Fatty streak formation occurs in human fetal aortas and is greatly enhanced by maternal hypercholesterolemia. Intimal accumulation of low density lipoprotein and its oxidation precede monocyte recruitment into early atherosclerotic lesions

To determine whether oxidized LDL enhances atherogenesis by promoting monocyte recruitment into the vascular intima, we investigated whether LDL accumulation and oxidation precede intimal accumulation of monocytes in human fetal aortas (from spontaneous abortions and premature newborns who died within 12 h; fetal age 6.2+/-1.3 mo). For this purpose, a systematic assessment of fatty streak formation was carried out in fetal aortas from normocholesterolemic mothers (n = 22), hypercholesterolemic mothers (n = 33), and mothers who were hypercholesterolemic only during pregnancy (n = 27). Fetal plasma cholesterol levels showed a strong inverse correlation with fetal age (R = -0.88, P < 0.0001). In fetuses younger than 6 mo, fetal plasma cholesterol levels correlated with maternal ones (R = 0.86, P = 0.001), whereas in older fetuses no such correlation existed. Fetal aortas from hypercholesterolemic mothers and mothers with temporary hypercholesterolemia contained significantly more and larger lesions (758,651+/-87,449 and 451,255+/-37,448 micron2 per section, respectively; mean+/-SD) than aortas from normocholesterolemic mothers (61,862+/-9,555 micron2; P < 0.00005). Serial sections of the arch, thoracic, and abdominal aortas were immunostained for recognized markers of atherosclerosis: macrophages, apo B, and two different oxidation-specific epitopes (malondialdehyde- and 4-hydroxynonenal-lysine). Of the atherogenic sites that showed positive immunostaining for at least one of these markers, 58.6% were established lesions containing both macrophage/foam cells and oxidized LDL (OxLDL). 17.3% of all sites contained only native LDL, and 13.3% contained only OxLDL without monocyte/ macrophages. In contrast, only 4.3% of sites contained isolated monocytes in the absence of native or oxidized LDL. In addition, 6.3% of sites contained LDL and macrophages but few oxidation-specific epitopes. These results demonstrate that LDL oxidation and formation of fatty streaks occurs already during fetal development, and that both phenomena are greatly enhanced by maternal hypercholesterolemia. The fact that in very early lesions LDL and OxLDL are frequently found in the absence of monocyte/macrophages, whereas the opposite is rare, suggests that intimal LDL accumulation and oxidation contributes to monocyte recruitment in vivo.     

Energy consumption in RC tree circuits

In this paper, resistance-capacitance (RC) tree networks are modeled in terms of their energy consumption associated with an input transition. This work significantly extends the results that the same authors previously obtained in the specific case of ladder networks with only ramp signals. The proposed approach to model the energy consumption is based on a single-pole approximation, in which an equivalent time constant is analytically derived from an exact analysis for very slow and very fast input transitions. The model is then extended to arbitrary values of the input rise time by exploiting some intrinsic properties of RC tree networks. The approach is completely analytical and leads to closed-form results. Analytical results are explicitly derived for different inputs, such as the ramp and the exponential waveforms which are usually encountered in current VLSI circuits, as well as the saturated sine input. Due to its simplicity, the proposed energy expression is suitable for pencil-and-paper evaluation and allows for an intuitive understanding of the network dissipation. The energy expression proposed is shown to be accurate enough for modeling purposes through comparison with SPICE simulations.     

Design guidelines of CMOS class-AB output stages: a tutorial

This article presents useful guidelines for designing CMOS class-AB output stages. Three Quality Factors, which allow analysis and comparison of different output stages, are used to design two CMOS class-AB stages. We show that using the proposed Quality Factors and the related strategy leads to an efficient design in terms trade-off among area, current consumption, bandwidth and distortion. Indeed, for one of the two stages adopted as example, the design through the Quality Factors results in superior distortion performance with respect to the design suggested in the original article. Design examples and simulations are provided to validate the design strategy.     

Coupling Impedance in a Circular Particle Accelerator, a Particular Case: Circular Beam, Elliptic Chamber

As a first step the concept of coupling impedance (c.i.) is extended to characterize the relationship between cause and effect relevant to distinct points. Then we can exploit a new law that relates the transverse c.i. to the lonitudinal one by means of a second derivative. When cause and effect coincide we get the standard definition of c.i. At a first sight the computation of the coupling impedance for the present model seems a trivial problem. In fact the c.i. is proportional to the Green function of the relevant model, which can be found as an open series, for instance in the treatise of Morse and Feshbach. But the authors themselves warn that this series is poorly convergent and in addition should not be differentiated. We succeeded in closing the series. The problem formally seems to be solved. But this procedure could however turn out to be sterile for numerical purposes, where we obviously need series expansions, unless one finds better alternative expansions. This is the final and possibly the most important step, where a different extremely rapidly convergent expansion is found. The use of this expansion has led to the recognition of a vast number of numerical results that are synthesized in the graphic representations of this work. The longitudinal c.i. is scarsely affected by the ellipticity and excentricity of the beam, so that, unless the beam is far off the central beam position, it behaves as in a circular cross section pipe.     

Hydrogen and sulfur from hydrogen sulfide—IV. Quenching the effluent from a solar furnace

Solar thermochemical production of H₂ and sulfur from H₂S were studied, using a 4.2 m solar furnace as a source of process heat. We used two reactor configurations. The independent variables were temperature, feed rate and pressure. Hydrogen production rate, yield, and the quench fraction (fractional yield) were measured. High yields (of the order 0.5) and quench fractions (of the order 0.7) were obtained over a range of temperatures and feed rates. Yields were a monotonically increasing, almost linear, function of the temperature.The observations are rationalized by a kinetic model that concludes that gas phase reaction rates are too low to account for the observed yields; a good reactor should embody the heating of the feed stream in contact with a surface to facilitate decomposition of H₂S, and the product stream should be quenched in such a way as to minimize surface reactions.The reactors are described. Mullite, Al₂O₃, Fiberfrax and ZrO₂ are suitable materials of construction from a chemical standpoint. Mullite underwent some sintering, deformation and thinning in the hottest parts of the reactor, where it may have been exposed to high temperature excursions and some cracking, apparently due to thermal stress, where it came in contact with a separator.     

Evaluation of energy consumption in RC ladder circuits driven by a ramp input

In this paper, the energy consumption of RC ladder networks, which can represent chains of transmission gate or long wire interconnections, is modeled. Their energy dependence on the input rise time is analyzed by assuming a ramp input waveform. Since the analysis can be carried out in a straightforward manner only for very simple RC ladder networks, the exact analysis is first limited to asymptotic values of the input rise time T (i.e., for T/spl rarr/0 and T/spl rarr//spl infin/). Successively, the energy expression is extended to arbitrary values of the input rise time by introducing a suitable equivalent first-order RC circuit, whose resistance and capacitance are simply related to the resistances and capacitances of the original network. The energy expression found is useful for pencil-and-paper evaluation and affords an intuitive understanding of the network dissipation, since each term has an evident physical meaning. By comparison with SPICE simulations, the energy expression proposed is showed to be accurate enough for modeling purposes.     

Biocompatible α-aminoacids based aliphatic polyamides

Summary. Biodegradable aliphatic polyamides have been prepared from C10 and C14 dicarboxylic acids and amide-diamines containing one or two preformed amide linkages susceptible to enzymatic cleavage in their molecules. L-phenylalanine, either by itself or together with L-valine, was used to generated amide bonds which are cleavable by chimotrypsine. Improved chain flexibility and hydrophilicity of the polyamides was obtained using a triethyleneoxy based amide-diamine. Characterization of the novel monomers and polymers by FTIR and ¹H-NMR spectroscopy confirms the expected structures. Thermal data and solubility tests indicate that both T _m and solubility depend on the length and nature of the aliphatic segment present in the amide-diamine as well as on the "density" of interchain hydrogen bonds. Finally the polymers tested are capable of supporting fibroblast adherence and proliferation, and proved to be non cytotoxic. Received: 28 May 1997/Revised: 16 July 1997/Accepted: 16 July 1997     

Thermoelastic Phase Analysis (TPA): a new method for fatigue behaviour analysis of steels

In literature, there are already well‐established thermal methods which allow for the estimation of fatigue limit, in particular for metallic materials such as austenitic steels. These methods are based on heat source generation analysis or on surface temperature evaluation of material subjected to different types of cyclic loading. General application of methodology found limitation in those cases in which temperature changes on material related to fatigue damage were very low and, furthermore, thermal methods require high‐performance equipment and a difficult setup. This is the case, for instance, with brittle materials (such as martensitic steels), welded joints and aluminium alloys. In this work, a new thermal method named Thermoelastic Phase Analysis is used to evaluate the fatigue limit of martensitic steels. This thermal method is based on an empirical approach. The main idea is that phase of thermoelastic response of the material subjected to fatigue loading is influenced by the presence of a heat source due to dissipative phenomena related to damage. Monitoring of the phase parameter provides a more stable setup and an independent means of identifying the fatigue limit of material. The method has also proven to be potentially one order of magnitude faster than traditional thermal methods.