Rotating "Black Holes" with Holes in the Horizon

Kerr-Schild solutions of the Einstein-Maxwell field equations, containing semi-infinite axial singular lines, are investigated. It is shown that axial singularities break up the black hole, forming holes in the horizon. As a result, a tube-like region appears which allows matter to escape from the interior without crossing the horizon. It is argued that axial singularities of this kind, leading to very narrow beams, can be created in black holes by external electromagnetic or gravitational excitations and may be at the origin of astrophysically observable effects such as jet formation.Comment: Revtex, 6 pages, 3 figures. Corrected version. To appear in Phys Rev D, Rapid Communication

Theoretical framework for quantum networks

We present a framework to treat quantum networks and all possible transformations thereof, including as special cases all possible manipulations of quantum states, measurements, and channels, such as, e.g., cloning, discrimination, estimation, and tomography. Our framework is based on the concepts of quantum comb-which describes all transformations achievable by a given quantum network-and link product-the operation of connecting two quantum networks. Quantum networks are treated both from a constructive point of view-based on connections of elementary circuits-and from an axiomatic one-based on a hierarchy of admissible quantum maps. In the axiomatic context a fundamental property is shown, which we call universality of quantum memory channels: any admissible transformation of quantum networks can be realized by a suitable sequence of memory channels. The open problem whether this property fails for some nonquantum theory, e.g., for no-signaling boxes, is posed.Comment: 23 pages, revtex

New mathematical framework for spherical gravitational collapse

A theorem, giving necessary and sufficient condition for naked singularity formation in spherically symmetric non static spacetimes under hypotheses of physical acceptability, is formulated and proved. The theorem relates existence of singular null geodesics to existence of regular curves which are super-solutions of the radial null geodesic equation, and allows us to treat all the known examples of naked singularities from a unified viewpoint. New examples are also found using this approach, and perspectives are discussed.Comment: 8 pages, LaTeX2

Statistics of non-linear stochastic dynamical systems under L\'evy noises by a convolution quadrature approach

This paper describes a novel numerical approach to find the statistics of the non-stationary response of scalar non-linear systems excited by L\'evy white noises. The proposed numerical procedure relies on the introduction of an integral transform of Wiener-Hopf type into the equation governing the characteristic function. Once this equation is rewritten as partial integro-differential equation, it is then solved by applying the method of convolution quadrature originally proposed by Lubich, here extended to deal with this particular integral transform. The proposed approach is relevant for two reasons: 1) Statistics of systems with several different drift terms can be handled in an efficient way, independently from the kind of white noise; 2) The particular form of Wiener-Hopf integral transform and its numerical evaluation, both introduced in this study, are generalizations of fractional integro-differential operators of potential type and Gr\"unwald-Letnikov fractional derivatives, respectively.Comment: 20 pages, 5 figure

Dreaming Characteristics in Non-Rapid Eye Movement Parasomnia and Idiopathic Rapid Eye Movement Sleep Behaviour Disorder: Similarities and Differences

Background: Speech graph analysis (SGA) of dreams has recently shown promise as an objective and language-invariant diagnostic tool that can aid neuropsychiatric diagnosis. Whilst the notion that dreaming mentations reflect distinct physiologic processes is not new, such studies in patients with sleep disorders remain exceptionally scarce. Here, using SGA and other dream content analyses, we set to investigate structural and thematic differences in morning dream recalls of patients diagnosed with Non-Rapid Eye Movement Parasomnia (NREMP) and Idiopathic REM Sleep Behavior Disorder (iRBD). Methods: A retrospective cross-sectional study of morning dream recalls of iRBD and NREMP patients was undertaken. Traditional dream content analyses, such as Orlinsky and Hall and Van de Castle analyses, were initially conducted. Subsequently, SGA was performed in order to objectively quantify structural speech differences between the dream recalls of the two patient groups. Results: Comparable rate of morning recall of dreams in the sleep laboratory was recorded; 25% of iRBD and 18.35% of NREMP patients. Aggression in dreams was recorded by 28.57% iRBD versus 20.00% in NREMP group. iRBD patients were more likely to recall dreams (iRBD vs NREMP; P = 0.007), but they also had more white dreams, ie having a feeling of having dreamt, but with no memory of it. Visual and quantitative graph speech analyses of iRBD dreams suggested stable sequential structure, reflecting the linearity of the chronological narrative. Conversely, NREMP dream reports displayed more recursive, less stable systems, with significantly higher scores of graph connectivity measures. Conclusion: The findings of our exploratory study suggest that iRBD and NREMP patients may not only differ on what is recalled in their dreams but also, perhaps more strikingly, on how dreams are recalled. It is hoped that future SGA-led dream investigations of larger groups of patients will help discern distinct mechanistic underpinnings and any associated clinical implications

Covariant quantum measurements which maximize the likelihood

We derive the class of covariant measurements which are optimal according to the maximum likelihood criterion. The optimization problem is fully resolved in the case of pure input states, under the physically meaningful hypotheses of unimodularity of the covariance group and measurability of the stability subgroup. The general result is applied to the case of covariant state estimation for finite dimension, and to the Weyl-Heisenberg displacement estimation in infinite dimension. We also consider estimation with multiple copies, and compare collective measurements on identical copies with the scheme of independent measurements on each copy. A "continuous-variables" analogue of the measurement of direction of the angular momentum with two anti-parallel spins by Gisin and Popescu is given.Comment: 8 pages, RevTex style, submitted to Phys. Rev.

Pressure-induced oversaturation and phase transition in zeolitic imidazolate frameworks with remarkable mechanical stability.

Zeolitic imidazolate frameworks (ZIFs) 7 and 9 are excellent candidates for CO2 adsorption and storage. Here, high-pressure X-ray diffraction is used to further understand their potential in realistic industrial applications. ZIF-7 and ZIF-9 are shown be able to withstand high hydrostatic pressures whilst retaining their porosity and structural integrity through a new ferroelastic phase transition. This stability is attributed to the presence of sterically large organic ligands. Results confirm the notable influence of guest occupancy on the response of ZIFs to pressure; oversaturation of ZIFs with solvent molecules greatly decreases their compressibility and increases their resistance to amorphisation. By comparing the behaviours of both ZIFs under high pressure, it is demonstrated that their mechanical stability is not affected by metal substitution. The evacuated ZIF-7 phase, ZIF-7-II, is shown to be able to recover to the ZIF-7 structure with excellent resistance to pressure. Examining the pressure-related structural behaviours of ZIF-7 and ZIF-9, we have assessed the great industrial potential of ZIFs.This work was supported by the Cambridge Commonwealth, European and International Trust; China Scholarship Council; Trinity Hall, University of Cambridge; UK Science & Technology Facilities Council. We thank anonymous reviewers for their valuable suggestions on the improvement of this manuscript.This is the final version of the article. It first appeared from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C4DT02680

Geopolymer Materials for Low-Pressure Injections in Coarse Grained Soil: Multiscale Approach to the Study of the Mechanical Behaviour and Environmental Impact

The term soil improvement is commonly referred to the modification of soil structure in order to obtain a material with better physical and mechanical properties such as strength, stiffness or permeability. With this purpose, one of the most commonly used applications, particularly in coarse-grained soils, is the low pressure injection of cementitious mixtures. In recent years, there has been a growing demand for solutions with limited environmental impact and limited CO2 emissions and, in this regard, the cement present in the injected grout is evidently the weak point of traditional solutions. In this work, the experimental study of geopolymer materials as a substitute of cement mixture for low-pressure injection for coarse-grained soils improvement is presented. The study started with a focus on the geopolymer fresh mixture properties (density, viscosity, horizontal ellipsis ) and the evolution over the time of the mechanical properties (compression and tensile strength and stiffness) comparing three different mix designs at three different monitoring temperatures. The same evaluations were repeated on sand samples injected with the different types of mixtures previously analyzed. For a selected mix design, a permeation test was carried out under controlled conditions to test the pumpability and effectiveness of geopolymer injection. Finally, to deepen the chemical interaction between the injected mixture and interstitial water, an injection test was carried out using a scaled model of a real injection system. The experimental study carried out was aimed both at the analysis of the characteristics of the geopolymer material and at its physical interaction with coarse-grained soil, passing through the measurement of the mechanical characteristics of the geopolymer material and of the solid sand skeleton mixed with geopolymers. Finally, the possible chemical interaction of the mixtures with groundwater was also evaluated in order to highlight any environmental issues. The results shown provide a preliminary but sufficiently broad picture of the behavior of geopolymer mixtures for low-pressure injection for coarse-grained soil improvement purposes both from physical-mechanical and chemical points of view

Ferroelectric precursor behavior in PbSc0.5Ta0.5O3 detected by field-induced resonant piezoelectric spectroscopy

A novel experimental technique, resonant piezoelectric spectroscopy (RPS), has been applied to investigate polar precursor effects in highly (65%) B-site ordered PbSc0.5Ta0.5O3 (PST), which undergoes a ferroelectric phase transition near 300 K. The cubic-rhombohedral transition is weakly first order, with a coexistence interval of ∼4 K, and is accompanied by a significant elastic anomaly over a wide temperature interval. Precursor polarity in the cubic phase was detected as elastic vibrations generated by local piezoelectric excitations in the frequency range 250–710 kHz. The RPS resonance frequencies follow exactly the frequencies of elastic resonances generated by conventional resonant ultrasound spectroscopy (RUS) but RPS signals disappear on heating beyond an onset temperature, Tonset, of 425 K. Differences between the RPS and RUS responses can be understood if the PST structure in the precursor regime between Tonset and the transition point, Ttrans=300 K, has locally polar symmetry even while it remains macroscopically cubic. It is proposed that this precursor behavior could involve the development of a tweed microstructure arising by coupling between strain and multiple order parameters, which can be understood from the perspective of Landau theory. As a function of temperature the transition is driven by the polar displacement P and the order parameter for cation ordering on the crystallographic B site Qod. Results in the literature show that, as a function of pressure, there is a separate instability driven by octahedral tilting for which the assigned order parameter is Q. The two mainly displacive order parameters, P and Q, are unfavorably coupled via a biquadratic term Q2P2, and complex tweedlike fluctuations in the precursor regime would be expected to combine aspects of all the order parameters. This would be different from the development of polar nanoregions, which are more usually evoked to explain relaxor ferroelectric behavior, such as occurs in PST with a lower degree of B-site order

A systematic review of manic/hypomanic and depressive switches in patients with bipolar disorder in naturalistic settings: The role of antidepressant and antipsychotic drugs

The present systematic review was aimed at critically summarizing the evidence about treatmentemergent manic/hypomanic and depressive switches during the course of bipolar disorder (BD). A systematic search of the MEDLINE, EMBASE, CINAHL, Web of Science, and PsycInfo electronic databases was conducted until March 24th , 2021, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Observational studies clearly reporting data regarding the prevalence of treatment-emergent mood switches in patients with BD were considered for inclusion. Thirty-two original studies met the inclusion criteria. In the majority of cases, manic switches were analyzed; only 3 papers investigated depressive switches in type I BD. Treatment-emergent mania/hypomania in BD subjects ranged from 17.3% to 48.8% and was more frequent with antidepressant monotherapy compared to combination treatment with mood stabilizers, especially lithium, or second-generation antipsychotics. A higher likelihood of mood switch has been reported with tricyclics and a lower rate with bupropion. Depressive switches were detected in 5-16% of type I BD subjects and were associated with first-generation antipsychotic use, the concomitant use of first- and second-generation antipsychotics, and benzodiazepines. The included studies presented considerable methodological heterogeneity, small sample sizes and comparability flaws. In conclusion, many studies, although heterogeneous and partly discordant, have been conducted on manic/hypomanic switches, whereas depressive switches during treatment with antipsychotics are poorly investigated. In BD subjects, both antidepressant and antipsychotic medications seems to play a role in the occurrence of mood switches, although the effects of different pharmacological compounds have yet to be fully investigated