Band Boundaries Research Articles

Revisiting localized deformation in sand with complex systems

Complex systems techniques are used to analyse X-ray micro-CT measurements of grain kinematics in Hostun sand under triaxial compression. Network nodes with the least mean shortest path length to all other nodes, or highest relative closeness centrality, reside in the region where the persistent shear band ultimately develops. This trend, whereby a group of grains distinguishes themselves from the rest in the sample, remarkably manifests from the onset of loading. The shear band's boundaries and thickness, evident from the network communities' borders and essentially constant mean size, provide corroborating evidence of early detection of strain localization. Our findings raise the possibility that the formation and the location of the persistent shear band may be decided in the nascent stages of loading, well before peak shear stress. Grain-scale digital image correlation strain measurements and statistical tests confirm the results are robust. Moreover, the trends are unambiguously reproduced in a discrete element simulation of plane strain compression.

Mass Dependence of Iron Isotope Fractionation in Fe(II)–Fe(III) Electron Exchange Equilibration

A one hundred meter long ion-exchange chromatograph was used to establish rigorously the mass effects in the iron isotope fractionation in the Fe(II)-Fe(III) electron exchange equilibration.We used a highly porous, strongly basic anion exchange resin packed in glass columns. The abundance ratios of all natural iron isotopes, 54Fe, 56Fe, 57Fe, and 58Fe, in the effluent at the iron adsorption band boundary were measured with a mass spectrometer. The enrichment correlations among these isotopes were analyzed by three-isotope plots. The results clearly showed that the isotope fractionation of Fe(II)-Fe(III) is governed by the normal mass effect; the iron isotope fractionation is not proportional to the nuclear size, but proportional to the reduced mass difference of the pair of iron isotopes.

Calculating the Energy Spectrum of Complex Low-Dimensional Heterostructures in the Electric Field

An algorithm for solving the steady-state Schrödinger equation for a complex piecewise-constant potential in the presence of the E-field is developed and implemented. The algorithm is based on the consecutive matching of solutions given by the Airy functions at the band boundaries with the matrix rank increasing by no more than two orders, which enables the characteristic solution to be obtained in the convenient form for search of the roots. The algorithm developed allows valid solutions to be obtained for the electric field magnitudes larger than the ground-state energy level, that is, when the perturbation method is not suitable.

Quantitative analysis of the effect of zidovudine, efavirenz, and ritonavir on insulin aggregation by multivariate curve resolution alternating least squares of infrared spectra

Quantification of the effect of antiretroviral drugs on the insulin aggregation process is an important area of research due to the serious metabolic diseases observed in AIDS patients after prolonged treatment with these drugs. In this work, multivariate curve resolution alternating least squares (MCR-ALS) was applied to infrared monitoring of the insulin aggregation process in the presence of three antiretroviral drugs to quantify their effect. To evidence concentration dependence in this process, mixtures at two different insulin:drug molar ratios were used. The interaction between insulin and each drug was analysed by 1H NMR spectroscopy. In all cases, the aggregation process was monitored during 45min by infrared spectroscopy. The aggregates were further characterised by scanning electron microscopy (SEM). MCR-ALS provided the spectral and concentration profiles of the different insulin–drug conformations that are involved in the process. Their feasible band boundaries were calculated using the MCR-BANDS methodology. The kinetic profiles describe the aggregation pathway and the spectral profiles characterise the conformations involved. The retrieved results show that each of the three drugs modifies insulin conformation in a different way, promoting the formation of aggregates. Ritonavir shows the strongest promotion of aggregation, followed by efavirenz and zidovudine. In the studied concentration range, concentration dependence was only observed for zidovudine, with shorter aggregation time obtained as the amount of zidovudine increased. This factor also affected the aggregation pathway.

Replication timing in a single human chromosome 11 transferred into the Chinese hamster ovary (CHO) cell line

DNA replication in eukaryotes initiates from discrete genomic regions, termed origins, according to a strict and often tissue-specific temporal program. However, the genetic program that controls activation of replication origins has still not been fully elucidated in mammalian cells. Previously, we measured replication timing at the sequence level along human chromosomes 11q and 21q. In the present study, we sought to obtain a greater understanding of the relationship between replication timing programs and human chromosomes by analysis of the timing of replication of a single human chromosome 11 that had been transferred into the Chinese hamster ovary (CHO) cell line by chromosome engineering. Timing of replication was compared for three 11q chromosomal regions in the transformed CHO cell line (CHO(h11)) and the original human fibroblast cell line, namely, the R/G-band boundary at 11q13.5/q14.1, the centromere and the distal telomere. We found that the pattern of replication timing in and around the R/G band boundary at 11q13.5/q14.1 was similar in CHO(h11) cells and fibroblasts. The 11q centromeric region, which replicates late in human fibroblasts, replicated in the second half of S phase in CHO(h11) cells. By contrast, however, the telomeric region at 11q25, which is late replicating in fibroblasts (and in several other human cell lines), replicated in the first half of S phase or in very early S phase in CHO(h11) cells. Our observations suggest that the replication timing programs of the R/G-band boundary and the centromeric region of human chromosome 11q are maintained in CHO(h11) cells, whereas that for the telomeric region is altered. The replication timing program of telomeric regions on human chromosomes might be regulated by specific mechanisms that differ from those for other chromosomal regions.

Non-linear oscillatory rheological properties of a generic continuum foam model: Comparison with experiments and shear-banding predictions

The occurrence of shear bands in a complex fluid is generally understood as resulting from a structural evolution of the material under shear, which leads (from a theoretical perspective) to a non-monotonic stationary flow curve related to the coexistence of different states of the material under shear. In this paper we present a scenario for shear-banding in a particular class of complex fluids, namely foams and concentrated emulsions, which differs from other scenarios in two important ways. First, the appearance of shear bands is shown to be possible both without any intrinsic physical evolution of the material (e.g. via a parameter coupled to the flow such as concentration or entanglements) and without any finite critical shear rate below which the flow does not remain stationary and homogeneous. Secondly, the appearance of shear bands depends on the initial conditions, i.e. the preparation of the material. In other words, it is history dependent. This behaviour relies on the tensorial character of the underlying model (2D or 3D) and is triggered by an initially inhomogeneous strain distribution in the material. The shear rate displays a discontinuity at the band boundary whose amplitude is history dependent and thus depends on the sample preparation.

S-Wave Bound- and Resonant States of Two Fermions in Simple Cubic Lattice

Resonant two-electron states are examined in attractive Hubbard model on simple cubic lattice and exact formula for scattering cross section in the limit of low density (empty lattice) is calculated. S-wave pair is considered by means of lattice Green functions (LGF). Analytical form of these functions found by Joyce is used facilitating calculations, which were greatly hindered before by the necessity of using LGF's tabulated values. It is found that the actual peak of scattering cross-section is formed on the lower band boundary in discrepancy with formulae of the theory of scattering in solids.

Superelastic Deformation of TiNi Shape Memory Alloy Subjected to Various Subloop Loadings

This paper investigates the superelastic deformation behaviors of a TiNi shape-memory alloy (SMA) tape subjected to various subloop loadings in relation to local temperature variations and observed surface changes during a tension test. The results obtained are: (1) Upper and lower stress plateaus appear during loading and unloading accompanying the spreading and shrinking of the stress-induced martensitic transformation (SIMT) bands. In the case of unloading from the upper stress plateau under low stress rate, strain increases due to the spreading of the SIMT bands at the start of the unloading. (2) If stress at the upper stress plateau is held constant, creep deformation appears with the spread of the SIMT bands. The volume fraction in the martensitic phase increases in proportion to the increase in strain. (3) Where the strain is made to vary at the stress plateaus during loading or unloading, a return point memory effect can be seen in the reloading stress­strain curve. The spreading or shrinking of the SIMT bands starts from the boundary of the previous SIMT bands remaining from the preceding process. (4) The inclination angle of the SIMT band boundaries to the tensile axis of the tape is 33° for an aspect ratio of 5. The inclination angle is 42° in the center of the tape and 37° in the vicinity of the end secured by the grip, for an aspect ratio of 10. [doi:10.2320/matertrans.M2011288]

Crystallography of the Low Angle Lamellar Band Boundaries in ARB- Processed Aluminum Sheet

Lamellar bands are the primary structural features in accumulative roll bonding (ARB) of sheet metals. The structural refinement in ARB sheets occur by forming a dense distribution of lamellar band boundaries. The lamellar band boundaries initiate as low angle interfaces, parallel to the existing lamellar band boundaries, irrespective of the crystallographic orientations of the parent lamellar bands. From an extensive investigation it was found that the transverse directions across the lamellar band boundaries are rotated by an angle equal to their misorientations. Such a phenomenon is not sustained when the boundaries turn to high angle.

Evaluation of Property Scatter of Nickel Base Alloy IN 738 LC

The nickel base alloy IN 738 LC is in use for gas turbine blades since more than 25 years. In high temperature creep testing the conventionally cast alloy exhibits a comparably large property scatter which requires high safety margins in design and dimensioning and subsequently causes an incomplete exploitation of the materials potential. The reasons for this property scatter were investigated and traced back to different influencing factors. Parallel to investigations on the microstructure of post-exposure material and conventional scatter band analysis, artificial neural networks were successfully applied to discover relations between the chemical composition of the individual melt and the position of the corresponding test results within the global scatter band. Recommendations for a lifting of the lower scatter band boundary and the mean curve are derived.

Numerical study of chain conformation on shear banding using diffusive Rolie-Poly model

Shear-banding phenomenon in the entangled polymer systems was investigated in a planar Couette cell with the diffusive Rolie-Poly (ROuse LInear Entangled POLYmers) model, a single-mode constitutive model derived from a tube-based molecular theory. The steady-state shear stress σ s was constant in the shear gradient direction while the local shear rate changed abruptly, i.e., split into the bands. We focused on the molecular conformation (also calculated from the Rolie-Poly model) around the band boundary. A band was found also for the conformation, but its boundary was much broader than that for the shear rate. Correspondingly, the first normal stress difference (N 1) gradually changed in this diffuse boundary of the conformational bands (this change of N 1 was compensated by a change of the local pressure). For both shear rate and conformation, the boundary widths were quite insensitive to the macroscopic shear rate but changed with various parameters such as the diffusion constant and the relaxation times (the reptation and the Rouse times). The broadness of the conformational banding, associated by the gradual change of N 1, was attributed to competition between the molecular diffusion (in the shear gradient direction) and the conformational relaxation under a constraint of constant σ s.

Study of photodegradation kinetics of melatonin by multivariate curve resolution (MCR) with estimation of feasible band boundaries

Multivariate curve resolution-alternating least squares (MCR-ALS) has been applied to data collected from UV spectrophotometric analysis of melatonin samples exposed to light with varying irradiance power. MCR-ALS was able to explain the degradation kinetics of this drug, deducing the pure spectra and concentration changes of the different species present throughout the entire process. Possible rotational ambiguities associated with MCR solutions were investigated and their extent was evaluated. The extent of the rotation ambiguity was estimated from the band boundaries of feasible solutions calculated using the MCR-BANDS procedure. The use of a non-linear fitting routine allowed improving kinetic information and provided a method of evaluation of the rate constants of the degradation process. The degradation pathway was found to follow a first-order reaction model, in which melatonin underwent photo-oxidation of the indole ring to give a formylamine group. Kinetics of the reaction was shown to be dependent on irradiation conditions, with an increase of the rate constants when light power also increased.

The initial stages of formation of low angle boundaries within lamellar bands during accumulative roll bonding of aluminum

The nature of newly forming lamellar band boundaries was investigated in accumulative roll bonded aluminum. These boundaries initiate as low angle interfaces parallel to the existing lamellar band boundaries irrespective of the crystallographic orientation of the parent lamellar band. The transverse directions of the divided segments were found to rotate at an angle equal to the degree of misorientation between segments. Such a phenomenon is not sustained when the boundaries become high angle.

Mechanism for Modulation Response Improvement in Mutually Injection-Locked Semiconductor Lasers

The modulation response (MR) improvement in mutually injection-locked semiconductor lasers is analyzed. We show that the system becomes increasingly sensitive to the modulation when its operation point approaches the lock band boundary, suggesting that the MR enhancement results from a modulation-induced transition between locked and unlocked operations of the laser system.

Semimetal-Semiconductor Transitions in Semimetal Bismuth-Antimony Nanowires Induced by Size Quantization, Strain, and Magnetic Field

ABSTRACTIn this work, we study glass-coated single-crystal Bi98Sb02 wires obtained by liquid phase casting.Semimetal Bi98Sb02 nanowires exhibited a "semiconductor" behavior of the temperature dependence R(T) for wire diameters <400 nm, which is significantly higher than the critical diameter (70 nm) for similar dependences R(T) of pure bismuth nanowires. The thermopower sign reversal in the temperature dependence α(T) was found to depend on the wire diameter d. The effect is interpreted in terms of manifestation of the quantum size effect, based on the appearance a new scattering channel stimulated by fluctuations in the diameter d.The effect of negative magnetoresistance in a perpendicular magnetic field was observed for the first time both at H | | C3 and H | | C2 in magnetic fields of 1 T.It is shown that a semimetal-semiconductor transition can be controlled using an elastic strain and a strong magnetic field, which lead to a significant shift of the band boundaries of the energy extrema in the bands

Microstructural characterization and evolution mechanism of adiabatic shear band in a near beta-Ti alloy

The adiabatic shear band (ASB) was obtained by split Hopkinson pressure bar (SHPB) technique in the hat-shaped specimen of a near beta-Ti alloy. The microstructure and the phase transformation within the ASB were investigated by means of TEM. The results show that the elongated subgrains with the width of 0.2–0.4μm have been observed in the shear band boundary, while the microstructure inside the ASB consists of fine equiaxed subgrains that are three orders of magnitude smaller than the grains in the matrix. The β→ω(althermal) phase transformation has been observed in the ASB, and further analysis indicates that the shear band offers thermodynamic and kinetic conditions for the ω(althermal) phase formation and the high alloying of this alloy is another essential factor for this transformation to take place. The thermo-mechanical history during the shear localization is calculated. The rotational dynamic recrystallization (RDR) mechanism is used to explain the microstructure evolution mechanism in the shear band. Kinetic calculations indicate that the recrystallized fine subgrains are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.

Effect of Carbon Content on Cracking Phenomenon Occurring during Cold Rolling of Three Light-Weight Steel Plates

Effects of carbon content on cracking phenomenon, which often occurred in cold-rolled light-weight steel plates, were investigated in this study. Three steels were fabricated by varying carbon content, and their microstructures and tensile properties were investigated. The steel containing low carbon content of 0.1 wt pct consisted of thin κ-carbide bands, coarse band boundary κ-carbides, and ferrites. As the carbon content increased, volume fractions of κ-carbide bands and total κ-carbides increased, and band boundary κ-carbides were finely distributed in relatively wide band boundary areas. Microstructural observation of the deformed region of tensile specimens revealed that coarse κ-carbides continuously formed along band boundaries worked to initiate the cracking or to facilitate the abrupt crack propagation into ferrites or band boundaries in a cleavage fracture mode, while bands densely populated with fine, lamellar κ-carbides did not play a critical role in the cracking. Thus, the increase in carbon content effectively minimized the formation of band boundary carbides and reduced their size, thereby resulting in the prevention of cracking during cold rolling and in the simultaneous improvement of ductility and strength.

Mechanisms of Genomic Instabilities Underlying Two Common Fragile-Site-Associated Loci, PARK2 and DMD, in Germ Cell and Cancer Cell Lines

Common fragile sites (CFSs) are specific chromosome regions that exhibit an increased frequency of breaks when cells are exposed to a DNA-replication inhibitor such as aphidicolin. PARK2 and DMD, the causative genes for autosomal-recessive juvenile Parkinsonism and Duchenne and Becker muscular dystrophy, respectively, are two very large genes that are located within aphidicolin-induced CFSs. Gross rearrangements within these two genes are frequently observed as the causative mutations for these diseases, and similar alterations within the large fragile sites that surround these genes are frequently observed in cancer cells. To elucidate the molecular mechanisms underlying this fragility, we performed a custom-designed high-density comparative genomic hybridization analysis to determine the junction sequences of approximately 500 breakpoints in germ cell lines and cancer cell lines involving PARK2 or DMD. The sequence signatures where these breakpoints occur share some similar features both in germ cell lines and in cancer cell lines. Detailed analyses of these structures revealed that microhomologies are predominantly involved in rearrangement processes. Furthermore, breakpoint-clustering regions coincide with the latest-replicating region and with large nuclear-lamina-associated domains and are flanked by the highest-flexibility peaks and R/G band boundaries, suggesting that factors affecting replication timing collectively contribute to the vulnerability for rearrangement in both germ cell and somatic cell lines.

The Effects of Different Precipitation States on the Annealing Behaviour of AA6111

In this work the nucleation of the Cube recrystallised grains in AA6111 was investigated. The alloys were cold rolled to 85% and then annealed at different temperatures in an air circulation furnace. X-ray diffraction was used to obtain global textures and for specific area of interest, Electron-Back Scattered Pattern (EBSP) was used. In order to observe the microstructures after rolling and partially annealing, Scanning Electron Microscopy (SEM) was used. It was found that the recrystallisation textures are strongly related to the annealing temperature. The recrystallisation texture after low temperature annealing gives a strong retained rolling texture and at high temperature, a fairly random texture with weak Cube and rotated Cube components. The difference in the volume fraction of Cube with different alloys and annealing temperature are related to the deformation microstructures. Cube bands are observed to be deformation bands on the rolling plane. During annealing, precipitates are formed on the deformation band boundaries and Cube nuclei which are formed in the deformation Cube band are restricted to growth due to the precipitates.

Spatiotemporal Regulation of DNA Replication in the Human Genome and its Association with Genomic Instability and Disease

The transmission of genetic information relies on a coordinated network of cell cycle controls. Abnormalities in this network can result in genomic instability and lead to the transformation of normal cells into cancer cells. Chromosomal DNA replication is not only central to cellular division but also plays a crucial role in the maintenance of genomic integrity. DNA replication errors increase genetic instability, and may be a causative factor in diseases such as cancer and neuronal disorders. Replication in eukaryotes initiates from discrete genomic regions, termed origins, according to a strict, often tissue-specific, temporal program. The genetic program that controls activation of replication origins in mammalian cells has still not been elucidated. There is evidence that specification of replication sites and timing of replication are dynamic processes that are regulated by tissue-specific and developmental cues and that are responsive to epigenetic modifications. Here, we focus on the spatiotemporal regulation of DNA replication in the human genome. There is growing evidence that chromosome band patterns and epigenetic transformation of chromatin influence the timing of replication. On the basis of this evidence, we propose that the chromatin regions showing switches in replication timing from early to late in S phase are correlated with chromosome band boundaries. These chromatin regions generally display transitions in GC contents and include more non-B-form DNA structures than other genomic regions. We also examine here the effect of changes in replication timing on genomic stability and the possible role of replication timing in the etiology of diseases such as cancer. Replication timing assays are one of many promising techniques under investigation that may in future allow much earlier cancer detection than is possible today.