Increasing Separation Distance Research Articles

Studying the potential of QQq at finite temperature in a holographic model * *Supported by the National Natural Science Foundation of China (12175100, 11975132) and the Research Foundation of Education Bureau of Hunan Province, China (21B0402, 21A0280, 20C1594)

Using gauge/gravity duality, we investigate the string breaking and dissolution of two heavy quarks coupled to a light quark at finite temperature. It is found that three configurations of QQqexist with the increase in separation distance for heavy quarks in the confined phase. Furthermore, string breaking occurs at the distance ( ) for the decay mode . In the deconfined phase, QQq melts at a certain distance and then becomes free quarks. Finally, we compare the potential of QQq with that of , and it is found that is more stable than QQqat high temperatures.

On the study of the psychological effects of blocked views on dwellers in high dense urban environments

This paper studies the effects of neighbourhood views of densely packed high-rise buildings on human perceptions of oppressiveness and noise annoyance. Earlier studies have found that views containing close-by tall buildings would not only negatively affect annoyance induced by road traffic noises but also develop an oppressive feeling. However, there is very limited understanding about the extent to which views blocked by buildings with tight spacing and separation distance affects the responses of oppressiveness and noise annoyance. Moreover, few studies have explored the potential of vertical greening and façade condition on attenuating those responses. This study aimed at formulating multivariate models to predict the probability of evoking perceived oppressiveness and noise annoyance when exposed to blocked views from indoors in a canyon-like setting conditioned by those spatial and façade attributes at road traffic noise levels between 55 and 65 dBA. Sixteen audio-visual composite scenarios were presented to 53 participants through immersive virtual reality for annoyance and oppressiveness ratings. The results showed that the probability of high noise annoyance responses could be significantly lowered with a larger separation distance, the presence of vertical greening, and maintenance on building façades. In addition, decreasing noise level, increasing separation distance, presence of building spacing, vertical greening and well-maintained building façades were likely to reduce oppressive feeling. Further, the model revealed that participants had higher sensitivity to vertical greening than to the openness of view when perceiving noise annoyance. The effect of separation distance was significantly stronger on perceived oppressiveness than on noise annoyance.

Effects of cross airflow and burner distance on temperature profile and flame morphology of dual tandem pool fires

Understanding multiple fire sources interactions in cross airflow that frequently occur in wildland fire or industrial process accident scenario is helpful for establishing guidelines for fire protection engineering. This paper experimentally studies the thermal characteristic and flame behavior of dual tandem pool fires with equal- and unequal- heat release rates in varying separation distances (S) under cross airflow (u). Two square diffusion burners were used employing propane as fuel with varied heat release rates (HRR) at six separation distances, with a total of 216 experimental conditions were considered comprehensively. Flame merging condition, IR-measured flame temperature profile, flame height and flame horizontal projection length were quantified and analyzed. Results show that the flames tend to merge more easily in cross airflow when the HRR of the upstream flame is larger. The maximum temperature in the flame region increases with the increasing cross airflow velocity for both merging and non-merging flames, and the downstream pool fire's maximum temperature is lower than that of the upstream pool fire in the cases of non-merging. For merging cases, flame horizontal projection length decreases as S/D increases, while flame height changes little for varying S. For non-merging cases, flame height of downstream pool fire has an increasing trend with the increasing separation distance, while flame horizontal projection length declines in reverse due to the flame blockage effect. Three combustion states of dual fires are identified according to their force interactions: State I-pressure thrust dominated, State II-pressure thrust competes with cross airflow inertial force, State III-cross airflow inertial force dominated. Finally, a scaling analysis is performed to characterize the flame height and horizontal flame projection length based upon the competition mechanisms between total buoyant flow flux and cross airflow momentum flux for merging flame and non-merging flame in state III. This study provides experimental data and a scaling analysis into the fundamental physics of equal and unequal multiple pool fires interactions under cross airflow.

Seismic Pounding Response of Neighboring Structure using Various Codes with Soil-Structure Interaction effects: Focus on Separation Gap

Due to the high cost and less availability of land, the buildings are constructed adjacent to each other with a significantly smaller separation gap. Whenever seismic forces act on adjacent structures, they collide and cause significant structural and architectural damage. Soil-Structure Interaction (SSI) effects cause more complications in the adjacent structures. This paper assesses the gap distance between RC bare frame adjacent structures of varying heights in medium and soft soil with and without SSI to avoid the pounding effect of an earthquake. The main objectives are to find the separation distance between adjacent buildings by the provisions of FEMA 356, IS 1893 (Part 1):2002, IS 1893 (Part 1):2016 and EN 1998-1:2004. The separation gap between different codes was then compared to determine the minimum separation required to prevent pounding between the structures. The maximum lateral displacement on the roof and the time period of the adjacent buildings are compared with and without SSI. There is a significant increase in lateral displacement, separation distance, and time period considering SSI. It is found that the Indian code overestimates the separation distance. Thus, this study guides structural engineers to maintain a minimum separation distance between buildings erected on medium and soft soils in high seismic zones of India. Doi: 10.28991/CEJ-2022-08-02-09 Full Text: PDF

Layout optimization for safety evaluation on LNG-fueled ship under an accidental fuel release using mixed-integer nonlinear programming

The Liquefied Natural Gas (LNG)-fueled ship is an alternative solution to deal with the Emission Control Area (ECA) issued by the International Maritime Organization (IMO). LNG fuel has eco-green characteristics since sulfur oxide and particulate matter are eliminated. The equipment sitting on the Fuel Gas Supply System (FGSS) layout needs a good arrangement to prevent the domino effect. This study’s scopes are to establish the feasible FGSS layout based on the equipment position and conduct an accidental LNG release that adopts the Computational Fluid Dynamics (CFD). Mixed-Integer Nonlinear Programming (MINLP) is provided as an optimization tool. The MINLP framework is written in the Python programming language. The minimum separation distance, deck size, and non-overlapping functions of equipment are included as the MINLP constraint. The separation distances are provided based on the Center of Chemical Process Safety (CCPS) recommendation. Also, several options of the separation distance are added that consist of 5.0, 6.0, and 7.0 m to observe the congestion effect. The total pipe length is considered as the MINLP objective that can be used to estimate the pipe cost. The proposed MINLP framework is designated to generate a feasible layout that has an adequate separation distance and minimum cost of the pipe. CFD results show that the increase of separation distance can reduce the gas accumulation effectively which eventually reduces the severity of other consequences. Finally, the feasible layout is proposed based on a series of several consequences under an accidental LNG release, such as gas dispersion, fire, and vapor cloud explosion.

Dynamic Behaviors of Exciplex States in Rubrene/ C60 -Based OLEDs with Sub-Band-Gap Turn-On Electroluminescence

Although the origin of sub-band-gap electroluminescence has been extensively studied for organic light-emitting diodes (OLEDs) with a planar heterojunction of rubrene-fullerene (${\mathrm{C}}_{60}$), the dynamic behaviors of exciplexes formed at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface are still vague. Herein, employing magnetoconductance (MC) and magnetoelectroluminescence (MEL) detection techniques, we find an unreported reverse intersystem crossing (RISC, ${\mathrm{EX}}^{3}$ \ensuremath{\rightarrow} ${\mathrm{EX}}^{1}$) from triplet to singlet exciplexes dominated at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface. Besides this RISC evolution channel, the triplet exciplexes also participate in another two processes: one is the scattering channel of triplet-charge annihilation (TCASC, ${\mathrm{EX}}^{3}$ + $\stackrel{\ensuremath{\leftarrow}}{e}$ \ensuremath{\rightarrow} ${S}_{0}$+ \ensuremath{\downarrow}e) with excessive charge carriers, which is disadvantageous for RISC to occur, and the other is Dexter-energy transfer to produce a triplet exciton (${\mathrm{EX}}^{3}$ \ensuremath{\rightarrow} ${T}_{1}$) in rubrene followed by triplet-triplet annihilation (TTA, ${T}_{1}$+ ${T}_{1}$ \ensuremath{\rightarrow} ${S}_{1}$+ ${S}_{0}$ \ensuremath{\rightarrow} h\ensuremath{\nu}\ensuremath{\uparrow} + 2${S}_{0}$). This TTA is the physical origin of sub-band-gap EL because TTA needs no respective injection of electrons and holes into the LUMO and HOMO energy levels and requires no direct recombination of LUMO electrons with HOMO holes in rubrene. Moreover, both the bias-current dependences of MC and MEL traces reveal that the RISC process is more obvious in relatively balanced devices due to weak TCASC processes, and they show a monotonic decrease and nonmonotonic variation in unbalanced and relatively balanced $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs, respectively, because of the combined effects of the applied electrical field and the TCASC process. Theoretically, a stronger RISC process should be observed in devices by inserting a thin bathocuproine (BCP) interlayer to modify the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface due to the increased separation distance between electron and hole in exciplex states, but the opposite experimental results are obtained because of strong TCASC channels simultaneously occurred with the insertion of a BCP interlayer. The RISC process decreases monotonically upon lowering the operational temperature due to its endothermic property. This work deepens our comprehensive understanding of the dynamic behaviors of exciplexes and the physical origin of sub-gap EL features in $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs.

Effect of the magnetization parameter on electron acceleration during relativistic magnetic reconnection in ultra-intense laser-produced plasma

Relativistic magnetic reconnection (MR) driven by two ultra-intense lasers with different spot separation distances is simulated by a three-dimensional (3D) kinetic relativistic particle-in-cell (PIC) code. We find that changing the separation distance between two laser spots can lead to different magnetization parameters of the laser plasma environment. As the separation distance becomes larger, the magnetization parameter σ becomes smaller. The electrons are accelerated in these MR processes and their energy spectra can be fitted with double power-law spectra whose index will increase with increasing separation distance. Moreover, the collisionless shocks’ contribution to energetic electrons is close to the magnetic reconnection contribution with σ decreasing, which results in a steeper electron energy spectrum. Basing on the 3D outflow momentum configuration, the energetic electron spectra are recounted and their spectrum index is close to 1 in these three cases because the magnetization parameter σ is very high in the 3D outflow area.

Consequence modeling and domino effects analysis of synergistic effect for pool fires based on computational fluid dynamic

Synergistic effects of pool fires in fire-induced domino accidents can result in greater damage than single pool fire. Existing research mainly adopts a superposition method based on simplified assumptions to analyze the contribution of synergistic effect of pool fires for domino effects. Therefore, the synergistic effect of pool fires has not been well understood. In this study, a new CFD-based method is developed to model the synergistic effect of pool fires. Case studies were carried out taking double pool fires as an example. The influence of key factors, including wind speed, vertical fire location, fuel type, and separation distance has been investigated quantitatively. The results demonstrated that the proposed CFD based approach can model the consequences of pool fires more comprehensively and assess the domino effects under synergistic effect more precisely than the traditional superposition method. Compared with the single pool fire, the synergistic effect of double pool fires can increase the probability of domino accidents for the adjacent tanks at the downwind by six orders of magnitude. In addition, it is observed that the received maximum radiation heat flux and escalation probability of the target tank in the downwind direction rise with increased wind speed. While the maximum radiation heat flux received by target tanks and escalation probability reduced with increased separation distance and vertical fire location. Moreover, according to the minimum safety distance recommended by present design standards, the synergistic effect of double pool fires in diesel storage tank farms will lead to a higher escalation probability of near equipment than gasoline storage tank farms. This study can be used to predict accident consequences and assess the domino effect under the synergistic effect of pool fires, and guide the layout optimization of the chemical storage tank area.

Effects of surface charge and environmental factors on the electrostatic interaction of fiber with virus-like particle: A case of coronavirus.

We propose a theoretical model to elucidate intermolecular electrostatic interactions between a virus and a substrate. Our model treats the virus as a homogeneous particle having surface charge and the polymer fiber of the respirator as a charged plane. Electric potentials surrounding the virus and fiber are influenced by the surface charge distribution of the virus. We use Poisson–Boltzmann equations to calculate electric potentials. Then, Derjaguin’s approximation and a linear superposition of the potential function are extended to determine the electrostatic force. In this work, we apply this model for coronavirus or SARS-CoV-2 case and numerical results quantitatively agree with prior simulation. We find that the influence of fiber’s potential on the surface charge of the virus is important and is considered in interaction calculations to obtain better accuracy. The electrostatic interaction significantly decays with increasing separation distance, and this curve becomes steeper when adding more salt. Although the interaction force increases with heating, one can observe the repulsive–attractive transition when the environment is acidic.

Experimental study on the diffusion burning and radiative heat delivery of two adjacent heptane pool fires

This paper investigated the effect of separation distance on the flame appearance and radiation heat flux of medium-scale pool fires dominated by radiation. A series of experiments were conducted on two adjacent heptane pool fires with diameters of 20 cm, 40 cm and 60 cm at separation distances ranging from 0 to 60 cm. According to experimental results, flame height and flame inclination angle increase monotonously with the increase of pool diameter. As separation distance increases, flame height increases first and decreases gradually for 3 different sized pool fires. However, the variation law of flame inclination angle with separation distance varies with pool diameter. The normalized flame height (Hf/D) is found to increase exponentially with the dimensionless heat release rate (Q*) with an exponent of 0.71. The radiative heat flux at the center of the pool surface peaks at the critical separation distance of flame merging, which results from increased flame emissivity and view factor. Based on thermal analysis, a model to predict the radiative heat flux on the fuel surface is developed. The predicted radiative heat fluxes quantitatively match the experimental results but with 20% overvalued, due to the neglection of radiation blockage effect of cool fuel vapors zone and soot. The blockage effect is more pronounced for the merging pool fires with a diameter of 60 cm.

Analysis of offshore wind spectra and coherence under neutral stability condition using the two LES models PALM and SOWFA

The Parallelized Large-Eddy Model (PALM) and the Simulator for Wind Farm Applications (SOWFA) have been used to simulate the marine boundary layer flows under neutral stability condition. The present work aims to investigate the capability of the two models in reproducing the structure of turbulence in the offshore environment through comparative analysis with a focus on wind spectra and coherence. Wind spectra obtained from the two LES solvers agree well with the empirical spectral model near the surface but show lower turbulence intensity in the low frequency range above the surface layer. Both models also produce highly consistent estimates of coherence with different horizontal and vertical separations, which match well with Davenport and IEC coherence models at height of 180m and 140m respectively. As the height decreases, LES predicts lower vertical coherence compared with the IEC model and the fitted decay coefficient for Davenport model grows as the separation distance increases.

Quantifying the Separation of Positive and Negative Areas in Electrostatic Potential for Predicting Feasibility of Ammonium Sulfate for Protein Crystallization.

Ammonium sulfate (AS) and poly(ethylene glycol) (PEG) are the most popular precipitants in protein crystallization. Some proteins are preferably crystallized by AS, while some are by PEG. The electrostatic potential is related to the preference of the precipitant agents. The iso-surfaces of the electrostatic potentials for the AS-crystallized proteins display a common shape and a distinct separation between the positive and negative areas. In contrast, the PEG-crystallized proteins show unclear positive and negative separation. In this work, we propose schemes to quantitatively evaluate the separation for predicting which precipitant is favorable for crystal growth between AS or PEG. Three methods were attempted to quantify the amplitude of the separation, separation distance, dipole moment, and shape regularity. The positive and negative areas are approximated to the spherical potentials caused by point charges. The first method is a measurement of the distance between the positive and negative point charges. The second one is an assessment including the quantity of electric charge into the distance. The last one is an approach monitoring the clarity of the positive and negative separation. The average value for 25 kinds of AS-preferring proteins was higher than that for the PEG-preferring ones in all three methods. Therefore, every method can distinguish the proteins preferring AS for crystal growth from those preferring PEG. These methods require an iso-surface of the electrostatic potential depicted at a certain contouring value. The shape of the iso-surface depends on the contouring value. The dependency on contour was examined by depicting the iso-surfaces of electrostatic potential with three values at ±0.8, ±0.5, and ±0.2 kT/e. While reducing the contouring value leads to the increase in separation distance and the decrease in shape regularity, dipole moment is independent of the alteration of contouring value. While the AS-preferring proteins are distinguishable from the PEG-preferring ones in any contouring values, the iso-surface at ±0.5 kT/e seems adequate for regular use. The dipole moment assessment is feasible for the choice of potent precipitants for crystal growth in experiments.

Numerical study on mean flow field of turbulent dual offset jet

A numerical investigation on the mean flow and turbulence characteristics of dual offset jet for various separation distances between the two jets with a fixed offset height of the lower jet from the bottom wall is reported in this study. The numerical simulations have been performed by solving the Reynolds-averaged Navier-Stokes equations (RANS) with two-equation standard [Formula: see text] turbulence model. The Reynolds number based on the jet width and the inlet turbulence intensity are considered as 15,000 and 5%, respectively. The computational results for the mean flow reveal that after issuing from the nozzles, the adjacent shear layers of the offset jets meet together at the merging point and then the merged jets reattaches on the bottom wall at the reattachment point before they combine together at the combined point forming a single jet flow. In the far downstream, the flow field behaves like a classical single wall jet flow. The self-similarity of mean flow field is achieved at far down stream of combined point. An increase in separation distance between the two jets [Formula: see text] results in a decrease in magnitude of the streamwise maximum velocity of the combined jet but with same rate of decay. The converging region of the jets has depicted considerable growth of turbulence as the jet centrelines bend towards the merging point. According to the mean flow results, the distances of the reattachment point and the combined point from the nozzle exit gradually increase with the progressive increase in separation distance between the two jets within the range d/ w = 3–8.

Numerical study on the flow characteristics and smoke temperature evolution under double fires condition with a metro train in tunnel

Metro system as the most effective transportation method in urban area, greatly relieve the traffic pressure. The fire safety problem of metro system cannot be ignored as it is easy to develop into a large-area fire due to the relatively closed condition of the metro system. Double fire source is an important process in the development to large-area fire, however, there is still no relevant researches studying the flow characteristics and smoke movement under double fire sources with a metro train in the tunnel. This paper conducted a series of the full-scale numerical simulation to investigate the evolution of longitudinal temperature profile and maximum temperature rise under condition of double fire source with metro train in the tunnel. The velocity and temperature profile along the tunnel ceiling was measured and analyzed. It is found that (1) the longitudinal temperature distribution of tunnel fire smoke is still exponentially attenuated under different fire source separation distance with a metro train in the tunnel, and the decay coefficient decreases with the increase of fire source separation distance; (2) the maximum temperature rise of fire smoke under the tunnel ceiling decreases with the increase of the distance between the fire sources. Correlations were developed to describe the longitudinal temperature profile and maximum temperature rise under condition of double fire sources with a metro train in the tunnel through the analysis of the effect of additional air entrainment area, smoke interaction as well as the blockage effect of the metro train. The new findings in this paper can provide basic understanding of smoke movement under condition of double fire sources with a metro train in the tunnel, the proposed correlations can provide support for the safety operation of the metro system.

A sectional soot formation kinetics scheme with a new model for coagulation efficiency

A sectional scheme for soot formation is combined with a novel model for coagulation efficiency based on the thermal rebound concept and involves the minimisation of the Lennard-Jones potential energy between two colliding particles. Here, a novel generalisation of the interaction potential well depth is formulated for particles of any size or material composition that contains a free parameter λ which is related to the soot particle void fraction. A simplification that expresses the coagulation rate in an Arrhenius-like form is proposed so that the entire gas-phase and soot kinetics can be easily coupled and integrated using existing chemical kinetics solvers. The model is included in the sectional scheme, which accounts for nucleation, surface growth/oxidation, coagulation and fragmentation, and is validated against experimental data for a series of ethylene burner stabilised stagnation (BSS) premixed flames and a methane laminar coflow diffusion flame. The soot kinetics is discretised into lumped species according to soot particle size (or number of carbon atoms) and the soot evolution follows a 23-step abstract reaction scheme that is a reduced form of an existing multisectional soot kinetics scheme (Sirignano et al., Energy & Fuels 27, 2013). Overall, the model predictions produce a satisfactory agreement with the experimental data but there is considerable sensitivity to λ. In particular, λ has a strong effect on the soot particle size distribution (PSD) in the BSS flames. λ=1 or 1.25 lead to an overprediction of large particle concentrations but result in the correct transition to a bimodal PSD as the stagnation plate separation distance increases, whereas λ=2 is found to produce accurate predictions for nascent soot but suppresses the transition to a bimodal PSD. In the methane coflow diffusion flame increasing λ reduces the soot volume fraction but the predictions are also found to be very sensitive to the chosen numerical threshold for the lower soot size detection limit and results are presented for 2 nm and 7 nm thresholds for comparison against both laser-based and probe-based experimental data.

Structure and Combustion Characteristics of Methane/Air Premixed Flame under the Action of Wall

In order to obtain the combustion characteristics of the CH4/Air premixed flame under the action of the wall interaction, a study on the impact of the jet flame on the wall at different separation distances was carried out. The separation distance from the burner outlet to the lower surface of the wall is changed and the flame structure is obtained through experiments. The temperature, velocity and reaction rate are obtained through numerical simulation, and the law of flame characteristics change is obtained through analysis. The results show that as the separation distance increases, the premixing cone inside the flame gradually changes from a horn shape to a complete cone shape and the length of the premixing cone profile increases. Also, the peak temperature and velocity of the mixture in the axial direction gradually increase, and the temperature and velocity in the radial direction first increase and then decrease. The temperature gradient and velocity reach the maximum when the separation distance is 11 mm. The peaks of reactants (CH4) net reaction rate intermediate products (CO) and products (CO2, H2O) on the axis and the axial distance corresponding to the peaks increase accordingly. The chemical reaction rate near the wall also gradually decreases with the increase of the separation distance.

Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Summary Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.

Operation parameters optimization of a separating system for non-ferrous metal scraps from end-of-life vehicles based on coupled simulation

End-of-life vehicles (ELVs) provide a particularly potent source of non-ferrous metal scraps. At presents, conveyor belt and air-jet nozzle are widely used in the existing separation system for non-ferrous metal scraps. Parameters such as shape of the scraps, conveyor belt speed (v), nozzle air pressure (P) and nozzle angle (α) have a significant influences on the separating accuracy and efficiency. To investigate the interaction between these parameters and their influences on the separation distance, a coupled simulation model of (Discrete Element Method) DEM and (Finite Element Method) FEM was employed to simulate the motion of the scraps and the separation process, the trajectory of the scraps under different circumstances was recorded and analyzed, the simulation model was verified using a separation platform. The results indicated that block shaped scraps have the largest separation distance followed by rod and slice shaped scraps. The separation distance of rod and slice shaped scraps increases when each of the three parameters increases, and the speed of conveyor belt (v) plays a dominant role. For blocks shaped scraps, when nozzle pressure is high, the separation distance increase with the increase of conveyor belt speed, when nozzle pressure is low, the separation distance decrease with the increase of conveyor belt speed. The nozzle pressure (P) was found to have the most noticeable impact on separation distance for block shaped scraps. For the platform in this study, the optimal operation parameters obtained were v = 1.9 m/s, P = 0.53 MPa, and α = 42°.

Vs30 değerine bağlı koherans modeli

Strong ground motion caused by earthquakes at every point of extended structures would not be same. This difference in ground movement has an important effect on the design of these types of structures. Meanwhile, the seismic resistant design has been lead to investigate the variability of earthquake ground motion over last decades. This variability of strong ground motion can define in terms of frequency or time. In this study, frequency domained variability named coherency is considered. Several coherency models have been proposed without considering soil effect. In this context, spatial variation of seismic ground motion based on the average shear wave velocity over the upper 30 m of depth, Vs30 is analyzed. Initially, coherency values are calculated using data triggered during six earthquakes recorded by the Istanbul Earthquake Rapid Response System. Lagged coherency data is considered in the process to get the coherency model. Nonlinear regression analysis is used for the model to obtain a good-fit to observed data. A coefficient is defined based on Vs30 values of the station-pairs. The cohereny model based on this coefficient of Vs30 is derived for EW and NS components. It is expected that coherency function decreases with the increase of frequency and separation distance. The decrease in the coefficient of Vs30 causes decrease in coherency. The variance in the coherency model between EW and NS components is small. This coherency model is used to simulate spatial variable ground motion for the accurate seismic design of elongated structures for the future studies.

Comparison of VMAT complexity-reduction strategies for single-target cranial radiosurgery with the Eclipse treatment planning system.

Complexity in MLC‐based radiosurgery treatment delivery can be characterized by the efficiency of monitor unit (MU) utilization and the average MLC leaf separation distance for a treatment plan. A reduction in plan complexity may be desirable if plan quality is not impacted. In this study, a number of strategies are explored to determine how plan quality is affected by efforts to reduce plan complexity. Ten radiosurgery cases of varying complexity are retrospectively planned using six optimization strategies: an unconstrained volumetric modulated arc therapy (VMAT) technique, a MU‐constrained VMAT technique, three techniques using various strengths of the aperture shape controller (ASC), and a hybrid technique consisting of a final‐stage VMAT optimization applied to a dynamic conformal arc leaf sequence (ODCA). The plans are compared in terms of MU efficiency, MLC leaf‐separation, conformity index (CI), gradient index (GI), and QA measurement results. The five VMAT techniques exhibited only minor differences in CI and GI values, though the ASC and MU‐constrained techniques did require 6–20% fewer MU and had mean field apertures 5–19% larger. On average, the ODCA technique had CI values 3.5% lower and GI values 1.0–2.5% higher than the VMAT techniques, but also had a mean field aperture 24–47% larger and required 16–32% fewer MU. The QA measurement results showed a 0.61% variation in mean per‐field 2%/1 mm gamma passing rates across all techniques (range 96.81%–97.42%), with no observed correlation between passing rate and technique. For simple targets, the ODCA technique achieved CI results that were equivalent to the unconstrained VMAT technique with an average 30% reduction in required MU, an average 50% increase in mean leaf separation distance, and brain V12Gy values within 0.38 cc of the VMAT technique for targets up to approximately 2 cm diameter. For MLC‐based single‐target radiosurgery, plan complexity can often be significantly reduced without an equivalent reduction in plan quality.