Density - Velocity Relationship and Prediction of Lithology Variation Using Physical Analysis in Kf-4 Well of The Kifl Oil Field, Yamama Formation, South of Iraq

The density-velocity relation is an important tool used to predict one of these two parameters from the other. A new empirical density –velocity equation was derived in Kf-4 well at Kifl Oil Field, south of Iraq. The density was derived from Gardner equation and the results obtained were compared with the density log (ROHB) in Kl-4 well. The petrophysical analysis was used to predict the variations in lithology of Yamama Formation depending on the well logs data, such as density, gamma, and neutron logs. The physical analysis of rocks depended on the density, Vp, and Vs values to estimate the elastic parameters, i.e. acoustic impedance (AI) and Vp/Vs ratio, to predict the lithology and hydrocarbon indicators. According to the results of physical properties, Yamama Formation is divided into five units in Kf-4 well at Kifl Oil Field. The lithology of Yamama Formation was found to consist of limestone, dolomite, shale, and anhydrite rocks.

On the adhesion–velocity relation and length adaptation of motile cells on stepped fibronectin lanes

The biphasic adhesion–velocity relation is a universal observation in mesenchymal cell motility. It has been explained by adhesion-promoted forces pushing the front and resisting motion at the rear. Yet, there is little quantitative understanding of how these forces control cell velocity. We study motion of MDA-MB-231 cells on microlanes with fields of alternating Fibronectin densities to address this topic and derive a mathematical model from the leading-edge force balance and the force-dependent polymerization rate. It reproduces quantitatively our measured adhesion–velocity relation and results with keratocytes, PtK1 cells, and CHO cells. Our results confirm that the force pushing the leading-edge membrane drives lamellipodial retrograde flow. Forces resisting motion originate along the whole cell length. All motion-related forces are controlled by adhesion and velocity, which allows motion, even with higher Fibronectin density at the rear than at the front. We find the pathway from Fibronectin density to adhesion structures to involve strong positive feedbacks. Suppressing myosin activity reduces the positive feedback. At transitions between different Fibronectin densities, steady motion is perturbed and leads to changes of cell length and front and rear velocity. Cells exhibit an intrinsic length set by adhesion strength, which, together with the length dynamics, suggests a spring-like front–rear interaction force. We provide a quantitative mechanistic picture of the adhesion–velocity relation and cell response to adhesion changes integrating force-dependent polymerization, retrograde flow, positive feedback from integrin to adhesion structures, and spring-like front–rear interaction.

THE EFFECT OF DENSITY-VELOCITY RELATION PARAMETERS ON DENSITY CURVES IN TAU (τ) FIELD, NIGER DELTA BASIN

We considered the constants obtained for tau (𝜏)Field in the Niger Delta basin from well-log data of three wells (A,B,C) to investigate the effect of inclusion of these constants on density-velocity relation using Hampson Russell Software to generate density curve in tau field. The curves were compared to those generated from Gardner and Lindseth constants and in-situ density curves. Many researchers have worked on constants for density-velocity equations for different Fields; their results always differ from Gardner and Lindseth constants including the constants of Atat et al., 2020 which are considered in this investigation as Tau Field local fit constants. Our findings support the results of these researchers. Results indicate over estimation of density curves when using Gardner and Lindseth constants. The challenge is that in-situ density curves are not accurate due to sand-shale overlap of density values. The most improved and accurate result is given by the density curves obtained using the constants for specific sand and shale lithologies (local fits). This verifies the need for the determination of constants for local fit of the oil field under investigation. The pink curves truly indicate the density estimation for the tau field which is very reliable in the characterisation of reservoir.

The load dependence and the force-velocity relation in intact myosin filaments from skeletal and smooth muscles

In the present study we evaluated the load dependence of force produced by isolated muscle myosin filaments interacting with fluorescently labeled actin filaments, using for the first time whole native myosin filaments. We used a newly developed approach that allowed the use of physiological levels of ATP. Single filaments composed of either skeletal or smooth muscle myosin and single filaments of actin were attached between pairs of nano-fabricated cantilevers of known stiffness. The filaments were brought into contact to produce force, which caused sliding of the actin filaments over the myosin filaments. We applied load to the system by either pushing or pulling the filaments during interactions and observed that increasing the load increased the force produced by myosin and decreasing the load decreased the force. We also performed additional experiments in which we clamped the filaments at predetermined levels of force, which caused the filaments to slide to adjust the different loads, allowing us to measure the velocity of length changes to construct a force-velocity relation. Force values were in the range observed previously with myosin filaments and molecules. The force-velocity curves for skeletal and smooth muscle myosins resembled the relations observed for muscle fibers. The technique can be used to investigate many issues of interest and debate in the field of muscle biophysics.

Bistability and oscillations in cooperative microtubule and kinetochore dynamics in the mitotic spindle

In the mitotic spindle microtubules attach to kinetochores via catch bonds during metaphase. We investigate the cooperative stochastic microtubule dynamics in spindle models consisting of ensembles of parallel microtubules, which attach to a kinetochore via elastic linkers. We include the dynamic instability of microtubules and forces on microtubules and kinetochores from elastic linkers. We start with a one-sided model, where an external force acts on the kinetochore. A mean-field approach based on Fokker-Planck equations enables us to analytically solve the one-sided spindle model, which establishes a bistable force-velocity relation of the microtubule ensemble. All results are in agreement with stochastic simulations. We derive constraints on linker stiffness and microtubule number for bistability. The bistable force-velocity relation of the one-sided spindle model gives rise to oscillations in the two-sided model, which can explain stochastic chromosome oscillations in metaphase (directional instability). We also derive constraints on linker stiffness and microtubule number for metaphase chromosome oscillations. We can include poleward microtubule flux and polar ejection forces into the model and provide an explanation for the experimentally observed suppression of chromosome oscillations in cells with high poleward flux velocities. Chromosome oscillations persist in the presence of polar ejection forces, however, with a reduced amplitude and a phase shift between sister kinetochores. Moreover, polar ejection forces are necessary to align the chromosomes at the spindle equator and stabilize an alternating oscillation pattern of the two kinetochores. Finally, we modify the model such that microtubules can only exert tensile forces on the kinetochore resulting in a tug-of-war between the two microtubule ensembles. Then, induced microtubule catastrophes after reaching the kinetochore are necessary to stimulate oscillations.Author summaryThe mitotic spindle is responsible for proper separation of chromosomes during cell division. Microtubules are dynamic protein filaments that actively pull chromosomes apart during separation. Two ensembles of microtubules grow from the two spindle poles towards the chromosomes, attach on opposite sides, and pull chromosomes by depolymerization forces. In order to exert pulling forces, microtubules attach to chromosomes at protein complexes called kinetochores. Before the final separation, stochastic oscillations of chromosomes are observed, where the two opposing ensembles of microtubules move chromosome pairs back an forth in a tug-of-war.Using a a combined computational and theoretical approach we quantitatively analyze the emerging chromosome dynamics starting from the stochastic growth dynamics of individual microtubules. Each of the opposing microtubule ensembles is a bistable system, and coupling two such systems in a tug-of-war results in stochastic oscillations. We can quantify constraints on the microtubule-kinetochore linker stiffness and the microtubule number both for bistability of the one-sided system and for oscillations in the full two-sided spindle system, which can rationalize several experimental observations. Our model can provide additional information on the microtubule-kinetochore linkers whose molecular nature is not completely known up to now.