Effects of flow rates and composition of the filter, and decay/ingrowth correction factors involved with the determination of in situ particulate \u3csup\u3e210\u3c/sup\u3ePo and \u3csup\u3e210\u3c/sup\u3ePb in seawater

Accurate measurements of particulate 210Po (210Pop) and 210Pb (210Pbp) are required in the investigation of (i) partitioning of Po and Pb between particulate and dissolved phases and (ii) export estimates of carbon and other key trace metals from the euphotic zone via sinking particulate matter. Based on the intercomparison of different composition of the filter material (QMA, Supor, Millipore, and Pall GN6) and flow rates (2 to 8 L min), we show how these factors affect the measured concentrations of 210Pop and 210Pbp and their activity ratios (AR). As such, we recommend using Supor 0.4 μm filter and a flow rate of up to 8 L/min for the measurements of210Pop and 210Pbp. Furthermore, we inter-compared 210Pop and 210Pbp obtained by small-volume McLane and large-volume MULVFS pumps. The activities of 210Pop in MULVFS filter samples are somewhat higher than that of McLane filter samples, whereas the 210Pop/210Pb AR collected by McLane pump is distinctly lower, suggesting some fractionation in the collection process by the pumping systems. Likewise comparison of vertical profiles of 210Pop and 210Pbp obtained using McLane pumps by two independent research groups at the two intercalibration stations in the Pacific Ocean show quite similar values except in the mesopelagic waters, suggesting possible uneven loading and presence of larger gelatinous plankton in the filter. Finally, we append a detailed analysis of various correction factors for the accurate calculation of in situ 210Po and 210Pb. Presented results are relevant to the worldwide community that uses 210Po-210Pb as tracers in aquatic systems

Intercalibration studies of \u3csup\u3e210\u3c/sup\u3ePo and \u3csup\u3e210\u3c/sup\u3ePb in dissolved and particulate seawater samples

Documented is an intercalibration (IC) exercise for both 210Po and 210Pb in seawater aliquots distributed between up to eight international laboratories that followed individual protocols. Dissolved and particulate samples were provided by GEOTRACES during two IC cruises at baseline stations in the North Atlantic and North Pacific oceans. Included were surface and/or deep dissolved and particulate samples at each site, plus complete profiles analyzed by the laboratory of the lead author. An unspecified solid phase standard was also distributed with 210Po and 210Pb in secular equilibrium to confirm spike calibrations. The 210Po activities reported n = 8) for the standard were very similar with a relative standard deviation (RSD) of 3.6% and mean value indistinguishable from the certified value, confirming accurate calibration of Po spikes. For seawater samples, the agreement was strongly dependent for both nuclides on the activity of the samples. The agreement was relatively good for dissolved seawater samples (RSD = 9% to 29%, n = 4), moderate for the particulate samples (RSD = 12% to 80%, n = 8), and poor for particulate dip blanks (RSD = 50% to 200%, n = 8). Noted is the higher apparent affinity of 210Po versus 210Pb for polysulphone filter material. Some lack of reproducibility between labs may have been caused by unspecified differences in individual lab protocols and calculations. A minimum sample activity of 0.1 dpm for both nuclides is recommended for an adequate reproducible sample activity. It is suggested that a consistent set of procedures and calculations be used to optimize future 210Po and 210Pb analyses in seawater samples

Peptide exchange on MHC-I by TAPBPR is driven by a negative allostery release cycle.

Chaperones TAPBPR and tapasin associate with class I major histocompatibility complexes (MHC-I) to promote optimization (editing) of peptide cargo. Here, we use solution NMR to investigate the mechanism of peptide exchange. We identify TAPBPR-induced conformational changes on conserved MHC-I molecular surfaces, consistent with our independently determined X-ray structure of the complex. Dynamics present in the empty MHC-I are stabilized by TAPBPR and become progressively dampened with increasing peptide occupancy. Incoming peptides are recognized according to the global stability of the final pMHC-I product and anneal in a native-like conformation to be edited by TAPBPR. Our results demonstrate an inverse relationship between MHC-I peptide occupancy and TAPBPR binding affinity, wherein the lifetime and structural features of transiently bound peptides control the regulation of a conformational switch located near the TAPBPR binding site, which triggers TAPBPR release. These results suggest a similar mechanism for the function of tapasin in the peptide-loading complex

Effect of stopper-rod misalignment on fluid flow in continuous casting of steel

Misalignment of metal-delivery systems can cause asymmetric fluid flow in the mold region of continuous casters, leading to abnormal surface turbulence, insufficient superheat transport to the meniscus, slag entrainment, inclusion entrapment, and other quality problems. This work investigates the effect of stopper-rod misalignment on nozzle and mold flow velocities in a conventional continuous casting process using both a water model and a computational model. Three stopper-rod configurations are studied (aligned, front misaligned by 2 mm, and left misaligned by 2 mm). The 3-D steady k-e finite-volume model matched well with impeller probe measurements of both velocity and its fluctuations. Negligible asymmetry was found near the narrow faces. Asymmetry close to submerged entry nozzle is the main cause of vortex formation observed in all cases. The left-misaligned stopper-rod produces a shallower jet with a higher flow rate from the right port, leading to higher surface velocities on the right surface. This produced substantially more large vortices on the left side. The asymmetry produced by the nozzle length bore diameter ratio of~21 in this work is consistent with the theoretical critical entrance length of~24 for turbulent pipe flow

Mitochondrial phylogeography and demographic history of the Vicuña: implications for conservation

The vicuña (Vicugna vicugna; Miller, 1924) is a conservation success story, having recovered from near extinction in the 1960s to current population levels estimated at 275 000. However, lack of information about its demographic history and genetic diversity has limited both our understanding of its recovery and the development of science-based conservation measures. To examine the evolution and recent demographic history of the vicuña across its current range and to assess its genetic variation and population structure, we sequenced mitochondrial DNA from the control region (CR) for 261 individuals from 29 populations across Peru, Chile and Argentina. Our results suggest that populations currently designated as Vicugna vicugna vicugna and Vicugna vicugna mensalis comprise separate mitochondrial lineages. The current population distribution appears to be the result of a recent demographic expansion associated with the last major glacial event of the Pleistocene in the northern (18 to 22°S) dry Andes 14–12 000 years ago and the establishment of an extremely arid belt known as the 'Dry Diagonal' to 29°S. Within the Dry Diagonal, small populations of V. v. vicugna appear to have survived showing the genetic signature of demographic isolation, whereas to the north V. v. mensalis populations underwent a rapid demographic expansion before recent anthropogenic impacts

Adipocyte-specific protein tyrosine phosphatase 1B deletion increases lipogenesis, adipocyte cell size and is a minor regulator of glucose homeostasis

Peer reviewedPublisher PD

Flow through a circular tube with a permeable Navier slip boundary

For Newtonian fluid flow in a right circular tube, with a linear Navier slip boundary, we show that a second flow field arises which is different to conventional Poiseuille flow in the sense that the corresponding pressure is quadratic in its dependence on the length along the tube, rather than a linear dependence which applies for conventional Poiseuille flow. However, assuming that the quadratic pressure is determined, say from known experimental data, then the new solution only exists for a precisely prescribed permeability along the boundary. While this cannot occur for conventional pipe flow, for fluid flow through carbon nanotubes embedded in a porous matrix, it may well be an entirely realistic possibility, and could well explain some of the high flow rates which have been reported in the literature. Alternatively, if the radial boundary flow is prescribed, then the new flow field exists only for a given quadratic pressure. Our primary purpose here is to demonstrate the existence of a new pipe flow field for a permeable Navier slip boundary and to present a numerical solution and two approximate analytical solutions. The maximum flow rate possible for the new solution is precisely twice that for the conventional Poiseuille flow, which occurs for constant inward directed flow across the boundary

Investigating the highest melting temperature materials : a laser melting study of the TaC-HfC system

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (\u3e4000 K) among other properties.  The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current  research, they were reassessed, for the first time in the last fifty years, using a laser heating technique.  They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest.  Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now