Precision and accuracy of total body bone mass and body composition measurements in the rat using x-ray-based dual photon absorptiometry

Lean body mass (LBM), total body bone mineral mass (BMC), total body bone areal density (BMD), and body fat mass (FM) were measured in rats by dual photon absorptiometry (DXA), using two different instruments. The coefficients of variation for repeated measurements of LBM and FM were about 0.4 and 2.5%, respectively, over an animal body weight range of 150 to 600 g. For BMC and BMD, the coefficients of variation were less than 2%. The correlation coefficients for LBM, FM, BMC, and BMD measured on the two densitometers were all greater than 0.94. The slope of the regression line relating LBM measured by DXA and LBM measured by carcass analysis was 0.999, and the correlation coefficient was 0.99. For FM the slope was 1.05, and the correlation coefficient was 0.98. BMC measures by DXA were falsely low in small animals. For larger animals, the correlation between BMC and ash weight was 0.93, but the slope of the regression line was 0.78. DXA measures of LBM and FM were accurate and reproducible for rats weighing between 150 and 600 g. There was a size-dependent error in BMC, which will be significant in longitudinal measurements of bone mass.     

Strange chaotic attractor crowding in boost converter model

A set of chaotic attractors is observed on a boost converter model. The union of their Poincare maps is strange. The attractors are densely packed such that they are sensitive to initial conditions. However every attractor in the set is stable with a finite (may be long) period     

Focal segmental glomerulosclerosis in primates infected with a simian immunodeficiency virus

Focal and segmental glomerulosclerosis (FSG) with endothelial tubuloreticular inclusions (TRIs) is the typical lesion of human HIV-associated glomerulopathy. Autopsy studies showed the presence of FSG in 3 of 15 macaques dying 15-120 weeks after experimental infection with a simian immunodeficiency virus (SIVMne). Ultrastructural studies generally revealed numerous endothelial TRIs (also present in normals), mesangial expansion, and evidence of mesangial cell injury. One additional animal had a small-vessel polyarteritis with a proliferative and focally crescentic glomerulonephritis; seven animals had mild, multifocal interstitial nephritis. All animals had documented viremia after infection; 14 of 15 developed antibodies to SIV postinoculation. Additional postmortem findings included severe enterocolitis, encephalitis, and opportunistic infections. In contrast, autopsy studies of macaques infected with a type D simian retrovirus (SAIDS-D/Washington, SRV-2) for similar periods of time (n = 40) showed no evidence of FSG. One SRV-infected animal had a mild proliferative glomerulonephritis. These studies indicate SIV-infected primates may provide a relevant model for study of human HIV-associated nephropathy. They also indicate the variable pathology that can be seen in primate infections of distinct retrovirus types, each of which produces a simian immunodeficiency state that resembles human AIDS.     

Gel-entrapment of perfluorocarbons: a fluorine-19 NMR spectroscopic method for monitoring oxygen concentration in cell perfusion systems

Oxygenation is a major determinant of the physiological state of cultured cells. 19F NMR can be used to determine the oxygen concentration available to cells immobilized in a gel matrix by measuring the relaxation rate (1/T1) of perfluorocarbons (PFC) incorporated into the gel matrix. In calcium alginate gel beads without cells the relaxation rate (1/T1) of the trifluoromethyl group of perfluorotripropylamine (FTPA) varies linearly with oxygen concentration, with a slope of 1.26 +/- 0.15 x 10(-3) s-1 microM-1 and an intercept of 0.50 +/- 0.04 s-1. During perfusion with medium equilibrated with 95%/5% O2/CO2, changes in PFC T1s indicate that the average oxygen concentration was reduced from 894 +/- 102 microM in the absence of cells to 476 +/- 65 microM and 475 +/- 50 microM in the presence of 0.7 x 10(8) EMT6/Ro and RIF-1 murine tumor cells per milliliter of gel, respectively. The presence of 0.2 microliters of FTPA/ml of gel had no effect on the energy status of the cells as indicated by 31P NMR spectra. To calculate oxygen gradients within the beads from the average PFC T1 of the sample, a mathematical model was used assuming that oxygen is the limiting nutrient for cell metabolism and that the cellular oxygen consumption rate is independent of oxygen concentration. Data for EMT6/Ro cells were fit using experimentally determined perfusion parameters together with literature values for cell volume and oxygen consumption rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Numerical simulation model of vibration responses of rectangular plates embedded with piezoelectric actuators

A numerical simulation model for random large amplitude vibration control of composite plate using piezoelectric material is presented. The H_∞ control design is employed to suppress the large amplitude vibrations of composites plates under random loading. The numerical simulation model is developed and based on the finite element method. The finite element governing equation includes fully coupled structural and electrical nodal degrees of freedom, and consider the von Karman large amplitude vibration. The modal reduction method using the structural modes is adopted to reduce the finite element equations into a set of modal equations with fewer degrees of freedom. The modal equations are then employed for controller design and time domain simulation. In the simulations without control, the value of the linear mode to the nonlinear deflection is quantified; and the minimum number of linear modes needed for accurate model is obtained. In the simulations with control, it is shown that the truncated modes, which are neglected in the control design, deteriorate the controller performance. Generally, the vibration reduction level is not monotonically increasing with the size of the piezoelectric actuator. The optimal piezoelectric actuator size depends on the excitation level. For higher excitation level, optimal actuator size is larger. The H_∞ controller based on the linear finite element formulation gives better vibration reduction for small amplitude vibration, but it still gives reasonable performance for large amplitude vibration provided that the piezoelectric actuator is big and powerful enough.     

Study on the propagation of inlet flow distortion in axial compressor using an integral method

 An integral method is investigated and developed in the current work. The effects of the parameters of inlet distortions on the trend of downstream flow feature in compressor are simulated. Other than the drag-to-lift ratio of the blade and the inlet incidence angle, it is found that the distorted inlet velocity is another essential parameter to control the distortion in propagation. Based on this study, a novel critical distortion line and corresponding critical distortion factor are proposed to express the effect of the two essential inlet parameters on the propagation of distortion, namely, the inlet incidence angle and the distorted inlet velocity. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion is further described by a compressor critical performance and its critical characteristic. The results present a useful physical insight to an axial flow compressor behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the active role of compressor in determining the velocity distribution when compressor responds to an inlet flow distortion. Received: 20 December 2001 / Accepted: 21 August 2002 The authors would like to thank HQ RSAF for permission to publish this work, their financial support and encouragement. The first author wants to acknowledge Prof. Frank Marble of California Institute of Technology, for bringing the problem to the author's attention and for his helpful discussion.