Mass Change Method Research Articles

Scaling Mode Shapes in Output-Only Systems by a Consecutive Mass Change Method

In operational modal analysis (OMA) mode shapes can be obtained only with arbitrary normalization. There are many applications where mass normalized mode shapes are required, such as response prediction and stress analysis. A method to scale the mode shapes in OMA is to modify the dynamic behaviour of the structure by adding masses and then to use the modal parameters of both the original and modified structure. Several mass change methods have been proposed in recent years for estimating the scaling factors, where a distributed array of added masses are needed to obtain good results. In this work a new mass change approach based on performing several individual mass changes is presented. This approach requires only a small number of masses that are located at different points in each individual experiment. The results of the individual tests are then combined to estimate the scaling factors. The approach is developed and validated by measurements carried out on a 15-tonne prestressed concrete slab strip and a steel cantilever beam. The results show that a good accuracy can be obtained by this method when a proper mass change strategy is used.

Scaling-factor estimation using an optimized mass-change strategy

In operational modal analysis, only unscaled mode shapes can be obtained. The mass-change method is in many cases the simplest way to estimate the scaling factors, which involves repeated modal testing after changing the mass at different points of the structure where the mode shapes are known. With this method, the scaling factors are determined using the natural frequencies and mode shapes of both the modified and the unmodified structure. However, the uncertainty on the scaling-factor estimation depends on the modal-analysis accuracy and the mass-change strategy (number, magnitude, and location of the masses) used to modify the dynamic behavior of the structure. In this paper, a procedure to optimize the mass-change strategy is proposed, which uses the modal parameters (natural frequencies and mode shapes) of the original structure as the basic information.

Determination of bulk etch rate for CR-39 nuclear track detectors using an X-ray fluorescence method

The thickness of a CR-39 detector is determined using an energy dispersive X-ray fluorescence (EDXRF) method of analysis. The method is based on exciting a suitable target and measuring the intensity of its fluorescence X-ray lines passing through the CR-39 sample in a fixed geometry. By properly selecting the target material, the method succeeds in assessing the thickness change of CR-39 detectors etched for different time intervals. The bulk etch rate (Vb) may thus be obtained, which is an important parameter for any solid state nuclear track detector. Application of the EDXRF method yielded a value of Vb=(2.01±0.04) μmh−1 for etching in a 6N NaOH solution at 75°C. This value agrees with the bulk etch rate of (1.90±0.03) μmh−1, obtained by the conventional mass-change method.

Comparison and limitations of three different bulk etch rate measurement methods used for gamma irradiated PM-355 detectors

Samples of Nuclear Track Detectors (PM-355) were exposed to high gamma doses from 1×10 5 Gy (10 Mrad) up to 1.2×10 6 Gy (120 Mrad) at an incremental dose of 1×10 5 Gy (10 Mrad ). The gamma source was a 9.03 PBq ( 244 kCi ) Co-60 source used for sterilization of medical syringes. The bulk etch rate ( V b) was measured for various high gamma doses by three different methods: 1—thickness change method; 2—mass change method; 3—fission track diametric method. The study gives a comparison and limitations of these three methods used for bulk etch rate measurements in the detectors as a function of high gamma doses. The track etch rate ( V t) and the sensitivity ( V) of the detector were also measured using the fission track diametric method. It was observed that V b increases with the increase of the gamma absorbed dose at a fixed etching time in each bulk etch measuring method. The bulk etch rate decreases exponentially with the etching time at a fixed gamma absorbed dose in all three methods. The thickness change and mass change methods have successfully been applied to measure V b at higher gamma doses up to 1.2×10 6 Gy (120 Mrad ). The bulk etch rate determined by the mass change and thickness change methods was almost the same at a certain gamma dose and etching time whereas it was quite low in the case of the fission track diametric method due to its limitations at higher doses. Also in this method it was not possible to measure the fission fragment track diameters at higher doses due to the quick disappearance of the fission tracks and therefore the V b could not be estimated at higher gamma doses.{

142 ヘリウム・空気置換流の流量測定と傾斜管内の流れの可視化

This paper deals with experimental investigation on buoyancy- driven exchange flow through an inclined tube. The effect of the density at the tube top end and density difference between light and heavy gases on exchange flow rate were investigated and discussed. Smoke wire method was applied to visualize the flow in the tube, and compered with the mass change method.

Investigation of the kinetics of macromolecule adsorption by means of the quartz microbalance and double-layer capacitance measurement: Application to the adsorption of bovine serum albumin onto gold electrode

The time variations of the double layer capacitance and of the oscillation frequency of an electrochemical quartz microbalance are simultaneously recorded to determine the kinetics of adsorption of bovine serum albumin on a gold electrode. Both variations which can be fitted by a sum of exponential functions corroborate a consecutive irreversible step model already proposed. It is established that for the steps associated with a mass change both methods provide the same values for the time constants. This result validates the double-layer capacitance measurement method (which is indirect) as a tool for determining in situ the kinetics of protein adsorption. In addition to the information common to the two methods, these methods provide complementary information: number of adsorbed monolayers for the quartz microbalance; change of the layer structure at constant thickness for the double layer capacitance. Thus, according to the sign of the electrical charge of the interface, two or three monolayers are adsorbed end-on during the adsorption process. Finally, it is established that in our conditions the quartz oscillation modifies with respect to the non-oscillating quartz, the kinetics of adsorption and the structure of the adsorbed layer.

Comparison of the Quartz‐Crystal Microbalance and the Double‐Layer Capacitance Methods for Measuring the Kinetics of the Adsorption of Bovine Serum Albumin onto a Gold Electrode

The time‐variations of the double‐layer capacitance and of the oscillation frequency of an electrochemical quartz crystal microbalance are simultaneously recorded to determine the kinetics of adsorption of bovine serum albumin on a gold electrode. Both variations can be fitted by a sum of exponential functions. It is established that for the steps associated with a mass change both methods provide the same values for the time‐constants. This result validates the double‐layer capacitance measurement method, which is indirect, as a tool for determining, in situ, the kinetics of protein adsorption. Finally, it is established that, in the experimental conditions used here, the oscillation of the quartz crystal modifies, with respect to the nonoscillating quartz, the kinetics of adsorption of the macromolecules.

Sputtering of titanium and zirconium by fusion plasma impurity ions

Sputtering yields of the getter materials titanium and zirconium for incident ion energies in the range of 100 eV to 20 keV are reported. In addition to ions of the respective target materials, O + and Ne + ions were also used as projectiles. Measurements were made at room temperature and in the case of oxygen also at a target temperature of 550°C to investigate chemical effects. Experimental data are determined by the integral mass change method. Experimental results are compared with those calculated from an analytical relation based on a modified collision cascade theory.

Low energy selfsputtering yields of nickel

The selfsputtering yield of nickel has been measured by the mass change method for normal incidence in the energy region from 75eV–3.0keV. In this energy region the yield varies from 0.07–3.0atmos/ion. The results are discussed in view of their importance to the plasma-wall interaction in fusion devices.