Origin of pulsed emission from the young supernova remnant SN 1987A

To overcome difficulties in understanding the origin of the submillisecond optical pulses from SN 1987A a model similar to that of Kundt and Krotscheck for pulsed synchrotron emission from the Crab was applied. The interaction of the expected ultrarelativistic e(sup + or -) pulsar wind with the pulsar dipole electromagnetic wave reflected from the walls of a pulsar cavity within the SN 1987A nubula can generate pulsed optical emission with efficiency at most eta(sub max) is approximately equal to 10(exp -3). The maximum luminosity of the source is reproduced and other observational constraints can be satisfied for an average wind energy flow is approximately equal to 10(exp 38) erg/(s steradian) and for electron Lorentz factor gamma is approximately equal to 10(exp 5). This model applied to the Crab yields pulsations of much lower luminosity and frequency

GRO: Black hole models for gamma-ray bursts

The possibility of creating gamma ray bursts (GRB's) from accretion flows on to black holes is investigated. The mechanism of initial energy release in the form of a burst is not understood yet. The typical time scales involved in this energy release and the initial distribution of photons as a function of energy are studied. As a first step the problem is formulated in the Minkowski spacetime for a homogeneous and isotropic burst. For an arbitrary initial distribution of photons, the equations of relativistic kinetic theory are formulated for nonequilibrium plasmas which can take into account various particle creation and annihilation processes and various scattering processes

Does mass accretion lead to field decay in neutron stars

The recent discovery of cyclotron lines from gamma-ray bursts indicates that the strong magnetic fields of isolated neutron stars might not decay. The possible inverse correlation between the strength of the magnetic field and the mass accreted by the neutron star suggests that mass accretion itself may lead to the decay of the magnetic field. The spin and magnetic field evolution of the neutron star was calculated under the hypothesis of the accretion-induced field decay. It is shown that the calculated results are consistent with the observations of binary and millisecond radio pulsars

Non-thermal radiative pair plasmas: processes and spectra

We study the emission and absorption spectra due to various photon and pair processes in a non-equilibrium pair plasma containing a significant density of photons. We present here some preliminary results from Monte-Carlo simulations. These investigations are likely to be useful in understanding the radiation and relaxation mechanisms in non-thermal gamma-ray sources in astrophysics.Comment: 5 pages, uuencoded postscript fil

Does SN 1987A contain a rapidly vibrating neutron star

If the recently reported 0.5 ms-period pulsed optical signal from the direction of Supernova 1987A originated in a young neutron star, its interpretation as a rotational period has difficulties. The surface magnetic field would have to be much lower than expected, and the high rotation rate may rule out preferred nuclear equations of state. It is pointed out here that a remnant radial vibration of a neutron star, excited in the supernova event, may survive for several years with about the observed (gravitationally redshifted) period. Heavy ions at the low-density stellar surface, periodically shocked by the vibration, may efficiently produce narrow pulses of optical cyclotron radiation in a surface field of about a trillion gauss

FIND: A Function Description Benchmark for Evaluating Interpretability Methods

Labeling neural network submodules with human-legible descriptions is useful for many downstream tasks: such descriptions can surface failures, guide interventions, and perhaps even explain important model behaviors. To date, most mechanistic descriptions of trained networks have involved small models, narrowly delimited phenomena, and large amounts of human labor. Labeling all human-interpretable sub-computations in models of increasing size and complexity will almost certainly require tools that can generate and validate descriptions automatically. Recently, techniques that use learned models in-the-loop for labeling have begun to gain traction, but methods for evaluating their efficacy are limited and ad-hoc. How should we validate and compare open-ended labeling tools? This paper introduces FIND (Function INterpretation and Description), a benchmark suite for evaluating the building blocks of automated interpretability methods. FIND contains functions that resemble components of trained neural networks, and accompanying descriptions of the kind we seek to generate. The functions span textual and numeric domains, and involve a range of real-world complexities. We evaluate methods that use pretrained language models (LMs) to produce descriptions of function behavior in natural language and code. Additionally, we introduce a new interactive method in which an Automated Interpretability Agent (AIA) generates function descriptions. We find that an AIA, built from an LM with black-box access to functions, can infer function structure, acting as a scientist by forming hypotheses, proposing experiments, and updating descriptions in light of new data. However, AIA descriptions tend to capture global function behavior and miss local details. These results suggest that FIND will be useful for evaluating more sophisticated interpretability methods before they are applied to real-world models.Comment: 28 pages, 10 figure

Kinetics of electron-positron pair plasmas using an adaptive Monte Carlo method

A new algorithm for implementing the adaptive Monte Carlo method is given. It is used to solve the relativistic Boltzmann equations that describe the time evolution of a nonequilibrium electron-positron pair plasma containing high-energy photons and pairs. The collision kernels for the photons as well as pairs are constructed for Compton scattering, pair annihilation and creation, bremsstrahlung, and Bhabha & Moller scattering. For a homogeneous and isotropic plasma, analytical equilibrium solutions are obtained in terms of the initial conditions. For two non-equilibrium models, the time evolution of the photon and pair spectra is determined using the new method. The asymptotic numerical solutions are found to be in a good agreement with the analytical equilibrium states. Astrophysical applications of this scheme are discussed.Comment: 43 pages, 7 postscript figures, to appear in the Astrophysical Journa

Development of SYK NanoBRET cellular target engagement assays for gain–of–function variants

Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase that is activated by phosphorylation events downstream of FcR, B-cell and T-cell receptors, integrins, and C-type lectin receptors. When the tandem Src homology 2 (SH2) domains of SYK bind to phosphorylated immunoreceptor tyrosine-based activation motifs (pITAMs) contained within these immunoreceptors, or when SYK is phosphorylated in interdomain regions A and B, SYK is activated. SYK gain-of-function (GoF) variants were previously identified in six patients that had higher levels of phosphorylated SYK and phosphorylated downstream proteins JNK and ERK. Furthermore, the increased SYK activation resulted in the clinical manifestation of immune dysregulation, organ inflammation, and a predisposition for lymphoma. The knowledge that the SYK GoF variants have enhanced activity was leveraged to develop a SYK NanoBRET cellular target engagement assay in intact live cells with constructs for the SYK GoF variants. Herein, we developed a potent SYK-targeted NanoBRET tracer using a SYK donated chemical probe, MRL-SYKi, that enabled a NanoBRET cellular target engagement assay for SYK GoF variants, SYK(S550Y), SYK(S550F), and SYK(P342T). We determined that ATP-competitive SYK inhibitors bind potently to these SYK variants in intact live cells. Additionally, we demonstrated that MRL-SYKi can effectively reduce the catalytic activity of SYK variants, and the phosphorylation levels of SYK(S550Y) in an epithelial cell line (SW480) stably expressing SYK(S550Y)

Half a century of amyloids: past, present and future

Amyloid diseases are global epidemics with profound health, social and economic implications and yet remain without a cure. This dire situation calls for research into the origin and pathological manifestations of amyloidosis to stimulate continued development of new therapeutics. In basic science and engineering, the cross-ß architecture has been a constant thread underlying the structural characteristics of pathological and functional amyloids, and realizing that amyloid structures can be both pathological and functional in nature has fuelled innovations in artificial amyloids, whose use today ranges from water purification to 3D printing. At the conclusion of a half century since Eanes and Glenner's seminal study of amyloids in humans, this review commemorates the occasion by documenting the major milestones in amyloid research to date, from the perspectives of structural biology, biophysics, medicine, microbiology, engineering and nanotechnology. We also discuss new challenges and opportunities to drive this interdisciplinary field moving forward. This journal i

SUPERFLUIDITY IN NEUTRON STARS

A des densités ≥ 4.3 x 1011 g/cc, la matière contient probablement des neutrons à la fois dans les noyaux et à l'état libre dans un état superfluide. Selon la valeur du moment de Fermi les nucléons produisent "le trou d'énergie" (nécessaire pour la superfluidité) par une interaction 1S0 (aux densités les moins élevées) ou 3P2 (aux plus hautes densités). Au-dessus de (2-2.4) 1014 g/cc les protons deviennent supraconducteurs, au moment où les noyaux se dissolvent. Les électrons ne deviennent pas superfluides aux températures auxquelles on s'intéresse, mais un condensat de pions peut apparaître aux densités plus élevées. Protons et neutrons foment des réseaux de vortex quantifiés. Les premiers, en réponse à la rotation de l'étoile, les seconds en réponse au champ magnétique. La structure détaillée de ces réseaux dans l'étoile dépend en premier lieu de la température et des profils de densité ainsi que du passé cinématique de l'étoile. La dynamique des vortex fait intervenir les modes cohérents des vortex libres ("ondes sonores"), l'accrochage des axes des vortex sur les noyaux ou leur insertion interstitielle dans le réseau de noyaux et la diffusion des axes des vortex par les sites d'accrochage et par les composants chargés de la matière stellaire. Cette dynamique peut être décrite en termes de particules ponctuelles tant que les vitesses et les forces varient sur des échelles plus grandes que les dimensions d'un vortex et tant que les effets de la frontière sphérique sont petits. Dans la phase 3P2 la dégénérescence du niveau à deux neutrons J = 2 peut conduire à une plus grande complexité dynamique. Les conséquences observationnelles et la confirmation de la superfluidité dans les étoiles à neutrons (pulsars cornme sources X) peuvent être, entre autres : i) les échelles de temps macroscopiques après les "glitch", résultant du couplage entre composantes "normale" et superfluide ; ii) les "glitches" causés par les décrochages des vortex ou par des brisures de croûte dues aux vortex accrochés ; iii) la modulation possible à long terme de la période de rotation par les modes cohérents des vortex ; et iv) les effets gyroscopiques dus à l'accrochage de la vorticité.Matter at densities ≥ 4.3 x 1011 g/cc is expected to contain neutrons both inside and outside of nuclei, which are in a superfluid state. At the relevant Fermi momenta, the effective gap-producing nucleon-nucleon interaction is 1S0 (lower densities) or 3P2 (higher densities). At densities ≥ 2-2.4) x 1014 g/cc the protons become superconducting too, as nuclei dissolve. Electrons are not expected to be superfluid at the relevant temperatures but a pionic Bose condensate may appear at higher densities. Both neutrons and protons form quantized vortex arrays : The first - in response to the stellar rotation, the second - in response to its magnetic field. The detailed structure of these arrays throughout the star depends primarily on the temperature and density profiles and on the kinematic history of the star. Vortex dynamics include coherent ("sound waves") modes of free vortices, pinning of vortex cores onto nuclei or as interstitials in the nuclear lattice and scattering of vortex cores by pinning sites and by the charges stellar components. This dynamics can be described as the dynamics of point particles, as long as velocities and forces vary only on scales larger than the size of vortex cores and as long as effects of the spherical boundary are small. In the 3P2 phase, the degeneracy of the J = 2 two-neutron state may lead to further dynamical complexity. Observational consequences - and confirmation - or the interior superfluid state of neutron stars, both as pulsars and as X-ray sources, can be, among others : (i) The macroscopic "post-glitch" time scales, resulting from coupling between "normal" and superfluid components ; (ii) "glitches" due to unpinning events or to crust breaking by pinning vortices ; (iii) Possible long term modulation in rotation period, resulting from vortex coherent modes ; and (iv) Gyroscopic effects of pinned vorticity