Dissociation Mode Research Articles

010] and [001] dislocations in laser clad NbAl3on Nb

Abstract The dislocation structure, the dislocation dissociation and the Burgers vectors in laser clad NbAl3 on a Nb substrate were investigated by transmission electron microscopy including weak beam contrast analysis by the g.b equals; 0 criterion, contrast width associated with edge and screw dislocations and high resolution electron microscopy (HREM). High densities of dislocations were observed in NbAl, grains. Contrast analysis by the g.b equals; 0 criterion and contrast width showed the presence of [010] and [001] dislocations. HREM revealed many ½[010] (partial) edge dislocations and ½[001] (partial) edge dislocations, suggesting the didocation dissociation modes: [010]→½[010] + ½[010] and [001]→½[001] +½[001]. It is suggested that such dislocations were introduced by the rapid cooling at high temperatures involved in the laser cladding process.

A weak-beam analysis of dissociation modes of superlattice dislocations in Ni 3(Al, Ti)

Dislocation mechanisms and their influence on mechanical properties (e.g. flow stress and work-hardening) can be studied in detail by critical prestraining experiments. In this study, the influence of prestrain on the flow stress of an Ni 3(Al, Ti) alloy with L1 2 long-range order structure was investigated. The yield strength has a positive temperature dependence (it increases with increasing temperature) from room temperature (RT) up to 450 °C. Prestraining of Ni 3(Al, Ti) single crystals at 800 °C activated the primary ± a[1 10](001) cube slip system. Climb dissociated segments interconnect superlattice dislocations of Lomer-Cottrell (LC) type. A subsequent additional deformation at RT introduced superlattice dislocations of the primary ± a[10 1](111) glide system. This subsequent deformation results in almost the same flow stress as the flow stress found in single crystals subjected to RT deformation only. Prestraining was found to have a huge influence on work-hardening. This is consistent with dislocation interactions of cube and octahedral glide systems. It is concluded that yielding is an intrinsic property of dislocation motion due to extended core configurations.

Dislocation structure in L1 2 Mn-stabilized Al 3Ti deformed between 77 and 873 K

Polycrystalline samples of L1 2 Mn-stabilized Al 3Ti were deformed in compression from low temperature to the temperature of the flow stress plateau. The fine structure of the superdislocations was analyzed under weak-beam conditions with particular attention paid to the operating glide systems at different temperatures. The dissociation mode of the dislocations was also addressed in order to discriminate between antiphase boundary-coupled dislocations and Superlattice Intrinsic Stacking Fault (SISF)-coupled partial dislocations. The existence of a strong Peierls effect on undissociated 〈110〉 dislocations during deformation at 573 K is reported, as well as the observation at low temperature of dislocations with 〈100〉 and 〈112〉 Burgers vectors.

Studies on the sedative activity of crude extract of root bark of Rauvolfia canescens on rats

Monoterpene indole alkaloids (MIAs) are medicinally important class of compounds abundant in the roots of Rauwolfia species (Apocynaceae). MIAs such as yohimbine (aphrodisiac agent) and reserpine (antihypertensive, tranquilizer) are the official drugs included in Model List of Essential Drugs of World Health Organization (WHO). Therefore, we have attempt to identify and characterize the MIAs in the crude extracts of six Rauwolfia species using ultrahigh-performance liquid chromatography coupled with Orbitrap Velos Pro hybrid mass spectrometer. The identity of the MIAs were construed using the high resolution tandem mass spectrometry (HRMS/MS) spectra of standard compounds ‘yohimbine’ and ‘reserpine’ in higher energy collisional dissociation (HCD) and collision-induced dissociation (CID) modes. The diagnostic fragment ions found in HCD mode was highly affected by variation of normalized collision energy (NCE) and gave few product ions (‘C–F’) while CID produced intense and more diagnostic product ions (‘A–F’). Consequently, CID-MS/MS mode provided significantly more structural information about basic skeleton and therefore the recommended mode for analysis of MIAs. Furthermore, six diagnostic fragmentation pathways were established by multi-stage mass analysis (MSn (n = 5)) analysis which gave information regarding the substitution. Fragment ions ‘A–F’ revealed the number and position of substituents on indole and terpene moieties. The proposed diagnostic fragmentation pathways have been successfully applied for identification and characterization of MIAs in crude root extracts of six Rauwolfia species. Ten bioactive reserpine class of MIAs were tentatively identified and characterized on the basis of chromatographic and mass spectrometric features as well as HRMS/MS an MSn (n = 4) analysis.

On the decay modes of hydrogen-helium mesic molecules

Radiative, Auger and two-particle dissociation modes of hydrogen-helium mesic molecules are considered. Auger rate is shown to be independent of the isotopic content of the molecule and amounts to ∼25% of radiative one. Two-particle decay rate strongly depends on the isotopic content and for light isotopes is an order of magnitude higher than the radiative rate.

Electron impact‐induced fragmentation of 2,1‐benzisothiazoline 2,2‐dioxide

AbstractThe electron impact‐induced fragmentation patterns of 2,1‐benzisothiazoline 2,2‐dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked‐scan), parent ion, and constant neutral loss spectra in metastable and collision‐induced dissociation modes and deuterium labelling.

Anion complexes between a macrocyclic cyclophane and squaric acid: The crystal structure reveals the ideal receptor topology ordered by the substrate

Abstract The expected [1:2] complex between a tetraprotonated tetraazapara-cyclophane and squaric acid is not formed and the ligand undergoes drastic deformation. The peculiar features of this structure is the coexistence, in the same crystal cell, of 2 types of crystal lattice inclusions, corresponding to 2 different dissociation modes of squaric acid.

Dissociation of glide dislocations and apb energy in L12(Al,Cr)3Ti alloys

The L1[sub 2] trialuminides with a cubic structure are receiving much attention because of the importance as potential high temperature structural materials. These alloys contain a high amount of alumium and thus have an advantage of good economy. Among them, chromium-modified (Al,Cr,)[sub 3]Ti has been reported to have high resistance to high temperature oxidation, as well as ambient compressive ductility. The alloys show good compressive ductility even at room temperature, but only a fraction of per cent of tensile elongation has been reported. However, no clear explanation has been made for the origin of this rather peculiar behavior of the alloys. Moreover, it is still in question as to whether or not the observed ductility behavior comes from the intrinsic nature of the alloys. In the present investigation, observation by TEM was made of dislocation structures in chromium-modified alloys induced by compressive deformation. Focus was on the dissociation mode of glide dislocations and also on the energy of the planar defect in connection with possible ductility of the alloys.

Dislocation structure in L1 2 long-range-ordered Ni 3(Al,Ti) deformed in the temperature regime between −196°C and 800°C

Ni 3(Al,Ti) belongs to the large category whose representatives illustrate anomalous flow stress behaviour. Up to 450°C the flow stress increases with increasing temperature. It is therefore a challenge to study the structure of superlattice dislocations and their intrinsic properties in compressed L1 2 long-range-ordered Ni 3(Al,Ti) by means of transmission electron microscopy (TEM). A detailed analysis of the changes in the dislocation structure in the wide temperature range between −196°C and 800°C is presented. The fine structure and dissociation modes of dislocations were identified by weak-beam microscopy. Slip behaviour and transition of slip systems are discussed with respect to comprehending yielding properties. The onset of the flow stress anomaly is strongly correlated with the observation of screw superlattice b = ± a[10 1] dislocations are predominant and octahedral (1 11 ) cross-slip occurs. Approaching the temperature temperatures edge dislocations are predominant and octahedral (1 1 1) cross-slip occurs. Approaching the temperature where the flow stress reaches its maximum, octahedral ±a[10 1](111) slip is gradually replaced by cube ± a[110](001) slip. Above the peak temperature single cube slip controls deformation. Thermally assisted exhaustion of primary octahedral slip by cube cross-slip is regarded as responsible for the anomalous yielding behaviour.

Transmission electron microscopy study of dislocation structures in iron-doped al3ti with the l12structure

Abstract The dislocation structures and dissociation modes of superdislocations in L12-modified A167Fe8Ti25 deformed at room temperature and 600[ddot]C were investigated by means of transmission electron microscopy. It was revealed that in samples deformed at room temperature, dislocations dissociated into two (a/3) superpartials separated by superlattice intrinsic stacking faults on {111} planes with a strong tendency to form dipoles. In samples deformed at 600[ddot]C, dislocations dissociated into two (a/2) superpartials separated by antipnase boundaries on the cube {001} planes, predominantly with near-edge character. The factors controlling the plastic behaviour and brittleness of the L12-modified Al3Ti at low and high temperatures are discussed in relation to the observed dissociation modes of superdislocations in this material.

TEM evidence of various glide modes in experimentally strained CuFeS2crystals

Abstract TEM studies at 200°C (0.41 Tm) on experimentally deformed chalcopyrite (CuFeS2) single crystals reveal a variety of structural defects in the planes {112}, (001) and {100}. In {112} several glide modes have been identified. The majority of dislocations in {112} have (presumably) b = 1/2<311> and are accumulated in separated slip bands of high dislocation density. Line directions and dissociation modes of these dislocations depend on the orientation of the applied stress. Dislocations of the slip mode {112} <311>, mainly parallel to <110> or <021>, are dissociated into three non-collinear partials. Dislocations of the slip mode {112} <311>, often parallel to <111>, are dissociated into four non-collinear partials. Dislocations of the subordinate slip mode {112} <111> with b = 1/2 {111} commonly are screws, dissociated into three collinear partials. Perfect dislocations with b = <211> seem to decompose into pairs of perfect dislocations with b = 1/2<311> and b = 1/2<111>. Dislocations with b = <110> enter {112} by cross slip from (001). The twinning mode {112}<111> develops from the movement of dislocations with b = 1/6<111>. Dislocations of the slip mode (001)<111> are generally split into two collinear partials. Cross slip into {112} takes place with or without recombination of the partials. The slip mode {100}⟨010⟩ has been activated in the surroundings of high-density {112} slip bands. Dislocations with b = ⟨010⟩ form square loops with long segments along ⟨021⟩ and are split into two non-collinear partials b = 1/4⟨021⟩. Models of the dissociation of the diverse perfect dislocations are discussed.

Mass spectra of hydrazides and alkylhydrazides or fluorinated alkanecarboxylic acids

Main pathways in the electron-impact induced mass spectrometric fragmentation of hydrazides and alkylhydrazides of alkanecarboxylic acids have been studied. The effect of the structure of fluorinated acyl group and hydrocarbon radical on the dissociation mode has been established.

Secondary photon emission induced by particle bombardment of alkali chlorides

We have bombarded polycrystalline targets of LiCl, NaCl, KCl, RbCl, or CsCl with H + , H 2 + , H 3 + , at 30 keV/amu or Ar + at 2 keV/amu and studied the spectra of secondary photons emitted in the wavelength interval 200–900 nm. The optical emission spectra consist of atomic line radiation emitted from sputtered alkali atoms or hydrogen superimposed on continua emitted from the solid targets. For each compound, the shapes of the continua induced by light or heavy ion bombardement are largely the same but the continua observed here are very different in shape from recombination luminescence spectra observed previously from alkali chlorides exposed to X-rays or electrons. Also, H 2 + and H 3 + produce less continuum radiation per proton than H + . Hydrogen projectiles produce much less excitation of sputtered atoms than Ar + projectiles. There is no clear correlation between the intensity of the continuum and the yield of excited, sputtered atoms. In other words, there is no clear correlation between the electronic excitation of the solid target and the yield of excited sputtered atoms. Also, there is no correlation between the yield of excited, sputtered atoms and the dissociation mode (whether being ionic or atomic) of the target material.

Fault energies in ordered and disordered Ni3Fe

Abstract The weak-beam method of electron microscopy has been used to study the dissociation and the fault energies in disordered and ordered Ni3Fe. For the ordered structure this is of particular interest since in this case the plastic behaviour is determined by the dissociation mode of the superlattice dislocations. Single crystals of Ni3Fe were quenched to suppress the formation of the long-range ordered phase and strained at room temperature. From the dissociation of the Shockley partials the stacking fault energy of the disordered f.c.c. phase γ = 95 ± 14 mJ m −2 was deduced. A section of the disordered and deformed crystal was subsequently fully ordered (Ll2 superlattice structure) and additionally deformed. The complex stacking fault energy γcsF = 123 ± 13 mJ m −2 was deduced from dissociated unit dislocations which were sessile since they had been introduced before ordering. The deformation of the ordered crystal proceeds by the formation of superlattice dislocations. These dislocations show a fou...

Systematics of exclusive diffraction dissociation modes inK � p interactions at 32 GeV/c

We present results of an investigation of diffraction dissociation in exclusive channels inK ± p interactions at 32 GeV/c. Total cross sections are determined forK ±→K ±π+π−,K ±2π+2π−,K 0π±π± K ±2π+π−,K ± K + K −,K ±p $$\bar p$$ , $$\bar \Lambda $$ p, andp→pπ +π−,p2π+2π−,pK +K−,ΛK +,ΛK +π+π− dissociation modes, ranging from a high of ≃ 300 μb to ∼ 3 μb. Thedσ/dt′ differential cross sections of most of the systems studied exhibit structure, with breaks of slope att′ ∼ 0.2 to 0.5 GeV2; some modes have a sharp forward spike with a slope exceeding 10 GeV−2. A systematic investigation of two-body dissociation modesK→A+B andp→A′+B′ shows that these cross sections decrease with increasing threshold massM A+M B, that they are comparable for kaon and proton dissociations at similar diffractive excitation masses and are systematically suppressed by a factor 3–4 for dissociations requiring an $$s\bar s$$ quark pair creation when compared to $$u\bar u$$ pair creation indicating a breakdown ofSU 3 symmetry for the $$q\bar q$$ sea.

Dissociation of dislocation witha/2〈111〉 Burgers vectors in YIG single crystals deformed at high temperature

Abstract It is shown that dislocations with a/2〈111〉 Burgers vector in yttrium iron garnet (YTG) deformed in compression above 0.8T M are dissociated into two partials following: a/2〈111〉→a/4〈111〉 + a/4〈111〉. The dissociation mode involves a climb component which renders the glide motion of the dislocation difficult. The dissociation width is not constant and cannot be used to derive a stacking-fault energy intrinsic to the crystal. The variations in width are probably associated with local interactions with point defects. Pure climb motion of the dislocations, consistent with the dissociation, is experimentally observed.

The control region for erythromycin resistance: free energy changes related to induction and mutation to constitutive expression.

The mRNA sequence in plasmid pE194 encoding the gene responsible for erythromycin resistance has been deduced from the corresponding DNA sequence. The putative control region of this gene located at the 5′ end of the messenger transcribed along with the coding sequence comprises a series of inverted complementary repeat sequences that can redistribute and assume alternative double stranded conformations. Activation of the messenger depends on the degree to which ribosomes inhibited (“stalled”) by erythromycin disrupt the secondary structure in a part of the control region that simultaneously codes for a small peptide and overlaps two of the inverted repeat sequences. In this model, ribosome stall is produced by erythromycin, the inducer, and the result of inverted repeat sequence redistribution is the unmasking of a ribosome binding site for synthesis of the protein that mediates the resistance phenotype. Free energy calculations have been made for the postulated “active” and “inactive” conformations of the control region as well as for 4 classes of mutants that have been mapped in the control region. In addition, calculations have been made for hypothetical sequence alterations corresponding to mutants not yet found. Two modes of induction have been defined and their associated free energy changes calculated; these are (i) preemptive induction, in which ribosome stall resulting in disruption of stem sequence conformation causes one inverted repeat sequence to preempt a second. In the resultant redistribution of complementary inverted repeat sequences, the control region assumes the “active” conformation owing to unmasking of a sequestered ribosome binding site, and (ii) direct dissociation of the critical stem sequences to unmask the sequenstered ribosome binding site, a reaction that bypasses the preemptive association mechanism. The base change found in one of the mutants is consistent with the preemptive mode of induction according to which ribosome stall to an extent that destabilizes the firt three of 13 possible paired bases in the inactive form of the messenger suffices to induce expression of the resistance phenotype. The single-base-change mutations to constitutive expression most commonly found are precisely those that produce the greatest loss of negative free energy; this majority group affects the control region sequence further downstream and appears to act by the direct dissociation mode. Finally, a pair of weakly interacting inverted repeat sequences flanking the more strongly interacting repeats is present; it is postulated that this outer pair serves during the initial phase of induction, as well as later, to turn off expression of the induced messenger after removal of an inductive stimulus. The wide variety of possible mutations capable of disrupting stability of the control region suggests a model to explain the diversity of “partial constitutive” phenotypes found in earlier studies.

Hypnotic dissociation, dichotic listening, and active versus passive modes of attention.

Hypnotic dissociation, dichotic listening, and active versus passive modes of attention.

A simple comparative test of multiple versus single-centered spherical gaussians

HeH++ was selected as a simple model for the comparison of relative efficiencies of single and multi-centered Gaussian functions in computing molecular orbitals and their corresponding energies. One-, two-, and three-center linear combinations of twelve basis functions were applied to the calculation of potential curves for the ground state and lowest two excited sigma states of HeH++. A point-by-point comparison was made with the same states generated by an exact solution calculation. This comparison demonstrated that the multi-centered functions were capable of reproducing energy minima, potential curve crossings and dissociation modes in agreement with the exact calculation. The single center functions were not capable of duplicating this behavior.

Hypnotic dissociation, dichotic listening, and active versus passive modes of attention.

Hypnotic dissociation, dichotic listening, and active versus passive modes of attention.