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A series of zinc borosilicate glasses with a molar composition (65-x) ZnO–x ZnF2-15B2O3-20SiO2, where x ranged from 0 to 5 mol%, were prepared by a melt quenching technique. The effect of zinc fluoride (ZnF2) substitution for ZnO on the structural, thermal and crystallization features of the glasses was investigated. Structural information via vibration modes was provided by FTIR analysis that revealed an increased band definition and intensity for the highest content of ZnF2. The incorporation of F− ions caused the Si O Si bond breakage and appearance of non-bridging oxygens in the network. DTA results indicated that ZnF2 addition decreased slightly the onset and peak crystallization temperatures, lowering the thermal stability of the glasses. XRD analysis of glasses heat-treated at 615 °C revealed the formation of willemite (Zn2SiO4) crystals, which was enhanced in glasses containing the highest ZnF2 addition. Microstructural observations by SEM of heat-treated glasses confirmed that the amount and the mean size of willemite crystals precipitated within the glass matrix increased with the addition of ZnF2, which acted as a crystallization promoting agent.

Chitosan with three different molecular weights (538 ± 48, 229 ± 45 and 13 ± 3 kDa) was used to develop biodegradable Inverted Colloidal Crystal (ICC) scaffolds with uniform pore size and interconnected pore network. Mass loss and compression modulus were analyzed after hydrolytic degradation in order to understand the influence of molecular weight on structural and mechanical degradation of chitosan ICC structures. Results show that medium molecular weight chitosan (229 ± 45 kDa) retains ICC structure and compression modulus for an extended period (4 weeks) and is therefore the preferred one for the production of ICC for soft tissue engineering.

Glass samples with a molar composition (64+ x )ZnO–(16− x )B 2 O 3 –20SiO 2 , where x =0 or 1, were successfully synthesized using a melt-quenching technique. Based on differential thermal analysis data, the produced glass samples were submitted to controlled heat-treatments at selected temperatures (610, 615 and 620 °C) during various times ranging from 8 to 30 h. The crystallization of willemite (Zn 2 SiO 4 ) within the glass matrix was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Under specific heat-treatment conditions, transparent nanocomposite glass-ceramics were obtained, as confirmed by UV–vis spectroscopy. The influence of temperature, holding time and glass composition on crystal growth was investigated. The mean crystallite size was determined by image analysis on SEM micrographs. The results indicated an increase on the crystallite size and density with time and temperature. The change of crystallite size with time for the heat-treatments at 615 and 620 °C depended on the glass composition. Under fixed heat-treatment conditions, the crystallite density was comparatively higher for the glass composition with higher ZnO content.

Different glasses based on the ZnO–B 2 O 3 –SiO 2 system, with a ZnO content ≥ 60 mol% and a fixed SiO 2 content (20 mol%), were synthesised using a melt-quenching method. Glass samples with zinc oxide concentrations as high as 65 mol% were prepared successfully without deteriorating the glass-forming ability. The glass samples were submitted to controlled heat-treatments, and the effect of the ZnO/B 2 O 3 molar ratio on the formation of crystalline phases within the glass matrix was investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). DTA results indicated that the glass transition and the onset crystallization temperatures of the studied glasses tended to increase with the increment on the ZnO/B 2 O 3 ratio. XRD data showed that the zinc binary crystalline phases, willemite (Zn 2 SiO 4 ), a zinc orthosilicate, and zinc borate (Zn 3 B 2 O 6 ) could be present in the crystallized glasses, depending on the heat-treatment conditions. The formation of willemite was promoted by an increasing ZnO/B 2 O 3 ratio. Microstructural observations performed by SEM indicated that under controlled experimental parameters (glass composition, heat-treatment temperature and time) the precipitation of nanocrystals within the glass matrix can be achieved, resulting in transparent and translucent willemite glass-ceramics.

A new elliptical sharp-crested weir was developed to address discharge, pollution, and maintenance concerns associated with detention ponds. The elliptical weir was specifically designed to decrease the time and cost associated with clearing debris following storm events. A 2∶1 Froude-scale physical model was constructed and stage-discharge data were collected to analyze the stage-discharge relationship of the new weir. A total of 45 steady-state tests were conducted encompassing nine unique weir geometric configurations. The ellipse ratio varied from 12 to 16, and the gap width varied from 1.5 to 9.1 mm (0.005 to 0.030 ft). Empirical power-regression coefficients were determined for each of the configurations. Also, a theoretical rating equation was derived for the elliptical weir and a discharge coefficient of 0.642 was determined from analyzing the physical-model data. Trapezoidal integral approximation was used to develop an explicit approximate solution for the theoretical rating equation. By...

Cultures of freshwater algae were assembled into artificial communities consisting of 2, 3, 4 and 8 species. The same species were also grown simultaneously in unialgal cultures in separate containers. Different combinations of algae in the same-sized artificial communities were grown three times for 17 weeks. Data obtained from the algae grown separately were treated in the same manner as those from algae grown in the artificial communities. The algae grown as unicultures in separate containers were found to grow in a descending order of abundance: a hierarchical order. When they grew as part of a community, several things happened: (1) all species were inhibited in growth; (2) the inhibition among the species was not uniform; (3) the species often exchanged numerical position in the hierarchy; and (4) the hierarchical order always increased, the degree of hierarchy being determined from the formula −Σpi ln pi . The greater hierarchy in the communities means there was less evenness of numerical distribut...

Capping of contaminated sediments with cleaner sediments is a technique that has been used by the US Army Corps of Engineers, New England Division (NED) since 1979, to avoid or minimize the impacts of contaminated sediments disposed at open water sites. A case study of contaminated sediments from a project on the Thames River, capped at a disposal site offshore of New London, Connecticut, illustrates the application of this technique. Several steps, both regulatory and operational, must be accomplished to ensure proper employment of this technique. First, once it is determined through the permit evaluation process that material to be dredged from a project is not suitable for unconfined open water disposal, the quantity of uncontaminated dredged material needed to achieve a desired cap thickness of 50 to 100 cm must be identified. This quantity may be determined by the use of a computer model - the DAMOS (Disposal Area Monitoring System) Capping Model - which simulates the disposal events and mound formation. Next, the applicant/project proponent must submit a capping plan to NED, which includes provisions for obtaining the necessary quantity of cap material and a schedule for dredging and disposal of both contaminated and cap materials. Upon approval of this plan by NED, the contaminated material may be dredged and disposed at a taut-wire moored buoy located at a specified set of coordinates. The use of such a buoy is critical to the success of capping, since it aids in limiting the distribution of the contaminated material on the seafloor. Post-disposal bathymetric and sediment-profile camera surveys of the contaminated material are conducted to delineate the areal extent of the mound formed during disposal. Several sets of coordinates are then chosen by NED for disposal of the cap material, with the aim of covering all contaminated sediments. The operational success of the capping technique is measured by adequate areal coverage and thickness of the cap over the contaminated material. Thus, following disposal (and sometimes during disposal) of cap material, additional surveys are conducted for this purpose.

Geochemical analysis and visual inspection of cores collected from capped dredged material mounds revealed that in many cores, cap material was clearly distinguishable, both visually and chemically...

Radiofrequency (RF) generated thermal brain lesions are widely used in functional neurosurgery. The size, shape and development of the lesions depends on system parameter settings and the electrode configuration. Difficulties in studying the effect of these factors in vivo stimulated us to develop an in vitro system for standardized comparison between different electrodes and physical parameters. A computer-assisted video system was set-up allowing continuous video recording of RF-generated coagulations in either a standard albumin solution or in the fresh white of a hen's egg as transparent test substrates. Ten lesions were made with each test electrode (two bipolar and three monopolar) in each of the two substrates at 70 degrees, 80 degrees and 90 degrees C (t = 60 sec). Due to the better homogeneity the lesions in the albumin solution were much more regular and reproducible. This made it possible to calculate the size (width 2.2 +/- 0.1 to 5.3 +/- 0.1 mm and length 3.0 +/- 0.1 to 8.7 +/- 0.3 mm) as well as the volume (8.5 +/- 1.4 mm3 to 133.5 +/- 26.8 mm3). It is concluded that this in vitro system offers a reproducible way to study and document the effect of different electrode configurations and RF-generator settings on the formation of a heat lesion. Even if the results are not directly applicable to the living human brain they give an estimate of the form and size of a coagulation lesion and can be of value for standardized comparisons between different electrodes.

The recovery of the hypothalamus-pituitary-adrenal axis after high-dose short-term steroid treatment was investigated in 18 patients undergoing stereotactic thalamotomy during local anaesthesia, in whom perioperative betamethasone was given in a high dose for 4-5 days and withdrawn without tapering. There were no untoward clinical effects of the abrupt withdrawal of the steroid. Seven patients undergoing the same operation without steroid treatment served as controls. The recovery of the hypothalamus-pituitary-adrenal axis after steroid treatment was studied by basal plasma cortisol levels. In 12 patients the reserve capacity of the system was investigated by the cortisol response to insulin induced hypoglycemia as well. It was found that the basal plasma cortisol levels had normalized 2 days after the abrupt withdrawal of betamethasone. In spite of normalized basal cortisol levels the capacity to respond to stress was reduced for a further 3 days. Six to seven days after the steroid withdrawal the stress response was, however, completely restored. It is concluded that high dose, short term steroid treatment can be withdrawn abruptly, omitting the usual tapering of the dose. During the first week after steroid withdrawal the cortisol response to stress is reduced even in the presence of normal basal cortisol levels. During this period extra corticosteroids must be supplied in case of an emergency situation or an operation.

Several thermal spring effluents of western Montana were studied for agal diversity along temperature gradients. Individual communities found at intervals along the effluents were sampled to determine for each species the number of individuals and the volume. Dominance—diversity curves present the data to emphasize the individual communities; population curves and diversity index curves emphasize the gradient communities. See full-text article at JSTOR

Repeated CT examinations were performed following stereotactic placement of radiofrequency lesions in 25 patients in Order to study the appearance of the lesions.

Administration of hypertonic solutions of mannitol as a means of reducing intracranial pressure (ICP) was introduced by WISE and CHATER in 1961 (7) and has since then been widely used in clinical practice for the purpose of temporary as well as long-term control of raised ICP. To what extent such treatment is effective is not clear, however. Several studies (2, 4–8) have demonstrated the temporary pressure fall produced by a single infusion of mannitol but doses varied and data on the effect are given for few patients only. Systematic studies on the value of protracted mannitol treatment are few and do not permit definite conclusions (1, 3). In order to obtain more information on the pressure reduction achieved with mannitol treatment, we started a review of the material of ventricular fluid pressure (VFP) recordings collected in the neurosurgical department in Lund over the years when mannitol has been in use. The results obtained so far are presented.

Fundamentally X-ray photography has not improved since Rontgen photographed his wife’s hand almost eighty years ago. If one looks at radiological journals of the first decade of this century, one can see that such structures as the sella turcica and mastoid cellular system were just as sharply defined then as today. Certainly more care and attention was required to immobilise the structure being X-rayed because the weak X-ray tubes demanded a long exposure, and the processing of the glass plates needed technical skill.

S The development of Flexible Manufacturing Systems comprising welding with high productivity in small lot production is discussed with reference to the changing picture in industry. In many cases the welding processes are now integrated into production cells, where the product concept should be considered to obtain highest productivity for the total production. The integration of the manufacturing processes into such systems underlines the importance of planning, preparation, off-line programming and the use of adaptive control by adding sensor interactivity to the systems. On the manufacturing side this may be regarded as Plateshop Engineering (PSE) in line with CAD/CAM, CAE and other similar expressions. In this connection quality control and quality assurance are bullt into the system. Recent industrial applications are discussed against the background of an ever changing industry. Automatic welding and welding robots also play an important part in the restructuring of the welding industry. The product shares of leading welding companies for hand welding electrodes are decreasing. This development is due to the following: - The decrease in heavy constructions - The introduction of Higher Strength Steels with less weld volume and lighter constructions - Increase in semi-automatic welding - Increase in automatic and robotic welding

When the intracranial pressure is recorded for extended periods of time, the information contained in the record may be difficult to glean from mere inspection of the long, irregular tracing. Some sort of condensing and ordering procedure may be desirable to depict the characteristic features. We have chosen to analyze the quantitative representation of different pressure classes in the record, i.e. the pressure-class frequency distribution. In an earlier study [1] based on this method the data was extracted from the curves manually. Since then a special apparatus has been constructed which performs the analysis.

Remotely sensed data such as spectral reflectance and infrared canopy temperature can be used to quantify crop canopy cover and/or crop water stress, often through the use of vegetation indices calculated from the near-infrared and red bands, and stress indices calculated from the thermal wavelengths. Standardized dual crop coefficient methods calculate both a non-stressed transpiration coefficient (Kcb) that is related to canopy cover, and a stress or transpiration reduction coefficient (Ks) that can be related to soil water deficit or other stress factors (e.g. disease). This study compares several remote sensing methods to determine Kcb and Ks and resulting evapotranspiration (ET) in a deficit irrigation experiment of corn (Zea mays L.) near Greeley, Colorado. Three methods were used to calculate Kcb (tabular, normalized difference vegetation index – NDVI, and canopy cover). Four canopy temperature based methods were used to calculate Ks: Crop Water Stress Index – CWSI, Canopy Temperature Ratio – Tcratio, Degrees Above Non-Stressed – DANS, Degrees Above Canopy Threshold – DACT. Crop ET predicted by these methods was compared to observation and water balance based ET measurements. Thermal indices DANS and DACT were calibrated to convert to Ks. Results showed that stress coefficient methods with less data requirements such as DANS and DACT are responsive to crop water stress as demonstrated by low RMSE of ET calculations, comparable to more data intensive methods such as CWSI. Results indicate which remote sensing methods are appropriate to use given certain data availability and irrigation level, in addition to providing an estimation of the associated error in ET.

Algal samples from a hot spring in Yellowstone National Park, Wyoming, were taken at 10 temperature intervals, 10 m apart, from 57.2 C downstream to 45.7 C, and then the entire visible community was removed. Sampling was continued at the same intervals during the 1st, 3rd, 5th 7th-week successional stages. No successional stage had more than 17 species but four species were noticeably the dominants in the descending order of: Synechococcus lividus, Mastigocladus laminosus, Phormidium laminosum and P. angustissimum. These dominants comprised 94.56%o of the frequency and 70.69% of the volume in the climax community, increasing to 97.37% of the frequency and 91.77% of the volume in the 1st week seral stage. The four dominants alone were sampled at the highest temperature interval in the climax community but only two were present in the lst-week seral stage at the same temperature interval. Other species entered the community as the water cooled in all seral stages. The minor species reappeared in the lst-week seral stage at a mean temperature 2.23 C lower than in the climax community. The uniform conditions in the hot spring environment, and the uniformity of the community (blue green algae) created a situation paradoxical with the competitive exclusion principle by which hierarchal order and diversity were maintained during the seral stages. Succession progressed without the community changing the environment, and without being affected by changing external factors. The combined actions of individual populations, each in exponential growth, may have been responsible for the community overshooting the carrying capacity of the environment for diversity before returning to the carrying capacity of the climax community. INTRODUCTION Community succession is one of the oldest of ecological concepts and has numerous interpretations resulting from varied field studies and, more recently, ecological models. An interpretation by Clements (1905, 1916) considered the community as a single entity that develops, as would an organism, to maturity. This organismic interpretation of succession has been embraced by numerous ecologists for its apparen.t logic, ease of comprehension and the status of its advocate. Clements believed that succession was an orderly process in which a community progressed to a more complex community and that all successional stages in a region would culminate in one monoclimax. From Clements' aspect "community and succession concepts were lineal descendants of a long tradition of natural philosophy which held that there were design, purpose and unity in nature and that these required a holistic approach to their understanding" (McIntosh, 1980). Gleason (1926), as perhaps the most prominent early ecologist to reject Clements' interpretation of succession, considered succession to be an ecological process of the mass effect of individual plants acting within the community the core of the individualistic concept of succession. The long span of time involved in successional studies has been a disadvantage in studying the process on one site (McIntosh, 1980). Henry and Swan (1974) believed that one generation of white pine can dominate a forest for 200-250 years before other species begin replacing them. Gleason (1927) wrote that, "Succession in general is very slow, and the vegetational history of any particular habitat is more apt to be measured in thousands of years, or even in tens of thousands, than in centuries or decades." Because of this slow rate of terrestrial succession and because meteorological records at the time (1927) extended less than a century, Gleason further stated that a studied community might actually be in retrogression. Hot spring communities offer an excellent 1 This study was supported in part by the Grants and Research Funding Committee, Southeast Missouri State University.

Cover, volume and dry weight of the aquatic macrophytes of Portage Creek in Kalamazoo Co., Michigan, were studied. Two series of water analyses 4 years apart were made for the length of the stream. The stream began in an unpopulated, uncultivated area and flowed into an urban area where it received paper mill wastes, after which the aquatic macrophytes were completely absent. The second series of analyses, made 1 year after the cessation of paper mill effluents, showed a tenfold reduction of turbidity in the polluted portion, suggesting that turbidity was the most probable cause for the absence of macrophytes in previous years. The substrate cover by macrophytes in the upstream unpolluted portion was 41%. On the basis of the total plant cover, the two dominant species were Potamogeton pectinatus (44%) and Sparganium americanum (18%). The portion of the water volume occupied by aquatic macrophytes was 0.043%. Four of the 10 species found occupied 82.8% of the total plant volume (Nasturtium officinale, 25.4%; Potamogeton crispus, 22.0%; P. pectinatus, 18.4%; Elodea canadensis, 17.0%). The same four species comprised 83.3% of the dry weight (E. canadensis, 23.7%; P. crispus, 21.8%; N. officinale, 19.9%; P. pectinatus, 18.5%).

An experimental approach was used to evaluate the effect of interspecific competition on succession in a hot spring algal community in Yellowstone National Park, Wyoming. The algae in the spring were sampled at ten, 10-m intervals along a thermal gradient from 57.2 C to 45.7 C. Percent frequency of each algal species in each sample was determined using standard microscopic techniques. Following the initial sampling, algae were removed from the hot spring substrate by sweeping. Successional buildup of the algae community was then monitored by sampling at the same 1 0-m intervals at 1, 3, 5 and 7 wk after the disturbance. Distributions of the 14 major species along the thermal and temporal gradients were analyzed using stepwise multiple regression techniques. The niche breadth of each species and the interspecific overlaps were also analyzed along the temporal gradient. The major algal species were distributed differently with respect to the thermal gradient, and the distributions of the species along the thermal gradient changed significantly from the initial sampling to the 7th wk after removal, After removal, niche breadths and interspecific overlaps increased until about the 3rd wk. However, from the 3rd wk to the 7th wk, mean niche breadth and overlap decreased to a point similar to those of the predisturbance community. These patterns are consistent with the hypothesis that significant competition for space occurs following the establishment of an algal mat.

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