Search

When bright solar-system objects are observed by GHz-THz regime telescopes, off-axis signals bounce around locally and re-enter the signal path with a time delay, causing sinusoidal ripples in output spectra. Ripples that are unstable over time are challenging to remove. A typical detection limit for planetary spectral lines is a fraction of order 0.001 of continuum signal, restricting searches for minor atmospheric trace-gases. Modern wideband spectra of Venus demonstrate a plethora of effects, at three example telescopes spanning nearly a factor of 50 in frequency. Characterisation of instrumental effects as families of pure sine-waves via Fourier-analysis is shown to improve dynamic range by factors of a few. An example upper limit on sulphuric acid vapour in the Venusian mesosphere, from fully-automated data-cleaning of a 3.5 GHz band containing 10 line components, goes as deep as the best previously-published limit. The most challenging cases are searches for single lines of width comparable to ripple periods. Traditional polynomial-fitting approaches can be deployed to test for false positives, to demonstrate robustness at a level of zero 'fake lines' in more than 1000 comparisons. Fourier-based data-cleaning avoids subjectivity and can be fully automated, and synthetic spectra can be injected before processing to test to what degree signals are lost in cleaning. An ideal robustness strategy is mitigation at the data-acquisition stage, e.g. using slow drifts in target-velocity with respect to the telescope to isolate a planetary line from a quasi-static instrumental ripple pattern., Comment: Accepted in RAS Techniques and Instruments (RASTI) on 4 Nov 2024; 12 pages and 13 figures

We present 850 $\mu$m polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation (BISTRO) survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power-law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis-Chandrasekhar-Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45-2.20 and 0.63-2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament is 0.33-1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale ($\sim$ 0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS., Comment: Accepted for publication in ApJ. 21 pages, 12 figures

In this Roadmap, we present a vision for the future of submillimetre and millimetre astronomy in the United Kingdom over the next decade and beyond. This Roadmap has been developed in response to the recommendation of the Astronomy Advisory Panel (AAP) of the STFC in the AAP Astronomy Roadmap 2022. In order to develop our stragetic priorities and recommendations, we surveyed the UK submillimetre and millimetre community to determine their key priorities for both the near-term and long-term future of the field. We further performed detailed reviews of UK leadership in submillimetre/millimetre science and instrumentation. Our key strategic priorities are as follows: 1. The UK must be a key partner in the forthcoming AtLAST telescope, for which it is essential that the UK remains a key partner in the JCMT in the intermediate term. 2. The UK must maintain, and if possible enhance, access to ALMA and aim to lead parts of instrument development for ALMA2040. Our strategic priorities complement one another: AtLAST (a 50m single-dish telescope) and an upgraded ALMA (a large configurable interferometric array) would be in synergy, not competition, with one another. Both have identified and are working towards the same overarching science goals, and both are required in order to fully address these goals., Comment: 91 pages plus cover, 38 figures. Submitted to the Science and Technology Facilities Council, August 2024. One figure corrected (v2); new appendix with STFC Q&A; corrected SMA access statement; updated references, acronyms & author list (v3)

The region of $N\approx Z\approx 40$ has long been associated with strongly deformed nuclear configurations. The presence of this strong deformation was recently confirmed through lifetime measurements in $N\approx Z$ Sr and Zr nuclei. Theoretically, however, these nuclei present a challenge due to the vast valence space required to incorporate all deformation driving interactions. Recent state-of-the-art predictions indicate a near axial prolate deformation for $N=Z$ and $N=Z+2$ nuclei between $N=Z=36$ and $N=Z=40$. In this work we investigate the shores of this island of deformation through a sub-barrier Coulomb excitation study of the $N=Z+4$ nucleus, \textsuperscript{80}Sr. Extracting a spectroscopic quadrupole moment of $Q_s(2^+_1) = 0.45^{+0.83}_{-0.88}$~eb, we find that \textsuperscript{80}Sr is inconsistent with significant axial prolate deformation. This indicates that the predicted region of strong prolate deformation around $N=Z=40$ is tightly constrained to the quartet of nuclei: \textsuperscript{76,78}Sr and \textsuperscript{78,80}Zr., Comment: Submitted to Physics Letters B

We exhibit non-switching-isomorphic signed graphs that share a common underlying graph and common chromatic polynomials, thereby answering a question posed by Zaslavsky. For various joins of all-positive or all-negative signed complete graphs, we derive a closed-form expression for their chromatic polynomials. As a generalisation of the chromatic polynomials for a signed graph, we introduce a new pair of bivariate chromatic polynomials. We establish recursive dominating-vertex deletion formulae for these bivariate chromatic polynomials. Finally, we show that for certain families of signed threshold graphs, isomorphism is equivalent to the equality of bivariate chromatic polynomials., Comment: 24 pages

We characterise graphs that have three distinct eigenvalues and coherent ranks 8 and 9, linking the former to certain symmetric 2-designs and the latter to specific quasi-symmetric 2-designs. This characterisation leads to the discovery of a new biregular graph with three distinct eigenvalues. Additionally, we demonstrate that the coherent rank of a triregular graph with three distinct eigenvalues is at least 14. Finally, we introduce a conjecturally infinite family of biregular graphs with three distinct eigenvalues, obtained by switching the block graphs of orthogonal arrays., Comment: 36 pages

Existing strategies for managing risks from advanced AI systems often focus on affecting what AI systems are developed and how they diffuse. However, this approach becomes less feasible as the number of developers of advanced AI grows, and impedes beneficial use-cases as well as harmful ones. In response, we urge a complementary approach: increasing societal adaptation to advanced AI, that is, reducing the expected negative impacts from a given level of diffusion of a given AI capability. We introduce a conceptual framework which helps identify adaptive interventions that avoid, defend against and remedy potentially harmful uses of AI systems, illustrated with examples in election manipulation, cyberterrorism, and loss of control to AI decision-makers. We discuss a three-step cycle that society can implement to adapt to AI. Increasing society's ability to implement this cycle builds its resilience to advanced AI. We conclude with concrete recommendations for governments, industry, and third-parties.

Random matrix theory is a useful tool in the study of the physics of multiple scattering systems, often striking a balance between computation speed and physical rigour. Propagation of waves through thick disordered media, as arises in for example optical scattering or electron transport, typically necessitates cascading of multiple random matrices drawn from an underlying ensemble for thin media, greatly increasing computational burden. Here we propose a dual pool based bootstrapping approach to speed up statistical studies of scattering in thick random media. We examine how potential matrix reuse in a pool based approach can impact statistical estimates of population averages. Specifically, we discuss how both bias and additional variance in the sample mean estimator are introduced through bootstrapping. In the diffusive scattering regime, the extra estimator variance is shown to originate from samples in which cascaded transfer matrices are permuted matrix products. Through analysis of the combinatorics and cycle structure of permutations we quantify the resulting correlations. Proofs of several analytic formulae enumerating the frequency with which correlations of different strengths occur are derived. Extension to the ballistic regime is briefly considered., Comment: 1 figure, 3 tables, 13 pages, submitted to journal 11 Sep 23. Supplementary movies available upon request

We provide a method to construct $t$-designs from weighing matrices and walk-regular graphs. One instance of our method can produce a $3$-design from any (symmetric or skew-symmetric) conference matrix, thereby providing a partial answer to a question of Gunderson and Semeraro JCTB 2017. We explore variations of our method on some matrices that satisfy certain combinatorial restrictions. In particular, we show that there exist various infinite families of partially balanced incomplete block designs with block size four on the binary Hamming schemes and the $3$-class association schemes attached to symmetric designs, and regular pairwise balanced designs with block sizes three and four., Comment: 31 pages

We report 850 $\mu$m continuum polarization observations toward the filamentary high-mass star-forming region NGC 2264, taken as part of the B-fields In STar forming Regions Observations (BISTRO) large program on the James Clerk Maxwell Telescope (JCMT). These data reveal a well-structured non-uniform magnetic field in the NGC 2264C and 2264D regions with a prevailing orientation around 30 deg from north to east. Field strengths estimates and a virial analysis for the major clumps indicate that NGC 2264C is globally dominated by gravity while in 2264D magnetic, gravitational, and kinetic energies are roughly balanced. We present an analysis scheme that utilizes the locally resolved magnetic field structures, together with the locally measured gravitational vector field and the extracted filamentary network. From this, we infer statistical trends showing that this network consists of two main groups of filaments oriented approximately perpendicular to one another. Additionally, gravity shows one dominating converging direction that is roughly perpendicular to one of the filament orientations, which is suggestive of mass accretion along this direction. Beyond these statistical trends, we identify two types of filaments. The type-I filament is perpendicular to the magnetic field with local gravity transitioning from parallel to perpendicular to the magnetic field from the outside to the filament ridge. The type-II filament is parallel to the magnetic field and local gravity. We interpret these two types of filaments as originating from the competition between radial collapsing, driven by filament self-gravity, and the longitudinal collapsing, driven by the region's global gravity., Comment: Accepted for publication in the Astrophysical Journal. 43 pages, 32 figures, and 4 tables (including Appendix)

The properties of a nanosecond isomer in $^{32}$Si, disputed in previous studies, depend on the evolution of proton and neutron shell gaps near the `island of inversion'. We have placed the isomer at 5505.2(2) keV with $J^{\pi} = 5^-$, decaying primarily via an $E3$ transition to the $2^+_1$ state. The $E3$ strength of 0.0841(10) W.u. is unusually small and suggests that this isomer is dominated by the $(\nu d_{3/2})^{-1} \otimes (\nu f_{7/2})^{1}$ configuration, which is sensitive to the $N=20$ shell gap. A newly observed $4^+_1$ state is placed at 5881.4(13) keV; its energy is enhanced by the $Z=14$ subshell closure. This indicates that the isomer is located in a `yrast trap', a feature rarely seen at low mass numbers., Comment: Accepted, Physical Review C

We show that the VC-dimension of a graph can be computed in time $n^{\log d+1} d^{O(d)}$, where $d$ is the degeneracy of the input graph. The core idea of our algorithm is a data structure to efficiently query the number of vertices that see a specific subset of vertices inside of a (small) query set. The construction of this data structure takes time $O(d2^dn)$, afterwards queries can be computed efficiently using fast M\"obius inversion. This data structure turns out to be useful for a range of tasks, especially for finding bipartite patterns in degenerate graphs, and we outline an efficient algorithms for counting the number of times specific patterns occur in a graph. The largest factor in the running time of this algorithm is $O(n^c)$, where $c$ is a parameter of the pattern we call its left covering number. Concrete applications of this algorithm include counting the number of (non-induced) bicliques in linear time, the number of co-matchings in quadratic time, as well as a constant-factor approximation of the ladder index in linear time. Finally, we supplement our theoretical results with several implementations and run experiments on more than 200 real-world datasets -- the largest of which has 8 million edges -- where we obtain interesting insights into the VC-dimension of real-world networks., Comment: Accepted for publication in the 18th International Symposium on Parameterized and Exact Computation (IPEC 2023)

Multi-level magnetic recording is a new concept for increasing the data storage capacity of hard disk drives. However, its implementation has been limited by a lack of suitable media capable of storing information at multiple levels. Herein, we overcome this problem by developing dual FePt-C nanogranular films separated by a Ru-C breaking layer with a cubic crystal structure. The FePt grains in the bottom and top layers of the developed media exhibited different effective magnetocrystalline anisotropies and Curie temperatures. The former is realized by different degrees of ordering in the L10-FePt grains, whereas the latter was attributed to the diffusion of Ru, thereby enabling separate magnetic recordings at each layer under different magnetic fields and temperatures. Furthermore, the magnetic measurements and heat-assisted magnetic recording simulations showed that these media enabled 3-level recording and could potentially be extended to 4-level recording, as the up-down and down-up states exhibited non-zero magnetization.

North star metrics and online experimentation play a central role in how technology companies improve their products. In many practical settings, however, evaluating experiments based on the north star metric directly can be difficult. The two most significant issues are 1) low sensitivity of the north star metric and 2) differences between the short-term and long-term impact on the north star metric. A common solution is to rely on proxy metrics rather than the north star in experiment evaluation and launch decisions. Existing literature on proxy metrics concentrates mainly on the estimation of the long-term impact from short-term experimental data. In this paper, instead, we focus on the trade-off between the estimation of the long-term impact and the sensitivity in the short term. In particular, we propose the Pareto optimal proxy metrics method, which simultaneously optimizes prediction accuracy and sensitivity. In addition, we give an efficient multi-objective optimization algorithm that outperforms standard methods. We applied our methodology to experiments from a large industrial recommendation system, and found proxy metrics that are eight times more sensitive than the north star and consistently moved in the same direction, increasing the velocity and the quality of the decisions to launch new features.

Ti and Cr beryllides are materials of potential importance as neutron multipliers for tritium breeding in nuclear fusion reactors. The n-to-2n transmutation reaction also produces tritium and helium, which form bubbles. Neutron irradiation from fusion plasma also introduces point defects. The effect on beryllides' microstructure is important for understanding their mechanical properties and evolution in the fusion reactor environment. This study determines and describes the microstructural features that occur in TiBe12 and CrBe12 when He and fast-particle-induced point defects are introduced at fusion reactor neutron breeder relevant temperatures. Beryllide samples were implanted with 300kV He at temperatures between $387-900^{\circ}C$, sectioned down through the implantation surface with a focused ion beam post-irradiation, and the resulting microstructures examined using transmission electron microscopy, electron-dispersive spectroscopy (EDS) and precession diffraction mapping. Nanometre bubbles grew in both TiBe12 and CrBe12 at $600^{\circ}C$; larger (100 nm and over) bubbles, some faceted, grew at $900^{\circ}C$. Some bubbles in CrBe12 were lined with Cr, some oxidised. TiBe12 developed planar faults, on $\{110\}$ planes at $600^{\circ}C$ and below but on $\{111\}$ at $900^{\circ}C$. Faults were preferentially associated with large bubbles. The displacement vectors of faults on the $\{110\}$ planes had some commonality with previous studies that found displacement vectors of families $R=\langle 011\rangle$ and $R= \langle 110\rangle$; the present study also found faults that matched neither previously found type. CrBe12 also developed planar faults with an appearance quite different from the typical striped appearance of planar stacking faults; their nature remains unknown. Oxide particles were found in both beryllides, most prominently in CrBe12., Comment: 35 pages, 25 figures. Paper writing: Jo Sharp. Paper editing: everybody. Manufacture of beryllide material: Ramil Gaisin. FIB sample prep: Viacheslav Kuksenko. Irradiation: Jo Sharp and Graeme Greaves. Characterisation: Jo Sharp. Obtaining funding: Jonathan Hinks, Graeme Greaves, Stephen Donnelly, Pavel Vladimirov. Submitted to Journal of Nuclear Materials

Recommendation system serves as a conduit connecting users to an incredibly large, diverse and ever growing collection of contents. In practice, missing information on fresh (and tail) contents needs to be filled in order for them to be exposed and discovered by their audience. We here share our success stories in building a dedicated fresh content recommendation stack on a large commercial platform. To nominate fresh contents, we built a multi-funnel nomination system that combines (i) a two-tower model with strong generalization power for coverage, and (ii) a sequence model with near real-time update on user feedback for relevance. The multi-funnel setup effectively balances between coverage and relevance. An in-depth study uncovers the relationship between user activity level and their proximity toward fresh contents, which further motivates a contextual multi-funnel setup. Nominated fresh candidates are then scored and ranked by systems considering prediction uncertainty to further bootstrap content with less exposure. We evaluate the benefits of the dedicated fresh content recommendation stack, and the multi-funnel nomination system in particular, through user corpus co-diverted live experiments. We conduct multiple rounds of live experiments on a commercial platform serving billion of users demonstrating efficacy of our proposed methods., Comment: Accepted by KDD 2023