Structural Modulation and Phase Transitions in Melilites

Crystals can often be seen in our daily life and a variety of high-tech aspects. The ideal crystal has three-dimensional lattice periodicity, which can be described by the developed space group. The existence of a lattice periodicity is apparent in the diffraction pattern which consists of sharp spots located on points of a reciprocal lattice. Half century ago, the crystal with a diffraction pattern involving sharp spots not belonging to a reciprocal lattice was founded. These sharp spots, so-called satellite reflections, are not simple fractions with respect to the lattice of main reflections. Those fractional indices are interpreted as due to a long-period ordering. The observation of satellite peaks showing a continuous temperature dependency leads to the concept of an incommensurate crystal structure. Since then, many more incommensurate crystal phases have been observed, including quasi-one-dimensional conductors (Comes et al., 1976), ferroelectrics (Dmitriev et al., 1998), alloys (Portier and Gratias, 1980), minerals (Hemingway et al., 1986; Seifert et al., 1987), composite crystal (Heimann et al., 1979), and so on. According to the origin of the incommensurability, the incommensurate crystals have been divided into different types. An important class is that of the modulated structures. These crystals can be described in terms of a basic structure with three-dimensional space group symmetry and a periodic derivation (the modulation) which in the incommensurate case has a period that does not belong to the lattice of the basic space group. The melilite families, occurring as solid solution minerals in natural rock assemblages, are observed independently with the incommensurately modulated features by Hemingway et al. (Hemingway et al., 1986) and Seifert et al. (Seifert et al., 1987) in synthetic end-member of Ca2MgSi2O7 åkermanite. The reason for the formation of the modulated structure is the misfit between the large X cations and the sheet-like tetrahedral framework. Changing the structural misfit by substitution of other cations or by temperature variation affects the amplitude of the modulation and the length of the modulation vector (Böhm, 1983; Iishi et al., 1990; Jiang et al., 1998; Röthlishberger et al., 1990; Schosnig et al., 2000). X-ray refinement in the (3+2)-dimensional space suggests that the modulation is mainly caused by a displacive shift of the constituent atoms resulting in a rotation and deformation of the T1 and T2 tetrahedra (Brown et al., 1994; Hagiya and Ohmasa, 1993). These changes are accompanied by changes of the interlayer X-cation environment in a way that reduces the coordination number of X from eight to seven or even six (Bagautdinov et al., 2000; Bindi et al., 2001; Riester et al., 2000; Tamura et al., 1996). It is further assumed that the flattened T1-tetrahedra surrounded by low-coordinated X cations show the tendency to form octagonal clusters, and that the arrangement of these clusters determines the strength of the overall modulation (Kusaka et al., 2001; Kusaka et al., 1998; Riester et al., 2000). The investigations of their composition and properties play an important role to understand the formation of rocks and furthermore, the evolution of the earth. It Synthetic melilite solid solutions extended this family and made it possible to study their structure features and other properties. Special end-members of melilite like Ca2Al2SiO7 and Ca2MgSi2O7 have potential applications as laser active materials (Le Boulanger et al., 2000) and (Foing et al., 1998) and long-lasting phosphorescent materials (Kodama et al., 1999), (Yamaga et al., 2002) and (Jiang et al., 2003). On the other hand, an interesting feature is that many melilites exhibit at room temperature a two-dimensional modulated structure. The modulation depends on temperature and composition. Although it is now clear that the general reason causing the modulation is due to the misfit between the intermediate large X cations and the sheet-like tetrahedral framework, the detailed nature of the modulation is not clear completely. Single crystal X-ray diffraction and the developing (3+2)-dimensional refinement provide evidence that the modulation attributes to the displacement of the constituent atoms as well as to the formation of the octagonal clusters arranging by four low coordinated Ca polyhedra and one T1-tetrahedron. Further, the modulation in melilites varies with composition. For example, an occupational modulation is observed in Sr/Ca-melilites. The transition from the incommensurate to the commensurate lock-in phase accompanying the formation of domains in melilites is not clear until now. Also, the studies of the structural modulated features of Co/Zn-melilite series are still lack till now. In this work, the first aim is to grown a series of high-quality single crystals including Ca2Mg1-xZnxSi2O7, Ca2Co1-xZnxSi2O7 and (Ca1-xSrx)2CoSi2O7 by the floating zone melting technique. The second aim is to investigate the variations of the modulation with composition and temperature, and to find out the transition features from the incommensurate phase to the low-temperature commensurate phase and the details of microdomains formed during the phase transition. Transmission electron microscopy and electron diffraction as well as XRD and DSC as compensatory way are used to study the structural modulation in selected melilites

Structural Modulation and Phase Transitions in Melilites

Crystals can often be seen in our daily life and a variety of high-tech aspects. The ideal crystal has three-dimensional lattice periodicity, which can be described by the developed space group. The existence of a lattice periodicity is apparent in the diffraction pattern which consists of sharp spots located on points of a reciprocal lattice. Half century ago, the crystal with a diffraction pattern involving sharp spots not belonging to a reciprocal lattice was founded. These sharp spots, so-called satellite reflections, are not simple fractions with respect to the lattice of main reflections. Those fractional indices are interpreted as due to a long-period ordering. The observation of satellite peaks showing a continuous temperature dependency leads to the concept of an incommensurate crystal structure. Since then, many more incommensurate crystal phases have been observed, including quasi-one-dimensional conductors (Comes et al., 1976), ferroelectrics (Dmitriev et al., 1998), alloys (Portier and Gratias, 1980), minerals (Hemingway et al., 1986; Seifert et al., 1987), composite crystal (Heimann et al., 1979), and so on. According to the origin of the incommensurability, the incommensurate crystals have been divided into different types. An important class is that of the modulated structures. These crystals can be described in terms of a basic structure with three-dimensional space group symmetry and a periodic derivation (the modulation) which in the incommensurate case has a period that does not belong to the lattice of the basic space group. The melilite families, occurring as solid solution minerals in natural rock assemblages, are observed independently with the incommensurately modulated features by Hemingway et al. (Hemingway et al., 1986) and Seifert et al. (Seifert et al., 1987) in synthetic end-member of Ca2MgSi2O7 åkermanite. The reason for the formation of the modulated structure is the misfit between the large X cations and the sheet-like tetrahedral framework. Changing the structural misfit by substitution of other cations or by temperature variation affects the amplitude of the modulation and the length of the modulation vector (Böhm, 1983; Iishi et al., 1990; Jiang et al., 1998; Röthlishberger et al., 1990; Schosnig et al., 2000). X-ray refinement in the (3+2)-dimensional space suggests that the modulation is mainly caused by a displacive shift of the constituent atoms resulting in a rotation and deformation of the T1 and T2 tetrahedra (Brown et al., 1994; Hagiya and Ohmasa, 1993). These changes are accompanied by changes of the interlayer X-cation environment in a way that reduces the coordination number of X from eight to seven or even six (Bagautdinov et al., 2000; Bindi et al., 2001; Riester et al., 2000; Tamura et al., 1996). It is further assumed that the flattened T1-tetrahedra surrounded by low-coordinated X cations show the tendency to form octagonal clusters, and that the arrangement of these clusters determines the strength of the overall modulation (Kusaka et al., 2001; Kusaka et al., 1998; Riester et al., 2000). The investigations of their composition and properties play an important role to understand the formation of rocks and furthermore, the evolution of the earth. It Synthetic melilite solid solutions extended this family and made it possible to study their structure features and other properties. Special end-members of melilite like Ca2Al2SiO7 and Ca2MgSi2O7 have potential applications as laser active materials (Le Boulanger et al., 2000) and (Foing et al., 1998) and long-lasting phosphorescent materials (Kodama et al., 1999), (Yamaga et al., 2002) and (Jiang et al., 2003). On the other hand, an interesting feature is that many melilites exhibit at room temperature a two-dimensional modulated structure. The modulation depends on temperature and composition. Although it is now clear that the general reason causing the modulation is due to the misfit between the intermediate large X cations and the sheet-like tetrahedral framework, the detailed nature of the modulation is not clear completely. Single crystal X-ray diffraction and the developing (3+2)-dimensional refinement provide evidence that the modulation attributes to the displacement of the constituent atoms as well as to the formation of the octagonal clusters arranging by four low coordinated Ca polyhedra and one T1-tetrahedron. Further, the modulation in melilites varies with composition. For example, an occupational modulation is observed in Sr/Ca-melilites. The transition from the incommensurate to the commensurate lock-in phase accompanying the formation of domains in melilites is not clear until now. Also, the studies of the structural modulated features of Co/Zn-melilite series are still lack till now. In this work, the first aim is to grown a series of high-quality single crystals including Ca2Mg1-xZnxSi2O7, Ca2Co1-xZnxSi2O7 and (Ca1-xSrx)2CoSi2O7 by the floating zone melting technique. The second aim is to investigate the variations of the modulation with composition and temperature, and to find out the transition features from the incommensurate phase to the low-temperature commensurate phase and the details of microdomains formed during the phase transition. Transmission electron microscopy and electron diffraction as well as XRD and DSC as compensatory way are used to study the structural modulation in selected melilites

Contingency ranking for on-line voltage stability assessment

Voltage stability is one of the challenging problems in power system operation. This thesis deals with fast algorithms for Contingency Screening and Ranking (CS&R) for power system voltage stability studies. CS&R is one of the important components of on-line voltage stability assessment. Its purpose is to rapidly and accurately determine which contingencies may cause power system voltage instability according to their severity. -- First, two popular voltage stability analysis methods, Continuation Power Flow (CPF) and minimum singular value of Jacobian matrix, are studied in this thesis. Then, several existing CS&R methods are reviewed. Two of them, Reactive Support Index (RSI) and Generalized Curve Fitting (GCF) methods, are investigated in detail. -- Finally, based on the GCF method, two novel methods for CS&R are proposed in this thesis. After employing the two improved methods, reselecting curve fitting points and filtering out unreasonable nose points, the simulation results show that the proposed methods have the ability to provide a fast estimate of voltage stability margins and thus select the most severe contingencies. The proposed methods have been applied for different power systems. These methods have the potential to be implemented in any online voltage stability assessment scheme

Intergenerational Test Generation for Natural Language Processing Applications

The development of modern NLP applications often relies on various benchmark datasets containing plenty of manually labeled tests to evaluate performance. While constructing datasets often costs many resources, the performance on the held-out data may not properly reflect their capability in real-world application scenarios and thus cause tremendous misunderstanding and monetary loss. To alleviate this problem, in this paper, we propose an automated test generation method for detecting erroneous behaviors of various NLP applications. Our method is designed based on the sentence parsing process of classic linguistics, and thus it is capable of assembling basic grammatical elements and adjuncts into a grammatically correct test with proper oracle information. We implement this method into NLPLego, which is designed to fully exploit the potential of seed sentences to automate the test generation. NLPLego disassembles the seed sentence into the template and adjuncts and then generates new sentences by assembling context-appropriate adjuncts with the template in a specific order. Unlike the taskspecific methods, the tests generated by NLPLego have derivation relations and different degrees of variation, which makes constructing appropriate metamorphic relations easier. Thus, NLPLego is general, meaning it can meet the testing requirements of various NLP applications. To validate NLPLego, we experiment with three common NLP tasks, identifying failures in four state-of-art models. Given seed tests from SQuAD 2.0, SST, and QQP, NLPLego successfully detects 1,732, 5301, and 261,879 incorrect behaviors with around 95.7% precision in three tasks, respectively

2D-Shapley: A Framework for Fragmented Data Valuation

Data valuation -- quantifying the contribution of individual data sources to certain predictive behaviors of a model -- is of great importance to enhancing the transparency of machine learning and designing incentive systems for data sharing. Existing work has focused on evaluating data sources with the shared feature or sample space. How to valuate fragmented data sources of which each only contains partial features and samples remains an open question. We start by presenting a method to calculate the counterfactual of removing a fragment from the aggregated data matrix. Based on the counterfactual calculation, we further propose 2D-Shapley, a theoretical framework for fragmented data valuation that uniquely satisfies some appealing axioms in the fragmented data context. 2D-Shapley empowers a range of new use cases, such as selecting useful data fragments, providing interpretation for sample-wise data values, and fine-grained data issue diagnosis.Comment: ICML 202

Power Allocation Strategies for Secure Spatial Modulation

In this paper, power allocation (PA) strategies in secure spatial modulation networks, are investigated under the total power constraint. Considering that there is no closed-form expression for secrecy rate (SR), an approximate closed-form expression of SR is derived as an efficient metric to optimize PA factor, which can greatly reduce the computation complexity. Based on this expression, a convex optimization (CO) method of maximizing SR (Max-SR) is proposed accordingly. Furthermore, a method of maximizing the product of signal-to-leakage and noise ratio (SLNR) and artificial noise-to-leakage and noise ratio (Max-P-SAN) is proposed to provide an analytic solution for PA factor with extremely low complexity. Simulation results demonstrate that the SR performance of the proposed CO method is close to that of the optimal PA strategy with exhaustive search, and is better than that of Max-P-SAN in the high signal-to-noise ratio (SNR) region. However, in the low and medium SNR regions, the proposed Max-P-SAN slightly outperforms the proposed CO scheme in terms of SR performance

Analysis of high-position landslide characteristics based on multi-source remote sensing data：A case study of the Yanwo Village landslide in Rongshan Town, Lizhou District, Guangyuan City

On October 6, 2021, a high-position landslide disaster occurred in Yanwo Village，Rongshan Town, Lizhou District, Guangyuan City,Sichuan Province, around 13: 00. The landslide resulted in the destruction of 4 houses, 3 power lines, the burial of a 170-meter-long rural road, and the blockage of a 350-meter-long river channel. By utilizing a variety of remote sensing information sources, including multi-period satellite data before and after landslide, high-precision UAV aerial images, and airborne LiDAR data, the characteristics of high landslide and its sliding mode are studied by using a four-dimensional analysis approach combining three-dimensional space with time. Starting from the development background of high landslide, the deformation and failure characteristics and sliding mode of high landslide are summarized by analyzing the deformation characteristics before sliding and the dynamic procession of the high landslide. Based on the deduced landslide progression and the stability evaluation of the residual landslide at the rear, three sliding modes for future high-position landslide events are predicted and analyzed: Firstly, the back edge of landslide continues to be disjointed and move, causing a direct shear failure of the front part of the landslide by squeezing. Secondly, the trailing edge of the landslide continues to be disjointed and move, resulting in the sliding landslide occurs along the existing landslide channel. Thirdly, the initiation of the front part of the landslide trigger a tractional landslide in the middle and rear parts of the landslide. High-position landslides are common in the southwest mountainous areas, and during early geological hazard investigations, they should be effectively identified, and disaster prevention and mitigation measures should be strengthened

Genetic immunization with Hantavirus vaccine combining expression of G2 glycoprotein and fused interleukin-2

In this research, we developed a novel chimeric HTNV-IL-2-G2 DNA vaccine plasmid by genetically linking IL-2 gene to the G2 segment DNA and tested whether it could be a candidate vaccine. Chimeric gene was first expressed in eukaryotic expression system pcDNA3.1 (+). The HTNV-IL-2-G2 expressed a 72 kDa fusion protein in COS-7 cells. Meanwhile, the fusion protein kept the activity of its parental proteins. Furthermore, BALB/c mice were vaccinated by the chimeric gene. ELISA, cell microculture neutralization test in vitro were used to detect the humoral immune response in immunized BALB/c mice. Lymphocyte proliferation assay was used to detect the cellular immune response.- The results showed that the chimeric gene could simultaneously evoke specific antibody against G2 glycoprotein and IL-2. And the immunized mice of every group elicited neutralizing antibodies with different titers. Lymphocyte proliferation assay results showed that the stimulation indexes of splenocytes of chimeric gene to G2 and IL-2 were significantly higher than that of other groups. Our results suggest that IL-2-based HTNV G2 DNA can induce both humoral and cellular immune response specific for HTNV G2 and can be a candidate DNA vaccine for HTNV infection