Cyclic Configuration Research Articles

Initial pyrolysis of perhydroacenaphthene conformers: A multi-scale simulation and experimental analysis

The enduring quest for a fuel that embodies both high density and superior heat sink capacity has been a long-standing goal within the scientific community. Perhydroacenaphthene (PHAN) fuels, characterized by five-membered ring structure that enhances density, also serve as hydrogen donors to inhibit coking, showcasing significant potential in fuel applications. Given their "strain-free" cyclic configuration, PHAN fuels manifest diverse conformations like chair, boat, and twist, among others, each influencing fuel properties and subsequently affecting pyrolysis process and the utilization of heat sink. In this work, leveraging the five preferred PHAN conformers substantiated by experiments, we embarked on a comprehensive investigation into their microstructures, properties, pyrolysis behavior, and initial pyrolysis mechanisms combining with molecular simulation and experimental analysis. Among them, interaction region indicator (IRI) analysis was employed to elucidate the differences in density. Upon this foundation, taking trans-trans-trans and cis-cis-cis PHAN with minimum and maximum density as models, the effects of different conformations on the initial pyrolysis reaction were explored by micro-pyrolysis system attached to an online GC-MS/FID strategy. It was found that compared to the trans-trans-trans conformation, the cis-cis-cis conformation manifested superior initial pyrolysis activity and more substantial heat sink capacity. Moreover, upon delving into the reaction mechanism and microkinetic analysis, it became evident that the favored initial reaction type of PHAN pyrolysis was H-abstraction reaction, and cis-cis-cis PHAN presented a lower barrier and a faster reaction rate than trans-trans-trans. Additionally, in conjunction with the calculation of free energy barrier and reaction heat of numerous reactions, the kinetic and thermodynamic dominances for the initial pyrolysis pathways of trans-trans-trans and cis-cis-cis PHAN were identified. Finally, utilizing intermolecular interaction energy (ΔE), independent gradient model based on Hirshfeld partition (IGMH) and Xiamen energy decomposition analysis (XEDA), the microscale justification for cis-cis-cis PHAN conformation displaying superior initial pyrolysis activity was further unveiled. This endeavors pioneer innovative pathways for the directional development and application of PHAN conformers.

Combined effect of Ag element and temperature gradient on the formation of highly orientated Sn grains in micro solder joints

Sn–Ag solders are widely used for advanced electronic packaging. The combined effect of Ag element and temperature gradient (TG) on the formation of Sn grains in Cu/Sn-xAg/Cu micro solder joints was elucidated systematically. Numerous small-sized β-Sn grains were formed in both Cu/Sn/Cu and Cu/Sn-0.5Ag/Cu micro solder joints after reflow with or without TG. The Cu/Sn-0.5Ag/Cu joint was found to have more twinning β-Sn structures. The formation of the multiple β-Sn grains in these two joints was attributed to the presence of multiple tetrahedral metastable short-range order (SRO) structures which acted as nuclei for the nucleation and growth of β-Sn. The existence of TG slightly enhanced the preferred orientation characteristics of Sn grains. For the joints with Ag content was or higher than 2 wt%, several Sn grains were formed without TG, while a single or highly oriented Sn grains were observed with TG. The number and orientation of Sn grains were affected by the combined effect of Ag element and TG significantly. The β-Sn grains formed without TG were based on the {101} type cyclic twinning configuration clusters that stabilized by Ag atoms and acted as nuclei. The formation of a single or highly preferred β-Sn grains was benefit from the combined effect of Ag element and TG. The results provide theoretical guidance for optimizing the composition of Sn–Ag solders and controlling the microstructure of the joints, thereby contributing to the advancement of electronic packaging technologies.

Motion properties of the variable mass smallest body in cyclic kite configuration with kerr-like oblate heterogeneous primaries

The aim of this paper is to motion of the smallest body in the 5-body problem where 4 bodies construct the cyclic kite configuration. Out of five bodies four bodies are placed at the vertices of a cyclic kite and the shapes of these bodies are considered as oblate heterogeneous with the supposition that these bodies are spinning around their own axes. It is also supposed that the smallest and fifth body is varying its mass according to Jeans law. The motion of smallest body is also affected by the coriolis and centrifugal forces. The equations of motion are determined under the above said perturbations. And then we numerically illustrated the locations of fixed points, their stability, the zero-velocity surfaces with projections and Poincare surfaces of section.

Generalisation of a synchronous solution of the parity problem on cyclic configurations over a non-circulant graph

The parity problem is a classical binary benchmark for addressing the computational ability and limitations of automata networks. It refers to conceiving a local rule to allow deciding whether the number of 1-states in the nodes of an arbitrary network is an odd or even number, without global access to the nodes. In its standard formulation, the automata network has an odd number of nodes whose states, arranged as a cyclic configuration, should converge to a fixed point of all 0s, if the initial configuration has an even number of 1s, or to a fixed point of all 1s, otherwise. It has been shown that a local rule alone is able to solve the problem in this formulation, including a synchronous solution we have recently shown, totally based on the local parity rule of the cellular automata elementary space (number 150), with a certain pattern of connection between the nodes. Here, we generalise this solution, showing how to construct many others, combining rule 150 with rules 170 and 240, which are the local shifts of the same space, in such a way that the original solution is just one among countless possibilities. Such solutions may have different convergence times for specific configurations, but are equivalent in the context of all configurations of a given size; also, various solutions form symmetric pairs, in terms of the actual rules they used. The solutions were evaluated computationally and presented here without their formal proofs, but empirical evidences strongly suggest that they can be obtained by the same kind of technique we used in the solution exclusively with rule 150.

First-Principles Investigation of the Optical Properties of Eumelanin Protomolecules.

Using first-principles calculations, we investigate the absorption spectra (in the near-infrared, visible, and first UV range) of the two most probable eumelanin tetrameric molecules exhibiting either a linear open-chain or a cyclic porphyrine-like configuration. In order to simulate a realistic molecular system, an implicit solvent model is used in our calculations to mimic the effect of the solvated environment around the eumelanin molecule. Although the presence of solvent is found not to significantly affect the absorption pattern of both molecules, the onset of the spectra are shifted toward higher energies, especially for the linear tetramer. Interestingly, the absorption spectra and optical onsets of the two molecules differ significantly both in a vacuum and in ethanol. However, the two predicted spectra do not allow us to definitely discriminate between the two configurations when comparing the theoretical predictions with the available experimental spectrum. In addition, a mix of the two eumelanin configurations (close to fifty-fifty) leads to a maximum overlap between theoretical and experimental spectra. Consequently, this theoretical research shows that deeper insight can be gained using beyond DFT techniques on the real form of eumelanin protomolecules present in living systems as well as on their possible use in hybrid solar cells.

Hydrodynamic investigation of a parabolic breakwater for wave energy focusing

The integration of wave energy converters (WECs) with a breakwater can reduce construction and maintenance costs and enhance the energy conversion performance of WECs. Intelligent use of a parabolic breakwater to focus water waves to a specific region can significantly increase the available wave energy. However, the theoretically calculated focal point of a parabolic breakwater may not always coincide with the observed wave focusing position. To determine the actual position of the focal point for installing the WEC, both numerical simulations and experimental research are conducted to investigate hydrodynamic characteristics of the parabolic breakwater. The realized focal point is found to be located at a position separated from the theoretical position, and its location varies with the incident wavelength. The underlying cause of this behavior is identified and investigated. The effects of chord length, parabolic wall aspect ratio, and incident wave directions on the wave amplitude at the focal point are examined. It is found that the shift in the actual focusing position exhibits a cyclic configuration as the incident wavelength changes, with the observed focal point revolving around the theoretical focal point. The position of the recorded focal point is determined by the interaction between the incident and reflected wave crests. The wave amplitudes at the theoretical focal point reaches their maxima when the focal lengths are nearly equal to integer multiples of half incident wavelength. The wave amplitudes at both the theoretical and observed focal points are shown to magnify with increasing chord length and with decreasing focal length. The parabolic wall is demonstrated to consistently maintain a substantial focusing effect for incident wave angles up to 15°.

Rigidity transitions in zero-temperature polygons.

We study geometrical clues of a rigidity transition due to the emergence of a system-spanning state of self-stress in underconstrained systems of individual polygons and spring networks constructed from such polygons. When a polygon with harmonic bond edges and an area spring constraint is subject to an expansive strain, we observe that convexity of the polygon is a necessary condition for such a self-stress. We prove that the cyclic configuration of the polygon is a sufficient condition for the self-stress. This correspondence of geometry and rigidity is akin to the straightening of a one dimensional chain of springs to rigidify it. We predict the onset of the rigidity transition and estimate the transition strain using purely geometrical methods. These findings help determine the rigidity of an area-preserving polygon just by knowing its geometry. Since two-dimensional spring networks can be considered as a network of polygons, we look for similar geometric features in underconstrained spring networks under isotropic expansive strain. We observe that all polygons attain convexity at the rigidity transition such that the fraction of convex, but not cyclic, polygons predicts the onset of the rigidity transition. Acyclic polygons in the network correlate with larger tensions, forming effective force chains.

On-Surface Debromination of C6Br6: C6 Ring versus C6 Chain

Carbon allotropes comprising sp-hybridized carbon atoms have been investigated for decades for their molecular structure. One of the unsolved mysteries is whether they should take a linear or cyclic configuration in condensed phases due to the lack of atomistic characterizations. Herein, we designed a molecule with a C6 skeleton as a model system to address this issue, which was achieved by eliminating Br atoms from hexabromobenzene (C6Br6) molecule on the Ag(111) substrate via thermal treatment. It is found that the C6 ring intermediate resulting from complete debromination is energetically unstable at room temperature based on theoretical calculations. It subsequently transforms into the C6 polyynic chain via a ring-opening process and ultimately polymerizes into the organometallic polyyne, whose triyne structural unit is revealed by bond-resolved noncontact atomic force microscopy. Theoretical calculations demonstrated an energetically favorable pathway in which the ring-opening process occurs after complete debromination of C6Br6. Our study provides a platform for the synthesis of elusive carbon-rich materials.

Nonreciprocal transition between two indirectly coupled energy levels

We propose a theoretical scheme to realize nonreciprocal transition between two energy levels that can not coupled directly. Suppose they are coupled indirectly by two auxiliary levels with a cyclic four-level configuration, and the four transitions in the cyclic configuration are controlled by external fields. The indirectly transition become nonreciprocal when the time reversal symmetry of the system is broken by the synthetic magnetic flux, i.e., the total phase of the external driving fields through the cyclic four-level configuration. The nonreciprocal transition can be identified by the elimination of a spectral line in the spontaneous emission spectrum. Our work introduces a feasible way to observe nonreciprocal transition in a wide range of multi-level systems, including natural atoms or ions with parity symmetry.

Non-covalent interactions in small thiophene clusters

Theoretical understanding of the thiophene solvent is subjected to the knowledge of the structures and the interactions taking place in thiophene clusters. Despite the importance of the thiophene clusters in understanding the thiophene solvent, there are not many reported studies on thiophene clusters. In this work, we have performed quantum chemical computations to understand the nature and number of non-covalent interactions that stabilize the structures of the thiophene clusters. For this purpose, we have started by exploring the potential energy surfaces (PESs) of the thiophene dimer, trimer, and tetramer, using classical molecular dynamics in order to generate initial guessed structures. These generated structures were then optimized at the MP2/aug-cc-pVDZ level of theory. As a result, it is found that the thiophene dimer prefers the sandwich/stacking configuration over the T-shaped configuration while for the thiophene trimer, only the cyclic configuration has been located. After locating the stable structures of the thiophene dimer, trimer and tetramer, we have performed a quantum theory of atoms in molecules (QTAIM) analysis on the investigated structures. The results show that six different non-covalent interactions have been identified in thiophene clusters: C⋯C (or π⋯π) bonding, CH⋯C (or CH⋯π) hydrogen bonding, CH⋯S hydrogen bonding, C⋯S (or π⋯S) bonding, S⋯S bonding and H⋯H bonding interactions. In addition, we have assessed the performance of eleven functionals of the density functional theory (DFT) in calculating the binding energies of the thiophene clusters. It is found that the functionals M052X and M06 showed the best performance with DLPNO-CCSD(T)/CBS used as reference.

Structures, binding energies and non-covalent interactions of furan clusters

Understanding of the furan solvent is subjected to the knowledge of the structures of the furan clusters and interactions taking place therein. Although, furan clusters can be very important to determine the dynamics and the properties of the furan solvent, there has been only a few investigations reported on furan dimer. In this work, we have explored the potential energy surfaces (PESs) of the furan clusters using two incremental levels of theory. Structures have been initially generated using classical molecular dynamics followed by full optimization at the MP2/aug-cc-pVDZ level of theory. The results show that the most stable structure of the furan dimer has a stacking configuration while that of the trimer has a cyclic configuration. We have noted that the structures of the furan tetramer have no definite configurations. In addition, we have performed a quantum theory of atoms in molecule (QTAIM) analysis to identify all possible non-covalent interactions of the furan clusters. The results show that six different types of non-covalent interactions can be identified in furan clusters. We have noted that the CH⋯C and CH⋯O hydrogen bondings are the strongest non-covalent interactions while the H⋯H bonding interaction is found to be the weakest. Furthermore, we have assessed the performance of ten DFT functionals in calculating the binding energies of the furan clusters. The ten DFT functionals (M05, M05-2X, M06, M06-2X, M08HX, PBE0, ωB97XD, PW6B95D3, APFD and MN15) have been benchmarked to DLPNO-CCSD(T)/CBS. The functionals M05-2X and M06 are recommended for further affordable investigations of the furan clusters.

Erratum to “Comparative study on the reachable workspaces of regular and irregular axially symmetric hexapod robots”

Six-legged hexapod walking robots are well-known for their intrinsic stability during navigation and 6-DoF object manipulation. The robot must be operated under a stable workspace envelope to attain effective manipulation. The structural parameters of the robot dramatically influence the characteristics of the workspace. Most studies analyze the workspace only by varying the leg parameter of the robot, maintaining the base configuration constant. This study aims to investigate the effect of change in the base plate characteristics on the workspace for an axially symmetric hexapod robot with cyclic and elliptical configurations. Superimposing the lateral 2D workspace of each pair of legs evolved to obtain a 3D workspace. The quantitative data analysis of the workspace shows that the cyclic configuration has an average increase of 23.74 %, and the elliptical configuration has a reduction of 1.97 % reachable workspace volume compared with regular hexapods. Furthermore, regular, cyclic, and elliptical hexapods are fabricated and validated with the selective workspace analysis data to reinforce the results. This study shows that the change in the hexagonal base plate configuration has a significant influence on workspace characteristics.

Exchange of optical vortices in symmetry-broken quantum systems

We investigate the interaction of laser pulses carrying orbital angular momentum (OAM) with a symmetry-broken ladder-type quantum coupling scheme involving three internal states. A weak probe beam acts on the lower leg of the ladder scheme, while a control beam of higher intensity drives the upper leg. In contrast to natural atoms, such a model with broken symmetry allows generating a sum-frequency signal beam between the most upper and lower quantum states, forming a cyclic closed-loop configuration of light-matter interaction. We propose situations for the efficient transfer of optical vortices to the generated signal beam via a nonlinear three-wave mixing process. It is demonstrated that the exchange process can occur both in the electromagnetically induced transparency (EIT) and the Autler-Townes splitting (ATS) regimes. The transition between the EIT and ATS conversion schemes can smoothly happen by simply tuning the knob of the control field. It is shown that the ATS regime is considerably more favorable than the EIT to achieve maximum energy conversion efficiency between light beams carrying the OAM. The results may provide an applications-based perspective to the ongoing research centered on vortex conversion-based comparisons between the ATS and EIT.

Alternating Donor–Acceptor π‐Conjugated Macrocycle Exhibiting Efficient Thermally Activated Delayed Fluorescence and Spontaneous Horizontal Molecular Orientation

A versatile design of thermally activated delayed fluorescence (TADF) π‐conjugated macrocycles incorporating electron‐donor (D) and acceptor (A) units into a cyclo‐meta‐phenylene motif with an alternating pattern is presented. The new π‐conjugated macrocycle, which combines three 5‐(N‐carbazolyl)‐phenylen‐1,3‐diyl as D units and three 6‐phenyl‐1,3,5‐triazin‐2,4‐diyl as A units, possesses a small singlet–triplet energy gap and hence can emit efficient green TADF both in solution and doped thin films. Comparative experimental and computational investigations of the electronic and photophysical properties of the macrocycle with its analogous noncyclic compound reveal key advantages of the cyclic molecular configuration for actual emitters. Organic light‐emitting diodes incorporating the TADF π‐conjugated macrocycle as an emitter demonstrate high external electroluminescence quantum efficiencies of up to 15.7%, outperforming the devices based on the noncyclic emitter. Herein, the importance of geometric design for producing novel organic emitters with fascinating optoelectronic and morphological characteristics is highlighted.

Binding Interactions of Peptide Aptamers.

Peptide aptamers are short amino acid chains that are capable of binding specifically to ligands in the same way as their much larger counterparts, antibodies. Ligands of therapeutic interest that can be targeted are other peptide chains or loops located on the surface of protein receptors (e.g., GCPR), which take part in cell-to-cell communications either directly or via the intermediary of hormones or signalling molecules. To confer on aptamers the same sort of conformational rigidity that characterises an antibody binding site, aptamers are often constructed in the form of cyclic peptides, on the assumption that this will encourage stronger binding interactions than would occur if the aptamers were simply linear chains. However, no formal studies have been conducted to confirm the hypothesis that linear peptides will engage in stronger binding interactions with cyclic peptides than with other linear peptides. In this study, the interaction of a model cyclic decamer with a series of linear peptide constructs was compared with that of a linear peptide with the same sequence, showing that the cyclic configuration does confer benefits by increasing the strength of binding.

Two-Path Interference for Enantiomer-Selective State Transfer of Chiral Molecules

With a microwave-regime cyclic three-state configuration, an enantiomer-selective state transfer~(ESST) is carried out through the two-path interference between a direct one-photon coupling and an effective two-photon coupling. The $\pi$-phase difference in the one-photon process between two enantiomers makes the interference constructive for one enantiomer but destructive for the other. Therefore only one enantiomer is excited into a higher rotational state while the other remains in the ground state. The scheme is of flexibility in the pulse waveforms and the time order of two paths. We simulate the scheme in a sample of cyclohexylmethanol~(C$_7$H$_{14}$O) molecules. Simulative results show the robust and high-fidelity ESST can be obtained when experimental concerns are considered. Finally, we propose to employ the finished ESST in implementing enantio-separation and determining enantiomeric excess.

Utilization of the cyclic interferometer in polarization phase-shifting technique to determine the thickness of transparent thin-films

An alternative polarization phase-shifting technique is proposed to determine the thickness of transparent thin-films. In this study, the cyclic interferometric configuration is chosen to maintain the stability of the operation against external vibrations. The incident light is simply split by a non-polarizing beam splitter cube to generate test and reference beams, which are subsequently polarized by a polarizing beam splitter. Both linearly polarized beams are orthogonal and counter-propagating within the interferometer. A wave plate is inserted into the common paths to introduce an intrinsic phase difference between the orthogonal polarized beams. A transparent thin-film sample, placed in one of the beam tracks, modifies the output signal in terms of the phase retardation in comparison with the reference beam. The proposed phase-shifting technique uses a moving mirror with a set of “fixed” polarizing elements, namely, a quarter-wave retarder and a polarizer, to facilitate phase extraction without rotating any polarizing devices. The measured thicknesses are compared with the measurements of the same films acquired using standard equipment such as the field-emission scanning electron microscope and spectroscopic ellipsometer. Experimental results with the corresponding measured values are in good agreement with commercial measurements. The system can be reliably utilized for non-destructive thickness measurements of transparent thin-films.

Enhanced photon drag in closed-loop quantum systems

In recent years, photon drag has attracted enormous attention owing to both fundamental and practical interests. In this paper, we investigate dragging effect in quantum systems with closed-loop interaction. First, we demonstrate an enhanced photon drag in a moving atomic medium with a three-level Λ-type structure. By incorporating the interference of spontaneous emissions, the properties of the atomic medium can be easily controlled by the relative phase of applied fields so that a large group index along with a transparency or even a gain can be achieved. As the photon drag is proportional to the group index, the enhancement can be also found in the dragging of light. Such enhanced dragging effect can be applied for the efficient modulators of light, position control, and the detection of slow motion. We then investigate the Fresnel’s light drag effect in another closed-loop structure, i.e. chiral molecules with a cyclic three-level Δ-type configuration, and show that left- and right-handed chiral molecules exhibit different dragging effects. This provides a possible way to probe the molecular chirality, which may find applications in the sorting and separation of chiral molecules.

Diradical-singlet character of 1,3-dipoles affects reactivity of 1,3-dipolar cycloaddition reactions and intramolecular cyclization.

1,3-Dipolar cycloaddition (1,3-DC) reactions are powerful synthetic tool to obtain highly functionalized 5-membered heterocycles, starting from a 1,3-dipole and a dipolarophile in a single step. The reactivity of these systems is usually rationalized in terms of Frontier Molecular Orbital Theory (FMOT), which neglects a possible contribution of an open-shell weakly coupled singlet-diradical specie. In this work, the broken-symmetry approach is used to estimate the singlet-diradical character of 18 dipoles of the second period of the periodic table, classified as allyl-type N-centered, allyl-type O-centered, and propargyl-type 1,3-dipoles, providing a rationalization for 1,3-DC reactivity. The intramolecular cyclization of bent allyl-type N- and O-centered dipoles into 3-membered rings was also analyzed, and revealed that the energetic change is associated with the spin densities of peripheral atoms. Finally, a close relationship between the energy for the ring-opening process of the cyclic configuration and the reactivity of 1,3-dipoles toward 1,3-dipolar cycloaddition reaction was also found. Graphical abstract.

Synthesis of magnetic-photo-Fenton catalyst for degradation of emerging pollutant

In this study, magnetic iron particles doped with TiO2 were synthetized to be used as a photo electro Fenton catalyst, being easily eliminated from the treated solution. Thus, the synergistic and scarcely reported combination of photocatalyst with electro Fenton process was evaluated for the degradation of an emerging pollutant: the ionic liquid 1-butyl-2, 3-dimethyl imidazolium chloride. To increase the radiation leverage, a cyclic two-cell configuration reactor was set, so the photolysis is applied directly and without obstacles in one cell and the electrolysis in another. The effect of the catalyst synthesis method and the ratio Fe/TiO2 were evaluated. With the most active bifunctional catalyst, a deep study of the two-cell reactor was done in terms of recirculation flow, applied intensity and catalyst dosage. Under the best conditions (respectively, 480 mL min−1, 70 mA and 1 g L−1), complete pollutant removal (in 10 min) and high mineralization (100% in 2 h) was achieved. Encouragingly, the results were almost equal when degrading the model pollutant on a real wastewater matrix. The reusability of the catalyst was also confirmed after three trials without almost no detriment on the performance.