Abstract

A multi-robotic exploration with the requirement of communication link to a fixed base station is presented in this paper. The robots organize themselves into roles of maintainers of communication (hinged robots or robot nodes) or explorers of the environment ensuring that every robot is in contact with the base station directly or through the hinged robots. A two phased strategy for the same is presented. The first phase is characterized by a recursive growth of trees that starts from the root node or the base station and then repeated from other nodes of the hitherto grown tree in a depth first fashion. The second phase constitutes the recursive tree growth invoked repeatedly from the frontier nodes. While the first phase rapidly explores areas around the base station in a concentric fashion, the second phase extends the depth of the explored area to increase the limits of coverage. The strategy is consistent in that none of the robots loose contact with the base station. Extensive simulations confirm the efficacy of the method and comparisons portray performance gain in terms of exploration time and absence of deadlocks vis-a-vis the few methods previously reported in the literature.

Abstract

Making the experience of e-learning more effective requires interactive and collaborative systems to be adaptive and customizable. Specialized learning systems tend to be monolithic and difficult to extend. We present an alternative approach, where we synthesize a customizable learning environment from existing tools (Trac, SVN, reST, SQLite). The system presents the student not just with content, but an immersive experience that allows both individual and group annotations, versioning of the student's work, custom querying, and a uniform markup language to store content. We report the motivation and design of such an environment. We demonstrate the use of this system and its ability to plug into other environments by showcasing a custom interactive workbook, built for teaching and learning the principles of programming.

Abstract

We present here three different approaches to the problem of modeling mathematically the concept of a non-deterministic mechanism. Each of these three approaches leads to a mathematical definition. We then show that all the three mathematical concepts are equivalent to one another. This insight gives us the option of approaching the wp-formalism of Dijkstra from a different viewpoint that is easier to understand and to teach.

Abstract

The objective of this work is to characterize certain important features of excitation of speech, namely, detecting the regions of glottal activity and estimating the strength of excita-tion in each glottal cycle. The proposed method is based on the assumption that the excitation to the vocal-tract system can be ap- proximated by a sequence of impulses of varying strengths. The effect due to an impulse in the time-domain is spread uniformly across the frequency-domain including at zero-frequency. We propose the use of a zero-frequency resonator to extract the characteristics of excitation source from speech signals by filtering out most of the time-varying vocal-tract information. The regions of glottal activity and the strengths of excitation estimated from the speech signal are in close agreement with those observed from the simultaneously recorded electro-glotto-graph signals. The performance of the proposed glottal activity detection is evaluated under different noisy environments at varying levels of degradation.

Abstract

Time dependent quantum dynamics and optimal control theory are used for selective vibrational excitation of the N6-H (amino N-H) bond in free adenine and in the adenine-thymine (A-T) base pair. For the N6-H bond in free adenine we have used a one dimensional model while for the hydrogen bond, N6-H (A)...O4(T), present in the A-T base pair, a two mathematical dimensional model is employed. The conjugate gradient method is used for the optimization of the field dependent cost functional. Optimal laser fields are obtained for selective population transfer in both the model systems, which give virtually 100% excitation probability to preselected vibrational levels. The effect of the optimized laser field on the other hydrogen bond, N1(A)...H- N3(T), present in A-T base pair is also investigated.

Abstract

We provide theoretical insights for the observed preference of cyclodimerization over intramolecular cyclization reactions in tetrahydrofuran amino acid using high level DFT quantum chemical methods, in the gas phase as well as in continuum solvent medium. Thermodynamic results obtained from Hessian calculations indicate the higher stability of intermolecularly cyclized dimer over intramolecularly cyclized monomer. NBO and AIM analysis also support the existence of additional stabilizing hydrogen bond interactions in intermolecularly cyclized products. Further justification for the presence of stabilizing interactions in intermolecularly cyclized products comes from the molecular electrostatic potentials and electron density surfaces.

Abstract

Conventionally optimal control theory [1, 2, 3] has been used in the theoretical design of laser pulses through the direct variation of the electric field of the laser pulse as a function of time. This often leads to designed laser pulses which contain a broad and seemingly arbitrary frequency structure that varies in time in a manner which may be difficult to realize experimentally. In contrast, in Genetic Algorithm (GA) approach, a few control parameters are used, which are actually available to the experimentalist. In this work, we investigate the possibility of using GA optimization methods in the theoretical design of laser pulses to bring about quantum state transitions in molecules. This allows us to select only a small limited number of parameters to vary and to choose these parameters so that they correspond to those available to the experimentalist. In this work, we apply our methods to the vibrational-rotational excitation of the HF molecule. We choose a small limited number of frequencies and vary only the associated electric field amplitudes and pulse envelopes. We show that laser pulses designed in this way can lead to very high transition probabilities. The mechanism of population transfer during the excitation process is investigated by projecting the laser driven nuclear wave function onto the eigenstates of the system. We have also investigated the possibility of photodissociation of HF molecule by climbing up the vibrational ladder using this genetic algorithm approach.

Abstract

Quantum optimal control theory along with time dependent quantum dynamics is used to control the nuclear motion in the hydrogen bonds of adenine-thymine (A-T) DNA base pair [1]. Optimal infrared laser pulses are designed for selective excitations of (a) single N-H


O hydrogen bond and (b) both N-H


O and N-H


N bonds simultaneously. The conjuagte gradient method is employed to optimize the constructed eld dependent grand functional. Optimal laser elds are realized which give more than 99% population transfer to the preselected vibrational states. The mechanism of population transfer during the vibrational excitation process is investigated by projecting the laser driven nuclear wavefunction onto the vibrational states of the system.

Abstract

Cyclic peptides incorporating a 5 membered ring such as furan mimic naturally occurring cyclic peptides[1]. The preferred conformation of linear and cyclic tripeptides incorporating such sugar amino acids depends on the stereochemistry at the chiral center. Control of stereochemistry at C position of amino ethyl furan carboxylic acid (AEFC) unit in the linear and cyclic tripeptides is investigated using structural parameters and energetics data obtained from density functional theory (DFT) based calculations at B3LYP/6-31G(d,p) level of theory. We found that R-isomer of AEFC unit prefers to form bond with its S-isomer. Thermodynamic analysis revealed that linear tripeptide formed by two R-configured isomers of AEFC and one S-configured isomer of AEFC (RRS or RSR linear) is more stable than that formed by three R-configured isomers of AEFC (RRR linear). It is found that the cyclic tripeptide formed by two R-configured isomers of AEFC and one S-configured isomer of AEFC, i. e., cyclic RRS product is formed with high yield than that formed by three R-configured isomers of AEFC (RRR cyclic) though cyclic RRR trimer is more stable than cyclic RRS trimer. This is substantiated by kinetic control of reactions leading to cyclic tripeptides from linear tripeptides. Using NBO analysis stabilizing interactions in all the linear and cyclic tripeptides are identified. Molecular electrostatic potential (MESP) surfaces of cyclic tripeptides provide insights of intramolecular hydrogen bond interactions. The MESP mapped electron density surfaces have shown the charge distribution around the cyclic peptides.

Abstract

Peptides incorporating 5 membered rings such as furan and tetrahydrofuran (THF) adopt secondary folding patterns and thus mimic natural peptides. The preferred conformation of linear and cyclized peptides incorporating sugar amino acids depends on the stereochemistry of at the chiral center. Control of stereochemistry of THF amino acid (TAA) in the structure of the linear tripeptide Boc-TAA-Leu-Val-OMe containing (2R,5S)-cis TAA, (2S,5R)-cis TAA, (2R,5R)-trans TAA and (2S,5S)-trans TAA is investigated using structural parameters and energetics data obtained from density functional theory (DFT) based calculations at B3LYP/6-31G(d,p) level of theory. We found that the conformations associated with -, - turn structures are stabilized by intramolecular hydrogen bonding interactions. Kinetic control of reactions leading to intra and inter molecular cyclization of tripeptide TAA-Gly-Gly containing (2S,5R)-cis TAA and (2S,5S)-trans TAA is studied at the same level of theory in gas phase[1]. We observe that kinetic control favors cyclodimerization instead of intramolecular cyclization. Theoretical study of reactions leading to linear and cyclic trimerization of backbone altered -peptide, i. e., amino ethyl furan carboxylic acid (AEFC) at the same level of theory have revealed the role of stereochemistry at C position of AEFC in the preferential formation of asymmetric RRS cyclic tripeptide formed by R-, R- and S- stereo isomers of AEFC.