Isocausal spacetimes may have different causal boundaries

We construct an example which shows that two isocausal spacetimes, in the sense introduced by Garc\'ia-Parrado and Senovilla, may have c-boundaries which are not equal (more precisely, not equivalent, as no bijection between the completions can preserve all the binary relations induced by causality). This example also suggests that isocausality can be useful for the understanding and computation of the c-boundary.Comment: Minor modifications, including the title, which matches now with the published version. 12 pages, 3 figure

Full two-photon downconversion of just a single photon

We demonstrate, both numerically and analytically, that it is possible to generate two photons from one and only one photon. We characterize the output two photon field and make our calculations close to reality by including losses. Our proposal relies on real or artificial three-level atoms with a cyclic transition strongly coupled to a one-dimensional waveguide. We show that close to perfect downconversion with efficiency over 99% is reachable using state-of-the-art Waveguide QED architectures such as photonic crystals or superconducting circuits. In particular, we sketch an implementation in circuit QED, where the three level atom is a transmon

Historical floods in the southeastern Iberian Peninsula since the 16th century: Trends and regional analysis of extreme flood events

Studies related to historical floods have generated much knowledge about flood patterns and frequencies in recent years. Extending the series of floods to a longer range of time allows society to clarify what has happened in the past, and thus know what may happen in the future. From the descriptions of primary and secondary sources, a classification of historical floods has been carried out following a method specifically adapted for the study area. The southeastern Iberian Peninsula is the last region to compile historical floods in the Mediterranean Iberian Peninsula. Therefore, the main objective of the present study is to extend the flood series of historical events for four river basins: the Almanzora, Antas, Aguas and Andarax. First, flood events are classified according to their descriptions, generating a dataset of all flood events from 1500 to the present day for each basin. Second, we analyze the trends in the historical series, identifying four trend periods linked with the availability of records: 1500–1850, 1850–1900, 1900–1955 and 1955–2000. Notably, the trend in recent decades has broken with normality because of the large number of lower magnitude events. Lastly, we compare our dataset with seven historical series from different rivers elsewhere in the Iberian Peninsula. The results show a high correlation with all southeastern basins and less with the northern and Atlantic basins. For the purposes of the analysis, we considered only the extraordinary and catastrophic floods in all basins, that is, the floods of magnitude 3 or 4 (M3 or M4), and we identified two flood gaps in 1500–1540 and 1660–1720; two flood-poor periods in 1790–1845 and 1955–1970; and five flood-rich periods in 1540–1560, 1610–1654, 1720–1745, 1860–1891 and 1970–1990 in relation to the four river basins in the study area and the other seven Iberian basins, the last century is highly biased by the construction of reservoirs in all basins. The analysis of historical floods shows a link between the flood-gap periods and negative phases of NAOi and TSI. From 1970, lower flood magnitudes occurred during periods of highest amounts of information, an increase in tourism areas. Consequently, the last flood-rich period clearly stands out because of the disparity of the data, and the consequences are biased, for example, by surface runoff in urban areas where non-irrigated agricultural areas were traditionally located, resulting in an increase in economic damage

Computability of the causal boundary by using isocausality

Recently, a new viewpoint on the classical c-boundary in Mathematical Relativity has been developed, the relations of this boundary with the conformal one and other classical boundaries have been analyzed, and its computation in some classes of spacetimes, as the standard stationary ones, has been carried out. In the present paper, we consider the notion of isocausality given by Garc\'ia-Parrado and Senovilla, and introduce a framework to carry out isocausal comparisons with standard stationary spacetimes. As a consequence, the qualitative behavior of the c-boundary (at the three levels: point set, chronology and topology) of a wide class of spacetimes, is obtained.Comment: 44 pages, 5 Figures, latex. Version with minor changes and the inclusion of Figure

Recent ASDEX Upgrade research in support of ITER and DEMO

Recent experiments on the ASDEX Upgrade tokamak aim at improving the physics base for ITER and DEMO to aid the machine design and prepare efficient operation. Type I edge localized mode (ELM) mitigation using resonant magnetic perturbations (RMPs) has been shown at low pedestal collisionality ( ν ∗ ped < 0 . 4 ) . In contrast to the previous high ν ∗ regime, suppression only occurs in a narrow RMP spectral window, indicating a resonant process, and a concomitant confinement drop is observed due to a reduction of pedestal top density and electron temperature. Strong evidence is found for the ion heat flux to be the decisive element for the L–H power threshold. A physics based scaling of the density at which the minimum P LH occurs indicates that ITER could take advantage of it to initiate H-mode at lower density than that of the final Q = 10 operational point. Core density fluctuation measurements resolved in radius and wave number show that an increase of R/L T e introduced by off-axis electron cyclotron resonance heating (ECRH) mainly increases the large scale fluctuations. The radial variation of the fluctuation level is in agreement with simulations using the GENE code. Fast particles are shown to undergo classical slowing down in the absence of large scale magnetohydrodynamic (MHD) events and for low heating power, but show signs of anomalous radial redistribution at large heating power, consistent with a broadened off-axis neutral beam current drive current profile under these conditions. Neoclassical tearing mode (NTM) suppression experiments using electron cyclotron current drive (ECCD) with feedback controlled deposition have allowed to test several control strategies for ITER, including automated control of (3,2) and (2,1) NTMs during a single discharge. Disruption mitigation studies using massive gas injection (MGI) can show an increased fuelling efficiency with high field side injection, but a saturation of the fuelling efficiency is observed at high injected mass as needed for runaway electron suppression. Large locked modes can significantly decrease the fuelling efficiency and increase the asymmetry of radiated power during MGI mitigation. Concerning power exhaust, the partially detached ITER divertor scenario has been demonstrated at P sep /R = 10 MW m − 1 in ASDEX Upgrade, with a peak time averaged target load around 5MWm − 2 , well consistent with the component limits for ITER. Developing this towards DEMO, full detachment was achieved at P sep /R = 7MWm − 1 and stationary discharges with core radiation fraction of the order of DEMO requirements (70% instead of the 30% needed for ITER) were demonstrated. Finally, it remains difficult to establish the standard ITER Q = 10 scenario at low q 95 = 3 in the all-tungsten (all-W) ASDEX Upgrade due to the observed poor confinement at low β N . This is mainly due to a degraded pedestal performance and hence investigations at shifting the operational point to higher β N by lowering the current have been started. At higher q 95 , pedestal performance can be recovered by seeding N 2 as well as CD 4 , which is interpreted as improved pedestal stability due to the decrease of bootstrap current with increasing Z eff . Concerning advanced scenarios, the upgrade of ECRH power has allowed experiments with central ctr-ECCD to modify the q -profile in improved H-mode scenarios, showing an increase in confinement at still good MHD stability with flat elevated q -profiles at values between 1.5 and 2.European Commission (EUROfusion 633053

Deep into the Water Fountains: The case of IRAS 18043-2116

(Abridged) The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Here we report the results of the observations towards the WF nebula IRAS 18043$-$2116: Detection of radio continuum emission in the frequency range 1.5GHz - 8.0GHz; H$_{2}$O maser spectral features and radio continuum emission detected at 22GHz, and H$_{2}$ ro-vibrational emission lines detected at the near infrared. The high-velocity H$_{2}$O maser spectral features, and the shock-excited H$_{2}$ emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H$_{2}$ column density, we estimated a molecular mass-loss rate of the order of $10^{-9}$M$_{\odot}$yr$^{-1}$. On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10$^{-5}$M$_{\odot}$yr$^{-1}$. The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.Comment: 10 pages, 5 figures. Accepted for publication in A&