The development of materials with excellent microwave absorption(MWA)and electromagnetic interference(EMI)shielding performances has currently received attention.Herein,mesophase pitch-based carbon foam(MPCF)with 3D i...The development of materials with excellent microwave absorption(MWA)and electromagnetic interference(EMI)shielding performances has currently received attention.Herein,mesophase pitch-based carbon foam(MPCF)with 3D interconnected pore structure was prepared through the high pressure pyrolysis of mesophase coal tar pitch.It is found that the 3D interconnected cellular pores of MPCF facilitate multiple reflections of electromagnetic waves,which results in the minimum reflection loss(RLmin)value of MPCF reaches-37.84 dB with the effective absorption bandwidth(EAB)of 5.44 GHz at a thickness of 2.70 mm,and the total average electromagnetic shielding effectiveness(SE_(T))under 3.00 mm thickness achieves 26.52 dB in X-band.Subsequently,MPCF is activated by KOH to obtain activated carbon foam(A-MPCF).The average SE_(T)of A-MPCF achieves 103.00 dB for abundant nanopores on the pore cell walls,which leads to a transition from the multiple reflections of electromagnetic waves on the walls to diffuse reflection.Unfortunately,the reflection coefficient(R)of A-MPCF increases from 0.78 to 0.90.To reduce the R value,Fe_(3)O_(4)/A-MPCF was fabricated via the in situ growth of nano Fe_(3)O_(4)on A-MPCF.Consequently,the R value of Fe_(3)O_(4)/A-MPCF was reduced from 0.90 to 0.74,whereas the MWA performance was only slightly decreased.This work proposes a simple strategy for simultaneously adjusting MWA and EMI shielding performances of materials.展开更多
Reducing the amount of aluminum chloride needed for the catalytic preparation of high quality mesophase and carbon materials is important and we have found that using terephthalic acid(PTA)as a co-catalyst serves this...Reducing the amount of aluminum chloride needed for the catalytic preparation of high quality mesophase and carbon materials is important and we have found that using terephthalic acid(PTA)as a co-catalyst serves this purpose.By adding 3%(mass fraction)AlCl_(3)and 0.9%(mass fraction)PTA to the coal tar pitch,approximately 90%mesophase was synthesized.The product(M-3-0.9)had a high stacking order(L_(c)=3.1 nm,n=10.14)and aromaticity(0.942).By adding PTA,a larger anisotropy content was produced using a smaller amount of AlCl_(3).The PTA participated in the polycondensation reaction through its own benzene ring structure to increase the catalytic activity.However,when its content was higher than 1.5%,the number of oxygen-containing groups in the product increased which was unfavorable for the aromatic lamellar stacking and gave rise to more isotropic structures.The work opens up a new way to prepare mesophase by a catalytic method.展开更多
To propel the application of a bottom-hinged flap breakwater in real sea conditions,a two-dimensional computational fluid dynamics numerical model was conducted to investigate the pitching motion response and wave att...To propel the application of a bottom-hinged flap breakwater in real sea conditions,a two-dimensional computational fluid dynamics numerical model was conducted to investigate the pitching motion response and wave attenuation in random waves.First,the flow velocity distribution characteristic of the pitching flap at typical times was summarized.Then,the effects of random wave and flap parameters on the flap’s significant pitching angle amplitude θ_(s) and hydrodynamic coefficients were investigated.The results reveal that θ_(s) and wave reflection coefficient K_(r) values increase with increasing significant wave height Hs,random wave steepnessλs,and flap relative height.As Hs andλs increase,the wave transmission coefficient K_(t) increases while the wave dissipation coefficient K_(d) decreases.Additionally,K_(t) decreases with increasing flap relative height.With increasing equivalent damping coefficient ratio,θ_(s) and K_(t) decrease,while K_(r) and K_(d) increase.The relationships betweenλs and flap relative height on the one hand andθ_(s),K_(r),K_(t),and K_(d) in random waves on the other hand are compared to those in regular waves.Based on the equal incident wave energy and the equal incident wave energy flux,the pitching flap performs better in the wave attenuation capability under random waves than in regular waves.Finally,the dimensionless parameters with respect to random wave and flap were used to derive the K_(r) and K_(t) for-mulae,which were validated with the related data.展开更多
Pitch produced by the lique-faction of coal was divided into two frac-tions:soluble in toluene(TS)and insol-uble in toluene but soluble in pyridine(TI-PS),and their differences in molecu-lar structure and oxidation ac...Pitch produced by the lique-faction of coal was divided into two frac-tions:soluble in toluene(TS)and insol-uble in toluene but soluble in pyridine(TI-PS),and their differences in molecu-lar structure and oxidation activity were studied.Several different carbon materi-als were produced from them by oxida-tion in air(350℃,300 mL/min)fol-lowed by carbonization(1000℃ in Ar),and the effect of the cross-linked structure on their structure and sodium storage properties was investigated.The results showed that the two pitch fractions were obviously different after the air oxidation.The TS fraction with a low degree of condensation and abundant side chains had a stronger oxidation activity and thus introduced more cross-linked oxygen-containing functional groups C(O)―O which prevented carbon layer rearrangement during the carbonization.As a result,a disordered hard carbon with more defects was formed,which improved the electrochemical performance.Therefore,the carbon materials derived from TS(O-TS-1000)had an obvious disordered structure and a larger layer spacing,giving them better sodium storage perform-ance than those derived from the TI-PS fraction(O-TI-PS-1000).The specific capacity of O-TS-1000 was about 250 mAh/g at 20 mA/g,which was 1.67 times higher than that of O-TI-PS-1000(150 mAh/g).展开更多
Mesophase pitch carbon fibers have an ultra-high modulus and thermal conductivity that are unmatched by other carbon fibers,making it irreplaceable in many fields.However,due to the high temperature dependence of the ...Mesophase pitch carbon fibers have an ultra-high modulus and thermal conductivity that are unmatched by other carbon fibers,making it irreplaceable in many fields.However,due to the high temperature dependence of the viscosity of the melted pitch and the poor mechanical properties of pitch fibers,it is difficult to reduce the fiber diameter when using continuous spinning.We used the Mathworks Matlab software to optimize the mesophase pitch melt spinning model and to simulate the effects of spinning temperature,mass flow rate,winder speed,and quenching air temperature near the spinneret on the maximum shear rate during drawing.Simulation results demonstrate that applying gradient cooling to the melt upon exiting the spinneret significantly reduces the maximum shear rate and extends the drawing zone,thereby promoting the spinning stability and helping reduce the fiber diameter.In the experiment,instead of quenching in air,we applied gradient cooling to the melt,whose temperature decreased according to the equation Ta=298+278exp(−11.4z),where Ta is the final air temperature in Kelvin,and z is the distance from the spinneret in meters.It was found the gradient cooling greatly improved the draw-down ratio,reducing the average diameter of the pitch fibers from 20.8 to 13.1μm,along with improved process stability.The experimental results are in excellent agreement with the predictions.At the same time,the tensile strength of the 1150°C carbonized fibers increased from 0.6 to 1.1 GPa.Although the degree of orientation of the fibers decreased slightly,the tight bonding between microcrystals,the suppression of splitting,and the smaller diameter improved the mechanical properties of carbon fibers.This study provides an effective method for reducing the fiber diameter while improving continuity.展开更多
Pitch is a complex mixture of polycyclic aromatic hydrocarbons and their non-metal derivatives that has a high carbon content.Using pitch as a precursor for carbon materials in alkali metal ion(Li^(+)/Na^(+)/K^(+))bat...Pitch is a complex mixture of polycyclic aromatic hydrocarbons and their non-metal derivatives that has a high carbon content.Using pitch as a precursor for carbon materials in alkali metal ion(Li^(+)/Na^(+)/K^(+))batteries has become of great interest.However,its direct pyrolysis often leads to microstructures with a high orientation and small interlayer spacing due to uncontrolled liquid-phase carbonization,resulting in subpar electrochemical performance.It is therefore important to control the microstructures of pitch-derived carbon materials in order to improve their electrochemical properties.We evaluate the latest progress in the development of these materials using various microstructural engineering approaches,highlighting their use in metal-ion batteries and supercapacitors.The advantages and limitations of pitch molecules and their carbon derivatives are outlined,together with strategies for their modification in order to improve their properties for specific applications.Future research possibilities for structure optimization,scalable production,and waste pitch recycling are also considered.展开更多
The determination of musical pitch has been a major concern of music theory,East and West,in all climes and cultures,throughout the ages.This paper discusses the intricacies of pitch determination from historic,geogra...The determination of musical pitch has been a major concern of music theory,East and West,in all climes and cultures,throughout the ages.This paper discusses the intricacies of pitch determination from historic,geographic,and scientific perspectives.Its standardization nowadays has permitted the manufacture and tuning of musical instruments on a universal scale.展开更多
This study investigates the effects of radiation force due to the rotational pitch motion of a wave energy device,which comprises a coaxial bottom-mounted cylindrical caisson in a two-layer fluid,along with a submerge...This study investigates the effects of radiation force due to the rotational pitch motion of a wave energy device,which comprises a coaxial bottom-mounted cylindrical caisson in a two-layer fluid,along with a submerged cylindrical buoy.The system is modeled as a two-layer fluid with infinite horizontal extent and finite depth.The radiation problem is analyzed in the context of linear water waves.The fluid domain is divided into outer and inner zones,and mathematical solutions for the pitch radiating potential are derived for the corresponding boundary valve problem in these zones using the separation of variables approach.Using the matching eigenfunction expansion method,the unknown coefficients in the analytical expression of the radiation potentials are evaluated.The resulting radiation potential is then used to compute the added mass and damping coefficients.Several numerical results for the added mass and damping coefficients are investigated for numerous parameters,particularly the effects of the cylinder radius,the draft of the submerged cylinder,and the density proportion between the two fluid layers across different frequency ranges.The major findings are presented and discussed.展开更多
The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-do...The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-domain impulse theory for subcavitating flow(σ=8.0)and cavitating flow(σ=3.0),and to quantify the distinct impact of individual vortex structures on the transient lift to appreciate the interplay among cavitation,flow structures,and vortex dynamics.The motion of the hydrofoil is set to pitch up clockwise with an almost constant rate from 0°to 15°and then back to 0°,for the Reynolds number,7.5×105,and the frequency,0.2 Hz,respectively.The results reveal that the presence of cavities delays the migration of the laminar separation bubble(LSB)from the trailing edge(TE)to the leading edge(LE),consequently postponing the hysteresis in the inflection of lift coefficients.The eventual stall under the sub-cavitation regime is the result of LSB bursting.While the instabilities within the leading-edge LSB induce the convection of cavitation-dominated vortices under the cavitation regime instead.Having validated the lift coefficients on the hydrofoil through the finite-domain impulse theory using the standard force expression,the Lamb vector integral emerges as the main contribution to the generation of unsteady lift.Moreover,the typical vortices’contributions to the transient lift during dynamic stall are accurately quantified.The analysis indicates that the clockwise leading-edge vortex(−LEV)contributes positively,while the counterclockwise trailing-edge vortex(+TEV)contributes negatively.The negative influence becomes particularly pronounced after reaching the peak of total lift,as the shedding of the concentrated wake vortex precipitates a sharp decline due to a predominant negative lift contribution from the TEV region.Generally,the vortices’contribution is relatively modest in sub-cavitating flow,but it is notably more significant in the context of incipient cavitating flow.展开更多
The pitch bearing is a component in wind turbine units used to adjust the angle of the fan blades to adapt to the wind direction,so as to maximize the utilization of wind energy.Due to the different working mode of th...The pitch bearing is a component in wind turbine units used to adjust the angle of the fan blades to adapt to the wind direction,so as to maximize the utilization of wind energy.Due to the different working mode of the pitch bearing itself compared with ordinary small bearings and the harsh working environment,the pitch bearing is prone to faults such as cracking and deformation.In severe cases,it will lead to overall damage to the pitch bearing,causing the blade to fall from a high altitude and even injuring personnel.Therefore,this paper conducts a patent analysis and technical decomposition of the deformation monitoring device for pitch bearings,analyzes and summarizes the development process of existing deformation monitoring devices for pitch bearings.Combined with the TRIZ evolution theory and based on the S-curve,it is concluded that the current deformation monitoring device for pitch bearings is in the transitional stage between the infant period and the growth period,and discusses the possible subsequent evolution directions.Through reviewing relevant literature,it is found that inner ring cracks first appear near the upper and lower surfaces of the bolt holes in the inner ring of the pitch bearing.To this end,a new type of deformation monitoring device for pitch bearings is designed.The fiber optic displacement sensor is used for qualitative monitoring of initial cracks near the surface of the bolt holes in the inner ring of the pitch bearing.After cracks are detected,the eddy current sensor is used for quantitative monitoring of whether there are extended cracks between the cracked bolt holes and adjacent bolt holes.Finally,the work done in this paper is summarized and prospected.展开更多
High-salinity wastewater treatment has always been a challenging issue.In this study,coal tar pitch was used as the carbon source and melamine as the nitrogen source to prepare coal tar pitch-based nanosheets(CPN-9)us...High-salinity wastewater treatment has always been a challenging issue.In this study,coal tar pitch was used as the carbon source and melamine as the nitrogen source to prepare coal tar pitch-based nanosheets(CPN-9)using a salt-template method.The desalination performance of CPN-9 was evaluated using flow-electrode capacitive deionization technology.The results showed that CPN-9 has a high specific surface area(466.34 m^(2)/g),a rich pore structure(micro-/meso-pore volume was 0.28),excellent rheological properties,and hydrophilicity(contact angle of 20.44°),thereby accelerating ion transport.Electrochemical results indicated that CPN-9 exhibits a significant double-layer ion storage mechanism,with a specific capacitance of 176.66 F/g at a current density of 0.5 A/g.CPN-9 has a very low charge transfer resistance.The synergistic effect of aromatic carbon and nitrogen doping(the content of pyrrole and pyridine nitrogen was 36.40%and 35.83%,respectively)in coal tar pitch accelerates electron transfer in CPN-9.The good ion diffusion performance and low impedance of CPN-9 accelerate the ion exchange rate,resulting in outstanding desalination performance.At 1.2 V and 3%mass loading,with a CPN-9 to conductive carbon black ratio of 4:1,the average desalination rate,charge efficiency,and energy consumption reached 0.039 mg/(cm^(2)·min),48.47%,and 0.012 kWh/mol,respectively.In summary,this study optimized the structure of CPN-9 from the perspective of electronic and ionic transport,enhancing its desalination performance and providing theoretical support for the deionization of high-salinity wastewater.展开更多
The controversies about the mechanism of sodium storage in hard carbon(HC)hinder its rational structural design.A series of porous HC materials using coal tar pitch show a reversible capacity of 377 mAh g^(−1) and an ...The controversies about the mechanism of sodium storage in hard carbon(HC)hinder its rational structural design.A series of porous HC materials using coal tar pitch show a reversible capacity of 377 mAh g^(−1) and an initial Coulombic efficiency(ICE)of 87%as well as excellent cycling performance.More attention is paid to exploration of the relationships between the sodium status on various storage sites at different sodiation states and the ICE by solidstate^(23)Na nuclear magnetic resonance spectroscopy.The adsorbed Na ions contribute the most to the irreversible capacity.The de-solvated Na ions entering the closed pores are reduced to Na atoms and aggregated to Na clusters.Also,this process contributes the most to the reversible capacity and is characteristic of a long plateau in the voltage profile.Intercalation is partially reversible;it is the main source of capacity for slope-type HCs but plays a minor role in the reversible capacity of plateau-type HCs.Therefore,increasing the content of the closed pores can improve the reversible plateau capacity and reducing the open mesopores of HC increases the ICE.These findings provide insights into the structural design and cost-efficient preparation of high-performance HC anode materials for advanced sodium-ion batteries.展开更多
Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of th...Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of their high power capture.Forces on blades are considerably higher in marine currents,presenting challenges to turbine design.Current research focuses on blade optimization and the selection of reliable transmission systems,and data from experiments conducted in natural environments are lacking.This paper focuses on a five-bladed vertical axis marine current turbine with a direct drive generator especially designed for low rotational speed and presents data from real-world experiments and 3D simulation models.The paper specifically investigates the influence of blade pitch angle on power capture.Experiments have been conducted at 1.42 m/s with a turbine in a river for blade pitch angles of 0°and+3°(the angle is defined as the leading edge of the blade rotating outward,perpendicular to,and opposite of the turbine axis).Two numerical 3D models,namely a vortex model and an actuator line model,have been used to simulate the turbine under the same conditions(1.42 m/s and 0°,+3°).The experimental and simulation results show that a 0°pitch angle gives a higher power capture power than a+3°pitch angle.In addition,simulation models were used to simulate the performance for an extended range at pitch angles of−3°to+3°,a fixed tip-speed ratio,and a step size of 1°.The simulations show that+1°gives the highest power coefficient and increases the average power capture by up to 0.6%.The performance of vertical axis marine current turbines can be improved by increasing the pitch angle to 1°in the positive direction.By contrast,a negative pitch angle can increase the average power capture of wind turbines.展开更多
The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solve...The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solved by choosing an appropriate initial pitch candidate F00. The theoretical choice guideline in a pitch epoch is obtained as ensuring the true pitch F0 satisfying F00/2 〈 F0 〈 3F00/2. The validity of the choice guideline is verified by the F00 experiment. Meanwhile, the algorithm is extended to the pitch determination in the noisy case and compared with the method of subharmonic-to-harmonic ratio （SHR）. The experimental results show that the improved algorithm bears comparison with SHR and it runs much faster than SHR.展开更多
The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive per...The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.展开更多
Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fi...Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination-dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble(CTP-THFs) is demonstrated in this study.The results show that CTP-THFs contains more light components than CTP;CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination-dehydrobro mination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 ℃. The pericondensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation;however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products.展开更多
In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the bla...In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.展开更多
Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis ...Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT)with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD)prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.展开更多
A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on do...A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.展开更多
The forbidden pitch ＂dip＂ in the critical dimension （CD） through the pitch curve is a well-known optical proximity effect. The CD and CD process window near the ＂dip＂,usually found near a pitch range of 1.1 to 1...The forbidden pitch ＂dip＂ in the critical dimension （CD） through the pitch curve is a well-known optical proximity effect. The CD and CD process window near the ＂dip＂,usually found near a pitch range of 1.1 to 1.4 wavelength/ NA （numerical aperture）,is smaller when compared with other pitches. This is caused by inadequate imaging contrast for an unequal line and space grating. Although this effect is relatively well-known, its relationship with typical process condition parameters,such as the effective image blur caused by the photo-acid diffusion during the post exposure bake or the aberration in the imaging lens, has not been systematically studied. In this paper, we will examine the correlation between the image blur and the effect on the CD, including the decrease in the CD value （the depth of the ＂dip＂） and the CD process window. We find that both the decrease in the CD value and the focus latitude near the forbidden pitch correlate very well with the effective Gaussian image blur. Longer effective diffusion length correlates well with a smaller process window and a deeper CD ＂dip＂. We conclude that the dip depth is very sensitive to the change in image contrast.展开更多
基金Supported by the National Natural Science Foundation of China(22378181).
文摘The development of materials with excellent microwave absorption(MWA)and electromagnetic interference(EMI)shielding performances has currently received attention.Herein,mesophase pitch-based carbon foam(MPCF)with 3D interconnected pore structure was prepared through the high pressure pyrolysis of mesophase coal tar pitch.It is found that the 3D interconnected cellular pores of MPCF facilitate multiple reflections of electromagnetic waves,which results in the minimum reflection loss(RLmin)value of MPCF reaches-37.84 dB with the effective absorption bandwidth(EAB)of 5.44 GHz at a thickness of 2.70 mm,and the total average electromagnetic shielding effectiveness(SE_(T))under 3.00 mm thickness achieves 26.52 dB in X-band.Subsequently,MPCF is activated by KOH to obtain activated carbon foam(A-MPCF).The average SE_(T)of A-MPCF achieves 103.00 dB for abundant nanopores on the pore cell walls,which leads to a transition from the multiple reflections of electromagnetic waves on the walls to diffuse reflection.Unfortunately,the reflection coefficient(R)of A-MPCF increases from 0.78 to 0.90.To reduce the R value,Fe_(3)O_(4)/A-MPCF was fabricated via the in situ growth of nano Fe_(3)O_(4)on A-MPCF.Consequently,the R value of Fe_(3)O_(4)/A-MPCF was reduced from 0.90 to 0.74,whereas the MWA performance was only slightly decreased.This work proposes a simple strategy for simultaneously adjusting MWA and EMI shielding performances of materials.
文摘Reducing the amount of aluminum chloride needed for the catalytic preparation of high quality mesophase and carbon materials is important and we have found that using terephthalic acid(PTA)as a co-catalyst serves this purpose.By adding 3%(mass fraction)AlCl_(3)and 0.9%(mass fraction)PTA to the coal tar pitch,approximately 90%mesophase was synthesized.The product(M-3-0.9)had a high stacking order(L_(c)=3.1 nm,n=10.14)and aromaticity(0.942).By adding PTA,a larger anisotropy content was produced using a smaller amount of AlCl_(3).The PTA participated in the polycondensation reaction through its own benzene ring structure to increase the catalytic activity.However,when its content was higher than 1.5%,the number of oxygen-containing groups in the product increased which was unfavorable for the aromatic lamellar stacking and gave rise to more isotropic structures.The work opens up a new way to prepare mesophase by a catalytic method.
基金supported by the National Natural Science Foundation of China(Nos.52271295,52088102).
文摘To propel the application of a bottom-hinged flap breakwater in real sea conditions,a two-dimensional computational fluid dynamics numerical model was conducted to investigate the pitching motion response and wave attenuation in random waves.First,the flow velocity distribution characteristic of the pitching flap at typical times was summarized.Then,the effects of random wave and flap parameters on the flap’s significant pitching angle amplitude θ_(s) and hydrodynamic coefficients were investigated.The results reveal that θ_(s) and wave reflection coefficient K_(r) values increase with increasing significant wave height Hs,random wave steepnessλs,and flap relative height.As Hs andλs increase,the wave transmission coefficient K_(t) increases while the wave dissipation coefficient K_(d) decreases.Additionally,K_(t) decreases with increasing flap relative height.With increasing equivalent damping coefficient ratio,θ_(s) and K_(t) decrease,while K_(r) and K_(d) increase.The relationships betweenλs and flap relative height on the one hand andθ_(s),K_(r),K_(t),and K_(d) in random waves on the other hand are compared to those in regular waves.Based on the equal incident wave energy and the equal incident wave energy flux,the pitching flap performs better in the wave attenuation capability under random waves than in regular waves.Finally,the dimensionless parameters with respect to random wave and flap were used to derive the K_(r) and K_(t) for-mulae,which were validated with the related data.
文摘Pitch produced by the lique-faction of coal was divided into two frac-tions:soluble in toluene(TS)and insol-uble in toluene but soluble in pyridine(TI-PS),and their differences in molecu-lar structure and oxidation activity were studied.Several different carbon materi-als were produced from them by oxida-tion in air(350℃,300 mL/min)fol-lowed by carbonization(1000℃ in Ar),and the effect of the cross-linked structure on their structure and sodium storage properties was investigated.The results showed that the two pitch fractions were obviously different after the air oxidation.The TS fraction with a low degree of condensation and abundant side chains had a stronger oxidation activity and thus introduced more cross-linked oxygen-containing functional groups C(O)―O which prevented carbon layer rearrangement during the carbonization.As a result,a disordered hard carbon with more defects was formed,which improved the electrochemical performance.Therefore,the carbon materials derived from TS(O-TS-1000)had an obvious disordered structure and a larger layer spacing,giving them better sodium storage perform-ance than those derived from the TI-PS fraction(O-TI-PS-1000).The specific capacity of O-TS-1000 was about 250 mAh/g at 20 mA/g,which was 1.67 times higher than that of O-TI-PS-1000(150 mAh/g).
文摘Mesophase pitch carbon fibers have an ultra-high modulus and thermal conductivity that are unmatched by other carbon fibers,making it irreplaceable in many fields.However,due to the high temperature dependence of the viscosity of the melted pitch and the poor mechanical properties of pitch fibers,it is difficult to reduce the fiber diameter when using continuous spinning.We used the Mathworks Matlab software to optimize the mesophase pitch melt spinning model and to simulate the effects of spinning temperature,mass flow rate,winder speed,and quenching air temperature near the spinneret on the maximum shear rate during drawing.Simulation results demonstrate that applying gradient cooling to the melt upon exiting the spinneret significantly reduces the maximum shear rate and extends the drawing zone,thereby promoting the spinning stability and helping reduce the fiber diameter.In the experiment,instead of quenching in air,we applied gradient cooling to the melt,whose temperature decreased according to the equation Ta=298+278exp(−11.4z),where Ta is the final air temperature in Kelvin,and z is the distance from the spinneret in meters.It was found the gradient cooling greatly improved the draw-down ratio,reducing the average diameter of the pitch fibers from 20.8 to 13.1μm,along with improved process stability.The experimental results are in excellent agreement with the predictions.At the same time,the tensile strength of the 1150°C carbonized fibers increased from 0.6 to 1.1 GPa.Although the degree of orientation of the fibers decreased slightly,the tight bonding between microcrystals,the suppression of splitting,and the smaller diameter improved the mechanical properties of carbon fibers.This study provides an effective method for reducing the fiber diameter while improving continuity.
文摘Pitch is a complex mixture of polycyclic aromatic hydrocarbons and their non-metal derivatives that has a high carbon content.Using pitch as a precursor for carbon materials in alkali metal ion(Li^(+)/Na^(+)/K^(+))batteries has become of great interest.However,its direct pyrolysis often leads to microstructures with a high orientation and small interlayer spacing due to uncontrolled liquid-phase carbonization,resulting in subpar electrochemical performance.It is therefore important to control the microstructures of pitch-derived carbon materials in order to improve their electrochemical properties.We evaluate the latest progress in the development of these materials using various microstructural engineering approaches,highlighting their use in metal-ion batteries and supercapacitors.The advantages and limitations of pitch molecules and their carbon derivatives are outlined,together with strategies for their modification in order to improve their properties for specific applications.Future research possibilities for structure optimization,scalable production,and waste pitch recycling are also considered.
文摘The determination of musical pitch has been a major concern of music theory,East and West,in all climes and cultures,throughout the ages.This paper discusses the intricacies of pitch determination from historic,geographic,and scientific perspectives.Its standardization nowadays has permitted the manufacture and tuning of musical instruments on a universal scale.
基金supported by MHRD as researcher C.K.Neog received the MHRD Institute GATE scholarship from Govt.of India.
文摘This study investigates the effects of radiation force due to the rotational pitch motion of a wave energy device,which comprises a coaxial bottom-mounted cylindrical caisson in a two-layer fluid,along with a submerged cylindrical buoy.The system is modeled as a two-layer fluid with infinite horizontal extent and finite depth.The radiation problem is analyzed in the context of linear water waves.The fluid domain is divided into outer and inner zones,and mathematical solutions for the pitch radiating potential are derived for the corresponding boundary valve problem in these zones using the separation of variables approach.Using the matching eigenfunction expansion method,the unknown coefficients in the analytical expression of the radiation potentials are evaluated.The resulting radiation potential is then used to compute the added mass and damping coefficients.Several numerical results for the added mass and damping coefficients are investigated for numerous parameters,particularly the effects of the cylinder radius,the draft of the submerged cylinder,and the density proportion between the two fluid layers across different frequency ranges.The major findings are presented and discussed.
基金supported by the National Science Foundation of China (Grant Nos.52279081,and 51839001).
文摘The behaviors of unsteady flow structures and corresponding hydrodynamics for a pitching hydrofoil are investigated numerically and theoretically in the present paper.The aims are to derive the total lift by finite-domain impulse theory for subcavitating flow(σ=8.0)and cavitating flow(σ=3.0),and to quantify the distinct impact of individual vortex structures on the transient lift to appreciate the interplay among cavitation,flow structures,and vortex dynamics.The motion of the hydrofoil is set to pitch up clockwise with an almost constant rate from 0°to 15°and then back to 0°,for the Reynolds number,7.5×105,and the frequency,0.2 Hz,respectively.The results reveal that the presence of cavities delays the migration of the laminar separation bubble(LSB)from the trailing edge(TE)to the leading edge(LE),consequently postponing the hysteresis in the inflection of lift coefficients.The eventual stall under the sub-cavitation regime is the result of LSB bursting.While the instabilities within the leading-edge LSB induce the convection of cavitation-dominated vortices under the cavitation regime instead.Having validated the lift coefficients on the hydrofoil through the finite-domain impulse theory using the standard force expression,the Lamb vector integral emerges as the main contribution to the generation of unsteady lift.Moreover,the typical vortices’contributions to the transient lift during dynamic stall are accurately quantified.The analysis indicates that the clockwise leading-edge vortex(−LEV)contributes positively,while the counterclockwise trailing-edge vortex(+TEV)contributes negatively.The negative influence becomes particularly pronounced after reaching the peak of total lift,as the shedding of the concentrated wake vortex precipitates a sharp decline due to a predominant negative lift contribution from the TEV region.Generally,the vortices’contribution is relatively modest in sub-cavitating flow,but it is notably more significant in the context of incipient cavitating flow.
文摘The pitch bearing is a component in wind turbine units used to adjust the angle of the fan blades to adapt to the wind direction,so as to maximize the utilization of wind energy.Due to the different working mode of the pitch bearing itself compared with ordinary small bearings and the harsh working environment,the pitch bearing is prone to faults such as cracking and deformation.In severe cases,it will lead to overall damage to the pitch bearing,causing the blade to fall from a high altitude and even injuring personnel.Therefore,this paper conducts a patent analysis and technical decomposition of the deformation monitoring device for pitch bearings,analyzes and summarizes the development process of existing deformation monitoring devices for pitch bearings.Combined with the TRIZ evolution theory and based on the S-curve,it is concluded that the current deformation monitoring device for pitch bearings is in the transitional stage between the infant period and the growth period,and discusses the possible subsequent evolution directions.Through reviewing relevant literature,it is found that inner ring cracks first appear near the upper and lower surfaces of the bolt holes in the inner ring of the pitch bearing.To this end,a new type of deformation monitoring device for pitch bearings is designed.The fiber optic displacement sensor is used for qualitative monitoring of initial cracks near the surface of the bolt holes in the inner ring of the pitch bearing.After cracks are detected,the eddy current sensor is used for quantitative monitoring of whether there are extended cracks between the cracked bolt holes and adjacent bolt holes.Finally,the work done in this paper is summarized and prospected.
基金financially supported by National Natural Science Foundation of China(Nos.52374286 and 52274279)the National Key Research and Development Program of China(No.2021YFC2902604)。
文摘High-salinity wastewater treatment has always been a challenging issue.In this study,coal tar pitch was used as the carbon source and melamine as the nitrogen source to prepare coal tar pitch-based nanosheets(CPN-9)using a salt-template method.The desalination performance of CPN-9 was evaluated using flow-electrode capacitive deionization technology.The results showed that CPN-9 has a high specific surface area(466.34 m^(2)/g),a rich pore structure(micro-/meso-pore volume was 0.28),excellent rheological properties,and hydrophilicity(contact angle of 20.44°),thereby accelerating ion transport.Electrochemical results indicated that CPN-9 exhibits a significant double-layer ion storage mechanism,with a specific capacitance of 176.66 F/g at a current density of 0.5 A/g.CPN-9 has a very low charge transfer resistance.The synergistic effect of aromatic carbon and nitrogen doping(the content of pyrrole and pyridine nitrogen was 36.40%and 35.83%,respectively)in coal tar pitch accelerates electron transfer in CPN-9.The good ion diffusion performance and low impedance of CPN-9 accelerate the ion exchange rate,resulting in outstanding desalination performance.At 1.2 V and 3%mass loading,with a CPN-9 to conductive carbon black ratio of 4:1,the average desalination rate,charge efficiency,and energy consumption reached 0.039 mg/(cm^(2)·min),48.47%,and 0.012 kWh/mol,respectively.In summary,this study optimized the structure of CPN-9 from the perspective of electronic and ionic transport,enhancing its desalination performance and providing theoretical support for the deionization of high-salinity wastewater.
文摘The controversies about the mechanism of sodium storage in hard carbon(HC)hinder its rational structural design.A series of porous HC materials using coal tar pitch show a reversible capacity of 377 mAh g^(−1) and an initial Coulombic efficiency(ICE)of 87%as well as excellent cycling performance.More attention is paid to exploration of the relationships between the sodium status on various storage sites at different sodiation states and the ICE by solidstate^(23)Na nuclear magnetic resonance spectroscopy.The adsorbed Na ions contribute the most to the irreversible capacity.The de-solvated Na ions entering the closed pores are reduced to Na atoms and aggregated to Na clusters.Also,this process contributes the most to the reversible capacity and is characteristic of a long plateau in the voltage profile.Intercalation is partially reversible;it is the main source of capacity for slope-type HCs but plays a minor role in the reversible capacity of plateau-type HCs.Therefore,increasing the content of the closed pores can improve the reversible plateau capacity and reducing the open mesopores of HC increases the ICE.These findings provide insights into the structural design and cost-efficient preparation of high-performance HC anode materials for advanced sodium-ion batteries.
基金Supported by Jgust Richert,Standup for Energy and Vattenfall,the Swedish National Infrastructure for Computing(SNIC)at NSC at Linköping University partially funded by the Swedish Research Council under Grant Nos.2021/23-539 and 2021/5-443.
文摘Marine current energy conversion with turbines is a growing field of interest owing to its high energy density and predictability.For wind energy,three-bladed horizontal-axis turbines are the most common because of their high power capture.Forces on blades are considerably higher in marine currents,presenting challenges to turbine design.Current research focuses on blade optimization and the selection of reliable transmission systems,and data from experiments conducted in natural environments are lacking.This paper focuses on a five-bladed vertical axis marine current turbine with a direct drive generator especially designed for low rotational speed and presents data from real-world experiments and 3D simulation models.The paper specifically investigates the influence of blade pitch angle on power capture.Experiments have been conducted at 1.42 m/s with a turbine in a river for blade pitch angles of 0°and+3°(the angle is defined as the leading edge of the blade rotating outward,perpendicular to,and opposite of the turbine axis).Two numerical 3D models,namely a vortex model and an actuator line model,have been used to simulate the turbine under the same conditions(1.42 m/s and 0°,+3°).The experimental and simulation results show that a 0°pitch angle gives a higher power capture power than a+3°pitch angle.In addition,simulation models were used to simulate the performance for an extended range at pitch angles of−3°to+3°,a fixed tip-speed ratio,and a step size of 1°.The simulations show that+1°gives the highest power coefficient and increases the average power capture by up to 0.6%.The performance of vertical axis marine current turbines can be improved by increasing the pitch angle to 1°in the positive direction.By contrast,a negative pitch angle can increase the average power capture of wind turbines.
基金The National Basic Research Program of China (973Program) (No2002CB312102)
文摘The underlying principle of pitch determination based on the mean shift algorithm is studied, and the cause of pitch error propagation in the original pseudo code is analyzed. The problem of error propagation is solved by choosing an appropriate initial pitch candidate F00. The theoretical choice guideline in a pitch epoch is obtained as ensuring the true pitch F0 satisfying F00/2 〈 F0 〈 3F00/2. The validity of the choice guideline is verified by the F00 experiment. Meanwhile, the algorithm is extended to the pitch determination in the noisy case and compared with the method of subharmonic-to-harmonic ratio （SHR）. The experimental results show that the improved algorithm bears comparison with SHR and it runs much faster than SHR.
基金Supported by the National Natural Science Foundation of China under Grant No.50879031
文摘The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.
基金the financial support provided by the National Natural Science Foundation of China (22008254)the Fundamental Research Funds for the Central Universities (2020XJHH01)+1 种基金the National Training Program of Innovation and Entrepreneurship for Undergraduates (C202003309)China University of Mining and Technology (Beijing) Yueqi Outstanding Scholar Project (2020JCB02)。
文摘Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination-dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble(CTP-THFs) is demonstrated in this study.The results show that CTP-THFs contains more light components than CTP;CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination-dehydrobro mination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 ℃. The pericondensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation;however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products.
基金financially supported by National "863" Program (Grant No.2007AA05Z450, No. 200805040)National S&T Program (No.2008BAA15B04)+2 种基金2010 National Ocean Special Funds(No.ZJME2010GC01, No. ZJME2010CY01, No.GHME2010GC02)supported by the Fundamental Research Funds of the Universities(No.HEUCF130105)supported by "111 project" foundation(No. B07019) from State Administration of Foreign Experts Affairs of China and Ministry of Education of China
文摘In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.
基金Project(E201216)supported by Heilongjiang Provincial Natural Science Foundation,China
文摘Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity.Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT)with or without pitch control was conducted from the aspects of aerodynamic force,flow structure and power coefficient.The computational fluid dynamics(CFD)prediction results show a significant increase in power coefficient for SB-VAWT with pitch control.According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios(TSRs),the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade;especially,the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case.Furthermore,experiment was carried out to verify the feasibility of pitch control methods.The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT,and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.
基金the National Natural Science Foundation of China(Grant Nos.U1706227 and 51979063)the Harbin Applied Technology Research and Development Project(Grant No.2015RQXXJ016)the Basic Research and Cutting-Edge Technology Projects of State Administration of Science(Grant No.JCKY2019604C003).
文摘A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine(VEVT).A scheme of eccentric disc pitch control mechanism based on doubleblock mechanism is proposed.The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine,and the three-dimensional model of the turbine is established.Kinematics analysis of the eccentric disc pitch control mechanism is carried out.Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived.Kinematics analysis and simulation are carried out,and the motion law of the corresponding mechanical system is obtained.By analyzing the force and motion of blade of VEVT,the expressions of the important parameters such as deflection angle,attack angle and energy utilization coefficient are obtained.The lateral induced velocity coefficient is acquired by momentum theorem,the hydrodynamic parameters such as energy utilization coefficient are derived,and the hydrodynamic characteristics of VEVT are also obtained.The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions,which verifies that VEVT has good self-startup performance and high energy capture efficiency.
文摘The forbidden pitch ＂dip＂ in the critical dimension （CD） through the pitch curve is a well-known optical proximity effect. The CD and CD process window near the ＂dip＂,usually found near a pitch range of 1.1 to 1.4 wavelength/ NA （numerical aperture）,is smaller when compared with other pitches. This is caused by inadequate imaging contrast for an unequal line and space grating. Although this effect is relatively well-known, its relationship with typical process condition parameters,such as the effective image blur caused by the photo-acid diffusion during the post exposure bake or the aberration in the imaging lens, has not been systematically studied. In this paper, we will examine the correlation between the image blur and the effect on the CD, including the decrease in the CD value （the depth of the ＂dip＂） and the CD process window. We find that both the decrease in the CD value and the focus latitude near the forbidden pitch correlate very well with the effective Gaussian image blur. Longer effective diffusion length correlates well with a smaller process window and a deeper CD ＂dip＂. We conclude that the dip depth is very sensitive to the change in image contrast.
