Thermodynamic and kinetic aspects on the selective surface oxidation of binary, ternary and quarternary model alloys

Segregation and selective oxidation phenomena of minor alloying elements during annealing of steel sheets lead to the formation of bare spots after hot dip galvanizing. In order to understand the influence of common alloying elements on the surface chemistry after annealing, model alloys of binary (Fe-2Si, Fe-2Mn and Fe-0.8Cr), ternary (Fe-2Mn-2Si, Fe-2Mn-0.8Cr and Fe-2Si-0.8Cr) and quarternary (Fe-2Mn-2Si-0.8Cr) systems were investigated. The specimens were annealed for 60 s at 820 °C in N₂-5% H₂ gas atmospheres with different dew points −80 and −40 °C, respectively. Surface chemistry of the annealed specimens was obtained by using X-ray photoelectron spectroscopy (XPS). The field emission scanning electron microscopy (FE-SEM) was used to view surface morphology. At low dew point −80 °C, apart from the thermodynamical calculations such as solubility product of oxides and their critical solute concentrations, kinetics play a decisive role on the selective oxidation, i.e. oxygen competition. As expected, the amount of external selective oxidation of alloying elements are well pronounced at higher dew point −40 °C. An attempt has been made to explain the dominant process of Si and Mn on Cr-oxidation and segregation. It is observed that annealing of quarternary system at higher dew point shifts the Cr-oxidation from external to internal.     

Do formalin fixation and freeze‐thaw affect near‐infrared Raman spectroscopy of cartilaginous tissue? A preliminary ex vivo analysis of native human articular cartilage

Near‐infrared (NIR) Raman microprobe spectroscopy has been applied to the non‐invasive characterization of the biochemical structure of extracellular matrix in articular cartilage, a step forward along the path of in vivo diagnostic application of chondropathy. In most studies handling ex vivo cartilage specimens, formalin fixation or freeze‐thaw treatments have been applied in order to stabilize tissue and cell constituents prior to spectroscopic measurements. However, these pre‐processing manipulations might significantly affect certain target bands of the cartilage spectra, thus introducing biases in the characterizations, and potentially leading to data misinterpretation. In this study, we evaluated how formalin fixing and freeze‐thaw processes affect Raman spectra from human femur cartilage. Healthy cartilage specimens were fixed/stored either in a 10% neutral buffered formalin solution or in a deep freezer set at −80 °C. The results of this study show that formalin fixation significantly affects the NIR Raman spectra of cartilage specimens due to concurrent formalin absorption and water dehydration within both collagen and glycosaminoglycan macromolecules. Water dehydration was also confirmed in the amide I structure in the frozen‐thawed specimen, but to a much lesser extent. Furthermore, soaking the tissues in phosphate‐buffered saline solution minimized the storage‐induced Raman artifacts, but its immersion had limited effectiveness in formalin‐fixed specimens, predominantly due to an overlap of signals from the formalin liquid (i.e. emitting at 1046 and 1492 cm⁻¹). Therefore, to provide a highly accurate biochemical evaluation of extracellular matrix using NIR Raman spectroscopy, freeze‐thaw processes are more suitable for ex vivo samples of human cartilage than formalin fixation. Copyright © 2015 John Wiley & Sons, Ltd.     

Compressed sensing sodium MRI of cartilage at 7T: preliminary study

Sodium MRI has been shown to be highly specific for glycosaminoglycan (GAG) content in articular cartilage, the loss of which is an early sign of osteoarthritis (OA). Quantitative sodium MRI techniques are therefore under development in order to detect and assess early biochemical degradation of cartilage, but due to low sodium NMR sensitivity and its low concentration, sodium images need long acquisition times (15-25 min) even at high magnetic fields and are typically of low resolution. In this preliminary study, we show that compressed sensing can be applied to reduce the acquisition time by a factor of 2 at 7 T without losing sodium quantification accuracy. Alternatively, the nonlinear reconstruction technique can be used to denoise fully-sampled images. We expect to even further reduce this acquisition time by using parallel imaging techniques combined with SNR-improved 3D sequences at 3T and 7 T.     

Aberration athermal design for infrared search and trace optical system

To satisfy environment requirement of infrared search and trace optical system, an infrared diffractive/refractive hybrid optical system in 3.7–4.8 μm with 11.42° of field of view for passive athermalization is presented. The system is consisted of three lenses, including two aspheric surfaces and a diffraction surface, which has only two materials Ge and Si. The optical system has compact structure, small volume and light weight. The image quality of the system approaches the diffraction limit in the temperature range −80 °C to 160 °C. It is compatible with staring focal plane array which has a format of 320 × 240 and the pixel pitch of 30 μm. The system need not move the compensated lens repeatedly to obtain the best images from −80 °C to 160 °C and enhances the performance of target tracking and recognition.     

Studies on cryoprotectant toxicity to zebrafish (Danio rerio) ovarian tissue fragments

Cryopreservation of ovarian tissue is a viable alternative to cryopreservation of oocytes and embryos in many species but it has not been studied in fish. Selection of cryoprotectant is an important step in designing cryopreservation protocols. In order to identify the optimum cryoprotectant (CPA) in a suitable concentration for zebrafish ovarian tissue cryopreservation, studies on toxicities of five commonly used cryoprotectants methanol, ethanol, dimethyl sulfoxide (DMSO), ethylene glycol (EG) and propylene glycol (PG) were carried out. Experiments were conducted on ovarian tissue fragments consisting of stage I and stage II ovarian follicles. Ovarian tissue fragments were incubated in 90% L-15 medium (pH 9) containing 1-4M cryoprotectants for 30min at 22°C. Three different tests were used to assess ovarian tissue fragment viability: trypan blue (TB) staining, fluorescein diacetate (FDA) combined with propidium iodide (PI) staining and adenosine 5′- triphosphate (ATP) assay. Results from these tests showed that ATP assay was more sensitive than FDA+PI or TB staining for assessing cryoprotectant toxicity to follicles in tissue fragments. Methanol and ethanol were the least toxic cryoprotectants tested. Cryoprotectant toxicity increased in the order of methanol/ethanol, DMSO, PG and EG. Ethanol was used for zebrafish ovarian tissue for the first time and the results showed that the effect of methanol and ethanol on ovarian tissue fragments were comparable. As methanol has been shown to be the most effective cryoprotectant for zebrafish ovarian follicles in our laboratory, the use of ethanol will also be considered in assisting future freezing protocol design. The present study also showed that stage II ovarian follicles are more sensitive to cryoprotectant treatment than stage I follicles in tissue fragments. The results obtained in this study provided useful information for ovarian tissue fragment cryopreservation protocol design in the future.     

Cryopreservation of adult bovine testicular tissue for spermatogonia enrichment

To develop a procedure for cryopreservation of adult bovine testis tissue, the effects of dimethyl sulphoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), and their concentrations (v/v), as well as different thawing temperatures, on the cell viability of bovine testis tissue after freezing/thawing were examined. The highest testicular cell viabilities came from the media containing DMSO (85.3 ± 1.2 percent), PG (82 ± 1.0 percent) and EG (83.4 ± 1.0 percent) at 10 percent concentration respectively. Using 10 percent DMSO gave significantly higher spermatogonia percentage (61.1 ± 1.2 percent, P < 0.001) than processing with 10 percent PG (54.3 ± 0.6 percent) or 10 percent EG (55 ± 1.8 percent) after differential plating. Thawing in water bath of 37 or 97-100 degree C also provided significantly higher viabilities (85.1 ± 1.0, 85 ± 1.0 percent, P < 0.01, respectively) and spermatogonia percentages (56.6 ± 2.0, 56.6 ± 2.6 percent, P < 0.01, respectively) than that thawing at 4C (23.4 ± 0.8 percent for total viability, 8.97 ± 1.0 percent for spermatogonia percentage). Collectively, 10 percent DMSO and thawing in 37-100 degree C water baths were appropriate for the cryopreservation of bovine testicular tissue and subsequent spermatogonia enrichment.     

Process optimization and stability of D-limonene-in-water nanoemulsions prepared by ultrasonic emulsification using response surface methodology

d-limonene in water nanoemulsion was prepared by ultrasonic emulsification using mixed surfactants of sorbitane trioleate and polyoxyethylene (20) oleyl ether. Investigation using response surface methodology revealed that 10% d-limonene nanoemulsions formed at S₀ ratio (d-limonene concentration to mixed surfactant concentration) 0.6-0.7 and applied power 18 W for 120 s had droplet size below 100 nm. The zeta potential of the nanoemulsion was approximately −20 mV at original pH 6.4, closed to zero around pH 4.0, and around −30 mV at pH 12.0. The main destabilization mechanism of the systems is Ostwald ripening. The ripening rate at 25 °C (0.39 m³ s⁻¹ × 10²⁹) was lower than that at 4 °C (1.44 m³ s⁻¹ × 10²⁹), which was in agreement with the Lifshitz-Slezov-Wagner (LSW) theory. Despite of Ostwald ripening, the droplet size of d-limonene nanoemulsion remained stable after 8 weeks of storage.     

Electrical properties of KTiOPO4 single crystal in the temperature range from −100 °C to 100 °C

The electrical property of a KTiOPO₄ single crystal was studied by means of a dielectric spectroscopy method in the temperature range from −100 to 100 °C. Dielectric dispersion began at a temperature, T_S=−80 °C. It is believed that this dielectric dispersion is related to the ionic hopping conduction, which arises mainly from the jumping of K⁺ ions. The activation energy concerned with hopping conduction is E_a∼0.20 eV above T_S. T_S=−80 °C can be the minimum temperature for the hopping K⁺ ion.     

Assessing the effect of football play on knee articular cartilage using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC)

The prevalence of cartilage lesions is much higher in football athletes than in the general population. Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) has been shown to quantify regional variations of glycosaminoglycan (GAG) concentrations which is an indicator of early cartilage degeneration. The goal of this study is to determine whether dGEMRIC can be used to assess the influence in cartilage GAG concentration due to college level football play. Thirteen collegiate football players with one to four years of collegiate football play experience were recruited and both knee joints were scanned using a dedicated 8-channel phased array knee coil on a 3 T MRI system. The contrast concentrations within cartilage were calculated based on the T₁ values from dGEMRIC scans. No substantial differences were found in the contrast concentrations between the pre- and post-season across all the cartilage compartments. One year collegiate football players presented an average contrast concentration at the pre-season of 0.116 ± 0.011 mM and post-season of 0.116 ± 0.011 mM. In players with multiple years of football play, contrast uptake was elevated to 0.141 ± 0.012 mM at the pre-season and 0.139 ± 0.012 mM at the post-season. The pre-season 0.023 ± 0.016 mM and post-season 0.025 ± 0.016 mM increase in contrast concentration within the group with multiple years of experience presented with a > 20% increase in contrast uptake. This may indicate the gradual, cumulative damage of football play to the articular cartilage over years, even though the effect may not be noticeable after a season of play. Playing collegiate football for a longer period of time may lead to cartilage microstructural alterations, which may be linked to early knee cartilage degeneration.     

The electrochemical preparation and microwave absorption properties of magnetic carbon fibers coated with Fe3O4 films

Electrodeposition was employed to fabricate magnetite (Fe₃O₄) coated carbon fibers (MCCFs). Temperature and fiber surface pretreatment had a significant influence on the composition and morphology of Fe₃O₄ films. Uniform and compact Fe₃O₄ films were fabricated at 75 °C on both nitric acid treated and untreated carbon fibers, while the films prepared at 60 °C were continuous and rough. Microwave measurements of MCCF/paraffin composites (50 wt.% of MCCFs, pretreated carbon fibers as deposition substrates) were carried out in the 2-18 GHz frequency range. MCCFs prepared at 60 °C obtained a much higher loss factor than that prepared at 75 °C. However, the calculation results of reflection loss were very abnormal that MCCFs prepared at 60 °C almost had no absorption property. While MCCFs prepared at 75 °C exhibited a good absorption property and obtained −10 dB and −20 dB refection loss in wide matching thickness ranges (1.0-6.0 mm and 1.7-6.0 mm range, respectively). A secondary attenuation peak could also be observed when the thickness of MCCF/paraffin composite exceeded 4.0 mm. The minimum reflection loss was lower.     

Shuttle-like ZnO nano/microrods: Facile synthesis, optical characterization and high formaldehyde sensing properties

Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 °C), “green” (without any organic solvent or surfactant) and simple hydrothermal process in the solution of zinc chloride and ammonia water. X-ray diffraction and Raman spectroscopy indicated that the ZnO nano/microrods are a well-crystallized hexagonal wurtzite structure. Yet photoluminescence analysis showed that abundant intrinsic defects (52.97% electron donor defects and 45.49% electron acceptor defects) exist on the surface of ZnO crystals. Gas sensors based on the shuttle-like ZnO nano/microrods exhibited high sensitivity, rapid response-recovery and good selectivity to formaldehyde in the range of 10-1000 ppm at an optimum operating temperature of 400 °C. Through applying linear fitting to the plot of sensitivity versus formaldehyde concentration in logarithmic forms, the chemisorbed oxygen species on the ZnO surface were found to be O²⁻ (highly active among O₂, O₂⁻ and O⁻ species). Notably, formaldehyde can be easily distinguished from acetaldehyde with a selectivity of about 3. The high formaldehyde sensitivity is mainly attributed to the synergistic effect of abundant electron donor defects (52.97%) and highly active oxidants (surface adsorbed O²⁻ species) co-existed on the surfaces of ZnO.     

Design of midwave infrared athermalization optical system with a large focal plane array

Based on the most advanced staring focal plane array which had a format of 640 × 480 and the pixel pitch of 15 μm, a set of all-sphere midwave infrared ahermalization optical system was designed. The working wavelength was in 3–5 μm, the full field of view was 8.58°, the relative aperture was 1/2, the efficient focal length (EFL) was 80 m. The opticalsystem consisted of four lenses with three kinds of material – Ge, ZnSe and Si. All surfaces were sphere, which was easier to process test, making the cost inexpensive, and it could avoid using diffractive surface and aspheric surface. The image quality of the system approaches the diffraction limit in the temperature range −60 °C-180 °C. The design results proved that, the high resolution midwave infrared optical system had compact structure, small volume, high resolution and excellent image quality, meeting the design requirements, so that it could be used for photoelectric detection and tracking system.     

Quantitative MRI using T1ρ and T2 in human osteoarthritic cartilage specimens: correlation with biochemical measurements and histology

Purpose

A direct correlation between T_1ρ, T₂ and quantified proteoglycan and collagen contents in human osteoarthritic cartilage has yet to be documented. We aimed to investigate the orientation effect on T_1ρ and T₂ values in human osteoarthritic cartilage and to quantify the correlation between T_1ρ, T₂ vs. biochemical composition and histology in human osteoarthritic cartilage.

Materials and methods

Thirty-three cartilage specimens were collected from patients who underwent total knee arthroplasty due to severe osteoarthritis and scanned with a 3T MR scanner for T_1ρ and T₂ quantification. Nine specimens were scanned at three different orientations with respect to the B₀: 0°, 90° and 54.7°. Core punches were taken after MRI. Collagen and proteoglycan contents were quantified using biochemical assays. Histology sections were graded using Mankin scores. The correlation between imaging parameters, biochemical contents and histological scores were studied.

Results

Both mean T_1ρ and T₂ at 54.7° were significantly higher than those measured at 90° and 0°, with T_1ρ showing less increase compared to T₂. R_1ρ (1/T_1ρ) values had a significant but moderate correlation with proteoglycan contents (R=.45, P=.002), while R₂ (1/T₂) was not correlated with proteoglycan. No significant correlation was found between relaxation times (T_1ρ or T₂) and collagen contents. The T_1ρ values of specimen sections with high Mankin scores were significantly higher than those with low Mankin scores (P<.05).

Conclusions

Quantitative MRI has a great potential to provide noninvasive imaging biomarkers for cartilage degeneration in osteoarthritis.     

Comparison of quantitative imaging of cartilage for osteoarthritis: T2, T1ρ, dGEMRIC and contrast-enhanced computed tomography

Evaluation of glycosaminoglycan (GAG) concentration in articular cartilage is of particular interest to the study of degenerative joint diseases such as osteoarthritis (OA). Noninvasive imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT) have demonstrated the potential to assess biochemical markers of cartilage integrity such as GAG content; however, many imaging techniques are available and the optimization of particular techniques in the diagnosis of joint disease remains an active area of research. In order to highlight the differences between these various approaches, this work compares MRI (T1, T2 and T1ρ) and contrast-enhanced CT in human articular cartilage, in both the presence and absence of gadolinium-based contrast agent. Pre- and postcontrast T2 values were found to be similar on a regional level and correlated with each other. As expected, T1 values were shortened significantly on both a global and a spatial basis in the presence of gadolinium (Gd); similar results were found for T1ρ. T2 values were found to correlate mildly with postcontrast T1, T1(Gd) and with precontrast T1ρ values. In addition, contrast-enhanced CT values correlated with both precontrast T1ρ and T1(Gd) more strongly than with precontrast T2. Finally, T1(Gd) and precontrast T1ρ were found to be moderately correlated with CT data. However, T1(Gd) and precontrast T1ρ were found to be almost completely uncorrelated. Together, these results indicate that T1ρ, T2 and contrast-enhanced techniques may provide complementary information about the molecular environment in cartilage during the evolution of OA.     

A novel polyol method to synthesize colloidal silver nanoparticles by ultrasonic irradiation

A polyol synthesis of silver nanoparticles in the presence of ultrasonic irradiation was compared with other configurations (at ambient temperature, 120 °C, and 120 °C with injected solutions) in the absence of ultrasonic irradiation in order to obtain systematic results for morphology and size distribution. For applying ultrasonic irradiation, rather fine and uniform spherical silver particles (21 ± 3.7 nm) were obtained in a simple (at ambient temperature without mechanical stirring) and fast (within 4 min, 3.61 × 10⁻³ mol min⁻¹) manner than other cases (at ambient temperature (for 8 h, 0.03 × 10⁻³ mol min⁻¹): 86 ± 16.8 nm, 120 °C (for 12 min, 1.16 × 10⁻³ mol min⁻¹): 64 ± 14.9 nm, and 120 °C with injected solutions (during 12 min): 35 ± 6.8 nm; all other cases contained anisotropic shaped particles). Even though the temperature of polyol reaction reached only at 80 °C (<120 °C) in the presence of ultrasonic irradiation, a uniform mixing (i.e. enhanced collision between silver particle and surrounding components) by ultrasonic irradiation might induce a better formation kinetics and morphological uniformity.     

Studies on cryopreservation of luc gene transfected bluegill sunfish fibroblast cell line

The effect of cryopreservation on the survival of luc gene transfected bluegill sunfish fibroblast (BF-2) cells was investigated. Propane-1,2-diol was found to be the least toxic cryoprotectant when compared with DMSO and methanol. Both propane-1,2-diol and DMSO are effective in protecting cells from freezing damage. Whilst there were no significant differences in cell survival between cryoprotectant concentration (10 or 15%) and culture age used in this study, 7-day old culture appeared to be more resistant to freezing without cryoprotectant when compared with 3- and 14-day old culture. The highest cell survival values obtained with propane-1,2-diol (10%) and DMSO (10%) protection were 96.2 1.2% and 94.0 3.1% respectively. Initial subsequent cell growth after cryopreservation was slower than their non-frozen controls. The survival of transfected BF-2 cells (BF-2/luc1) after cryopreservation were very similar to those obtained with wild type cells being: 94.0 3.1% and 95.2 1.5% respectively with 10% DMSO protection. These results suggested that genetically modified fish cell lines may be equally amenable to cryopreservation as the wild type.     

Effect of GaInP intermediate barrier in 1.3 μm compressive-strained GaInAsP/GaInAsP multiple-quantum-wells laser diodes

In this article, 1.3 μm Ga_0.27In_0.63As_0.67P_0.33/Ga_0.11In_0.89As_0.24P_0.76 compressive-strain multiple-quantum-wells (CS-MQWs) with Ga_0.09In_0.91P intermediate barrier (IB) laser diodes (LDs) have been grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The photoluminescence (PL) measurement indicates that the CS-MQWs with 20 Å Ga_0.09In_0.91P IB have the narrowest full width at half maximum (FWHM) of 43.9 meV. The 55-μm-width metal contact and 900-μm cavity length as-cleaved broad-area LDs with the Ga_0.09In_0.91P IB have the better performance than those of LDs without Ga_0.09In_0.91P IB, including a threshold current density of 0.86 kA/cm², a differential quantum efficiency of 25.6%, an internal quantum efficiency of 50%, and an internal optical loss of 25 cm⁻¹. Finally, the GaInAsP/GaInAsP CS-MQWs with the Ga_0.09In_0.91P IB LDs were processed as 4-μm-width ridge and an as-cleaved 600-μm-cavity length. It exhibits a threshold current of 38.5 mA, a slope efficiency of 0.16 W/A, a characteristic temperature of 80.5 K, a maximum operating temperature up to 80 °C without power saturation, and a red-shift rate of 0.38 nm/°C, and a relaxation frequency response of 5.8 GHz. The 3-dB bandwidth for the LDs with GaInP IB is as high as 9 GHz without considering the damping factor and coupling loss.     

Empirical evaluation of metal deposition for the analysis of organic compounds with static secondary ion mass spectrometry (S-SIMS)

Metal-assisted (MetA) SIMS using the deposition of a thin Au or Ag layer on non-conducting samples prior to analysis has been advocated as a means to improve the secondary ion (S.I.) yields of organic analytes. This study focuses on the influence of time and temperature on the yield enhancement in MetA-SIMS using thick layers of poly(vinylbutyral-co-vinylalcohol-co-vinylacetate) (PVB) containing dihydroxybenzophenone (DHBPh) or a cationic carbocyanine dye (CBC) and spin-coated layers of the cationic dye on Si. Pristine samples as well as Au- and Ag-coated ones were kept between −8 °C and 80 °C and analysed with S-SIMS at intervals of a few days over a period of 1 month. The yield enhancement was found to depend strongly on the kind of evaporated metal, the storage temperature and time between coating and analysis.     

Effect of substrate bias voltages on the diffusion barrier properties of Zr-N films in Cu metallization

Zr-N diffusion barriers were deposited on the Si substrates by rf reactive magnetron sputtering under various substrate bias voltages. Cu films were subsequently sputtered onto the Zr-N films by dc pulse magnetron sputtering without breaking vacuum. The Cu/Zr-N/Si specimens were then annealed up to 650 °C in N₂ ambient for an hour. The effects of deposition bias on growth rate, film resistivity, microstructure, and diffusion barrier properties of Zr-N films were investigated. An increase in negative substrate bias resulted in a decrease in deposition rate together with a decrease in resistivity. It was found that the sheet resistances of Cu/Zr-N(−200 V)/Si contact system were lower than those of Cu/Zr-N(−50 V)/Si specimens after annealing at 650 °C. Cu/Zr-N(−200 V)/Si contact systems showed better thermal stability so that the Cu₃Si phase could not be detected.     

Production and corrosion resistance of NdFeBZr magnets with an improved response to thermal variations during sintering

This study describes an attempt to produce NdFeB magnets that are insensitive to the sintering temperature. It was found that addition of Zr to NdFeB magnets significantly augmented the thermal stability of this magnetic material during sintering at high temperature even at industrial scale. The best sintered magnets were produced by jet-milling the powder (to achieve an average 3.4 μm particle size), and then aligned, pressed and sintered under argon at 1100 °C for 3 h followed by appropriate heat treatment. The magnetic properties of the resulting magnets were: (BH)_m=403.8 kJ m⁻³ (±4.7 kJ m⁻³), B_r=1430 mT (±9 mT) and _iH_c=907 kA m⁻¹ (±12 kA m⁻¹). Large grain growth, in excess of 100 μm in the Zr-free magnets, was observed during sintering at 1100 °C. This did not occur in the presence of Zr. These observations imply that the sensitivity of this class of magnets to high sintering temperatures is greatly reduced by Zr addition. Corrosion resistance of NdFeB was therefore significantly improved by the addition of small amounts of Zr.