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The acquisition of electrochemical noise is always connected with the question of appropriate measuring devices. The noise measurement system shall allow to process the apparent fluctuations in an electrochemical cell in the low millivolt or microampere range and to record them without any changes. The measurement amplifier is an essential part of the measurement system, but its behavior in the chain of signal processing is difficult to define by a corrosion expert. The present article shows possibilities for the determination of the performance of a noise measurement amplifier. A dummy cell model is often used to get a realistic approach to the sources of electrochemical noise. This article introduces a model describing the generation of single transients from the basic electrochemical corrosion reactions. The model determines fluctuations in the potential which can be measured as voltage fluctuations on a real dummy cell circuit. With the help of a special arbitrary signal generator, artificial noise transients based on this description are applied to a commercial noise measurement system. The acquired signals are compared with the original signals from the signal source and the influences of the noise amplifier on the signals are discussed.

Starting from the elementary corrosion reactions on a passive metal surface a model is developed for the origin of electrochemical noise. The ion currents flowing at the electrochemical reactions are described by the electrons remaining in the metal and then interpreted as a measuring signal. The measurable sum current is composed of the superimposition of the electron currents of the partial reactions. Due to the inhomogeneity of the metal surface, local metal dissolutions take place in preferential areas until the area is consumed or repassivated after short times. The short-time surplus of free electrons leads for every metal dissolution event to a current transient, which itself consists of the partial currents of the elementary anodic and cathodic reactions. Due to the different reaction speeds, there are temporary charge disequilibria and thus measurable noise transients. In model calculations the influence of the diffusion of the oxygen on the sum signal as well as the variation of the anodic current is shown. Furthermore, the results show that a measurable noise signal can only arise under certain conditions. This signal arisen directly at the metal surface is not, however, ascertainable without further amplification. In the measurement amplifiers filter stages play an important role for signal conditioning. The influence of the measuring technique is shown at the filtration of a simulated test signal in different frequency domains. It is discussed how the signal distortion affects the detectability of the partial reactions described at the beginning and in which way the noise signal is estimated. Indications for the layout of suitable measuring parameters are given.

Passive layers on high alloyed chromium nickel steels protect the metal from corrosion. The protective effect of the passive layer, however, does not immediately exist after the final surface treatment. Some time is necessary to form the protective layer. The exposure conditions are also decisive for the formation and further development of the passive layer besides the surface treatment. Samples of different chromium nickel steels are pickled and active passivated before they are exposed under laboratory conditions and in outdoor climates at different locations. The state of the corrosion resistance of the surface is determined with electrochemical noise measurements after different exposure times. The decreasing activity of the surface with an increasing exposure time indicates the further formation process of the protective qualities of the passive layer. An index which quantifies the state of the surface at the time of the measuring is calculated from the measured potential and potential noise signals. With these results, the development of the passive layer can be assessed and the corrosion resistance of the metal can then be estimated.

Endothelial cells of different vascular systems may express site-specific adhesion molecules to attract leukocyte subsets. This study describes a method to visualize and compare leukocyte-endothelial interactions in three vascular beds within the same eye in mice.Digital in vivo fluorescence microscopy was used to record a trans-corneal iris view, a superficial limbus view, and a trans-scleral anterior choroid view of mouse tissue. Uveitis was induced by intravitreal injection of E. coli endotoxin into BALB/c mice. Leukocytes were labeled systemically with SYTO-16 or rhodamine 6G. Leukocyte rolling and sticking were quantified at baseline and 4, 6, and 24 hours after endotoxin injection.In a normal animal, the limbus had 18 times the number of rolling leukocytes and 6 times the number of sticking leukocytes relative to the iris. All three vascular beds were affected by intravitreal injection of endotoxin. Although they each showed increased numbers of rolling and sticking cells, the levels and kinetics of these increases differed. Rolling peaked at 6 hours in the iris (34-fold increase from baseline) and limbus (7-fold increase) but was maximal in the choroid earlier with a 16-fold increase. Sticking was maximal at 4 hours for iris (96-fold increase) and choroid (19-fold increase) but peaked in the limbus at 6 hours (47-fold increase from baseline).This study demonstrates that leukocyte-endothelial dynamics are not the same in different vascular beds in the normal mouse eye. Furthermore, site-specific differences in responses to intravitreally injected endotoxin, beyond what can be readily explained by differential distribution of endotoxin, were observed. The methodology can be used to test the hypothesis that endothelial cells within the eye have site-specific patterns of adhesion molecule expression.

Cholesterol side chain cleavage is determined by means of separation of (26-C14)-cholesterol and its radioactively labeled side chain (1-C14)k-isocaproic acid. Alumina minicolumn assay (AMCA): adsorption of cholesterol from an aqueous phase by aluminium oxide, while isocaproic acid can percolate through the column. In modification of a previously described technique (1), cholesterol is quantitatively eluted by ethanol. Filter assay (FA): retention of cholesterol by a membrane filter (pore size less than or equal to 0.1 um) while isocaproic acid can pass the filter. Two-phase scintillation assay (TPSA): pH-dependent partition of isocaproic acid between an organic scintillation mixture and an aqueous phase. The TPSA can be applied for all enzymatic reaction in which the polarity of the radioactive residue which is split off depends on pH values or when the total charge of a polar molecule is changed to an apolar state by cleaving one non-radioactive group (e.g. steroid sulfates) and vice versa. The criteria or reliability of the test systems are described. Bovine adrenal mitochondria were incubated and the side chain cleavage of (26-C14)-cholesterol was studied by the new tests systems and compared to the conversion rates of (4-C14)-cholesterol to its metabolites are determined by thin layer chromatography. A good agreement of all tests was found.

After preincubation of term placental tissue in organ culture for 24 h, progesterone synthesis is 2-3 fold lower than without preincubation. By adding human male serum proteins (MW less than 12,400), we obtained 2-3.5 fold lower tissue levels of progesterone. Serum proteins with high molecular weight (MW greater than 12,400) are postulated to facilitate progesterone release by binding free medium progesterone. In test series without preincubation, there are no significant (p less than 0.05) differences in progesterone formation in the presence of cholesterol (C), cholesteryl linoleate (CL), and LDL. In test series with preincubation, LDL causes a twofold increase in medium progesterone with C (0.1 and 1 mM) and CL (0.1 mM) in the presence of the low molecular weight serum protein (MW less than 12,400) solution. A decrease of 50% was obtained by 1 mM CL with/and without LDL. In culture medium containing high molecular weight serum proteins (MW greater than 12,400), 0.1 and 1 mM C and CL induce a twofold increase in progesterone production without any significant (p less than 0.05) differences between the single values. No further stimulation could be observed by LDL because there was sufficient LDL for maximal progesterone formation. In conclusion, LDL enhances the utilization of cholesterol and cholesteryl linoleate for progesterone production in term placenta. A lipoprotein cholesterol receptor is suspected.

To investigate possible variations in plasma progesterone levels during the hyperthermic phase of the menstrual cycle and during early and late pregnancy, venous blood samples were taken at 4-hour intervals during periods of 24 hours. Progestrone determinations were done by gas-liquid chromatography. No significant circadian variation in peripheral plasma progesterone concentration was determined in the 10 women studied during the hyperthermic phase of their menstrual cycles or in 14 women studied during early pregnancy. However in the 15 women studied in late pregnancy a statistically significant rise was found from 8 a.m. until 4 or 8 p.m. (p less than .001), followed by a decrease until 4 to 8 a.m. Results indicate a daily change in peripheral plasma progesterone level during the last trimester of pregnancy. The cause of this diurnal variation is not known.