In this paper we present a numerical method for solving Riemann type problem for the fifth order improperly elliptic equation in complex plane .We reduce this problem to the boundary value problems for properly ellipt...In this paper we present a numerical method for solving Riemann type problem for the fifth order improperly elliptic equation in complex plane .We reduce this problem to the boundary value problems for properly elliptic equations, and then solve those problems by the grid methods.展开更多
In this paper, we derive the continuous dependence on the initial-time geometry for the solution of a parabolic equation from dynamo theory. The forward in time problem and backward in time problem are considered. An ...In this paper, we derive the continuous dependence on the initial-time geometry for the solution of a parabolic equation from dynamo theory. The forward in time problem and backward in time problem are considered. An explicit continuous dependence inequality is obtained even with different prescribed data.展开更多
Some new inequalities involving improper integrals are established in the paper which generalize the related results due to Pachpatte and Rodrigues.Discrete analogues of the integral inequalities obtained are also der...Some new inequalities involving improper integrals are established in the paper which generalize the related results due to Pachpatte and Rodrigues.Discrete analogues of the integral inequalities obtained are also derived.An example is given to show that the bound in Theorem 1 is not improvable.展开更多
Under improper transformations,the traditional transformation laws for cross products,the permutation tensor,and rotations are incorrect.For a cross product,using a counter-example the left-hand rule is proved wrong.T...Under improper transformations,the traditional transformation laws for cross products,the permutation tensor,and rotations are incorrect.For a cross product,using a counter-example the left-hand rule is proved wrong.The unique rule for a cross product is the right-hand rule.Coordinate systems have handedness,while a cross product is frame-indifference.Since the permutation tensor is defined as a triple product including a cross product,the law for the permutation tensor is false.For a rotation,its pseudovector representation is incorrect,because the mirror is an auxiliary device to produce the virtual image rather than a new coordinate system or reference frame.展开更多
Bayesian quantile regression has drawn more attention in widespread applications recently. Yu and Moyeed (2001) proposed an asymmetric Laplace distribution to provide likelihood based mechanism for Bayesian inference ...Bayesian quantile regression has drawn more attention in widespread applications recently. Yu and Moyeed (2001) proposed an asymmetric Laplace distribution to provide likelihood based mechanism for Bayesian inference of quantile regression models. In this work, the primary objective is to evaluate the performance of Bayesian quantile regression compared with simple regression and quantile regression through simulation and with application to a crime dataset from 50 USA states for assessing the effect of potential risk factors on the violent crime rate. This paper also explores improper priors, and conducts sensitivity analysis on the parameter estimates. The data analysis reveals that the percent of population that are single parents always has a significant positive influence on violent crimes occurrence, and Bayesian quantile regression provides more comprehensive statistical description of this association.展开更多
Objective:To investigate a proteomics analysis of liver proteins from rats with spleen-deficiency syndrome (SDS) induced by chronic improper diet consumption and fatigue.Methods:This study used a liver proteomic profi...Objective:To investigate a proteomics analysis of liver proteins from rats with spleen-deficiency syndrome (SDS) induced by chronic improper diet consumption and fatigue.Methods:This study used a liver proteomic profiling method to identify differentially expressed proteins and altered pathways involved in SDS rats.Specifically,we collected liver samples from a control group and a group with SDS induced by chronic improper diet consumption and fatigue for 4 weeks.The pooled liver proteins in each group were labeled with 8-plex isobaric tags for relative and absolute quantitation reagents.The labeled control and SDS group samples were pooled together and separated by high-pH reverse-phase liquid chromatography.The differentially expressed proteins from the liver proteomes were analyzed to identify potential biomarkers of SDS.Differentially expressed proteins were selected in conjunction with gene ontology and ingenuity pathway analysis.Results:We identified 2176 protein clusters with more than two peptides in the SDS group,with 141 proteins quantified as differentially expressed proteins.Of these,75 proteins were up-regulated,and 66 were down-regulated.Three activated signaling pathways,the thrombin,CXCR4 and synaptic long term depression signaling pathways,and a large multi-protein complex within the network were revealed in the liver proteomic analysis of SDS rats.Conclusions:This is the first report of a differential liver proteome under SDS conditions.The results suggest that the liver proteome partially reflects the pathological changes involved in SDS.The findings provide important information for comprehensively understanding the mechanisms of dysfunction or injury in the liver at the molecular level as a result of SDS.Furthermore,they provide a novel understanding of the connotation of SDS in the fleld of traditional Chinese Medicine.展开更多
A graph G is called（k,d）＊-choosable if for every list assignment L satisfying ｜L（v）｜=k for all v ∈ V（G）,there is an L-coloring of G such that each vertex of G has at most d neighbors colored with the same co...A graph G is called（k,d）＊-choosable if for every list assignment L satisfying ｜L（v）｜=k for all v ∈ V（G）,there is an L-coloring of G such that each vertex of G has at most d neighbors colored with the same color as itself.In this paper,it is shown that every planar graph without 6-circuits and a triangle adjacent to itself or a quadrangle is（3,1）＊-choosable.展开更多
The authors thank the discusser for his interest and careful review of the paper and his valuable comments. They also welcome this discussion,because it gives the authors the opportunity to clarify several points whic...The authors thank the discusser for his interest and careful review of the paper and his valuable comments. They also welcome this discussion,because it gives the authors the opportunity to clarify several points which were not explained in sufficient detail in the paper,due展开更多
A novel practical and universal method of mask-wearing detection has been proposed to prevent viral respiratory infections.The proposed method quickly and accurately detects mask and facial regions using welltrained Y...A novel practical and universal method of mask-wearing detection has been proposed to prevent viral respiratory infections.The proposed method quickly and accurately detects mask and facial regions using welltrained You Only Look Once(YOLO)detector,then applies image coordinates of the detected bounding box(bbox).First,the data that is used to train our model is collected under various circumstances such as light disturbances,distances,time variations,and different climate conditions.It also contains various mask types to detect in general and universal application of the model.To detect mask-wearing status,it is important to detect facial and mask region accurately and we created our own dataset by taking picture of images.Furthermore,the Convolutional Neural Network(CNN)model is trained with both our own dataset and open dataset to detect under heavy foot-traffic(Indoors).To make the model robust and reliable in various environment and situations,we collected various sample data in different distances.And through the experiment,we found out that there is a particular gradient according to the mask-wearing status.The proposed method searches the point where the distance between the gradient for each state and the coordinate information of the detected object is the minimum.Then it carry out the classification of mask-wearing status of detected object.Lastly,we defined and classified three different mask-wearing states according to the mask’s position(With mask,Wear a mask around chin and Without mask).The gradient according to the mask-wearing status,is analyzed through linear regression.The regression interpretation is based on coordinate information of mask-wearing status and the sample data collected in simulated environment that considering distances between objects and the camera in the World Coordinate System.Through the experiments,we found out that linear regression analysis is more suitable than logistic regression analysis for classification of people wearing masks in general-purpose environments.And the proposed method,through linear regression analysis,classifies in a very concise way than the others.展开更多
The authors thank the discusser for the additional information,which is provided related to the historical interventions of the church through the centuries. This information was known to the authors,however they deci...The authors thank the discusser for the additional information,which is provided related to the historical interventions of the church through the centuries. This information was known to the authors,however they decided not to include it in the paper because of lack of space.Additional details regarding the retrofit展开更多
The thesis of the paper,which is the object of this Discussion,is that the considerable damage suffered by the Basilica,after the earthquake of L’Aquila in 2009,was the exclusive result of the intervention of seismic...The thesis of the paper,which is the object of this Discussion,is that the considerable damage suffered by the Basilica,after the earthquake of L’Aquila in 2009,was the exclusive result of the intervention of seismic improvement of the naves,made in 2000;such展开更多
从所周知,欧拉不等式2r≤R2(3)^(1/3)r≤3^(1/3)R。(1765)我们可加细到2(3)^(1/3)r≤(abc)1/3≤1/3(a+b+c)≤3^(1/3)R;(1)2(3)^(1/3)r≤(abc)^(1/3)≤{P integral from n=1 to ∞(+8)[(a+x)(b+x)(c+x)]^-(P+1)3dx}-1/P≤1/3(a+b+c)≤3^(...从所周知,欧拉不等式2r≤R2(3)^(1/3)r≤3^(1/3)R。(1765)我们可加细到2(3)^(1/3)r≤(abc)1/3≤1/3(a+b+c)≤3^(1/3)R;(1)2(3)^(1/3)r≤(abc)^(1/3)≤{P integral from n=1 to ∞(+8)[(a+x)(b+x)(c+x)]^-(P+1)3dx}-1/P≤1/3(a+b+c)≤3^(1/3)R;(2)2(3)^(1/3)≤(abc)^(1/3){P integral from n=1 to ∞(+8)[(a+x)(b+x)(c+x)]^-(P+1)/3dx}^-(1/P)≤{Pintegral from n=1 to ∞(+8)λ^(-1)[(ι+λ)(a+x))^(1/3)(ι+λ(b+x))^(1/3)(ι+λ(c+x))^(1/3)-ι]^(-P-1)dx}^(-1/P)≤1/3(a+b+c)≤3^(1/3)R。(3)展开更多
When the event of interest never occurs for a proportion of subjects during the study period, survival models with a cure fraction are more appropriate in analyzing this type of data. Considering the non-linear relati...When the event of interest never occurs for a proportion of subjects during the study period, survival models with a cure fraction are more appropriate in analyzing this type of data. Considering the non-linear relationship between response variable and covariates, we propose a class of generalized transformation models motivated by Zeng et al. [1] transformed proportional time cure model, in which fractional polynomials are used instead of the simple linear combination of the covariates. Statistical properties of the proposed models are investigated, including identifiability of the parameters, asymptotic consistency, and asymptotic normality of the estimated regression coefficients. A simulation study is carried out to examine the performance of the power selection procedure. The generalized transformation cure rate models are applied to the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (NHANES1) for the purpose of examining the relationship between survival time of patients and several risk factors.展开更多
Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper(R-P)structures.However,the experimentally reported ferr...Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper(R-P)structures.However,the experimentally reported ferroelectric materials based on triple-layer R-P structures are rare,and the weak ferroelectricity impedes its practical application.In the present work,the single-phase Li_(2)Nd_(2)Ti_(3)O_(10)ceramics with A-site cation ordered triple-layer R-P structure was obtained by spark plasma sintering technique,and the crystal structure of P2_(1)ab symmetry was revealed by neutron powder diffraction and transmission electron microscope analysis.Furthermore,the switchable ferroelectricity in Li_(2)Nd_(2)Ti_(3)O_(10)ceramics has been observed at room temperature,and the saturated polarization-electric field hysteresis loop was obtained with P_(r)=0.4μC/cm^(2)under the electric field of 250 kV/cm.The phase transition behavior of Li_(2)Nd_(2)Ti_(3)O_(10)oxides was revealed by the temperature-dependence Raman and dielectric spectra combined with the piezoelectric property.展开更多
Given a list assignment of L to graph G,assign a list L(υ)of colors to each υ∈V(G).An(L,d)^(*)-coloring is a mapping π that assigns a color π(υ)∈L(υ)to each vertex υ∈V(G)such that at most d neighbors of υ r...Given a list assignment of L to graph G,assign a list L(υ)of colors to each υ∈V(G).An(L,d)^(*)-coloring is a mapping π that assigns a color π(υ)∈L(υ)to each vertex υ∈V(G)such that at most d neighbors of υ receive the color υ.If there exists an(L,d)^(*)-coloring for every list assignment L with|L(υ)|≥k for all υ∈ V(G),then G is called to be(k,d)^(*)-choosable.In this paper,we prove every planar graph G without adjacent k-cycles is(3,1)^(*)-choosable,where k ∈{3,4,5}.展开更多
In this paper we study solutions to a forward Dynamo equation depending continuously on the velocity on an exterior domain,using Logarithmic Convexity Methods.We obtain some more weaker conditions by introducing the u...In this paper we study solutions to a forward Dynamo equation depending continuously on the velocity on an exterior domain,using Logarithmic Convexity Methods.We obtain some more weaker conditions by introducing the unbounded domain.展开更多
Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition thr...Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition through dielectric characterization.According to the previous theoretical design rule,the Curie temperature can be suppressed by increasing the tolerance factor.So,in the present work,high-quality Ca_(3-x)LaxTi_(2-x)Al_(x)O_(7)(x=0.0,0.1,0.2,0.3)ceramics with increased tolerance factors were successfully prepared.The amplitude of oxygen octahedral tilt mode indeed decreases with increasing tolerance factors,leading to a degeneration of ferroelectric polarization.However,the unexpected rigid rotation mode causes the composition-invariable coercive fields.The Curie temperatures decrease linearly with increasing x and tolerance factors.The variable-temperature dielectric constant confirms first-order improper ferroelectric transitions in Ca_(3)Ti_(2)O_(7)-based ceramics.The results of variable temperature Xray diffraction reveal the coexistence of two-phases below Curie temperature.The present work confidently confirms the first-order improper ferroelectric transition in Ca_(3)Ti_(2)O_(7)-based ceramics by combining results of variable-temperature dielectric response and in-situ X-ray powder diffraction.展开更多
In this paper, we present a proper reparametrization algorithm for rational ruled surfaces. That is, for an improper rational parametrization of a ruled surface, we construct a proper rational parametrization for the ...In this paper, we present a proper reparametrization algorithm for rational ruled surfaces. That is, for an improper rational parametrization of a ruled surface, we construct a proper rational parametrization for the same surface. The algorithm consists of three steps. We first reparametrize the improper rational parametrization caused by improper supports. Then the improper rational parametrization is transformed to a new one which is proper in one of the parameters. Finally, the problem is reduced to the proper reparametrization of planar rational algebraic curves.展开更多
文摘In this paper we present a numerical method for solving Riemann type problem for the fifth order improperly elliptic equation in complex plane .We reduce this problem to the boundary value problems for properly elliptic equations, and then solve those problems by the grid methods.
文摘In this paper, we derive the continuous dependence on the initial-time geometry for the solution of a parabolic equation from dynamo theory. The forward in time problem and backward in time problem are considered. An explicit continuous dependence inequality is obtained even with different prescribed data.
基金Supported by the Natural Science Foundation of Guangdong Pronvince( 0 1 1 471 ) and Education Bu-reau( 0 1 76)
文摘Some new inequalities involving improper integrals are established in the paper which generalize the related results due to Pachpatte and Rodrigues.Discrete analogues of the integral inequalities obtained are also derived.An example is given to show that the bound in Theorem 1 is not improvable.
基金National Natural Science Foundation of China(No.51978166)the Research Fund of Sanjiang University(No.2018SJKY005)。
文摘Under improper transformations,the traditional transformation laws for cross products,the permutation tensor,and rotations are incorrect.For a cross product,using a counter-example the left-hand rule is proved wrong.The unique rule for a cross product is the right-hand rule.Coordinate systems have handedness,while a cross product is frame-indifference.Since the permutation tensor is defined as a triple product including a cross product,the law for the permutation tensor is false.For a rotation,its pseudovector representation is incorrect,because the mirror is an auxiliary device to produce the virtual image rather than a new coordinate system or reference frame.
文摘Bayesian quantile regression has drawn more attention in widespread applications recently. Yu and Moyeed (2001) proposed an asymmetric Laplace distribution to provide likelihood based mechanism for Bayesian inference of quantile regression models. In this work, the primary objective is to evaluate the performance of Bayesian quantile regression compared with simple regression and quantile regression through simulation and with application to a crime dataset from 50 USA states for assessing the effect of potential risk factors on the violent crime rate. This paper also explores improper priors, and conducts sensitivity analysis on the parameter estimates. The data analysis reveals that the percent of population that are single parents always has a significant positive influence on violent crimes occurrence, and Bayesian quantile regression provides more comprehensive statistical description of this association.
基金The research was supported by the National Natural Science Foundation of China(81173193).
文摘Objective:To investigate a proteomics analysis of liver proteins from rats with spleen-deficiency syndrome (SDS) induced by chronic improper diet consumption and fatigue.Methods:This study used a liver proteomic profiling method to identify differentially expressed proteins and altered pathways involved in SDS rats.Specifically,we collected liver samples from a control group and a group with SDS induced by chronic improper diet consumption and fatigue for 4 weeks.The pooled liver proteins in each group were labeled with 8-plex isobaric tags for relative and absolute quantitation reagents.The labeled control and SDS group samples were pooled together and separated by high-pH reverse-phase liquid chromatography.The differentially expressed proteins from the liver proteomes were analyzed to identify potential biomarkers of SDS.Differentially expressed proteins were selected in conjunction with gene ontology and ingenuity pathway analysis.Results:We identified 2176 protein clusters with more than two peptides in the SDS group,with 141 proteins quantified as differentially expressed proteins.Of these,75 proteins were up-regulated,and 66 were down-regulated.Three activated signaling pathways,the thrombin,CXCR4 and synaptic long term depression signaling pathways,and a large multi-protein complex within the network were revealed in the liver proteomic analysis of SDS rats.Conclusions:This is the first report of a differential liver proteome under SDS conditions.The results suggest that the liver proteome partially reflects the pathological changes involved in SDS.The findings provide important information for comprehensively understanding the mechanisms of dysfunction or injury in the liver at the molecular level as a result of SDS.Furthermore,they provide a novel understanding of the connotation of SDS in the fleld of traditional Chinese Medicine.
基金Supported by the Natural Science Research Project of Ordinary Universities in Jiangsu(08KJB110002)Supported by the Program for ETHYTC(08QNZCK03)Supported by the NSFC(10671095)
文摘A graph G is called（k,d）＊-choosable if for every list assignment L satisfying ｜L（v）｜=k for all v ∈ V（G）,there is an L-coloring of G such that each vertex of G has at most d neighbors colored with the same color as itself.In this paper,it is shown that every planar graph without 6-circuits and a triangle adjacent to itself or a quadrangle is（3,1）＊-choosable.
文摘The authors thank the discusser for his interest and careful review of the paper and his valuable comments. They also welcome this discussion,because it gives the authors the opportunity to clarify several points which were not explained in sufficient detail in the paper,due
基金This research was supported by a grant(2019-MOIS32-027)of Regional Specialized Disaster-Safety Research Support Program funded by the Ministry of Interior and Safety(MOIS,Korea)This work was supported by Institute of Information&communications Technology Planning&Evaluation(IITP)grant funded by the Korea government(MSIT)(No.2021-0-01972).
文摘A novel practical and universal method of mask-wearing detection has been proposed to prevent viral respiratory infections.The proposed method quickly and accurately detects mask and facial regions using welltrained You Only Look Once(YOLO)detector,then applies image coordinates of the detected bounding box(bbox).First,the data that is used to train our model is collected under various circumstances such as light disturbances,distances,time variations,and different climate conditions.It also contains various mask types to detect in general and universal application of the model.To detect mask-wearing status,it is important to detect facial and mask region accurately and we created our own dataset by taking picture of images.Furthermore,the Convolutional Neural Network(CNN)model is trained with both our own dataset and open dataset to detect under heavy foot-traffic(Indoors).To make the model robust and reliable in various environment and situations,we collected various sample data in different distances.And through the experiment,we found out that there is a particular gradient according to the mask-wearing status.The proposed method searches the point where the distance between the gradient for each state and the coordinate information of the detected object is the minimum.Then it carry out the classification of mask-wearing status of detected object.Lastly,we defined and classified three different mask-wearing states according to the mask’s position(With mask,Wear a mask around chin and Without mask).The gradient according to the mask-wearing status,is analyzed through linear regression.The regression interpretation is based on coordinate information of mask-wearing status and the sample data collected in simulated environment that considering distances between objects and the camera in the World Coordinate System.Through the experiments,we found out that linear regression analysis is more suitable than logistic regression analysis for classification of people wearing masks in general-purpose environments.And the proposed method,through linear regression analysis,classifies in a very concise way than the others.
文摘The authors thank the discusser for the additional information,which is provided related to the historical interventions of the church through the centuries. This information was known to the authors,however they decided not to include it in the paper because of lack of space.Additional details regarding the retrofit
文摘The thesis of the paper,which is the object of this Discussion,is that the considerable damage suffered by the Basilica,after the earthquake of L’Aquila in 2009,was the exclusive result of the intervention of seismic improvement of the naves,made in 2000;such
文摘从所周知,欧拉不等式2r≤R2(3)^(1/3)r≤3^(1/3)R。(1765)我们可加细到2(3)^(1/3)r≤(abc)1/3≤1/3(a+b+c)≤3^(1/3)R;(1)2(3)^(1/3)r≤(abc)^(1/3)≤{P integral from n=1 to ∞(+8)[(a+x)(b+x)(c+x)]^-(P+1)3dx}-1/P≤1/3(a+b+c)≤3^(1/3)R;(2)2(3)^(1/3)≤(abc)^(1/3){P integral from n=1 to ∞(+8)[(a+x)(b+x)(c+x)]^-(P+1)/3dx}^-(1/P)≤{Pintegral from n=1 to ∞(+8)λ^(-1)[(ι+λ)(a+x))^(1/3)(ι+λ(b+x))^(1/3)(ι+λ(c+x))^(1/3)-ι]^(-P-1)dx}^(-1/P)≤1/3(a+b+c)≤3^(1/3)R。(3)
文摘When the event of interest never occurs for a proportion of subjects during the study period, survival models with a cure fraction are more appropriate in analyzing this type of data. Considering the non-linear relationship between response variable and covariates, we propose a class of generalized transformation models motivated by Zeng et al. [1] transformed proportional time cure model, in which fractional polynomials are used instead of the simple linear combination of the covariates. Statistical properties of the proposed models are investigated, including identifiability of the parameters, asymptotic consistency, and asymptotic normality of the estimated regression coefficients. A simulation study is carried out to examine the performance of the power selection procedure. The generalized transformation cure rate models are applied to the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (NHANES1) for the purpose of examining the relationship between survival time of patients and several risk factors.
基金supported by the National Key R&D Program of China under Grant No.2022YFB3807602the National Natural Science Foundation of China under Grant No.52172131the outstanding doctoral dissertation funding of Zhejiang University under Grant No.422048A.
文摘Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper(R-P)structures.However,the experimentally reported ferroelectric materials based on triple-layer R-P structures are rare,and the weak ferroelectricity impedes its practical application.In the present work,the single-phase Li_(2)Nd_(2)Ti_(3)O_(10)ceramics with A-site cation ordered triple-layer R-P structure was obtained by spark plasma sintering technique,and the crystal structure of P2_(1)ab symmetry was revealed by neutron powder diffraction and transmission electron microscope analysis.Furthermore,the switchable ferroelectricity in Li_(2)Nd_(2)Ti_(3)O_(10)ceramics has been observed at room temperature,and the saturated polarization-electric field hysteresis loop was obtained with P_(r)=0.4μC/cm^(2)under the electric field of 250 kV/cm.The phase transition behavior of Li_(2)Nd_(2)Ti_(3)O_(10)oxides was revealed by the temperature-dependence Raman and dielectric spectra combined with the piezoelectric property.
文摘Given a list assignment of L to graph G,assign a list L(υ)of colors to each υ∈V(G).An(L,d)^(*)-coloring is a mapping π that assigns a color π(υ)∈L(υ)to each vertex υ∈V(G)such that at most d neighbors of υ receive the color υ.If there exists an(L,d)^(*)-coloring for every list assignment L with|L(υ)|≥k for all υ∈ V(G),then G is called to be(k,d)^(*)-choosable.In this paper,we prove every planar graph G without adjacent k-cycles is(3,1)^(*)-choosable,where k ∈{3,4,5}.
基金supported by the Foundation of Fujian Education Bureau (0030-826156JB08024)
文摘In this paper we study solutions to a forward Dynamo equation depending continuously on the velocity on an exterior domain,using Logarithmic Convexity Methods.We obtain some more weaker conditions by introducing the unbounded domain.
基金financially supported by the National Natural Science Foundation of China under Grant Nos.51772266 and 51790493the National Key R&D Program of China under Grant No.2016YFA0300101.
文摘Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition through dielectric characterization.According to the previous theoretical design rule,the Curie temperature can be suppressed by increasing the tolerance factor.So,in the present work,high-quality Ca_(3-x)LaxTi_(2-x)Al_(x)O_(7)(x=0.0,0.1,0.2,0.3)ceramics with increased tolerance factors were successfully prepared.The amplitude of oxygen octahedral tilt mode indeed decreases with increasing tolerance factors,leading to a degeneration of ferroelectric polarization.However,the unexpected rigid rotation mode causes the composition-invariable coercive fields.The Curie temperatures decrease linearly with increasing x and tolerance factors.The variable-temperature dielectric constant confirms first-order improper ferroelectric transitions in Ca_(3)Ti_(2)O_(7)-based ceramics.The results of variable temperature Xray diffraction reveal the coexistence of two-phases below Curie temperature.The present work confidently confirms the first-order improper ferroelectric transition in Ca_(3)Ti_(2)O_(7)-based ceramics by combining results of variable-temperature dielectric response and in-situ X-ray powder diffraction.
基金This paper is partially supported by the National Fundamental Research 973 Program of China under Grant No.2004CB318000.
文摘In this paper, we present a proper reparametrization algorithm for rational ruled surfaces. That is, for an improper rational parametrization of a ruled surface, we construct a proper rational parametrization for the same surface. The algorithm consists of three steps. We first reparametrize the improper rational parametrization caused by improper supports. Then the improper rational parametrization is transformed to a new one which is proper in one of the parameters. Finally, the problem is reduced to the proper reparametrization of planar rational algebraic curves.
