Maximum Density Line Research Articles

Thermodynamics, phase diagram, structure and anomalies of supercooled aqueous solutions of trehalose: A molecular dynamics study

We perform molecular dynamics simulations of supercooled solutions of trehalose in TIP4P/2005 water, with concentrations of 20 and 40 wt% (weight percentage) in trehalose, a disaccharide often used in cryopreserving solutions. We analyze the thermodynamics and the structure of these solutions. From the isochores we find that in the 20 wt% solution the temperature of maximum density (TMD) line is still present and it is shifted to lower temperatures with respect to that of pure water. We also find that the Widom line and the liquid-liquid critical point (LLCP) are still present for this concentration and we estimate the position of the LLCP to be shifted at lower temperatures and slightly lower pressures with respect to that of pure water. In the 40 wt% solution we find that the TMD line still persists, but the region of density anomaly shrinks. No LLCP is observed down to the lowest temperature investigated, and maxima of the isothermal compressibility, used as proxy for the Widom line, become weaker. The water oxygen - water oxygen radial distribution functions keep on showing the typical distinction between high density and low density liquid found in pure water, but at low temperatures the presence of trehalose appears to favor the high density phase of water more than in pure water. The number of water molecules of the solvation shell confirms this picture.

Strength Formation and Failure Mechanism Analysis of Cement-Stabilized Laterite Granules Based on Numerical Simulation

The poor grading and significant differences in the mechanical properties of laterite granules in West Africa limit the application of this typical material in road structures. In this paper, the poorly graded laterite granule was blended with fine sand and stabilized with cement to improve the strength of laterite granules. An innovative combination of laboratory tests and numerical simulation analysis using the numerical simulation software PFC2D 5.0 was used to investigate the cement-stabilized laterite granule’s strength formation and failure mechanisms. Laboratory test results show that when the sand content is 40%, the grading curve is close to the maximum theoretical density lines (MTDLs), and the unconfined compressive strength of cement-stabilized laterite granules increased by 35.2% as the cement dosage increased from 2.5% to 5.0%. Numerical simulation tests show that the strength failure of cement-stabilized laterite granules is shear. The failure surface is tilted and through with the axial direction, and the compressive and tensile stresses between the particles cause the failure of the specimen. The simulation test results are close to the laboratory test results, and the deviation rate is less than 10%. It can guide the optimal grading design and strength prediction of cement-stabilized laterite granular materials and provides a basis for reducing laboratory tests and accurate design for such research in the future.

High-compactability asphalt mix design framework based on binary aggregate packing

High compactability is desired for asphalt mixtures to ensure adequate field density and, therefore, the overall quality of asphalt pavements. However, compactability is typically not considered in standard mix design procedures, and existing methods for improving compactability are largely empirical. This paper proposes a mix design framework that considers the compactability of mixtures, anchored by a rational method to adjust aggregate gradation. The method is developed based on the binary aggregate packing model. The proposed mix design is applied to modify four traditional Superpave mixtures into high-compactability mixtures, to demonstrate the concept. The proposed method is compared with two empirical methods used to adjust aggregate gradation: the maximum density line (MDL) and the Bailey method. The results show that the proposed method provides a theoretical explanation of the two empirical methods and reveals their limitations. Mechanical properties related to rutting resistance, low-temperature cracking, and structural capacity of the mixtures are checked by laboratory performance tests to validate the high-compactability mix designs. The results show that, due to their denser aggregate packing, the high-compactability mixtures outperform the traditional Superpave mixtures. Therefore, the proposed high-compactability mix design framework provides a rational and practical approach to improve the field density and the overall quality of asphalt pavements.

Phase behavior of metastable water based on fully ab initio simulations

Based on the strongly constrained and appropriately normed (SCAN) functional, phase behavior of metastable water is studied by ab initio molecular dynamics simulations. A clear van der Waals loop or two-phase coexistence line is observed in the simulated isotherms from 230 to 380 K, providing ab initio evidence for a first-order phase transition. The stability limit line formed by connecting the calculated spinodal points is observed to be a continuous reentrant curve, and the liquid-liquid critical point appears to be hidden at its minimum. The line of maximum density also tends to end at this minimum. These results suggest that the phase behavior of metastable water favors a critical-point-free scenario. Due to the potential limitations of the SCAN functional itself and the failure to take nuclear quantum effects into account, it remains to be further investigated whether the phase behavior of real water remains as predicted in the present work.

Effects of site productive capacity and stand density management on the maximum density line for Eucalyptus pilularis (blackbutt)

ABSTRACT Data were available from two measurements of each stand of a set of stands in native regrowth and plantation forests of Eucalyptus pilularis (blackbutt) in subtropical New South Wales and Queensland. Measurements were made after competition-induced mortality had started in each stand. Most of the regrowth forest had been thinned some time before the measurements. Based on the Reineke model that relates stand stocking density to quadratic mean diameter, a maximum density line was determined for each stand based on methods developed by Vanclay and Sands. It was found that the intercept of the maximum density line increased both with increasing stand site productive capacity and in the thinned regrowth stands. The latter finding does not seem to have been reported for forests before; it is hypothesised to be a result of the delayed redevelopment of inter-tree competitive processes following the major reduction in stand density resulting from thinning. Both effects will have consequences for the structure of density management diagrams commonly used to assist in forest management practice.

Research Concerning the Impact of Geometrical Characteristics of Natural Quarry Aggregates Used in the Composition of Asphalt Concrete

The paper presents studies and laboratory tests concerning the influence of the way the natural quarry aggregates are processed upon the composition of an asphaltic concrete with a maximum grain size of 16 mm (BA 16). The research included the realization of grading curves on certain aggregates, curves lately compared to the maximum density line. This approach aims at classifying certain aspects concerning some of the physical-mechanical characteristics of the asphalt concretes determined through static and dynamic laboratory tests. The research resulted from the fact that in Romania, the elementary gradings on granular fractions from the same source, entering the composition of a certain asphalt mix, differ most of the times depending on the manipulation and the processing manner, respectively. This finding is based on the experience of the laboratory testing, where different values concerning the volume weight, apparent volume weight, voids and rigidity module were obtained on the same asphalt mix dosage prepared according to the prescription in two separate samples.Thus, in order to emphasize the impact of the processing manner (crushing) of the natural aggregates, the authors determined the percentage distribution on intermediate granular fractions of the gradings entering the composition of an asphalt concrete. Since the Romanian Standard for asphalt mixtures stipulates a large grading envelope between the standard sizes corresponding to each grading, the authors considered that there is no uniform distribution ratio depending on the size of the grains entering its composition. The study started from different research methods found in the specialized literature dealing with the calibration of the optimal grading curve. The results of the laboratory tests performed on the asphalt mixture confirm the importance of the particle size analysis in obtaining high quality physical-mechanical characteristics.

Диагностика границ аврорального овала на основе техники инверсии магнитограмм

It is shown that the convection reversal boundary is a fundamental parameter of the magnetosphere-ionosphere coupling, which determines a strong analogy between the electrostatic potential of the ionosphere and the equivalent current function in the dipole geomagnetic field approximation and the uniform ionospheric conductance. We have developed a new ground-based method for automatically diagnosing boundaries of the auroral oval using output data obtained with the magnetogram inversion technique (MIT). Using maps of the current function and field-aligned currents, calculated at the first stage of MIT with uniform ionospheric conductance, we determine the convection reversal boundary, polar cap boundary, equatorial boundary of the auroral oval, and line of maximum density of auroral electrojets. These parameters have previously been determined by a visual-manual method: analyzing maps of field-aligned and equivalent currents on the monitor screen and carrying out predetermined boundaries with the mouse — this took a very long time (weeks and months). The comparison between manually and automatically obtained boundaries has shown that the correlation coefficient between the two boundaries is, on average, 0.85, and the root-mean-square deviation does not exceed 2° in latitude. By providing an adequate accuracy for the boundary determination, the automatic method reduces the time for map processing by a factor of 2–3 (to minutes and hours), releasing a researcher from laborious visual work. The new method is implemented as one of the important modules in the updated MIT software.

Diagnostics of auroral oval boundaries on the basis of the magnetogram inversion technique

It is shown that the convection reversal boundary is a fundamental parameter of the magnetosphere-ionosphere coupling, which determines a strong analogy between the electrostatic potential of the ionosphere and the equivalent current function in the dipole geomagnetic field approximation and the uniform ionospheric conductance. We have developed a new ground-based method for automatically diagnosing boundaries of the auroral oval using output data obtained with the magnetogram inversion technique (MIT). Using maps of the current function and field-aligned currents, calculated at the first stage of MIT with uniform ionospheric conductance, we determine the convection reversal boundary, polar cap boundary, equatorial boundary of the auroral oval, and line of maximum density of auroral electrojets. These parameters have previously been determined by a visual-manual method: analyzing maps of field-aligned and equivalent currents on the monitor screen and carrying out predetermined boundaries with the mouse — this took a very long time (weeks and months). The comparison between manually and automatically obtained boundaries has shown that the correlation coefficient between the two boundaries is, on average, 0.85, and the root-mean-square deviation does not exceed 2° in latitude. By providing an adequate accuracy for the boundary determination, the automatic method reduces the time for map processing by a factor of 2–3 (to minutes and hours), releasing a researcher from laborious visual work. The new method is implemented as one of the important modules in the updated MIT software.

Liquid state anomalies and the relationship to the crystalline phase diagram.

A relationship between the observation of a density anomaly and the underlying crystalline phase diagram is demonstrated. The crystal phase diagram and temperature of maximum density (TMD) lines are calculated over a range of parameter space using a Stillinger-Weber potential. Relationships between the loci of density maxima in the PT plane for the liquid state and the underlying crystalline phase diagram are investigated. Two key potential parameters are systematically varied in order to control the balance between the model two- and three-body interaction terms, and the relative effects of varying the potential parameters analyzed. The respective TMD lines diverge at extreme values with one set of lines showing a reentrant behavior. For each parameter set the TMD lines are extrapolated to T=0K. The corresponding pressures are related to the crystalline phase diagram and are found to lie on or near specific crystal-crystal coexistence lines for a wide range of potential parameters. The density anomaly is observed to vanish corresponding to regions in the crystal phase diagram which lack crystal-crystal coexistence lines potentially offering a new interpretation for the emergence of anomalous behavior.

Diagrama de manejo de la densidad para los bosques mezclados de la región de El Salto, Durango

Introduction: Density management diagrams (DMDs) are useful tools for characterizing andmanaging stand density. Objective: To develop a DMD to schedule thinnings in the natural mixed-species forests of theEl Salto region, Durango. Materials and methods: The data were collected in 441 temporary sampling plots in 263 mixed-species stands with mainly species of the Pinus and Quercus genus. The DMD was based on theHart-Becking index and a relationship of two allometric equations: 1) the quadratic meandiameter (dg, cm) with the density (N, trees·ha−1) and dominant height (Hd, m), and 2) the volume(V, m3·ha−1) with the dg, Hd and N. In fitting equations, the ordinary Nonlinear Least Squares(NLS) method was used simultaneously. The maximum density limit was estimated by potentialquantile regression that related N to Hd. Results and discussion: Efficient goodness-of-fit statistics were reported in the fitted models, interms of Root Mean Square Error (2.29) and coefficient of determination (0.86). The DMDsuggests applying thinnings below the maximum density line to avoid mortality. Through theDMD it is possible to evaluate different silvicultural alternatives, schedule thinnings, maximizegrowth space, promote tree growth and improve forest products. Conclusion: The DMD developed is useful for thinning scheduling to obtain saw-timber atrotation age

Autoaclareo y manejo de la densidad en rodales coetáneos de Pinus patula Schiede ex Schlechtdl. & Cham.

La comunidad de Ixtlán de Juárez, Oaxaca, posee un potencial maderable importante debido a la productividad alta de su bosque. Una de las especies con mayor importancia es Pinus patula debido a la distribución y valor comercial alto; además, es de crecimiento rápido. Por lo tanto, es necesario determinar los límites de la densidad máxima posible que los rodales pueden sustentar para dirigir acciones encaminadas al control de la competencia y redistribución del espacio de crecimiento. En este estudio se estimó la línea de densidad máxima (límite superior del autoaclareo) con el modelo de Reineke mediante dos enfoques de estimación de los parámetros: (1) mínimos cuadrados ordinarios (MCO) y (2) regresión de frontera estocástica (RFE) con los modelos de tipo seminormal (half-normal) y normal truncado (truncated-normal). Para el ajuste del modelo se utilizaron datos de 64 parcelas permanentes de investigación silvícola de 400 m2 de rodales puros y coetáneos de P. patula. La estimación del límite superior del autoaclareo con el modelo de RFE en la forma seminormal fue eficiente y permitió conocer el índice de densidad máxima de los rodales estudiados. La línea de densidad máxima representó el insumo primordial para construir una guía de densidad; herramienta indispensable para la definición de regímenes de aclareo y optimización del espacio de crecimiento.

DENSITY MANAGEMENT DIAGRAMS FOR STANDS OF Eucalyptus grandis W. Hill RS, BRAZIL

ABSTRACT Density Management Diagrams (DMD) contribute to the forester, as they allow the understanding of the current situation of the stand, in addition to helping predict its future conditions. The aim of this study is to develop Density Management Diagrams for Eucalyptus grandis Hill ex Maiden, which will serve as auxiliary models for this species, and to establish appropriate density variation, or management zone, for managing stands to be demarcated on the diagram. Full density stands will be used for the study area. The construction of the diagram will be based on the maximum density line (A-line) obtained from fully stocked stands. From this line, stand density indices (B-line and C-line) will be generated in a gradual and proportional manner. The management zone will be made according to the required thinning weight, and afterwards it will generate Density Management Diagram (DMD). This study allowed us to find a possible adjustment of stand density of Eucalyptus grandis Hill, which is fundamental for management of the stand.

INVESTIGATION ON INDICES OF WORKABILITY AND RUTTING RESISTANCE FOR WEARING COURSE MIXTURES

Simple indices easily help to evaluate a performance of hot mix asphalt mixtures. This study aimed to develop a simple workability index and rutting resistance index for wearing course mixtures. Seven aggregate gradations were prepared to investigate dense, coarse, and fine-graded hot mix asphalt mixtures. The study used the Marshall compactor to fabricate specimens. The Superpave Gyratory Compaction was employed to measure the workability of the seven blends, namely the workability energy parameter of asphalt mixtures. The study also conducted Wheel Tracking Test to evaluate rutting resistance of those mixtures. The results showed a strong relationship between the workability index and the workability energy of hot mix asphalt mixtures, namely increasing the workability energy of mixtures with increasing the workability index value. The workability energy value of an asphalt mixture may be high when the area of continuous maximum density for a proportion of stone, which illustrates a degree of far away from the Fuller maximum density line, is low. Moreover, the rutting resistance index correlated well with rutting resistance of the hot mix asphalt mixtures.

Effect of Superpave restricted zone on volumetric and compaction properties of asphalt mixtures

The Superpave aggregate criteria originally include a restricted zone that lies along the maximum density line and through which gradations are not recommended to pass. The debate with regard to whether or not such a restriction needs to be imposed has been ongoing and inconclusive. In this study, fifteen different gradations of limestone aggregate having three nominal maximum aggregate sizes (NMAS) of 19.0, 12.5, and 9.5mm and covering five types: above, below, crossover through, hump through, and through restricted zone (ARZ, BRZ, CRZ, HRZ, and TRZ) were used to investigate the effect of restricted zone on mixture properties. The Superpave gyratory compactor (SGC) was used to produce the asphalt mixture samples according to the Superpave system. Findings of the study showed that the CRZ, HRZ, and TRZ mixtures generally could meet the Superpave voids in mineral aggregate (VMA) criteria easier than the BRZ and ARZ mixtures. Contrary to the expected trend, the VMA values for the BRZ mixtures were found to be higher than those of the ARZ mixtures for the 19.0-mm NMAS. The HRZ mixtures similar to the ARZ and BRZ mixtures had high effective asphalt binder content. ARZ mixtures generally could violate the Superpave criteria for compaction properties (% of maximum specific gravity at the initial number of gyrations, %Gmm at Ninitial, and% of maximum specific gravity at the maximum number of gyrations, %Gmm at Nmaximum). The TRZ mixtures in general provided the highest dust proportion (DP) values, whereas, the BRZ mixtures provided the lowest DP values.

Species proportions by area in mixtures of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.)

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species’ proportions estimated with this method are best approximated by the proportions of the species’ leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach.

Maximum density-size line for Larix olgensis plantations based on quantile regression.

Based on 378 permanent and 415 temporary plots from Northeast China, the relationship of maximum stand density and quadratic mean diameter at breast height of treesfor Larix olgensis plantation was developed. Linear quantile regression model with different quantiles (τ=0.90, 0.95, 0.99) was used and the optimal model for the maximum density-size line model was selected. The ordinary least square (OLS) and maximum likelihood (ML) regression were also employed to develop the maximum density-size line by using the arbitrary selected data. Generalized Pareto model of extreme value theory was used to calculate the number of limited maximum trees based on the current stands so that the limited density-size line was developed. The linear quantile regression model was compared with the other methods. The results showed that selecting 5 points within the whole diameter class for the maximum density-size line model development would get the satisfying prediction model. The fitting line would deviate from the maximum density-size line with the increasing points selected. The method of ML was superior to OLS in parameter estimation. The linear quantile regression model with the quantile of 0.99 achieved similar fitting results compared with ML regression and the estimation results was much stable. Traditional approach that selecting fittng data was considered arbitrary so that linear quantile regression with quantile of 0.99 was selected as the best model to construct the maximum density-size line with the estimates for the parameters as k=11.790 and β=-1.586, and k=11.820 and β=-1.594 for the limited density-size line model. The determined limited density-size line was above the maximum density-size line but the difference was not pronounced. The validation results by using the data of permanent sample plots showed the models were suitable to predict the maximum and limited density line of the current forest stands, which would provide basis for the sustainable management of L. olgensis plantation.

Phase behaviour of a continuous shouldered well model fluid. A grand canonical Monte Carlo study.

The phase behavior of the continuous shouldered well model fluid proposed by Franzese [J. Mol. Liq. 136 (2007) 267] was examined using the Monte Carlo computer simulations in the grand canonical ensemble. The essential parts of the vapour-liquid and liquid-liquid coexistence envelopes were obtained. The Widom lines departing from coexistence envelopes were calculated using maxima of the fluctuations of the number of particles as a function of chemical potential along various isotherms. The region embracing anomalies in the properties of the model was located using the approximate criterion that involves the excess pair entropy.. The temperature of maximum density line was built by performing canonical Monte Carlo simulations. Our results are consistent with previous results from molecular dynamics constant pressure-constant temperature simulations and provide wider insight into the phase behavior of the model by using the chemical potential as the external parameter.

A Study on Aggregate Gradation of 10 mm Dense-graded Asphalt Mixture using Slag Aggregate

The purpose of this paper is to suggest 10 mm aggregate specification for thin layer asphalt pavement using steel slag. Aggregate gradations of conventional dense-graded asphalt mixtures were made by fuller's model, whereas 10 mm dense-graded asphalt mixture was obtained tender mix due to close to the maximum density line. The proposed aggregate gradation specification was made to have enough VMA and well-interlocking refer to foreign standards. The correlation between the proposed aggregate gradation and the properties of mixtures were analyzed using Gradation Ratio (GR) and Compacted Aggregate Density (CAD). The CAD index has a high of 0.86-0.99 because the CAD index is able to reflect various aggregate properties. As the results of evaluation by CAD index the proposed aggregate gradation provides more reliable stability and VMA. The percent passing (%) of aggregate size smaller than 0.3 mm was limited 10% or more for improving crack resistance. This limitation increased for 15% of the asphalt mixture's toughness.

Confinement effects on the liquid-liquid phase transition and anomalous properties of a monatomic water-like liquid.

We use molecular dynamics simulations to study the effects of confinement on the phase behavior of a water-like monatomic liquid that exhibits a liquid-liquid phase transition (LLPT) and a liquid-liquid critical point (LLCP). The liquid is confined between parallel walls and we focus on the effects of wall separation and surface chemistry (solvophobicity/solvophilicity) on the location of the LLCP, temperature of maximum density (TMD) line, and loci of compressibility maxima (CM). It is found that, independently of the surface solvophobicity/solvophilicity, the LLCP, TMD, and CM lines shift rapidly towards higher pressures and lower temperatures as the wall separation is reduced. It follows that the effects of confinement on the TMD and CM lines are indicative of the confinement effects on the LLCP/LLPT. Confinement effects are observable already when the liquid particles form ≈15 layers between the walls. For the case of water, this corresponds to a separation of ≈4-5 nm between the surfaces, larger than the confining dimension of the nanopores commonly used to study the hypothesized LLPT in confined water. Hence, our results suggest that such experiments should not be interpreted in terms of the phase diagrams proposed for bulk water.

Evaluating management regimes for European beech forests using dynamic programming

Aim of study: This contribution describes a systematic search method for identifying optimum thinning regimes for beech forests (Fagus sylvatica L.) by using a combination of optimization heuristics and a simple whole stand growth prediction model. Area of study: Data to build the model come from standard and management forest inventories as well as yield tables from the Northern and Western part of Germany and from southern and central Denmark.Material and Methods: Growth projections are made from equations to project basal area and top height. The remaining stand variables are recovered from additional equations fitted from forest inventory data or acquired from other authors. Mortality is estimated through an algorithm based on the maximum density line. The optimization routine uses a two-state dynamic programming model. Thinning type is defined by the NG index, which describes the ratio of the proportion of removed trees and basal area with respect to the same proportion before thinning. Main results: Growth equations fitted from inventory data show high goodness of fit with R2 values larger than 0.85 and high significance levels for the parameter estimates. The mortality algorithm converges quickly providing mortality estimates within the expected range.Research Highlights: The combination of a simple growth and yield model within a Dynamic Programming framework in conjunction with NG values as indicators of thinning type yield good estimates of practical thinning schedules compared to thinning recommendations provided by diverse authors.Keywords: beech (Fagus sylvatica L.); NG ratio; thinning optimization; growth and yield simulation; mortality.