Woody species diversity and forest structure from lowland to montane forest in Hyrcanian forest ecoregion

Alborz Mountains host Caspian Hyrcanian forest ecoregion along the northern slopes and forest steppe ecoregion in highlands. Hyrcanian forest covers the southeastern part of Caucasus biodiversity hotspot and is of great biogeographic importance. Altitudinal pattern and correlation between woody species biodiversity (DIV), forest structure ((stem density (DEN), mean basal area (MBA) and mean height class (MHC)) and disturbance (DIS) were explored along 2,400 m altitudinal gradient in Hyrcanian relict forest, Central Alborz Mountains. Vegetation changes from lowland forest (LoF) to mid- altitude forest (MiF) and montane forest (MoF) in this area. The altitudinal gradient was divided into twelve 200 m elevational belts. Point centered quarter method (PCQM) with 96 sampling points and 83 vegetation samples by plot method (PM) were used to record field data. Shannon-Wiener index and Pearson coefficient were used for diversity and correlation analysis. The results showed that DEN decreased linearly, MBA and MHC showed relatively hump shaped and DIS showed a reverse hump shaped pattern of change along altitudinal gradient. Woody species diversity decreased non-steadily from LoF to MoF. Transitional vegetations of Carpinus-Fagus and Fagus-Quercus represented higher diversity of woody taxa compared to adjacent homogenous communities. Significant correlation was observed between altitude and all parameters: DEN with MBA, DIS and DIV; MBA with DIS; MHC with DIS along with DIV; and DIS with DIV at the study area scale. Surprisingly,correlation between studied parameters differed within each vegetation type. Altitude probably acts as a proxy for human and environmental driving forces in this area. Stability of warm and wet condition, season length, soil depth along with forest accessibility probably influences the altitudinal pattern of the studied parameters. Disturbance affects forest structure and consequently diversity; especially in lowlands. The obtained results recommend using both forest biodiversity and mensuration data in management process of forest ecosystems.     

Analysis of stochastic characteristics of the Benue River flow process

Stochastic characteristics of the Benue River streamflow process are examined under conditions of data austerity. The streamflow process is investigated for trend, non-stationarity and seasonality for a time period of 26 years. Results of trend analyses with Mann-Kendall test show that there is no trend in the annual mean discharges. Monthly flow series examined with seasonal Kendall test indicate the presence of positive change in the trend for some months, especially the months of August, January, and February. For the stationarity test, daily and monthly flow series appear to be stationary whereas at 1%, 5%, and 10% significant levels, the stationarity alternative hypothesis is rejected for the annual flow series. Though monthly flow appears to be stationary going by this test, because of high seasonality, it could be said to exhibit periodic stationarity based on the seasonality analysis. The following conclusions are drawn： （1） There is seasonality in both the mean and variance with unimodal distribution. （2） Days with high mean also have high variance. （3） Skewness coefficients for the months within the dry season period are greater than those of the wet season period, and seasonal autocorrelations for streamflow during dry season are generally larger than those of the wet season. Precisely, they are significantly different for most of the months. （4） The autocorrelation functions estimated ＂over time＂ are greater in the absolute value for data that have not been deseasonalised but were initially normalised by logarithmic transformation only, while autocorrelation functions for i = 1, 2 365 estimated ＂over realisations＂ have their coefficients significantly different from other coefficients.     

Thermal stability of a layer with permeable boundaries and variable gravitational field

The aim of this paper is to investigate the thermal stability of a fluid layer with permeable boundaries and a variable gravitational field. It is observed that the principle of exchange of stabilities is valid when the layer is heated form below and the complex growth rate of an arbitrary oscillatory mode exists outside of a circle whose radius depends upon the permeability parameter, Prandtl number and wavelength of the mode. In the case of a layer heated from below, gravity increasing upward has a destabilizing effect whereas the permeability parameter has a stabilizing effect.     

A systematic review of strong gravitational lens modeling software

Despite expanding research activity in gravitational lens modeling, there is no particular software which is considered a standard. Much of the gravitational lens modeling software is written by individual investigators for their own use. Some gravitational lens modeling software is freely available for download but is widely variable with regard to ease of use and quality of documentation. This review of 13 software packages was undertaken to provide a single source of information. Gravitational lens models are classified as parametric models or non-parametric models, and can be further divided into research and educational software. Software used in research includes the GRAVLENS package (with both gravlens and lensmodel), Lenstool, LensPerfect, glafic, PixeLens, SimpLens, Lensview, and GRALE. In this review, GravLensHD, G-Lens, Gravitational Lensing, lens and MOWGLI are categorized as educational programs that are useful for demonstrating various aspects of lensing. Each of the 13 software packages is reviewed with regard to software features (installation, documentation, files provided, etc.) and lensing features (type of model, input data, output data, etc.) as well as a brief review of studies where they have been used. Recent studies have demonstrated the utility of strong gravitational lensing data for mass mapping, and suggest increased use of these techniques in the future. Coupled with the advent of greatly improved imaging, new approaches to modeling of strong gravitational lens systems are needed. This is the first systematic review of strong gravitational lens modeling software, providing investigators with a starting point for future software development to further advance gravitational lens modeling research.     

Lee yang theory for cosmological many body problem

We study the phase transition in a gravitating system by analyzing grand canonical partition function as a function of complex fugacity. We extend the Yang-Lee theory to study phase transitions in the gravitational galaxy clustering of galaxies having a variety of masses. This generalizes our previous work based on the same theory for the single-component system to a multicomponent system. We find that galaxy clustering is sensitive to masses and number densities of individual galaxies at early stages while at later stages collective behavior of the particles is more pronounced. This validates our earlier work obtained from different considerations.     

Development in modeling cyclic loading of sands based on kinematic hardening

In this paper, there is presented an elastoplastic constitutive model to predict sandy soils behavior under monotonic and cyclic loadings. This model is based on an existing model (Cambou‐Jafari‐Sidoroff) that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule used in the deviatoric mechanism is non‐associated and a mixed hardening law controls the evolution of the yield surface. In this research the critical state surface and history surface, which separates the virgin and cyclic states in stress space, are defined. Kinematic hardening modulus and stress–dilatancy law for monotonic and cyclic loadings are effectively modified. With taking hardening modulus as a function of deviatoric and volumetric plastic strain and with defining the history surface and stress reversal, the model has the ability to predict the sandy soils' behavior. All of the model parameters have clear physical meanings and can be determined from usual laboratory tests. In order to validate the model, the results of homogeneous tests on Hostun and Toyoura sands are used. The results of validation show a good capability of the proposed model. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigation of rangeland indicator species using parametric and non-parametric methods in hilly landscapes of central Iran

This study aimed to identify indicator species and explore the most important environmental and management variables contributing to vegetation distribution in a hilly upper dam landscape in Zagros Mountain chain, Iran. A stratified random sampling method was used to collect topographic, edaphic, management and vegetation data. The density and cover percentage of perennial species were measured quantitatively. Indicator species were identified using the two-way indicator species analysis. Besides calculating physiognomic factors in sample sites, 24 soil samples were collected from 0 to 30 cm of soil depth and analyzed in terms of gravel percentage, texture, saturation moisture, organic matter, pH and electrical conductivity in saturation extract, lime percentage, soluble calcium and magnesium, available phosphorus, Cation Exchange Capacity(CEC) and soluble sodium and potassium. Multivariate techniques including Canonical Correspondence Analysis and Multi-Dimensional Scaling were used to explore the relationships of species with environmental and management variables. Seven plants were identified as indicator species due to being significantly correlated with management(grazing or non-grazing) and edaphic variables such as CEC, soil texture, pH, CaCO_3 percentage and physiographic variable including slope, elevation, and convex and concave formations(p 0.05). Overall, overgrazing and its subsequent effects on soil characteristics, loss of vegetation cover and trampling were found as the major causes of deterioration. Sustainable and integrated management practices such as the implementation of appropriate grazing systems were suggested to enhance soil quality and reduce the accelerated erosion in upper dam zones.     

Experimental study of headcut erosion in cohesive soils under different consolidation types and hydraulic parameters

Headcut is a change in stream channel elevation, where there is concentrated flow. Most of the past studies focus on non-cohesive soils, although many problems on the streams occur because of cohesive beds and banks. In this study, eight samples of cohesive soils, with a different composition of silt and clay, for different waterfall heights and flow velocity under long- and short-term natural consolidation conditions were tested. In one of the tests, a sand layer was settled on the headcut bed to investigate its impact on headcut erosion. By increasing clay content, the headcut will remain vertical as it moves backward. Result showed that the effect of clay content reduction was more noticeable under the long-term consolidation condition. In general, the effect of clay percentage variation on the measured parameters is much higher than the effects of waterfall height or flow velocity, and the effect of consolidation type and adding a sand layer on the measured values is much higher than the effect of clay percentage variation on the waterfall height and flow velocity.     

Evaluating evapotranspiration using data mining instead of physical-based model in remote sensing

Theoretical and Applied Climatology - Precise calculations for determining the water requirements of plants and the extent of evapotranspiration are crucial in determining the volume of water...