Synchrotron self-Compton models of high brightness temperature radio sources

We re-examine the maximum brightness temperature that a synchrotron source can sustain by adapting standard synchrotron theory to an electron distribution that exhibits a deficit at low energy. The absence of low energy electrons reduces the absorption of synchrotron photons, allowing the source to reach a higher brightness temperature without the onset of catastrophic cooling. We find that a temperature of ∼10¹⁴ K is possible at GHz frequencies. In addition, a high degree of intrinsic circular polarisation is produced. We compute the stationary, synchrotron and self-Compton spectrum arising from the continuous injection of such a distribution (modelled as a double power-law) balanced by radiative losses and escape, and compare it with the simultaneously observed multi-wavelength spectrum of the BL Lac object S5 0716+714. This framework may provide an explanation of other high brightness-temperature sources without the need for mechanisms such as coherent emission or proton synchrotron radiation.     

Discriminating between background and mine-impacted groundwater at the Phoenix mine,Nevada USA

Differentiating between mineralized and non-mineralized background groundwater chemistry at a mine site can be challenging if there is an overprint of past and/or current mining on naturally mineralized conditions. At the Phoenix mine in the Copper Canyon mining district of Nevada, quantile–quantile H⁺/SO₄ plots were used to segregate four wells clearly impacted by historical mining activity. The mineralogy of rock at the elevation of the well screen interval was used to partition the 53 remaining wells into mineralized and non-mineralized populations. For each class, groundwater chemistry was examined to identify if SO₄ and H⁺ trends were stable (unimpacted) or increasing (impacted). Then each well was mapped as one of four resulting groundwater types across the mine site, defining the spatial extent of the different groups. Several groundwater regions were identified. A group of mineralized, mine-impacted wells (Type II) are located in Philadelphia Canyon adjacent to the Cu leach facility, with the anthropogenically impacted area bounded by several hydrologically downgradient, mineralized, unimpacted wells (Type I) to the south and east. There is a set of non-mineralized, impacted wells (Type III) downgradient from the tailings pond facility, where a historical release of SO₄ is apparent in the well record. However, in some downgradient wells the tailings pond pump-back mitigation system has resulted in recovery of the groundwater quality to a non-mineralized background condition. Finally, in the vicinity of the Reona heap leach pad, there is a group of non-mineralized, unimpacted wells (Type IV). Not surprisingly, most mineralized wells (Types I and II) are located in or near mined areas, while non-mineralized wells (Types III and IV) tend to be in the southern portion of the facility in the alluvia of Buffalo and Reese River valleys.     

Random dynamic response of a tethered buoyant platform production riser

A new normal mode spectral analysis method is presented for calculating r.m.s. riser deflections, bending stresses and lower ball joint angles. Forces on the riser consist of: (a) non-linear fluid drag taking account of the relative velocity due to tethered buoyant platform (TBP) motion, riser elastic deflection and wave induced fluid velocity, (b) wave induced fluid acceleration, (c) inertia forces due to TBP acceleration, and (d) buoyancy. The non-linear fluid drag forces are linearized using Tung and Wu's approximation based on the r.m.s. relative fluid velocity and current. A wide range of results is presented for risers in water depths up to 1000 m and it is observed that 6 normal modes are sufficient for calculating bending stresses. A static analysis is also presented for bending stresses due to wave and current induced drag forces and riser offset.     

Machine learning classifiers for attributing tephra to source volcanoes: an evaluation of methods for Alaska tephras

Glass composition-based correlations of volcanic ash (tephra) traditionally rely on extensive manual plotting. Many previous statistical methods for testing correlations are limited by using geochemical means, masking diagnostic variability. We suggest that machine learning classifiers can expedite correlation, quickly narrowing the list of likely candidates using well-trained models. Eruptives from Alaska's Aleutian Arc-Alaska Peninsula and Wrangell volcanic field were used as a test environment for 11 supervised classification algorithms, trained on nearly 2000 electron probe microanalysis measurements of glass major oxides, representing 10 volcanic sources. Artificial neural networks and random forests were consistently among the top-performing learners (accuracy and kappa > 0.96). Their combination as an average ensemble effectively improves their performance. Using this combined model on tephras from Eklutna Lake, south-central Alaska, showed that predictions match traditional methods and can speed correlation. Although classifiers are useful tools, they should aid expert analysis, not replace it. The Eklutna Lake tephras are mostly from Redoubt Volcano. Besides tephras from known Holocene-active sources, Holocene tephra geochemically consistent with Pleistocene Emmons Lake Volcanic Center (Dawson tephra), but from a yet unknown source, is evident. These tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers.     

SCUBA polarization observations of the magnetic fields in the pre-stellar cores L1498 and L1517B

We have mapped linearly polarized dust emission from the pre-stellar cores L1498 and L1517B with the James Clerk Maxwell Telescope (JCMT) using the Submillimetre Common User Bolometer Array (SCUBA) and its polarimeter (SCUBAPOL) at a wavelength of 850 μm. We use these measurements to determine the plane-of-sky magnetic field orientation in the cores. In L1498, we see a magnetic field across the peak of the core that lies at an offset of ∼19°± 12° to the short axis of the core. This is similar to the offsets seen in previous observations of pre-stellar cores. To the south-east of the peak, in the filamentary tail of the core, we see that the magnetic field has rotated to lie almost parallel to the long axis of the filament. We hypothesize that the field in the core may have decoupled from the field in the filament that connects the core to the rest of the cloud. We use the Chandrasekhar–Fermi (CF) method to measure the plane-of-sky field strength in the core of L1498 to be ∼10 ± 7 μG.
In L1517B, we see a more gradual turn in the field direction from the northern part of the core to the south. This appears to follow a twist in the filament in which the core is buried, with the field staying at a roughly constant ∼25°± 6° offset to the short axis of the filament, consistent with previous observations of pre-stellar cores. Hence these two clouds in an apparently similar evolutionary state, that exhibit similar masses, morphologies and densities, have very different magnetic field configurations. We again use the CF method and calculate the magnetic field strength in L1517B to be ∼30 ± 10 μG. Both cores appear to be roughly virialized. Comparison with our previous work on somewhat denser cores shows that, for the denser cores, thermal and non-thermal (including magnetic) support are approximately equal, while for the lower density cores studied here, thermal support dominates.     

The Stratigraphy,Sedimentology, and Fossils of the Haughton Formation: A Post-Impact Crater-Fill,Devon Island,N.W.T., Canada

Abstract— After the impact that formed Haughton crater, 22.4 ± 1.4 Ma ago (early Miocene), the cavity filled with water and began to accumulate lacustrine sediments. These preserve detailed evidence of pre-impact stratigraphy and post-impact morphology and development of the crater, as well as of the climatic and biotic regime in which it lay. In this report we formally designate these sediments as the Haughton Formation, of which only a 48 m thick remnant covering approximately 7 km² still exists. Dolomite-rich, poorly-sorted silt, fine sand, and mud are the principal lithologies. The formation unconformably overlies a blanket of allochthonous impact breccia forming the floor of the original crater. Presence of a debris-flow deposit in the base of the sequence indicates that lacustine deposition began very shortly after crater formation. The Haughton Formation contains a moderately diverse and highly endemic vertebrate fauna as well as palynomorphs and plant macrofossils that indicate a cool-temperate climatic regime. A small percentage of reworked Late Cretaceous and early Tertiary palynomorphs point to the former existence of the Eureka Sound Formation in the drainage area of the crater. In addition, the distribution of the lake beds indicates the absence of an inner ring on the west side of the crater, and the 3° to 3.5° inward dip of Haughton strata implies that the central mass has subsided approximately 300 to 350 m since deposition began.     

Analytical Solutions for Flow Fields near Drain-and-Gate Reactive Barriers

Permeable reactive barriers (PRBs) are a popular technology for passive contaminant remediation in aquifers through installation of reactive materials in the pathway of a plume. Of fundamental importance are the degree of remediation inside the reactor (residence time) and the portion of groundwater intercepted by a PRB (capture width). Based on a two-dimensional conformal mapping approach (previously used in related work), the latter is studied in the present work for drain-and-gate (DG) PRBs, which may possess a collector and a distributor drain (“full” configuration) or a collector drain only (“simple” configuration). Inherent assumptions are a homogeneous unbounded aquifer with a uniform far field, in which highly permeable drains establish constant head boundaries. Solutions for aquifer flow fields in terms of the complex potential are derived, illustrated, and analyzed for doubly symmetric DG configurations and arbitrary reactor hydraulic resistance as well as ambient groundwater flow direction. A series of practitioner-friendly charts for capture width is given to assist in PRB design and optimization without requiring complex mathematics. DG PRBs are identified as more susceptible to flow divergence around the reactor than configurations using impermeable side structures (e.g., funnel-and-gate), and deployment of impermeable walls on drains is seen to mitigate this problem under certain circumstances.     

The Potential for Rural Heritage Tourism in the Clarence Valley of Northern New South Wales

In the past, heritage tourism has been associated with urban sites but there is now an acceptance of the application of this concept to rural areas. In the Clarence Valley in northern New South Wales there is potential for an extension of agritourism associated with working dairy farms to include safari tours to clusters of dairy heritage sites which are scattered throughout the area. Remnants of the old dairy industry, which began in the Clarence River Valley of New South Wales in the late nineteenth century, are scattered throughout the landscape. Over 300 dairy milking bails remain—ghosts of the former thriving industry when over 2000 dairy farms were operating. Concrete foundations of some creameries built in the 1890s can still be found, and three factory buildings still stand. These relics are disappearing quite rapidly and if the importance of the industry is to be recognised by future generations then it seems that some heritage conservation is overdue. At the same time, in order to survive in a post-deregulated economic environment, the remaining 10 dairy farmers in the Clarence Valley are diversifying their activities, with one form of pluriactivity being agritourism. Currently few of these farmers have entered this field but most of them see its potential to broaden their income base. Associated with agritourism at the farm level, the local government authorities see heritage tourism as a way of increasing employment in the region.