Search

In this White Paper, we present recommendations for the scientific community and funding agencies to foster the infrastructure for a collaborative multi-messenger and time-domain astronomy (MMA/TDA) ecosystem. MMA/TDA is poised for breakthrough discoveries in the coming decade. In much the same way that expanding beyond the optical bandpass revealed entirely new and unexpected discoveries, cosmic messengers beyond light (i.e., gravitational waves, neutrinos, and cosmic rays) open entirely new windows to answer some of the most fundamental questions in (astro)physics: heavy element synthesis, equation of state of dense matter, particle acceleration, etc. This field was prioritized as a frontier scientific pursuit in the 2020 Decadal Survey on Astronomy and Astrophysics via its "New Windows on the Dynamic Universe" theme. MMA/TDA science presents technical challenges distinct from those experienced in other disciplines. Successful observations require coordination across myriad boundaries -- different cosmic messengers, ground vs. space, international borders, etc. -- all for sources that may not be well localized, and whose brightness may be changing rapidly with time. Add that all of this work is undertaken by real human beings, with distinct backgrounds, experiences, cultures, and expectations, that often conflict. To address these challenges and help MMA/TDA realize its full scientific potential in the coming decade (and beyond), the second in a series of community workshops sponsored by the U.S. National Science Foundation (NSF) and NASA titled "Windows on the Universe: Establishing the Infrastructure for a Collaborative Multi-Messenger Ecosystem" was held on October 16-18, 2023 in Tucson, AZ. Here we present the primary recommendations from this workshop focused on three key topics -- hardware, software, and people and policy. [abridged], Comment: Workshop white paper

Intel's software guard extensions (SGX) provide hardware enclaves to guarantee confidentiality and integrity for sensitive code and data. However, systems leveraging such security mechanisms must often pay high performance overheads. A major source of this overhead is SGX enclave transitions which induce expensive cross-enclave context switches. The Intel SGX SDK mitigates this with a switchless call mechanism for transitionless cross-enclave calls using worker threads. Intel's SGX switchless call implementation improves performance but provides limited flexibility: developers need to statically fix the system configuration at build time, which is error-prone and misconfigurations lead to performance degradations and waste of CPU resources. ZC-SWITCHLESS is a configless and efficient technique to drive the execution of SGX switchless calls. Its dynamic approach optimises the total switchless worker threads at runtime to minimise CPU waste. The experimental evaluation shows that ZC-SWITCHLESS obviates the performance penalty of misconfigured switchless systems while minimising CPU waste., Comment: 10 pages, 53rd Annual IEEE/IFIP International Conference on Dependable Systems and Networks (DSN)

The increasing application of machine learning techniques in everyday decision-making processes has brought concerns about the fairness of algorithmic decision-making. This paper concerns the problem of collider bias which produces spurious associations in fairness assessment and develops theorems to guide fairness assessment avoiding the collider bias. We consider a real-world application of auditing a trained classifier by an audit agency. We propose an unbiased assessment algorithm by utilising the developed theorems to reduce collider biases in the assessment. Experiments and simulations show the proposed algorithm reduces collider biases significantly in the assessment and is promising in auditing trained classifiers., Comment: 16 pages, 7 figures and 9 tables. The work has been accepted by PAKDD2022

We present the Phase A Science Case for the Multi-conjugate Adaptive-optics Visible Imager-Spectrograph (MAVIS), planned for the Adaptive Optics Facility (AOF) of the Very Large Telescope (VLT). MAVIS is a general-purpose instrument for exploiting the highest possible angular resolution of any single optical telescope available in the next decade, either on Earth or in space, and with sensitivity comparable to (or better than) larger aperture facilities. MAVIS uses two deformable mirrors in addition to the deformable secondary mirror of the AOF, providing a mean V-band Strehl ratio of >10% (goal >15%) across a relatively large (30 arc second) science field. This equates to a resolution of <20mas at 550nm - comparable to the K-band diffraction limit of the next generation of extremely large telescopes, making MAVIS a genuine optical counterpart to future IR-optimised facilities like JWST and the ELT. Moreover, MAVIS will have unprecedented sky coverage for a high-order AO system, accessing at least 50% of the sky at the Galactic Pole, making MAVIS a truly general purpose facility instrument. As such, MAVIS will have both a Nyquist-sampled imager (30x30 arcsec field), and a powerful integral field spectrograph with multiple spatial and spectral modes spanning 370-1000nm. This science case presents a distilled set of thematically linked science cases drawn from the MAVIS White Papers (www.mavis-ao.org/whitepapers), selected to illustrate the driving requirements of the instrument resulting from the recent MAVIS Phase A study., Comment: 141 pages, 79 figures, 10Mb. Modified version of the Phase A Science Case submitted to ESO in April 2020 as part of the MAVIS Phase A design study. Full resolution version available upon request

We show that attractors are semicontinuous for closed relations on compact Hausdorff spaces. Semicontinuity is what guarantees that small changes to a system do not result in massive growth of certain features, notably attractors. That is, there is a certain preservation of structure. When it comes to flows, semiflows, and maps, it is well established that attractors are semicontinuous. In [2], relations were established as a way to generalize maps, and a formal definition of attractors was established. Relations (in the dynamical systems sense) represent discrete time systems, which may lack uniqueness (or existence) in forward time., Comment: 8 pages, 3 figures (one with two parts)

We already know a great deal about dynamical systems with uniqueness in forward time. Indeed, flows, semiflows, and maps (both invertible and not) have been studied at length. A view that has proven particularly fruitful is topological: consider invariant sets (attractors, repellers, periodic orbits, etc.) as topological objects, and the connecting sets between them form gradient like flows. In the case of systems with uniqueness in forward time, an attractor in one system is related to nearby attractors in a family of other, "close enough" systems. One way of seeing that connection is through the Conley decomposition (and the Conley index) [2], [13]. This approach requires focusing on isolated invariant sets - that is, invariant sets with isolating neighborhoods. If there is an invariant set $I$, which has an isolating neighborhood $N$ $\ldots$. This approach was expanded to discrete time systems which lack uniqueness in forward time, using relations, in [7] and [11]. Relations do not rely on uniqueness in forward time, but the graph of any map is a relation; thus they serve to generalize maps. Some of this is reviewed in the next few sections. In addition, I expanded on work done in [7] to show that in compact metric spaces, attractors for closed relations continue (see Section 6). On the continuous time side, more work needs to be done. This paper is a step toward a more systematic approach for continuous time systems which lack uniqueness in forward time. This work applies to Filippov systems [4] and in control theory [12]. In the following pages, we establish a tool (multiflows) for discussing the continuous time case and develop a framework for understanding attractors (and therefore stability) in these systems. A crucial part of this work was establishing attractor / attracting neighborhood pairs, which happens in Section 5.5., Comment: 52 pages, 20 figures; author's dissertation

The purpose of this study was to examine the ways that teachers use Connected Classroom Technology (CCT) to potentially support achievement on translation problems that require moving between algebraic representations. Four mathematics classrooms were chosen based on their gain scores on pre- and post-test Algebraic translation problems. Two classrooms with the highest and the lowest gain scores were chosen among the classrooms with pre-test scores that were below 50%. This study used video-recorded observational data and found that teachers in effective classrooms created environments wherein students used multiple representations simultaneously and translated between representations through discussion. In contrast, teachers in less effective classrooms fostered environments wherein students used representations independently and missed opportunities to translate representations through discussion. [For the complete proceedings, see ED583608.]

This white paper summarizes the conclusions of the Snowmass White Paper "Spectroscopic Needs for Imaging Dark Energy Experiments" (arXiv:1309.5384) which are relevant to the calibration of LSST photometric redshifts; i.e., the accurate characterization of biases and uncertainties in photo-z's. Any significant miscalibration will lead to systematic errors in photo-z's, impacting nearly all extragalactic science with LSST. As existing deep redshift samples have failed to yield highly-secure redshifts for a systematic 20%-60% of their targets, it is a strong possibility that future deep spectroscopic samples will not solve the calibration problem on their own. The best options in this scenario are provided by cross-correlation methods that utilize clustering with objects from spectroscopic surveys (which need not be fully representative) to trace the redshift distribution of the full sample. For spectroscopy, the eBOSS survey would enable a basic calibration of LSST photometric redshifts, while the expected LSST-DESI overlap would be more than sufficient for an accurate calibration at z>0.2. A DESI survey of nearby galaxies conducted in bright time would enable accurate calibration down to z~0. The expanded areal coverage provided by the transfer of the DESI instrument (or duplication of it at the Blanco Telescope) would enable the best possible calibration from cross-correlations, in addition to other science gains., Comment: White paper submitted to the National Research Council Committee on a Strategy Optimize the U.S. O/IR System in the Era of the LSST, 4 pages

This white paper summarizes those conclusions of the Snowmass White Paper "Spectroscopic Needs for Imaging Dark Energy Experiments" (arXiv:1309.5384) which are relevant to the training of LSST photometric redshifts; i.e., the use of spectroscopic redshifts to improve algorithms and reduce photo-z errors. The larger and more complete the available training set is, the smaller the RMS error in photo-z estimates should be, increasing LSST's constraining power. Among the better US-based options for this work are the proposed MANIFEST fiber feed for the Giant Magellan Telescope or (with lower survey speed) the WFOS spectrograph on the Thirty Meter Telescope (TMT). Due to its larger field of view and higher multiplexing, the PFS spectrograph on Subaru would be able to obtain a baseline training sample faster than TMT; comparable performance could be achieved with a highly-multiplexed spectrograph on Gemini with at least a 20 arcmin diameter field of view., Comment: White paper submitted to the National Research Council Committee on a Strategy Optimize the U.S. O/IR System in the Era of the LSST, 5 pages