Radial Spacing Research Articles

PENGARUH PEMANASAN BAHAN BAKAR MELALUI 2 PIPA TEMBAGA BERSIRIP RADIAL PADA UPPER TANK RADIATOR DAN PENAMBAHAN ETANOL PADA BAHAN BAKAR TERHADAP EMISI GAS BUANG MOBIL SUZUKI APV

<p><em>This research aims to : 1) Investigate the effect of heating fuel through radial finned copper pipe in the upper tank of the radiator exhaust emissions on cars Suzuki APV; 2) Investigate the effect of adding ethanol to the fuel pertalite against exhaust emissions on cars Suzuki APV; 3) Investigate the effect of heating fuel through radial finned copper pipe in the upper tank of the radiator and the addition of ethanol to the fuel pertalite against exhaust emissions on cars Suzuki APV; 4) Analyze the comparison between the results of the fuel mixture pertalite heating and heating fuel ethanol pertamax through two copper pipe to the exhaust emissions of the Suzuki APV. This research use you right experimental method with a comparative descriptive data analysis. The sample used is a Suzuki APV with G15A1D100006 machine number. Data were obtained from a large measurement exhaust emission levels CO and HC for 20 seconds at idle rotation with variations mix pertalite and ethanol as much as 0%, 5%, 10%, 15%, 20%, 25%, and 30% using the method without heating fuel and the use of heating fuel through a copper pipe finned radial variation fin spacing of 10 mm, 20 mm and 30 mm In the upper radiator tank. Data obtained from the research that is inserted into the table and displayed in a graph, and then analyzed. The results of this study were: 1) heating fuel pertalite in radial finned pipe through the upper radiator tank to the injection cars Suzuki APV can decrease the value of exhaust emissions of CO and HC;2) Addition of ethanol in fuel pertalite with higher levels of 0% to 20% decline in the value of exhaust emissions of CO and HC. Exhaust emissions of CO and HC to increase again in the levels of ethanolblending with levels of 25% and 30%; 3) heating fuel in a radial finned pipe through the upper radiator tank to the injection Suzuki APV car down the value of exhaust emissions of CO and HC. Value exhaust emissions lowest CO occur in the application of finned pipe distance of 10 mm with a mixture of 20% ethanol content of 19% and HC 0.3 by 2 24 to 33 ppm; 4) The value of exhaust emissions of CO and HC in blending ethanol content to 20% lower than the lowest value of the results of exhaust emissions of CO and HC pertamax pure with a value of 0.354% levels of CO and HC at 229.67 Ppm.</em></p>

Experimental study of flow field in geometric Type-I vortex chamber at low water abstraction ratio

ABSTRACTIn this paper, an attempt has been made to critically examine the flow field inside a cylindrical model vortex chamber type sediment extractor with 1.0 m diameter. Data on velocity distribution along tangential and radial directions have been collected by Programmable Electro Magnetic Shunt (PEMS) meter in a circular cylindrical model of vortex chamber in the laboratory. Data were for wide range of flow rate, water abstraction ratios, vertical, radial and transverse spacing. In this paper only result of one lowest water abstraction ratio that is 8% is presented. The results are presented in the form of graphical representation. Also, the segments with similar flow field have been identified.

Heat transfer investigations on impinging flame jets of a multi-port convex burner

Multi-port curved surface burners are used in industrial boilers, preheating of large diameter pipes, textile industries, preheating of cylindrical metal billets and other industrial applications. The present work reports the heat transfer characteristics of convex shaped burner with 49 inline ports arranged in an array of 7 each. The methane-air premixed flame jets are impinged on the concave surface of a curved plate placed with radial spacing of 12 mm. Two different burners with port diameters of 2 mm and 3 mm with pitch to diameter ratio of 2.33 are used. The flame jet is studied for Reynolds number (Re) ranging from 75 to 200 and equivalence ratio of 0.9–1.5. The characterisation is done by impinging the pre-characterised air jets of various flow rates on the rear surface and capturing the wall temperature. The wall temperature is analysed to get the distributions of Nusselt number and effectiveness. The variation of coefficient of variance of Nusselt number, average Nusselt number and thermal efficiency is reported in the present work. The Nusselt number and effectiveness distributions increase with the increase in mixture Reynolds number. For a fixed mixture Reynolds number, the optimum heat transfer is obtained for stoichiometric flame. The thermal efficiency and average heat transfer of 2 mm port diameter is observed to be 18–25% higher as compared with burner with port diameter of 3 mm. Correlations are developed to predict the average Nusselt number, average effectiveness, coefficient of variance (COV) of Nusselt number distribution and thermal efficiency.

On the Numerical Robustness of the Streaming Instability: Particle Concentration and Gas Dynamics in Protoplanetary Disks

Abstract The streaming instability (SI) is a mechanism to concentrate solids in protoplanetary disks. Nonlinear particle clumping from the SI can trigger gravitational collapse into planetesimals. To better understand the numerical robustness of the SI, we perform a suite of vertically stratified 3D simulations with fixed physical parameters known to produce strong clumping. We vary the numerical implementation, namely, the computational domain size and the vertical boundary conditions (vBCs), comparing newly implemented outflow vBCs to the previously used periodic and reflecting vBCs. We find strong particle clumping by the SI is mostly independent of the vBCs. However, peak particle densities are higher in larger simulation domains due to a larger particle mass reservoir. We report SI-triggered zonal flows, i.e., azimuthally banded radial variations of gas pressure. These structures have low amplitudes, insufficient to halt particle radial drift, confirming that particle trapping in gas pressure maxima is not the mechanism of the SI. We find that outflow vBCs produce artificially large gas outflow rates at vertical boundaries. However, the outflow vBCs reduce artificial reflections at vertical boundaries, allowing more particle sedimentation, and showing less temporal variation and better convergence with box size. The radial spacing of dense particle filaments is ∼0.15 gas scale heights (H) for all vBCs, which sets the feeding zone for planetesimal growth in self-gravitating simulations. Our results validate the use of the outflow vBCs in SI simulations, even with vertical boundaries close (≤0.4H) to the disk midplane. Overall, our study demonstrates the numerical robustness of nonlinear particle clumping by the SI.

Dynamical Evolution of the Early Solar System

Several properties of the Solar System, including the wide radial spacing of the giant planets, can be explained if planets radially migrated by exchanging orbital energy and momentum with outer disk planetesimals. Neptune's planetesimal-driven migration, in particular, has a strong advocate in the dynamical structure of the Kuiper belt. A dynamical instability is thought to have occurred during the early stages with Jupiter having close encounters with a Neptune-class planet. As a result of the encounters, Jupiter acquired its current orbital eccentricity and jumped inward by a fraction of an astronomical unit, as required for the survival of the terrestrial planets and from asteroid belt constraints. Planetary encounters also contributed to capture of Jupiter Trojans and irregular satellites of the giant planets. Here we discuss the dynamical evolution of the early Solar System with an eye to determining how models of planetary migration/instability can be constrained from its present architecture. Specifically, we review arguments suggesting that the Solar System may have originally contained a third ice giant on a resonant orbit between Saturn and Uranus. This hypothesized planet was presumably ejected into interstellar space during the instability. The Kuiper belt kernel and other dynamical structures in the trans-Neptunian region may provide evidence for the ejected planet. We favor the early version of the instability where Neptune migrated into the outer planetesimal disk within a few tens of millions of years after the dispersal of the protosolar nebula. If so, the planetary migration/instability was not the cause of the Late Heavy Bombardment. Mercury's orbit may have been excited during the instability.

Suppression of vortex-induced vibrations using flexible shrouding—An experimental study

A number of offshore compliant structures such as risers, mono-columns, tension leg platforms (TLPs), spars, etc., which are deployed in the offshore field are subjected to vortex-induced vibration (VIV). The harsh environmental conditions often lead to failure of these structures well before their design life period resulting in fatal accidents. To minimize VIV, several investigations were conducted by other researchers. The present study focuses on the experimental investigations of an elastically mounted circular cylinder shrouded with net substructure called as Ventilated Net (VN) to suppress VIV. The VN is an omnidirectional, economical, customizablenet substructure comprising of flexible hollow tubes in a systematic arrangement. This device could be retrofitted to the offshore structures/risers, to attenuate VIV, thereby preventing the structure from fatigue failure. Experimental investigations are conducted to address the reduction of VIV and drag forces acting on the oscillating cylinder shrouded with VN of various configurations. The experiments are performed in towing tank facility in Department of Ocean Engineering, IIT Madras, India. The primary objective of the present investigation is to quantify the VIV amplitudes by employing VN shrouding the cylinder, at high Re regime, ranging from (0.22–2.50) × 105. The effect of spaces between the flexible hollow tubes and shrouding radii of VN around the cylinder are also addressed in this article. From the measurements, it is observed that cylinder with VN of dense mesh at a radial spacing of twice the diameter of the bare cylinder, suppresses VIV by 98% and drag force by 40% at Re of 1.2 × 105.

Aero-thermodynamic and chemical process interactions in an axial high-pressure turbine of aircraft engines

Precise investigation of aero-thermodynamic and chemical processes relating to environmental precursor pollutants in an aircraft turbine is challenging because of the complexity of transformation processes at high temperature and high pressure. We present here, for the first time, new insights into the study of aero-thermodynamic processes, formation of nitrate and sulfate aerosol precursors, and investigate the influence of chemical processes on aero-thermodynamics. We also shed light on the effect of three-dimensional blade profile, radial spacing, and rotor speed on the performance of a high-pressure turbine. We highlight that flow vortex and the variation of chemical formation which appear in both rear stator blades and rear rotor blades. We found that the chemical processes were affected by the evolution of temperature (maximum of 16.9%) and flow velocity (maximum of 38.8%). Contrary to the conservative one-dimensional and two-dimensional modeling, which provide only the flow trends and flow evolution at cylindrical surface, respectively, our three-dimensional modeling approach offers the possibility of combining information on radial spacing and rotor-speed effect by providing three-dimensional images of spatial-geometry effect on aero-thermodynamic and chemical processes. Quantitatively, the magnitude of change in aero-thermodynamics and nitrogen oxidation may be expected to be up to 17% and 48%, respectively, over a stage of the high-pressure turbine.

Experimental study of directional propagation of hydraulic fracture guided by multi-radial slim holes

The conventional hydraulic fracturing fails in the target oil/gas zone (remaining oil, closed reservoir, etc.) which is not located in the azimuth of maximum horizontal stress of available wellbores. The technology of directional propagation of hydraulic fracture guided by vertical multi-radial slim holes is innovatively developed. In order to verify this technology, lots of true triaxial hydraulic fracturing simulation experiments were carried out with artificial cores, aiming at investigating the influence of in-situ stress, fracturing fluid displacement, and azimuth, diameter, number, and spacing of radial slim holes on fracture propagation. The results show that directional propagation of hydraulic fractures guided by vertical multi-radial slim holes is feasible. Regardless of varied radial slim hole and in-situ stress parameters, hydraulic fracture always initiates in the heel of radial slim hole. For hydraulic fracturing assisted by single radial slim hole, smaller horizontal stress difference (3 MPa, σH/σh = 1.25) and smaller radial slim hole azimuth (15°) may guide propagation of hydraulic fractures along radial slim hole, and larger horizontal stress difference (6 MPa, σH/σh = 1.67) can sharply reduce guidance of radial slim hole. Affected by mutual interference from guidance of radial slim holes and controlling of horizontal in-situ stress, fractures tend to distort along fracture length and fracture height. For hydraulic fracturing assisted by vertical multi-radial slim holes, horizontal stress difference is one of key factors influencing the directional propagation effect of hydraulic fracture. Larger horizontal in-situ stress difference (>6 MPa, σH/σh > 1.67) hardly results in directional propagation of hydraulic fracture along radial slim hole row, and creates bigger diversion angle of fracture, and larger azimuth (>45°) of radial slim hole row reduces the guidance strength, resulting small fracture diversion radius. In conditions of larger angle between target zone and maximum horizontal stress, and requirement of large azimuth of radial slim hole row, the effective hydraulic fracture propagation along radial slim holes and ideal fracture height will be achieved through human intervention, e.g. increment of the number and diameter of radial slim holes, reduction of radial slim holes spacing, increment of fracturing fluid displacement, etc. The simulation results provide methods for designing directional propagation of hydraulic fractures guided by vertical multi-radial slim holes.

Numerical simulation of directional propagation of hydraulic fracture guided by vertical multi-radial boreholes

The conventional hydraulic fracturing is not effective in the target oil development zone (remaining oil or gas, trap reservoir, etc.) with available wellbores located in the azimuth of non-maximum horizontal in-situ stress. The technology of directional propagation of hydraulic fracture guided by vertical multi-radial boreholes was innovatively developed. In order to verify the technology, a 3D extended finite element numerical model of hydraulic fracturing promoted by vertical multi-radial boreholes was established using Abaqus Software, and the influence of horizontal in-situ stress differences, azimuth, diameters, spacing, and lengths of radial boreholes, rates and viscosities of fracturing fluids, Young modulus and Poisson's ratio of rock, and reservoir permeability on propagation of hydraulic fracture guided by radial borehole row were comprehensively analyzed. Moreover, the term ‘Guidance factor (G)’ was introduced for the first time to effectively quantify guidance of radial borehole row. Finally, the guidance of the above ten factors is comprehensively evaluated through gray correlation analysis. The results showed that the directional propagation of hydraulic fracture is realized through scientifically arranged vertical radial borehole row, and ‘G’ reflects the real guidance strength of radial borehole row to hydraulic fracture. The azimuth of radial borehole row increases by 75°, G increases by 18 times. Horizontal in-situ stress difference increases by 9 MPa, G increases by 95%. The borehole diameter increases by 4 cm, G decreases by 54%. The borehole spacing increases by 0.5 m, G increases by 18%. The borehole length increases by 10 m, G decreases by 40%. Young's modulus of reservoir rock increases by 20 GPa, G decreases by 23%. Poisson's ratio increases by 0.1, G increases by 57%. Permeability of reservoir increases by 100 times, G increases by 3.3 times. Injection rate increases by 9 m3/min, G decreases by 63%. Both excessively high and low viscosities are adverse to guidance of radial borehole to hydraulic fracture, and 50 mPa s fracturing fluid creates best guidance to propagation of hydraulic fracture. The gray correlation analysis showed that the influences (from strong to weak) of the above factors on guidance of radial borehole were listed as follows: azimuth of radial borehole > injection rate of fracturing fluid > horizontal in-situ stress differences > Young's modulus of rock > viscosity of fracturing fluid > borehole diameter of radial borehole > radial borehole spacing > reservoir permeability > length of radial borehole > Poisson's ratio. This study provided theoretical evidence for directional propagation of hydraulic fracture promoted by radial borehole, and it predicted the guidance of radial borehole to hydraulic fracture in a certain extent, which is helpful for planning well-completion and fracturing operation in technology of hydraulic fracturing promoted by radial borehole.

Thermo-mechanical effects in Majorana type quantum devices

We have developed a multi-scale model, consisting of an atomistic model in LAMMPS of an InSb nano-wire, and a continuum model in COMSOL of a so-called Majorana research device, to study the effects of thermo-mechanical deformations during the cool down from room temperature to the operating temperature of about 50mK. For the simulation of the InSb nano-wire suitable potentials were implemented in LAMMPS. The simulation results of the nano-wire show size dependent Young's moduli and gradients in the radial lattice spacing during uniaxial straining. The material properties that were derived from the atomistic model, were introduced in the continuum model. Cool down of the device from room temperature to its operating temperature introduced significant deformation. However, the stresses in the system are moderate and no fracture or damage is expected. Still, deformation of the device will induce shifts in band gap behavior of the device. Band gap shifts using a simple approximation are estimated to be about 34%.

Titin strain contributes to the Frank–Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins

The Frank-Starling mechanism of the heart is due, in part, to modulation of myofilament Ca(2+) sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank-Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.

Effect of Shear Studs and High Moments on Punching Behavior of GFRP-RC Slab–Column Edge Connections

AbstractThis paper presents test results of six full-scale glass fiber-reinforced polymer (GFRP) reinforced concrete slab–column edge connections. The test connections included two series with three connections each. The connections of Series 1 investigated the effect of a new type of GFRP shear reinforcement on the punching shear behavior of slab-column edge connections, while those of Series 2 investigated the effect of moment-to-shear ratio. For Series 1, one connection did not have shear reinforcement, while the other two connections had ribbed-deformed GFRP shear studs with headed ends at different radial spacing (120 and 80 mm). For Series 2, three different moment-to-shear ratios were applied to the connections (0.2, 0.4, and 0.6 m). The typical dimensions of the slabs were 2,800×1,550×200 mm with a 300-mm square column extending above and below the slab. The headed ends of the studs provided adequate anchorage, which allowed the studs to control the propagation of shear cracks and to increase the...

Design and Verification of a Rail-Borne Energy Harvester for Powering Wireless Sensor Networks in the Railway Industry

Design, modeling, simulation, and vibration testing related to electromagnetic energy harvesters are investigated in this paper. A rail-borne electromagnetic energy harvester with copper-beads spacing is proposed and fabricated, the suitable for harvesting vibration-induced energy of the wheelset/track system. A vehicle-track model considering vehicle traveling load is constructed and numerically solved by fast explicit integration methods. An electromagnetic model is established to predict the induced voltage. The track irregularity power spectrum density is applied as excitation source on the track. Based on the calculation results, both the resonant harvester and the magnetic levitation harvester are designed. The solution utilizes copper beads as radial spacing, which guarantees reliable unidirectional movement of magnets inside a multilayer-multirow coil. Vibration tests are conducted with the proposed track-borne device, and a hydraulic driven system is exploited to generate the realistic wheelset/rail interaction force. The proposed rail-borne energy harvester can be mounted to the track easily and extensively. The magnetic levitation harvester offers an approach for harvesting broadband low-frequency (3–7Hz) wheelset/track interaction with the rail displacement of 0.6 to 1.2 mm. For the resonant harvester, the output power of 119 mW and the output peak-peak voltage of 2.32 V are achieved with the rail displacement of 1.2 mm, the coil height of 48 mm, the load resistance of 45 $\Omega $ , the coil inductance of 105.572 mH, and 3000 numbers of turns. Furthermore, a dc–dc boost converter is proposed, which is capable of converting the alternating voltage of the transducer into 5 V/10-mA dc output at the resonant frequency of 6 Hz, the rail displacement of 2 mm, and the induced voltage of 3.4 V.

Operational Response of a Soil-Borehole Thermal Energy Storage System

AbstractThis study focuses on an evaluation of the subsurface ground temperature distribution during operation of a soil-borehole thermal energy storage (SBTES) system. The system consists of an array of five 9 m-deep geothermal heat exchangers, configured as a central heat exchanger surrounded by four other heat exchangers at a radial spacing of 2.5 m. In addition to monitoring the temperature of the fluid entering and exiting each heat exchanger, 5 thermistor strings were embedded in boreholes inside and outside of the array to monitor changes in ground temperature with depth. After 75 days of heat injection at a constant rate of 20 W/m, corresponding to 11.5 GJ of thermal energy, the average ground temperature in the array increased by 7°C. However, depending on the storage volume definition, only 2.43–4.86 GJ of thermal energy was stored attributable to heat losses. After a 4-month rest period the heat storage was observed to decrease by 60% owing to further heat losses. The trends in subsurface temp...

Respiratory Motion Compensation for Simultaneous PET/MR based on strongly undersampled radial MR data.

We propose a new method for PET/MR respiratory motion compensation, which is based on strongly undersampled measured MR data and a) runs in parallel with the PET acquisition, b) can be interlaced with clinical MR sequences, and c) can be acquired with measurement times as short as 0.5 min per bed position. An MR dataset covering the free-breathing thorax and abdomen of a volunteer was acquired with a Siemens Biograph mMR system. We applied a 3D encoded radial stack-of- stars sequence with a golden angle radial spacing (acquisition time: 5.0 min). Respiratory motion amplitudes were estimated from measured k-space centers allowing for a retrospective gating into 20 overlapping motion phase bins with a width of 10%. In addition, two highly undersampled datasets consisting of 300 and 600 spokes were created corresponding to acquisition times of 0.5 min and 1.0 min, respectively. 4D gated MR images of the three datasets (0.5, 1.0 and 5.0 min acquisition time) were reconstructed iteratively. For each of the three resulting image sets, MVFs were estimated. A 4D PET volume of the volunteer with four artificial hot lesions in the lungs and abdomen was simulated. 3D PET and MoCo 4D PET images based on the three sets of motion vector fields derived from MR were reconstructed and compared to a reference gated 4D reconstruction with ten-fold acquisition time. Visual inspection of the reconstructed PET images showed that blurring was reduced in MoCo 4D images for all acquisition times compared to the 3D reconstruction. A quantitative evaluation in the end-exhale and a mid-ventilation motion phase demonstrated that MoCo 4D reconstructions outperformed the 3D reconstruction in terms of SUVmean values for all lesions and acquisition times compared to the reference gated 4D reconstruction.

Parameter Modeling Analysis and Experimental Verification on Magnetic Shielding Cylinder of All-Optical Atomic Spin Magnetometer

The ultrahigh sensitivity atomic spin magnetometer as the magnetic measurement sensor has received much concern. The performance of the magnetic shielding cylinder is one of the key factors constraining the atomic spin magnetometer’s sensitivity. In order to effectively improve the performances of the magnetic shielding, the parameter optimization models of the magnetic shielding cylinder were established in this paper. Under the condition of changing only one parameter while the others keeping constant, the effects of various parameters influencing the axial shielding coefficient were comprehensively analyzed, and the results showed that the smaller the innermost length, the innermost radius, and the radial spacing were, and the greater the axial spacing was, the better the shielding performance could be obtained. According to these results and the actual needs, the magnetic shielding cylinder was optimally designed, and then the shielding effects were simulated via the software Ansoft. The simulation results showed that the optimized magnetic shielding cylinder had the advantages of small size, high shielding performance, and lager uniformity than that of the nonoptimized one. The actual measurement results showed that the residual magnetism in the optimized magnetic shielding cylinder was below 0.1 nT, which was 2~4 times lower than the nonoptimized one.

Load-Sharing Characteristics of Power-Split Transmission System Based on Deformation Compatibility and Loaded Tooth Contact Analysis

In order to implement the uniform load distribution of the power-split transmission system, a pseudostatic model is built. Based on the loaded tooth contact analysis (LTCA) technique, the actual meshing process of each gear pair is simulated and the fitting curve of time-varying mesh stiffness is obtained. And then, the torsional angle deformation compatibility conditions are proposed according to the closed-loop characteristic of power flow, which will be combined with the torque equilibrium conditions and elastic support conditions to calculate the transfer torque of each gear pair. Finally, the load-sharing coefficient of the power-split transmission system is obtained, and the influences of the installation errors are analyzed. The results show that the above-mentioned installation errors comprehensively influence the load-sharing characteristics, and the reduction of only one error could not effectively achieve perfect load-sharing characteristics. Allowing for the spline clearance floating and constrained by the radial spacing ring, the influence of the floating pinion is analyzed. It shows that the floating pinion can improve the load-sharing characteristics. Through the comparison between the theoretical and related experimental data, the reasonability and feasibility of the above-proposed method and model are verified.

A Small Surrogate for the Golden Angle in Time-Resolved Radial MRI Based on Generalized Fibonacci Sequences.

In golden angle radial magnetic resonance imaging a constant azimuthal radial profile spacing of 111.246...(°) guarantees a nearly uniform azimuthal profile distribution in k-space for an arbitrary number of radial profiles. Even though this profile order is advantageous for various real-time imaging methods, in combination with balanced steady-state free precession (SSFP) sequences the large azimuthal angle increment may lead to strong image artifacts, due to the varying eddy currents introduced by the rapidly switching gradient scheme. Based on a generalized Fibonacci sequence, a new sequence of smaller irrational angles is introduced ( 49.750...(°), 32.039...(°), 27.198...(°), 23.628...(°), ... ). The subsequent profile orders guarantee the same sampling efficiency as the golden angle if at least a minimum number of radial profiles is used for reconstruction. The suggested angular increments are applied for dynamic imaging of the heart and the temporomandibular joint. It is shown that for balanced SSFP sequences, trajectories using the smaller golden angle surrogates strongly reduce the image artifacts, while the free retrospective choice of the reconstruction window width is maintained.

Abstract 18852: Myofilament Length Dependent Activation: Role of Titin

The cellular basis of the Frank-Starling mechanism is sarcomere length (SL) modulation of myofilament Ca 2+ sensitivity (LDA). The molecular mechanism(s) that underlie LDA are unknown, but recent evidence has implicated the giant protein titin as possible sarcomeric strain sensor responsible for LDA by an, as of yet unidentified, signal transduction pathway. Accordingly, the aim of the present study was to elucidate the impact of SL (from slack=2.0 μm to stretch=2.4 μm) on LDA and sarcomere structure in isolated rat myocardium from either wild-type (WT) or mutant (HM) rats expressing a giant splice isoform of titin. At stretch, WT muscles showed reduced increase in passive tension (-20%) and twitch force (-58%); also, LDA was significantly blunted at the myofilament level. Time-resolved small angle x-ray diffraction of intact twitching muscles during diastole revealed at stretch a significant increase in intensity and spacing of: myosin M2 (+121% & +0.4%) and troponin T3 (+174% & +1.0%); Myosin binding protein C (MyoBPC) also trended to increase (C1%C2). These SL dependent changes in sarcomere structure were absent in HM muscles. Cross-bridge radial spacing (layer line analysis) was significantly reduced at stretch in WT (-8.0%); in HM muscles radial spacing was further, but similarly reduced at both slack and stretch (~-20%). Equatorial spacings and intensity ratios were similar between WT and HM at both slack and stretch. Electron density reconstruction revealed, only in WT, increased mass in both thick and thin filament, and the appearance of an as of yet unidentified moiety spanning the space between the thick and thin filaments at stretch. These results were independently confirmed in skinned myocyte fragments in which endogenous TnC was replaced with fluorescently labelled TnC. Conclusion: Stretch induces structural changes in both thick and thin filaments mediated by titin strain. Moreover, MyoBPC may interact with actin to mediate LDA.

Radial spacing distributions from planar point sets.

This paper explores the radial projection method for locally finite planar point sets and provides numerical examples for different types of order. The main question is whether the method is suitable to analyse order in a quantitative way. The findings indicate that the answer is affirmative. In this context, local visibility conditions are also studied for certain types of aperiodic point sets.