Application of Strong Fluctuation Random Medium Theory to Scattering from Vegetation-Like Half Space

A model for vegetation scatter is developed using the theory of electromagnetic wave propagation in random medium with strong permittivity fluctuations. In applying the strong fluctuation theory, the singularity of the dyadic Green's function is taken into account. Backscattering coefficients are computed using the distorted Born approximation and illustrated as a function of incidence angle, frequency and moisture content of the vegetation. The mixing formula of the de Loor [28] was used in estimating the permittivity of leaves. The correlation function of Fung and Fung [18], and Fung and Ulaby [19] is used for the random medium.     

A Simple Relation between Active And Passive Microwave Remote Sensing Measurements of Earth Terrain

A simple approximate relation between backscattering coefficient and emissivity measurements is derived. The relation is applicable to active and passive microwave remote sensing of earth terrain where volume scattering plays a dominant role. From the relation, one can obtain a rough estimate of the backscattering coefficient from the emissivity and vice versa. Such estimation is useful in checking experimental measurements and also helps to ascertain the validity of theoretical models. It also safeguards against obtaining arbitrarily high values for both backscattering coefficients and emissivities.     

Delivery of total parenteral nutrition (TPN) via umbilical catheterization: development of a piglet model to investigate therapies to improve gastrointestinal structure and enzyme activity during TPN

Nutritional support of preterm infants by total parental nutrition (TPN) is common; however, TPN compromises intestinal structure and enzyme activity. Our goal was to develop a piglet model to assess the effect of limited enteral stimulation with formula and insulin-like growth factor-I (IGF-I) on intestinal morphology and enzyme activity. A nutritionally complete TPN solution was infused for 7 days and piglets were gavaged twice daily with 4 ml sterile water, formula, or formula containing 1,000 micrograms/l IGF-I. Litter mate piglets fed formula served as orally fed controls. On day 7, body weights and plasma hormone profiles of TPN and orally fed piglets were similar. However, intestinal weight, jejunal and ileal villus height and surface area, and mucosal lactase and sucrase activity of TPN piglets was reduced by approximately 50%. No effect of limited enteral stimulation or IGF-I was observed likely due to the small volume of formula administered enterally, which resulted in a low dose of IGF-I (4.3 micrograms IGF-I/kg/day).     

Biologic characteristics of cultured human vitiligo melanocytes

BACKGROUND: Vitiligo is a pigmentary disorder of unknown cause characterized by depigmented patches due to destruction of melanocytes. Recently, the inherent cellular defect theory has been discussed. To investigate the biologic characteristics of cultured melanocytes from normal and vitiligo subjects, this study had the purpose to examine the functional and ultrastructural characteristics of these melanocytes and to observe the morphologic and functional changes of melanocytes in response to ultraviolet B irradiation. METHODS: Melanocytes were isolated and cultured from foreskin and arm skin of normal and vitiligo subjects. The DNA synthesis, tyrosinase activity assay, transmission and scanning electron microscopic examination, and the effects of ultraviolet B(UVB)-irradiation on cultured melanocytes were studied. RESULTS: Vitiligo melanocytes showed no significant differences in DNA synthesis and tyrosinase activity compared with normal melanocytes, but the vitiligo melanocytes contained dilated and/or circular rough endoplasmic reticulum (RER) on transmission electron microscopic examination. Exposure of the cultured melanocytes to UVB resulted in increased protein synthesis and tyrosinase activity. Morphologic alterations and changes in DNA synthesis were also noted. Compared with normal melanocytes, the responses of vitiligo melanocyte to UVB showed no significant difference. CONCLUSIONS: Normal and vitiligo melanocytes showed similar biologic characteristics except in the changes of RERs in the vitiligo melanocytes. The ultrastructural aberrations in vitiligo subjects do not seem to be directly related to the biologic characteristics and the responses to UVB irradiation in vitiligo melanocytes.     

Acute renal failure in blacks and Indians in South Africa--comparison after 10 years

Acute renal failure (ARF) has changed in its aetiology in developed Western countries. This study compares our experiences of the aetiology and incidence of ARF a decade after a previously recorded paper in the literature. The data of 226 patients with a diagnosis of ARF during a 3-year period from 1986 to 1988 was analysed. ARF in our study occurred at a younger age. Medical causes of ARF remain the dominant subgroup. There were female patients presenting with ARF associated with self-induced abortions. Toxins of a herbal variety and infections remain the commonest aetiological factors in the medical subgroup. Infections have replaced nephrotoxins as being the principal medical cause. There has been no major change in the incidence or aetiology of ARF over a decade. The prevention of ARF in blacks in sub-Saharan Africa is primarily concerned with the eradication of nephrotoxins and infections and a laxity in the abortion laws of the country. Only by an improvement in education, nutrition, socio-economic status and sanitation can one eradicate or diminish ARF in developing countries.     

Feedforward-feedback control of a solid oxide fuel cell power system

One of the main challenges for wide-spread utilization of the solid oxide fuel cell (SOFC) power systems is how to achieve high electrical efficiency without increasing the degradation rate of the fuel cells. To run the SOFC power system at high efficiency over a long period of time, properly designed controllers are indispensable.Although a number of various approaches to control SOFC have been proposed so far, it seems that the design of control system, along with simple tuning procedure, has not been treated in a consistent manner. This issue is addressed in the present paper resulting in a feedforward-feedback control structure. The feedforward part is based on the stoichiometry of electro-oxidation, reforming and combustion reactions, which allow immediate response to variable current demand. The feedback part performs additional fine adjustment of fuel and air supply in order to minimize the undesired system temperatures variations. The selection of pairings of manipulated and controlled variables for control is based on physical knowledge of the system. Input/output pairing for single-loop feedback control is assessed by the relative gain analysis. An efficient procedure for tuning the parameters of the feedback controllers is suggested, relying on simple open-loop step responses of the system.The proposed low-level control is assessed on a detailed physical model of a 2.5 kW SOFC power system by simulating two nonstationary load regimes. Simulations show that the control provides a robust operation under large load variations while meeting the operating constraints. Due to its simplicity, the control is feasible for implementation on a real SOFC system.     

Two modes of ligand binding in maltose-binding protein of Escherichia coli. Electron paramagnetic resonance study of ligand-induced global conformational changes by site-directed spin labeling

Binding of ligands to the maltose-binding protein (MBP) of Escherichia coli often causes a global conformational change involving the closure of its two lobes. We have introduced a cysteine residue onto each of these lobes by site-directed mutagenesis and modified these residues with spin labels. Using EPR spectroscopy, we examined the changes, caused by the ligand binding, in distance between the two spin labels, hence between the two lobes. The binding of both maltose and maltotetraose induced a considerable closure of the N- and C-terminal lobes of MBP. Little closure occurred upon the binding of maltotetraitol or beta-cyclodextrin. Previous study by fluorescence and UV differential absorbance spectroscopy (Hall, J. A., Gehring, K., and Nikaido, H. (1997) J. Biol. Chem. 272, 17605-17609) showed that maltose and a large portion of maltotetraose bound to MBP via one mode (R mode or "end-on" mode), which is physiologically active and leads to the subsequent transport of the ligands across the cytoplasmic membrane. In contrast, maltotetraitol and beta-cyclodextrin bound to MBP via a different mode (B mode or "middle" mode), which is physiologically inactive. The present work suggests that the B mode is nonproductive because ligands binding in this manner prevent the closure of the two domains of MBP, and, as a result, the resulting ligand-MBP complex is incapable of interacting properly with the inner membrane-associated transporter complex.