Quasi-Periodic Eruptions (QPEs) are extreme high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes in galactic nuclei. It is ...currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole. Here we present the detection of QPEs in two further galaxies, obtained with a blind and systematic search over half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow typical of active nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the newly discovered QPEs are inconsistent with current models that invoke radiation-pressure driven accretion disk instabilities. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the
mass of the secondary object to be much smaller than the main body and future X-ray observations may constrain possible changes in the period due to orbital evolution. This scenario could make QPEs a viable candidate for the electromagnetic counterparts of the so-called extreme mass ratio inspirals, with considerable implications for multi-messenger astrophysics and cosmology.
Quantum discord, a kind of quantum correlation based on entropic measures, is defined as the difference between quantum mutual information and classical correlation in a bipartite system. Procedures ...are available for analytical calculation of discord when one of the parties is a qubit with dimension two and measurements made on it to get that one-way discord. We extend now to systems when both parties are of larger dimension and of interest to qudit–quDit with
d
,
D
≥
3
or spin chains of spins
≥
1
. While recognizing that no universal scheme is feasible, applicable to all density matrices, nevertheless, a procedure similar to that for
d
=
2
that works for many mixed-state density matrices remains of interest as shown by recent such applications. We focus on this method that uses unitary operations to describe measurements, reducing them to a compact form so as to minimize the number of variables needed for extremizing the classical correlation, often the most difficult part of the discord calculation. Results are boiled down to a simple recipe for that extremization; for some classes of density matrices, the procedure even gives trivially the final value of the classical correlation without that extremization. A qutrit–qutrit (
d
=
D
=
3
) system is discussed in detail with specific applications to density matrices for whom other calculations involved difficult numerics. Special attention is given to the so-called
X
-states and Werner and isotropic states when the calculations become particularly simple. An appendix discusses an independent but related question of the systematics of
X
-states of arbitrary dimension. It forms a second, separate, part of this paper, extending our previous group-theoretic considerations of systematics for qubits now to higher
d
.
Objective: Many health sciences librarians enter the profession without specific health sciences training. Some LIS programs have health sciences courses or tracks, but health sciences training ...within an LIS program is only one path to entering health sciences librarianship. To develop a map of pathways into health sciences librarianship, an immersion session at the Medical Library Association conference in 2022 asked health sciences librarians to share how they entered the profession. Methods: The immersion session was structured in three parts: facilitator introductions, small group discussions, and a whole group summary discussion. Guided by questions from the facilitators, small groups discussed what pathways currently exist, how to promote existing pathways, what new pathways should be created, and how to develop and promote pathways that make the profession more equitable, diverse, and inclusive. Results: Through in-the-moment thematic analysis of the small group discussions, the following emerged as key pathways: library school education; internships and practica; the Library and Information Science (LIS) pipeline; on- thejob training; mentoring; self-teaching/hands-on learning; and continuing education. Themes of equity, diversity, and inclusion arose throughout the session, especially in the concluding whole group discussion. Conclusion: Small group discussions in a conference immersion session showed the value of community building in a profession that has multiple pathways for entrance, highlighting the importance of unearthing hidden knowledge about avenues for exploring and enhancing career pathways. The article seeks to address barriers to entry into the profession and adds to the literature on strengthening the field of health sciences librarianship. Keywords: Health sciences librarianship; mentoring; Career Development; Library Staffing; Training; Continuing Education; Internships; LIS programs; self-teaching; Diversity and Inclusion in Libraries
Abstract
Stars that interact with supermassive black holes (SMBHs) can be either completely or partially destroyed by tides. In a partial tidal disruption event (TDE), the high-density core of the ...star remains intact, and the low-density outer envelope of the star is stripped and feeds a luminous accretion episode. The TDE AT 2018fyk, with an inferred black hole mass of 10
7.7±0.4
M
⊙
, experienced an extreme dimming event at X-ray (factor of >6000) and UV (factor of ∼15) wavelengths ∼500–600 days after discovery. Here we report on the reemergence of these emission components roughly 1200 days after discovery. We find that the source properties are similar to those of the predimming accretion state, suggesting that the accretion flow was rejuvenated to a similar state. We propose that a repeated partial TDE, where the partially disrupted star is on an ∼1200 day orbit about the SMBH and periodically stripped of mass during each pericenter passage, powers its unique light curve. This scenario provides a plausible explanation for AT 2018fyk’s overall properties, including the rapid dimming event and the rebrightening at late times. We also provide testable predictions for the behavior of the accretion flow in the future; if the second encounter was also a partial disruption, then we predict another strong dimming event around day 1800 (2023 August) and a subsequent rebrightening around day 2400 (2025 March). This source provides strong evidence of the partial disruption of a star by an SMBH.
Recent research suggests that drawing activities can help students learn concepts in the science, technology, engineering, and mathematics (STEM) disciplines. In particular, drawing activities, which ...mimic the practices of STEM professionals, can help students engage with visual-spatial content. However, prior work has also shown that students struggle to learn from drawing activities. One major issue is that the learning processes underlying the effects of drawing activities are mostly unknown, and therefore, it is unclear how best to design effective drawing activities in STEM learning environments. To address this gap, our review of prior research investigates which learning processes may explain how drawing activities facilitate learning of STEM content. Specifically, we reviewed prior research across cognitive and sociocultural theoretical perspectives. We identified six learning processes fostered by drawing activities. Each learning process describes how drawing can change the way students interact with the content. Our review shows how instructional support for drawing activities that targets each learning process can enhance learning. Our findings have theoretical implications regarding how drawing activities have been studied and yield open questions about the mechanisms accounting for the effects of drawing activities on students' learning in STEM disciplines. Further, our findings suggest practical recommendations on how to effectively implement drawing activities that help students learn STEM content.
Context.
High-redshift quasars signpost the early accretion history of the Universe. The penetrating nature of X-rays enables a less absorption-biased census of the population of these luminous and ...persistent sources compared to optical/near-infrared colour selection. The ongoing SRG/eROSITA X-ray all-sky survey offers a unique opportunity to uncover the bright end of the high-
z
quasar population and probe new regions of colour parameter space.
Aims.
We searched for high-
z
quasars within the X-ray source population detected in the contiguous ~140 deg
2
field observed by eROSITA during the performance verification phase. With the purpose of demonstrating the unique survey science capabilities of eROSITA, this field was observed at the depth of the final all-sky survey. The blind X-ray selection of high-redshift sources in a large contiguous, near-uniform survey with a well-understood selection function can be directly translated into constraints on the X-ray luminosity function (XLF), which encodes the luminosity-dependent evolution of accretion through cosmic time.
Methods.
We collected the available spectroscopic information in the eFEDS field, including the sample of all currently known optically selected
z
> 5.5 quasars and cross-matched secure Legacy DR8 counterparts of eROSITA-detected X-ray point-like sources with this spectroscopic sample.
Results.
We report the X-ray detection of eFEDSU J083644.0+005459, an eROSITA source securely matched to the well-known quasar SDSS J083643.85+005453.3 (
z
= 5.81). The soft X-ray flux of the source derived from eROSITA is consistent with previous
Chandra
observations. The detection of SDSS J083643.85+005453.3 allows us to place the first constraints on the XLF at
z
> 5.5 based on a secure spectroscopic redshift. Compared to extrapolations from lower-redshift observations, this favours a relatively flat slope for the XLF at
z
~ 6 beyond
L
*
, the knee in the luminosity function. In addition, we report the detection of the quasar with LOFAR at 145 MHz and ASKAP at 888 MHz. The reported flux densities confirm a spectral flattening at lower frequencies in the emission of the radio core, indicating that SDSS J083643.85+005453.3 could be a (sub-) gigahertz peaked spectrum source. The inferred spectral shape and the parsec-scale radio morphology of SDSS J083643.85+005453.3 indicate that it is in an early stage of its evolution into a large-scale radio source or confined in a dense environment. We find no indications for a strong jet contribution to the X-ray emission of the quasar, which is therefore likely to be linked to accretion processes.
Conclusions.
Our results indicate that the population of X-ray luminous AGNs at high redshift may be larger than previously thought. From our XLF constraints, we make the conservative prediction that eROSITA will detect ~90 X-ray luminous AGNs at redshifts 5.7 <
z
< 6.4 in the full-sky survey (De+RU). While subject to different jet physics, both high-redshift quasars detected by eROSITA so far are radio-loud; a hint at the great potential of combined X-ray and radio surveys for the search of luminous high-redshift quasars.
During the last 3 years, a number of approaches for the normalization of RNA sequencing data have emerged in the literature, differing both in the type of bias adjustment and in the statistical ...strategy adopted. However, as data continue to accumulate, there has been no clear consensus on the appropriate normalization method to be used or the impact of a chosen method on the downstream analysis. In this work, we focus on a comprehensive comparison of seven recently proposed normalization methods for the differential analysis of RNA-seq data, with an emphasis on the use of varied real and simulated datasets involving different species and experimental designs to represent data characteristics commonly observed in practice. Based on this comparison study, we propose practical recommendations on the appropriate normalization method to be used and its impact on the differential analysis of RNA-seq data.
This paper analyzes seasonal effects and their potential drivers in charitable giving. We conduct two studies to analyze whether donations to the German Red Cross differ between the Christmas season ...and summer. In study 1 we find that in the pre-Christmas shopping season prosocial subjects almost donate 50% less compared to prosocials in summer. In study 2 we replicate the low donations in the Christmas season. In an extensive questionnaire we control for several causes of this effect. The data suggest that the higher prosocials' self-reported stress level, the lower the donations. The higher their relative savings, the lower the giving. Our questionnaire rules out that "donation fatigue" matters. That is, donations do not depend on the number of charitable campaigns subjects are confronted with and their engagement in these activities during Christmas season outside the lab.
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