Actin-ring segment switching drives nonadhesive gap closure

Gap closure to eliminate physical discontinuities and restore tissue integrity is a fundamental process in normal development and repair of damaged tissues and organs. Here, we demonstrate a nonadhesive gap closure model in which collective cell migration, large-scale actin-network fusion, and purse-string contraction orchestrate to restore the gap. Proliferative pressure drives migrating cells to attach onto the gap front at which a pluricellular actin ring is already assembled. An actin-ring segment switching process then occurs by fusion of actin fibers from the newly attached cells into the actin cable and defusion from the previously lined cells, thereby narrowing the gap. Such actin-cable segment switching occurs favorably at high curvature edges of the gap, yielding size-dependent gap closure. Cellular force microscopies evidence that a persistent rise in the radial component of inward traction force signifies successful actin-cable segment switching. A kinetic model that integrates cell proliferation, actin fiber fusion, and purse-string contraction is formulated to quantitatively account for the gap-closure dynamics. Our data reveal a previously unexplored mechanism in which cells exploit multifaceted strategies in a highly cooperative manner to close nonadhesive gaps.

Critical Water Depth and Installation Curves for Submarine Cable Deployment Process

The purpose of the present paper is to propose installation curves for submarine cable deployment process for different water depths and tension deployment, emphasizing on the importance of modelling the “out of water” cable segment and the friction force between cable and overboard chute of the installation vessel. A custom-made analysis tool has been further expanded and used for the calculation of the cable hydraulic critical responses. Moreover, the concept of the critical water depth is proposed analytically for first time to define the cases in which the “out of water” cable segment can be ignored without denoting the accuracy of the minimum bending radius calculation. In addition, correction factors are proposed in relation to water depth and bottom tension values in order to eliminate the error of the safety factor calculation. Numerical formulation of the friction has been incorporated in the custom-made analysis tool as a further development. The analysis of various cable deployment cases proves that the inclusion of the “out of water” segment in the analysis is critical in shallow water areas. In contradiction, the modelling of the friction force is critical in deep water areas. However, both parameters are potential causes of important analysis errors.

Estimation of Impedance and Susceptance Parameters of a 3-Phase Cable System Using PMU Data

This paper proposes a new regression-based method to estimate resistance, reactance, and susceptance parameters of a 3-phase cable segment using phasor measurement unit (PMU) data. The novelty of this method is that it gives accurate parameter estimates in the presence of unknown bias errors in the measurements. Bias errors are fixed errors present in the measurement equipment and have been neglected in previous such attempts of estimating parameters of a 3-phase line or cable segment. In power system networks, the sensors used for current and voltage measurements have inherent magnitude and phase errors whose measurements need to be corrected using calibrated correction coefficients. Neglecting or using wrong error correction coefficients causes fixed bias errors in the measured current and voltage signals. Measured current and voltage signals at different time instances are the variables in the regression model used to estimate the cable parameters. Thus, the bias errors in the sensors become fixed errors in the variables. This error in variables leads to inaccuracy in the estimated parameters. To avoid this, the proposed method uses a new regression model using extra parameters which facilitate the modeling of present but unknown bias errors in the measurement system. These added parameters account for the errors present in the non- or wrongly calibrated sensors. Apart from the measurement bias, random measurement errors also contribute to the total uncertainty of the estimated parameters. This paper also presents and compares methods to estimate the total uncertainty in the estimated parameters caused by the bias and random errors present in the measurement system. Results from simulation-based and laboratory experiments are presented to show the efficacy of the proposed method. A discussion about analyzing the obtained results is also presented.

A Novel Fault Location Method for a Cross-Bonded HV Cable System Based on Sheath Current Monitoring

In order to improve the practice in the operation and maintenance of high voltage (HV) cables, this paper proposes a fault location method based on the monitoring of cable sheath currents for use in cross-bonded HV cable systems. This method first analyzes the power–frequency component of the sheath current, which can be acquired at cable terminals and cable link boxes, using a Fast Fourier Transform (FFT). The cable segment where a fault occurs can be localized by the phase difference between the sheath currents at the two ends of the cable segment, because current would flow in the opposite direction towards the two ends of the cable segment with fault. Conversely, in other healthy cable segments of the same circuit, sheath currents would flow in the same direction. The exact fault position can then be located via electromagnetic time reversal (EMTR) analysis of the fault transients of the sheath current. The sheath currents have been simulated and analyzed by assuming a single-phase short-circuit fault to occur in every cable segment of a selected cross-bonded high voltage cable circuit. The sheath current monitoring system has been implemented in a 110 kV cable circuit in China. Results indicate that the proposed method is feasible and effective in location of HV cable short circuit faults.

Theoretical and Practical Considerations of Helical Cable Elements Subject to End Effects at Cable Bending

Most cable elements of subsea cables and umbilicals are helical. If helical cable elements are restrained from sliding freely when the cable is bent, large axial strains and stresses will arise in the elements. This paper focuses on the case where the helical cable elements are fixed to end terminations, or to the beneath cable layer, at two points along the cable’s length. The elements can slide freely between these two points. Mathematical expressions are derived to calculate the strains that arise in the helical cable elements when bending the cable segment. The mathematical results have intuitive, practical interpretations that are thoroughly explained. It is shown that the maximum strains and stresses arise when the length of the cable segment is an integer number of pitch lengths plus one half pitch length.

A Trigger Residue for Transmembrane Signaling in the Escherichia coli Serine Chemoreceptor

ABSTRACTThe transmembrane Tsr protein ofEscherichia colimediates chemotactic responses to environmental serine gradients. Serine binds to the periplasmic domain of the homodimeric Tsr molecule, promoting a small inward displacement of one transmembrane helix (TM2). TM2 piston displacements, in turn, modulate the structural stability of the Tsr-HAMP domain on the cytoplasmic side of the membrane to control the autophosphorylation activity of the signaling CheA kinase bound to the membrane-distal cytoplasmic tip of Tsr. A five-residue control cable segment connects TM2 to the AS1 helix of HAMP and transmits stimulus and sensory adaptation signals between them. To explore the possible role of control cable helicity in transmembrane signaling by Tsr, we characterized the signaling properties of mutant receptors with various control cable alterations. An all-alanine control cable shifted Tsr output toward the kinase-on state, whereas an all-glycine control cable prevented Tsr from reaching either a fully on or fully off output state. Restoration of the native isoleucine (I214) in these synthetic control cables largely alleviated their signaling defects. Single amino acid replacements at Tsr-I214 shifted output toward the kinase-off (L, N, H, and R) or kinase-on (A and G) states, whereas other control cable residues tolerated most amino acid replacements with little change in signaling behavior. These findings indicate that changes in control cable helicity might mediate transitions between the kinase-on and kinase-off states during transmembrane signaling by chemoreceptors. Moreover, the Tsr-I214 side chain plays a key role, possibly through interaction with the membrane interfacial environment, in triggering signaling changes in response to TM2 piston displacements.IMPORTANCEThe Tsr protein ofE. colimediates chemotactic responses to environmental serine gradients. Stimulus signals from the Tsr periplasmic sensing domain reach its cytoplasmic kinase control domain through piston displacements of a membrane-spanning helix and an adjoining five-residue control cable segment. We characterized the signaling properties of Tsr variants to elucidate the transmembrane signaling role of the control cable, an element present in many microbial sensory proteins. Both the kinase-on and kinase-off output states of Tsr depended on control cable helicity, but only one residue, I214, was critical for triggering responses to attractant inputs. These findings suggest that signal transmission in Tsr involves modulation of control cable helicity through interaction of the I214 side chain with the cytoplasmic membrane.

A Calculation Method Based on Tension Distribution and Temperature Compensation for Sliding Cables

The calculation of sliding cable is difficult because it can dynamically pass through prescribed nodes and the length is variable. In order to solve the above problem, a calculation method based on tension distribution and temperature compensation for sliding cables was put forward. At first, the sliding cable was supposed to be fixed cable and the internal force of each cable segment was calculated. Then, the unbalanced tensions between neighboring cable segments were distributed to make the tensions equal. And then different temperatures were applied to the corresponding cable segments, which could cause temperature stress to compensate the unbalanced tensions between the initial calculated tensions and distributed tensions. At last the calculation was carried on again after applying the temperature to each cable segment. Moreover, an example was presented to verify the precision and validity of this method. The results show that the calculation method based on tension distribution and temperature compensation for sliding cables is effective.

An Accurate Collision Detection Method for Cable Simulation

In this paper, we present a fast and robust collision detection (CD) and resolution scheme for deformable cable using a new method based on the shortest distance of cable segment axis. We employ a bounding sphere hierarchy (BVH) by exploiting the topology of cable for reducing the collision detection query space. After searching the collision through the bounding sphere hierarchy, the collision detection algorithm will find the two segments which are close enough to require an exact collision check. Furthermore, the exact collision state is decided by our proposed method. Penalty force method is applied to the collision resolution. The comparative experiments show that the proposed method performs more accurate than existing algorithms for deformable cable simulation without substantial computational cost.