474 research outputs found
Temporary Work on the Bakken Shale
In this thesis, I explore what accounts for worker consent to precarious employment in the context of rapid industrial change in the rural United States. In recent years, domestic oil development has transformed the landscape of western North Dakota and Eastern Montana into a zone of oil production now known as “the Bakken.” The acute demand for labor brought about by this development resulted in vastly inflated wages, which in turn drew workers from around the U.S. and the world. State and private labor market intermediaries, including temporary labor agencies, formed to organize and market this labor force for employers in the area. Just as global demand for oil flagged in late summer of 2015, I completed six weeks of participant observation as a temporary laborer in the Bakken. Using the observational data I collected during my fieldwork, I examine how a private temporary labor agency organized and redistributed the labor force still present in the Bakken, as well as how workers themselves participated in and resisted the commodification of their labor. I find that the interplay of worker aspirations for class mobility, the removal of the labor process from worker-employer negotiations, and the inability of migrant workers to invest in the local community account for consent to this precarious organization of labor, and present major obstacles to worker mobilization
On Solving a Generalized Chinese Remainder Theorem in the Presence of Remainder Errors
In estimating frequencies given that the signal waveforms are undersampled
multiple times, Xia et. al. proposed to use a generalized version of Chinese
remainder Theorem (CRT), where the moduli are which are
not necessarily pairwise coprime. If the errors of the corrupted remainders are
within \tau=\sds \max_{1\le i\le k} \min_{\stackrel{1\le j\le k}{j\neq i}}
\frac{\gcd(M_i,M_j)}4, their schemes can be used to construct an approximation
of the solution to the generalized CRT with an error smaller than .
Accurately finding the quotients is a critical ingredient in their approach. In
this paper, we shall start with a faithful historical account of the
generalized CRT. We then present two treatments of the problem of solving
generalized CRT with erroneous remainders. The first treatment follows the
route of Wang and Xia to find the quotients, but with a simplified process. The
second treatment considers a simplified model of generalized CRT and takes a
different approach by working on the corrupted remainders directly. This
approach also reveals some useful information about the remainders by
inspecting extreme values of the erroneous remainders modulo . Both of
our treatments produce efficient algorithms with essentially optimal
performance. Finally, this paper constructs a counterexample to prove the
sharpness of the error bound
A Unified Picture of Short and Long Gamma-ray Bursts from Compact Binary Mergers
The recent detections of the -s long -ray bursts (GRBs)
211211A and 230307A followed by softer temporally extended emission (EE) and
kilonovae, point to a new GRB class. Using state-of-the-art first-principles
simulations, we introduce a unifying theoretical framework that connects binary
neutron star (BNS) and black hole-NS (BH-NS) merger populations with the
fundamental physics governing compact-binary GRBs (cbGRBs). For binaries with
large total masses , the compact remnant
created by the merger promptly collapses into a BH, surrounded by an accretion
disk. The duration of the magnetically arrested disk (MAD) phase sets the
duration of the roughly constant power cbGRB and could be influenced by the
disk mass, : long cbGRBs such as 211211A are produced by massive disks
(), which form for large binary mass ratio
in BNS or in BH-NS mergers. Once the disk becomes
MAD, the jet power drops with the mass accretion rate as ,
establishing the EE decay. Two scenarios are plausible for short cbGRBs. They
can be powered by BHs with less massive disks, which form for other values.
Alternatively, for binaries with , mergers
should go through a hypermassive NS (HMNS) phase, as inferred for GW170817.
Magnetized outflows from such HMNSs, which typically live for , offer an alternative progenitor for short cbGRBs. The first scenario is
challenged by the bimodal distribution of cbGRB durations and the fact that the
Galactic BNS population peaks at sufficiently low masses that most mergers
should go through a HMNS phase. HMNS-powered jets also more readily account for
other light curve features, from precursor flares to EE characteristics
Surface Composition of Pluto's Kiladze Area and Relationship to Cryovolcanism
A link between exposures of water (HO) ice with traces of an
ammoniated compound (e.g., a salt) and the probable effusion of a water-rich
cryolava onto the surface of Pluto has been established in previous
investigations (Dalle Ore et al. 2019). Here we present the results from the
application of a machine learning technique and a radiative transfer model to a
water-ice-rich exposure in Kiladze area and surroundings on Pluto. We
demonstrate the presence of an ammoniated material suggestive of an
undetermined but relatively recent emplacement event. Kiladze lies in a region
of Pluto's surface that is structurally distinct from that of the areas where
similar evidence points to cryovolcanic activity at some undetermined time in
the planet's history. Although the Kiladze depression superficially resembles
an impact crater, a close inspection of higher-resolution images indicates that
the feature lacks the typical morphology of a crater. Here we suggest that a
cryolava water carrying an ammoniated component may have come onto the surface
at the Kiladze area via one or more volcanic collapses, as in a resurgent
volcanic caldera complex. Large regions east of Kiladze also exhibit the
presence of HO ice and have graben-like structures suggestive of
cryovolcanic activity, but with existing data are not amenable to the detailed
search that might reveal an ammoniated component.Comment: 28 pages, 11 figures, submitted to Icaru
Quaoar: New, Longitudinaly Resolved, Spectroscopic Characterization of Its Surface
(50000) Quaoar, one of the largest Trans-neptunian objects, is comparable in size to Pluto's moon Charon. However, while Charon's surface is rich almost exclusively in H2O ice, Quaoar's surface characterized by ices of CH4, N2, as well as C2H6, a product of irradiation of CH4 (Dalle Ore et al. 2009). Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition, however, its relatively small size did not make it a prime candidate for presence of volatile ices in the study by Schaller and Brown (2007). Furthermore, based on the Brown et al. (2011) study (Brown, Schaller, & Fraser, 2011. A Hypothesis for the Color Diversity of the Kuiper Belt. ApJL, 739, L60) its red coloration points to CH3OH as the ice which, when irradiated, might have produced the red material. We present new visible to near-infrared (0.3-2.48 micrometers) spectro-photometric data obtained with the XSHOOTER (Vernet et al. 2011, A&A, 536A, 105 ) instrument at the VLT-ESO facility at four different longitudes on the surface of Quaoar. The data are complemented by previously published photometric observations obtained in the near-infrared (3.6, 4.5 micrometers) with the Spitzer Space Telescope, which provide an extra set of constraints in the model calculation process in spite of the different observing times that preclude establishing the spatial consistency between the two sets. For each of the four spectra we perform spectral modeling of the entire wavelength range -from 0.3 to 4.5 micrometers- by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We obtain spatially resolved compositional information for the surface of Quaoar supporting the presence of CH4 and C2H6, as previously reported, along with evidence for N2 and NH3OH. The albedo at the two Spitzer bands indicates the likely presence of CO and CO2. CH3OH, predicted on the basis of Quaoar's coloration (Brown et al. 2011), is not found at any of the four longitudes, implying that the presence of this ice is a sufficient, but not necessary condition for reddening of TNO surfaces. Other ices, in particular CH4 (Brunetto et al. 2006), have been shown to be plausible precursors for reddening of TNO surfaces
Composition of KBO (50000) Quaoar
Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune-the new frontiers of the Solar System-and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body. Methods. We present new near-infrared (3.6 and 4.5 mu m) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 mu m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range-from 0.3 to 4.5 mu m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H(2)O ice making use of the crystalline feature at 1.65 mu m. Results. We present a model confirming previous results regarding the presence of crystalline H(2)O and CH(4) ice, as well as C(2)H(6) and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination. Conclusions. Model fits indicate that N(2) may be a significant component, along with a component that is bright at lambda > 3.3 mu m, which we suggest at this time could be amorphous H(2)O ice in tiny grains or thin grain coatings. Irradiated crystalline H(2)O could be the source of small-grained amorphous H(2)O ice. The albedo and composition of Quaoar, in particular the presence of N(2), if confirmed, make this TNO quite similar to Triton and Pluto
An Election Energy Threshold Based Multi-Hop Routing Protocol in a Grid-Clustered Wireless Sensor Network
Owing to the limited energy of sensor nodes (SNs) in a wireless sensor network (WSN), it is important to reduce and balance the energy consumption of the SNs in order to extend the WSN lifetime. Clustering mechanism is a highly efficient and effective mechanism for minimizing the amount of energy that SNs consume during the transmission of data packets. In this paper, an election energy threshold based multi-hop routing protocol (mEEMRP) is presented. In order to minimize energy consumption, this routing protocol uses grid clustering, where the network field is divided into grid clusters. SNs in each grid cluster select a cluster head (CH) based on a weight factor that takes the node location, node’s residual energy (RE) as well as the node’s distance from the base station into consideration. An energy efficient multi-hop routing algorithm is adopted during the transmission of data packets from the cluster heads (CHs) to the base station (BS). This multi-hop routing algorithm uses an election energy threshold value, TnhCH that takes into consideration the RE of CHs as well as the distance between CHs. Simulation results show a 1.77% and 10.65% improvement in terms of network lifetime for two network field scenarios over Energy Efficient Multi-hop Routing Protocol (EEMRP)
Extended BRST invariance in topological Yang Mills theory revisited
Extended BRST invariance (BRST plus anti-BRST invariances) provides in
principle a natural way of introducing the complete gauge fixing structure
associated to a gauge field theory in the minimum representation of the
algebra. However, as it happens in topological Yang Mills theory, not all gauge
fixings can be obtained from a symmetrical extended BRST algebra, where
antighosts belong to the same representation of the Lorentz group of the
corresponding ghosts. We show here that, at non interacting level, a simple
field redefinition makes it possible to start with an extended BRST algebra
with symmetric ghost antighost spectrum and arrive at the gauge fixing action
of topological Yang Mills theory.Comment: Interaction terms heve been included in all the calculations. Two
references added. Version to be published in Phys. Rev. D. 7 pages, Latex, no
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