Microstructural evolution during laser resolidification of Fe-25 atom percent Ge alloy

The microstructural evolution of concentrated alloys is relatively less understood both in terms of experiments as well as theory. Laser resolidification represents a powerful technique to study the solidification behavior under controlled growth conditions. This technique has been utilized in the current study to probe experimentally microstructural selection during rapid solidification of concentrated Fe-25 atom pct Ge alloy. Under the equilibrium solidification condition, the alloy undergoes a peritectic reaction between ordered alpha(2) (B2) and its liquid, leading to the formation of ordered hexagonal intermetallic phase epsilon (DO19). In general, the as-cast microstructure consists of epsilon phase and e-p eutectic and alpha(2) that forms as a result of an incomplete peritectic reaction. With increasing laser scanning velocity, the solidification front undergoes a number of morphological transitions leading to the selection of the microstructure corresponding to metastable alpha(2)/beta eutectic to alpha(2) dendrite + alpha(2)/beta eutectic to alpha(2) dendrite. The transition velocities as obtained from the experiments are well characterized. The microstructural selection is discussed using competitive growth kinetics.

Detection of alpha(2u)-globulin and its bound putative pheromones in the preputial gland of the Indian commensal rat (Rattus rattus) using mass spectrometry

The role of pheromones and pheromone-binding proteins in the laboratory rat has been extensively investigated. However, we have previously reported that the preputial gland of the Indian commensal rat produces a variety of pheromonal molecules and preputial glands would seem to be the predominant source for pheromonal communication. The presence of pheromone-binding proteins has not yet been identified in the preputial gland of the Indian commensal rat; therefore, the experiments were designed to unravel the alpha(2u)-globulin (alpha 2u) and its bound volatiles in the commensal rat. Total preputial glandular proteins were first fractionated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and subsequently analyzed by mass spectrometry. Further, we purified alpha 2u and screened for the presence of bound pheromonal molecules with the aid of gas chromatography/mass spectrometry (GC/MS). A novel alpha 2u was identified with a high score and this protein has not been previously described as present in the preputial gland of Indian commensal rats.This novel alpha 2u was then characterized by tandem mass spectrometry (MS/MS). Peptides with m/z values of 969, 1192, 1303 and 1876 were further fragmented with the aid of MS/MS and generated de novo sequences which provided additional evidence for the presence of alpha 2u in the preputial gland. Finally, we identified the presence of farnesol 1 and 2 bound to alpha 2u. The present investigation confirms the presence of alpha 2u (18.54 kDa) in the preputial gland of the Indian commensal rat and identifies farnesol 1 and 2 as probably involved in chemo-communication by the Indian commensal rat.Copyright (C) 2010 John Wiley & Sons, Ltd.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfied linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc - Cys - Pro - Leu - Cys - NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of (CH)-H-alpha or (CH)-H-beta protons of Cys residues, with Subsequent elimination of H2S or H2S2. The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S-2. (J Am Soc Mass Spectrom 2009, 20, 783-791) (C) 2009 American Society for Mass Spectrometry.

Characterization of Alkali Induced Formation of Lanthionine, Trisulfides, and Tetrasulfides from Peptide Disulfides using Negative Ion Mass Spectrometry

Peptide disulfides are unstable under alkaline conditions, resulting in the formation of products containing lanthionine and polysulfied linkages. Electrospray ionization mass spectrometry has been used to characterize major species obtained when cyclic and acyclic peptide disulfides are exposed to alkaline media. Studies on a model cyclic peptide disulfide (Boc - Cys - Pro - Leu - Cys - NHMe) and an acyclic peptide, oxidized glutathione, bis ((gamma)Glu Cys - Gly - COOH), are described. Disulfide cleavage reactions are initiated by the abstraction of (CH)-H-alpha or (CH)-H-beta protons of Cys residues, with Subsequent elimination of H2S or H2S2. The buildup of reactive thiol species which act on intermediates containing dehydroalanine residues, rationalizes the formation of lanthionine and polysulfide products. In the case of the cyclic peptide disulfide, the formation of cyclic products is facilitated by the intramolecular nature of the Michael addition reaction of thiols to the dehydroalanine residue. Mass spectral evidence for the intermediate species is presented by using alkylation of thiol groups as a trapping method. Mass spectral fragmentation in the negative ion mode of the peptides derived from trisulfides and tetrasulfides results in elimination of S-2. (J Am Soc Mass Spectrom 2009, 20, 783-791) (C) 2009 American Society for Mass Spectrometry.

Characterization of a continuous CO2 laser-welded Fe-Cu dissimilar couple

Continuous CO2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different process conditions is studied. The process conditions are varied to identify and characterize the microstructural features that are independent of the welding mode. The study presents a characterization of the microstructure and mechanical properties of the welds. Detailed microstructural analysis of the weld/base-metal interface shows features that are different on the two sides of the weld. The iron side can grow into the weld with a local change in length scale, whereas the interface on the copper side indicates a barrier to growth. The interface is jagged, and a banded microstructure consisting of iron-rich layers could be observed next to the weld/Cu interface. The observations suggest that solidification initiates inside the melt, where iron and copper are mixed due to convective flow. The transmission electron microscopy (TEM) of the weld region also indicates the occasional presence of droplets of iron and copper. The microstructural observations are rationalized using arguments drawn from a thermodynamic analysis of the Fe-Cu system.

Microstructural Evolution during Laser Resolidification of Fe-18 At. Pct Ge Alloy

The technique of laser resolidification has been used to study the rapid solidification behavior of concentrated Fe-18 at. pct Ge alloy. The microstructural evolution has been studied as a function of scanning rate of laser beam. Scanning electron microscopy (SEM) reveals the formation of a two-layer (designated as "A" and "B") microstructure in the remelted pool. The A layer shows a band consisting of a network of interconnected channels and walls, quite similar to cell walls. The B layer shows dendritic growth. Transmission electron microscopic observations reveal the formation of bcc alpha-FeGe in the B layer. Laser melting has been found to play an important role in formation of the A layer. Microstructural evolution in B has been analyzed using the competitive growth criterion, and formation of bcc alpha-FeGe has been rationalized in the remelted layers.

Primary Structural Documentation of the Major Urinary Protein of the Indian Commensal Rat (Rattus rattus) Using a Proteomics Platform

Purpose: A number of proteome studies have been performed recently to identify pheromone-related protein expression and their molecular function using genetically modified rodents' urine. However, no such studies have used Indian commensal rodents; interestingly, in a previous investigation, we confirmed the presence of volatile molecules in commensal rodents urine and these molecules seem to be actively involved in pheromonal communication. Therefore, the present study aims to identify the major urinary protein [MUP] present in commensal rat urine, which will help us to understand the protein's expression pattern and intrinsic properties among the rodents globally. Experimental Design: Initially, the total urinary proteins were separated by 1-D and 2-D electrophoresis and then subsequently analyzed by Matrix Assisted Laser Desorption Ionization-Time of Flight and Mass Spectrometer (MALDI-TOF/MS). Furthermore, they were then fragmented with the aid of a Tandem Mass Spectrometer (TOF/TOF) and the identified sequences aligned and confirmed using similarity with the deduced primary structures of members of the lipocalin superfamily.Results: The SDS-PAGE protein profiles showed distinct proteins with molecular masses of 15, 22.4, 25, 28, 42, 50, 55, 68, and 91 kDa. Of these proteins, the 22.4 kDa protein was considered to be target candidate. When 2D electrophoresis was carried out, about similar to 50 spots were detected with different masses and various pI ranges. The 22.4 kDa protein was found to have a pI of about 4.9. This 22.4 kDa protein spot was digested and subjected to mass spectrometry; it was identified as rat MUP. The fragmented peptides from the rat MUP at 935, 1026, 1192, and 1303 m/z were further fragmented with the aid of MS/MS and generated de novo sequence and this confirmed this protein to be the MUP present in the urine of commensal rats.Conclusion: The present investigation confirms the presence of MUP with a molecular mass of 22.4 kDa in the urine of commensal rats. This protein may be involved in the binding of volatile molecules and opens up a discussion about how volatile and non-volatile molecules in the commensal rats' urine may contribute chemo-communication.

A fast time-domain algorithm for the assessment of tissue blood flow in laser-Doppler flowmetry

In this study, we derive a fast, novel time-domain algorithm to compute the nth-order moment of the power spectral density of the photoelectric current as measured in laser-Doppler flowmetry (LDF). It is well established that in the LDF literature these moments are closely related to fundamental physiological parameters, i.e. concentration of moving erythrocytes and blood flow. In particular, we take advantage of the link between moments in the Fourier domain and fractional derivatives in the temporal domain. Using Parseval's theorem, we establish an exact analytical equivalence between the time-domain expression and the conventional frequency-domain counterpart. Moreover, we demonstrate the appropriateness of estimating the zeroth-, first- and second-order moments using Monte Carlo simulations. Finally, we briefly discuss the feasibility of implementing the proposed algorithm in hardware.

Laser processing of high-Tc superconducting thin films

High-Tc superconducting thin films can be deposited and processed by pulsed and CW lasers, and a respectable materials technology for the Y-Ba-Cu-O superconductor is rapidly emerging. The pulsed laser deposition technique is simple because it produces films with compositions nearly identical to those of the target pellets. A larger variety of substrates can be used, compared to other deposition technologies, because of the relatively low temperature requirements. The laser deposition mechanism has been investigated. As-deposited superconducting films, epitaxial films with smooth surfaces, and multilayer structures with abrupt interfaces have been produced. The electrical transport properties can be changed locally using a focused argon-ion laser by modifying the oxygen stoichiometry. This laser writing can be erased by room-temperature exposure to an oxygen plasma. Other laser patterning methods such as material removal, melt-quench, and direct pattern transfer are being developed.

Heteroepitaxial Yba2cu3o7-X-Prba2cu3o7-X-Yba2cu3o7-X Weak Links Grown By Laser Deposition

Summary form only given. The authors have developed a controllable HTSC (high-temperature superconductor) weak-link fabrication process for producing weak links from the high-temperature superconductor YBa2Cu3O7-x (YBCO), using PrBa2Cu3O7-x (PBCO) as a lattice-matched semiconducting barrier layer. The devices obtained show current-voltage characteristics similar to those observed for low-temperature superconductor/normal-metal/superconductor (SNS) devices. The authors found good scaling of the critical currents Ic with area, A, and scaling of the resistances Rj with 1/A; the typical values of the IcRj product of 3.5 mV are consistent with traditional SNS behavior. The authors observed Shapiro steps in response to 100-GHz millimeter-wave radiation and oscillation of the DC supercurrent in a transverse magnetic field, thus demonstrating that both the AC and DC Josephson effects occur in these devices.

Low temperature processing and chacterization of SrBi2Nb2O9 thin films grown by pulsed laser ablation

Ex-situ grown thin films of SrBi2Nb2O9 (SBN) were deposited on platinum substrates using laser ablation technique. A low substrate-temperature-processing route was chosen to avoid any diffusion of bismuth into the Pt electrode. It was observed that the as grown films showed an oriented growth along the 'c'-axis (with zero spontaneous polarization). The as grown films were subsequently annealed to enhance crystallization. Upon annealing, these films transformed into a polycrystalline structure, and exhibited excellent ferroelectric properties. The switching was made to be possible by lowering the thickness without losing the electrically insulating behavior of the films. The hysteresis results showed an excellent square-shaped loop with results (P-r = 4 muC/cm(2) E-c = 90 kV/cm) in good agreement with the earlier reports. The films also exhibited a dielectric constant of 190 and a dissipation factor of 0.02, which showed dispersion at low frequencies. The frequency dispersion was found to obey Jonscher's universal power law relation, and was attributed to the ionic charge hopping process according to earlier reports. The de transport studies indicated an ohmic behavior in the low voltage region, while higher voltages induced a bulk space charge and resulted in non-linear current-voltage dependence.

Time-dependent analysis of an N2O gasdynamic laser

A simplified two-temperature model is presented for the vibrational energy levels of the N2O and N2 molecules of an N2O-N2-He gasdynamic laser (GDL), and the governing equations for the unsteady flow of the gas mixture in a convergent-divergent contour nozzle are solved using a time-dependent numerical technique. Final steady-state distributions are obtained for vibrational temperatures, population inversion, and the small-signal laser gain along the nozzle. It is demonstrated that, for plenum temperatures lower than 1200 K, an N2O GDL such as the present is more efficient than a CO2 GDL in identical operating conditions

Dielectric response in pulsed laser ablated (Ba,Sr)TiO3 thin films

The dielectric response of pulsed laser ablated barium strontium titanate thin films were studied as a function of frequency and ambient temperature (from room temperature to 320 degrees C) by employing impedance spectroscopy. Combined modulus and impedance spectroscopic plots were used to study the response of the film, which in general may contain the grain, grain boundary, and the electrode/film interface as capacitive elements. The spectroscopic plots revealed that the major response was due to the grains, while contributions from the grain boundary or the electrode/film interface was negligible. Further observation from the complex impedance plot showed data points lying on a single semicircle, implying the response originated from a single capacitive element corresponding to the bulk grains. Conductivity plots against frequency at different temperatures suggested a response obeying the 'universal power law'. The value of the activation energies computed from the Arrhenius plots of both ac and dc conductivities with 1000/T were 0.97 and 1.04 eV, respectively. This was found to be in excellent agreement with published literature, and was attributed to the motion of oxygen vacancies within the bulk. (C) 2000 American Institute of Physics. [S0021-8979(00)02801-2].

Formation of crystalline diamond from amorphous diamond-like carbon films by pulsed laser irradiation

The formation of crystalline diamond films from amorphous diamond-like carbon films by pulsed laser irradiation with a 300 μs non-Q-switched Nd:YAG laser has been established by a combined study of transmission electron microscopy, x-ray photoelectron spectroscopy, and electrical resistivity. The films have been prepared by glow discharge decomposition of a mixture of propane, n-butane, and hydrogen in a rf plasma operating at a frequency of 13.56 MHz. Prior to laser irradiation, the films have been found to be amorphous by transmission electron microscope studies. After irradiation, the electron diffraction patterns clearly point out the formation of cubic diamond structure with a lattice spacing of 3.555 Å. However, the close similarity between diamond and graphite electron diffraction patterns could sometimes be misleading regarding the formation of a diamond structure, and hence, x-ray photoelectron spectroscopic studies have been carried out to confirm the results. A chemical shift in the C 1s core level binding energies towards higher values, viz., from 286.5 to 287.8 eV after laser irradiation, and a high electrical resistivity >1013 Ω cm are consistent with the growth of diamond structure. This novel "low-temperature, low-pressure" synthesis of diamond films offers enormous potential in terms of device compatibility with other solid-state devices.

Reduction in magnetic field induced broadening of the resistive transition in laser‐deposited YBa2Cu3O7−x thin films on MgO

The magnetic field induced broadening of the normal to superconducting resistive transition of YBa2Cu3O7−x thin films laser deposited on (100) MgO substrates for field oriented parallel to the c axis is found to be significantly reduced in comparison with that found previously in single crystals and in films deposited on SrTiO3. This reduction in broadening is associated with a high density of defects which, while causing a slight decrease in Tc and an increase in the zero‐field transition width, seems to provide strong vortex pinning centers that reduce flux creep