621 research outputs found
Corrigendum: Planning for livelihoods under hydrosocial uncertainty in periurban Pune(Front. Water, (2022), 4, (831464), 10.3389/frwa.2022.831464)
No full textIn the published article, there was an error in the author list, and authors “Sharlene L. Gomes, Shreya Chakraborty, and Leon M. Hermans” were erroneously excluded. The corrected author list appears below. “Sarah Luft Faculty of Mathematics and Natural Sciences, Institute for Geography, University of Cologne, Cologne, Germany Sharlene L. Gomes Faculty of Governance and Global Affairs, Institute of Public Administration, Leiden University, The Hague, Netherlands Shreya Chakraborty South Asia Consortium for Interdisciplinary Water Resources Studies, Hyderabad, India Leon M. Hermans Faculty of Technology, Policy, and Management, Delft University of Technology, Delft, Netherlands and Land andWaterManagement Department, IHE Delft Institute forWater Education, Delft, Netherlands.Policy Analysi
Electronic characterization of mass-selected acyclic, polycyclic and oxygenated hydrocarbons in neon matrices
Get PDFInterstellar chemistry embarked with the discovery of CH, CH+, and CN in extraterrestrial clouds. Presently, a large number of molecules have been identified in different galactic environments mostly by millimeter-wave and infrared spectroscopy. Molecular complexity and the spectral features dramatically depend on the particle density and the temperature of the astronomical region where they reside. Hence, spectroscopic analysis of extraterrestrial molecules has a valid mean to probe the physical and chemical condition and history of galactic media.
Life on Earth is carbon based and surprisingly, similar tendency has been found in interstellar molecules. Almost 80 percent of detected species contain carbon as a major constituent. Hence, a better characterization of the molecular universe may elucidate the origin of terrestrial life.
Two long standing riddles in molecular astrophysics are the diffuse interstellar absorption lines in the visible and the broad emission features in the mid-infrared. Carbonaceous systems ranging from small acyclic to polycyclic aromatics are considered to be the carriers of these absorption and emission bands. To recognize individual molecules responsible for these transitions, spectroscopic analysis of astrophysically relevant species in the laboratory is needed; comparison studies between astronomical measurements and laboratory spectra are the way for identification. These exotic molecules may be stable in galactic clouds under very cold and low density conditions but are extremely short-lived in the laboratory framework. Therefore, noncontemporary synthesizing and sensitive characterizing methods are required.
The matrix isolation spectroscopy is considered as an outdated-technique after the discovery of laser-based experiments but in combination with theory, it still serves a pivotal role in characterization of transient species. Exotic organics are synthesized in electrical discharge for the respective precursors. The ions of interest are co-deposited with neon on a cold surface (6 K) after mass-selection. Neutrals are generated in the matrix by UV irradiation.
The acyclic unsaturated organics possess very unique structural flexibility. By mass selective deposition of a particular m/z ratio in solid neon, several isomers have been detected. An advantage of the matrix isolation technique is that all possible electronic transitions of trapped species in the experimental measurement range can be recorded at once. Rare gases provide an environment in which the guest-host interactions slightly perturb the experimental band positions as compared to the gas-phase. Still matrix isolated spectrum is a good starting point for high resolution study and thence astrophysical findings.
Moderately intense absorptions are observed both in the visible and UV for C7Hn+/0 and C5Hn+/0, and charged oxygen containing polycarbon chains H2C6O+, HC7O+, and C4O2+ in neon matrices. The structural assignments of the electronic systems have been made on the basis of calculated ground-state stabilities with DFT and MP2 level of theory and computed excitation energies with TD DFT, SAC-CI, and CASPT2 methods. However, some of these ions and radicals have strong possibility to be the carriers of diffuse interstellar bands. The neutral oxygenated hydrocarbons are excluded as the carriers because no transition was detected after irradiation of the matrix. Theory explains that they possess strong transition in the deep UV. In addition, protonated PAHs and their oxygen containing analogs, which are credited for unidentified emission features, have been studied. Strong optical transitions suggest that they could be carriers of diffuse interstellar bands as well. A key species in combustion chemistry likely responsible for PAHs formation via mass-growth processes, fulvenallenyl radical, has been electronically characterized.
A part of this dissertation is devoted to physical organic chemistry. Reaction intermediates are too short-lived to probe. Nevertheless, identification of these species helps to infer a probable synthetic mechanism. Vibrationally resolved electronic spectra of fluorenylium, phenalenylium and fluorenyl radical have been measured in a neon matrix.
This electronic transition database of transient molecules created in the thesis can be used for their further gas-phase analysis and in situ detection in reaction or combustion systems
TWO-PROTON PHOTOTAUTOMERIZATION DYNAMICS OF 7-AZAINDOLE COMPLEXES
No full textAuthor Institution: Department of Physical Chemistry, Indian Association for the cultivation of science, Calcutta 700032, India.E-mail: [email protected] tautomerization of 7-azaindole in doubly hydrogen-bonded dimeric complexes is one of the extensively investigated photoisomerization processes in recent years. The reaction, in the case of homodimer, takes place with equal ease in non-polar liquids at room temperature as well as in a cold supersonic jet expansion. A lot of studies were devoted arguing whether the double proton transfer occurs sequentially or in a concerted manner. Over the past three decades it has been assumed, on the basis of the observations of some low-temperature photophysical measurements, the double proton exchange barrier of the dimer is . However, we notice that such measurements are flawed by artifact; the apparent barrier depends on sample concentration in the solutions. The tautomerization of the isolated dimer is found stopped at 10 K in an argon matrix, and we propose that the double proton exchange is coupled with the large amplitude hydrogen bond vibrations. Furthermore, the process in several complexes of the molecule with pyrazole and amides displays remarkable contrasts with that of the homodimer. While the tautomerization in the former cases occurs extremely efficiently in hydrocarbon solutions, is hindered fully in supersonic jet expansion condition.The observations also imply that the effective barrier of phototautomerization in the complexes is intimately correlated with the details of double proton transfer mechanism. The details of our findings along with the predictions of some electronic structure calculations will be presented in the talk. References: \\begin{enumerate} \item "Ultraviolet and infrared spectroscopy of matrix-isolated 7-azaindole dimer: Matrix effect on excited state tautomerization", M. Mukherjee, B. Bandyopadhyay and T. Chakraborty, Chem. Phys. Lett. 546, 74-79 (2012). \item "Excited State Tautomerization of 7-Azaindole in a 1:1 Complex with -Valerolactam: A Comparative Study with the Homodimer", M. Mukherjee, S. Karmakar and T. Chakraborty, J. Phys. Chem. A, 116, 9888-9896 (2012). \item "Excited state tautomerization of 7-azaindole catalyzed by pyrazole", S. Karmakar, M. Mukherjee and T. Chakraborty, Chem. Phys. Lett. 561-562, 46-51 (2013). \\end{enumerate
Real-Time AMPC for Loss Reduction in 48 V Six-Phase Synchronous Motor Drives
No full textThis article presents an adaptive model predictive control (AMPC) algorithm for real-time management of a six-phase permanent magnet synchronous motor. The system optimizes both speed control and power dissipation, featuring an automated power derating mechanism for overload conditions. AMPC demonstrated advantages over traditional field-oriented control, including reduced losses and lower energy consumption, while maintaining robust performance and high speed control precision. Validation through hardware-in-the-loop testing on the dSPACE platform confirmed its effectiveness. The contribution focuses on enhanced stability, robustness, and integrating predictive features to further improve efficiency and adaptability in electric drive systems. © 2025 The Author(s). IET Power Electronics published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
Shivram Chakraborty\u27s Short Stories: An expression of the seriousness of life behind the humor/ শিবরাম চক্রবর্তীর ছোটগল্প : হাস্যরসের অন্তরালে জীবনের গাম্ভীর্যের বহিঃপ্রকাশ
No full textSibram Chakraborty is popular as a children\u27s literature and humorist, but several of his stories have been written for adults as well. Besides, he has highlighted the serious issues of life behind the humor in many stories. The deep feelings of life are served under the cover of humor in various works of Sibram. Sibram’s own life has always been a sad one and many tragic aspects of his own life find their place in his writings. Though In his personal life he went through many ups and downs, but these things he never expressed directly in his writings. However, it was because of these ups and down and tragic aspects of his life deep and profound words have been emerged behind the smile in his writings. He even made fun of himself through self-criticism.
Sibram Chakraborty in many of his stories has covered various serious issues under the cover of humor, for example, in a short story named ‘Jibandarshan’, he has shown that life is not limited to the educated and polite society, but life is also flowing in the dark alleys every day. Even if the people of the so-called polite society do not accept them, they are also part of this society. In the ‘Prajapatya’ short story, Sibram criticizes the dowry system through his scathing remarks. In the short story named ‘Shur-Ola Baba!’ he showed the results of honesty. Although at the end of the story due to Satyapriyababu\u27s honesty his life become painful.
Sibram wrote more humorous genre short stories, but many of the humorous stories purpose is not just to make people laugh, but through jokes, the author expresses the deep reality of life and society. Sibram’s own thought, vision and style of writing set him apart from other writers
Three essays on using text analytic techniques for accounting research
No full textThe wide variety of corporate as well as academic documents accessible online provides tremendous opportunities for data collection but at the same time presents a challenge for users to extract appropriate information from this immensely diverse corpus. Financial decisions are often based on different types of reports provided by firms including the financial statements as well as disclosures. To ensure simplified access to critical information from these reports data tagging is recommended, which creates the need for the development of taxonomies. A hybrid method of taxonomy creation using historical data from pension footnotes of 10K statements is proposed here instead of the pre-existing normative approach (detailed in the first essay). A comparison of the hybrid vs. normative approach (XBRL) pension footnote taxonomy reveals that generally firms tend to aggregate more while reporting, conflicting with findings from the XBRL pension taxonomy. Two experiments are conducted within the fold of the second essay to recognize whether (i) the type of industry (ii) firm size are factors significantly influencing the pension disclosure reporting of firms. It is found that while firm size is a significant factor the type of industry is not. Corporate reports as well as academic accounting literature are experiencing an unprecedented proliferation. The third essay explores the potential of using text analytic techniques to develop a methodology for automatic classification of academic articles in accounting based on different criteria. Three different experiments were conducted to seek the most effective method to accurately and automatically classify accounting literature. Results from the experiments indicate that automatic classification is more effective when using abstracts rather than using only keywords. Proposing a new hybrid method for taxonomy creation as well as the initial study that adopts automatic classification method in categorizing accounting literature by predetermined taxonomy classes is a contribution to accounting information systems literature. Understanding the impact of industry type and firm size on pension disclosure is a contribution towards accounting literature. Future research could be conducted with increased size of data corpuses, by experimenting with more advanced methods to replace all the manual steps with complete automation.Ph. D.Includes bibliographical referencesIncludes vitaby Vasundhara Chakrabort
Single-molecule fluorescence analysis of opening and closing of the RNA polymerase clamp
No full textCrystal structures of RNA polymerase (RNAP) indicate that the RNAP β’ pincer (“clamp”) can exist in conformational states, ranging from a fully open conformation that permits entry and exit of DNA, to a fully closed conformation that prevents entry and exit of DNA. It has been hypothesized that the clamp also adopts multiple conformational states in solution and conformational changes in the clamp are important for function. In this work, a single-molecule fluorescence resonance energy transfer (smFRET) approach was developed that enables determination of RNAPclamp conformation in solution. smFRET was measured between a probe at the tip of the RNAP clamp and a probe at a fixed reference point in RNAP. A computational framework was then employed to interpret measured FRET efficiencies in terms of structural changes. Using this approach, RNAP clamp conformation was defined in each step of 70-dependent transcription initiation and elongation and in each step in σ54-dependent transcription initiation. Additionally, effects of four RNAP inhibitors, myxopyronin, corallopyronin, ripostatin and Gp2 on RNAP clamp conformation were assessed. It was observed that the clamp is predominantly open in free RNAP and in all steps leading up to the formation of a catalytically-competent-transcription-initiation complex. Upon formation of a catalytically-competent-transcription-initiation complex, the clamp closes, and continues to remain closed during transcription elongation. It was further observed that myxopyronin, corallopyronin, ripostatin and Gp2, prevent opening of the RNAP clamp. The results lead to the proposal that, the open clamp state is important for entry of DNA into, and unwinding of DNA in, the RNAP active center cleft during formation of a catalytically-competent-transcription initiation complex. The results lead to the proposal that, after entry of DNA into the RNAP active-center cleft upon formation of the catalytically competent transcription initiation complex, electrostatic interactions between the negatively charged DNA and the positively charged inner facet of the clamp, induce and/or stabilize clamp closure. The results are in agreement with the proposal that, clamp closure is important for stability of the catalytically competent transcription initiation complex and for stability and processivity of the transcription elongation complex.Ph. D.Includes bibliographical referencesby Anirban Chakrabort
Object category recognition through visual-semantic context networks
No full textUnderstanding and interacting with one’s environment requires parsing the image of the environment and recognizing a wide range of objects within it. Despite wide variations, such as viewpoint, occlusion and background clutter, humans can achieve this task effortlessly and almost instantaneously. In this thesis, we explore computational algorithms that teach computers to recognize objects in natural scenes. Inspired by the findings in human cognition, our algorithms are based on the notion that visual inference involves not only recognizing individual objects in isolation but also exploiting rich visual and semantic associations between object categories that form complex scenes. We view artificial object recognition as a fusion of information from two interconnected representations. The first is the inter-image representation in which an image location is visually associated with previously learnt object categories based on appearance models to find the most likely interpretations. The second is the intra-image representation in which the objects in an image are semantically associated with each other to find the most meaningful spatial and structural arrangements. The two representations are interconnected in that the visual process proposes object candidates to the semantic process, while the semantic process verifies and corrects the visual processs hypotheses. The primary goal of this thesis is to develop computational models for visual recognition that characterize the visual and semantic associations and their inter-dependencies to resolve object identities. In order to do so, we model object associations in contextual spaces. Unlike traditional approaches for object recognition that use context as a postprocessing filter to discard inconsistent object labels, we stratify scene generation into a Bayesian hierarchy and simultaneously learn semantic and visual context models for objects in scenes. The semantic-visual contexts among objects are represented through latent variables in this hierarchy. The intra-image associations within a scene are modeled as semantic context while the inter-image relations due to appearance similarities between object categories are modeled as visual context. To combine the complementary information derived from the two spaces, object labels are inferred by context switching; labels activated by appearance matches constrain semantic search while semantic coherence, in turn, constrains object identities. We demonstrate how this novel context network for modeling associations between objects leads to highly accurate object detection and scene understanding in natural images, especially when training data is impoverished and negative exemplars are not easily available.Ph. D.Includes bibliographical referencesby Ishani Chakrabort
Design development and experimental investigation of adsorption cooling cum desalination
No full textWith the increasing need for access to fresh water, desalination can be considered as one of the solution to this problem. However, conventional desalination methods, such as reverse osmosis, are energy intensive and they bring about negative environmental impacts. Adsorption desalination (AD) is an emerging low cost thermal desalination method which utilises waste heat to produce two useful effects, the cooling of space and fresh water production. This report presents on the work done by the author in the design development and experimental investigation of AD systems in NTU. The report begins with an introduction to the theory of Adsorption and basic AD cycle, which is then followed by a literature survey on the past studies done on various type of adsorbents, AD systems and formulations to predict the water uptake of AD cycle. The author also reviewed the report of a previous Final Year Project on the design of a two evaporator system by Lee [1] in order to propose modifications to his design. Firstly, the author added an additional inlet to the adsorption bed cylinder to cater for the two evaporators in the system. The heat exchanger used in the adsorption bed is redesigned to provide a more stable structure. As part of the development work, the author also reported on the installation phases of this AD system. Then, experimental investigations on the performance of zeolite-based commercial adsorption chiller, in terms of specific water production, were performed. By varying the driving temperature, the author was able to estimate the specific water production of the system using a proposed formulation by Sun and Chakraborty [2]. Through the analysis of the results, it is found that the specific water production curves display a cyclic trend and the specific water production peaks at approximately 0.07 kg water/ kg zeolite at a driving temperature of 75°C. Finally, recommendations were made to modify the commercial chiller to ease data collection and also solve the water leakage issue of the chiller. Recommended operating parameters for water production were also given to improve the reliability and accuracy of the results.Bachelor of Engineering (Mechanical Engineering
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