study of low-temperature gas phase neutral-neutral reactions, including clustering processes, is presented. It combines a supersonic flow reactor with Vacuum Ultra-Violet (VUV) synchrotron photoionization time of flight mass spectrometry. A photoion-photoelectron coincidence detection scheme has been adopted to optimize the particle counting efficiency. The characteristics of the instrument are detailed along with its capabilities illustrated through a few results obtained at low temperatures (< 100 K) including a {photoionization spectrum} of n-butane, the detection of formic acid dimer formation as well as the observation of diacetylene molecules formed by the reaction between the C$_2$H radical and C$_2$H$_2$.

We propose a simple approach to optimally select the number of control units in k nearest neighbors (kNN) algorithm focusing in minimizing the mean squared error for the average treatment effects. Our approach is non-parametric where confidence intervals for the treatment effects were calculated using asymptotic results with bias correction. Simulation exercises show that our approach gets relative small mean squared errors, and a balance between confidence intervals length and type I error. We analyzed the average treatment effects on treated (ATET) of participation in 401(k) plans on accumulated net financial assets confirming significant effects on amount and positive probability of net asset. Our optimal k selection produces significant narrower ATET confidence intervals compared with common practice of using k=1., Comment: 24 pages, 13 figures, 5 tables

We present a set of self-consistent cross sections for electron transport in gaseous tetrahydrofuran (THF), that refines the set published in our previous study [J. de Urquijo et al., J. Chem. Phys. 151, 054309 (2019)] by proposing modifications to the quasielastic momentum transfer, neutral dissociation, ionisation and electron attachment cross sections. These adjustments are made through the analysis of pulsed-Townsend swarm transport coefficients, for electron transport in pure THF and in mixtures of THF with argon. To automate this analysis, we employ a neural network model that is trained to solve this inverse swarm problem for realistic cross sections from the LXCat project. The accuracy, completeness and self-consistency of the proposed refined THF cross section set is assessed by comparing the analysed swarm transport coefficient measurements to those simulated via the numerical solution of Boltzmann's equation., Comment: 20 pages, 8 figures, submitted to Plasma Sources Science and Technology

We argue about the (non) existence of {\it superregular} scalar clouds (i.e., bound states of a massive and complex-valued scalar field $\Psi$) around exact {\it extremal} ($a = M$) Kerr black holes (BH's) possessing {\it bounded radial derivatives at the horizon} (in Boyer-Lindquist coordinates) as opposed to similar cloud solutions that exist but with unbounded derivatives in the same coordinate system. The latter solutions have been reported recently both analytically and numerically. The superregular clouds cannot be obtained from the regular clouds around subextremal Kerr BH's ($|a|< M$) in the limit of extremality $(a\rightarrow M)$ as in this limit the radial derivatives of $\Psi$ at the horizon $r_H$ diverge when $r_H\rightarrow r_H^{\rm ext}:=M=a$, thus, such superregular clouds must be analyzed separately. We conclude that the superregular clouds, which are found in the {\it exact} extremal scenario ($a = M$), are not continuously connected with the regular ones in the limit of extremality $(a\rightarrow M)$. Remarkably, the spectrum leading to the existence of the radial part of the full solution of these superregular clouds (which obeys a Teukolsky equation) is given by the exact formula $M=a=\frac{1}{2\mu}\sqrt{m^2 + \left[-\kappa+\sqrt{\kappa^2+m^2}\,\right]^2}$, which depends on three (positive) integers: the principal number $n$, the {\it magnetic number} $m$, and an integer $j$, related with the {\it type} of regularity at the horizon. Here $\kappa= j +n$, and $\mu$ is the mass associated with $\Psi$. This spectrum depends implicitly on the {\it orbital} number $l$, an integer number that determines the existence of well behaved spheroidal harmonics which are associated with the angular part of the cloud solution. Since the separation constants that are obtained from the superregularity conditions in the radial part of the solution do {\it not} coincide in general with the standard separation constants required for the spheroidal harmonics to be well behaved on the axis of symmetry, we conclude that non-trivial boson clouds having such superregularity conditions cannot exist in the background of an exact extremal Kerr BH. The only exception to this conclusion is in the limit $n\rightarrow \infty$ and $m\ll n$. In such a large $n$ limit consistency in the separation constants leads to a quadratic Diophantine equation of Pell's type for the integer numbers $(l,m)$. Such Pell's equation can be readily solved using standard techniques. In that instance well behaved spheroidal harmonics are obtained, and thus, well behaved non-trivial superregular clouds can be computed. Of course, this situation, does not preclude the existence of other kind of smooth cloud solutions for any other $n$, not necessarily large (e.g. clouds with a non-integer $\kappa$) when using a better behaved coordinate system at the horizon (e.g. Wheeler's tortoise coordinate or proper radial distance)., Comment: 16 pages and 14 figures

The perspective is advanced that the time parameter in quantum mechanics corresponds to the time coordinate in a Minkowski flat spacetime local approximation to the actual dynamical curved spacetime of General Relativity, rather than to an external Newtonian reference frame. There is no incompatibility, as generally assumed in the extensively discussed "problem of time" in Quantum Gravity., Comment: 5 pages

Thanks to the Cassini Huygens mission, it is now established that the first aerosols in Titan s upper atmosphere are found from an altitude of about 1200 km. Once they are formed and through their descent towards the surface, these nanoparticles are submitted to persistent Far Ultra-Violet (FUV) radiation that can reach lower atmospheric layers. Such an interaction has an impact, especially on the chemistry and charge budget of the atmospheric compounds. Models are useful to understand this photoprocessing, but they lack important input data such as the photoemission threshold or the absolute photoabsorption/emission cross sections of the aerosols. In order to quantify the photoemission processes, analogs of Titan s aerosols have been studied with the DESIRS FUV beamline at the synchrotron SOLEIL as isolated substrate-free nanoparticles. We present here the corresponding ARPES (Angle-Resolved PhotoElectron Spectroscopy) data recorded at different FUV photon energies. The results show a very low photoionization threshold (6.0 +/- 0.1 eV~ 207 nm) and very high absolute ionization cross sections (~106 Mb) indicating that FUV photoemission from aerosols is an intense source of slow electrons which has to be taken into account in photochemical models of Titan s atmosphere.

We show that the integral method used to prove the no-hair theorem for Black Holes (BH's) in spherically symmetric and static spacetimes within the framework of general relativity with matter composed by a complex-valued scalar-field does not lead to a straightforward conclusion about the absence of hair in the stationary and rotating (axisymmetric) scenario. We argue that such a failure can be used to justify in a simple and heuristic way the existence of non-trivial boson clouds or hair found numerically by Herdeiro and Radu [1,2] and analytically by Hod in the test field limit [3-5]. This is due to the presence of a contribution that is negative when rotation exists which allows for an integral to vanish even when a non-trivial boson hair is present. The presence of such a negative contribution that depends on the rotation properties of the BH is perfectly correlated with the eigenvalue problem associated with the boson-field equation. Conversely, when the rotation is absent the integral turns to be composed only by non negative (i.e. positive semidefinite) terms and thus the only way it can vanish is when the hair is completely absent. This analysis poses serious challenges and obstructions towards the elaboration of no-hair theorems for more general spacetimes endowed with a BH region even when including matter fields that obey the energy conditions. Thus rotating boson stars, if collapsed, may lead indeed to a new type of rotating BH, like the ones found in [1,2]. In order to achieve this analysis we solve numerically the eigenvalue problem for the boson field in the Kerr-BH background by imposing rigorous regularity conditions at the BH horizon for the non-extremal case ($0