110 research outputs found
Ab-initio Modeling and Designing of Materials for Thermoelectrics, Optoelectronics and High Temperature Applications
No full textDesigning a material for a particular application requires an atomistic understanding of its
properties. Recent development in first principles methods and supercomputing speeds has
enabled researchers to compute materials properties accurately. This has opened up a window
for computational designing of materials for various applications such as optoelectronics,
thermoelectrics, magnetic shape memory alloys etc. In this thesis, first principles methods
have been utilized to understand the properties of various materials such as TiS2, TiS3, GeO2,
Co3(MoTaAl) alloys, Ni2MnGa and graphene. This thesis has been organized as follows:
• Chapter 1 introduces various functional materials and their application in the thermoelectric,
optoelectronic, high temperature and magnetic shape memory. The microscopic
understanding of materials properties such as structure, energetics, electronic structure,
electronic transport, and lattice dynamics etc. can lead to novel ways of designing materials
properties for various applications.
• Chapter 2 describes the theoretical methodology adopted in this work. It gives a brief
understanding of first principles based density functional theory (DFT) and various approximations
to obtain accurate electronic properties. Methods employed for calculation
of electronic and thermal transport are also discussed briefly.
• In Chapter 3 we explore the tuning of the electronic structure of the transition metal
dichalogenide TiS2. We show that by engineering its electronic structure, it transforms
from a semimetal to a semiconductor under biaxial strain. The thermoelectrics study
shows that a 3 fold enhancement in thermopower can be achieved by application of 5%
biaxial strain. This enhancement is driven by a small bandgap opening of ∼0.15 eV, which
increases its thermopower at the same time decreasing its lattice thermal conductivity
indicating improvement in ZT.
• In Chapter 4 we study the possibility of inherent stacking fault in bulk TiS3 and its effect
on the electronic properties. We find that TiS3 can exist in AB′ and AB′′ geometries. The
energy difference between two structures is about 0.011 eV/f.u. The electronic structure
is independent of the stacking fault due to the weak vdW interaction between the layers.
The calculated thermopower is 200 μV/K in the carrier concentration range of 1×1020
cm−3 - 5×1020 cm−3, which is comparable with other state of the art thermoelectric
materials. The high thermopower and electrical conductivity in the carrier concentration
range of 1×1020 cm−3 - 5×1020 cm−3 leads to a high power factor for both p- and n-type.
Moreover, the power factor for p-type is three times higher than that of n-type carriers
indicating that the thermoelectric performance for p-type will be much better than that
of n-type.
• Chapter 5 reveals the origin behind the large variation in the band gap (∼ 2 eV) of
GeO2 calculated by standard DFT within LDA/GGA, which had remained unresolved.
Using the many-body perturbation theory (GW approximation), we find that this large
variation observed in literature is independent of the method used and depends strongly
on the lattice parameter (volume strain). This strong dependence originates from a change
in hybridization among O-p and Ge-(s and p) orbitals.
• Chapter 6 deals with the structural stability of order intermetallic Co-based superalloys.
We have shown that W free Co3Al order structure can be stabilized in L12 structure by
addition of Mo and Ta atoms. The enthalpy of formation of L12 structure significantly
becomes more negative compared to the DO19 structure by the addition of ≥ 4% of Ta
atoms. This implies that the L12 structure of Co3(Al,Mo,Ta) structure is more stable
compared to DO19. The lowering in the enthalpy of formation is found due to the formation
of the pseudo gap and the decrease in the states at the pseudo gap with increasing Ta
concentration. The stability of the L12 structure can be further improved by the addition
of Ni and Ti atoms.
• In Chapter 7, the lattice dynamics and electronic structure of X2YZ [where X = Ni,
Fe, Co; Y = Mn; Z = Al, Ga, Ge, In, Sn, Sb] stoichiometry compounds are investigated.
The lattice instability of X2MnZ depends on the position of the Fermi energy (EF ) with
respect to the pseudo gap. The phonon mode softening along the Γ-K symmetry direction
is observed for Ni2MnZ in the austenite phase since EF is located above the pseudo gap.
This mode softening is mainly responsible for the MSM effect. On the other hand, Fe2MnZ
and Co2MnZ [Z = Al, Ga, Ge, In, Sn, Sb] in the cubic phase do not show any phonon
mode softening because EF lies in the vicinity of the pseudo gap or at the pseudo gap.
Thus, alloying Fe or Co at the Ni site in Ni2Mn (Z = groups-IV and V) can tune the lattice
modulation. In addition, the magnetic moments of Fe2Mn (Z = groups-IV and V) and
Co2Mn (Z = groups-IV and V) are much higher than those of Ni2Mn (Z = groups-IV and
V), indicating that the magnetic moments of Ni2MnZ can be enhanced. The calculated
phonon dispersion with magnetic moment indicates that the phonon mode softening is
sensitive to the change in the local magnetic moment of the atoms, thereby enabling
tunability in the MSM effect.
• In chapter 8, we show that the mono vacancy defects in graphene can be used as precursors
to form novel clipped structures without explicit use of functional groups. These
clipped structures can be transformed into one-dimensional (1D) double wall nanotubes
(DWCNT) or multi-layered three dimensional (3D) structures. The clipped structures
show good mechanical strength due to covalent bonding between multi-layers. Clipping
also provides a unique way to simultaneously harness the conductivity of both walls of
a double wall nanotube through covalently bonded scattering junctions. With additional
conducting channels and improved mechanical stability, these clipped structures can lead
to a myriad of applications in novel devices.
• Chapter 9 summarizes and concludes the work presented in this thesis
On the role of head motion in affective expression
Get PDFNon-verbal behavioral cues, such as head movement, play a significant role in human communication and affective expression. Although facial expression and gestures have been extensively studied in the context of emotion understanding, the head motion (which accompany both) is relatively less understood. This paper studies the significance of head movement in adult's affect communication using videos from movies. These videos are taken from the Acted Facial Expression in the Wild (AFEW) database and are labeled with seven basic emotion categories: anger, disgust, fear, joy, neutral, sadness, and surprise. Considering human head as a rigid body, we estimate the head pose at each video frame in terms of the three Euler angles, and obtain a time-series representation of head motion. First, we investigate the importance of the energy of angular head motion dynamics (displacement, velocity and acceleration) in discriminating among emotions. Next, we analyze the temporal variation of head motion by fitting an autoregressive model to the head motion time series. We observe that head motion carries sufficient information to distinguish any emotion from the rest with high accuracy and this information is complementary to that of facial expression as it helps improve emotion recognition accuracy
Emotion sensing from head motion capture
Get PDFComputational analysis of emotion from verbal and non-verbal behavioral cues is critical for human-centric intelligent systems. Among the non-verbal cues, head motion has received relatively less attention, although its importance has been noted in several research. We propose a new approach for emotion recognition using head motion captured using Motion Capture (MoCap). Our approach is motivated by the well known kinesics-phonetic analogy, which advocates that, analogous to human speech being composed of phonemes, head motion is composed of kinemes i.e., elementary motion units. We discover a set of kinemes from head motion in an unsupervised manner by projecting them onto a learned basis domain and subsequently clustering them. This transforms any head motion to a sequence of kinemes. Next, we learn the temporal latent structures within the kineme sequence pertaining to each emotion. For this purpose, we explore two separate approaches – one using Hidden Markov Model and another using artificial neural network. This class-specific, kineme-based representation of head motion is used to perform emotion recognition on the popular IEMOCAP database. We achieve high recognition accuracy (61.8% for three class) for various emotion recognition tasks using head motion alone. This work adds to our understanding of head motion dynamics, and has applications in emotion analysis and head motion animation and synthesis
Novel Approaches for Offline Data-Driven Evolutionary Multiobjective Optimization
No full textMost multiobjective evolutionary algorithms (MOEAs) assume that analytical functions or simulation models are available while solving a multiobjective optimization problem (MOP). However, in some cases we must start with data and build approximation models known as surrogates that are later used to solve the MOP by an MOEA. These types of problems are called data-driven MOPs. This
thesis is devoted to solving so-called offline data-driven MOPs that are particularly challenging as no new data is available during the optimization process.
The author first presents approaches to utilize the uncertainty in the prediction of Kriging or Gaussian process (GP) surrogates as additional objectives. However, these approaches increase the complexity of the MOP being solved. Hence, the author proposes probabilistic selection approaches that can be embedded in a decomposition-based MOEA without further analytical derivations.
These approaches utilize Monte Carlo sampling and kernel density estimation to calculate the probability of selection criterion of the MOEA and later select individuals based on them. Next, the author proposes an interactive optimization framework that utilizes decision maker’s preferences for uncertainties in addition to preferences for objective values. The framework was further extended to use probabilistic selection approaches for a decomposition-based MOEA and a custom reference vector adaptation technique to consider uncertainty in the solutions during the adaptation process.
Building GPs with all the provided data becomes computationally expensive when the size of the data is large. Hence, the author finally proposes treed GP surrogates for multiobjective optimization (TGP-MO). They can be built with a relatively low computational cost and have a good accuracy exclusively in the regions around the optimal solutions. This thesis provides multiple novel approaches
and detailed experimental studies for solving offline data-driven MOPs with decision support that will enhance real-world problem-solving capabilities.
Keywords: metamodelling, surrogates, Pareto optimality, Kriging, Gaussian processes, evolutionary algorithm, decision making, uncertainty, interactive methods, preference informationunknown accessibilityei tietoa saavutettavuudest
A brief description of the writings, author and period of composition etc. in the family memoir book/ পারিবারিক স্মৃতিলিপি পুস্তকে লেখা, লেখক ও রচনাকাল প্রভৃতির সংক্ষিপ্ত বিবরণ
No full textThe Proverbial Professor Pasupati Sasmal once researched the family memoirs of Jorasanko Thakurbari. Mainly following his research, a brief list of various writings including serial number, title of part of the first line, author, period of composition, page of manuscript etc. is presented here. This is the first part of the given description. The second part of it is as follows: After writing No.105, the list and description (in the second part) of all the remaining writings which are not given serial numbers are also given. Interested Rabindra-inquisitors can know almost all the information at a glance from this list
Enantiopure 1,4,5-trisubstituted 1,2,3-triazoles from carbohydrates: applications of organoselenium chemistry
No full textA wide range of stable vinyl selenone-modified furanosides has been synthesized for the first time. These 2π-partners undergo 1,3-dipolar cycloaddition reactions with a wide range of organic azides to afford enantiopure trisubstituted triazoles. Furanosyl rings opened up during triazole synthesis to generate polyfunctionalized molecules, ready to undergo further transformations. This strategy is one of the most convenient methods for the synthesis of enantiopure 1,4,5-trisubstituted 1,2,3-triazoles where the chiral components are attached to C-4 or C-5 position of triazole ring. These triazoles are formed in a regioselective manner, and several pairs of regioisomeric triazoles have also been synthesized. The approach affords densely functionalized triazoles, which are amenable to further modifications because of the presence of aldehyde and hydroxyl groups. This powerful and practical route adds to the arsenals of chemists and biologists interested in the synthesis and applications of triazoles
Ultra-sensitive pressure dependence of bandgap of rutile-GeO2 revealed by many body perturbation theory
No full textThe reported values of bandgap of rutile GeO2 calculated by the standard density functional theory within local-density approximation (LDA)/generalized gradient approximation (GGA) show a wide variation (similar to 2 eV), whose origin remains unresolved. Here, we investigate the reasons for this variation by studying the electronic structure of rutile-GeO2 using many-body perturbation theory within the GW framework. The bandgap as well as valence bandwidth at Gamma-point of rutile phase shows a strong dependence on volume change, which is independent of bandgap underestimation problem of LDA/GGA. This strong dependence originates from a change in hybridization among O-p and Ge-(s and p) orbitals. Furthermore, the parabolic nature of first conduction band along X-Gamma-M direction changes towards a linear dispersion with volume expansion. (C) 2015 AIP Publishing LLC
ChemInform Abstract: Enantiopure 1,4,5‐Trisubstituted 1,2,3‐Triazoles from Carbohydrates: Applications of Organoselenium Chemistry.
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