Centric Structure Research Articles

Second Harmonic Generation in β-K2TeW3O12: An Acentric Crystal Designed from Centric Phase via Pressure Modulation.

The latent value of nonlinear optical (NLO) crystals applied in solid-state laser equipment necessitates the development of applicable strategies for constructing noncentrosymmetric (NCS) crystals. By modulating the synthetic temperature and pressure to achieve the rearrangement of [TeO3]2- groups, a new NCS tellurium tungstate, β-K2TeW3O12 (β-KTW), with a strong second harmonic generation (SHG) response was synthesized based on its centrosymmetric polymorphic phase α-K2TeW3O12 (α-KTW). Computational calculation reveals that the large SHG response of β-KTW (15 × KH2PO4@1064 and 1.5 × KTiOPO4@1950 nm) could be attributed to the uniform arrangement of the NLO-active [TeO3]2- and [WO6]6- groups. β-KTW also exhibits enlarged birefringence (0.196@1064 nm) and a high laser damage threshold (42.3 MW cm-2), showing great potential as a nonlinear crystalline material. This work also provides a new route for the construction of NLO crystals based on centric structure, i.e., reverse pressure regulation.

NaMoO3(IO3)(H2O): water molecule introduction induces strong second harmonic generation response, widened band gap and large anisotropy.

Exploring feasible tactics to induce the formation of non-centrosymmetric (NCS) structures, especially from centrosymmetric (CS) structures, is essential for the development of nonlinear optical crystals with more potential. An NCS alkali metal-containing molybdenum iodate hydrate, namely, NaMoO3(IO3)(H2O), was designed based on the CS matrix NaMoO3(IO3) via introducing a water molecule into the structure. The introduction of one crystalline water molecule results in the rearrangement of Λ-shaped cis-[MoO4(IO3)2] units, and the proper array of the cis-[MoO4(IO3)2] units in NaMoO3(IO3)(H2O) results in its strong SHG response of 4.6 × KH2PO4. In addition, NaMoO3(IO3)(H2O) exhibits a wider optical bandgap of 3.44 eV and a larger birefringence of 0.231 than its matrix. Furthermore, the framework of NaMoO3(IO3)(H2O) is highly similar to that of α-KMoO3(IO3), with water molecules assisting Na+ cations in occupying the position of K+. However, due to the extra hydrogen bond of water molecules, the [MoO3(IO3)]∞ layers in NaMoO3(IO3)(H2O) retain a parallel-stacking arrangement, different from the antiparallel arrangement of layers in α-KMoO3(IO3) with a centric structure. This study confirms the feasibility of applying a water molecule to adjust the orientation of basic building block units to assemble an NCS structure based on CS crystals.

The Results of New Research in the Tigray Region, Ethiopia: Three Rock-hewn Churches of Kola Tembien as Historical Sources

The article is devoted to the results of research focused on three rock-hewn churches, which are not well-represented in literature, in Kola Tembien of the Tigray region in Ethiopia. Fieldwork was carried out with the financial support of the Russian foundation for Basic Research. Trips to the site were conducted in the autumn of 2019 and 2020. The problems of dating and typology is the focus of this research. In the article, three churches are described — Mikaʼel ʽAddi Kawa, Abunä Fäqadä Amlak in ʽAdi Śərä and Maryam Degol Chako. Special reference is made to the architectural ties of these three monuments with others of the region in order to reveal the possible mutual influence of architectural constructions and some decorative elements. Information on these churches has not been published since the time of cooperative research by Ruth Plant and David Buxton in the 1970s. Particular attention in the article is paid to the churches Abunä Fäqadä Amlak inʽAdi Śərä and Maryam Degol Chako as they have very rich paintings on canvas dating from the middle of the XX century. These paintings are valuable not only as art objects of Christian Ethiopia, but also as important sources of the cultural and political history of Tigray. Unfortunately, the preservation of these paintings in the studied churches raises concerns. The article presents new authentic material on the described churches. Photographs of the interiors are published for the first time. In addition, on the basis of the iconographic and architectural analysis, a number of hypotheses by the author are presented for further discussion and verification. It is worth noting the possibility of reconstructing the previous basilica rock-hewn churches into centric structures by building the interior the walls.

Beyond the multidisciplinary in fan studies: Learning how to talk among disciplines

In light of the Fan Studies Network's statement regarding fan studies being overrun with whiteness, we are in a unique position to engage in scholarship that challenges the overwhelmingly white and Global North–centric structures that define how we study fan cultures. Multidisciplinarity, which may be understood as disciplines laid side by side, should be contrasted with interdisciplinarity, which requires true dialogue. Despite recent field-shifting work by fan studies scholars such as Bertha Chin, Lori Morimoto, Rukmini Pande, and Rebecca Wanzo, more work needs to be done to both acknowledge and build on current research in transcultural fandom. In a dialogue that reflects the progress of our own striving toward interdisciplinary and transcultural work in fan studies, we seek to demonstrate a possible way forward for the field of fan studies to become more truly interdisciplinary and transcultural in its focus.

Investigation of the Nature of the Economic Cluster as a Quasintegration Form of a Spatial Organization of Economic Activity

The growing global competition, as well as other factors of the changing economic situation are shifting the investors attention from countries as a whole to the territories and regions in which the synergistic effect of the interaction of various-scale enterprises not only increases the individual performance efficiency of each company but develops a significant innovative potential of their integration and creation of new competitive innovative products. Therefore, the rigid centric structures of administrative management with a response only to the price signals cease to respond to the demands of reality and are replaced by a more flexible and integrated model of building links - network interaction. Russian companies are highly interested in the accumulated experience of foreign countries in tooling search for cluster initiatives, their development, including the intra-cluster structure, and their support taking into consideration the whole spectrum of factors that both contribute to and hinder the viability of the cluster. The article presents a brief analysis of the cluster concept development, examines the present-day systems of managing the cluster-network interaction. It offers the author's definition of the cluster.

Partial substitution induced centrosymmetric to noncentrosymmetric structure transformation and promising second-order nonlinear optical properties of (K0.38Ba0.81)Ga2Se4.

Partial substitution of Ba by K in the Ba sites of BaGa2Se4 creates a new selenide (K0.38Ba0.81)Ga2Se4 (1), which is crystallized in the noncentrosymmetric space group I4cm, different from the centric structures of all the ternary MI-MIII2-Q4 (MII = divalent Sr, Ba, Pb, Sn, Eu; MIII = trivalent Ga, In; Q = S and Se) chalcogenides. Its 1D structure features {[GaSe2]-}∞ chains, and K/Ba occupying the interchain cavities as the counter cations. Its powder sample demonstrates a second-harmonic generation intensity which is around 0.9 times that of AgGaS2 at 2.1 μm, and a laser-induced damage threshold which is 13.4 times that of AgGaS2. DFT calculations on its electronic structure and optical properties were also performed.

Exploring the Interaction Between Internal Customer Satisfaction and Talent Waste: A Lean Management Perspective

Principles of lean management have become more popular in recent years and the implementation area of Lean, spread from manufacturing environment to service sectors due to its wide applicability. Human centric structure of service sector reveals the need of lean principles which focuses on improvements related to employees. In lean thinking, elimination of wastes is one of the priority and it is essential to eliminate them for organizational enhancements. Wastes in lean were firstly defined under seven categories as overproduction, over-processing, waiting, motion, inventory, defect, transportation for manufacturing environment. However, these wastes were not found adequate, since one of the most important factor in organizations, human, was ignored. Therefore, the 8th waste of lean was presented as “talent” in order to include the human factor and it refers to underutilization of people’s talent, knowledge, skills and abilities. As eliminating talent waste has been perceived as an important concept, it should be a significant driver of increasing internal customer satisfaction. This study aims to explore the relation between talent waste and internal customer satisfaction while considering level of top management commitment. Within this context a survey was conducted with the participation of whitecollar internal customers to understand their perception of talent waste related to their jobs. At the end of the study, it is found that talent waste partially mediates the relationship between top management commitment and internal customer satisfaction.

‘Remote’ areas and minoritized spatial orders at the Russia – Mongolia border

The article first outlines how ‘remoteness’ was conceived and constructed during the Soviet and post-Soviet periods in Russia. Using the ideas of the social geographer Boris Rodoman, it argues that centric structures of power, communications and state provision created scalar zones of non-development and isolation at borders between internal administrative regions. In post-Soviet times this structure continued, but according to Vladimir Kagansky it has been disturbed by recent ‘spontaneous transformations’ whereby state international borders are becoming areas of contact and enterprise, rather than isolation. The paper suggests to the contrary that, with the increasing centralisation of the Putin era, Kagansky’s theory has not been realised on the Russia-Mongolia-China border, and that the reduction of border crossing points in fact deepen the residents’ sense of being situated ‘at a dead end’. However, the indigenous people living in border zones, notably the Buryat, operate not only with these state-constructed geographies, but also with their own quite different spatial concepts. These are so much the converse to the Russian that they can be seen as a distinctive minoritized vision. The Buryat ideas and ritual practices reach across political boundaries. In effect they create a subtle challenge to the spatiality of the Russian state. It is argued that roads in this situation become particularly concentrated vectors of contradictory values.

SHeRo: Scalable hexapod robot for maintenance, repair, and operations

Abstract Improper maintenance, repair, and operations of societal centric structures can lead to catastrophic failures that drastically affect global economy, the environment, and everyday life. Due to the remote, cramped and highly irregular environmental nature of these structures, routine manual procedures and operations can be rather tedious, dangerous, and hazardous for humans. Automating maintenance, repair, and operations removes human workers from having to crawl within highly cluttered and constrained spaces, breathing in stale air mixed with fumes from welding or particulate from repair work, and provides higher reliability and consistency in the repair work. This paper introduces SHeRo, a scalable hexapod robot designed for maintenance, repair, and operations within remote, inaccessible, irregular, and hazardous environments. The scalability of the design enhances traditional hexapod robot designs by incorporating two prismatic joints into each leg. A detailed discussion on the design and realization of SHeRo is provided. An analysis on the stability and workspace of SHeRo is presented and a dynamic criterion is developed to integrate the concepts of robot stability and constant orientation workspace into a stable workspace. The analytical solution of the lateral stable workspace of SHeRo is derived along with a metric for comparing stable workspace between different robot configurations. A simulated demonstration and two physical experimental demonstrations are presented showing the advantage of introducing scalability into the hexapod robot design along with the workspace enhancement and flexibility of the scalable hexapod robot.

부산광역시 다핵구조의 공간적 변동성 측정

Recently metropolitan cities pursue multi centric urban spatial structure for sustainable development and efficient urban management. Thus, this study calculated population potential using data on population distributed among road nodes for the last 50 years, and based on the results. We measured the spatial variability of the multi centric structure of Busan Metropolitan City. According to the results, the multi centralization process has been continued up to recently in Busan Metropolitan City. As population potential is concentrated on sub centers, Hadan, Gupo and Haeundae areas were playing an increasingly powerful role as the center of the respective district, and Sasang and Dongrae had been losing their role as the center of their respective districts since 2000 and 1990, respectively. Additionally, in all the multi centric districts except Haeundae was observed the increase of oblongity, which is the change of spatial structure in an unbalanced way toward a specific area or direction.

Von Massenproduktion zu Co-Produktion Kunden als Wertschöpfungspartner

The idea of integrating users into the design and production processes is a promising strategy for companies being forced to react to the growing individualization of demand. Many of the new models of industrial value creation refer to customer integration as a distinctive principle. The paper argues that modern information technologies play an important part to implement customer centric structures in mass markets. The combination of flexible manufacturing with modern interaction technologies allows only today to fulfill many of the promises that were discussed in the CIM context already decades ago. The objective of this paper is to lay a foundation for creating modern, customer orientated manufacturing concepts by dedicated information systems and processes. After discussing some new forms of value creation in manufacturing, we identify information structures and processes for customer integration. The paper ends with an agenda for further research from a business informatics perspective.

Growth-Induced Evolution of Polarity in Organic Crystals

A Markov-mean-field model is developed to describe growth-induced polarity in single-component organic crystals formed by dipolar molecules. Results of an analytical theory agree well with corresponding Monte Carlo simulations. Polarity formation is analyzed in terms of three basic energy differences, two of them resulting from the interaction of functional groups (synthons) and a third one accounting for the lateral interaction. Basic packing types are discussed with respect to polarity formation. The Markov model provides a general description of the phenomenological behavior when moving energetically from centric to polar structures. Keeping synthon interactions within reasonable limits, the range for designing lateral coupling is limited to a few kilojoules per mole for a square lattice: Between a gap of about −2 kJ/mol ≤ ΔE⊥ ≤ 3−4 kJ/mol (300 K), the stochastic process of orientational disorder is either significantly increasing (centric structures) or decreasing (polar structures) polarity. Outside of these borders, orientational disorder represents only a small perturbation to centric or polar structures. With respect to the existence of structure types, the model predicts that a molecular packing where the lateral energy difference between a parallel and an antiparallel alignment of molecules is larger than about 3 kJ/mol (square lattice, 300 K) most likely results in a centric structure featuring a low level of orientational disorder. A fundamentally new behavior for the growth of polar crystals is predicted: As a consequence of the Markov model, one of the two inequivalent growth directions of a polar axis is metastable against a 180° flipping of most of the dipoles. This type of a continuous process of twinning is different from geometrical twinning. A first set of data on real crystals is given, demonstrating polarity formation in crystal structures for which the X-ray analysis has reported only centric space groups.

A new mapping of the world for the new millennium

A new mapping of the world derived from connections between cities is presented as a complement to the traditional world map of countries. Under conditions of contemporary globalization world cities have emerged as global service centres. These have been created by the location strategies of leading corporate service firms (e.g. in accountancy) in setting up their global office networks. Data on the offices of 46 global service firms in 55 world cities are used to define service connections between cities. Connections are converted into measures of network proximity and a multidimensional scaling is applied to these ‘distances’ to create a ‘global service space’ of cities. This new mapping of the world shows a distinctive centric structure with the major world cities (e.g. London) at the core. Investigation of this general structure reveals more subtle patterns of interacting regional and hierarchical tendencies.

P4/nandP4nclong-range ordering in low-temperature vesuvianites

Low-temperature vesuvianites crystallize in the two space groups P4/n or P4nc due to different arrangements of Ca-dodecahedra and M 2+,3+ square pyramids that form strings along the fourfold axes. Long-range ordered vesuvianites of acentric P4nc symmetry may have the same diffraction symmetry as centrosymmetric disordered P4/nnc vesuvianites. In contrast, P4/n long-range ordered vesuvianites exhibit glide plane violating reflections and can easily be identified. We report the first successful Xray single-crystal structure refinement of a P4nc vesuvianite, a = 15.487(2), c = 11.764(2) Å from the N’chwaning II mine of the Kalahari manganese fields (RSA). This untwinned crystal has Cu 2+ and Mn 2+ , Mn 3+ forming the square pyramid and exhibits an acentric ordering pattern with 85% string A and 15% string B. This is compared to a reinvestigation of the structure of a P4/n vesuvianite from Asbestos Quebec (Canada), a = 15.531(2), c = 11.817(2) Å. The crystal is composed of a merohedral (110) twin with a close to 1:1 twin ratio and has mainly Fe 3+ in square pyramidal coordination. In this centric structure, string A is 84% and string B is 16% occupied. Criteria to determine the symmetry of low-temperature vesuvianites, studied by diffraction experiments, are discussed.

On an intrinsic mechanism of surface defect formation producing polar, multidomain real-structures in molecular crystals

Abstract Dipolar but achiral organic molecules may undergo orientational disorder in the bulk but particularly at the surface of a seed crystal. In cases where the activation energy for reversal of the dipoles in the bulk is much larger than that for reversal at the growing crystal faces, thermodynamic arguments predict that orientational disorder occurring at surface attachment sites can produce metastable but macroscopically large growth sectors, featuring different polar properties than the seed. If the process of nucleation produces a non-pyroelectric symmetry group, then orientational disorder at the surface may give rise to pyroelectric properties during subsequent growth. Similarly, for seeds belonging to a pyroelectric group, orientational disorder can reduce the initial pyroelectric effect. According to this new surface-related mechanism of intrinsic defect formation, acentric and achiral molecules are likely to form real-structures which show a pyroelectric effect, although from a crystallographic point of view, such crystals may be described topologically by e.g. a centric structure. These present views are applied to the space group P21/c, supplemented by comments on techniques available for an experimental investigation of the predicted real-structurs.

Acentric structure (P3) of bechererite, Zn7Cu(OH)13[SiO(OH)3SO4

The crystal structure of bechererite from the Tonopah-Belmont mine, Arizona, was reinvestigated using a single-crystal X-ray diffractometer (MoKalpha radiation) equipped with a CCD area detector. The structure was refined in space group P3 (a = 8.319(2), c = 7.377(1) A) with 1247 unique reflections up to (sintheta )/lambda = 0.65 leading to R1 = 2.7%, wR2 = 6.4%. In agreement with the previously reported centric structure (P3), bechererite is composed of (001) brucite-like sheets formed by edge-sharing (Zn,Cu)O 6 octahedra and 1/7 ordered octahedral vacancies. The layers are connected parallel to c by ditetrahedral (Zn,Cu) 2 (OH) 7 units. Due to the attractive force of a weak hydrogen bond, the bridging O atom of the ditetrahedral unit is displaced from the threefold axis. A characteristic feature of the structure is isolated tetrahedra, which connect only with one apex to the octahedral sheet. The acentric structure (P3) reveals ordering between SiO(OH) 3 and SO 4 tetrahedra yielding characteristic distortions of the neighboring (Zn,Cu)O 6 octahedra caused by bond-valence requirements of the shared O atoms. The [SiO(OH) 3 ] (super 1-) tetrahedron is only 70(1)% occupied and is partly substituted by tetrahedral [O 4 H 7 ] (super 1-) clusters. The existence of H 2 O molecules in the [O 4 H 7 ] (super 1-) cluster is supported by FTIR spectroscopy.

Raman study of NaClO3 as a function of temperature into the melt and the novel high temperature phase

Raman spectra have been measured for oriented single crystals of NaClO3 II from 77 K to the melting temperature, for the molten salt and the high temperature phase, NaClO3 I. The results for NaClO3 II were in excellent agreement with unit-cell group analysis. Apparent anomalies associated with the presence of weak bands due to naturally abundant 37Cl and 18O substituted ions have been accounted for on the basis of intermolecular coupling models. The unusual high temperature, ambient pressure phase transition for NaClO3 has been characterised by spectroscopic and thermal methods. The novel feature about the high temperature phase is the fact that it may only be reached by cooling the melt and it transforms back to the room temperature phase at about 510 K as the sample is cooled. The longitudinal optical mode at about 1030 cm-1 which was characteristic of the acentric room temperature phase (P213, T4) was conspicuously absent in the Raman spectrum of the high temperature phase. The Raman spectrum of the high temperature phase indicated that the crystal has a centric structure but the similarity of many bands with the spectrum of the room temperature phase suggested that the phase transition involved only small changes in atomic positions. The structure remained ordered but there was evidence of considerable band broadening due to increased thermal motion. The Raman results are consistent with the diffraction studies of Meyer and Gasperin (1973) who reported a monoclinic structure similar to room temperature KClO3, space group P21/a. Measurements of the heats of fusion and transition by differential scanning calorimetry gave values of Delta Hf=21.7 kJ mol-1, Delta Sf=40.6 J mol-1, Delta Ht=4.1 kJ mol-1, Delta St=8.2 J mol-1 K-1. The relatively small values of the heat and entropy of transition compared to those of fusion also indicated that the high temperature phase was not disordered.

Determination of the crystal structure of yttrium orthoferrite and refinement of gadolinium orthoferrite

Abstract : The crystal structure of yttrium orthoferrite has been determined from full three-dimensional counter data and refined in the space group Pbnm by least squares to an accuracy of about .001 and .01A in positional parameters of Y(3+) and O(2-) respectively. Parameters are compared with those of GdFeO3, derived by least squares refinement of Geller's intensity data. It is found that the distortions from the ideal perovskite lattice hardly affect the octahedral environment of the Fe(3+) ion, which makes it possible to predict Fe(3+)-O(2-)-Fe(3+) angles in other distorted perovskite structures of known cell dimensions. Refinement in the alternative non-centric space group Pbn2 sub 1, shows small possibly real deviations from a centric structure. (Author)

Détermination du groupe spatial de minéraux d'uranium

The probability distribution of X ray intensities of uranium minerals is altered by the presence of uranium atoms. These atoms affect the statistical tests that are used to distinguish centric from acentric structures. If the positions of the heavy atoms are known (from the Patterson map), distribution curves can be calculated for centric structures (Collin). We have applied the Collin's method to the group determination of the three uranium minerals : sklodowskite, jachimovite and kasolite.

Kristallstrukturelle Untersuchung von Xanthazol-Monohydrat

The crystal structure of xanthazol monohydrate (Fig. 1) is being investigated. It is triclinic with two molecules per unit cell. Results obtained by the methods ofRogers andWilson show a tendency to centrosymmetry. A complete three dimensional Patterson synthesis, calculated with about 1300 reflexions, yielded a layer structure with the molecules almost parallel (001) and a very short period of 3.14 A. The different possibilities for the structure were examined by steric considerations and Fourier projections. The figure gives a centric structure in which the water molecule (H2Ow) shows up quite clearly, and which is considered to be the right one. Very weak additional layer lines indicate some sort of super-structure.