89 research outputs found
HOUND: An Open-Source, Low-cost Research Platform for High-speed Off-road Underactuated Nonholonomic Driving
Off-road vehicles are susceptible to rollovers in terrains with large
elevation features, such as steep hills, ditches, and berms. One way to protect
them against rollovers is ruggedization through the use of industrial-grade
parts and physical modifications. However, this solution can be prohibitively
expensive for academic research labs. Our key insight is that a software-based
rollover-prevention system (RPS) enables the use of commercial-off-the-shelf
hardware parts that are cheaper than their industrial counterparts, thus
reducing overall cost. In this paper, we present HOUND, a small-scale,
inexpensive, off-road autonomy platform that can handle challenging outdoor
terrains at high speeds through the integration of an RPS. HOUND is integrated
with a complete stack for perception and control, geared towards aggressive
offroad driving. We deploy HOUND in the real world, at high speeds, on four
different terrains covering 50 km of driving and highlight its utility in
preventing rollovers and traversing difficult terrain. Additionally, through
integration with BeamNG, a state-of-the-art driving simulator, we demonstrate a
significant reduction in rollovers without compromising turning ability across
a series of simulated experiments. Supplementary material can be found on our
website, where we will also release all design documents for the platform:
https://sites.google.com/view/prl-hound .Comment: 6 Pages, 8 Figure
A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)Comment: 25 pages. 24 figures. Accepted for publication in MNRA
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The transcriptional landscape of αβ T cell differentiation
αβT cell differentiation from thymic precursors is a complex process, explored here with the breadth of ImmGen expression datasets, analyzing how differentiation of thymic precursors gives rise to transcriptomes. After surprisingly gradual changes though early T commitment, transit through the CD4+CD8+ stage involves a shutdown or rare breadth, and correlating tightly with MYC. MHC-driven selection promotes a large-scale transcriptional reactivation. We identify distinct signatures that mark cells destined for positive selection versus apoptotic deletion. Differential expression of surprisingly few genes accompany CD4 or CD8 commitment, a similarity that carries through to peripheral T cells and their activation, revealed by mass cytometry phosphoproteomics. The novel transcripts identified as candidate mediators of key transitions help define the “known unknown” of thymocyte differentiation
Rotation Speed of the First Stars
We estimate the rotation speed of Population III (Pop III) stars within a
minihalo at z ~ 20 using a smoothed particle hydrodynamics (SPH) simulation,
beginning from cosmological initial conditions. We follow the evolution of the
primordial gas up to densities of 10^12 cm^-3. Representing the growing
hydrostatic cores with accreting sink particles, we measure the velocities and
angular momenta of all particles that fall onto these protostellar regions.
This allows us to record the angular momentum of the sinks and estimate the
rotational velocity of the Pop III stars expected to form within them. The
rotation rate has important implications for the evolution of the star, the
fate encountered at the end of its life, and the potential for triggering a
gamma-ray burst (GRB). We find that there is sufficient angular momentum to
yield rapidly rotating stars (> 1000 km s^-1, or near break-up speeds). This
indicates that Pop III stars likely experienced strong rotational mixing,
impacting their structure and nucleosynthetic yields. A subset of them was also
likely to result in hypernova explosions, and possibly GRBs.Comment: 14 pages, 7 figures, accepted for publication in MNRA
An XMM-Newton observation of Ark 120: the X-ray spectrum of a `bare' Seyfert 1 nucleus
We report on a long (100 ks) XMM-Newton observation of the bright Seyfert 1
galaxy Arakelian 120. The source previously showed no signs of intrinsic
reddening in its infrared-ultraviolet continuum and previous observations had
shown no evidence for ionized absorption in either the ultraviolet or X-ray
bands. The new XMM-Newton RGS data place tight limits on the presence of an
ionized X-ray absorber and confirm that the X-ray spectrum of Ark 120 is
essentially unmodified by intervening matter. Thus Ark 120 can be considered a
`bare' Seyfert 1 nucleus. This observation therefore offers a clean view of the
X-ray spectrum of a `normal' Seyfert galaxy free from absorption effects. The
spectrum shows a Doppler broadened iron emission line (FWHM ~ 3*10^4 km/s) and
a smooth, continuous soft excess which appears to peak at an energy ~0.5 keV.
This adds weight to the claim that genuine soft excesses (i.e. those due to a
real steepening of the underlying continuum below ~2 keV) are ubiquitous in
Seyfert 1 spectra. However, the detailed shape of the excess could not be
reproduced by any of the simple models tested (power-laws, blackbodies,
Comptonised blackbodies, accretion disc reflection). This observation therefore
demonstrates both the need to understand the soft excess (as a significant
contributor to the luminosity of most Seyfert 1s) and the inability of the
existing, simple models to explain it.Comment: 14 pages. 13 figures. Accepted for publication in MNRA
The choice-structuring properties of security consumption: An exploratory study of security consumption culture within small shops
Using Manunta’s and Manunta’s (2006) theory of the security process and the concept of choice structuring properties as heuristic devices, this paper develops a conceptual framework designed to aid our understanding of the factors that drive security consumption within the context of small shops. The conceptual framework is developed through a number of exploratory interviews with the owners of convenience stores. These suggest a security consumption culture exists that is generated by a desire to protect businesses from crime threats and a sense of isolation from local criminal justice agencies. A self-protection mentality and functional form of worry is observed that creates demand for security, but decisions to purchase specific security objects are dictated by choice structuring properties focused around subjective anxieties about crime events, the extent security devices are seen to offer reassurance and financial constraints. Of course, these findings are (at best) tentative but help to set an agenda for further research in this area
Promotoras as Mental Health Practitioners in Primary Care: A Multi-Method Study of an Intervention to Address Contextual Sources of Depression
We assessed the role of promotoras—briefly trained community health workers—in depression care at community health centers. The intervention focused on four contextual sources of depression in underserved, low-income communities: underemployment, inadequate housing, food insecurity, and violence. A multi-method design included quantitative and ethnographic techniques to study predictors of depression and the intervention’s impact. After a structured training program, primary care practitioners (PCPs) and promotoras collaboratively followed a clinical algorithm in which PCPs prescribed medications and/or arranged consultations by mental health professionals and promotoras addressed the contextual sources of depression. Based on an intake interview with 464 randomly recruited patients, 120 patients with depression were randomized to enhanced care plus the promotora contextual intervention, or to enhanced care alone. All four contextual problems emerged as strong predictors of depression (chi square, p < .05); logistic regression revealed housing and food insecurity as the most important predictors (odds ratios both 2.40, p < .05). Unexpected challenges arose in the intervention’s implementation, involving infrastructure at the health centers, boundaries of the promotoras’ roles, and “turf” issues with medical assistants. In the quantitative assessment, the intervention did not lead to statistically significant improvements in depression (odds ratio 4.33, confidence interval overlapping 1). Ethnographic research demonstrated a predominantly positive response to the intervention among stakeholders, including patients, promotoras, PCPs, non-professional staff workers, administrators, and community advisory board members. Due to continuing unmet mental health needs, we favor further assessment of innovative roles for community health workers
Astrophysical magnetic fields and nonlinear dynamo theory
The current understanding of astrophysical magnetic fields is reviewed,
focusing on their generation and maintenance by turbulence. In the
astrophysical context this generation is usually explained by a self-excited
dynamo, which involves flows that can amplify a weak 'seed' magnetic field
exponentially fast. Particular emphasis is placed on the nonlinear saturation
of the dynamo. Analytic and numerical results are discussed both for small
scale dynamos, which are completely isotropic, and for large scale dynamos,
where some form of parity breaking is crucial. Central to the discussion of
large scale dynamos is the so-called alpha effect which explains the generation
of a mean field if the turbulence lacks mirror symmetry, i.e. if the flow has
kinetic helicity. Large scale dynamos produce small scale helical fields as a
waste product that quench the large scale dynamo and hence the alpha effect.
With this in mind, the microscopic theory of the alpha effect is revisited in
full detail and recent results for the loss of helical magnetic fields are
reviewed.Comment: 285 pages, 72 figures, accepted by Phys. Re
Sound localization by barn owls in a simulated echoic environment
*This article is free to read on the publisher's website* We examined the accuracy and precision with which the barn owl (Tyto alba) turns its head toward sound sources under conditions that evoke the precedence effect (PE) in humans. Stimuli consisted of 25-ms noise bursts emitted from two sources, separated horizontally by 40°, and temporally by 3–50 ms. At delays from 3 to 10 ms, head turns were always directed at the leading source, and were nearly as accurate and precise as turns toward single sources, indicating that the leading source dominates perception. This lead dominance is particularly remarkable, first, because on some trials, the lagging source was significantly higher in amplitude than the lead, arising from the directionality of the owl's ears, and second, because the temporal overlap of the two sounds can degrade the binaural cues with which the owl localizes sounds. With increasing delays, the influence of the lagging source became apparent as the head saccades became increasingly biased toward the lagging source. Furthermore, on some of the trials at delays ≥20 ms, the owl turned its head, first, in the direction of one source, and then the other, suggesting that it was able to resolve two separately localizable sources. At all delays <50 ms, response latencies were longer for paired sources than for single sources. With the possible exception of response latency, these findings demonstrate that the owl exhibits precedence phenomena in sound localization similar to those in humans and cats, and provide a basis for comparison with neurophysiological data
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