Preparation of catalysts The catalysts

2.2. Preparation of catalysts
The catalysts were prepared by incipient wetness impregnation of alumina supports with an aqueous solution containing ammonium heptamolybdate ((NH4)6Mo7O24·4H2O) and nickel nitrate (Ni(NO3)2·6H2O). The loading quantity of NiO and MoO3 was controlled to be 0.36 wt.% and 4.8 wt.%, respectively. The impregnated supports were dried overnight in air at 80 °C and calcined at 500 °C for 3 h. The corresponding catalysts were labeled as C-1, C-2, and C-ref, respectively.
2.3. Characterization
2.4. Activity test
The catalytic activity was tested in JTP74057 tank reactor. 1.25 g of fresh catalyst was sulfided in situ for each activity test. In food chain stage, 10.0 g of vacuum residue from Saudi Arabian light crude was diluted with 35.0 g of toluene. The resultant mixture was charged into the reactor (100 ml capacity), and then 0.4 g of CS2 was added with fresh catalyst. The reactor was purged five times with H2 to exchange the air inside. The reaction mixture was heated to the required temperature at a heating ramp of 3 °C/min. A two-step temperature-raising process was applied so that the fresh catalyst can be sulfided sufficiently. The sulfiding conditions were as follows: H2 initial pressure, 4.0 MPa; temperature, 200 °C for 4 h and 300 °C for 2 h; stirring speed, 750 rpm.

Both metal to calcium values in particular Pb Ca

Both metal-to-calcium values, in particular Pb/Ca, also fluctuated on seasonal time-scales (Fig. 3; seasonal variance of Pb/Ca = ca. 0.18 μmol/mol, Fe/Ca = 0.05 mmol/mol). Occasionally, the Pb/Ca peaks exceeded the running mean by more than 100%. The large majority of the highest and lowest metal-to-calcium values occurred between consecutive annual growth lines (Pb/Ca often half-way between consecutive annual growth lines), but rarely fell together with the annual growth lines (Fig. 3).
Some of the subfossil shells showed thin (<1 mm), friable and brightened rims (Fig. 4) that PA-824 were separated from the harder shell material further inside the hinge plate by a sharp boundary. These rims were bored by clionid sponges and contained strongly elevated concentrations of Pb, Fe, Mn, U and S (Fig. 4). Within these rims, element levels increased toward the shell surface to levels exceeding average values measured in the remainder of the shell by up to 1000 times (Fig. 4).
4. Discussion
According to the data from shells of the bivalve mollusk A. islandica presented here, lead and iron concentrations in the Greater North Sea underwent significant changes during the last millennium.

Fig shows the variation of the multiple combined

Fig. 11 shows the variation of the multiple combined forces with the displacement of the moving magnet. It can be seen that the proposed model is much more accurate than the previous model in analyzing the multistable mechanics, especially for the large deformation case. Considering the influence of the elastic force Fk, the magnetic force Fm, and the gravity force Fg, the nonlinear total force was obtained numerically, which is nearly consistent with the experimental results. There are five zero-force positions along the traveling range of the moving magnet. According to the RITA p53 variation principle, the moving magnet can keep stable at three pre-defined positions, at where the second-order derivative of the whole energy must be greater than zero. Therefore, the correctness and feasibility of the proposed mechanical–magnetic coupling model for designing tristability were validated. Importantly, the experiments have been repeated nearly 40 times with the same results of the stable state positions and the snapping forces, which adequately verified the high repeatability and positioning accuracy of the tristable mechanism. The deviations between the experimental data and the simulation were mainly located at two displacement ranges of [− 1.5 mm, − 1.0 mm] and [1.5 mm, 2.0 mm]. Within the two aforementioned displacement ranges, the snap-through procedure occurred in which the total reaction force was in opposite direction with the displacement. When the moving magnet was moved to the zero force position between the two stable states, the direction of the reaction force changed quickly, and the contact point between the moving mass and the gauge end of the testing machine also varies with the vertical displacement. Thus, the acting moment varies with the arm of force from the contact point to the beam origin, which is the main source of these deviations displayed in Fig. 11. According to the lever principle, to maintain a certain moment, the applied force can be reduced by increasing the arm of force. Actually, the arm of force between the contact point and the fixed origin increases during the snap-through procedure, thus reducing the reaction force applied to the force sensor, which is the main reason ovum the experimental force is a bit less than the simulated result.