Influence of Doping and Annealing on Structural, Optical and Electrical properties Amorphous ZnO Thin Films Prepared by PLD

The optical gap of the films was calculated from the curve of absorption coefficient (αhע)2 vs. hע and was found to be 3.8 eV at room temperature, and this value decreases from 3.8 to 3.58 eV with increasing of annealing temperature up to 473-673 K, and increases with the Ga doping. λ cutoff was calculated for ZnO and showed an increase with increasing annealing temperature and shifting to longer wavelength, while with doping the λcutoff shifted to shorter wavelength. The photoluminescence (PL) results indicate that the pure ZnO thin films grown at room temperature show strong peaks at 640 nm , but  GaO doped ZnO films showed a band emission in the yellow-green spectral region (380 to 450nm)

Plant Phenology and Water Relations in a Saline Pan-Dune Mosaic in the Western Mojave Desert

An extensive mosaic of small clay pans and low stable dunes exists within Edwards Air Force Base in the western Mojave Desert of California. This pan-dune ecosystem, positioned between the large Rosamond and Rogers dry lakes on the old Pleistocene lakebed of Lake Thompson, provides an opportunity to study the seasonal patterns in growth and flowering phenology and water relations in a saltbush scrub community dominated by a mix of C3 and C4 species. C3 shrubs initiated vegetative growth in February, with current shoot and leaf production largely ceasing in most species by mid-April. The deeply rooted Tetradymia stenolepis and Ericameria nauseosa continued vegetative growth through May. C4 species including Atriplex and the grass Distichilis spicata typically began vegetative growth in mid- to late March, 2–6 weeks later than the first group and continued this growth in most cases through June and July. Reproductive growth commonly did not begin until June and continued into July and/or August. Shrub species showed a general pattern of slowly declining water potentials (increased stress) through the late spring and summer months, reflecting more limited soil water availability. Smaller changes in predawn water potential over this period were seen in the deeply rooted species. Soil moisture availability in the widespread Atriplex confertifolia showed a pattern of variation between pan, dune and open flat microhabtats

Spatial analysis and urban land use planning with emphasis on hospital site selection, case study: Isfahan city

Providing appropriate and equal health care to various classes of society is among the major issues in social welfare. Optimum spatial distribution and equitable locating of health services is important. Due to high population and density in the metropolis of Isfahan, quantitative and qualitative evaluation of hospitals of the city based on the related standards and regulations seems to be necessary. In this study, a combination of GIS and network analysis was used to evaluate the catchment areas of existing hospitals in Isfahan. The results indicated that existing hospitals covered only 23.91 percent of active urban areas at standard time. To promote fair access for citizens and improve the spatial distribution of hospitals based on the related standards and regulations, valuation of urban land for locating new hospital is necessary. Thus, with effective data collection in the form of layers of information such as transportation network, population density, land use, etc. using GIS and AHP model, the authors categorized urban land in 7 categories from poor to very good for construction of hospital

Impact of Ground Water Depletion on the Mesquite Community at Edwards Air Force Base, Western Mojave Desert, California

Edwards Air Force Base (EAFB) provides a habitat refugium for mesquite woodlands in the western Mojave Desert of the Antelope Valley. Although many mesquite communities in the arid southwest are considered invasive as they reduce the extent of grazing lands, the community at EAFB is composed primarily of large, widely spaced trees that provide food and shelter for local wildlife species and recreational opportunities for base personnel. Unfortunately, the range of these mesquite trees appears to be contracting as mature and old individuals dominate the community. Although anecdotal evidence suggests that the fall in the local groundwater table is responsible for the decline of the mesquite community at EAFB, no research has been carried out to confirm this. Our results corroborate the hypothesis that the groundwater table at EAFB has declined in the second half of the 20th century and that the area of the mesquite community is diminishing. Although the mesquite community expanded vigorously from 1956 to 1968, it contracted considerably from 1984 to 2000. The evidence for this observed decline is reinforced by the results of the age-class analysis as the community in 2003 is made up largely of mature, old, dying and dead trees. Few saplings (older than 2 years) and no new seedlings (1–2 years) are present in the study sites, suggesting that the mesquite community may not be able to replenish itself

Ecophysiological Observations on Lane Mountain Milkvetch, Astragalus Jaegerianus (Fabaceae), a Proposed Endangered Species of the Mojave Desert

Astragalus jaegerianus, the Lane Mountain milkvetch, a perennial herbaceous legume, is a rare and very narrow endemic of the central Mojave Desert in San Bernardino County, California, and currently proposed to be listed as an endangered species. This herb grows in the protection of low shrubs. Anatomical observations revealed that leaflets are amphistomatic and have isolateral mesophyll, typical of full-sun desert leaves, and the green stem is an important photosynthetic organ, having abundant stomata and a cylinder of cortical chlore nchyma. Ecophysiological studies showed that this species requires high PFD (1400-1500 μmol m-2s-1) to achieve maximum photosynthetic rates and, therefore, is probably not utilizing the nurse shrub for shade but, instead, as a trellis for upper shoots to intercept high PFD. A study of δ15N indicated that this legume is a nitrogen fixer, with higher tissue nitrogen content than other associated species (3.1% versus 1.8%). The herb-shrub association is speculated to be mutualistic, in that the shrub may benefit from higher soil nitrogen when it grows with a nitrogen-fixing legume, and A. jaegerianus likely uses the nurse shrub for protection from herbivores

Community Structure and Demography in a Saline Pan-Dune Mosaic in the Western Mojave Desert

A unique saline ecological system formed by an extensive mosaic of small clay pans and low stable dunes exists within Edwards Air Force Base in the western Mojave Desert of California. This ecosystem lies between the large Rosamond and Rogers dry lakes on the old Pleistocene lakebed of Lake Thompson. Plant communities on the low and relatively stable dunes were broadly classed as saltbush scrub, with a total canopy cover of 30–36%. Atriplex confertifolia was the typical dominant, with Ericameria nauseosa as an important associate. Taller dunes of younger age and less saline soils had similar plant cover, but a distinct plant community with Atriplex canescens and Krascheninnikovia lanata as dominants and Yucca brevifolia as a common associate. Flat areas adjacent to the dunes were dominated by a virtual monoculture of Atriplex confertifolia. Aboveground shrub and bunchgrass biomass including dead material varied from 503 to 1204 kg ha−1, low in comparison to similar plant communities in the Great Basin. The absence of small saplings and seedlings of many shrub species suggests successful establishment is highly episodic. Seedlings were abundant only in Isocoma acradenia