2,506 research outputs found
Reading Culture through Code
The analysis of source code is an emerging approach to interpreting digital texts. This chapter introduces the methodologies of Critical Code Studies (CCS), situates it within the landscape of media and technology studies, and models the interpretive practices through a few case studies to demonstrate how understanding source code can enrich readings of technoculture through electronic texts
The Racial Formation of Chatbots
In his article The Racial Formation of Chatbots Mark C. Marino introduces electronic literature known as chatbot or conversation agent. These programs are all around us from automated help centers to smartphones (e.g., Siri). These conversation agents are often represented as text or disembodied voices. However, when programmers give them a body or the representation of a body (partial or full), other aspects of their identity become more apparent—particularly their racial or ethnic identity. Marino explores the ways racial identity is constructed through the embodied performance of chatbots and what that indicates for human identity construction on the internet
Generous Poetry Generators
A Critical Code Studies discussion of Nick Montfort's poetry generators, including Taroko Gorge and ppg25
Chain of Dependencies: A New Visual Heuristic to Discover the Underlying Logic of an Argument
This article introduces a new heuristic or technique for students to use when developing an argument for expository writing. The Chain of Dependencies builds on mind-mapping by directing the writer to create sequences of logically related material
Secondary gas in debris discs released following the decay of long-lived radioactive nuclides, catastrophic or resurfacing collisions
Kuiper-like belts of planetesimals orbiting stars other than the Sun are most
commonly detected from the thermal emission of small dust produced in
collisions. Emission from gas, most notably CO, highlights the cometary nature
of these planetesimals. Here we present models for the release of gas from
comet-like bodies in these belts, both due to their thermophysical evolution,
most notably the decay of long-lived radioactive nuclides and collisional
evolution, including catastrophic and gentler resurfacing collisions. We show
that the rate of gas release is not proportional to the rate of dust release,
if non-catastrophic collisions or thermal evolution dominate the release of CO
gas. In this case, care must be taken when inferring the composition of comets.
Non-catastrophic collisions dominate the gas production at earlier times than
catastrophic collisions, depending on the properties of the planetesimal belt.
We highlight the importance of the thermal evolution of comets, including
crucially the decay of long-lived radioactive nuclides, as a source of CO gas
around young (<50Myr) planetary systems, if large (10-100s kms) planetesimals
are present.Comment: Submitted to MNRAS, 16 page
Deprojecting and constraining the vertical thickness of exoKuiper belts
Constraining the vertical and radial structure of debris discs is crucial to
understanding their formation, evolution and dynamics. To measure both the
radial and vertical structure, a disc must be sufficiently inclined. However,
if a disc is too close to edge-on, deprojecting its emission becomes
non-trivial. In this paper we show how Frankenstein, a non-parametric tool to
extract the radial brightness profile of circumstellar discs, can be used to
deproject their emission at any inclination as long as they are optically thin
and axisymmetric. Furthermore, we extend Frankenstein to account for the
vertical thickness of an optically thin disc () and show how it can be
constrained by sampling its posterior probability distribution and assuming a
functional form (e.g. constant ), while fitting the radial profile
non-parametrically. We use this new method to determine the radial and vertical
structure of 16 highly inclined debris discs observed by ALMA. We find a wide
range of vertical aspect ratios, , ranging from (AU Mic) to
(HD 110058), which are consistent with parametric models. We find
a tentative correlation between and the disc fractional width, as expected
if wide discs were more stirred. Assuming discs are self-stirred, the thinnest
discs would require the presence of at least 500 km-sized planetesimals. The
thickest discs would likely require the presence of planets. We also recover
previously inferred and new radial structures, including a potential gap in the
radial distribution of HD 61005. Finally, our new extension of Frankenstein
also allows constraining how varies as a function of radius, which we test
on 49 Ceti, finding that is consistent with being constant.Comment: Accepted for publication in MNRAS. 17 pages. 16 figure
An ALMA Survey of M-dwarfs in the Beta Pictoris Moving Group with Two New Debris Disc Detections
Previous surveys in the far-infrared have found very few, if any, M-dwarf
debris discs among their samples. It has been questioned whether M-dwarf discs
are simply less common than earlier types, or whether the low detection rate
derives from the wavelengths and sensitivities available to those studies. The
highly sensitive, long wavelength Atacama Large Millimetre/submillimetre Array
can shed light on the problem. This paper presents a survey of M-dwarf stars in
the young and nearby Beta Pictoris Moving Group with ALMA at Band 7
(880\,m). From the observational sample we detect two new sub-mm excesses
that likely constitute unresolved debris discs around GJ\,2006\,A and
AT\,Mic\,A and model distributions of the disc fractional luminosities and
temperatures. From the science sample of 36 M-dwarfs including AU\,Mic we find
a disc detection rate of 4/36 or 11.1\% that rises to
23.1\% when adjusted for completeness. We conclude that this
detection rate is consistent with the detection rate of discs around G and K
type stars and that the disc properties are also likely consistent with earlier
type stars. We additionally conclude that M-dwarf stars are not less likely to
host debris discs, but instead their detection requires longer wavelength and
higher sensitivity observations than have previously been employed.Comment: Accepted to MNRA
Inner edges of planetesimal belts: collisionally eroded or truncated?
The radial structure of debris discs can encode important information about
their dynamical and collisional history. In this paper we present a 3-phase
analytical model to analyse the collisional evolution of solids in debris
discs, focusing on their joint radial and temporal dependence. Consistent with
previous models, we find that as the largest planetesimals reach collisional
equilibrium in the inner regions, the surface density of dust and solids
becomes proportional to within a certain critical radius. We
present simple equations to estimate the critical radius and surface density of
dust as a function of the maximum planetesimal size and initial surface density
in solids (and vice versa). We apply this model to ALMA observations of 7 wide
debris discs. We use both parametric and non-parametric modelling to test if
their inner edges are shallow and consistent with collisional evolution. We
find that 4 out of 7 have inner edges consistent with collisional evolution.
Three of these would require small maximum planetesimal sizes below 10 km, with
HR 8799's disc potentially lacking solids larger than a few centimeters. The
remaining systems have inner edges that are much sharper, which requires
maximum planetesimal sizes km. Their sharp inner edges suggest they
could have been truncated by planets, which JWST could detect. In the context
of our model, we find that the 7 discs require surface densities below a
Minimum Mass Solar Nebula, avoiding the so-called disc mass problem. Finally,
during the modelling of HD 107146 we discover that its wide gap is split into
two narrower ones, which could be due to two low-mass planets formed within the
disc.Comment: Accepted for publication in MNRAS, 21 pages, 11 figure
Cometary impactors on the TRAPPIST-1 planets can destroy all planetary atmospheres and rebuild secondary atmospheres on planets f, g, and h
The TRAPPIST-1 system is unique in that it has a chain of seven terrestrial Earth-like planets located close to or in its habitable zone. In this paper, we study the effect of potential cometary impacts on the TRAPPIST-1 planets and how they would affect the primordial atmospheres of these planets. We consider both atmospheric mass loss and volatile delivery with a view to assessing whether any sort of life has a chance to develop. We ran N-body simulations to investigate the orbital evolution of potential impacting comets, to determine which planets are more likely to be impacted and the distributions of impact velocities. We consider three scenarios that could potentially throw comets into the inner region (i.e. within 0.1 au where the seven planets are located) from an (as yet undetected) outer belt similar to the Kuiper belt or an Oort cloud: planet scattering, the Kozai–Lidov mechanism, and Galactic tides. For the different scenarios, we quantify, for each planet, how much atmospheric mass is lost and what mass of volatiles can be delivered over the age of the system depending on the mass scattered out of the outer belt. We find that the resulting high-velocity impacts can easily destroy the primordial atmospheres of all seven planets, even if the mass scattered from the outer belt is as low as that of the Kuiper belt. However, we find that the atmospheres of the outermost planets f, g, and h can also easily be replenished with cometary volatiles (e.g. ~ an Earth ocean mass of water could be delivered). These scenarios would thus imply that the atmospheres of these outermost planets could be more massive than those of the innermost planets, and have volatiles-enriched composition
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