To detect the genome of viruses (in environmental and clinical samples), we use electrophoresis running buffer after PCR reaction. Also, electrophoresis buffers were used widely to separate any DNA molecule. In this p...To detect the genome of viruses (in environmental and clinical samples), we use electrophoresis running buffer after PCR reaction. Also, electrophoresis buffers were used widely to separate any DNA molecule. In this paper, we used four types of previously known electrophoresis buffers to compare which is easy for preparation, simple in structure, low cost and good performance in agarose gel electrophoresis. For this, we used two agarose concentration (1%, 2%) and two types of DNA ladder (100 bp, 1 kb) represent both smaller and larger sizes of molecule for each type of buffers, from the result we found in first level both supper buffer and TAE buffer with good performance and in second level we found bicarbonate buffer also with good performance also. Finally, we found the tang buffer cannot pose any electrophoretic activity on DNA agarose gel electrophoresis.展开更多
Different from traditional aggregation method, the unreliable buffers are originally considered and a more general aggregation method is offered, in which not only the unreliable buffers are considered, but also the p...Different from traditional aggregation method, the unreliable buffers are originally considered and a more general aggregation method is offered, in which not only the unreliable buffers are considered, but also the probabilities of system states are obtained by a discrete model rather than the continuous flow model of unreliable manufacturing systems. The solution technique is offered to get the system sate probabilities. The method advances the traditional system aggregation techniques. Numerical results specify the extended aggregation method and also show that the unreliable limited buffers have a strong impact on the efficiency of the production lines.展开更多
The flow shop scheduling problem with limited buffers( LBFSP) widely exists in manufacturing systems. A hybrid discrete harmony search algorithm is proposed for the problem to minimize total flow time. The algorithm p...The flow shop scheduling problem with limited buffers( LBFSP) widely exists in manufacturing systems. A hybrid discrete harmony search algorithm is proposed for the problem to minimize total flow time. The algorithm presents a novel discrete improvisation and a differential evolution scheme with the jobpermutation-based representation. Moreover,the discrete harmony search is hybridized with the problem-dependent local search based on insert neighborhood to balance the global exploration and local exploitation. In addition, an orthogonal experiment design is employed to provide a receipt for turning the adjustable parameters of the algorithm. Comparisons based on the Taillard benchmarks indicate the superiority of the proposed algorithm in terms of effectiveness and efficiency.展开更多
The composite scheme based on preemption and small buffers is an efficient method for contention resolution. To support services differentiation, it is the first time that the analytical model of delay preemption base...The composite scheme based on preemption and small buffers is an efficient method for contention resolution. To support services differentiation, it is the first time that the analytical model of delay preemption based priority is built. Further, in order to guarantee the low-loss requirement for high priority bursts, an improved scheme is proposed and investigated by limiting the buffered right of low priority bursts within the specific traffic states. The simulation results show that, without the deterioration of blocking performance, there is more than 40% reduction on burst loss being achieved under the conditionρ=1.0 for high priority bursts.展开更多
A novel built-in self-test (BIST) approach to test the configurable input/output buffers in Xilinx Virtex series SoCs (system on a chip) using hard macro has been proposed in this paper. The proposed approach can ...A novel built-in self-test (BIST) approach to test the configurable input/output buffers in Xilinx Virtex series SoCs (system on a chip) using hard macro has been proposed in this paper. The proposed approach can completely detect single and multiple stuck-at gate-level faults as well as associated routing resources in I/O buffers. The proposed BIST architecture has been implemented and verified on Xilinx Virtex series FPGAs (field programmable gate configurations are required array). Only total of 10 to completely test the I/O buffers of Virtex devices.展开更多
This paper presents a serial synchronous scanning mode in fiat panel display (FPD) by adding a latch buffer between the serializer and the driving buffer. Comparing with conventional techniques, the proposed structu...This paper presents a serial synchronous scanning mode in fiat panel display (FPD) by adding a latch buffer between the serializer and the driving buffer. Comparing with conventional techniques, the proposed structure can efficiently reduce the brightness loss and improve the transmission performance. Theoretical analysis and experimental results show that the ratio between the lightest weight display time and the relative transmission time is a tradeoff between brightness loss and transmission efficiency.展开更多
Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulat...Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulating stepgraded InAsyP1-y buffer layers with a lattice mismatch of ~1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate.With an optimized buffer thickness,the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion.High-performance single-junction devices are demonstrated,with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2,which are measured under the standard solar simulator of air mass 1.5-global(AM 1.5 G).展开更多
Many studies have examined the effect of roads on landscape fragmentation.Yet they rarely considered local characteristics of the road and road buffer widths.Therefore,this study that took place in the Qingzang Highwa...Many studies have examined the effect of roads on landscape fragmentation.Yet they rarely considered local characteristics of the road and road buffer widths.Therefore,this study that took place in the Qingzang Highway(QH)examined the variations in road buffers and road sections of landscape fragmentation.The QH was divided into 32 sections with 23 buffer areas.Based on the indicators of landscape fragmentation from 1980 to 2018,we found significant spatial heterogeneity between sections and buffers.Generally,landscape fragmentation de-creased with increasing buffer distance to the QH.For different sections,the coefficients of variation between buffers were rather high and significantly different.Therefore,fixed-width buffers may overestimate or underes-timate the spatial scope and influence intensity of a road.The impacts of road sections around provincial capitals,prefecture-level cities and main counties on landscape fragmentation were relatively extensive and formed clus-ters of highly fragmented areas.Geodetector results indicated that natural and anthropogenic factors,such as altitude,climate,distance to major settlements and socioeconomic conditions,could well explain the spatiotem-poral characteristics of landscape fragmentation.Altitude,precipitation and the distance to major settlements had higher explanatory power for landscape fragmentation in permafrost regions,whereas slope and socioeconomic condition had higher explanatory power for non-permafrost regions in Xizang Autonomous Region.展开更多
CeO2 and Ce0.8M0.2O2-d films (M = Mn, Y, Gd, Sm, Nd and La) with (00l) preferred orientation have been prepared on biaxially textured Ni-W substrates by metal organic decomposition (MOD) method. The factors infl...CeO2 and Ce0.8M0.2O2-d films (M = Mn, Y, Gd, Sm, Nd and La) with (00l) preferred orientation have been prepared on biaxially textured Ni-W substrates by metal organic decomposition (MOD) method. The factors influencing the formation of cracks on the surface of these CeO2 and doped CeO2 films on Ni-W substrates were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM) analysis, atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The results indicate that many factors, such as the change of the ionic radii of doping cations, the transformation of crystal structure and the formation of oxygen vacancies in lattices at high annealing temperature, may be related to the formation of cracks on the surface of these films. However, the crack formation shows no dependence on the crystal lattice mismatch degree of the films with Ni-W substrates. Moreover, the suppression of surface cracks is related to the change of intrinsic elasticity of CeO2 film with doping of cations with a larger radius. SEM and AFM investigations of Ce0.8M0.2O2-d (M = Y, Gd, Sm, Nd and La) films reveal the dense, smooth and crack-free microstructure, and their lattice parameters match well with that of YBCO, illuminating that they are potentially suitable to be as buffer layer, especially as cap layer in multi-layer architecture of buffer layer for coated conductors.展开更多
The unity gain buffer will be good to design high frequency SCF if its resistiveeffects can be eliminated,and therefore the whole parasitic sensitivities will greatly be reduced.On the basis of this concept,a novel pa...The unity gain buffer will be good to design high frequency SCF if its resistiveeffects can be eliminated,and therefore the whole parasitic sensitivities will greatly be reduced.On the basis of this concept,a novel parasitic tolerant SC DTE(differential transconductanceelement)is proposed.SC floating inductor and integrator fit for high frequency applications areformed by the DTE.The computer simulation and experiment on a third order elliptic LP filterverify its validity.展开更多
Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dyn...Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dynamical delay time is carried out based on cascaded double loop optical buffers (I:)LOBs). It is found that pulse distortion can be restrained by a negative optical control mode when the optical packet is in the loop. Noise analysis indicates that it is feasible to realise a large variable delay range by cascaded DLOBs. These conclusions are validated by the experiment system with 4-stage cascaded DLOBs. Both the theoretical simulations and the experimental results indicate that a large delay range of 1-9999 times the basic delay unit and a fine granularity of 25 ns can be achieved by the cascaded DLOBs. The performance of the cascaded DLOBs is suitable for the all optical networks.展开更多
This study focused on riparian vegetation buffer zones on the basis of low influence development(LID) and landscape restoration. Three types of land were selected to conduct comparative study. The types are buffers in...This study focused on riparian vegetation buffer zones on the basis of low influence development(LID) and landscape restoration. Three types of land were selected to conduct comparative study. The types are buffers in urban districts,buffers in rural areas,and buffers in natural regions. These types basically reflect major ecological issues in different landuses. The follow conclusions were drawn:(1) there are different ecological issues in these 3 types,making the functions of buffers different.(2) The 3 types demand different ecological issues to be solved: Type A,functionally-diverse riparian landscape should be planned to enrich recreational activities and improve river's condition. Type B,agricultural areasource pollution needs to be cut down to sustain the stability of water conservation and ecological system. Type C,eco-conservation and various habitats for creatures are required.(3) Different planning methods were used respectively in the 3 types,construction methods were proposed for each type correspondingly and expressed in graphical ways in expectation of being instructive to the construction of eco-riparian landscape.展开更多
Good’s buffers have been widely applied in cell/organ culture over the past half a century as biocompatible pH stabilizers.However,the emergence of severe adverse effects,such as cellular uptake,lysosomal autophagic ...Good’s buffers have been widely applied in cell/organ culture over the past half a century as biocompatible pH stabilizers.However,the emergence of severe adverse effects,such as cellular uptake,lysosomal autophagic activation,and visible light-induced cytotoxicity,raises serious questions over its biocompatibility while underlying mechanism was unclear.Here we report that riboflavin(RF,component of cell culture medium)generates ^(1)O_(2),⋅OH,and O_(2)^(·-)under visible light exposure during regular cell manipulation.These short half-life reactive oxygen species(ROS)react with tertiary amine groups of HEPES,producing 106.6μM of H_(2)O_(2).Orders of magnitude elevated half-life of ROS in the medium caused severe cytotoxicity and systematic disorder of normal cell functions.We have further designed and validated zwitterionic betaines as the new generation biocompatible organic pH buffers,which is able to completely avoid the adverse effects that found on HEPES and derivate Good’s buffers.These findings may also open a new avenue for zwitterionic betaine based materials for biomedical applications.展开更多
Rock sheds are widely used to prevent rockfall disasters along roads in mountainous areas.To improve the capacity of rock sheds for resisting rockfall impact,a sand and expandable polyethylene(EPE)composite cushion wa...Rock sheds are widely used to prevent rockfall disasters along roads in mountainous areas.To improve the capacity of rock sheds for resisting rockfall impact,a sand and expandable polyethylene(EPE)composite cushion was proposed.A series of model experiments of rockfall impact on rock sheds were conducted,and the buried depth of the EPE foam board in the sand layer was considered.The impact load and dynamic response of the rock shed were investigated.The results show that the maximum impact load and dynamic response of the rock shed roof are all significantly less than those of the sand cushion.Moreover,as the distance between the EPE foam board and rock shed roof decreases,the maximum rockfall impact force and impact pressure gradually decrease,and the maximum displacement,acceleration and strain of the rock shed first decrease and then change little.In addition,the vibration acceleration and vertical displacement of the rock shed roof decrease from the centre to the edge and decrease faster along the longitudinal direction than that along the transverse direction.In conclusion,the buffering effect of the sand-EPE composite cushion is better than that of the pure sand cushion,and the EPE foam board at a depth of 1/3 the thickness of the sand layer is appropriate.展开更多
文摘To detect the genome of viruses (in environmental and clinical samples), we use electrophoresis running buffer after PCR reaction. Also, electrophoresis buffers were used widely to separate any DNA molecule. In this paper, we used four types of previously known electrophoresis buffers to compare which is easy for preparation, simple in structure, low cost and good performance in agarose gel electrophoresis. For this, we used two agarose concentration (1%, 2%) and two types of DNA ladder (100 bp, 1 kb) represent both smaller and larger sizes of molecule for each type of buffers, from the result we found in first level both supper buffer and TAE buffer with good performance and in second level we found bicarbonate buffer also with good performance also. Finally, we found the tang buffer cannot pose any electrophoretic activity on DNA agarose gel electrophoresis.
基金Great Technology Innovation of Gansu Province,China (No.2GS063-A52-005-01)Natural Science Foundation of Gansu Province,China (No.3ZS062-B25-034)Research Item of Education Department of Gansu Province,China (No.0703-06)
文摘Different from traditional aggregation method, the unreliable buffers are originally considered and a more general aggregation method is offered, in which not only the unreliable buffers are considered, but also the probabilities of system states are obtained by a discrete model rather than the continuous flow model of unreliable manufacturing systems. The solution technique is offered to get the system sate probabilities. The method advances the traditional system aggregation techniques. Numerical results specify the extended aggregation method and also show that the unreliable limited buffers have a strong impact on the efficiency of the production lines.
基金National Natural Science Foundations of China(Nos.61174040,61104178)Shanghai Commission of Science and Technology,China(No.12JC1403400)the Fundamental Research Funds for the Central Universities,China
文摘The flow shop scheduling problem with limited buffers( LBFSP) widely exists in manufacturing systems. A hybrid discrete harmony search algorithm is proposed for the problem to minimize total flow time. The algorithm presents a novel discrete improvisation and a differential evolution scheme with the jobpermutation-based representation. Moreover,the discrete harmony search is hybridized with the problem-dependent local search based on insert neighborhood to balance the global exploration and local exploitation. In addition, an orthogonal experiment design is employed to provide a receipt for turning the adjustable parameters of the algorithm. Comparisons based on the Taillard benchmarks indicate the superiority of the proposed algorithm in terms of effectiveness and efficiency.
文摘The composite scheme based on preemption and small buffers is an efficient method for contention resolution. To support services differentiation, it is the first time that the analytical model of delay preemption based priority is built. Further, in order to guarantee the low-loss requirement for high priority bursts, an improved scheme is proposed and investigated by limiting the buffered right of low priority bursts within the specific traffic states. The simulation results show that, without the deterioration of blocking performance, there is more than 40% reduction on burst loss being achieved under the conditionρ=1.0 for high priority bursts.
基金supported by the 44th China Postdoctoral Science Foundation funded project
文摘A novel built-in self-test (BIST) approach to test the configurable input/output buffers in Xilinx Virtex series SoCs (system on a chip) using hard macro has been proposed in this paper. The proposed approach can completely detect single and multiple stuck-at gate-level faults as well as associated routing resources in I/O buffers. The proposed BIST architecture has been implemented and verified on Xilinx Virtex series FPGAs (field programmable gate configurations are required array). Only total of 10 to completely test the I/O buffers of Virtex devices.
基金Project supported by the Science Foundation of Shanghai Municipal Commission of Science and Technology (Grant Nos.055207041, 047062012)
文摘This paper presents a serial synchronous scanning mode in fiat panel display (FPD) by adding a latch buffer between the serializer and the driving buffer. Comparing with conventional techniques, the proposed structure can efficiently reduce the brightness loss and improve the transmission performance. Theoretical analysis and experimental results show that the ratio between the lightest weight display time and the relative transmission time is a tradeoff between brightness loss and transmission efficiency.
基金Project supported by the National Basic Research Program of China (Grant No. 61176128)the Knowledge Innovation Project of the Chinese Academy of SciencesSuzhou Municipal Solar Cell Research Project,China (Grant No. SYG201145)
文摘Single-junction,lattice-mismatched In0.69Ga0.31As thermophotovoltaic(TPV) devices each with a bandgap of 0.6 eV are grown on InP substrate by metal-organic chemical vapour deposition(MOCVD).Compositionally undulating stepgraded InAsyP1-y buffer layers with a lattice mismatch of ~1.2% are used to mitigate the effect of lattice mismatch between the device layers and the InP substrate.With an optimized buffer thickness,the In0.69Ga0.31As active layers grown on the buffer display a high crystal quality with no measurable tetragonal distortion.High-performance single-junction devices are demonstrated,with an open-circuit voltage of 0.215 V and a photovoltaic conversion efficiency of 6.9% at a short-circuit current density of 47.6 mA/cm2,which are measured under the standard solar simulator of air mass 1.5-global(AM 1.5 G).
基金supported by The Second Tibetan Plateau Scientific Expedition and Research Program"Regional functional types and regionalization of ecological security"(Grant No.2019QZKK0406).
文摘Many studies have examined the effect of roads on landscape fragmentation.Yet they rarely considered local characteristics of the road and road buffer widths.Therefore,this study that took place in the Qingzang Highway(QH)examined the variations in road buffers and road sections of landscape fragmentation.The QH was divided into 32 sections with 23 buffer areas.Based on the indicators of landscape fragmentation from 1980 to 2018,we found significant spatial heterogeneity between sections and buffers.Generally,landscape fragmentation de-creased with increasing buffer distance to the QH.For different sections,the coefficients of variation between buffers were rather high and significantly different.Therefore,fixed-width buffers may overestimate or underes-timate the spatial scope and influence intensity of a road.The impacts of road sections around provincial capitals,prefecture-level cities and main counties on landscape fragmentation were relatively extensive and formed clus-ters of highly fragmented areas.Geodetector results indicated that natural and anthropogenic factors,such as altitude,climate,distance to major settlements and socioeconomic conditions,could well explain the spatiotem-poral characteristics of landscape fragmentation.Altitude,precipitation and the distance to major settlements had higher explanatory power for landscape fragmentation in permafrost regions,whereas slope and socioeconomic condition had higher explanatory power for non-permafrost regions in Xizang Autonomous Region.
基金Funded by the National Natural Science Foundation of ChinaNational 863 Program of China(Nos.50872115and2009AA03Z203)
文摘CeO2 and Ce0.8M0.2O2-d films (M = Mn, Y, Gd, Sm, Nd and La) with (00l) preferred orientation have been prepared on biaxially textured Ni-W substrates by metal organic decomposition (MOD) method. The factors influencing the formation of cracks on the surface of these CeO2 and doped CeO2 films on Ni-W substrates were explored by X-ray diffraction (XRD), scanning electron microscopy (SEM) analysis, atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The results indicate that many factors, such as the change of the ionic radii of doping cations, the transformation of crystal structure and the formation of oxygen vacancies in lattices at high annealing temperature, may be related to the formation of cracks on the surface of these films. However, the crack formation shows no dependence on the crystal lattice mismatch degree of the films with Ni-W substrates. Moreover, the suppression of surface cracks is related to the change of intrinsic elasticity of CeO2 film with doping of cations with a larger radius. SEM and AFM investigations of Ce0.8M0.2O2-d (M = Y, Gd, Sm, Nd and La) films reveal the dense, smooth and crack-free microstructure, and their lattice parameters match well with that of YBCO, illuminating that they are potentially suitable to be as buffer layer, especially as cap layer in multi-layer architecture of buffer layer for coated conductors.
文摘The unity gain buffer will be good to design high frequency SCF if its resistiveeffects can be eliminated,and therefore the whole parasitic sensitivities will greatly be reduced.On the basis of this concept,a novel parasitic tolerant SC DTE(differential transconductanceelement)is proposed.SC floating inductor and integrator fit for high frequency applications areformed by the DTE.The computer simulation and experiment on a third order elliptic LP filterverify its validity.
基金supported by the State Key Development Program for Basic Research of China (Grant No.2010CB328300)the National Natural Science Foundation of China (Grant Nos.60677004 and 60702049)+1 种基金the Program for the New Century Excellent Talents in University of China (Grant No.NECT-07-0111)the Innovation Plan for Youth of Beijing University of Posts and Telecommunications
文摘Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dynamical delay time is carried out based on cascaded double loop optical buffers (I:)LOBs). It is found that pulse distortion can be restrained by a negative optical control mode when the optical packet is in the loop. Noise analysis indicates that it is feasible to realise a large variable delay range by cascaded DLOBs. These conclusions are validated by the experiment system with 4-stage cascaded DLOBs. Both the theoretical simulations and the experimental results indicate that a large delay range of 1-9999 times the basic delay unit and a fine granularity of 25 ns can be achieved by the cascaded DLOBs. The performance of the cascaded DLOBs is suitable for the all optical networks.
基金Sponsored by 2016 Scientific Research Program of Wuhan Urban and Rural Construction Commission(201704)
文摘This study focused on riparian vegetation buffer zones on the basis of low influence development(LID) and landscape restoration. Three types of land were selected to conduct comparative study. The types are buffers in urban districts,buffers in rural areas,and buffers in natural regions. These types basically reflect major ecological issues in different landuses. The follow conclusions were drawn:(1) there are different ecological issues in these 3 types,making the functions of buffers different.(2) The 3 types demand different ecological issues to be solved: Type A,functionally-diverse riparian landscape should be planned to enrich recreational activities and improve river's condition. Type B,agricultural areasource pollution needs to be cut down to sustain the stability of water conservation and ecological system. Type C,eco-conservation and various habitats for creatures are required.(3) Different planning methods were used respectively in the 3 types,construction methods were proposed for each type correspondingly and expressed in graphical ways in expectation of being instructive to the construction of eco-riparian landscape.
基金support from National Natural Science Foundation of China(No.21504046)Natural Science Foundation of Jiangsu Province(No.BK20150970)+1 种基金the Six Talent Peaks Project in Jiangsu Province(SWYY-060)the Projects of Nanjing Normal University(No.184080H20192,184080H10386).
文摘Good’s buffers have been widely applied in cell/organ culture over the past half a century as biocompatible pH stabilizers.However,the emergence of severe adverse effects,such as cellular uptake,lysosomal autophagic activation,and visible light-induced cytotoxicity,raises serious questions over its biocompatibility while underlying mechanism was unclear.Here we report that riboflavin(RF,component of cell culture medium)generates ^(1)O_(2),⋅OH,and O_(2)^(·-)under visible light exposure during regular cell manipulation.These short half-life reactive oxygen species(ROS)react with tertiary amine groups of HEPES,producing 106.6μM of H_(2)O_(2).Orders of magnitude elevated half-life of ROS in the medium caused severe cytotoxicity and systematic disorder of normal cell functions.We have further designed and validated zwitterionic betaines as the new generation biocompatible organic pH buffers,which is able to completely avoid the adverse effects that found on HEPES and derivate Good’s buffers.These findings may also open a new avenue for zwitterionic betaine based materials for biomedical applications.
基金supported by the Natural Science Foundation of Sichuan Province(No.2022NSFSC1127)the Fundamental Research Funds for the Central Universities(No.2682023CX075).
文摘Rock sheds are widely used to prevent rockfall disasters along roads in mountainous areas.To improve the capacity of rock sheds for resisting rockfall impact,a sand and expandable polyethylene(EPE)composite cushion was proposed.A series of model experiments of rockfall impact on rock sheds were conducted,and the buried depth of the EPE foam board in the sand layer was considered.The impact load and dynamic response of the rock shed were investigated.The results show that the maximum impact load and dynamic response of the rock shed roof are all significantly less than those of the sand cushion.Moreover,as the distance between the EPE foam board and rock shed roof decreases,the maximum rockfall impact force and impact pressure gradually decrease,and the maximum displacement,acceleration and strain of the rock shed first decrease and then change little.In addition,the vibration acceleration and vertical displacement of the rock shed roof decrease from the centre to the edge and decrease faster along the longitudinal direction than that along the transverse direction.In conclusion,the buffering effect of the sand-EPE composite cushion is better than that of the pure sand cushion,and the EPE foam board at a depth of 1/3 the thickness of the sand layer is appropriate.