Data from large‐scale debris‐flow experiments are combined with modeling of particle‐size segregation to explain the formation of lateral levees enriched in coarse grains. The experimental flows ...consisted of 10 m3 of water‐saturated sand and gravel, which traveled ∼80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface. We measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage. Levees formed by progressive downslope accretion approximately 3.5 m behind the flow front, which advanced steadily at ∼2 m s−1 during most of the runout. Segregation was measured by placing ∼600 coarse tracer pebbles on the bed, which, when entrained into the flow, segregated upwards at ∼6–7.5 cm s−1. When excavated from the deposit these were distributed in a horseshoe‐shaped pattern that became increasingly elevated closer to the deposit termination. Although there was clear evidence for inverse grading during the flow, transect sampling revealed that the resulting leveed deposit was strongly graded laterally, with only weak vertical grading. We construct an empirical, three‐dimensional velocity field resembling the experimental observations, and use this with a particle‐size segregation model to predict the segregation and transport of material through the flow. We infer that coarse material segregates to the flow surface and is transported to the flow front by shear. Within the flow head, coarse material is overridden, then recirculates in spiral trajectories due to size‐segregation, before being advected to the flow edges and deposited to form coarse‐particle‐enriched levees.
Key Points
Coarse particle levees form in debris flows by progressive streamwise accretion
Coarse grains are transported to the flow front, then laterally into the levees
Grain size segregation profoundly affects flow dynamics and deposit structure
Shrublands globally have undergone structural changes due to plant invasions, including the expansion of native trees. Removal of native conifer trees, especially juniper (Juniperus spp.), is ...occurring across the Great Basin of the western U.S. to support declining sagebrush (Artemisia spp.) habitats and associated wildlife species, such as greater sage-grouse (Centrocercus urophasianus). One justification for conifer removal is that it may improve survival of sagebrush-associated wildlife by reducing the abundance of avian predators. However, the relationship between conifer expansion and predator distributions has not been explicitly evaluated. Further, although structural characteristics of habitat are important for generalist predators, overall prey abundance may also affect habitat use by predators. We examined habitat use of common ravens (Corvus corax) and red-tailed hawks (Buteo jamaicensis), two generalist predators whose populations are increasing in western North America, to variation in structural characteristics and prey distributions in sagebrush habitat that has experienced conifer expansion. Structural characteristics of habitat were important predictors of habitat use for both ravens and red-tailed hawks, whereas measures of prey abundance were unimportant for both species likely because generalist predators can use a wide variety of food resources. Ravens, but not red-tailed hawks, responded positively to increasing cover of juniper and the probability of habitat use was highest (> 0.95) where juniper cover within 100 m was > 20%. Habitat use by red-tailed hawks, but not ravens, was greater near cliffs but was not associated with juniper cover. Our study suggests that the removal of conifer in similar environments may lower the probability of habitat use for ravens, a common predator with significant impacts on many prey species. Therefore, we suggest conifer removal may improve sage-grouse reproductive success and survival depending on responses to conifer removal from other predators. Our results may be reflective of similar changes in rangeland ecosystems around the world undergoing expansion of conifer and other woody vegetation. Though species identities differ from sagebrush habitats, generalist avian predators in other habitats may have similar relationships with structural resources.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
During the last fifteen years there has been a paradigm shift in the continuum modelling of granular materials; most notably with the development of rheological models, such as the $\mu (I)$-rheology ...(where $\mu$ is the friction and I is the inertial number), but also with significant advances in theories for particle segregation. This paper details theoretical and numerical frameworks (based on OpenFOAM) which unify these currently disconnected endeavours. Coupling the segregation with the flow, and vice versa, is not only vital for a complete theory of granular materials, but is also beneficial for developing numerical methods to handle evolving free surfaces. This general approach is based on the partially regularized incompressible $\mu (I)$-rheology, which is coupled to the gravity-driven segregation theory of Gray & Ancey (J. Fluid Mech., vol. 678, 2011, pp. 353–588). These advection–diffusion–segregation equations describe the evolving concentrations of the constituents, which then couple back to the variable viscosity in the incompressible Navier–Stokes equations. A novel feature of this approach is that any number of differently sized phases may be included, which may have disparate frictional properties. Further inclusion of an excess air phase, which segregates away from the granular material, then allows the complex evolution of the free surface to be captured simultaneously. Three primary coupling mechanisms are identified: (i) advection of the particle concentrations by the bulk velocity, (ii) feedback of the particle-size and/or frictional properties on the bulk flow field and (iii) influence of the shear rate, pressure, gravity, particle size and particle-size ratio on the locally evolving segregation and diffusion rates. The numerical method is extensively tested in one-way coupled computations, before the fully coupled model is compared with the discrete element method simulations of Tripathi & Khakhar (Phys. Fluids, vol. 23, 2011, 113302) and used to compute the petal-like segregation pattern that spontaneously develops in a square rotating drum.
Abstract Protein turnover is critical for proteostasis, but turnover quantification is challenging, and even in well-studied E. coli , proteome-wide measurements remain scarce. Here, we quantify the ...turnover rates of ~3200 E. coli proteins under 13 conditions by combining heavy isotope labeling with complement reporter ion quantification and find that cytoplasmic proteins are recycled when nitrogen is limited. We use knockout experiments to assign substrates to the known cytoplasmic ATP-dependent proteases. Surprisingly, none of these proteases are responsible for the observed cytoplasmic protein degradation in nitrogen limitation, suggesting that a major proteolysis pathway in E. coli remains to be discovered. Lastly, we show that protein degradation rates are generally independent of cell division rates. Thus, we present broadly applicable technology for protein turnover measurements and provide a rich resource for protein half-lives and protease substrates in E. coli , complementary to genomics data, that will allow researchers to study the control of proteostasis.
When opening a box of mixed nuts, a common experience is to find the largest nuts at the top. This well-known effect is the result of size-segregation where differently sized 'particles' sort ...themselves into distinct layers when shaken, vibrated or sheared. Colloquially this is known as the 'Brazil-nut effect'. While there have been many studies into the phenomena, difficulties observing granular materials mean that we still know relatively little about the process by which irregular larger particles (the Brazil nuts) reach the top. Here, for the first time, we capture the complex dynamics of Brazil nut motion within a sheared nut mixture through time-lapse X-ray Computed Tomography (CT). We have found that the Brazil nuts do not start to rise until they have first rotated sufficiently towards the vertical axis and then ultimately return to a flat orientation when they reach the surface. We also consider why certain Brazil nuts do not rise through the pack. This study highlights the important role of particle shape and orientation in segregation. Further, this ability to track the motion in 3D will pave the way for new experimental studies of segregating mixtures and will open the door to even more realistic simulations and powerful predictive models. Understanding the effect of size and shape on segregation has implications far beyond food products including various anti-mixing behaviors critical to many industries such as pharmaceuticals and mining.
At Gale crater, Mars, ChemCam acquired its first laser-induced breakdown spectroscopy (LIBS) target on Sol 13 of the landed portion of the mission (a Sol is a Mars day). Up to Sol 800, more than 188 ...000 LIBS spectra were acquired on more than 5800 points distributed over about 650 individual targets. We present a comprehensive review of ChemCam scientific accomplishments during that period, together with a focus on the lessons learned from the first use of LIBS in space. For data processing, we describe new tools that had to be developed to account for the uniqueness of Mars data. With regard to chemistry, we present a summary of the composition range measured on Mars for major-element oxides (SiO
2
, TiO
2
, Al
2
O
3
, FeO
T
, MgO, CaO, Na
2
O, K
2
O) based on various multivariate models, with associated precisions. ChemCam also observed H, and the non-metallic elements C, O, P, and S, which are usually difficult to quantify with LIBS. F and Cl are observed through their molecular lines. We discuss the most relevant LIBS lines for detection of minor and trace elements (Li, Rb, Sr, Ba, Cr, Mn, Ni, and Zn). These results were obtained thanks to comprehensive ground reference datasets, which are set to mimic the expected mineralogy and chemistry on Mars. With regard to the first use of LIBS in space, we analyze and quantify, often for the first time, each of the advantages of using stand-off LIBS in space: no sample preparation, analysis within its petrological context, dust removal, sub-millimeter scale investigation, multi-point analysis, the ability to carry out statistical surveys and whole-rock analyses, and rapid data acquisition. We conclude with a discussion of ChemCam performance to survey the geochemistry of Mars, and its valuable support of decisions about selecting where and whether to make observations with more time and resource-intensive tools in the rover's instrument suite. In the end, we present a bird's-eye view of the many scientific results: discovery of felsic Noachian crust, first observation of hydrated soil, discovery of manganese-rich coatings and fracture fills indicating strong oxidation potential in Mars' early atmosphere, characterization of soils by grain size, and wide scale mapping of sedimentary strata, conglomerates, and diagenetic materials.
At Gale crater, Mars, ChemCam acquired its first laser-induced breakdown spectroscopy (LIBS) target on Sol 13 of the landed portion of the mission (a Sol is a Mars day).
In dogs with non-resectable hepatic neoplasia, treatment options are limited. The objectives of this study were to describe the use of a novel drug-eluting embolic microsphere containing paclitaxel ...for use during transarterial chemoembolization (TACE), to compare results of liver-specific owner questionnaires and tumor volume pre- and post-TACE, and to measure systemic paclitaxel concentration post-TACE. Client-owned dogs with non-resectable hepatic neoplasia were prospectively enrolled. All owners completed questionnaires validated for the assessment of subjective outcomes in dogs with cancer before the TACE procedure and approximately 4 weeks after the TACE procedure. A CT scan was performed before TACE and 1 month after TACE; results were compared. Blood samples were obtained at specified time points post-TACE to determine systemic paclitaxel concentrations. Seven dogs (median weight: 8.9 kg; range, 4.3-31 kg) were enrolled. TACE was successfully performed in all dogs, and no intra-procedural complications were encountered. Questionnaire scores improved significantly post-TACE. Among the 6 dogs for which full data were available, median pre-TACE tumor volume was 390 cc (range 152-1,484; interquartile range 231-1,139) and median post-TACE tumor volume was 203 cc (range 98-889; interquartile range 151-369), which was significantly (P = .028) lower. All 6 dogs had a reduction in volume at the post-TACE measurement. Mean percent change in tumor volume was -45.6% (95%CI -58.6 to -32.6%). The mean plasma paclitaxel concentration in canine blood peaked at 4 days post-TACE procedure and was 25.7 ng/mL (range = 3.09-110 ng/mL) Median survival time was 629 days (95%CI 18 to upper limit not reached). The use of a novel paclitaxel-eluting microsphere in this cohort of dogs successfully decreased tumor volume significantly after TACE and improved clinical signs. Future investigation into the use of TACE and other similar therapies is warranted due to the promising outcomes noted in this cohort.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background:Many drugs are unlicensed in children and consequently their doses have been scaled down from those used in adults.Objective:To compare the performance of three scaling models in ...predicting maintenance doses for children from those used in adults.Methods:Three scaling models based on body weight (BW), body surface area (BSA) and BW0.75 were used to predict maintenance doses across the paediatric age band from the equivalent adult doses for 30 different drugs. The predicted doses were compared with those in the British National Formulary for children 2006 (BNFc). Percentage error and mean squared prediction error were used as a measure of precision, and mean prediction error was used as a measure of bias.Results:In the 1-month and 12-month age groups, the different approaches ranked on their bias (least bias first) were BW<BW0.75<BSA and on their precision (most precise first) were BW>BW0.75>BSA. The BSA and BW0.75 methods predicted doses up to 2.86-fold higher than the BNFc in the 1-month and 1-year age group. In the 7-year and 12-year age groups, BW0.75 and BSA performed better than BW for precision and bias, and no predictions were more than 1.8-fold higher than the BNFc. The BW method tended to also under-predict dose across the paediatric age range.Conclusions:Dose scaling should only be used as a last resort for determining a suitable dose in children. No single method was suitable across the entire paediatric age range.
Patient groups prone to polypharmacy and special subpopulations are susceptible to suboptimal treatment. Refined dosing in special populations is imperative to improve therapeutic response and/or ...lowering the risk of toxicity. Model‐informed precision dosing (MIPD) may improve treatment outcomes by achieving the optimal dose for an individual patient. There is, however, relatively little published evidence of large‐scale utility and impact of MIPD, where it is often implemented as local collaborative efforts between academia and healthcare. This article highlights some successful applications of bringing MIPD to clinical care and proposes strategies for wider integration in healthcare. Considerations are brought up herein that will need addressing to see MIPD become “widespread clinical practice,” among those, wider interdisciplinary collaborations and the necessity for further evidence‐based efficacy and cost–benefit analysis of MIPD in healthcare. The implications of MIPD on regulatory policies and pharmaceutical development are also discussed as part of the roadmap.
Dense granular flows can spontaneously self-channelise by forming a pair of parallel-sided static levees on either side of a central flowing channel. This process prevents lateral spreading and ...maintains the flow thickness, and hence mobility, enabling the grains to run out considerably further than a spreading flow on shallow slopes. Since levees commonly form in hazardous geophysical mass flows, such as snow avalanches, debris flows, lahars and pyroclastic flows, this has important implications for risk management in mountainous and volcanic regions. In this paper an avalanche model that incorporates frictional hysteresis, as well as depth-averaged viscous terms derived from the
$\unicodeSTIX{x1D707}(I)$
-rheology, is used to quantitatively model self-channelisation and levee formation. The viscous terms are crucial for determining a smoothly varying steady-state velocity profile across the flowing channel, which has the important property that it does not exert any shear stresses at the levee–channel interfaces. For a fixed mass flux, the resulting boundary value problem for the velocity profile also uniquely determines the width and height of the channel, and the predictions are in very good agreement with existing experimental data for both spherical and angular particles. It is also shown that in the absence of viscous (second-order gradient) terms, the problem degenerates, to produce plug flow in the channel with two frictionless contact discontinuities at the levee–channel margins. Such solutions are not observed in experiments. Moreover, the steady-state inviscid problem lacks a thickness or width selection mechanism and consequently there is no unique solution. The viscous theory is therefore a significant step forward. Fully time-dependent numerical simulations to the viscous model are able to quantitatively capture the process in which the flow self-channelises and show how the levees are initially emplaced behind the flow head. Both experiments and numerical simulations show that the height and width of the channel are not necessarily fixed by these initial values, but respond to changes in the supplied mass flux, allowing narrowing and widening of the channel long after the initial front has passed by. In addition, below a critical mass flux the steady-state solutions become unstable and time-dependent numerical simulations are able to capture the transition to periodic erosion–deposition waves observed in experiments.
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