15 research outputs found
An extension of biconservative timelike hypersurfaces in Einstein space
No full textA well-known conjecture of Bang-Yen Chen says that the only biharmonic Euclidean submanifolds are minimal ones, which affirmed by himself for surfaces in 3-dimensional Euclidean space, E³. We consider an extended version of Chen conjecture (namely, Lk-conjecture) on Lorentzian hypersurfaces of the pseudo-Euclidean space E⁴₁ (i.e. the Einstein space). The biconservative submanifolds in the Euclidean spaces are submanifolds with conservative stress-energy with respect to the bienergy functional. In this paper, we consider an extended condition (namely, Lk-biconservativity) on non-degenerate timelike hypersurfaces of the Einstein space E⁴₁ . A Lorentzian hypersurface x : M³₁ → E⁴₁ is called Lk-biconservative if the tangent part of L²k x vanishes identically. We show that Lk-biconservativity of a timelike hypersurface of E⁴₁ (with constant kth mean curvature and some additional conditions) implies that its (k + 1) th mean curvature is constant
On hypersurfaces of Lorentzian standard 4-space forms satisfying a biconservativity condition
No full textIn this manuscript, we consider an extended version of biconservativity condition (namely, -biconservativity) on the Riemannian hypersurfaces of Lorentzian standard 4-space forms. This new condition is obtained by substituting the Cheng-Yau operator instead of the Laplace operator . We show that every -biconservative Riemannian hypersurface of a Lorentzian 4-space form with constant mean curvature has constant scalar curvature
Weakly convex hypersurfaces of pseudo-Euclidean spaces satisfying the condition LkHk+1 = λHk+1
No full textIn this paper, we try to give a classification of spacelike hypersurfaces of the Lorentz-Minkowski space-time E1n+1, whose mean curvature vector field of order (k+ 1) is an eigenvector of the kth linearized operator Lk, for a non-negative integer k less than n. The operator Lk is defined as the linear part of the first variation of the (k + 1)th mean curvature of a hypersurface arising from its normal variations. We show that any spacelike hypersurface of E1n+1 satisfying the condition LkHk+1 = λHk+1 (where 0 ≤ k ≤ n − 1) belongs to the class of Lk-biharmonic, Lk-1-type or Lk-null-2-type hypersurface. Furthermore, we study the above condition on a well-known family of spacelike hypersurfaces of Lorentz-Minkowski spaces, named the weakly convex hypersurfaces (i.e. on which all of principle curvatures are nonnegative). We prove that, on any weakly convex spacelike hypersurface satisfying the above condition for an integer k (where, 0 ≤ r ≤ n−1), the (k + 1)th mean curvature will be constant. As an interesting result, any weakly convex spacelike hypersurfaces, having assumed to be Lk-biharmonic, has to be k-maximal.
On the classification of hypersurfaces in Euclidean spaces satisfying LrHr+1 = AHr+1
No full textIn this paper, we study isometrically immersed hypersurfaces of the Euclidean space En+1 satisfying the condition LrH r+i = λHr+1for an integer r ( 0 ≤ r ≤ n — 1), where Hr+i is the (r + 1)th mean curvature vector field on the hypersurface, Lr is the linearized operator of the first variation of the (r + 1) th mean curvature of hypersurface arising from its normal variations. Having assumed that on a hypersurface x : Mn → En+1, the vector field Hr+i be an eigenvector of the operator Lr with a constant real eigenvalue λ, we show that, Mn has to be an Lr-biharmonic, Lr-1-type, or Lr-null-2-type hypersurface. Furthermore, we study the above condition on a well-known family of hypersurfaces, named the weakly convex hypersurfaces (i.e. on which principal curvatures are nonnegative). We prove that, any weakly convex Euclidean hypersurface satisfying the condition Lr Hr+i = λ Hr+i for an integer r ( 0 ≤ r ≤ n — 1), has constant mean curvature of order (r + 1). As an interesting result, we have that, the Lr-biharmonicity condition on the weakly convex Euclidean hypersurfaces implies the r-minimality
-biharmonic spacelike hypersurfaces in Minkowski -space
No full textBiharmonic surfaces in Euclidean space are firstly studied from a differential geometric point of view by Bang-Yen Chen, who showed that the only biharmonic surfaces are minimal ones. A surface is called biharmonic if , where is the Laplace operator of . We study the -biharmonic spacelike hypersurfaces in the -dimentional pseudo-Euclidean space with an additional condition that the principal curvatures are distinct. A hypersurface is called -biharmonic if (for ), where is the linearized operator associated to the first variation of -th mean curvature of . Since , the matter of -biharmonicity is a natural generalization of biharmonicity. On any -biharmonic spacelike hypersurfaces in with distinct principal curvatures, by, assuming to be constant, we get that is constant. Furthermore, we show that -biharmonic spacelike hypersurfaces in with constant are -maximal
On extended biharmonic hypersurfaces with three curvatures
No full textThe subject of harmonic and biharmonic submanifolds, with important role in mathematical physics and differential geometry, arises from the variation problems of ordinary mean curvature vector field. Generally, harmonic submanifolds are biharmonic, but not vice versa. Of course, many examples of biharmonic hypersurfaces are harmonic. A well-known conjecture of Bang-Yen Chen on Euclidean spaces says that every biharmonic submanifold is harmonic. Although the conjecture has not been proven (in general case), it has been affirmed in many cases, and this has led to its spread to various types of submanifolds. Inspired by the conjecture, we study the Lorentz submanifolds of the Lorentz-Minkowski spaces. We consider an advanced versión of the conjecture (namely, L1-conjecture) on Lorentz hypersurfaces of the pseudo-Euclidean 5-space L5 := E15 (i.e. the Minkowski 5-space). We confirm the extended conjecture on Lorentz hypersurfaces with three principal curvatures
Simile with an Emphasis on the Link between Poetry and Form in Nafthatolmasdoor
No full textShahabuddin Mohammad Khrndzy Zydary's Nafthatolmasdoor is considered to be beyond the enduring masterpieces of prose and Metcalf in the seventh century AD. This book ismore a historical-literal one than a literal-historical one. In this book, emotional aspects are represented more than the historical ones. The point of view in this book is first person and is used to express excitement, emotions, and feelings. The link between poetic and form is one of the features that is highlighted in the book. Illusion, as an element of creating form, and simile are delicately used. In total, the use of the element of simile is high and mainly for the purpose of creating emotions. Metaphors are often perceived to be reasonable. The society inside and outside of the author is like an indirect analogy.
This article investigates secondary purposes of simile along with three categories of: stylistic look for the artist, the choice of words, and deviating from the norm, according to the analysis of imagery in the text
Little Black Fish and Readers: From Passive Reading to Active Dialogue
No full textIn the middle of the twentieth century, the discourse of literary criticism was considered. The story of "Little Black Fish" (1347), for some reasons, including the type of text, its special structure, and the range of audiences, has been faced with different interpretations. In this research, with a descriptive-analytical method and based on the approach of reader-oriented theories, the way of interaction between the reader and the text has been studied in a diachronically and synchronically manner. The results show that the readers' reaction before 1957, according to the dominant paradigm, was a critique of taste, based on ideology, and had a social approach in which the hero's action was highlighted and the readings were informative. There was no dialogue between the text and the reader, and the meaning was imposed on the text. From 1957 to the end of the 1980s, the receptions were combined criticism, and based on the literary expectation horizon, they had a frequency in the field of narratology. These readings created uncertainty, and the reader constructed a new form of textual object in a semi-active dialogue with the text. From the late 1980s to the late 1990s, readings were theory-based, and the semiotic approach had the highest frequency among other approaches. The readings were often dialectical with the readings of the previous period, and from the uncertainty until the receipt of correction was figured in the previous readings, and as a result of the integration of social and literary expectation horizons, they offered a wider semantic horizon.Keywords: Reader Response Criticism, Reception Theory, Samad Behrangi, Little Black Fish. IntroductionTraditional criticism based on the intention of the author prevailed over other methods of literary criticism until the end of the 19th century and did not pay attention to the element of the reader, who was one of the main factors in narrative communication. One of the most important reasons for the transformation of the criticism cycle towards the reader is "reader-centered debates among literary criticism theorists" (Benton, 2009: 22). In the middle of the 20th century, I. E. Richards emphasized changing the self-based approach to criticism and the importance of the act of reading and the reaction of the reader. The collection of reader-centered criticism approaches continued to grow in two origins after World War II, influenced by the philosophy of phenomenology and the science of interpretation. First, the approach of "reader reaction" in America and the other, the approach of "reception or the Constance school" in Germany (Taslimi, 1388: 108). The common feature of the two listed approaches was the phenomenological encounter with subject/object duality.Research Question(s)Due to the success of critics and readers, the story of the little black fish has been read many times after its publication. According to the different readings of this story in six decades (1340 to the end of 1390), in the present research we aim to specify: 1- The interaction between the reader and the text in the story "Little Black Fish" in the creation of meaning - as how was the simultaneity and in time? -2- To what extent do the readers read the work under the influence of their minds - consciously and unconsciously - 3- How did the existing discourses in each era influence these readings? Literature ReviewRegarding reader-oriented theories, including the theory of reader reaction and the theory of reception, there are many materials in articles and books of criticism, literary theory, and encyclopedias, but the application of this theory has been done in different ways in the articles. For example, some have examined the work according to the reader in the text. Some researchers have also examined the work or text from the point of view of the reader's reception and reaction; or, in one case, the scene of the play is considered a text, and the process of receiving the audience has been investigated in it. By researching the indexing databases of articles, it was found that the number of articles that examined the existing readings of a work during one or more periods and presented the history of aesthetics from the reception of readers is small. This article examines and analyzes this aspect of the readings and the aesthetic history of the reception of the readers of this work. MethodologyBy researching the indexing databases of the articles, it was found that the number of articles that examined the existing readings of a work during one or more periods and presented the history of aesthetics from the reception of the readers is small. A total of 33 articles and one book about "Little Black Fish" were collected in the books, which included a collection of reviews written about Samad Behrangi's works. Then, the reviews were placed in three time frames based on the dominant aspects of reading, including reading for taste, synthesis, and based on theory, and were examined and analyzed using a descriptive-analytical method based on the approach of theories aimed at the reader. The time format of the courses is based on the dominant aspect of the critic's encounter with the work in the period from 1340 to the end of 1390, and at the same time, it also pays attention to ideological discourses. ConclusionIn the readings before 1957, the dominant aspect of the approaches wasthe reading of taste based on ideology. In this approach, the reader encounters the text based on presuppositions and extratextual positions and deals with it as a passive object. In the readings from 1957 to the end of the 80s, due to the predominance of the discourse of reforms and distancing from the ideological discourse, the readers revised and reconsidered the previous readings in experiencing the effect of reading; the readings from the late 80s to the end of the 90s suggest a wide semantic horizon for this work, which is a result of the special narrative structure and textual signs specific to this work
The effect of green chemistry education based on practical activity on learning and attitude of pre-service chemistry teachers
No full textBackground and Objective:Chemistry plays a fundamental role in human civilization and its place in economics, politics and life is becoming more and more prominent and covers a wide range of chemical products such as drugs, dyes, fertilizers, etc. However, the environmental damage caused by it is a major human concern. Many of us today take steps to reduce environmental impact, for example by participating in chemical recycling programs and using energy-saving light bulbs; we buy local products and maybe drive hybrid cars. But what if "we could somehow prevent pollution from the start?" Thus, with a new approach called green chemistry, chemists are being led to a new phase of research activities to develop green reactions and use them instead of the old methods, to help human health and society by eliminating toxins from chemical processes. The purpose of this research is education of green chemistry through the curriculum related to the principles of green chemistry in General Chemistry Lab 1and the effect of this educational course on learning and attitude of the pre-service chemistry teachers toward green chemistry principles. Methods: This educational course involves two green experiments implemented according to green chemistry principles. The experiments include determination of molar mass relation in a chemical reaction and determination of the amount of ascorbic acid in a tablet of vitamin C. The research methods are practical, experimental and quasi-experimental and the used instruments were the researcher-constructed tests in the field of learning and attitude domain. Statistic population of this study consists of experimental group (N=30) and control group (N=30) of the student teachers at Shahid Rajaee Teacher Training University in the academic year 2017-2018. Data analysis was done using descriptive and inferential statistics with SPSS software. Findings: The obtained results show that among12 principles of Green Chemistry, students have learned the principles of 1 to 4 and 7 to 12 of these 12 principles and they have been attracted to them. In addition, the implementation of a curriculum related to the principles of green chemistry has had a positive impact on the attitude of the pre-service chemistry teachers. Conclusion: Findings from the research show that teaching the principles of green chemistry can be done based on the activity-oriented approach in the chemistry curriculum as in most developed countries. Student-teacher education can lead them to develop a positive attitude towards green chemistry and to have more motivation and desire to study chemistry based on the principles of green chemistry and to pass this attitude on to their students in the teaching process. Also, in designing the curriculum, it should be noted that in the sequence of practical activities, it should be done in such a way that it includes all the principles of green chemistry so that education based on it can give all the principles of green chemistry to learners or give them a positive attitude. ===================================================================================== COPYRIGHTS ©2019 The author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, as long as the original authors and source are cited. No permission is required from the authors or the publishers. ====================================================================================
Municipal solid waste management during COVID-19 pandemic: effects and repercussions
No full textThe COVID-19 pandemic has an adverse effect on the environment. This epidemic�s effect on the waste composition and management and the impacts of municipal solid waste management (MSWM) on disease transmission or controlling are considered a compelling experience of living in the COVID-19 pandemic that can effectively control the process. This systematic review research was conducted to determine the effects of COVID-19 on the quantity of waste and MSWM. Searches were conducted in three databases (using keywords covid 19, coronaviruses, and waste), and among the published articles from 2019 to 2021, 56 ones were selected containing information on the quantity and waste management during the COVID-19 pandemic. The results showed that COVID-19 caused the quantity variation and composition change of MSW. COVID-19 also has significant effects on waste recycling, medical waste management, quantity, and littered waste composition. On the other hand, the COVID-19 pandemic has changed waste compounds� management activities and waste generation sources. Recognizing these issues can help plan MSWM more efficiently and reduce virus transmission risk through waste. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
