5,108 research outputs found
Charge separation instability in an unmagnetized disk plasma around a Kerr black hole
In almost all of plasma theories for astrophysical objects, we have assumed
the charge quasi-neutrality of unmagnetized plasmas in global scales. This
assumption has been justified because if there is a charged plasma, it induces
electric field which attracts the opposite charge, and this opposite charge
reduces the charge separation. Here, we report a newly discovered instability
which causes a charge separation in a rotating plasma inside of an innermost
stable circular orbit (ISCO) around a black hole. The growth rate of the
instability is smaller than that of the disk instability even in the unstable
disk region and is forbidden in the stable disk region outside of the ISCO.
However, this growth rate becomes comparable to that of the disk instability
when the plasma density is much lower than a critical density inside of the
ISCO. In such case, the charge separation instability would become apparent and
cause the charged accretion into the black hole, thus charge the hole up.Comment: 15pages, 1 figur
The Lore of Low Methane Livestock:Co-Producing Technology and Animals for Reduced Climate Change Impact
Methane emissions from sheep and cattle production have gained increasing profile in the context of climate change. Policy and scientific research communities have suggested a number of technological approaches to mitigate these emissions. This paper uses the concept of co-production as an analytical framework to understand farmers’ evaluation of a 'good animal’. It examines how technology and sheep and beef cattle are co-produced in the context of concerns about the climate change impact of methane. Drawing on 42 semi-structured interviews, this paper demonstrates that methane emissions are viewed as a natural and integral part of sheep and beef cattle by farmers, rather than as a pollutant. Sheep and beef cattle farmers in the UK are found to be an extremely heterogeneous group that need to be understood in their specific social, environmental and consumer contexts. Some are more amenable to appropriating methane reducing measures than others, but largely because animals are already co-constructed from the natural and the technical for reasons of increased production efficiency
Magnetospheric Eclipses in the Binary Pulsar J0737-3039
(Abridged) In the binary radio pulsar system J0737-3039, the faster pulsar A
is eclipsed once per orbit. We construct a simple geometric model which
successfully reproduces the eclipse light curves, based on the idea that the
radio pulses are attenuated by synchrotron absorption on the closed magnetic
field lines of pulsar B. The model explains most of the properties of the
eclipse: its asymmetric form, the nearly frequency-independent duration, and
the modulation of the brightness of pulsar A at both once and twice the
rotation frequency of pulsar B in different parts of the eclipse. This detailed
agreement confirms the dipolar structure of the star's poloidal magnetic field.
The model makes clear predictions for the degree of linear polarization of the
transmitted radiation.
The weak frequency dependence of the eclipse duration implies that the
absorbing plasma is relativistic, with a density much larger than the
corotation charge density. Such hot, dense plasma can be effectively stored in
the outer magnetosphere, where cyclotron cooling is slow. The gradual loss of
particles inward through the cooling radius is compensated by an upward flux
driven by a fluctuating component of the current, and by the pumping of
magnetic helicity on the closed field lines. The trapped particles are heated
to relativistic energies by the damping of magnetospheric turbulence and, at a
slower rate, by the absorption of the radio emission of the companion pulsar.Comment: 45 pages, 13 figures, submitted to ApJ; minor typo correcte
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'Open Marxism' against and beyond the 'Great Enclosure'? Reflections on How (Not) to Crack Capitalism
The main purpose of this article is to provide an in-depth discussion of John Holloway’s recent book, Crack Capitalism. To this end, the paper offers a detailed account of the key strengths and weaknesses of Holloway’s version of ‘open Marxism’. The analysis is divided into two parts. The first part focuses on six significant strengths of Crack Capitalism: (1) its insistence upon the importance of autonomous forms of agenda-setting for both individual and collective emancipation; (2) its emphasis on the ordinary constitution of social struggles; (3) its fine-grained interpretation of the socio-ontological conditions underlying human agency; (4) its processual conception of radical social transformation; (5) its recognition of the elastic, adaptable, and integrative power of capitalism; and (6) its proposal for an alternative critical theory, commonly known as ‘open Marxism’ or ‘autonomous Marxism’. The second part of the study examines the principal weaknesses of Crack Capitalism: (1) the counterproductive implications of the preponderance of negativity, owing to a one-sided concern with critique, cracks, and crises; (2) conceptual vagueness; (3) an overuse of poetic and metaphorical language; (4) the absence of a serious engagement with the question of normativity; (5) a lack of substantive evidence; (6) a residual economic reductionism; (7) a simplistic notion of gender; (8) the continuing presence of various problematic ‘isms’; (9) the misleading distinction between ‘doing’ and ‘labour’; (10) a reductive understanding of capitalism; (11) an unrealistic view of society; and (12) socio-ontological idealis
Effect of Environmental Factors on How Older Pedestrians Detect an Upcoming Step
The relationships between environmental features and older people’s ability to safely move around a complex pedestrian environment are, as yet, poorly understood. Specifically, the impact of light levels on trip hazard detection during walking has received relatively little attention. This study investigates the effect of illuminance on people’s ability to detect steps of different heights in a laboratory-based controlled environment. Sixteen young and 15 older participants walked along a 13.2 m walkway towards an either ascending or descending step at 200 lux or 4 lux light levels. Trial time, gaze behaviour and distance at which the step was first visually fixated (detection distance) were measured using an eye-tracker. It was found that both the trial time and detection distance of older participants were affected by light level whereas the fixation number and fixation duration of young participants were affected by step-height. Shorter detection distance, greater number of fixations and longer fixation duration were found among older participants as opposed to young participants. The results suggest that the processing efficiency for visual information on an upcoming step is slower among older people than among young people. This implies that the vulnerability of older pedestrians maybe be reduced if better lighting or a simplified visual environment is provided
Gamma-ray Emission from an Outer-Gap Accelerator: Constraints on Magnetospheric Current, Magnetic Inclination, and Distance for PSR B1055-52
We investigate a stationary pair production cascade in the outer
magnetosphere of a spinning neutron star. The charge depletion due to global
flows of charged particles, causes a large electric field along the magnetic
field lines. Migratory electrons and/or positrons are accelerated by this field
to radiate curvature gamma-rays, some of which collide with the X-rays to
materialize as pairs in the gap. The replenished charges partially screen the
electric field, which is self-consistently solved, together with the
distribution functions of particles and gamma-rays. By solving the Vlasov
equations describing this pair production cascade, we demonstrate the existence
of a stationary gap in the outer magnetosphere of PSR B1055-52 for a wide range
of current densities flowing in the accelerator: From sub to super
Goldreich-Julian values. However, we find that the expected GeV spectrum
becomes very soft if the current density exceeds the Goldreich-Julian value. We
also demonstrate that the GeV spectrum softens with decreasing magnetic
inclination and with increasing distance to this pulsar. We thus conclude that
a sub-Goldreich-Julian current, a large magnetic inclination, and a small
distance (500 pc, say) are plausible to account for EGRET observations.
Furthermore, it is found that the TeV flux due to inverse Compton scatterings
of infrared photons whose spectrum is inferred from the Rayleigh-Jeans side of
the soft blackbody spectrum is much less than the observational upper limit.Comment: 16 pages, 13 figures, ApJ in pres
An annular gap acceleration model for -ray emission of pulsars
If the binding energy of the pulsar's surface is not so high (the case of a
neutron star), both the negative and positive charges will flow out freely from
the surface of the star. The annular free flow model for -ray emission
of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of
acceleration regions (annular and core) need to be taken into account. The
annular acceleration region is defined by the magnetic field lines that cross
the null charge surface within the light cylinder. (2). If the potential drop
in the annular region of a pulsar is high enough (normally the cases of young
pulsars), charges in both the annular and the core regions could be accelerated
and produce primary gamma-rays. Secondary pairs are generated in both regions
and stream outwards to power the broadband radiations. (3). The potential drop
in the annular region grows more rapidly than that in the core region. The
annular acceleration process is a key point to produce wide emission beams as
observed. (4). The advantages of both the polar cap and outer gap models are
retained in this model. The geometric properties of the -ray emission
from the annular flow is analogous to that presented in a previous work by Qiao
et al., which match the observations well. (5). Since charges with different
signs leave the pulsar through the annular and the core regions, respectively,
the current closure problem can be partially solved.Comment: 11 pages 2 figures, accepted by Chinese Journal of Astronomy and
Astrophysic
Earth Radiation Budget Experiment (ERBE) scanner instrument anomaly investigation
The results of an ad-hoc committee investigation of in-Earth orbit operational anomalies noted on two identical Earth Radiation Budget Experiment (ERBE) Scanner instruments on two different spacecraft busses is presented. The anomalies are attributed to the bearings and the lubrication scheme for the bearings. A detailed discussion of the pertinent instrument operations, the approach of the investigation team and the current status of the instruments now in Earth orbit is included. The team considered operational changes for these instruments, rework possibilities for the one instrument which is waiting to be launched, and preferable lubrication considerations for specific space operational requirements similar to those for the ERBE scanner bearings
Robotic milking technologies and renegotiating situated ethical relationships on UK dairy farms
Robotic or automatic milking systems (AMS) are novel technologies that take over the labor of dairy farming and reduce the need for human-animal interactions. Because robotic milking involves the replacement of 'conventional' twice-a-day milking managed by people with a system that supposedly allows cows the freedom to be milked automatically whenever they choose, some claim robotic milking has health and welfare benefits for cows, increases productivity, and has lifestyle advantages for dairy farmers. This paper examines how established ethical relations on dairy farms are unsettled by the intervention of a radically different technology such as AMS. The renegotiation of ethical relationships is thus an important dimension of how the actors involved are re-assembled around a new technology. The paper draws on in-depth research on UK dairy farms comparing those using conventional milking technologies with those using AMS. We explore the situated ethical relations that are negotiated in practice, focusing on the contingent and complex nature of human-animal-technology interactions. We show that ethical relations are situated and emergent, and that as the identities, roles, and subjectivities of humans and animals are unsettled through the intervention of a new technology, the ethical relations also shift. © 2013 Springer Science+Business Media Dordrecht
Generalized four-point characterization method for resistive and capacitive contacts
In this paper, a four-point characterization method is developed for
resistive samples connected to either resistive or capacitive contacts.
Provided the circuit equivalent of the complete measurement system is known
including coaxial cable and connector capacitances as well as source output and
amplifier input impedances, a frequency range and capacitive scaling factor can
be determined, whereby four-point characterization can be performed. The
technique is demonstrated with a discrete element test sample over a wide
frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The
data fit well with a circuit simulation of the entire measurement system. A
high impedance preamplifier input stage gives best results, since lock-in input
impedances may differ from manufacturer specifications. The analysis presented
here establishes the utility of capacitive contacts for four-point
characterizations at low frequency.Comment: 21 pages, 10 figure
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