Search

Structured internal representations (cognitive maps) shape cognition, from imagining the future and counterfactual past, to transferring knowledge to new settings. Our understanding of how such representations are formed and maintained in biological and artificial neural networks has grown enormously. The cognitive mapping hypothesis of schizophrenia extends this enquiry to psychiatry, proposing that diverse symptoms - from delusions to conceptual disorganisation - stem from abnormalities in how the brain forms structured representations. These abnormalities may arise from a confluence of neurophysiological perturbations (excitation-inhibition imbalance, resulting in attractor instability and impaired representational capacity), and/or environmental factors such as early life psychosocial stressors (which impinge on representation learning). This proposal thus links knowledge of neural circuit abnormalities, environmental risk factors, and symptoms., Comment: 25 pages, 2 figures, 1 table, 3 boxes. Final accepted version for publication at "Trends in Cognitive Science" 2024

(Abridged) Core-collapse supernova remnants (SNRs) display complex morphologies and asymmetries, reflecting anisotropies from the explosion and early interactions with the circumstellar medium (CSM). Spectral analysis of these remnants can provide critical insights into supernova (SN) engine dynamics, the nature of progenitor stars, and the final stages of stellar evolution, including mass-loss mechanisms in the millennia leading up to the SN. This white paper evaluates the potential of the Line Emission Mapper (LEM), an advanced X-ray probe concept proposed in response to NASA 2023 APEX call, to deliver high-resolution spectra of SNRs. Such capabilities would allow detailed analysis of parent SNe and progenitor stars, currently beyond our possibilities. We employed a hydrodynamic model that simulates the evolution of a neutrino-driven SN from core-collapse to a 2000-year-old mature remnant. This model successfully replicates the large-scale properties of Cassiopeia A at an age of about 350 years. Using this model, we synthesized mock LEM spectra from different regions of the SNR, considering factors like line shifts and broadening due to plasma bulk motion and thermal ion motion, deviations from ionization and temperature equilibrium, and interstellar medium absorption. Analyzing these mock spectra with standard tools revealed LEM impressive capabilities. We demonstrated that fitting these spectra with plasma models accurately recovers the line-of-sight velocity of the ejecta, enabling 3D structure exploration of shocked ejecta, similar to optical methods. LEM also distinguishes between Doppler and thermal broadening of ion lines and measures ion temperatures near the limb of SNRs, providing insights into ion heating at shock fronts and cooling in post-shock flows. This study highlights LEM potential to advance our understanding of core-collapse SN dynamics and related processes., Comment: 15 pages, 6 figures. White Paper for the Line Emission Mapper (LEM) X-ray Probe concept proposed in response to NASA's 2023 APEX call. Comments are welcome

A model of the TU Muscae binary system has been developed by a study of 23 SWP spectrophotometric images obtained with the IUE satellite telescope and downloaded from the IUE Archive. The images are well distributed in Keplerian orbital phase thereby permitting a simultaneous fitting of the C IV wind-line profile by the SEI method and the light curve for the same bandpass by means of a program similar to that of Wilson and Devinney. The result is a set of parameters characterizing the physical and geometric properties of the wind envelopes surrounding the stars. Surprisingly, there is no evidence for a P Cygni profile or strong, distinguishable shock front in the system, as has been found for similar investigations of EM Carinae and HD159176. This is probably a result of the contact nature of the binary and the high temperature environment of such a shock. That is, most of the carbon ions in the shock are more highly ionized. Based on the parameters for the SEI fit to the C IV profile, the value for the ionization fraction of C IV in the wind was calculated to be 10-4. With this value, the mass loss rate calculated from two independent equations, was found to be about 10-6 solar masses/yr. The line blanketing or metallicity was found to be erratically variable with orbital phase and time, indicating a variable amount of fast moving, dense clouds in the winds and/or a great amount of turbulence. The meaning of rotational velocities for the stars is problematic and depends on what point on the photospheres one is considering., Comment: 21 pages, 9 figures, 3 tables, appendix

Operator-splitting methods are widespread in the numerical solution of differential equations, especially the initial-value problems in ordinary differential equations that arise from a method-of-lines discretization of partial differential equations. Such problems can often be solved more effectively by treating the various terms individually with specialized methods rather than simultaneously in a monolithic fashion. This paper describes \pythOS, a Python software library for the systematic solution of differential equations by operator-splitting methods. The functionality of \pythOS\ focuses on fractional-step methods, including those with real and complex coefficients, but it also implements additive Runge--Kutta methods, generalized additive Runge--Kutta methods, and multi-rate, and multi-rate infinitesimal methods. Experimentation with the solution of practical problems is facilitated through an interface to the \Firedrake\ library for the finite element spatial discretization of partial differential equations and further enhanced by the convenient implementation of exponential time-integration methods and fully implicit Runge--Kutta methods available from the \Irksome\ software library. The functionality of \pythOS\ as well as some less generally appreciated aspects of operator-splitting methods are demonstrated by means of examples.

The use of operator-splitting methods to solve differential equations is widespread, but the methods are generally only defined for a given number of operators, most commonly two. Most operator-splitting methods are not generalizable to problems with $N$ operators for arbitrary $N$. In fact, there are only two known methods that can be applied to general $N$-split problems: the first-order Lie--Trotter (or Godunov) method and the second-order Strang (or Strang--Marchuk) method. In this paper, we derive two second-order operator-splitting methods that also generalize to $N$-split problems. These methods are complex valued but have positive real parts, giving them favorable stability properties, and require few sub-integrations per stage, making them computationally inexpensive. They can also be used as base methods from which to construct higher-order $N$-split operator-splitting methods with positive real parts. We verify the orders of accuracy of these new $N$-split methods and demonstrate their favorable efficiency properties against well-known real-valued operator-splitting methods on both real-valued and complex-valued differential equations.

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec- IFU spectroscopy of the young supernova remnant Cassiopeia A (Cas A). We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the reformation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3 - 5.5 microns) were obtained toward two representative knots in the NE and S fields. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar VI] and relatively weaker, variable strength ejecta lines of [Si IX], [Ca IV], [Ca V] and [Mg IV]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudo-continuum underneath, which is attributed to the high-velocity widths of CO lines. The CO also shows high J lines at different vibrational transitions. Our results with LTE modeling of CO emission indicate a temperature of 1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae, and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe., Comment: accepted for the ApJ letter (17 pages and 10 figures)

The current literature is rather vague regarding how to calculate the exact numerical value of the resonant ion scattering cross-section that should be used for a specific bandpass of finite width. Such a value was needed in order to calculate the ion and mass densities in the shock fronts of hot, close binary star systems. This was done based on a modeling of ultraviolet wind-line profiles, using IUE spectra. Therefore, a numerical integration has been carried out, in wavelength-space, of the exact expression for the cross-section over two band-passes of astrophysical interest. The exact expression employed was that derived from a solution of the Abraham-Lorentz equation. The numerical results depend on the resonant wavelength, which is taken to be at the center of the bandpass. Most texts on the subject derive an expression for the scattering cross-section in frequency-space, based on the assumption that the radiation reaction term in the Abraham-Lorentz equation may be approximated by a resistive term. The integral of this cross-section over the entire spectrum is independent of the resonant frequency, except for the transition probability. This has limited practical use when dealing with fluxes measured in a bandpass of finite width expressed in wavelength units and scattering is the only mechanism for producing the observed fluxes. Such is the case when dealing with the low densities encountered in stellar winds and shock fronts. Integrated cross-sections that depend on the resonant wavelength are used to determine the number and mass densities of C IV and N V ions in the shock fronts found in some hot, eclipsing binary star systems, for which several IUE spectra have been obtained over a Keplerian orbital period. This then leans to a determination of the mass density and total mass in the shock once the volume of the shock is determined., Comment: 11 pages, 4 figures, 4 tables, 16 numbered equations; Derivation of ion scattered stellar flux from binary star shock-fronts; IUE UV light curve fitting; Binary star modelling

In the absence of a parallax distance to a pulsar or a surviving binary in a supernova remnant (SNR), distances to Galactic SNRs are generally very uncertain. However, by combining Gaia data with wide field, multi-fiber echelle spectroscopy, it is now possible to obtain accurate distances to many SNRs with limited extinction by searching for the appearance of high velocity CaII or NaI absorption lines in hot stars as a function of distance. We demonstrate this for the SNR S147 using the spectra of 259 luminous, blue stars. We obtain a median distance of 1.37 kpc (1.30 to 1.47 kpc at 90% confidence) that is consistent with the median parallax distance to the pulsar of 1.46 kpc (1.12 to 2.10 kpc at 90% confidence), but with significantly smaller uncertainties. Our distance is also consistent with the distance to the candidate unbound binary companion in this SNR, HD37424. The presence of high velocity absorption lines is correlated with the emission line flux of the SNR but not with the radio flux., Comment: submitted to ApJ

We determined shock speed in the Galactic supernova remnant Cygnus Loop, using proper motion of its optical filaments and the latest estimate for its distance. The proper motion was measured by comparing H$\alpha$ images of the remnant observed in two epochs: 1993 (Kitt Peak National Observatory) and 2018/2019 (National Astronomical Observatory Rozhen and Astronomical station Vidojevica). We derived shock speed for 35 locations along different filaments, which is twice as much as in earlier studies of north-eastern part of Cygnus Loop. For the first time, we have measured shock speed of radiative filaments in this region. Three of the analyzed locations where we measured proper motion of filaments are radiative, based on their presence in [SII] images from the second epoch. The other filaments are non-radiative. The speed we obtained for the non-radiative filaments is in the range of 240-650 $\mathrm{km\ s^{-1}}$, with an estimate for the uncertainty of 70 $\mathrm{km\ s^{-1}}$. These values are mostly in agreement with previous studies. The radiative filaments have lower speed of 100-160$\pm${70} $\mathrm{km\ s^{-1}}$, which is in agreement with the assumption that they are older in evolutionary terms. This clear distinction between the speed of the two types of filaments proves that the [SII] emission can be used for identifying radiative filaments in supernova remnants., Comment: 10 pqges, published in Serbian Astronomical Journal

Detecting early-stage ovarian cancer accurately and efficiently is crucial for timely treatment. Various methods for early diagnosis have been explored, including a focus on features derived from protein mass spectra, but these tend to overlook the complex interplay across protein expression levels. We propose an innovative method to automate the search for diagnostic features in these spectra by analyzing their inherent scaling characteristics. We compare two techniques for estimating the self-similarity in a signal using the scaling behavior of its wavelet packet decomposition. The methods are applied to the mass spectra using a rolling window approach, yielding a collection of self-similarity indexes that capture protein interactions, potentially indicative of ovarian cancer. Then, the most discriminatory scaling descriptors from this collection are selected for use in classification algorithms. To assess their effectiveness for early diagnosis of ovarian cancer, the techniques are applied to two datasets from the American National Cancer Institute. Comparative evaluation against an existing wavelet-based method shows that one wavelet packet-based technique led to improved diagnostic performance for one of the analyzed datasets (95.67% vs. 96.78% test accuracy, respectively). This highlights the potential of wavelet packet-based methods to capture novel diagnostic information related to ovarian cancer. This innovative approach offers promise for better early detection and improved patient outcomes in ovarian cancer., Comment: 18 pages, 8 figures

We report on the X-ray spectral and spatial evolution of the Symbiotic star R Aqr. Through a multi-epoch observational campaign performed with Chandra between 2017 and 2022, we study the X-ray emission of this binary system, composed of an evolved red giant star and a white dwarf (WD). This analysis is particularly timely as the WD approached the periastron in late 2018/early 2019, thus mass transfer, jet emission and outburst phenomena are to be expected. Through detailed spectral analysis, we detect a significant rise in the soft X-ray (0.5-2 keV) emission of R Aqr, likely linked to jet emission, followed by a decay towards the previous quiescent state. The hard X-ray emission (5-8 keV), is not immediately affected by the periastron passage; the hard component, after maintaining the same flux level between 2017 and 2021, rapidly decays after 2022. Possible explanations for this are a change in the reflection properties of the medium surrounding the binary, obscuration of the central region by material ejected during the periastron passage, or even the partial/complete destruction of the inner regions of the accretion disc surrounding the WD. In addition to this activity in the central region, extended emission is also detected, likely linked to a hot spot in a pre-outburst-emitted jet, which can be observed moving away from the system's central region., Comment: 14 pages, 9 figures, 3 tables. Accepted for publication in ApJ

Gaining insight into the characteristics of epitaxial complex oxide films is essential to control the behavior of devices and catalytic processes. It is known that substrate induced strain, doping, and layer growth can affect the electronic and magnetic properties of the film's bulk. In this study, we demonstrate a clear distinction between the bulk and surface of thin films of La0.67Sr0.33MnO3 in terms of chemical composition, electronic disorder, and surface morphology. We employed a combined experimental approach of X-ray based characterization methods and scanning probe microscopy. X-ray diffraction and resonant X-ray reflectivity revealed surface non-stochiometry in the strontium and lanthanum, as well as an accumulation of oxygen vacancies. Scanning tunneling microscopy showed a staggered growth surface morphology accompanied by an electronic phase separation (EPS) related to this non-stochiometry. The EPS is likely responsible for the temperature-dependent resistivity transition and is a cause of a proposed mixed-phase ferromagnetic and paramagnetic state near room temperature in these thin films., Comment: 31 pages, 10 figures

To reach a long term viable green hydrogen economy, rational design of active oxygen evolution reaction (OER) catalysts is critical. An important hurdle in this reaction originates from the fact that the reactants are singlet molecules, whereas the oxygen molecule has a triplet ground state with parallel spin alignment, implying that magnetic order in the catalyst is essential. Accordingly, multiple experimentalists reported a positive effect of external magnetic fields on OER activity of ferromagnetic catalysts. However, it remains a challenge to investigate the influence of the intrinsic magnetic order on catalytic activity. Here, we tuned the intrinsic magnetic order of epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ thin film model catalysts from ferro- to paramagnetic by changing the temperature in-situ during water electrolysis. Using this strategy, we show that ferromagnetic ordering below the Curie temperature enhances OER activity. Moreover, we show a slight current density enhancement upon application of an external magnetic field and find that the dependence of magnetic field direction correlates with the magnetic anisotropy in the catalyst film. Our work thus suggests that both the intrinsic magnetic order in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films and magnetic domain alignment increase their catalytic activity. We observe no long-range magnetic order at the catalytic surface, implying that the OER enhancement is connected to the magnetic order of the bulk catalyst. Combining the effects found with existing literature, we propose a unifying picture for the spin-polarized enhancement in magnetic oxide catalysts., Comment: The following article will be submitted to Applied Physics Reviews. Main text (incl. references) 19 pages, 8 figures. Supplementary text 9 pages, 13 figures

The proximity and duration of the tidal disruption event (TDE) ASASSN-14li led to the discovery of narrow, blue-shifted absorption lines in X-rays and UV. The gas seen in X-ray absorption is consistent with bound material close to the apocenter of elliptical orbital paths, or with a disk wind similar to those seen in Seyfert-1 active galactic nuclei. We present a new analysis of the deepest high-resolution XMM-Newton and Chandra spectra of ASASSN-14li. Driven by the relative strengths of He-like and H-like charge states, the data require [N/C] > 2.4, in qualitative agreement with UV spectral results. Flows of the kind seen in the X-ray spectrum of ASASSN-14li were not clearly predicted in simulations of TDEs; this left open the possibility that the observed absorption might be tied to gas released in prior AGN activity. However, the abundance pattern revealed in this analysis points to a single star rather than a standard AGN accretion flow comprised of myriad gas contributions. The simplest explanation of the data is likely that a moderately massive star (M ~ 3 Msun) with significant CNO processing was disrupted. An alternative explanation is that a lower mass star was disrupted that had previously been stripped of its envelope. We discuss the strengths and limitations of our analysis and these interpretations., Comment: Accepted for publication in ApJ Letters