Adaptive instantaneous frequency estimation of multicomponent FMsignals using quadratic time-frequency distributions

An adaptive approach to the estimation of the instantaneous frequency (IF) of nonstationary mono- and multicomponent FM signals with additive Gaussian noise is presented. The IF estimation is based on the fact that quadratic time-frequency distributions (TFDs) have maxima around the IF law of the signal. It is shown that the bias and variance of the IF estimate are functions of the lag window length. If there is a bias-variance tradeoff, then the optimal window length for this tradeoff depends on the unknown IF law. Hence, an adaptive algorithm with a time-varying and data-driven window length is needed. The adaptive algorithm can utilize any quadratic TFD that satisfies the following three conditions: First, the IF estimation variance given by the chosen distribution should be a continuously decreasing function of the window length, whereas the bias should be continuously increasing so that the algorithm will converge at the optimal window length for the bias-variance tradeoff, second, the time-lag kernel filter of the chosen distribution should not perform narrowband filtering in the lag direction in order to not interfere with the adaptive window in that direction; third, the distribution should perform effective cross-terms reduction while keeping high resolution in order to be efficient for multicomponent signals. A quadratic distribution with high resolution, effective cross-terms reduction and no lag filtering is proposed. The algorithm estimates multiple IF laws by using a tracking algorithm for the signal components and utilizing the property that the proposed distribution enables nonparametric component amplitude estimation. An extension of the proposed TFD consisting of the use of time-only kernels for adaptive IF estimation is also proposed     

Friction of composite cushion bearings for total knee joint replacements under adverse lubrication conditions

Conventional joint replacements consist of a polished metallic or ceramic component articulating against a layer of polyethylene. Although the friction in the contact between these articulating surfaces is low, polyethylene wear is produced as a result of a boundary/mixed lubrication regime. Wear debris is generated by direct asperity contact, abrasion, adhesion and fatigue, and has been shown to cause adverse tissue reactions which can lead to joint failure. The introduction of soft compliant materials, similar in stiffness to articular cartilage, has shown that with cyclic loading and relative motion between the articulating surfaces typical of normal walking, a fluid film can be maintained through combined entraining and squeeze-film actions, and hence wear can be minimized. For 95 per cent of the time, however, we are not walking but standing still or moving slowly. A pendulum simulator has been used in the present study to investigate the effect of adverse tribological conditions which may lead to fluid film breakdown, such as severe cyclic loading, particularly in the swing phase, reduced sliding velocity, reduced stroke length and start-up after a period of constant loading. Friction of a model composite cushion knee bearing, manufactured from a graded modulus (20-1000 MPa) layer of polyurethane, sliding against a polished metal cylinder has been measured for various lubricants and the results have been analysed using a Stribeck assessment. Severe cyclic loading, decreased sliding velocity and decreased stroke length have been found to limit the degree of fluid entrainment previously allowed during the swing phase of normal walking, thus allowing breakdown of fluid films and elevated levels of friction and surface damage. Soft layer joint replacements must therefore be designed to operate with thick elastohydrodynamic fluid films to provide some degree of protection when tribological conditions become severe, or alternatively incorporate alternative boundary or mixed lubrication mechanisms. This study quantifies a potential limitation of the cushion bearing concept.     

The role of von Willebrand factor and fibrinogen in the initiation of platelet adhesion to thrombogenic surfaces

Platelets respond rapidly to alterations of endothelial cells by attaching firmly to the site of lesion, where exposure of subendothelial components may have occurred. The first layer of platelets is in contact with the thrombogenic surface (adhesion), whereas subsequent growth of the hemostatic plug depends on platelet-to-platelet interactions (aggregation). Both aspects of platelet function are influenced by von Willebrand factor and fibrinogen interaction with specific platelet membrane receptors. Multiple domains of von Willebrand factor and fibrinogen are involved in securing initiation and growth of platelet thrombi.     

Visualizing the expression of a human growth hormone (hGH) transgene in the liver: intrahepatic regional and intracellular differences of expression are associated with morphological alterations and hepatocellular proliferation

Growth hormone acts directly on liver cells; it binds to its receptor and induces a multitude of intracellular events leading, for example, to the production of insulin-like growth factor-1 (IGF-1). While much is known about the biochemical side of these events, their structural correlates are less well examined. Here, we examined livers of transgenic mice (TM) expressing human GH, in an attempt to correlate at the cellular level the site of GH gene expression with effects on morphology and mitotic behavior of liver cells within the hepatic architecture. Using in situ hybridization histochemistry we observed a striking expression pattern of the hGH gene in hepatocytes near the periportal spaces. In the same regions, the hGH protein, but no IGF-1 immunoreactive product, was detected using immunohistochemical methods. In the sections of TM livers, 6.8-31.9% of cells were hGH-immunoreactive. However, the cellular hGH staining pattern was not homogeneously distributed in the immunoreactive cells. Two main patterns became obvious. In the majority of the immunoreactive cells a cytoplasmic stain was present. These cells exhibited normal liver cell features and were not enlarged (type I). In the other group (type II), the staining was stronger and concentrated, sometimes punctuate, and often confined to cytoplasmic compartments which were in a perinuclear position. The latter staining pattern was generally seen in morphologically altered cells, which were enlarged and possessed intranuclear inclusions and invaginations. In the the periportal regions, mitotically active hepatocytes were evident, but these cells, as judged from immunocytochemistry, apparently did not express the transgene. In conclusion, different staining patterns for hGH may indicate different levels of transgene expression, which could be associated with difficulties in the cells with regard processing and/or secreting the hormone. In addition to the endocrine actions implied by the high hGH levels in the peripheral circulation of these TM, intracrine actions are also suggested (type II staining pattern), but para- and autocrine loops are possible as well (type I staining pattern). Whether IGF-1 is involved, and the mechanism underlying hepatocyte cell proliferation, remain to be examined.     

Double-strength beclomethasone dipropionate (84 micrograms/spray) aqueous nasal spray in the treatment of seasonal allergic rhinitis

Determination of microgram quantities of protein in the Bradford Coomassie brilliant blue assay is accomplished by measurement of absorbance at 590 nm. However, as intrinsic nonlinearity compromises the sensitivity and accuracy of this method. It is shown that under standard assay conditions, the ratio of the absorbances, 590 nm over 450 nm, is strictly linear with protein concentration. This simple procedure increases the accuracy and improves the sensitivity of the assay about 10-fold, permitting quantitation down to 50 ng of bovine serum albumin. Furthermore, protein assay in presence of up to 35-fold weight excess of sodium dodecyl sulfate (detergent) over bovine serum albumin (protein) can be performed. A linear equation that perfectly fits the experimental data is provided on the basis of mass action and Beer's law.     

Anxiogenic effect of naltrexone in social interaction test in rats

AIM: To study the anxiogenic effect of naltrexone (Nal) on the emotional state of rats. METHODS: The duration of active interaction was measured in the social interaction test in rats. RESULTS: Without influence on the locomotor activity, Nal (0.1-50 mg.kg-1) dose- and time-dependently decreased the duration of active interaction, which was antagonized by morphine (5 mg.kg-1) or fenclonine (Fen, 150 mg.kg-1 x 3 d) and was enhanced by 5-hydroxytryptophan (5-HTP, 50 mg.kg-1). CONCLUSION: Nal produced anxiety via its blockade of opioid receptors; central opioidergic neurons were involved in the regulation of anxiety through their tonic inhibitions in serotonergic neurons.     

Mobile unit velocity estimation based on the instantaneous frequency of the received signal

This paper presents a new mobile station velocity estimator based on the first moment of the instantaneous frequency (IF) of the received signal. The effects of shadowing, additive noise, and scattering distribution on the proposed velocity estimator are analyzed. We show that, unlike velocity estimators based on the envelope and quadrature components of the received signal, the proposed estimator is robust to shadowing. We also prove that the performance of the IF-based estimator is only mildly affected by the presence of additive noise. Finally, by using simulations we show that the performance of the proposed IF-based estimator is superior to that of existing velocity estimators.