50175 research outputs found
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Resolution of redundancy in robots and in a human arm
No full textThe author obtained his Ph. D. in 1986 under Professor Bernard Roth. In a publication from the research, it was shown that the redundant joints in a serial robot could be used to make the end-effector linear velocity distribution isotropic. In this work we revisit those results, present recent results on how redundancy is made use of in a human arm, and finally attempt to link the earlier work with new results. The human arm can be modeled as a redundant serial manipulator and the redundancy can be computed from the null-space of the Jacobian matrix. In a recent work, healthy adults were made to perform point-to-point reaching tasks in eight directions first without any disturbance, then with an applied force and finally with the force switched off. Statistical analyses show that trajectory and reaching errors due to the applied force die out with trials and subjects who explore the redundancy in the arm adapt faster to the external force. It is also shown that the anisotropy in the error distribution reduces with trials. These new results suggest that the redundancy in a human arm is used to reduce trajectory errors and anisotropy arising out of external disturbances. (C) 2017 Elsevier Ltd. All rights reserved
Symmetrized density matrix renormalization group algorithm for low-lying excited states of conjugated carbon systems: Application to 1,12-benzoperylene and polychrysene
No full textThe symmetry adapted density matrix renormalization group (SDMRG) technique has been an efficient method for studying low-lying eigenstates in one-and quasi-one-dimensional electronic systems. However, the SDMRG method had bottlenecks involving the construction of linearly independent symmetry adapted basis states as the symmetrymatrices in theDMRGbasis were not sparse. We have developed a modified algorithm to overcome this bottleneck. The newmethod incorporates end-to-end interchange symmetry (C-2), electron-hole symmetry (J), and parity or spin-flip symmetry (P) in these calculations. The one-to-one correspondence between direct-product basis states in the DMRG Hilbert space for these symmetry operations renders the symmetry matrices in the new basis with maximum sparseness, just one nonzero matrix element per row. Using methods similar to those employed in the exact diagonalization technique for Pariser-Parr-Pople (PPP) models, developed in the 1980s, it is possible to construct orthogonal SDMRG basis states while bypassing the slow step of the Gram-Schmidt orthonormalization procedure. Themethod together with the PPP modelwhich incorporates long-range electronic correlations is employed to study the correlated excited-state spectra of 1,12-benzoperylene and a narrow mixed graphene nanoribbon with a chrysene molecule as the building unit, comprising both zigzag and cove-edge structures
Two fold spin reorientation and field induced phase transition in Ho0.5Dy0.5FeO3 single crystal
No full textMagnetic measurements on oriented single crystals of Ho0.5Dy0.5FeO3 grown using optical floating zone furnace provide evidence for two spin reorientations of Fe3+ magnetic sublattice viz., Gamma(4) -> Gamma(1) -> Gamma(2) at temperatures T-SR1 = 49 K and T-SR2 = 26 K. As magnetic field along c axis increases, the sample resumes Gamma(4) spin configuration and a large field is likely to disrupt the spin reorientation process. It is evident from isothermal magnetization along c axis that field induced Gamma(1) -> Gamma(4) transition is feasible within the intermediate temperature range of T-SR1 - T-SR2 and can be triggered at a critical field. Such magnetic behavior is better understood as a consequence of anisotropic effective field, modified by the application of external magnetic field. (C) 2018 Elsevier B.V. All rights reserved
Effect of Tool Rotation Speed on Microstructure and Tensile Properties of FSW Joints of 2024-T351 and 7075-T651 Reinforced With SiC Nano Particle: The Role of FSW Single Pass
No full textFriction stir welding (FSW) dissimilar joints of aluminium alloys of 2024-T351 and 7075-T651 were produced by reinforcing silicon carbide nano particle (SiCNP) in the rectangular cut groove made on the adjoining surface of the two dissimilar alloy plates joined in the butt configuration. A FSW tool of taper threaded cylindrical shape is used for producing the FSW dissimilar joints reinforced with SiCNP in the weld nugget zone (WNZ) and to produce metal matrix nano composite (MMNC) at the WNZ. In the experimental investigation, the constant FSW tool traverse speed of 40 mm/min and tool plunge depth of 6.2 mm/min is kept as constant, while the FSW tool rotation speed was varied from 400 rpm to 1800 rpm. The effect continuous varying tool rotation speed range from 400 rpm to 1800 rpm along the weld length and on the distribution of SiCNP in WNZ is analysed by conducting macro and microstructure study using optical microscopy (OM) and scanning electron microscopy (SEM) provided with energy dispersive spectrometry (EDS). In the experimental investigation, the combination of continuous varying FSW tool rotation speed range from 900rpm to 1150 rpm, constant tool traverse speed range 40 mm/min and tool plunge depth of 6.2 mm results in defect free, proper distribution of SiCNP and highest tensile properties for the FSW dissimilar joints. The highest ultimate tensile strength (UTS) of 380 MPa and yield strength (YS) of 150 MPa was observed for the combination of FSW tool rotation speed of 1000 rpm and tool traverse speed of 40 mm/min. The increasing in FSW tool rotation speed above 1250 rpm results in non homogeneous distribution of SiCNP in WNZ, excessive flash in the weld crown area and shows decreasing tendency in the tensile properties of the FSW dissimilar weld joints produced with reinforcing the SiCNP in the WNZ
Analytic representations of m(K), F-K, m(eta), and F-eta in two loop SU(3) chiral perturbation theory
No full textIn this work, we consider expressions for the masses and decay constants of the pseudoscalar mesons in SU(3) chiral perturbation theory. These involve sunset diagrams and their derivatives evaluated at p(2) = m(P)(2) (P = pi, K, eta). Recalling that there are three mass scales in this theory, m(pi), m(K) and m(eta), there are instances when the finite part of the sunset diagrams do not admit an expression in terms of elementary functions, and have therefore been evaluated numerically in the past. In a recent publication, an expansion in the external momentum was performed to obtain approximate analytic expressions for m(pi) and F-pi, the pion mass and decay constant. We provide fully analytic exact expressions for m(K) and m(eta), the kaon and eta masses, and F-K and F-eta, the kaon and eta decay constants. These expressions, calculated using Mellin-Barnes methods, are in the form of double series in terms of two mass ratios. A numerical analysis of the results to evaluate the relative size of contributions coming from loops, chiral logarithms as well as phenomenological lowenergy constants is presented. We also present a set of approximate analytic expressions for m(K), F-K, m(eta) and F-eta that facilitate comparisons with lattice results. Finally, we show how exact analytic expressions for m(pi) and F-pi may be obtained, the latter having been used in conjunction with the results for F-K to produce a recently published analytic representation of F-K= F-pi
Solubility of trioctylmethylammonium chloride in supercritical carbon dioxide and the influence of co-solvents on the solubility behavior
No full textSolubility of trioctylmethylammonium chloride (TOMAC) in supercritical carbon dioxide (SCCO2) was measured at 313, 323 and 333 K with pressure ranging from 10 to 30 MPa. Solubilities (in mole fraction) ranged from 0.5 x 10(-5) to 12.7 x 10(-5) in the investigated region. Influence of co-solvents on the solubility of TOMAC was studied at 313 and 323 K. Among the four models employed for correlating solubility of TOMAC in neat SCCO2, association theory based on van Laar activity coefficient model resulted in average deviation of 2%, while use of other models resulted within 10%. Solubility data were found to be self-consistent based on the Mendez-Teja model. Two new models were developed for the ternary system (SCCO2 + co-solvent + liquid solute) based upon association theory along with the Wilson and van Laar activity coefficient models. These models successfully correlated solubility of TOMAC in SCCO2 + co-solvent with an average deviation of < 8%
Regulation of the gyr operon of Mycobacterium tuberculosis by overlapping promoters, DNA topology, and reiterative transcription
No full textDNA gyrase introduces negative supercoils into DNA to maintain topological homeostasis. The genes encoding gyrase, gyrB and gyrA, form a dicistronic operon in Mycobacterium tuberculosis (Mtb) and other actinobacteria. Earlier work indicated that DNA relaxation stimulates the expression of the gyr genes, a phenomenon termed relaxation-stimulated transcription (RST). The present study addresses the underlying mechanism of gyr operon regulation. The operon is regulated by overlapping and divergently oriented promoters located upstream of gyrB. The principal promoter, P-gyrB1, drives transcription of the operon, while a weak ``reverse'' promoter, P-gyrR, transcribes in opposite direction. We demonstrate that P-gyrR plays a role in fine tuning gyr gene expression by reiterative transcription (RT), a regulatory mechanism hitherto not found in Mtb. In vitro transcription assays showed that RT at P-gyrR depended on the negatively supercoiled state of the DNA template. The principal promoter, P-gyrB1, was also sensitive to DNA supercoiling, but it was stimulated by DNA relaxation. Moreover, RNA polymerase binding to the promoter was efficient at P-gyrB1 when template DNA was relaxed, whereas binding to P-gyrR was preferred when DNA was supercoiled. Thus, a collaboration between RST and RT governs the regulation of the gyr operon; the differing sensitivity of the two overlapping promoters to superhelix density explains how gyrase expression responds to changes in supercoiling to determine the efficiency of transcription initiation. (C) 2018 Elsevier Inc. All rights reserved
Conjugated Molecule Based Sensor for Microbial Detection in Water with E-coli as a Case Study and Elucidation of Interaction Mechanism
No full textWater testing for microbial contamination is essential to ensure safe drinking water. In the present work, an organic nanocomposite based sensor is designed and fabricated to detect the presence of E. coli in water. The detection is carried out by measuring the change in two parameters of the organic nanocomposite film - resistance and impedance. The lower detection limit of E. coli cell counts up to 10CFUmL(-1) and 10(7)CFUmL(-1) in 100mL test solution is observed by impedance spectroscopy and resistance change respectively. A conjugated molecule with a specific pendant amine group was used as the receptor moiety that can interact and exhibit affinity to the functional groups like carboxyl groups present on the outer membrane of the cell wall of the E. coli. The binding of E. coli cells to conjugated molecule was characterized by chemical, physical and structural properties. The electrostatic interaction between positively charged amine groups on conjugated molecule and negatively charged E. coli is utilized for sensing. This interaction is also observed to be acting as p-dopant to conjugated molecule which synergistically induces a change in electrical resistance in the composite. This work shows that the conjugated molecules designed with suitable moieties could be used for sensing microorganisms, when most sensors for detection of E. coli cells, use antibodies as detecting element
Lightweight Max Weight Scheduling Algorithms for Wireless Networks
No full textWe propose a class of binary queue length information based max-weight scheduling algorithms for wireless networks. In these algorithms, the scheduler, in addition to channel states, only needs to know when a link's queue length crosses a prescribed threshold. We show that these algorithms are throughput optimal. Further, we incorporate time-since-last service (TSLS) information to improve delay and service regularity of the scheduling algorithms while ensuring throughput optimality. We also perform simulations to illustrate throughput, delay and service regularity performance of the proposed algorithms
Generation of High-Resolution 12-Sided Voltage Space Vector Structure Using Low-Voltage Stacked and Cascaded Basic Inverter Cells
No full textThis paper proposes generation of a 15-level (14 concentric) dodecagonal voltage space vector structure (DVSVS) for a star connected induction motor drive. The proposed multilevel DVSVS is obtained by cascading two inverters, namely a primary and secondary inverter. The primary inverter is a five-level (5L) structure formed by stacking two three-level flying capacitors with individual reduced dc sources and the secondary inverter is also a 5L structure formed by cascading two capacitor-fed cascaded H-bridges (CHB). The active power is supplied by the primary inverter, while the secondary inverter acts as switched capacitor harmonics filter, and capacitors in the secondary inverter are balanced naturally irrespective of load power factor for entire modulation index. The high-voltage dc supply fed primary inverter is operated in quasi-square wave mode, while the high frequency switching is applied to low voltage CHBs, thus, reducing the overall switching loss. The proposed scheme gives the advantages of both DVSVS and multilevel structure, thus, making it one of the solutions for battery or stacked dc-fed applications. The paper also presents the experimental results as well as comparison study with the existing topologies to support the advantages of proposed scheme