Arnab Maity

Generalized Model Predictive Static Programming and Angle-Constrained Guidance of Air-to-Ground Missiles

A new generalized model predictive static programming technique is presented for rapidly solving a class of finite-horizon nonlinear optimal control problems with hard terminal constraints. Two key features for its high computational efficiency include one-time backward integration of a small-dimensional weighting matrix dynamics, followed bya static optimization formulation that requires only a static Lagrange multiplier to update the control history. It turns out that under Euler integration and rectangular approximation of finite integrals it is equivalent to the existing model predictive static programming technique. In addition to the benchmark double integrator problem, usefulness of the proposed technique is demonstrated by solving a three-dimensional angle-constrained guidance problem for an air-to-ground missile, which demands that the missile must meet constraints on both azimuth and elevation angles at the impact point in addition to achieving near-zero miss distance, while minimizing the lateral acceleration demand throughout its flight path. Simulation studies include maneuvering ground targets along with a first-order autopilot lag. Comparison studies with classical augmented proportional navigation guidance and modern general explicit guidance lead to the conclusion that the proposed guidance is superior to both and has a larger capture region as well.

Orientation of a TICT probe trapped in the peripheral confined water created by ionic surfactant envelope around silver nanoparticles.

Ionic surfactants are known to aggregate around the surface of a nanoparticle as a single layer in premicellar and a double layer in micellar concentrations. This motif of arrangement indicates the development of a layer of confined water of lower polarity than bulk water around the surface of the nanoparticle. We have demonstrated the behavior of a twisted intramolecular charge transfer (TICT) probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT), in the confined aqueous layer developed at the surface of spherical silver nanoparticles (Ag NPs) at and above the critical micellar concentrations (CMC) of a cationic and an anionic surfactant, namely, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). It is observed that the presence of charged surfactant head groups affects DMASBT differentially in the ground and the excited states. In presence of CTAB, DMASBT turns over in the excited state and interacts with the Ag NP surface, whereas in SDS the probe remains in its original orientation during the interaction. Steady-state and time-resolved fluorescence spectral studies provide enough evidence for orientation of the TICT probe in the peripheral water of Ag NP created by the surfactants. The results were confirmed by steady-state anisotropy measurements. The data show the difference between the properties of the confined peripheral water and the bulk aqueous environment. The TICT probe, DMASBT, is proved to be an excellent marker for the phenomenon.

Incorporation of Coumarin 6 in cyclodextrins: microcrystals to lamellar composites

Coumarin 6 precipitates in water as microcrystals resulting in a considerable loss in fluorescence yield. Differential interaction of the microcrystals with cyclodextrins of different cavity size enhances the fluorescence yield of the dye by 160 fold in some cases. Highly fluorescent ultrathin lamellar entities form through hydrogen bonding.

Higher order direct model reference adaptive control with generic uniform ultimate boundedness

This paper proposes a new higher order model reference adaptive control (HO-MRAC) approach following direct adaptive control philosophy, which estimates unknown time-varying parameters. This approach leads to a Lyapunov based conventional MRAC update law, augmented by an observer type parameter predictor dynamics. The predictor dynamics are composed of a stable known part, a feedback of the parameter error and unknown higher order parameters, which are updated using a Lyapunov based adaptive design. So, this HO-MRAC can cope with rapidly changing parameters, due to estimation of their time derivatives. Moreover, for stability analysis, a Lyapunov based generic ultimate boundedness theorem is presented, which allows for a computation of separate bounds for each state vector partition. Furthermore, this theorem formulates the explicit specification of transient and ultimate bounds, reaching time on the ultimate bounds and a set of admissible initial conditions. Two challenging illustrative examples demonstrate the effectiveness of the proposed approach.

Cyclodextrin cavity size induced formation of superstructures with embedded gold nanoclusters

L-cysteine double layer protected gold nanoclusters (Au NCs) have projected thiol groups that induce hydrophobicity around the NCs attracting the relatively hydrophobic cavities of cyclodextrins (CDs) to accumulate around. The different sizes of the CDs result into different accumulating patterns to form spherical to cuboid aggregates with embedded Au NCs.

Modulation of energy/electron transfer in gold nanoclusters by single walled carbon nanotubes and further consequences.

Semiconductor or metallic character in single-walled carbon nanotubes (SWCNTs) is developed because of their chirality and diameter. Depending upon the extent of these characters in a particular sample of SWCNT, various electronic and mechanical applications are formulated. In this work we used protein protected red emitting gold nanoclusters (AuNCs) to enhance the metallic character in SWCNTs through electron transfer induced by photonic excitation. The AuNCs have been synthesized following a known protocol that generates Au(+) protected Au(0) clusters. Normal and carboxylic acid functionalized SWCNTs were obtained commercially for usage in the experiments. The non-functionalized SWCNTs facilitate intersystem electron transfer while the functionalized ones defer the phenomenon, which, in turn, affects the metallic character in the nanotubes. Steady state and time resolved fluorescence spectroscopy prove the dynamics and electrochemistry supports the intersystem electron transfer process.

Effect of environment pH on the photophysics of fisetin in solid lipid nanoparticles

Photophysical modulation of fisetin has been extensively studied in bulk aqueous as well as solid lipid nanoparticles (SLN) by varying the pH of the medium. The solution pH was varied from 5 to 9 to mimic biological environments. Neutral and anionic forms of fisetin coexist in ground state in both acidic and alkaline conditions. However, in the excited state and at low pH, the anionic form of fisetin predominates over the proton transferred form, whereas in SLNs, the proton transferred form is the major emitting species. Higher pH showed enhancement in anionic emission to different extent in the two types of environments. Limited percolation of H(+) and OH(-) ions inside the SLNs that host fisetin molecules controls their photophysics. The experimental results encourage usage of fisetin as a drug depending on the ratio of the neutral and anionic as well as the proton transferred forms under various pH conditions.

[2,2′-Bipyridyl]-3,3′-diol in lipid vesicles: slowed down dynamics of proton transfer

(2,2′-Bipyridyl)-3-3′-diol [BP(OH)2] is a well-known compound that undergoes double proton transfer (DPT) that has been previously described as an intramolecular and excited state event in neat solvents and certain constrained environments. Herein, we have explored the interaction of BP(OH)2 with small unilamellar vesicles synthesized using two kinds of lipids, dimyristoyl-L-α-phosphatidylcholine (DMPC) and dimyristoyl-L-α-phosphatidylglycerol (DMPG), which are zwitterionic and anionic, respectively. BP(OH)2 is observed to undergo the formation of a monoketo and a diketo species in sequence along with the creation of dianions aided by the lipid membranes. Interestingly, in the present work, we could witness the formation of the dianionic species under neutral conditions in the presence of lipid vesicles. Moreover, the dynamics of the monoketo species could also be observed as the lipid vesicles supposedly slowed down the overall rate of proton transfer in BP(OH)2. In spite of monitoring in different emitting regions of the spectrum of BP(OH)2 in liposomes, no growth component was observed in the time-resolved fluorescence data. This indicates that in the presence of lipid vesicles all the subsequent species from the parent neutral probe develop in the ground electronic state.

Light induced dynamics of a charge transfer probe in lipid vesicles

Distribution of a model twisted intramolecular charge transfer (TICT) probe in zwitterionic lipid vesicles of variable interior water pool sizes has been studied using steady state and time resolved fluorescence spectroscopy. This has been achieved by preparing unilamellar vesicles of different sizes, viz., small (SUVs), large (LUVs) and giant (GUVs) in water. The characteristic fluorophore shows an hypsochromic shift of 65 nm in its emission maximum in SUVs compared to bulk water, whereas in GUVs and LUVs this shift is ∼58 nm. The decay profiles of the fluorescence probe are found to be comprised of three components in SUVs, LUVs and GUVs that could be due to the distribution of the molecule in the hydrophobic bilayer and the water molecules at the bulk and inner aqueous environments of the DPPC vesicles, respectively. This study indicates that TICT probes have specific distribution patterns in ground and excited states depending upon the size of the internal water pool of the lipid vesicles. Thus, the in vitro studies with these biomimicking lipid systems put forward the possible behaviour of such characteristic small molecules in biological cells.

Formation Flying of Satellites with G-MPSP Guidance

Using the recently developed generalized model predictive static programming (GMPSP) technique, a suboptimal guidance logic is proposed in this paper for formation flying of satellites. Unlike many available techniques, the proposed guidance scheme is valid both for high eccentricity chief satellite orbits as well as large separation distance between chief and deputy satellites. Moreover, since the G-MPSP can rapidly solve a class of finite-horizon nonlinear optimal control problems with hard terminal constraints, the final accuracy level is very high. The key feature of this technique is one-time backward propagation of a small-dimensional weighting matrix dynamics, which is used to update the entire control history. This key feature, as well as the fact that it leads to a static optimization problem, lead to its high computational efficiency. The proposed guidance scheme has been tested successfully for a variety of initial conditions and formation commands as well. Comparison with standard linear quadratic regulator solution (which serves as a guess solution for G-MPSP) reveals that G-MPSP guidance achieves the objective with lesser amount of control usage as well.