37,537 research outputs found
Autonomous attitude using potential function method under control input saturation
The potential function method has been used extensively in nonlinear control for the development of feedback laws which result in global asymptotic stability for a certain prescribed operating point of the closed-loop system. It is a variation of the Lyapunov direct method in the sense that here the Lyapunov function, also called potential function, is constructed in such a way that the undesired points of the system state space are avoided. The method has been considered for the space applications where the systems involved are usually composed of the cascaded subsystems of kinematics and dynamics and the kinematic states are mapped onto an appropriate potential function which is augmented for the overall system by the use of the method of integrator backstepping. The conventional backstepping controls, however, may result in an excessive control effort that may be beyond the saturation bound of the actuators. The present paper, while remaining within the framework of conventional backstepping control design, proposes analytical formulation for the control torque bound being a function of the tracking error and the control gains. The said formulation can be used to tune to the control gains to bound the control torque to a prescribed saturation bound of the control actuators
Effects of the Electronic Structure, Phase Transition and Localized Dynamics of Atoms in the Formation of Tiny Particles of Gold
In addition to the self-governing properties, tiny metallic colloids are the
building blocks of larger particles. This topic has been a subject of many
studies. Tiny particles of different sizes developed under three different
experiments are discussed in this work. The development of a tiny-sized
particle depends on the attained dynamics of atoms. When atoms of the compact
monolayer assembly bind by a nanoenergy packet, the developed tiny-sized
particle elongates atoms of arrays into the structures of smooth elements at
the solution surface. The impinging electron streams at a fixed angle can
elongate the already elongated atoms of arrays. Travelling photons along the
interface influence the modified atoms. Gold atoms can also develop different
tiny particles inside the solution. In addition to the dynamics of atoms,
miscellaneous factors can contribute in the development of such tiny particles.
Atoms in the form of tiny clusters can also amalgamate to develop a tiny-sized
particle. In the third kind of tiny particle, amalgamated atoms can bind by
executing electron dynamics. However, not all of the atoms can bind by the
electron dynamics. This study very concisely highlights the fundamental process
of developing a variety of tiny particles in which electronic structure, phase
transition and localized dynamics of gold atoms influence the structure. The
study targets the specific discussion that how atoms of tiny-sized particles
bind, and how travelling photons along the air-solution interface influence
their structure. Several possibilities may be opened through pulse-based
process to develop engineered materials
Large angle reorientation manoeuvre of spacecraft using robust backstepping control
The nonlinear control design problem for large angle reorientation manoeuvre of
spacecraft has a proper structure for the direct application of backstepping design as
its dynamics and kinematics are naturally in a cascade form. In this paper, the
robustness of the backstepping control against the uncertainties in the moment of
inertia matrix is investigated and a sufficient condition for the robust stability is
derived. Numerical simulations show the validity of the condition
Polymer packaging and ejection in viral capsids: shape matters
We use a mesoscale simulation approach to explore the impact of different
capsid geometries on the packaging and ejection dynamics of polymers of
different flexibility. We find that both packing and ejection times are faster
for flexible polymers. For such polymers a sphere packs more quickly and ejects
more slowly than an ellipsoid. For semiflexible polymers, however, the case
relevant to DNA, a sphere both packs and ejects more easily. We interpret our
results by considering both the thermodynamics and the relaxational dynamics of
the polymers. The predictions could be tested with bio-mimetic experiments with
synthetic polymers inside artificial vesicles. Our results suggest that phages
may have evolved to be roughly spherical in shape to optimise the speed of
genome ejection, which is the first stage in infection.Comment: 4 pages, 4 figure
Antitumor studies. Part 4: Design, synthesis, antitumor activity, and molecular docking study of novel 2-substituted 2-deoxoflavin-5-oxides, 2-deoxoalloxazine-5-oxides, and their 5-deaza analogs
Various novel 10-alkyl-2-deoxo-2-methylthioflavin-5-oxides and their 2-alkylamino derivatives were prepared by facile nitrosative cyclization of 6-(N-alkylanilino)-2-methylthiopyrimidin-4(3H)-ones followed by nucleophilic replacement of the 2-methylthio moiety by different amines, and acidic hydrolysis of the 2-methylthio moiety afforded the corresponding flavin derivatives. 2-Deoxo-2-methylthio-5-deazaalloxazines and 2-deoxo-2-methylthioalloxazine-5-oxides were also prepared by Vilsmeier reaction and by nitrosation of 6-anilino-2-methylthiopyrimidin-4(3H)-ones, respectively. Then, they were subjected to nucleophilic replacement with appropriate amines to produce the corresponding 2-alkylamino derivatives. Regiospecific N-3-alkylation of 2-deoxo-2-methylthioalloxazine-5-oxides was carried out with various alkylating agents in the usual way, The antitumor activities against CCRF-HSB-2 and KB tumor cells have been investigated in vitro, and many compounds showed promising antitumor activities. Furthermore, AutoDock molecular docking into PTK (PDB: 1t46) has been done for lead optimization of the aforementioned compounds as potential PTK inhibitors
Josephson effect in mesoscopic graphene strips with finite width
We study Josephson effect in a ballistic graphene strip of length smaller
than the superconducting coherence length and arbitrary width . We find that
the dependence of the critical supercurrent on is drastically
different for different types of the edges. For \textit{smooth} and
\textit{armchair} edges at low concentration of the carriers decreases
monotonically with decreasing and tends to a constant minimum for a
narrow strip . The minimum supercurrent is zero for smooth edges
but has a finite value for the armchair edges. At higher
concentration of the carriers, in addition to this overall monotonic variation,
the critical current undergoes a series of peaks with varying . On the other
hand in a strip with \textit{zigzag} edges the supercurrent is half-integer
quantized to , showing a step-wise variation with
.Comment: 4 pages, 3 figure
Bubble Nucleation of Spatial Vector Fields
We study domain-walls and bubble nucleation in a non-relativistic vector
field theory with different longitudinal and transverse speeds of sound. We
describe analytical and numerical methods to calculate the orientation
dependent domain-wall tension, . We then use this tension to
calculate the critical bubble shape. The longitudinally oriented domain-wall
tends to be the heaviest, and sometime suffers an instability. It can
spontaneously break into zigzag segments. In this case, the critical bubble
develops kinks, and its energy, and therefore the tunneling rate, scales with
the sound speeds very differently than what would be expected for a smooth
bubble.Comment: version 4, correction in the citation
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