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Michael D. Smith

Publications and source records attributed to Michael D. Smith.

At least 19 recordsLinked to original sources

Inducing Sustained Creativity and Diversity in Large Language Models

We address a not-widely-recognized subset of exploratory search, where a user sets out on a typically long "search quest" for the perfect wedding dress, overlooked research topic, killer company idea, etc. The first few outputs of current large language models (LLMs) may be helpful but only as a start, since the quest requires learning the search space and evaluating many diverse and creative alternatives along the way. Although LLMs encode an impressive fraction of the world's knowledge, common decoding methods are narrowly optimized for prompts with correct answers and thus return mostly homogeneous and conventional results. Other approaches, including those designed to increase diversity across a small set of answers, start to repeat themselves long before search quest users learn enough to make final choices, or offer a uniform type of "creativity" to every user asking similar questions. We develop a novel, easy-to-implement decoding scheme that induces sustained creativity and diversity in LLMs, producing as many conceptually unique results as desired, even without access to the inner workings of an LLM's vector space. The algorithm unlocks an LLM's vast knowledge, both orthodox and heterodox, well beyond modal decoding paths. With this approach, search quest users can more quickly explore the search space and find satisfying answers.

cs.CL

Diurnal temperature variations and migrating thermal tides in the Martian lower atmosphere observed by the Emirates Mars InfraRed Spectrometer

The Martian atmosphere experiences large diurnal variations due to the ~24.6 h planetary rotation and its low heat capacity. Understanding such variations on a planetary scale is limited due to the lack of observations, which are greatly addressed with the recent advent of the Emirates Mars Mission (EMM). As a result of its unique high-altitude orbit, instruments onboard are capable of obtaining a full geographic and local time coverage of the Martian atmosphere every 9-10 Martian days, approximately ~5° in solar longitude (LS). This enables investigations of the diurnal variation of the current climate on Mars on a planetary scale without significant local time (LT) gaps or confusions from correlated seasonal variations. Here, we present the results of diurnal temperature variations and thermal tides in the Martian atmosphere using temperature profiles retrieved from the Emirates Mars InfraRed Spectrometer (EMIRS) observations. The data during the primary mission is included, covering an entire Martian Year (MY) starting from MY 36 LS = 49°. The diurnal temperature patterns suggest a dominant diurnal tide in most seasons, while the semi-diurnal tide presents a similar amplitude near perihelion. The seasonal variation of the diurnal tide latitudinal distribution is well explained by the total vorticity due to zonal wind, while that of the semi-diurnal tide following both dust and water ice clouds, and the ter-diurnal tide following the dust only. Comparison with the updated Mars Planetary Climate Model (PCM, version 6) suggest improvements in simulating the dust and water cycles, as well as their radiative processes.

astro-ph.EP

Synthesis and transport properties of epitaxial Bi (111) films on GaAs (111) substrates

In recent decades, the growth of ultrathin epitaxial bismuth (Bi) films on various substrates has garnered interest due to their unique electronic properties. We report upon the growth and electrical transport properties of epitaxial Bi (111) films in the thickness range of 5-32 nm deposited directly on GaAs (111) substrates, without a buffer layer. The quality of Bi films is found to depend on conditions for substrate treatment using Ar+ ion-milling and annealing. Substrates milled at low ion beam currents display poor surface reconstruction after annealing, which hinders the growth of high-quality films. In contrast, substrates milled under optimized conditions led to reconstructed surfaces upon annealing, resulting in epitaxial Bi films with predominantly single-domain orientation. Although epitaxial films formed in both cases, transport measurements indicated significantly higher conductivity for films grown on optimally treated substrates. Measurements at low temperatures suggest that the transport properties are dominated by a surface state with high mobility electrons. Magneto-transport measurements suggest that conductivity and mobility improve progressively with increasing film thickness. For the thinnest 5 nm film, a hole-like state emerges, presumably as the electron-like state is gapped out. These results provide a robust methodology for growing high-quality epitaxial Bi films on GaAs (111) and offer insights into their unique transport properties, and our ability to tune them.

cond-mat.mtrl-sci

A "Perspectival" Mirror of the Elephant: Investigating Language Bias on Google, ChatGPT, YouTube, and Wikipedia

Contrary to Google Search's mission of delivering information from "many angles so you can form your own understanding of the world," we find that Google and its most prominent returned results - Wikipedia and YouTube - simply reflect a narrow set of culturally dominant views tied to the search language for complex topics like "Buddhism," "Liberalism," "colonization," "Iran" and "America." Simply stated, they present, to varying degrees, distinct information across the same search in different languages, a phenomenon we call language bias. This paper presents evidence and analysis of language bias and discusses its larger social implications. We find that our online searches and emerging tools like ChatGPT turn us into the proverbial blind person touching a small portion of an elephant, ignorant of the existence of other cultural perspectives. Language bias sets a strong yet invisible cultural barrier online, where each language group thinks they can see other groups through searches, but in fact, what they see is their own reflection.

cs.CY

Diurnal and Seasonal Mapping of Martian Ices With EMIRS

Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H$_2$O and CO$_2$ cycles, either from a seasonal or diurnal aspect. While most of the ice is located within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. Here, we use data from the Emirates Mars Infrared Spectrometer (EMIRS) onboard the Emirates Mars Mission (EMM) to monitor the diurnal and seasonal evolution of the ices at the surface of Mars over almost one Martian year. The unique local time coverage provided by the instrument allows us to observe the apparition of equatorial CO$_2$ frost in the second half of the Martian night around the equinoxes, to its sublimation at sunrise.

astro-ph.EP

Migrating Thermal Tides in the Martian Atmosphere during Aphelion Season Observed by EMM/EMIRS

Temperature profiles retrieved using the first set of data of the Emirates Mars InfraRed Spectrometer (EMIRS) obtained during the science phase of the Emirates Mars Mission (EMM) are used for the analysis of migrating thermal tides in the Martian atmosphere. The selected data cover a solar longitude (LS) range of 60°-90° of Martian Year (MY) 36. The novel orbit design of the Hope Probe leads to a good geographic and local time coverage that significantly improves the analysis. Wave mode decomposition suggests dominant diurnal tide and important semi-diurnal tide with maximal amplitudes of 6K and 2K, respectively, as well as the existence of ~0.5K ter-diurnal tide. The results agree well with predictions by the Mars Planetary Climate Model (PCM), but the observed diurnal tide has an earlier phase (3h), and the semi-diurnal tide has an unexpectedly large wavelength (~200km).

astro-ph.EP

Motivating Data Science Students to Participate and Learn

Data science education is increasingly involving human subjects and societal issues such as privacy, ethics, and fairness. Data scientists need to be equipped with skills to tackle the complexities of the societal context surrounding their data science work. In this paper, we offer insights into how to structure our data science classes so that they motivate students to deeply engage with material about societal context and lean into the types of conversations that will produce long lasting growth in critical thinking skills. In particular, we describe a novel assessment tool called participation portfolios, which is motivated by a framework that promotes student autonomy, self reflection, and the building of a learning community. We compare student participation before and after implementing this assessment tool, and our results suggest that this tool increased student participation and helped them move towards course learning objectives.

cs.CY

Influence via Ethos: On the Persuasive Power of Reputation in Deliberation Online

Deliberation among individuals online plays a key role in shaping the opinions that drive votes, purchases, donations and other critical offline behavior. Yet, the determinants of opinion-change via persuasion in deliberation online remain largely unexplored. Our research examines the persuasive power of $\textit{ethos}$ -- an individual's "reputation" -- using a 7-year panel of over a million debates from an argumentation platform containing explicit indicators of successful persuasion. We identify the causal effect of reputation on persuasion by constructing an instrument for reputation from a measure of past debate competition, and by controlling for unstructured argument text using neural models of language in the double machine-learning framework. We find that an individual's reputation significantly impacts their persuasion rate above and beyond the validity, strength and presentation of their arguments. In our setting, we find that having 10 additional reputation points causes a 31% increase in the probability of successful persuasion over the platform average. We also find that the impact of reputation is moderated by characteristics of the argument content, in a manner consistent with a theoretical model that attributes the persuasive power of reputation to heuristic information-processing under cognitive overload. We discuss managerial implications for platforms that facilitate deliberative decision-making for public and private organizations online.

econ.EM

The nature of a primary jet within a circumbinary disc outflow in a young stellar system

Most stars form in binaries, and both stars may grow by accreting material from a circumbinary disc onto their personal discs. We suspect that in many cases a wide molecular wind will envelope a collimated atomic jet emanating from close to an orbiting young star. This so-called Circumbinary Scenario is explored here in order to find common identifiable properties. The dynamical set up is studied with three dimensional simulations with chemistry and cooling included. We extract the properties on scales of order 100\,AU and compare to the Co-Orbital Scenario in which the wind and jet sources are in orbit. We find that the rapid orbital motion generates a wide ionised sheath around the jet core with a large opening angle at the base. This is independent of the presence of the surrounding molecular outflow. However, the atomic jet is recollimated beyond ~ 55 AU when the molecular outflow restricts the motion of the ambient medium which, in turn, confines the jet. These physical properties are relayed to the optical H-alpha imaging, providing a means of distinguishing between models. The high excitation sheath and recollimation region can be explored on these scales through the next generation of instruments. However, in general, the amount and location of the ionised material, whether in the knots or the sheath, will depend on several parameters including the orbital period, axis alignment and pulse amplitude.

astro-ph.SR

Strong variability of Martian water ice clouds during dust storms revealed from ExoMars Trace Gas Orbiter/NOMAD

Observations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from NOMAD/TGO that investigate the variation of water ice clouds in the perihelion season of Mars Year 34 (April 2018-19), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 Global Dust Storm. We show that this layer rose from 45 to 80 km in altitude on a timescale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 um), as well as mesospheric differences between the Global Dust Storm (<0.5 um) and the 2019 regional dust storm (1.0 um), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere.

astro-ph.EP

Binary outflows from young stars: interaction of co-orbital jet and wind

Jets from young stellar objects provide insight into the workings of the beating heart at the centre of star forming cores. In some cases, multiple pulsed outflows are detected such as the atomic and molecular jets from a proposed binary system in the T\,Tauri star HH30. We investigate here the development and propagation of duelling atomic and molecular outflows stemming from the two stars in co-orbit. We perform a series of numerical experiments with the {\small ZEUS-MP} code with enhanced cooling and chemistry modules. The aim of this work is to identify signatures on scales of order 100 AU. The jet sources are off the grid domain and so it is the propagation and interaction from ~ 20AU out to 100\,AU simulated here. We find that the molecular flow from the orbiting source significantly disturbs the atomic jet, deflecting and twisting the jet and disrupting the jet knots. Regions of high ionisation are generated as the atomic jet rams through the dense molecular outflow. Synthetic images in atomic and molecular lines are presented which demonstrate identifying signatures. In particular, the structure within the atomic jet is lost and H-alpha may trace the walls of the present CO cavity or where the walls have been recently. These results provide a framework for the interpretation of upcoming high resolution observations.

astro-ph.SR

The morphological classification of distant radio galaxies explored with three-dimensional simulations

We explore the observational implications of a large systematic study of high-resolution three dimensional simulations of radio galaxies driven by supersonic jets. For this fiducial study, we employ non-relativistic hydrodynamic adiabatic flows from nozzles into a constant pressure-matched environment. Synchrotron emissivity is approximated via the thermal pressure of injected material. We find that the morphological classification of a simulated radio galaxy depends significantly on several factors with increasing distance (i.e. decreasing observed resolution) and decreasing orientation often causing re-classification from FR\,II (limb-brightened) to FR\,I (limb-darkened) type. We introduce the Lobe or Limb Brightening Index (LBI) to measure the radio lobe type more precisely. The jet density also has an influence as expected with lower density leading to broader and bridged lobe morphologies as well as brighter radio jets. Hence, relating observed source type to the intrinsic jet dynamics is not straightforward. Precession of the jet direction may also be responsible for wide relaxed sources with lower LBI and FR class as well as for X-shaped and double-double structures. Helical structures are not generated because the precession is usually too slow. We conclude that distant radio galaxies could appear systematically more limb-darkened due to merger-related re-direction and precession as well as due to the resolution limitation.

astro-ph.GA

Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration

The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating + AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1-sigma sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5x5 degrees bins. Results show also that such numbers can be improved by a factor of 10 to 30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.

astro-ph.EP

Planetary Spectrum Generator: an accurate online radiative transfer suite for atmospheres, comets, small bodies and exoplanets

We have developed an online radiative-transfer suite (https://psg.gsfc.nasa.gov) applicable to a broad range of planetary objects (e.g., planets, moons, comets, asteroids, TNOs, KBOs, exoplanets). The Planetary Spectrum Generator (PSG) can synthesize planetary spectra (atmospheres and surfaces) for a broad range of wavelengths (UV/Vis/near-IR/IR/far-IR/THz/sub-mm/Radio) from any observatory (e.g., JWST, ALMA, Keck, SOFIA), any orbiter (e.g., ExoMars, Juno), or any lander (e.g., MSL). This is achieved by combining several state-of-the-art radiative transfer models, spectroscopic databases and planetary databases (i.e., climatological and orbital). PSG has a 3D (three-dimensional) orbital calculator for most bodies in the solar system, and all confirmed exoplanets, while the radiative-transfer models can ingest billions of spectral signatures for hundreds of species from several spectroscopic repositories. It integrates the latest radiative-transfer and scattering methods in order to compute high resolution spectra via line-by-line calculations, and utilizes the efficient correlated-k method at moderate resolutions, while for computing cometary spectra, PSG handles non-LTE and LTE excitation processes. PSG includes a realistic noise calculator that integrates several telescope / instrument configurations (e.g., interferometry, coronagraphs) and detector technologies (e.g., CCD, heterodyne detectors, bolometers). Such an integration of advanced spectroscopic methods into an online tool can greatly serve the planetary community, ultimately enabling the retrieval of planetary parameters from remote sensing data, efficient mission planning strategies, interpretation of current and future planetary data, calibration of spectroscopic data, and development of new instrument/spacecraft concepts.

astro-ph.EP

Saltation under Martian Gravity and its Influence on the Global Dust Distribution

Dust and sand motion are a common sight on Mars. Understanding the interaction of atmosphere and Martian soil is fundamental to describe the planet's weather, climate and surface morphology. We set up a wind tunnel to study the lift of a mixture between very fine sand and dust in a Mars simulant soil. The experiments were carried out under Martian gravity in a parabolic flight. The reduced gravity was provided by a centrifuge under external microgravity. The onset of saltation was measured for a fluid threshold shear velocity of 0.82$\pm$0.04 m/s. This is considerably lower than found under Earth gravity. In addition to a reduction in weight, this low threshold can be attributed to gravity dependent cohesive forces within the sand bed, which drop by 2/3 under Martian gravity. The new threshold for saltation leads to a simulation of the annual dust cycle with a Mars GCM that is in agreement with observations.

astro-ph.EP

The Thermophysical Properties of the Bagnold Dunes, Mars: Ground-truthing Orbital Data

In this work, we compare the thermophysical properties and particle sizes derived from the Mars Science Laboratory (MSL) rover's Ground Temperature Sensor (GTS) of the Bagnold dunes, specifically Namib dune, to those derived orbitally from Thermal Emission Imaging System (THEMIS), ultimately linking these measurements to ground-truth particle sizes determined from Mars Hand Lens Imager (MAHLI) images. In general, we find that all three datasets report consistent particle sizes for the Bagnold dunes (~110-350 microns, and are within measurement and model uncertainties), indicating that particle sizes of homogeneous materials determined from orbit are reliable. Furthermore, we examine the effects of two physical characteristics that could influence the modeled thermal inertia and particle sizes, including: 1) fine-scale (cm-m scale) ripples, and 2) thin layering of indurated/armored materials. To first order, we find small scale ripples and thin (approximately centimeter scale) layers do not significantly affect the determination of bulk thermal inertia from orbital thermal data determined from a single nighttime temperature. Modeling of a layer of coarse or indurated material reveals that a thin layer (< ~5 mm; similar to what was observed by the Curiosity rover) would not significantly change the observed thermal properties of the surface and would be dominated by the properties of the underlying material. Thermal inertia and grain sizes of relatively homogeneous materials derived from nighttime orbital data should be considered as reliable, as long as there are not significant sub-pixel anisothermality effects (e.g. lateral mixing of multiple thermophysically distinct materials).

astro-ph.EP

Retrieval of Water Vapor Column Abundance and Aerosol Properties from ChemCam Passive Sky Spectroscopy

We derive water vapor column abundances and aerosol properties from Mars Science Laboratory (MSL) ChemCam passive mode observations of scattered sky light. Each ChemCam passive sky observation acquires spectra at two different elevation angles. We fit these spectra with a discrete-ordinates multiple scattering radiative transfer model, using the correlated-k approximation for gas absorption bands. The retrieval proceeds by first fitting the continuum of the ratio of the two elevation angles to solve for aerosol properties, and then fitting the continuum-removed ratio to solve for gas abundances. The final step of the retrieval makes use of the observed CO2 absorptions and the known CO2 abundance to correct the retrieved water vapor abundance for the effects of the vertical distribution of scattering aerosols and to derive an aerosol scale height parameter. The ChemCam-retrieved water abundances show, with only a few exceptions, the same seasonal behavior and the same timing of seasonal minima and maxima as the TES, CRISM, and REMS-H data sets that we compare them to. However ChemCam-retrieved water abundances are generally lower than zonal and regional scale from-orbit water vapor data, while at the same time being significantly larger than pre-dawn REMS-H abundances. Pending further analysis of REMS-H volume mixing ratio uncertainties, the differences between ChemCam and REMS-H pre-dawn mixing ratios appear to be much too large to be explained by large scale circulations and thus they tend to support the hypothesis of substantial diurnal interactions of water vapor with the surface. Our preliminary aerosol results, meanwhile, show the expected seasonal pattern in dust particle size but also indicate a surprising inter-annual increase in water-ice cloud opacities.

astro-ph.EP

The physical structure of radio galaxies explored with three-dimensional simulations

We present a large systematic study of hydrodynamic simulations of supersonic adiabatic jets in three dimensions to provide a definitive set of results on exploring jet density, Mach number and precession angle as variables. We restrict the set-up to non-relativistic pressure-equilibrium flows into a homogeneous environment. We first focus on the distribution and evolution of physical parameters associated with radio galaxies. We find that the jet density has limited influence on the structure for a given jet Mach number. The speed of advance varies by a small factor for jet densities between 0.1 and 0.0001 of the ambient density while the cocoon and cavity evolution change from narrow pressure balanced to wide over-pressure as the ratio falls. We also find that the fraction of energy transferred to the ambient medium increases with decreasing jet-ambient density ratio, reaching approx 80%. This energy is predominantly in thermal energy with almost all the remainder in ambient kinetic form. The total energy remaining in the lobe is typically under 5\%. We find that radio galaxies with wide transverse cocoons can be generated through slow precession at low Mach numbers. We explore a slow precession model in which the jet direction changes very slowly relative to the jet flow dynamical time. This reveals two separated bow shocks propagating into the ambient medium, one associated with the entire lobe expansion and the other with the immediate impact zone. The lobes generated are generally consistent with observations, displaying straight jets but asymmetric lobes.

astro-ph.GA