375 research outputs found
An Investigation into the effect of monocultural plantation of eucalyptus camaldulensis on soil fertility status
The effect of Eucalyptus camaldulensis monoculture on soil fertility statusin the dry zone was studied comparatively with another monoculture of Tectonagrandis and a naturalforest located in the same area over a period of 5 months.Total litter production of Eucalyptus was 370.68 kglha as compared with1349.07 kglha in Tectona grandis (study period overlapped the leaf senescence)and 217.75 kglha in the natural forest. Litter decomposition was 40.22% inEucalyptus while it was 40.27% and 44.95% in naturalforest, and Tectona respectively.Nutrient release to litter at the time of fall did not differ between thevegetation types. However, it differed between the tree components and nutrients,the orders being leaves>twigs>bark and N>P>K>Ca.Significant differences (p;;;::0.05)were seen in moisture content, pH, organicmatter content, total nitrogen percentage, available potassium and calcium betweenthe soils in the vegetation types
Characterising refractive index dispersion in chalcogenide glasses
Much effort has been devoted to the study of glasses that contain the chalcogen elements (sulfur, selenium and tellurium) for photonicsâ applications out to MIR wavelengths. In this paper we describe some techniques for determining the refractive index dispersion characteristics of these glasses. Knowledge of material dispersion is critical in delivering step-index fibres including with high numerical aperture for mid-infrared supercontinuum generation
(INVITED) Methods for determining the refractive indices and thermo-optic coefficients of chalcogenide glasses at MIR wavelengths
Chalcogenide glasses have attracted much attention for the realization of photonic components owing to their outstanding optical properties in the mid-infrared (MIR) region. However, relatively few refractive index dispersion data are presently available for these glasses at MIR wavelengths. This paper presents a mini review of methods we have both used and developed to determine the refractive indices and thermo-optic coefficients of chalcogenide glasses at MIR wavelengths, and is supported by new results. The mini review should be useful to both new and established researchers in the chalcogenide glass field and fields of MIR optics, fiber-optics and waveguides. Three groups of methods are distinguished: (1) spectroscopic ellipsometry, (2) prism-based methods, and (3) methods using Fourier transform infrared (FTIR) transmission data. The mini review is supported by a brief discussion of refractive index models
Determining the refractive index dispersion and thickness of hot-pressed chalcogenide thin films from an improved Swanepoel method
The well-known method presented by Swanepoel can be used to determine the refractive index dispersion of thin films in the near-infrared region from wavelength values at maxima and minima, only, of the transmission interference fringes. In order to extend this method into the mid-infrared (MIR) spectral region (our measurements are over the wavelength range from 2 to 25 ÎŒm), the method is improved by using a two-term Sellmeier model instead of the Cauchy model as the dispersive equation. Chalcogenide thin films of nominal batch composition As40Se60 (atomic %) and Ge16As24Se15.5Te44.5 (atomic %) are prepared by a hot-pressing technique. The refractive index dispersion of the chalcogenide thin films is determined by the improved method with a standard deviation of less than 0.0027. The accuracy of the method is shown to be better than 0.4% at a wavelength of 3.1 ÎŒm by comparison with a benchmark refractive index value obtained from prism measurements on Ge16As24Se15.5Te44.5 material taken from the same batch
Mid-IR supercontinuum generation in birefringent, low loss, ultra-high numerical aperture Ge-As-Se-Te chalcogenide step-index fiber
This work reports on the fabrication and subsequent supercontinuum generation in a Ge-As-Se-Te/Ge-As-Se core/clad chalcogenide step-index fiber with an elliptical-core and an ultra-high numerical aperture of 1.88â±â0.02 from 2.5 - 15â
”m wavelength. The fiber has very low transmission loss of < 2â
dB/m from 5-11â
”m and a minimum loss of 0.72â±â0.04â
dB/m at 8.56â
”m. Supercontinuum spanning from 2.1â
”m to 11.5â
”m with an average power of âŒ6.5â
mW was achieved by pumping a âŒ16â
cm fiber with a minor/major axis core diameter of 4.2/5.2â
”m with 250 fs pulses at 4.65â
”m wavelength and a repetition rate of 20.88â
MHz. The effect of the elliptical-core was investigated by means of mechanical rotation of the fiber relative to the linear pump polarization, and it was found to cause a shift in the supercontinuum spectral edges by several hundred nanometers
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
Benchmark problems for robust control design
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76996/1/AIAA-20949-475.pd
Theorizing construction industry practice within a disaster risk reduction setting: is it a panacea or an illusion?
Construction industry practice is strongly influenced by the culture surrounding its operations and, with the prevailing emphasis on achieving efficiency, there is a strong focus on outcome metrics such as profitability and employee productivity. With the recent increases in natural hazard events worldwide, and the likelihood that this will worsen still further with anticipated climate changes, the industry is increasingly contributing to building resilience within disaster-affected communities. Existing industry expertise, its educational approaches and the related theoretical frameworks, however, all require adjustment if these changing needs are to be fully addressed. Most importantly, an agenda shift is required from the philosophical side and a more pragmatic approach is needed if community resilience goals and objectives are to be met, rather than the narrower focus of the current metrics-driven management system. A synthesis of the current literature is therefore presented, along with relevant case histories illustrating how such an agenda shift within a disaster management context may influence the development of appropriate theory, as well as impacting upon grass-roots educational requirements. The research concludes by discussing how the âmainstreamingâ of disaster management within construction industry practice could drive forward developments in theorizing expertise and educational provisions across the constituent discipline
- âŠ