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We present a method to stabilize two lasers to an optical cavity using pulsed triple frequency modulation. The setup allows simultaneous Pound–Drever–Hall stabilization, as well as independent frequency control, while removing interference terms that limit the frequency scan range and allowing for smaller modulation depths. A review of single, dual, and triple frequency modulation is also presented in addition to a discussion of how to effectively turn pulsed triple frequency modulation into independent dual frequency modulation for each laser. This method would increase the scan range to half the free spectral range. [ABSTRACT FROM AUTHOR]

Introduces articles and research papers of the June 2004 issue of the journal "Lakes & Reservoirs: Research and Management."

AbstractSemi-arid and arid regions (i.e. drylands with annual mean rainfall between 25 and 500 mm) cover approximately one-third of the world’s land area and are inhabited by almost 400 million people. Because they are a resource in short supply, waters in drylands are under increasing human pressures, and many are threatened by rising salinities (salinisation) in particular. Rising salinities result from several causes. The salinities of many large natural salt lakes in drylands are rising as water is diverted from their inflows for irrigation and other uses. The excessive clearance of natural, deep-rooted vegetation from catchments and the discharge of saline agricultural wastewater causes the salinity of many freshwater lakes, wetlands and rivers to rise. The salinisation of some fresh waters is caused by rising saline groundwaters. And in some regions, increasing climatic aridity may be a cause of salinisation. Whatever the cause, salinisation has significant economic, social and environmental impacts. They are usually deleterious and often irreparable. Decreased biodiversity, changes in the natural character of aquatic ecosystems, and lower productivity are frequent ecological effects. In some dryland countries, salinisation is viewed as the single most important threat to water resources. However, the extent and importance of salinisation as a global threat has been greatly underestimated. Recognition of this is the first step in any attempt to manage it effectively. The aims of the present paper, therefore, are three-fold. First, it aims to define the problem and indicate its extent; second, it aims to outline the causes and effects of salinisation; third, it aims to highlight the social, economic and environmental costs and comment on management responses. An overarching aim is to draw attention to the importance of salinisation as a phenomenon of global significance to waters in drylands. [ABSTRACT FROM AUTHOR]

Of 18 nonblack patients with sickle cell disease, 14 had sickle cell anemia, 2 had hemoglobin SC disease, and 2 had hemoglobin S-beta o-thalassemia. The beta s gene cluster haplotypes that were determined in 7 patients were of African origin and were identified as Central African Republic, Central African Republic minor II, Benin, and Senegal. The haplotype Central African Republic minor II was present on the beta o-thalassemia chromosome in 2 patients. None of 10 patients whose alpha-gene status was determined had alpha-thalassemia-2. These data strongly support the concept that the beta s gene on chromosome 11 of these individuals is of African origin and that the alpha-gene locus on chromosome 16 is of white or native American origin. The clinical severity of the disease in these nonblack patients is appropriate to their haplotype without alpha-thalassemia-2 and is comparable with that of black patients. All persons with congenital hemolytic anemia should be examined for the presence of sickle cell disease regardless of physical appearance or ethnic background. [ABSTRACT FROM AUTHOR]

1. It is argued that modern limnology is excessively concerned with the study of fresh waters in the northern temperate region. Limnology has been and is unbalanced in its interests and emphases and, as a result, many widely held limnological concepts need revision. 2. The genesis of the argument is outlined. It involved the initial assumption that Australia was limnologically distinctive. Later, it was realized that since most of the world is arid, semi-arid, tropical or semi-tropical, Australia was much less distinctive than originally thought. 3. Other limnological assumptions considered in the paper concern saline lakes and salinization, the importance and nature of temporary bodies of standing fresh water, biological diversity in tropical fresh waters, the evolutionary importance of permanent freshwater lakes, and the global applicability of the River Continuum Concept. Consideration suggests that some widely-held views on these matters are erroneous. 4. Thus, saline lakes are more important (scientifically, commercially), widespread and numerous environments than is generally thought. Salinization is a significant environmental hazard for many rivers in semi-arid regions. Temporary bodies of standing fresh water are geographically widespread and abundant aquatic environments with high species diversity, and in which many species have restricted distributions and low dispersal abilities. Biological diversity appears to be low in tropical fresh waters. Permanent freshwater lakes are perhaps less important loci for the evolution of the freshwater biota than generally thought, temporary fresh waters more so. Finally, the River Continuum does not seem to be applicable to many running waters outside the north temperate region. 5. A number of suggestions are made of how a better balance in limnology may be arrived at: how a more globally comprehensive intellectual framework may be built. Suggestions include: an increased awareness of the frequently different natures of waters within and beyond the northern temperate region; recognition of the potential benefits to be gained from the study of waters outside the northern temperate region; and, increased caution in the application of many current limnological concepts to waters outside the northern temperate region. 6. Finally, a number of constraints placed upon limnologists domiciled outside North America or Europe is discussed (the need to use English, current trends in funding for limnological research, inequalities in the distribution of knowledge). [ABSTRACT FROM AUTHOR]

Measures the ingestion and assimilation of the Australian brine shrimp Parartemia zietziana in the lakes of Victoria. Reliance of P. zietziana relies on organic matter in lake sediment for food; Measurement of the rate of fecal pellet production; Reasons behind the variation in ingestion rate.

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using metalorganic chemical vapor deposition. A wet chemical etching process was used to expose the intersecting (111)Ga and (111)Ga planes with 6 μm periodicity. Charge collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation. [ABSTRACT FROM AUTHOR]

We report on the calibration of a temperature stabilized ultra-low expansion (ULE) cavity using previously measured molecular tellurium and atomic cesium lines. By means of a dual frequency modulation technique, the frequency dependence of the free spectral range of the ULE cavity is measured and was found to vary by less than 60 Hz over the ∼55 THz range of the calibration. This method of calibration enables the ULE cavity to measure absolute frequencies to better than 1.5 MHz. [ABSTRACT FROM AUTHOR]