A Model for Analyzing Lake Water Acidification on a Large Region Scale - Part 1: Model Structure

The International Institute for Applied Systems Analysis is developing a computer model which can be used by decision makers to evaluate policies for controlling the impact of acid rain in Europe. As part of this task, a simple dynamic model has been developed for describing the processes leading to acidification of surface waters. The simulation model is constructed of several modules, each of them providing an overview of a particular aspect of lake acidification. The meteorologic module calculates the amount of water and deposition entering the soil or the lake directly each month. The IIASA soil acidity submodel accounts for the soil solution chemistry. A simple hydrologic method is applied for simulating the routing of internal flows so that the convective flow of ions can be estimated. The lake response is calculated according to the equilibrium reactions of inorganic carbon species. These modules are described in this paper. In part 2 the application of the model on a large regional scale will be described. Monte Carlo techniques will be used to determine those ranges and combinations of input values that produce an acceptable present day lake acidity distribution, when the model is driven by a specified deposition

Acidification of Forest Soils: A Model for Analyzing Impacts of Acidic Deposition in Europe - Version II

Acidification is an unfavorable process in forest soils. Timber logging, natural accumulation of biomass in the ecosystem, and acidic deposition are sources of acidification. Acidification causes a risk of damage to plant roots and a subsequent risk of a decline in ecosystem productivity. A dynamic model is introduced for describing the acidification of forest soils. In one-year time steps the model calculates the soil pH as function of acid stress and the buffer mechanisms of the soil. Acid stress is defined as the hydrogen ion input into the top soil. The buffer mechanisms counteract acidification by providing a sink for hydrogen ions. The concepts buffer rate and buffer capacity are used to quantify the buffer mechanisms. The model compares (i) the rate of the acid stress (annual amount) to the buffer rate, and (ii) the accumulated acid stress (over several years) to the buffer capacity. The comparisons produce an estimate of the soil acidity as the output. Since the first version in May 1984 several changes have been implemented following the advice of the experts. For aluminum and iron buffer ranges an equilibrium approach has been introduced. The pH of the silicate, cation exchange and upper aluminum buffer ranges is now a function of base saturation. In the current version of the model forests are assumed to absorb sulfur compounds more effectively than agricultural lands and, moreover, forests are assumed to grow on poor soil types rather than on the average soil type of a grid. The model system as a whole is now available for analyzing the impact of different emission scenarios. The soil acidification model assumes sulfur deposition estimates from the other submodels as input, and as output it computes the total area of forests in Europe with the estimated soil pH lower than any selected threshold value. Additionally it produces estimates of the acidity of European forest soils in a map format

Dusty shells surrounding the carbon variables S Scuti and RT Capricorni

For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented spatial resolution of the PACS photometer on board the Herschel space observatory was employed to map the dusty environments of asymptotic giant branch (AGB) and red supergiant (RSG) stars. Among the morphologically heterogeneous sample, a small fraction of targets is enclosed by spherically symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160 {\mu}m wavelength bands, we investigated the surroundings of the two carbon semiregular variables S Sct and RT Cap, which both show evidence for a history of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric detached shell, 138" in diameter and co-spatial with an already known CO structure. Moreover, weak emission is detected at the outskirts, where the morphology seems indicative of a mild shaping by interaction of the wind with the interstellar medium, which is also supported by the stellar space motion. Two shells are found around RT Cap that were not known so far in either dust emission or from molecular line observations. The inner shell with a diameter of 188" shows an almost immaculate spherical symmetry, while the outer ~5' structure is more irregularly shaped. MoD, a modification of the DUSTY radiative transfer code, was used to model the detached shells. Dust temperatures, shell dust masses, and mass-loss rates are derived for both targets

A discretized integral hydrodynamics

Using an interpolant form for the gradient of a function of position, we write an integral version of the conservation equations for a fluid. In the appropriate limit, these become the usual conservation laws of mass, momentum and energy. We also discuss the special cases of the Navier-Stokes equations for viscous flow and the Fourier law for thermal conduction in the presence of hydrodynamic fluctuations. By means of a discretization procedure, we show how these equations can give rise to the so-called "particle dynamics" of Smoothed Particle Hydrodynamics and Dissipative Particle Dynamics.Comment: 10 pages, RevTex, submitted to Phys. Rev.

Sensitivity Analysis of a Regional Scale Soil Acidification Model

A dynamic model has been introduced for describing the acidification of forest soils. In one-year time steps the model calculates the soil pH as a function of the acid stress and the buffer mechanisms of the soil. Acid stress is defined as the hydrogen ion input into the top soil. The buffer mechanisms counteract acidification by providing a sink for hydrogen ions. The concepts buffer rate and buffer capacity are used to quantify the buffer mechanisms. The model compares (i) the rate of acid stress (annual amount) to the buffer rate, and (ii) the accumulated acid stress (over several years) to the buffer capacity. These two types of comparisons produce an estimate of the soil pH. The model has been incorporated into the RAINS model system of the International Institute for Applied Systems Analysis for analyzing the acidic deposition problem in Europe. The data on acid stress, entering the soils, is obtained from the other submodels. Data on buffer rate and buffer capacity has been collected from soil maps and geological maps. The sensitivity of the model to the forcing functions, parameter values and initialization of the soil variables is evaluated in this paper. The model's sensitivity to initial base saturation appears to be crucial. Base saturation varies widely in forest soils, while the variation of, e.g., total cation exchange capacity is normally not more than +/-50% of the average. Whenever possible, recent measurements about the status of the soil should be used. The difference of acid stress and the buffer rate of silicates determines whether the soil alkalinizes or acidifies. The sensitivity of the model to that difference varies in time and space, being highest in areas where the deposition rate nearly equals the silicate buffer rate, e.g. at present in Scandinavia

Dynamics of threads and polymers in turbulence: power-law distributions and synchronization

We study the behavior of threads and polymers in a turbulent flow. These objects have finite spatial extension, so the flow along them differs slightly. The corresponding drag forces produce a finite average stretching and the thread is stretched most of the time. Nevertheless, the probability of shrinking fluctuations is significant and is known to decay only as a power-law. We show that the exponent of the power law is a universal number independent of the statistics of the flow. For polymers the coil-stretch transition exists: the flow must have a sufficiently large Lyapunov exponent to overcome the elastic resistance and stretch the polymer from the coiled state it takes otherwise. The probability of shrinking from the stretched state above the transition again obeys a power law but with a non-universal exponent. We show that well above the transition the exponent becomes universal and derive the corresponding expression. Furthermore, we demonstrate synchronization: the end-to-end distances of threads or polymers above the transition are synchronized by the flow and become identical. Thus, the transition from Newtonian to non-Newtonian behavior in dilute polymer solutions can be seen as an ordering transition.Comment: 13 pages, version accepted to Journal of Statistical Mechanic

Value of cardiovascular MR in diagnosing left ventricular non-compaction cardiomyopathy and in discriminating between other cardiomyopathies

Objectives: To analyse the value of cardiovascular magnetic resonance (CMR)-derived myocardial parameters to differentiate left ventricular non-compaction cardiomyopathy (LVNC) from other cardiomyopathies and controls. Methods: We retrospectively analysed 12 patients with LVNC, 11 with dilated and 10 with hypertrophic cardiomyopathy and compared them to 24 controls. LVNC patients had to fulfil standard echocardiographic criteria as well as additional clinical and imaging criteria. Cine steady-state free precession and late gadolinium enhancement (LGE) imaging was performed. The total LV myocardial mass index (LV-MMI), compacted (LV-MMI(compacted)), non-compacted (LV-MMI(non-compacted)), percentage LV-MM(non-compacted), ventricular volumes and function were calculated. Data were compared using analysis of variance and Dunnett's test. Additionally, semi-quantitative segmental analyses of the occurrence of increased trabeculation were performed. Results: Total LV-MMI(non-compacted) and percentage LV-MM(non-compacted) were discriminators between patients with LVCN, healthy controls and those with other cardiomyopathies with cut-offs of 15 g/m(2) and 25 %, respectively. Furthermore, trabeculation in basal segments and a ratio of non-compacted/compacted myocardium of >/=3:1 were criteria for LVNC. A combination of these criteria provided sensitivities and specificities of up to 100 %. None of the LVNC patients demonstrated LGE. Conclusions: Absolute CMR quantification of the LV-MMI(non-compacted) or the percentage LV-MM(non-compacted) and increased trabeculation in basal segments allows one to reliably diagnose LVNC and to differentiate it from other cardiomyopathies. Key Points: Cardiac magnetic resonance imaging can reliably diagnose left ventricular non-compaction cardiomyopathy. Differentiation of LVNC from other cardiomyopathies and normal hearts is possible. The best diagnostic performance can be achieved if combined MRI criteria for the diagnosis are used

Simultaneous traveling convection vortex events and Pc1 wave bursts at cusp latitudes observed in Arctic Canada and Svalbard

Traveling convection vortices (TCVs), which appear in ground magnetometer records at near‐cusp latitudes as solitary ~5 mHz pulses, are a signature of dynamical processes in the ion foreshock upstream of the Earth's bow shock that can stimulate transient compressions of the dayside magnetosphere. These compressions can also increase the growth rate of electromagnetic ion cyclotron (EMIC) waves, which appear in ground records at these same latitudes as bursts of Pc1 pulsations. In this study we have identified TCVs and simultaneous Pc1 burst events in two regions, Eastern Arctic Canada and Svalbard, using a combination of fluxgate magnetometers and search coil magnetometers in each region. By looking for the presence of TCVs and Pc1 bursts in two different sequences, we have found that the distribution of Pc1 bursts was more tightly clustered near local noon than that of TCV events, that neither TCVs nor Pc1 bursts were always associated with the other, and even when they occurred simultaneously their amplitudes showed little correlation. Magnetometer data from GOES‐12 were also used to characterize the strength of the magnetic compressions at geosynchronous orbit near the magnetic equator. Compressions > 2 nT at GOES‐12 occurred during 57% of the Canadian TCV events, but during ~85% of the simultaneous TCV/Pc1 burst events. There was again little evident correlation between TCV and GOES‐12 compression amplitudes. We have also documented unusually low EMIC wave activity during this deep solar minimum interval, and we attribute the low occurrence percentage of combined events in this study to this minimum. Key Points TCVs and Pc1 bursts often occur together in high‐latitude magnetometer data Pc1 events were more tightly clustered near local noon than TCV events Pc1 activity was unusually low during the solar activity minimum in 2008–2010.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101826/1/jgra50604.pd

Soft disks in a narrow channel

The pressure components of "soft" disks in a two dimensional narrow channel are analyzed in the dilute gas regime using the Mayer cluster expansion and molecular dynamics. Channels with either periodic or reflecting boundaries are considered. It is found that when the two-body potential, u(r), is singular at some distance r_0, the dependence of the pressure components on the channel width exhibits a singularity at one or more channel widths which are simply related to r_0. In channels with periodic boundary conditions and for potentials which are discontinuous at r_0, the transverse and longitudinal pressure components exhibit a 1/2 and 3/2 singularity, respectively. Continuous potentials with a power law singularity result in weaker singularities of the pressure components. In channels with reflecting boundary conditions the singularities are found to be weaker than those corresponding to periodic boundaries

The Corona Australis star formation complex is accelerating away from the Galactic plane

We study the kinematics of the recently discovered Corona Australis (CrA) chain of clusters by examining the 3D space motion of its young stars using Gaia DR3 and APOGEE-2 data. While we observe linear expansion between the clusters in the Cartesian XY directions, the expansion along Z exhibits a curved pattern. To our knowledge, this is the first time such a nonlinear velocity-position relation has been observed for stellar clusters. We propose a scenario to explain our findings, in which the observed gradient is caused by stellar feedback, accelerating the gas away from the Galactic plane. A traceback analysis confirms that the CrA star formation complex was located near the central clusters of the Scorpius Centaurus (Sco-Cen) OB association 10-15 Myr ago. It contains massive stars and thus offers a natural source of feedback. Based on the velocity of the youngest unbound CrA cluster, we estimate that a median number of about two supernovae would have been sufficient to inject the present-day kinetic energy of the CrA molecular cloud. This number agrees with that of recent studies. The head-tail morphology of the CrA molecular cloud further supports the proposed feedback scenario, in which a feedback force pushed the primordial cloud from the Galactic north, leading to the current separation of 100 pc from the center of Sco-Cen. The formation of spatially and temporally well-defined star formation patterns, such as the CrA chain of clusters, is likely a common process in massive star-forming regions.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic