Pair Of Rings Research Articles

"Optical tentacle" of suspended polymer micro-rings on a multicore fiber facet for vapor sensing.

We designed a new type of gas sensor, an optical tentacle, made of highly integrated polymer micro-ring resonators in three-dimensional space on the tiny end-facet of a multicore optical fiber. Two pairs of three polymer micro-ring resonators were hung symmetrically on both sides of three suspended micro-waveguides as the sensing units. The micro-waveguides interlace to form a three-layer nested configuration, which makes the multicore optical fiber a "tentacle" for vapors of volatile organic compounds. Both experiments and theoretical simulation confirmed that the symmetrical coupling of multiple pairs of rings with the micro-waveguide had better resonance than the single ring setup. This is because the symmetrical light modes in the waveguides couple with the rings separately. All the optical micro-components were fabricated by the two-photon lithography technology on the end facet of multicore optical fiber. The optical tentacle shows good sensitivity and reversibility. This approach can also be adopted for sensor array design on a chip. Furthermore, optical sensors that can sense vapors with multiple constituents may be achieved in the future by adding selective sensitive materials to or on the surface of the rings.

Crystal structures and Hirshfeld surface analysis of (cat)2[FeIII(η3-dipic)(NCS)3] and (cat)[FeIII(η3-dipic)(H2O)(NCS)2] (dipic = dipicolinate)

Crystal and molecular structures of black (cat)2[FeIII(η3-dipic)(NCS)3] (cat = C9H7NH; C10H9NH); (HNC10H8NH)[FeIII(dipic)(NCS)3], and (C6H7NH)[FeIII(η3-dipic)(H2O)(NCS)2] (dipic pyridine-2,6-dicarboxylate (−2); C9H7NH = quinolinium; C10H9NH = 3-methylisoquinolinium; HNC10H8NH = 4,4-bipyridinium; C6H7NH = 2-picolinium) were determinated. These complexes crystallized in monoclinic crystal class. Each Fe(III) atom is six coordinated. The octahedron is build up unsymmetrically, one half side is creates by terdentate dipic–1O,2N,3O ligand and the other half by three monodentate (NCS)3 or (NCS)2(H2O) donor ligands. The terdentate dipic–1O,2N,3O ligand forms a pair of five-membered metallocyclic rings with the common central 2N atom of pyridine (1OC22NC23O) with the mean value of O–Fe–N bite angles of 75.5°. The mean value of trans1O–Fe–3O bond angles is 150.8° in complexes with an inner coordination spheres FeO2N4 and FeO3N3. The mean value of sum of all three ((Fe–1O) + (Fe–2N) + (Fe–3O)) bond distances is 6.217 Å (FeO2N4) and 6.183 Å (FeO3N3). The opposite side in FeO2N4 is created by three monodentate NCS groups with the sum of Fe–N(x3) bond distances of 6.050 Å and in the FeO3N3 two NCS groups with water create opposite side with the sum of (Fe–N(x2) + Fe–O) bond distances of 6.183 Å. One polymorph of complex (C10H9NH)2[FeIII(dipic)(NCS)3] contains two crystallographically independent molecules differ mostly by degree of distortion in Fe–L bond distances and L–Fe–L bond angles and are examples of distortion isomerism. The data of the complexes are compare and discuses with the data of familiar iron(III) complexes. The intermolecular interactions of all compounds are studied by Hirshfeld surface analysis.

Experimental Wear Study between Piston Ring and Cylinder Liner Pair with Mahua Oil as Lubricant for Automobiles

This paper developed a wear testing machine and investigated experimental study of wear among cylinder liner (CL) and piston ring (PR) pair for automobiles. Mahua oil is used as the lubricant between the CL and PR pair. The process parameters are controlled to reduce the weight loss of PR using response surface methodology (RSM). The three process parameters such as applied load, sliding velocity and quantity of oil are considered. It is observed that sliding velocity and applied load are the most influencing parameters whereas the interaction of quantity of oil has less influencing parameter on weight loss of PR. Experimental results are in good compatibility with the values from the theoretical model.

An allosteric switch regulates Mycobacterium tuberculosis ClpP1P2 protease function as established by cryo-EM and methyl-TROSY NMR

The 300-kDa ClpP1P2 protease from Mycobacterium tuberculosis collaborates with the AAA+ (ATPases associated with a variety of cellular activities) unfoldases, ClpC1 and ClpX, to degrade substrate proteins. Unlike in other bacteria, all of the components of the Clp system are essential for growth and virulence of mycobacteria, and their inhibitors show promise as antibiotics. MtClpP1P2 is unique in that it contains a pair of distinct ClpP1 and ClpP2 rings and also requires the presence of activator peptides, such as benzoyl-leucyl-leucine (Bz-LL), for function. Understanding the structural basis for this requirement has been elusive but is critical for the rational design and improvement of antituberculosis (anti-TB) therapeutics that target the Clp system. Here, we present a combined biophysical and biochemical study to explore the structure-dynamics-function relationship in MtClpP1P2. Electron cryomicroscopy (cryo-EM) structures of apo and acyldepsipeptide-bound MtClpP1P2 explain their lack of activity by showing loss of a key β-sheet in a sequence known as the handle region that is critical for the proper formation of the catalytic triad. Methyl transverse relaxation-optimized spectroscopy (TROSY)-based NMR, cryo-EM, and biochemical assays show that, on binding Bz-LL or covalent inhibitors, MtClpP1P2 undergoes a conformational change from an inactive compact state to an active extended structure that can be explained by a modified Monod-Wyman-Changeux model. Our study establishes a critical role for the handle region as an on/off switch for function and shows extensive allosteric interactions involving both intra- and interring communication that regulate MtClpP1P2 activity and that can potentially be exploited by small molecules to target M. tuberculosis.

Vortex generation in a finitely extensible nonlinear elastic Peterlin fluid initially at rest

AbstractIt is well known that the mixing of two or more species in flows at low Reynolds numbers cannot be easily achieved since inertial effects are essentially absent and molecular diffusion is slow. To achieve mixing in Newtonian fluids under these circumstances requires innovative new ideas such as the use of external body forces (eg, electromagnetic mixers) or the stretching and folding of fluid elements (eg, chaotic advection). For non‐Newtonian fluids with elasticity, mixing can be achieved by enabling the emergence of elastic instabilities that results in chaotic flows in which mixing is significantly enhanced. In this work, our goal is to demonstrate that clearly identifiable vortical structures (eg, vortex rings) can be generated in a viscoelastic fluid initially at rest by the release of elastic stresses. In turn, these vortex motions promote bulk mixing by transporting fluid elements from one location to another more efficiently than diffusion alone. We demonstrate this first theoretically by using the finitely extensible nonlinear elastic Peterlin (FENE‐P) model to show that elastic forces can generate torque. Using this model, we derive an expression for the time rate of change of vorticity in an elastic fluid initially at rest caused by a sudden release of stored elastic stress. This process can be thought of as the release of elastic energy from a stretched rubber band that is suddenly cut at its center. We confirm this ansatz by performing a series of direct numerical simulations based on an in‐house pseudo‐spectral code that couples the FENE‐P model to the equations of motion for an incompressible fluid. The simulations reveal that a pair of vortex rings traveling in opposite directions, with Reynolds numbers on the order of one, is generated from the sudden release of elastic stresses. Secondary vortical structures are also generated. In the concluding section of this work, we address the potential for vortex motions generated by elastic stresses to promote mixing in microflows, and we describe a possible experiment that may demonstrate this effect.

X-ray Structure at 150 K of the Polar Alkyl Mesogenic Compound 7CBB: 4-Cyanobiphenyl-4′-heptylbiphenyl Carboxylate

The compound under study 7CBB consists of two biphenyl moieties A–B and C–D linked by a carboxylate group. Ring A terminates in a 4-cyano group and C–D is linked to the terminal alkyl chain. A previously reported room temperature determination of the crystal structure employing MoKα X-radiation was thought to contain serious errors in describing the alkyl chain as being disordered. The X-ray structure factors were not deposited with this published structure and as a consequence two new X-ray data sets have been collected: (1) using MoKα radiation at room temperature 295 K (a repeat of the previous study) and (2) using CuKα radiation at 150 K in an attempt, which proved successful, to improve the overall quality of the structure determination. The corrected MoKα structure and the CuKα structure both reported here have enabled the previous errors to be identified, concluding that there is no disorder in the alkyl chain. The alkyl chain in the MoKα structure at 295 K was found to have anisotropic thermal factors slightly exaggerated with respect to the remainder of the structure. However, this effect is not observed in the CuKα structure at 150 K, all anisotropic thermal factors including those in the alkyl chain being reduced to cover a much smaller overall range of values. Consequently, it can be concluded that the effect observed in the alkyl chain at 295 K is merely one of a thermal nature, not one of disorder. There are no unusual bond lengths or angles present. The biphenyl moieties are planar within 0.035 A and 0.020 A respectively. The dihedral angles of all ring pairs have been calculated. Calculation of intermolecular distances between molecules related by a centre of symmetry reveals the existence of a number of van-der Waals interactions. The H-bonding motif typical of crystal structures of cyanobiphenyl compounds is observed. The molecular packing mode corresponds to that of a precursor of the smectic phase. The alkyl chain thermal ellipsoids for 7CBB (a) the Mo RT structure are noticeably exaggerated compared to those for the remainder of the structure, an effect which is not present in (b) the Cu LT structure (Drawn with Ortep/Raster (Barnes in J Appl Cryst 30:568, 1997; Merritt and Bacon in Methods Enzymol 277:505–524, 1997)). It may be concluded therefore that in the Mo RT structure this is a thermal effect and cannot be explained in terms of static disorder.

Some commutative ring extensions defined by almost Bézout condition

In this paper, we study the almost Bézout property in different commutative ring extensions, namely, in bi-amalgamated algebras and pairs of rings. In Section 2, we deal with almost Bézout domains issued from bi-amalgamations. Our results capitalize well known results on amalgamations and pullbacks as well as generate new original class of rings satisfying this property. Section 3 investigates pairs of rings where all intermediate rings are almost Bézout domains. As an application of our results, we characterize pairs of rings $(R,T)$, where $R$ arises from a $(T,M,D)$ construction to be an almost Bézout domain.

Design and experimental investigation of ultra-low frequency vibration isolation during neonatal transport

To resolve the tough issue of ultra-low frequency vibration isolation during neonatal transport, a new incubator with quasi-zero-stiffness (QZS) isolators is proposed. In the new incubator, the infant housing unit is supported by the QZS isolators to mitigate mechanical vibration being transmitted from the ambulance floor to the infant. Each of the QZS isolators is devised by combining a pair of permanent magnet rings and a coil spring, and the design parameters are realized by the equivalent magnetic charge method. Both the prototypes of the QZS isolator and incubator are manufactured, and their vibration isolation performances are tested. The results show that the QZS isolator can fulfil vibration isolation from 2 Hz, and the incubator with four such QZS isolators is effective from 3.2 Hz under the designated payload. Most importantly, the acceleration response of the infant model in the housing unit is much lower than the base excitation, when the incubator is driven by a random base excitation with frequency bandwidth from 2 Hz to 15 Hz.

A processive rotary mechanism couples substrate unfolding and proteolysis in the ClpXP degradation machinery.

The ClpXP degradation machine consists of a hexameric AAA+ unfoldase (ClpX) and a pair of heptameric serine protease rings (ClpP) that unfold, translocate, and subsequently degrade client proteins. ClpXP is an important target for drug development against infectious diseases. Although structures are available for isolated ClpX and ClpP rings, it remains unknown how symmetry mismatched ClpX and ClpP work in tandem for processive substrate translocation into the ClpP proteolytic chamber. Here, we present cryo-EM structures of the substrate-bound ClpXP complex from Neisseria meningitidis at 2.3 to 3.3 Å resolution. The structures allow development of a model in which the sequential hydrolysis of ATP is coupled to motions of ClpX loops that lead to directional substrate translocation and ClpX rotation relative to ClpP. Our data add to the growing body of evidence that AAA+ molecular machines generate translocating forces by a common mechanism.

Nonlinear Oscillations of a Pair of Charged Rings

Two electrically charged rings of different sizes are assembled along their common vertical symmetry axis through their centers. The bottom ring is secured on a horizontal support while the top one is loose. For a set of practical values characterizing the charged rings we envision a scenario where the mutual electric repulsion between the rings and the weight of the top ring results in stable nonlinear oscillations. To quantify the characteristics of the oscillations, we utilize a Computer Algebra System specifically Mathematica [1]. We accompany the analysis with a simulation for a comprehensive visual understanding.

OPTIMUM DESIGN METHODOLOGY FOR AXIALLY POLARIZED MULTI-RING RADIAL AND THRUST PERMANENT MAGNET BEARINGS

—This article deals with the generalized procedure of designing and optimizing multi-ring radial and thrust permanent magnet bearings (PMBs) with an axial air gap for maximum force and stiffness per volume of the magnet. Initially, the procedure of determining optimized design variables in both the configurations is presented using the MATLAB codes written for solving the three dimensional (3D) equations of force and stiffness in PMB having ‘n’ number of rings on the stator and rotor. The maximized results of the forces in both radial and thrust multi-ring PMBs are validated with the values obtained using finite element analysis (FEA). Then, the correlation between the optimized parameters and the air gap is obtained, and curve fit equations for the same are proposed in terms of stator outer diameter. Further, curve fit equations establishing the relationship between the maximized bearing features, and the aspect ratio (L/D4) of the bearing are expressed for different values of air gap in both the radial and thrust bearings. Finally, the generalized method of designing and optimizing the multi-ring PMB is demonstrated with a specific application. A designer can use the presented curve fit equations for optimizing design variables and calculating maximized bearing features in multi-ring radial and thrust PMBs easily just by knowing the bearing features for a single ring pair.

Origin of Regio- and Stereospecific Catalysis by 8-Lipoxygenase.

Lipoxygenases (lox's) are a group of non-heme iron containing enzymes that catalyze oxygenation of polyunsaturated fatty acids with precise regio- and stereoselectivities. The origin of regio- and stereospecific catalysis by 8-lox is explored in its wild-type (wt) form and in three mutants (Arg185Ala, Ala592Met, and Ala623His). The catalytic action of this enzyme progresses in two steps, namely, hydrogen abstraction from one double allylic carbon atom of substrate followed by oxygen insertion at the resulting prochiral carbon radical of the substrate. It is shown that the positional specificity of the hydrogen abstraction is a result of conformational dynamics of the bound substrate. While the C10 atom of the substrate is found to be the most probable site of hydrogen abstraction in the wt-lox, hydrogen abstraction from C13 is more favorable in the mutants. The present study discovers the presence of an interconnected network of a three-channel migration pathway operating in the protein matrix for efficient oxygen transport. Each migration channel is bestowed with a pocket at the peripheral region of protein as an oxygen access site, which transfers the oxygen to the active site through a well-connected migration path on a time scale of a few hundred picoseconds. By a careful geometric analysis of the oxygen pockets near the substrate binding cleft, the present study identifies the launching sites for oxygenation at the prochiral carbon centers C8, C11, C12, and C15 and the stereochemistry (R/S) of the corresponding products. It is found that the dominating 8R product in the wt-lox is due to the presence of the aromatic ring pair of Tyr181 and Phe173 acting as a gatekeeper for efficient delivery of oxygen at the pro-R face of C8. The change in the stereochemistry of the products in mutants is explained in terms of dynamic interactions between substrate and the surrounding residues.

Carbon Nanotubes Having Haeckelite Defects as Potential Drug Carriers. Molecular Dynamics Simulation.

Carbon nanotubes (CNTs) are valuable drug carriers since when properly functionalized they transport drugs and anchor directly to cancerous tumors whose more acidic pH causes the drug release. Herein, we study the so-called zigzag and armchair CNTs with haeckelite defects to rank their ability to adsorb doxorubicin (DOX) by determining the DOX-CNT binding free energies using the MM/PBSA and MM/GBSA methods implemented in AMBER. Our results reveal stronger DOX-CNT interactions for encapsulation of the drug inside the nanotube compared to its adsorption onto the defective nanotube external surface. Armchair CNTs with one and two defects exhibit better results compared with those with four and fifteen defects. Each haeckelite defect consists of a pair of square and octagonal rings. DOX-CNT binding free energies are predicted to be dependent on: (i) nanotube chirality and diameter, (ii) the number of defects, (iii) nitrogen doping and (iv) the position of the encapsulated DOX inside the nanotube. Armchair (10,10) nanotubes with two haeckelite defects, doped with nitrogen, exhibit the best drug-nanotube binding free energies compared with zigzag and fully hydrogenated nanotubes and, also previously reported ones with bumpy defects. These results contribute to further understanding drug-nanotube interactions and their potential application to the design of new drug delivery systems.

Molecule–Metal Bond of Alternant versus Nonalternant Aromatic Systems on Coinage Metal Surfaces: Naphthalene versus Azulene on Ag(111) and Cu(111)

Interfaces between polycyclic π-electron systems and metals play prominent roles in organic or graphene-based (opto)electronic devices, in which performance-related parameters depend critically on the properties of metal/semiconductor contacts. Here, we explore how the topology of the π-electron system influences the bonding and the electronic properties of the interface. We use azulene as a model for nonalternant pentagon–heptagon (5–7) ring pairs and compare it to its isomer naphthalene, which represents the alternant 6–6 ring pair. Their coverage-dependent interaction with Ag(111) and Cu(111) surfaces was studied with the normal-incidence X-ray standing wave (NIXSW) technique, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, UV and X-ray photoelectron spectroscopies (UPS and XPS), and density functional theory (DFT). Coverage-dependent adsorption heights and spectroscopic data reveal that azulene forms shorter interfacial bonds than naphthalene and engages in stronger electronic interactions with both surfaces. These differences are more pronounced on Cu. Increasing coverages lead to larger adsorption heights, indicating bond weakening by intermolecular repulsion. The extensive DFT calculations include dispersive interactions using (1) the DFT-D3 scheme, (2) the vdWsurf correction based on DFT-TS, (3) a many-body dispersion (MBD) correction scheme, and (4) the D3surf scheme. All methods predict the adsorption heights reasonably well with an average error below 0.1 A. The stronger bond of azulene is attributed to its nonalternant topology, which results in a reduced highest occupied molecular orbital (HOMO)–lowest occupied molecular orbital (LUMO) gap and brings the LUMO energetically close to the Fermi energy of the metal, causing stronger hybridization with electronic states of the metal surfaces.

Modules and their endomorphism rings

Let R and S be a pair of equivalent rings. We will prove that if R has property that a pair of modules over R are isomorphic if and only if their endomorphism rings are isomorphic than S has same property, i.e. a pair of modules over S are isomorphic if and only if their endomorphism rings are isomorphic.

Tres marcadores calendáricos en Cocotitlán, Edo. de México

En general las cruces punteadas o los “marcadores teotihuacanos” consisten de un par de círculos concéntricos (a veces reemplazado por los cuadrados concéntricos) centrado en un par de ejes ortogonales, plasmados en pisos estucados o en afloramientos rocosos durante el periodo Clásico en Mesoamérica. En el artículo se estudian tres marcadores recientemente descubiertos en la región de Cocotitlán, en la parte sur de la Cuenca México. El análisis revela el significado calendárico-astronómico potencial de los arreglos de agujeros y ejes que conforman esas figuras.

Stereo- and Enantioselective Addition of Organolithiums to 2-Oxazolinylazetidines as a Synthetic Route to 2-Acylazetidines.

A new synthetic route to N-alkyl-2-acylazetidines was developed through a highly stereoselective addition of organolithiums to N-alkyl-2-oxazolinylazetidines followed by acidic hydrolysis of the resulting oxazolidine intermediates. This study revealed an unusual reactivity of the C=N bond of the oxazoline group when reacted with organolithiums in a non-polar solvent such as toluene. The observed reactivity has been explained considering the role of the nitrogen lone pair of the azetidine ring as well as of the oxazolinyl group in promoting a complexation of the organolithium, thus ending up with the addition to the C=N double bond. The high level of stereoselectivity in this addition is supported by DFT calculations and NMR investigations, and a model is proposed for the formation of the oxazolidine intermediates, that have been isolated and fully characterized. Upon acidic conditions, the oxazolidine moieties were readily converted into 2-acylazetidines. This synthetic approach has been applied for the preparation of highly enantioenriched 2-acylazetidines starting from chiral not racemic N-alkyl-2-oxazolinylazetidines.

Vapor phase GC-IR identification of regioisomeric N-methoxybenzyl-4-substituted-2,5-dimethoxyphenethylamines (NBOMe)

The common NBOMe drugs of abuse, N-(2-methoxybenzyl)-4-iodo-2,5-dimethoxyphenethylamine (25I-NBOMe) and N-(2-methoxybenzyl)-4-bromo-2,5-dimethoxyphenethylamine (25B-NBOMe), can be differentiated from their corresponding 3- and 4-methoxybenzyl isomers by gas chromatography with vapor phase infrared spectroscopy. The mass spectra for these regioisomeric compounds are essentially identical providing only the identity of the halogen but no specific ions to identify the methoxy group position on the benzyl aromatic ring. The bands from single ring model compounds 2C-B, 2C-I, and all three positional methoxy substituted benzylamines were used to assign each vapor phase absorption band to either the halogenated 2,5 dimethoxybenzene ring or the methoxybenzylamine ring.A pair of aromatic ring stretching bands reflect the position of methoxy group substitution on the benzyl aromatic ring. The 1608 cm−1 band is specific for the two regioisomeric 4-methoxy-benzylamine isomers and this band occurs at 1593 cm−1 for the 2-methoxy isomer in both the 25I and 25B series and shifts to1597/1598 cm−1 for 3-methoxybenzyl 25I and 25B. Asymmetric aryl-O stretching frequencies shift with a change in methoxy substitution around the benzyl aromatic ring (Ring 2) and occur at 1237/1238 cm−1 for ortho, 1261 cm−1 for meta, and 1246 cm−1 for the para isomers. The overall shape and relative intensities of numerous bands in the vapor phase spectra provide clear identification for the individual methoxybenzyl isomers for the 25I-NBOMe and 25B-NBOMe series.

Crystal structure, Hirshfeld surface analysis and computational studies of 5-[(prop-2-en-1-yl)sulfan-yl]-1-[2-(tri-fluoro-meth-yl)phen-yl]-1H-tetra-zole.

The title compound, C11H9F3N4S, was synthesized from 2-(tri-fluoro-meth-yl)aniline by a multi-step reaction. It crystallizes in the non-centrosymmetric space group Pna21, with one mol-ecule in the asymmetric unit, and is constructed from a pair of aromatic rings [2-(tri-fluoro-meth-yl)phenyl and tetra-zole], which are twisted by 76.8 (1)° relative to each other because of significant steric hindrance of the tri-fluoro-methyl group at the ortho position of the benzene ring. In the crystal, very weak C-H⋯N and C-H⋯F hydrogen bonds and aromatic π-π stacking inter-actions link the mol-ecules into a three-dimensional network. To further analyse the inter-molecular inter-actions, a Hirshfeld surface analysis, as well as inter-action energy calculations, were performed.

Design, Analysis, and Experiment of Multiring Permanent Magnet Bearings by Means of Equally Distributed Sequences Based Monte Carlo Method

Load-carrying capacity analysis is an important procedure for designing the permanent magnet bearing (PMB). Generally, the magnetic force exerted between the ring magnets of PMB can be modeled by means of the equivalent magnetic charge method. In this case, the analytical methods are always simply compared to numerical methods; however, they are restricted by their applicability. The model based on the equivalent magnetic charge method contains multiple integrals; it is difficult to get the simulation results quickly through self-contained function of MATLAB. The equally distributed sequences based Monte Carlo method is used to simplify the complicated mathematical derivation and calculus of bearing capacity characteristics of multiring PMBs, and it might improve the computational efficiency of PMB structure design. The results of the Monte Carlo model are compared with the results of finite element analysis (FEA) using ANSYS, and the error correction factor is presented. The theoretical model is verified by the finite element analysis. Finally, the bearing forces in radial and axial directions of the PMBs with 4 pairs of magnetic rings were tested experimentally; the experiment result is approximately agreed with the simulation analysis. This method will be perfect for the engineering application involving multiring structural design of PMBs.