Slipped Structures Research Articles

Heat, pressure and light-induced interconversion of bisdithiazolyl radicals and dimers.

The heterocyclic bisdithiazolyl radical 1b (R1 = Me, R2 = F) crystallizes in two phases. The α-phase, space group P2₁/n, contains two radicals in the asymmetric unit, both of which adopt slipped π-stack structures. The β-phase, space group P2₁/c, consists of cross-braced π-stacked arrays of dimers in which the radicals are linked laterally by hypervalent 4-center 6-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility measurements on α-1b indicate Curie-Weiss behavior (with Θ = -14.9 K), while the dimer phase β-1b is diamagnetic, showing no indication of thermal dissociation below 400 K. High-pressure crystallographic measurements indicate that the cross-braced π-stacked arrays of dimers undergo a wine-rack compression, but the dimer remains intact up to 8 GPa (at ambient temperature). The resistance of β-1b to dissociate under pressure, also observed in its conductivity versus pressure profile, is in marked contrast to the behavior of the related dimer β-1a (R1 = Et, R2 = F), which readily dissociates into a pair of radicals at 0.8 GPa. The different response of the two dimers to pressure has been rationalized in terms of differences in their linear compressibilities occasioned by changes in the degree of cross-bracing of the π-stacks. Dissociation of both dimers can be effected by irradiation with visible (λ = 650 nm) light; the transformation has been monitored by optical spectroscopy, magnetic susceptibility measurements, and single crystal X-ray diffraction. The photoinduced radical pairs persist up to temperatures of 150 K (β-1b) and 242 K (β-1a) before reverting to the dimer state. Variable-temperature optical measurements on β-1b and β-1a have afforded Arrhenius activation energies of 8.3 and 19.6 kcal mol(-1), respectively, for the radical-to-dimer reconversion. DFT and CAS-SCF calculations have been used to probe the ground and excited electronic state structures of the dimer and radical pair. The results support the interpretation that the ground-state interconversion of the dimer and radical forms of β-1a and β-1b is symmetry forbidden, while the photochemical transformation is symmetry allowed.

Morphology of Edge Cracks of Rolled Magnesium Alloy Sheet

Magnesium alloys show low deformability at low temperature because of hcp structure and inactiveness of basal slip. Manufacturing of thin sheet is difficult in industries. Some approaches, such as small-draft multi-pass rolling, intermediate annealing, isothermal rolling and high-speed rolling were proposed to overcome the deformability. However, small edge cracks are still formed on the sheet. In this study, rolling speed of 1000m/min was employed to warm-roll AZ31B magnesium alloy in a single pass at different temperatures. The edge cracks formed after the rolling were classified into three main groups: minor, regular and zigzag edge cracks. ‘Crack contact length’ are introduced to explain the morphology of edge cracks. The results show that the critical reduction for crack initiation depends on the pre-heating temperature. The spacing between edge cracks increases linearly with the crack contact length regardless of roll diameter, speed and reduction. It is suggested that this approach is useful to understand the formation mechanism of edge cracks and to evaluate the rollability of magnesium alloys.

Dithienonaphthothiadiazole semiconductors: synthesis, properties, and application to ambipolar field effect transistors

To address the scarcity of small molecule semiconductors capable of ambipolar charge injection/transport in field effect transistors, three new dithienonaphthothiadiazoles 10, 11 & 12 with fused donor/acceptor motif were synthesized. Their optical and electrochemical properties were investigated in parallel to DFT calculations, revealing the effects of ring connectivity and alkyl substitution on the electronics of the push–pull systems. Single-crystal X-ray analysis revealed a transition from a quasi-herringbone structure in 10 to slipped π-stacked structures in 11 and 12, which changes the exciton delocalization and charge transport pathways. Accordingly, while alkylated compounds 11 and 12 were insulating, ambipolar charge transport was achieved in field-effect transistor devices using 10 with balanced hole and electron mobilities of up to ∼0.02 cm2 V−1 s−1 in single-crystal devices.

Spectroscopy of dimers, trimers and larger clusters of linear molecules

Rotationally resolved spectra of van der Waals clusters provide the most direct, precise and unambiguous experimental probe of intermolecular potential energy surfaces, particularly in the lower energy range of attractive forces. The spectroscopy of such weakly bound complexes is reviewed with a focus on those containing only the following five small linear molecules: N2O, CO2, OCS, CS2 and C2H2. Even with this limitation, there are over 30 such complexes for which high-resolution spectroscopic results are now available in the microwave, millimetre wave and infrared regions. Dimers formed from these five species tend to be planar with slipped parallel structures, though there are some exceptions. Trimers tend to be barrel-shaped, that is, non-planar with approximately parallel monomers. Larger clusters are almost invariably non-planar and sometimes highly symmetric. Three significant themes emerge here. First, the possibility of determining low-frequency intermolecular vibrational modes by means of mid-infrared combination bands. Second, the increasing number of complexes for which more than one structural form, or isomer, is observed. And finally, the growing amenability of even ‘large’ clusters (say, tetramers and larger) to spectroscopic study. All three factors help to probe potential energy surfaces more completely in regions away from the global minimum.

The Strength Analysis and Structure Optimization of Packer Slip Based on ANSYS

Packer is one of the main down-hole mining tools in oil field. When setting the packer prone to fracture under tremendous pressure, directly affect the sealing performance of the packer, which affects the process of mining and safety in production wells. The slip was analysised by using the finite element analysis software ANSYS Workbench. When the applied load is 140kN, the slips maximum stress is 230.11MPa, which exceeding the maximum compressive strength of this material. In the fracturing test of the slip packer test model, the test pressure is 186.33kN when slip fracturing, the compressive strength is measured 233Mpa. To optimize the structure of slip, the spacing size of slip tooth were 15 mm, 25 mm and 30 mm. According to the results of finite element analysis, when the spacing size of slip tooth is 30 mm, the distribution of the slip tooths stress and strain tends to uniform. The maximum load is 240kN. This slip structure size is reasonable, and it provides a reference for the optimization design of slip.

Origin and tectonic significance of the Huangling massif within the Yangtze craton, South China

As the oldest exposed basement and the typical sedimentary cover of the Yangtze craton, the Huangling massif is a suitable place to decipher the tectonics of South China block. Structural analysis shows that the Huangling massif has an elliptic domal shape with N–S striking long axis, an asymmetric antiform with a steep western flank and a gentle eastern flank. There, three litho-tectonic units are recognized, from inner to outer parts: (1) Archean–Paleoproterozoic metamorphic rocks intruded by Neoproterozoic granitoids; (2) Neoproterozoic to Jurassic sedimentary envelope around the dome core; (3) Cretaceous terrigeneous alluvial–fluvial deposits, unconformably overlying the dome flanks. Coeval with the uplifting of the massif, the pre-Cretaceous strata on the western and eastern flanks of the Huangling massif were involved in a series of folds with nearly N–S axes and layer-parallel slip structures with top-to-the-W and top-to-the-E motion, respectively. The subsequent brittle normal faulting controlled the deposition of the graben or half-graben basins on both flanks. Cooling history reveals that the Huangling massif underwent uplifting between 160Ma and 110Ma with an average cooling rate of 2–3°C/Ma. Moreover, the Huangling area was not significantly affected by the Early Paleozoic and Triassic orogenies of South China. Comparable with the contemporaneous extensional structures, such as metamorphic core complexs, syntectonic plutons bounded by ductile normal faults, and rift-related basins in eastern China, it is proposed that the Huangling massif, might be an extensional structure controlled by a weak crustal extension. In this case, it will represent the western front of the Late Mesozoic lithospheric thinning in entire eastern China. However the compressional model cannot be ruled out.

Characterization of deformation anisotropies in an α-Ti alloy by nanoindentation and electron microscopy

The crystallographic dependence of the mechanical responses of an α-Ti–7wt.% Al alloy was measured by nanoindentation using spherical and Berkovich indenters. Both elastic moduli and hardness responses of indents on the (0001), (1¯100) and (1¯21¯0) planes were quantified. The dislocation structures resulting from indentation were characterized by electron microscopy. While scanning electron microscopy techniques were used for the observation of surface slip structures, site-specific focused-ion-beam thin foil preparation and scanning transmission electron microscopy techniques were employed for the imaging of sub-surface dislocation structures. Elastic modulus, hardness and load at pop-in were found to vary with crystallographic orientation. Indentation-induced plasticity was found to occur by multiple slip/twin mechanisms and to be dependent on crystal orientation, although 〈a〉 slip on (0001) planes was found to be common to all orientations. The observed dislocation structures are rationalized on the basis of theoretical predictions based on the anisotropic elastic contact analysis and resolved shear stress calculations.

Theoretical studies of the CO2–N2O van der Waals complex: Ab initio potential energy surface, intermolecular vibrations, and rotational transition frequencies

Theoretical studies of the potential energy surface and bound states were performed for the CO(2)-N(2)O van der Waals complex. A four-dimensional intermolecular potential energy surface (PES) was constructed from 11,466 ab initio data points which were calculated at the coupled-cluster single double (triple) level with aug-cc-pVTZ basis set supplemented with bond functions. Three co-planar local minima were found on this surface. They correspond to two equivalent isomers with a slipped parallel structure in which the O atom in N(2)O is near the C atom in CO(2) and a T-shaped isomer in which the terminal N atom in N(2)O is closest to the C atom in CO(2). The two slipped parallel isomers are energetically more stable than the T-shaped isomer by 178 cm(-1). Four fundamental vibrational excited states for the slipped parallel isomers and two fundamental vibrational excited states (torsion and disrotation) for the T-shaped isomer were assigned via bound states calculations based on this PES. The theoretical vibrational frequencies are in good agreement with the available experimental values for the slipped parallel isomers. Rotational excitations (J = 0-6) for the ground vibrational state of the slipped parallel structure were calculated and the accuracy of the PES in the vicinity of minima is validated by the good agreement between the theoretical and experimental transition frequencies and spectroscopic parameters.

Direct and inverted repeats elicit genetic instability by both exploiting and eluding DNA double-strand break repair systems in mycobacteria.

Repetitive DNA sequences with the potential to form alternative DNA conformations, such as slipped structures and cruciforms, can induce genetic instability by promoting replication errors and by serving as a substrate for DNA repair proteins, which may lead to DNA double-strand breaks (DSBs). However, the contribution of each of the DSB repair pathways, homologous recombination (HR), non-homologous end-joining (NHEJ) and single-strand annealing (SSA), to this sort of genetic instability is not fully understood. Herein, we assessed the genome-wide distribution of repetitive DNA sequences in the Mycobacterium smegmatis, Mycobacterium tuberculosis and Escherichia coli genomes, and determined the types and frequencies of genetic instability induced by direct and inverted repeats, both in the presence and in the absence of HR, NHEJ, and SSA. All three genomes are strongly enriched in direct repeats and modestly enriched in inverted repeats. When using chromosomally integrated constructs in M. smegmatis, direct repeats induced the perfect deletion of their intervening sequences ∼1,000-fold above background. Absence of HR further enhanced these perfect deletions, whereas absence of NHEJ or SSA had no influence, suggesting compromised replication fidelity. In contrast, inverted repeats induced perfect deletions only in the absence of SSA. Both direct and inverted repeats stimulated excision of the constructs from the attB integration sites independently of HR, NHEJ, or SSA. With episomal constructs, direct and inverted repeats triggered DNA instability by activating nucleolytic activity, and absence of the DSB repair pathways (in the order NHEJ>HR>SSA) exacerbated this instability. Thus, direct and inverted repeats may elicit genetic instability in mycobacteria by 1) directly interfering with replication fidelity, 2) stimulating the three main DSB repair pathways, and 3) enticing L5 site-specific recombination.

Non-B DB v2.0: a database of predicted non-B DNA-forming motifs and its associated tools

The non-B DB, available at http://nonb.abcc.ncifcrf.gov, catalogs predicted non-B DNA-forming sequence motifs, including Z-DNA, G-quadruplex, A-phased repeats, inverted repeats, mirror repeats, direct repeats and their corresponding subsets: cruciforms, triplexes and slipped structures, in several genomes. Version 2.0 of the database revises and re-implements the motif discovery algorithms to better align with accepted definitions and thresholds for motifs, expands the non-B DNA-forming motifs coverage by including short tandem repeats and adds key visualization tools to compare motif locations relative to other genomic annotations. Non-B DB v2.0 extends the ability for comparative genomics by including re-annotation of the five organisms reported in non-B DB v1.0, human, chimpanzee, dog, macaque and mouse, and adds seven additional organisms: orangutan, rat, cow, pig, horse, platypus and Arabidopsis thaliana. Additionally, the non-B DB v2.0 provides an overall improved graphical user interface and faster query performance.

PERENCANAAN KONSTRUKSI BETON SLIPWAY - 150 LWT

Budhi Dharma, in paper Construction Planning of Slipway - 150 LWT Concrete explain that in shipyard planning major facility types shipyard slipway suitable transverse system was built in the open or closed.To ship with 150 tons LWT according to the register BKI got main dimension vessels = 34 meters LOA,30 meters LP, 6 meters B, the ship draft T = 2,2 meters, and empty vessel draft Tk = 1,18 meters and block coefficient = 0,68.Of the main dimension of the vessel were then long slipway, heavy lorries and heavy lorries transfer launchers after the total weight is obtained the dimensions of the placement of concrete beam rail and lorry.Keyword : Slip way and structure concrete

Functionalized Tetrathienoanthracene: Enhancing π–π Interactions Through Expansion of the π-Conjugated Framework

The functionalization of tetrathienoanthracene (TTA) with bromine and 2-hexylthiophene moieties is described, and their influence at both the molecular and solid-state level has been investigated. Comparative optical and electrochemical studies indicate an increase in conjugation for the thiophene derivative compared to the parent TTA. In the solid state, these materials form slipped π-stack structures with a number of close intermolecular contacts. Comparison of the two structures reveals a more steeply inclined slipped π-stack for the thiophene derivative resulting in a closer interplanar separation. This, coupled with the extended molecular framework, leads to an enhanced number of π–π interactions within the stack. The combination of increased conjugation at the molecular level, and π-stacked structures with strong intermolecular communication at the solid-state level, augurs well for the use of TTA materials in optoelectronic applications.

Explicit correlation and basis set superposition error: The structure and energy of carbon dioxide dimer

We have investigated the slipped parallel and t-shaped structures of carbon dioxide dimer [(CO(2))(2)] using both conventional and explicitly correlated coupled cluster methods, inclusive and exclusive of counterpoise (CP) correction. We have determined the geometry of both structures with conventional coupled cluster singles doubles and perturbative triples theory [CCSD(T)] and explicitly correlated cluster singles doubles and perturbative triples theory [CCSD(T)-F12b] at the complete basis set (CBS) limits using custom optimization routines. Consistent with previous investigations, we find that the slipped parallel structure corresponds to the global minimum and is 1.09 kJ mol(-1) lower in energy. For a given cardinal number, the optimized geometries and interaction energies of (CO(2))(2) obtained with the explicitly correlated CCSD(T)-F12b method are closer to the CBS limit than the corresponding conventional CCSD(T) results. Furthermore, the magnitude of basis set superposition error (BSSE) in the CCSD(T)-F12b optimized geometries and interaction energies is appreciably smaller than the magnitude of BSSE in the conventional CCSD(T) results. We decompose the CCSD(T) and CCSD(T)-F12b interaction energies into the constituent HF or HF CABS, CCSD or CCSD-F12b, and (T) contributions. We find that the complementary auxiliary basis set (CABS) singles correction and the F12b approximation significantly reduce the magnitude of BSSE at the HF and CCSD levels of theory, respectively. For a given cardinal number, we find that non-CP corrected, unscaled triples CCSD(T)-F12b/VXZ-F12 interaction energies are in overall best agreement with the CBS limit.

Cationic Cyclopentadienyl Zinc Complexes with Slipped Triple‐Decker and Half‐Sandwich Structures

Giving zinc the slip! Cationic triple-decker zinc complexes [Zn2Cp*3]+ [BArF4]− (Cp*=C5Me5; BArF4= B(3,5-(CF3)2C6H3)4, B(C6F5)4; see scheme) were prepared by protonation of [ZnCp*2]. The cations adopt an unusual slipped triple-decker structure and can act as a source of a {ZnCp*}+ entity.

Geological setting of the Paleoproterozoic Rosebel gold district, Guiana Shield, Suriname

Abstract The Rosebel gold district is hosted in a Paleoproterozoic greenstone belt of the Guiana Shield and has many characteristics that enable classification of the ores as an orogenic gold deposit. Host rocks have undergone several phases of deformation. However, gold deposition occurred late in the structural history of the belt, and is considered part of a late regional metallogenic event with respect to the geotectonic evolution of the Guiana Shield. Economic gold mineralization is hosted in felsic to mafic volcanic rocks and two sedimentary successions that are differentiated into turbiditic and arenitic depositional packages. The detailed lithostratigraphic characterization and the geochemistry enable the correlation of the local rock types with the Paramaka, the Armina, and the Rosebel formations respectively. The Rosebel district comprises eight discrete gold deposits distributed along two major structures. The northernmost structure is a sub-vertical WNW–ESE shear zone that preserves evidence of dextral strike–slip followed by normal faulting. The southern structure is an east–west reverse fault along which gold deposits are mainly hosted in the footwall. Gold mineralization is associated with quartz vein arrays developed along pre-existing structural heterogeneities, such as stratigraphic contacts and fold hinges. Four main sets of veins are recognized in the district: shear veins, north–south tension veins, stacks of north-dipping tension veins, and anticline-hosted tension veins. Mineralized quartz veins are typically associated with a wallrock alteration assemblage comprising sericite, chlorite, carbonate, tourmaline, pyrite, pyrrhotite, and plagioclase. The presence of a WNW–ESE dextral strike–slip structure, an east–west reverse fault, and north–south tension veins are consistent with the formation of a Riedel system during a simple shear event. All vein sets cut deformed sedimentary rocks that were deposited in a pull-apart basin, which together with their planar geometries, indicates a late-Transamazonian orogen timing for gold mineralization. Extensive dating of other orogenic gold deposits in the Guiana Shield has revealed ages between 2.023 and 1.955 Ga for gold mineralization, which is broadly coeval with the onset of late-Transamazonian calc-alkaline volcanism and plutonism (2.05–1.88 Ga) south of the Guiana Shield.

Endohedral Beryllium Atoms in Ten-Vertex Germanium Clusters: Effect of a Small Interstitial Atom on the Cluster Geometry

Ten-vertex clusters are unusually versatile because polyhedra with 3-, 4-, and 5-fold symmetry are possible and are found in experimentally known structures. Such clusters therefore provide useful probes for subtle effects on cluster structure such as changing the electron count or introducing an interstitial atom. In this connection, DFT shows that one of the smallest possible interstitial atoms, namely beryllium, has relatively little effect on the structures of Be@Ge(10)(z) (z = +2, 0, -2, -4) clusters. Thus the same C(3v) and D(4d) polyhedra are found as the lowest energy structures for the isoelectronic pairs Be@Ge(10)(2+)/Ge(10) and Be@Ge(10)/Ge(10)(2-). Even for the more complicated potential energy surfaces of the Be@Ge(10)(2-)/Ge(10)(4-) and Be@Ge(10)(4-)/Ge(10)(6-) systems, the lowest energy structures are remarkably similar. Thus the same C(2v) structures are the global minima for both Be@Ge(10)(2-) and Ge(10)(4-). Similarly, the same slipped pentagonal prism structures are the global minima for both Be@Ge(10)(4-) and Ge(10)(6-).

The Conformational Dynamics of Model Slipped Strand DNA Structures are Determined by Base Pairing in the Heteroduplex Arm

Slipped strand DNA is formed from the out-of-register pairing of direct repeats into thermodynamically stable hairpin structures. The formation of slipped strand DNA is hypothesized to be an important intermediate in triplet repeat expansion, a mechanism associated with many hereditary and anticipative neurodegenerative diseases. In this study, we use three-way DNA junctions as models for slipped strand DNA structures. Each of the three-way DNA molecules have two homoduplex arms and one heteroduplex arm, and the structures and conformational dynamics of the model substrates are characterized using single-molecule fluorescence resonance energy transfer (smFRET). FRET can measure changes in the relative distances between two fluorophores that are sufficiently close together (20-80 A). In our experiments, junctions are end-labeled with donor and acceptor fluorophores, and the efficiency of energy transfer E between the fluorophores is measured as a function of time to approximate the distances between the fluorophores and to monitor the conformational dynamics of the arms. We find that the junctions have trigonal pyramidal geometry. In addition, we observe that the junctions with two or more A-A mispairs on the heteroduplex arm transition between two conformational states with conformer transition rates that are dependent on ionic strength. This investigation sheds light on the structural and dynamical properties of junctions formed by slipped strand DNA which are important for understanding how enzymes recognize and process these structures.

Secondary slip structures in heated micro-geometries

Design of gaseous MEMS devices is currently very limited by restrictions of the experimental visualisation techniques. Flow behaviour on such scales resultant from the geometrical confinement is significantly affected by slip phenomena where curvature of the wall and gradients of density and temperature influence flow patterns. This paper presents a numerical study of steady low Reynolds (Re≪1) and low Knudsen (Kn≪0.1) numbers in heated microchannel systems with curved walls. The flows, that will be described here, are characterised by vortex structures despite their very low Reynolds numbers. The performed investigation gives new insight to the flow behaviour for such conditions with an extensive topological study of the resultant flow structures. As an application we propose gaseous microfluidic systems, such as a flow diode. This study is unique in its application of Navier–Stokes set of equations with a secondary slip wall boundary condition formulation for non-isothermal domains.

Atomistic modeling of lattice frame effects on laser-induced dislocation behaviors in nanopore mending processes

In recent years, the femtosecond laser technique has emerged as an effective tool for defect mending, especially for fault repairs of the conducting wire in three-dimensional integrated circuits. However, the nanodefect mending mechanism subjected to photothermal and mechanical stress introduced by ultrafast laser dynamics is still not well understood so far. In this paper, the microscopic dislocation behaviors of the lattice mending of metallic nanopore defects induced by femtosecond laser is presented using a modified continuum-atomistic modeling approach and the quantitative dislocation-based analysis. Two different cases of lattice frame effects are elaborated to characterize the dislocation behaviors and the nanopore mending mechanisms. The lattice frame is found to possess a direct effect on controlling the mechanisms of nucleation and growth of dislocation during laser interaction with metallic microdefects. The nanopore defect with a symmetric lattice frame is observed to form a prismaticlike slip structure around the pore region, and the dislocation loop consequently expands along its glide-prism plane. The growth of the loops continues even after they are fully mended to form sessile junctions by creating a local anisotropic hardening structure. On the other hand, the nanopore defect of an asymmetric lattice frame induces drastically irregular lattice glides, forming a tight network of junction loops around the mended area. It was found that the fast shock wave enhanced by the stress concentration factor around the pore that enabled a cooperative movement of sheets of atoms around the pore. This particular mechanism causes a rapid mending of the hole with a metastable lattice structure. The heterogeneous reaction dynamics of dislocation nucleation on the pore defect surface is analyzed in detail in this study. The photomechanical and thermally-activated plastic flow of mending processes is also clearly elucidated. The results provide vital insights into better dynamic behavior characterization of how the ultrafast laser interacts with metallic microdefects.

Non-B DB: a database of predicted non-B DNA-forming motifs in mammalian genomes

Although the capability of DNA to form a variety of non-canonical (non-B) structures has long been recognized, the overall significance of these alternate conformations in biology has only recently become accepted en masse. In order to provide access to genome-wide locations of these classes of predicted structures, we have developed non-B DB, a database integrating annotations and analysis of non-B DNA-forming sequence motifs. The database provides the most complete list of alternative DNA structure predictions available, including Z-DNA motifs, quadruplex-forming motifs, inverted repeats, mirror repeats and direct repeats and their associated subsets of cruciforms, triplex and slipped structures, respectively. The database also contains motifs predicted to form static DNA bends, short tandem repeats and homo(purine•pyrimidine) tracts that have been associated with disease. The database has been built using the latest releases of the human, chimp, dog, macaque and mouse genomes, so that the results can be compared directly with other data sources. In order to make the data interpretable in a genomic context, features such as genes, single-nucleotide polymorphisms and repetitive elements (SINE, LINE, etc.) have also been incorporated. The database is accessed through query pages that produce results with links to the UCSC browser and a GBrowse-based genomic viewer. It is freely accessible at http://nonb.abcc.ncifcrf.gov.