Characterization Of Structural Changes Research Articles

Influence of the DC Current Annealing Treatment on Magnetotransport Properties of Soft-Magnetic Alloys with Amorphous Precursors

Multistep current annealing (CA) treatments were performed on amorphous FINEMETtype Fe-Cu-V-Si-B, as well as on a novel Fe-Al-Ga-P-C-B alloy with a large supercooled liquid region, in order to optimize their magnetotransport properties. On-line and post-annealing electrical resistivity measurements, DSC, XRD and Mössbauer spectroscopy were used for characterization of structural changes evolved during CA treatments. Results on magnetoresistance (MR) and magnetoimpedance (MI) effects after CA in ribbon samples with relaxed amorphous as well as precipitated nanocrystalline structure are presented. Significant improvement in MI-response after CA up to Z/Z ≈ 50% was recorded at frequencies 2-3 MHz. The highest MI-element sensitivity was found for low magnetic field intensity where values of about 6 %/kA/m for samples of Fe-Al- Ga-P-C-B alloy were attained.

Detection and Characterization of Structural Changes in the Hard-Disk Fluid under Freezing and Melting Conditions

The fluid of two-dimensional hard disks is investigated over a range of densities by Monte Carlo simulations in order to detect and characterize structural changes which take place when the condition of freezing and melting is approached. A novel method is proposed based on the use of the Voronoi tessellation and a certain shape factor which turns out to be a clear indicator of the presence of different underlying substructures (domains). Close to the freezing condition the probability distribution of the shape factor develops a second distinct maximum corresponding to a predominant presence of near-regular hexagons, whereas the original peak, having its origin primarily in pentagons and distorted hexagons, diminishes and disappears at melting density.

Characterization of Structural Changes in Vimentin Bearing an Epidermolysis Bullosa Simplex-like Mutation Using Site-directed Spin Labeling and Electron Paramagnetic Resonance

Mutations in intermediate filament protein genes are responsible for a number of inherited genetic diseases including skin blistering diseases, corneal opacities, and neurological degenerations. Mutation of the arginine (Arg) residue of the highly conserved LNDR motif has been shown to be causative in inherited disorders in at least four different intermediate filament (IF) proteins found in skin, cornea, and the central nervous system. Thus this residue appears to be broadly important to IF assembly and/or function. While the genetic basis for these diseases has been clearly defined, the inability to determine crystal structure for IFs has precluded a determination of how these mutations affect assembly/structure/function of IFs. To investigate the impact of mutation at this site in IFs, we have mutated the LNDR to LNDS in vimentin, a Type III intermediate filament protein, and have examined the impact of this change on assembly using electron paramagnetic resonance. Compared with wild type vimentin, the mutant shows normal formation of the coiled coil dimer, with a slight reduction in the stability of the dimer in rod domain 1. Probing the dimer-dimer interactions shows the formation of normal dimer centered on residue 191 but a failure of dimerization at residue 348 in rod domain 2. These data point toward a specific stage of assembly at which a common disease-causing mutation in IF proteins interrupts assembly.

Structural phase transitions in the cyano-elpasolite CS 2NaCo(CN) 6, a neutron diffraction study

We have studied the phase transformations in the cyano-elpasolite Cs 2NaCo(CN) 6 by neutron powder diffraction in the temperature range 300–630 K. The temperature evolution of diffraction patterns clearly indicates two phase transitions at T 1=500 K and T 2=590 K. Detailed characterization of structural changes confirms the sequence of phase transitions proposed earlier (P2 1/n↔P4/mnc↔Fm3 m) and provides, for the first time, a microscopic picture of the transformations of Cs 2NaCo(CN) 6.

Characterization of Structural Changes of Poly(vinyl methyl ether) γ-Irradiated in Diluted Aqueous Solutions

An aqueous deoxygenated dilute PVME solution (cP = 0.5 mass %) was irradiated with gamma-rays at different radiation doses (D = 0.2-10 kGy). At these concentrations and doses contracted molecules are formed but no macroscopic networks. For the analysis of the structural changes, the irradiated samples were analyzed by size exclusion chromatography (SEC) with a triple detector system, static light scattering, and viscometry. SEC measurements necessitate for the application of the universal calibration principle the knowledge of the Kuhn-Mark-Houwink (KMH) parameters. To obtain these parameters commercially available poly(vinyl methyl ether) was fractionated and analyzed by the same means. We found at 30 degrees C a KMH relationship to [eta] = 0.0226 (mL/g) x Mw(0.67) in THF. We observed an increase in molar masses without any significant structural changing for D < 0.5 kGy. With increasing radiation dose, the intramolecular cross-linking reaction becomes more and more important. The results of viscosity measurements show a slight increase in contraction for 1.0 kGy. For irradiation dose higher than D > 1.5 kGy, a strong contraction occurs. For D > 5.0 kGy, the favored intramolecular reactions lead to the formation of microgels.

Characterization of structural changes in thermally enhanced Kevlar‐29 fiber

AbstractThis exploratory investigation examined the structural mechanism accounting for the enhanced compressive properties of heat‐treated Kevlar‐29 fibers. A novel theory was set forth that hydrogen‐bond disruption and concurrent misorientation of crystallites may account for the observed augmentation of compressive properties. To examine the said theory, as‐received Kevlar‐29 fibers were characterized by thermogravimetric analysis and differential scanning calorimetry in an effort to determine if crosslinking and/or hydrogen‐bond disruption was responsible for the improved behavior in compression. Additionally, Kevlar‐29 fibers that had been exposed to treatment temperatures of 400, 440, and 470°C were profiled by Fourier transform infrared spectrophotometry to determine if crosslinking and/or hydrogen‐bond obfuscation had been promoted. The results indicate that both mechanistic changes occurred within the Kevlar‐29, albeit in different regions of the rigid‐rod polymer. In particular, heat treatment of poly‐p‐phenylene terephthalamide appears to have resulted in crosslinking of its skin region and hydrogen‐bond disruption within the core realm. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 417–424, 2004

FTIR spectroscopic characterization of structural changes in polyamide-6 fibers during annealing and drawing

First, we report the development of Fourier transform infrared (FTIR) spectroscopic methods to determine the α/γ-crystalline phase ratio of polyamide-6 fibers and, in combination with density measurements, the total crystallinity. Using density determinations of the crystallinity of pure α and pure γ samples, we found the absorption coefficient ratio for the 930 (α) and 973 cm−1 (γ) bands to be 4.4, from which we could obtain the α/γ ratio for any polyamide-6 sample. The application of this FTIR method to the quantitative analysis of phase changes during thermal treatment and the drawing of polyamide-6 was then made. We confirmed that crystallization during thermal treatments involved increases in both phases and did not involve crystal-to-crystal transformation, whereas drawing involved both crystallization of the amorphous phase in the α form and γ→α transformation. Finally, we revisited the band assignments for the amorphous phase of polyamide-6 and found that the band at 1170 cm−1 was not an amorphous band but, because its absorbance was independent of crystallinity, could be used as an internal reference band. The band at 1124 cm−1 was reliably attributed to the amorphous phase. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 536–547, 2001

Effects of ozone on the plasma membrane proteins in Arabidopsis thaliana (L.) leaves

ABSTRACTThe protein pattern of leaf plasma membranes from Arabidopsis thaliana (L.) Landsberg erecta was analysed in order to detect changes induced by acute short‐term ozone treatment. Plasma membranes were isolated 0, 3 and 8 h after the end of a 2 h fumigation of the plants with 500 nmol mol−1 of O3. Proteins extracted from plasma membranes were separated by high‐performance two‐dimensional polyacrylamide gel electrophoresis. Eight hours after the end of fumigation, one new protein appeared and the amounts of two other proteins increased significantly. The reported study is a first step towards the identification of plasmalemma proteins altered by ozone and to a more detailed characterization of structural changes occurring in the plasma membrane after ozone exposure.

Characterisation of structural changes in the arterial elastic matrix by a new fractal feature: directional fractal curve.

A new fractal feature, the Directional Fractal Curve (DFC), defined over an arc of 180 and composed of 90 fractal dimensions determined at intervals of arc of 2, is developed to account for the anisotropic property of a fractal texture. The DFC algorithm is first applied to two images with different textural patterns, one without directional preference and one with a well-organised texture. The DFC of these images shows different patterns. The technique is then applied to quantify the structure of the elastic texture in the arterial wall where the elastic network was imaged by scanning electron microscopy following selective tissue digestion. The results suggest: (i) that images of the elastin matrix of the arterial wall exhibit fractal properties with directional preference, (ii) the DFC gives quantitative parameters which allow characterisation of structural changes in the elastin matrix of the arterial wall in terms of disorganisation and fragmentation of elastin fibres-conditions which are associated with medial degeneration due to normal ageing or presence of arterial disease.

TEM characterization of structural changes in glass associated to Bragg grating inscription in a germanosilicate optical fibre preform

Bragg gratings were written in a slice of an optical fibre preform using two interfering uv pulsed laser beams at 243 nm. Microstructural changes within the germanosilicate glass were studied by transmission electron microscopy (TEM) and infrared spectroscopy. TEM investigation shows that the glass is densified at the grating grooves. Infrared absorption spectra have been recorded on a germanosilicate glass sample before and after in irradiation by a fringeless uv pulsed beam. Our conclusion is that uv irradiation-induced bond breaking allows structural relaxation of the non-equilibrium glass network which tends to densify without any noticeable change in coordination.

10] Quantitative information from complicated nuclear magnetic resonance spectra of biological macromolecules

This chapter discusses a series of examples that illustrate the way optimum, quantitative information about biomacromolecules in solution can be obtained from NMR spectra by a nonlinear least-squares (LSQ) analysis of the frequency spectra in combination with a linear prediction (LP) analysis of the time-domain signal (free induction decay, FID). The examples include (1) determination of the exchange rates of slowly exchanging amide protons in a protein from a single two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY) spectrum, (2) estimation of the intensities of overlapping signals in 2D NMR spectra, and (3) characterization of structural changes in a protein as function of pH. In all three cases, the LSQ analyses are based on the complete analytical expression for the discrete Fourier transform NMR spectrum. To elucidate the importance of using this expression, a short introductory review of its form and its deviation from a true Lorentzian is presented.

Fractal dimension from radiographs of peridental alveolar bone: A possible diagnostic indicator of osteoporosis

The purpose of this study was to investigate whether a radiographic estimate of osseous fractal dimension is useful in the characterization of structural changes in alveolar bone. Ten dry mandibular bone segments were radiographed from three controlled projection angles (−5, 0, +5 degrees), before and after acid-induced partial decalcification. Fractal dimension was estimated by regression analysis of power spectra computed by Fourier transform of selected regions of interest in digitized images of the radiographs. Repeated-measures ANOVA showed that fractal dimension so determined varied over anatomic locations ( p < .01), but increased after acid-induced demineralization ( p < .0005), irrespective of the radiographic projection angles ( p > .99). In vivo fractal dimension was computed from randomly selected intraoral radiographs of six premenopausal (ages, 32.8 ± 3.9) and six postmenopausal (ages, 62.5 ± 4.1) women. A significantly ( p < .01) higher fractal dimension was observed in the older group.

Characterization of Structural Change during Carbonization of Coal-tar Pitch

Coal-tar pitch was heat-treated at various temperatures up to 1000°C and the weight loss (Δw/w) measurement, CHN analysis, polarized-light microscopic observation, IR and ESR spectra, and X-ray diffraction study were done. These data gave us the feature of structural change of coal-tar pitch through carbonization reaction, especially the change which occurred in the temperature range of pitch solidifying was remarkable. The behavior of structural change varied with the heat-treatment temperature (HTT) 500-600°C as a border. At HTT 600°C the bulk mesophase was formed completely and absorption bands except aromatic rings disappeared in IR spectrum, and the value of interlayer spacing showed for a typical disoriented carbon, that was 3.44A. The radical concentration (N) was the maximum at this HTT 600°C.By plotting log N against Δw/w, a linear relationship was observed. This relationship suggests that the amount of released components is in proportion to the amount of breaking hydrocarbon chains, and it brings the radical formation.

Characterization of Structural Changes and Defects in Ion Bombarded GaAs

ABSTRACTIn-situ time resolved reflectivity, Rutherford backscattering and channeling and transmission electron microscopy have been employed to characterise the evolution of Ar+ ion implantation damage in GaAs as a function of ion dose at various irradiation temperatures. Specific reflectivity signatures have been identified and characterised in terms of observed structural changes to the GaAs. Reflectivity provides a simple and convenient means of monitoring damage build up during ion implantation. In contrast to accepted models for amorphous phase formation in semiconductors, GaAs has been observed to undergo a sudden transformation from a crystal containing a dense network of extended defects to an amorphous phase under elevated temperature irradiation conditions.

Structural changes in coals during pyrolysis

Derivative thermogravimetry (DTG), emanation thermal analysis (ETA), gas adsorption methods for surface area and microporosity measurements, helium pycnometry and mercury porosimetry have been used for the characterization of structural changes in two bitumenous coals of British origin (Manvers Wath and Markham Main), during heating in argon up to 980 °C (heating rate 5 °C/min). The results are compared and advantages of the ETA for the assessment of the surface area and porosity changes in dynamical conditions of thermal treatment are demonstrated.

Cross-Sectional Tem Characterization of Structural Changes Produced In Silicon By One Micron Picosecond Pulses

ABSTRACTPlan and cross-sectional transmission electron microscopy (TEM) has been used to examine the various bulk and surface structural changes observed in crystalline silicon following melting caused by the absorption of 1-μm pulses that are 4 ps in duration. We show for the first time that for picosecond excitation polycrystalline Si (p-Si), rather than singlecrystal Si, is always formed when the melt resolidifies. Specifically, cross-sectional TEM analyses indicate that a thin layer of fine-grained p-Si is formed at the interface of the melted region with the bulk. When the incident fluence is more than 10% above the melting threshold, the region between the surface and the fine-grained p-Si regrows as largergrain p-Si. This is the first reported observation of a large-grain p-Si layer on a fine-grain p-Si base in crystalline material. If the incident fluence is less than 10% above threshold, the region near the surface resolidifies as amorphous Si, but the narrow layer of fine-grained p-Si remains at the interface with the single crystal material. Present models for resolidification must be modified to account for these features.

FTIR studies of calcium and sodium ionomers derived from an ethylene–methacrylic acid copolymer

AbstractA systematic study of the sodium and calcium salts of an ethylene–methacrylic acid copolymer is reported. Fourier‐transform infrared spectroscopy (in the midinfrared region) is applied to the characterization of structural changes as a function of temperature and time of annealing. In the spectra of calcium ionomers, bands associated with carboxylate dimers are identified and assignments of specific spectral features to multiplets and clusters are discussed. The spectroscopic changes observed in the spectra of sodium ionomers differ somewhat from their calcium counterparts in that a single infrared band attributed to isolated carboxylate groups is observed. Assignments of specific bands to multiplets and clusters can, however, be made in a manner consistent with the interpretation of the spectra of calcium ionomers.

Quantitative characterization of the structure changes in low crystalline poly(ethylene terephthalate) fibres by X‐ray diffraction

AbstractA method has been established for obtaining an isotropic X‐ray diagram of oriented fibres using a four‐circle automatic diffractometer. The method was applied to the determination of the degree of crystallinity of a series of poly(ethylene terrephthalate) fibres with different history. For the characterization of structural changes in these fibres, the apparent size of the crystallities, the unit cell dimensions and the degree of orientation were determined. It is shown that this group of parameters adequately describes structural changes in the fibres with a low degree of crystallinity.

Characterization of structural changes of amylose-iodine solutions by circular dichroism

C.d. measurements on amylose iodine solutions carried out at different degrees of iodine saturation show that the decrease of the Cotton effect, observed earlier below DP 50 11,12, is mainly due to the decreasing complex formation constants. The continuous decrease of the Cotton effect above DP 50 is even more pronounced at higher iodine concentration. Slow addition of iodine leads to especially high Cotton effects with a marked maximum at DP 47–50 and only a small increase of the Cotton effect upon standing of the solutions. Rapid addition of iodine leads to considerably lower Cotton effects but a prolonged time-dependent increase. Further ordering, however, does not reach the same high degree as when ioidine is added slowly. The results are discussed in the light of a single and multichain initiation process. Studies with aggregating solutions on the one hand and with very dilute solutions on the other hand, strongly indicate that the c.d. intensity is related to a conformational state of helix ordering and not to an ordering by chain folding or regular intermolecular association. Thus, the slow, time-dependent increase of the Cotton effect reflects substantial conformational changes of amylose on binding iodine. The results indicate that in the range of DP 47–50 a particularly well ordered helix is formed. For production of the typical blue colour in aqueous soluton and stabilization of aligned polyiodide subunits there is no need to stipulate a special colloid or crystalline state of the complex.

Ca2+ regulation of conformational states in the transport cycle of spin-labeled sarcoplasmic reticulum ATPase.

Addition of Ca2+ in the presence of a nucleotide causes a change in the ESR spectra of sarcoplasmic reticulum labeled with a spin probe on the ATPase protein. The Caa+ concentration dependence of this change was studied with sarcoplasmic reticulum vesicles treated with Triton X-100 or sonication in order to prevent Ca’+ accumulation. In the presence of AMP-P(NH)P (adenyl-B-y1 imidodiphosphate), an ATP analog which binds but does not phosphorylate ATPase, the spectral effect occurs at Ca’+ concentrations (micromolar) producing activation of the enzyme. In the presence of ATP, the effect shifts to a higher Caa+ range (millimolar) which produces enzyme inhibition. In both cases, plots of an empirical spectral parameter versus Ca2+ concentration are consistent with a cooperative mechanism for the production of the Ca*+ effect. It is suggested that the observed spectral effects reflect conformational changes due to Ca2’ binding to sites which undergo reduction of Ca2’ affinity upon phosphorylation with ATP. Since the ESR spectra are sensitive to the occupancy of the transport sites, it can be demonstrated that, during steady state turnover, most of the ATPase is in an intermediate step after inward Ca2+ release and before recycling to a high affinity form. Nucleotide is required for any Ca” binding effect to be seen in the ESR spectrum and, in fact, spectral effects of nucleotide binding are evident in all states of the enzymatic cycle observed here. Different nucleoside moieties introduce specific modifications in the ESR spectra, suggesting a conformational basis for the different rate constants obtained with each nucleotide. Isolated vesicles of sarcoplasmic reticulum exhibit active transport of Ca2+ coupled to ATP hydrolysis. Clarification of the transport mechanism includes characterization of structural changes in the membrane-bound Ca2+-ATPase, occurring in parallel with partial reactions of the enzyme cycle. In this regard, spin-labeling provides a useful tool for studying conformational effects in functioning systems, with little or no effect from the label itself. This is particularly true of the iodoacetamide spin label (ISL) which has been shown to be sensitive to specific conformational changes in the ATPase enzyme without affecting either the ATPase activity or Ca2+ uptake