Measurement of characteristic parameters of ultrasonic flaw detectors
In order to guarantee the liability and accuracy of ultrasonic flaw detectors, a system is developed for measuring the characteristics of ultrasonic flaw detectors. The parameters which evaluate the characteristics of the pulse excitation circuit include pulse amplitude voltage, pulse rise time, pulse duration, pulse repetition frequency, peak frequency, bandwidth and output impedance. The parameters which evaluate the characteristics of the amplifier circuit include cut-off frequency, pass band, dynamic range, input impedance and equivalent input noise. The parameters which evaluate the coupling characteristics of these two circuits include crosstalk and blocking time during transmission.
Thickness measurement of individual layers in sandwich structures with unknown ultrasound velocity
Recently ultrasound methods are widely used for thickness measurement of various products and constructions. They are especially useful where only oneside access to a particular object (tanks, tubes, wings of planes, fuselages [1]) is feasible. Nowadays the amount of industrial products with a sandwich structure increases. One of the most developing areas is the production of tubes with the variety in diameters and in thickness of walls manufactured of several different materials. That is why the use of ultrasonic methods for measurement of sandwich structures becomes of a great importance [2]. However, the effective and practical use of ultrasound for such purposes is still problematic. The methods, when there is no necessity to know in advance ultrasound velocity in the material are still not fully investigated. In order to measure the thickness of a particular object, it is necessary to know an ultrasound velocity in it [3, 4, 5]. In this way, using the impulse method we can measure the time interval between the sent and received impulses and from them to determine thickness of the structure. In most practical cases it takes some time to determine the velocity of ultrasound (which depends on the structure of material, intermixtures, defects, temperatures and etc.) in a particular material and requires additional expenses. The measured velocity will be correct only under the same conditions which were during the time of measuring. Therefore for many practical applications it is important to measure thickness without a priori knowledge of ultrasound velocity in the object under investigation. There are a few methods suggested in [6, 7], which analyse the thickness measurement of objects without knowledge of ultrasound velocity. Actually they are differential methods, when thickness of object is calculated from two measurements performed at two different points. In paper [6] theoretical description of the method is presented, however there are no experimental or simulation data proving feasibility and illustrating performance of the method proposed. Another version is based on two simultaneously operating channels: in one channel an ultrasonic wave propagates perpendicularly to the surface of the multi-layered object, in the second channel the wave is sent at the angle less than 90° [7]. In this case propagation paths in the channels are different, what enables to determine thickness of individual layers without a priori knowledge of ultrasound velocities. While radiating at the 90 ̊ angle to the object, it‘s quite difficult to avoid distortions of the received signals due to the interference of sent and received impulses. That should lead to additional measurement errors. Descriptions of the methods, presented in [6], and [7] are rather brief, experimental verification or analysis of measurement errors are missing. The objective of this paper is the analysis of the method for thickness measurement, which does not require a priori knowledge of ultrasound velocity in the material under investigation.
Nuclear sphingolipid metabolism.
Nuclear lipid metabolism is implicated in various processes, including transcription, splicing, and DNA repair. Sphingolipids play roles in numerous cellular functions, and an emerging body of literature has identified roles for these lipid mediators in distinct nuclear processes. Different sphingolipid species are localized in various subnuclear domains, including chromatin, the nuclear matrix, and the nuclear envelope, where sphingolipids exert specific regulatory and structural functions. Sphingomyelin, the most abundant nuclear sphingolipid, plays both structural and regulatory roles in chromatin assembly and dynamics in addition to being an integral component of the nuclear matrix. Sphingosine-1-phosphate modulates histone acetylation, sphingosine is a ligand for steroidogenic factor 1, and nuclear accumulation of ceramide has been implicated in apoptosis. Finally, nuclear membrane-associated ganglioside GM1 plays a pivotal role in Ca(2+) homeostasis. This review highlights research on the factors that control nuclear sphingolipid metabolism and summarizes the roles of these lipids in various nuclear processes.