Open-chain Systems Research Articles

Photophysical properties of four-membered BN3 heterocyclic compounds: theoretical insights.

Understanding the photochemistry of boron nitrogen (BN)-containing compounds is an important aspect to enhance the various optical and electronic applications. In this work, we have explored the structure, bonding, reactivity, electronic absorption (UV-Vis), and light harvesting efficiency (LHE) of a series of BN3 ring and open-chain systems. The frontier molecular orbitals (FMO) analysis found that ring systems have a low HOMO-LUMO energy gap as compared to the open-chain systems which insinuates the feasibility of ring systems in the optoelectronic materials. Also, the molecular electrostatic potential (MEP) maps have been computed to pursue the electrophilic and nucleophilic sites available at the surface of the compound. Interestingly, we have found that the open-chain compounds show more molecular charge distribution range rather than the ring compounds. The investigation of photophysical properties showed that the UV-Vis absorption significantly red-shifted in BN3 ring systems as compared to open-chain counterparts. Furthermore, light harvesting efficiency (LHE) was also found higher in the ring systems as compared to the BN3 open-chain systems. Moreover, the computed structural parameters are found well corroborated with the available X-ray data. Structures of all compounds were optimized by using density functional theory (DFT) method, with M06-2X/6-31G(d,p) level. All the calculations in this work are carried out in Gaussian 16 program package. GaussView6.1 software was used for the modeling of initial geometries and for the plotting of MEP plots. To account the solvent effect on geometries the polarized continuum model (PCM) was used and tetrahydrofuran (THF) taken as solvent. The NBO6.0 program (incorporated in G16 software) was used for the exploration of bonding nature and stabilization energies of B-N bond. The absorption spectra were simulated by using ORCA 4.2 program.

An Analytical Method for Sensitivity Analysis of Rigid Multibody System Dynamics Using Projective Geometric Algebra

Abstract The analytical sensitivity analysis, i.e., the analytical first-order partial derivatives of dynamical equations, is one key to improving descent-based optimization methods for motion planning and control of robots. This paper proposes an efficient algorithm that recursively evaluates the analytic gradient of the dynamical equations of a multibody system. The theory of projective geometric algebra (PGA) is used to generate the algorithm. It provides a systemic and geometrically intuitive interpretation for the multibody system dynamics, and the resulting algorithm is highly efficient, with concise formula. The algorithm is first applied to the open-chain system and extended for the cases when kinematic loops are contained. The runtime varying with respect to the degree-of-freedom (DOF) of the system is analyzed. The results are compared with that obtained from the algorithm based on spatial vector algebra (SVA) using open-source matlab codes. A 2DOF serial robot, a 3DOF robot with a kinematic loop and the PUMA560 robot are used for the validation of the minimum-effort motion planning, and it is verified that the proposed algorithm improves the efficiency.

Topological phase in a Kitaev chain with spatially separated pairing processes

The dynamic balance between pair creation and annihilation processes takes a crucial role to the topological superconductivity in the Kitaev model. Here we study the effect of spatial separation of creation and annihilation terms, i.e., sources and drains of pair are arranged alternatively. In this regard, a non-Hermitian Hamiltonian is naturally considered, which may possess complex energy branches. However, when the Bardeen-Cooper-Schrieffer pair excitation is only considered, the spectrum in such a subspace is fully real. In particular, the Zak phases extracted from the pair wave function are quantized and therefore able to characterize the different phases regardless of the breaking of time-reversal symmetry. For open chain system, the corresponding Majorana lattice is investigated. We find that although there are complex modes, all the edge modes have zero energy and obey the bulk-boundary correspondence. This results in the Kramer-type degeneracy of both the real and complex levels as a signature of the topologically nontrivial phase.

Evaluation of SSRT‐Test by Classical Gravimetric Analysis and Optical Topographic Measurement: A Comparative Study

AbstractTo establish a database of performance values in the small‐scale shock reactivity test (SSRT), common secondary explosives based on organic nitrates (e. g. PETN) and nitramines (e. g. RDX and HMX) as well as aromatic (e. g. TNT), heteroaromatic (e. g. TKX‐50 and MAD−X1) and open chain systems (e. g. FOX‐7) were investigated. The evaluation of the test results was carried out by two different methods. On the one hand, manually by weighing out the resulting dents with sand, and on the other hand, optically with the aid of a profilometer. The two analysis methods were compared and evaluated with respect to their absolute results and absolute as well as relative standard deviations.

Optimal design of adaptive robust control for a planar two-DOF redundantly actuated parallel robot

An adaptive robust control combined with a multi-objective parameter optimization method for a parallel robot under unknown uncertainty is proposed. In the active joint space, the model of the parallel robot can be obtained by combining the closed-chain constraint force and the open-chain system’s dynamic equation. Based on the Udwadia–Kalaba theory, the closed-chain constraint force imposed by the end effector can be calculated if no uncertainty. If there is uncertainty, we propose an adaptive robust control, based on a set of feasible design parameters, which guarantees deterministic performances, including uniform boundedness and uniform ultimate boundedness. To seek the optimal choice of the design parameters, among the feasible pool. We examine the system performance, which includes the transient performance, the steady state performance, and the control cost. By a fuzzy-theoretic D-operation, a performance index is formulated. The problem of choosing the optimal control parameters is equivalent to the problem of finding the minimum value of the performance index. An illustrative example demonstrates the superiority of the adaptive robust control. Mass uncertainty and external disturbance torque are introduced to test the effectiveness of the proposed control strategy.

Performance analysis for aerial-towing system

The dynamics of open chain systems have been widely investigated as a result of its increased applications such as aerial towing system, submerged towed cable applications, robot manipulators, and bio-mechanical applications. In this study, a practical engineering system, Mine Clearing Line Charge MICLIC system is taken as an example for an open chain system with accelerated end and varying number of segments. To validate the proposed model, a comparison between two different finite segment methods namely Kane’s method and Riccati transfer matrix method of linear multibody system (Riccati-MS-TMM) have been performed for a large open chain system. Results show that computational speed of Riccati-MS-TMM outperforms Kane’s method due to its huge matrix size to be solved. Then, using a predefined rocket motor total impulse, a parametric study has been performed on MICLIC system to illustrate the impact of different rocket motor thrust profiles on the resulted flight performance including the missile range, flight time, maximum tension applied on the rocket towing bridle, and the missile stability.

Amiaspochalasins A–H, Undescribed Aspochalasins with a C-21 Ester Carbonyl from Aspergillus micronesiensis

Amiaspochalasins A-H (1-8), eight undescribed aspochalasins, and trichalasin D (9), a known analogue, were isolated from the solid culture of Aspergillus micronesiensis. Compounds 1-9 are aspochalasins with a C-21 ester carbonyl, and their structures were determined by spectroscopic data, X-ray crystallographic analyses, electronic circular dichroism calculations, and chemical methods. The CH3-25 in compound 1 is located at C-16 rather than C-14 in the previously reported aspochalasins, endowing 1 with an unexpected carbon skeleton. Compounds 2 and 3 are the first examples of aspochalasins with an unprecedented 5/6/6/8 tetracyclic ring system. Compounds 4 and 5 are diastereomers of aspochalasins I and J, respectively. Compounds 6 and 7 are the first aspochalasins featuring a long open-chain system, and their absolute configurations were discussed by comparing the NMR data of the hydrolysis and methyl esterification products of 4 and 5. Compound 8 is an isomeride of 9. The cytotoxic and antimicrobial effects of 1-9 were tested.

Synthesis, Characterization, and Activity of a Triazine Bridged Antioxidant Small Molecule.

Metal-ion misregulation and oxidative stress continue to be components of the continually evolving hypothesis describing the molecular origins of Alzheimer's disease. Therefore, these features are viable targets for synthetic chemists to explore through hybridizations of metal-binding ligands and antioxidant units. To date, the metal-binding unit in potential therapeutic small molecules has largely been inspired by clioquinol with the exception of a handful of heterocyclic small molecules and open-chain systems. Heterocyclic small molecules such as cyclen (1,4,7,10-tetraazacyclododecane) have the advantage of straightforward N-based modifications, allowing the addition of functional groups. In this work, we report the synthesis of a triazine bridged system containing two cyclen metal-binding units and an antioxidant coumarin appendage inspired by nature. This new potential therapeutic molecule shows the ability to bind copper in a unique manner compared to other chelates proposed to treat Alzheimer's disease. DPPH and TEAC assays exploring the activity of N-(2-((4,6-di(1,4,7,10-tetraazacyclododecan-1-yl)-1,3,5-triazin-2-yl)amino)ethyl)-2-oxo-2H-chromene-3-carboxamide (molecule 1) show that the molecule is antioxidant. Cellular studies of molecule 1 indicate a low toxicity (EC50 = 80 μM) and the ability to protect HT-22 neuronal cells from cell death induced by Aβ + copper(II), thus demonstrating the potential for molecule 1 to serve as a multimodal therapeutic for Alzheimer's disease.

Adaptive Semi-Implicit Integrator for Articulated Mechanical Systems

This paper concerns the dynamic simulation of constrained mechanical systems in the context of real-time applications and stable integrators. The goal is to adaptively find a balance between the stability of an over-damped implicit scheme and the energetic consistency of the symplectic, semi-implicit Euler scheme. As a starting point, we investigate in detail the properties of a recently proposed timestepping scheme, which approximates a full nonlinear implicit solution with a single linear system, without compromising stability. This scheme introduces a geometric stiffness term that improves numerical stability up to a certain time-step size, but it does so at the cost of large mechanical dissipation in comparison to the traditional constrained dynamics formulation. Dissipation is sometimes undesirable from a mechanical point of view, especially if the dissipation is not quantified. In this paper, we propose to use an additional control parameter to regulate “how implicit” the Jacobian matrix is, and change the degree to which the geometric stiffness term contributes. For the selection of this parameter, adaptive schemes are proposed based on the monitoring of energy drift. The proposed adaptive method is verified through the simulation of open-chain systems.

Dynamic Behavior of Flexible Multiple Links Captured Inside a Closed Space

This work presents a systematic method for the dynamic modeling of flexible multiple links that are confined within a closed environment. The behavior of such a system can be completely formulated by two different mathematical models. Highly coupled differential equations are employed to model the confined multilink system when it has no impact with the surrounding walls; and algebraic equations are exploited whenever this open kinematic chain system collides with the confining surfaces. Here, to avoid using the 4 × 4 transformation matrices, which suffers from high computational complexities for deriving the governing equations of flexible multiple links, 3 × 3 rotational matrices based on the recursive Gibbs-Appell formulation has been utilized. In fact, the main aspect of this paper is the automatic approach, which is used to switch from the differential equations to the algebraic equations when this multilink chain collides with the surrounding walls. In this study, the flexible links are modeled according to the Euler–Bernoulli beam theory (EBBT) and the assumed mode method. Moreover, in deriving the motion equations, the manipulators are not limited to have only planar motions. In fact, for systematic modeling of the motion of a multiflexible-link system in 3D space, two imaginary links are added to the n real links of a manipulator in order to model the spatial rotations of the system. Finally, two case studies are simulated to demonstrate the correctness of the proposed approach.

A systematic method for the hybrid dynamic modeling of open kinematic chains confined in a closed environment

This work presents a systematic method for the dynamic modeling of multi-rigid links confined within a closed environment. The behavior of the system can be completely characterized by two different mathematical models: a set of highly coupled differential equations for modeling the confined multi-link system when it has no impact with surrounding walls; and a set of algebraic equations for expressing the collision of this open kinematic chain system with the confining surfaces. In order to avoid the Lagrangian formulation (which uses an excessive number of total and partial derivatives in deriving the governing equations of multi-rigid links), the motion equations of such a complex system are obtained according to the recursive Gibbs–Appell formulation. The main feature of this paper is the recursive approach, which is used to automatically derive the governing equations of motion. Moreover, in deriving the motion equations, the manipulators are not limited to planar motions only. In fact, for systematic modeling of the motion of a multi-rigid-link system in 3D space, two imaginary links are added to the \(n\)-real links of a manipulator in order to model the spatial rotations of the system. Finally, a 2D and a 3D case studies are simulated to demonstrate the effectiveness of the proposed approach.

Acyclic Pseudopeptidic Hosts as Molecular Receptors and Transporters for Anions

AbstractThe synthesis and characterization of different pseudopeptidic hosts derived from open chain systems with C2 and C3 symmetry has been achieved. These receptors are based on structures containing phenylalanine amino acid residues and amine, amide, urea and thiourea groups as the structural elements providing their capability to interact with anions. The transport of chloride and organic anions of biological relevance (L‐lactate, L‐maleate and L‐aspartate) through lipid bilayer membranes has been studied for these receptors. The chloride‐binding properties of the selected hosts have been studied in solution by NMR titrations. In addition, in order to rationalize the results, lipophilicity studies have been carried out. It has been observed that transport activity is affected by the nature of the aliphatic central spacer and the side chains, the most active receptors being 9b, derived from a tripodal precursor with the shortest aliphatic side chain and 3c, derived from a bis(amino amide) but having the longest spacer. These hosts are more selective for the anion chloride than for the studied organic anions.

Pseudo-cyclic structures of mono- and di-azaderivatives of malondialdehydes. Synthesis and conformational disentanglement by computational analyses.

Mono- and diaza-derivatives of malondialdehydes, namely 3-alkyl(aryl)amino-2-arylacroleins and 1,5-dialkyl(aryl)-3-arylvinamidines are open-chain systems in which extended electron delocalization and pseudoaromaticity can be envisaged. A set of diversely functionalized compounds has been synthesized and characterized by spectroscopic data and X-ray diffractometry. Quantum-chemical calculations were performed for all possible neutral tautomers and conformers in the gas phase and compared to those in polar solvents (CHCl3, DMSO, and EtOH) at the M06-2X/6-311++G(d,p) level. Tautomeric equilibria and conformational preferences can be rationalized in terms of structural factors, which can be roughly estimated as summation or subtractions of intramolecular interactions. As expected, a key role is played by intramolecular hydrogen bonds whose strength varies from the gas phase to polar ethanol. This issue also delves into the concept of resonance-assisted H-bond, where the donor and acceptor atoms are connected by a π-conjugated system. The most stable conformers (structures a and c) possess a high degree of pseudoaromaticity as inferred from HOMA indexes and other delocalization parameters.

The CUIK Suite: Analyzing the Motion Closed-Chain Multibody Systems

Many situations in robotics require the analysis of the motions of complex multibody systems. These are sets of articulated bodies arising in a variety of devices, including parallel manipulators, multifingered hands, or reconfigurable mechanisms, but they appear in other domains too as mechanical models of molecular compounds or nanostructures. Closed kinematic chains arise frequently in such systems, either due to their morphology or due to geometric or contact constraints to fulfill during operation, giving rise to configuration spaces of an intricate structure. Despite appearing very often in practice, there is a lack of general software tools to analyze and represent such configuration spaces. Existing packages are oriented either to open-chain systems or to specific robot types, which hinders the analysis and development of innovative manipulators. This article describes the CUIK suite, a software toolbox for the kinematic analysis of general multibody systems. The implemented tools can isolate the valid configurations, determine the motion range of the whole multibody system or of some of its parts, detect singular configurations leading to control or dexterity issues, or find collision- and singularity-free paths between configurations. The toolbox has applications in robot design and programming and is the result of several years of research and development within the Kinematics and Robot Design group at IRI, Barcelona. It is available under GPLv3 license from http://www.iri.upc.edu/cuik.

Application of the MEBDFV solver to dynamic simulation of some specific multibody systems: an example of a cervical spine model

Application of the MEBDFV code in multibody dynamics is discussed. The solver is based on the modified extended backward differentiation formulae of Cash. It is especially suited for the solution of differential-algebraic equations with time- and state-dependent mass matrix. Such a case can occur when motion of a multibody open-chain system is described within the classical Lagrangian formalism, which still has some advantages. An outline of the numerical algorithm is given. As an example, a simplified mathematical model of the human head-cervical spine system is presented. In a numerical experiment the model is used to analyze motion of the head–neck during rear-end impact which may lead to whiplash injury. The obtained results are compared to literature data. Performance of the MEBDFV solver is examined in terms of algorithmic energy conservation. The test is based on an appropriately formulated ‘kinetic energy–work’ relation.

Optimal spring balancing of robot manipulators in point-to-point motion

SUMMARYThe balancing of robotic systems is an important issue, because it allows significant reduction of torques. However, the literature review shows that the balancing of robotic systems is performed without considering the traveling trajectory. Although in static balancing the gravity effects on the actuators are removed, and in complete balancing the Coriolis, centripetal, gravitational, and cross-inertia terms are eliminated, but it does not mean that the required torque to move the manipulator from one point to another point is minimum. In this paper, “optimal spring balancing” is presented for open-chain robotic system based on indirect solution of open-loop optimal control problem. Indeed, optimal spring balancing is an optimal trajectory planning problem in which states, controls, and all the unknown parameters associated with the springs must be determined simultaneously to minimize the given performance index for a predefined point-to-point task. For this purpose, on the basis of the fundamental theorem of calculus of variations, the necessary conditions for optimality are derived that lead to the optimality conditions associated with Pontryagin's minimum principle and an additional condition associated with the constant parameters. The obtained optimality conditions are developed for a two-link manipulator in detail. Finally, the efficiency of the suggested approach is illustrated by simulation for a two-link manipulator and a PUMA-like robot. The obtained results show that the proposed method has dominant superiority over the previous methods such as static balancing or complete balancing.

Highly Diastereo- and Enantioselective Tandem Reaction toward Functionalized Pyrrolidines with Multiple Stereocenters

An efficient asymmetric tandem dual Michael reaction that constructs three contiguous stereocenters in acyclic open-chain systems with very high enantioselectivity and diastereoselectivity has been developed. This protocol provides a reliable and rapid approach for synthesis of chiral pyrrolidines with multiple stereocenters.

ChemInform Abstract: From Furan to Open-Chain Systems. Studies Towards the Synthesis of Tylonolide

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dynamic Model of an Astronaut Equipped with a Manned Maneuvering Unit in Virtual Reality

A virtual reality simulation system for a manned maneuvering unit (MMU) and a training system for an astronaut space walk is introduced. The system can simulate an astronaut’s outer space walk by means of manipulating the MMU, and it also can be used as a training environment by taking advantage of virtual reality properties of imagination, interaction, and immersion. As in microgravity space, an astronaut’s moving limbs cause changes in the MMU posture; these changes result in great offsets to correct direction and have a great effect on the MMU’s manipulation performance. A multibody astronaut model is developed by using relative coordinates according to the motion characteristics of an astronaut equipped with MMU. Motion information on the user’s limbs are captured by means of a motion capture subsystem and are mapped to an astronaut in virtual environment to simulate the astronaut’s limb motions while the astronaut is navigating in outer space. It is an open-chain system for an astronaut multibody mod...

String order and hidden topological symmetry in the SO(2n + 1) symmetric matrix product states

We have introduced a class of exactly soluble Hamiltonian with either SO(2n + 1) or SU(2) symmetry, whose ground states are the SO(2n + 1) symmetric matrix product states. The hidden topological order in these states can be fully identified and characterized by a set of nonlocal string order parameters. The Hamiltonian possesses a hidden (Z2 × Z2)n topological symmetry. The breaking of this hidden symmetry leads to 4n degenerate ground states with disentangled edge states in an open chain system. Such matrix product states can be regarded as cluster states, applicable to measurement-based quantum computation.