Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using In Situ Neutron Diffraction

Stacking fault energies (SFE) were determined in additively manufactured (AM) stainless steel (SS 316 L) and equiatomic CrCoNi medium-entropy alloys. AM specimens were fabricated via directed energy deposition and tensile loaded at room temperature. In situ neutron diffraction was performed to obtain a number of faulting-embedded diffraction peaks simultaneously from a set of (hkl) grains during deformation. The peak profiles diffracted from imperfect crystal structures were analyzed to correlate stacking fault probabilities and mean-square lattice strains to the SFE. The result shows that averaged SFEs are 32.8 mJ/m2 for the AM SS 316 L and 15.1 mJ/m2 for the AM CrCoNi alloys. Meanwhile, during deformation, the SFE varies from 46 to 21 mJ/m2 (AM SS 316 L) and 24 to 11 mJ/m2 (AM CrCoNi) from initial to stabilized stages, respectively. The transient SFEs are attributed to the deformation activity changes from dislocation slip to twinning as straining. The twinning deformation substructure and atomic stacking faults were confirmed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The significant variance of the SFE suggests the critical twinning stress as 830 ± 25 MPa for the AM SS 316 L and 790 ± 40 MPa for AM CrCoNi, respectively.

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

Reduced microvascular volume and hemispherically deficient vasoreactivity to hypercapnia in acute ischemia: MRI study using permanent middle cerebral artery occlusion rat model

Vasoreactivity to hypercapnia has been used for assessing cerebrovascular tone and control altered by ischemic stroke. Despite the high prognostic potential, traits of hypercapnia-induced hemodynamic changes have not been fully characterized in relation with baseline vascular states and brain tissue damage. To monitor cerebrovascular responses, T2- and T2*-weighted magnetic resonance imaging (MRI) images were acquired alternatively using spin- and gradient-echo echo plannar imaging (GESE EPI) sequence with 5% CO2 gas inhalation in normal (n=5) and acute stroke rats (n=10). Dynamic relative changes in cerebrovascular volume (CBV), microvascular volume (MVV), and vascular size index (VSI) were assessed from regions of interest (ROIs) delineated by the percent decrease of apparent diffusion coefficient (ADC). The baseline CBV was not affected by middle cerebral artery occlusion (MCAO) whereas the baseline MVV in ischemic areas was significantly lower than that in the rest of the brain and correlated with ADC. Vasoreactivity to hypercapnic challenge was considerably attenuated in the entire ipsilesional hemisphere including normal ADC regions, in which unsolicited, spreading depression-associated increases of CBV and MVV were observed. The lesion-dependent inhomogeneity in baseline MVV indicates the effective perfusion reserve for accurately delineating the true ischemic damage while the cascade of neuronal depolarization is probably responsible for the hemispherically lateralized changes in overall neurovascular physiology.

Robust MR assessment of cerebral blood volume and mean vessel size using SPION-enhanced ultrashort echo acquisition

Intravascular superparamagnetic iron oxide nanoparticles (SPION)-enhanced MR transverse relaxation rates (∆R2(⁎) and ∆R2) are widely used to investigate in vivo vascular parameters, such as the cerebral blood volume (CBV), microvascular volume (MVV), and mean vessel size index (mVSI, ∆R2(⁎)/∆R2). Although highly efficient, regional comparison of vascular parameters acquired using gradient-echo based ∆R2(⁎) is hampered by its high sensitivity to magnetic field perturbations arising from air-tissue interfaces and large vessels. To minimize such demerits, we took advantage of the dual contrast property of SPION and both theoretically and experimentally verified the direct benefit of replacing gradient-echo based ∆R2(⁎) measurement with ultra-short echo time (UTE)-based ∆R1 contrast to generate the robust CBV and mVSI maps. The UTE acquisition minimized the local measurement errors from susceptibility perturbations and enabled dose-independent CBV measurement using the vessel/tissue ∆R1 ratio, while independent spin-echo acquisition enabled simultaneous ∆R2 measurement and mVSI calculation of the cortex, cerebellum, and olfactory bulb, which are animal brain regions typified by significant susceptibility-associated measurement errors.

Contribution of mesenchymal proliferation in tooth root morphogenesis

In mouse tooth development, the roots of the first lower molar develop after crown formation to form 2 cylindrical roots by post-natal day 5. This study compared the morphogenesis and cellular events of the mesial-root-forming (MRF) and bifurcation-forming (BF) regions, located in the mesial and center of the first lower molar, to better define the developmental mechanisms involved in multi-rooted tooth formation. We found that the mesenchyme in the MRF showed relatively higher proliferation than the bifurcation region. This suggested that spatially regulated mesenchymal proliferation is required for creating cylindrical root structure. The mechanism may involve the mesenchyme forming a physical barrier to epithelial invagination of Hertwig's epithelial root sheath. To test these ideas, we cultured roots in the presence of pharmacological inhibitors of microtubule and actin polymerization, nocodazole and cytochalasin-D. Cytochalasin D also inhibits proliferation in epithelium and mesenchyme. Both drugs resulted in altered morphological changes in the tooth root structures. In particular, the nocodazole- and cytochalasin-D-treated specimens showed a loss of root diameter and formation of a single-root, respectively. Immunolocalization and three-dimensional reconstruction results confirmed these mesenchymal cellular events, with higher proliferation in MRF in multi-rooted tooth formation.

Developing technologies for rainwater utilization in urbanized area

Rainwater utilization has potential to recover the hydrological cycle, to buffer extreme run-off situations in the watercourses, and to reduce the costs for water supply in urban areas. However, relatively few works have been done for developing technologies to improve the water quality during rainwater utilization in large cities where the contamination of rainwater is anticipated. Therefore, this study focused on developing technologies for rainwater utilization subsystems including catchment, storage, treatment, infiltration, and use for buildings in urban areas. The rainwater samples collected from roof and roof garden were compared with wet deposition to analyze and identify the major components that may cause problems in rainwater utilization. Based on these results, novel techniques utilizing TiO2, sunlight, and bauxsol to minimize the contamination level by particles, microorganisms, and nutrients were developed for rainwater subsystems and applied to explore their suitability.

Measurements of the cross section for e(+)e(-) --> hadrons at center-of-mass energies from 2 to 5 GeV

We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.

Backbone dynamics of receptor binding and antigenic regions of a Pseudomonas aeruginosa pilin monomer

Pilin is the major structural protein that forms type IV pili of various pathogenic bacteria, including Pseudomonas aeruginosa. Pilin is involved in attachment of the bacterium to host cells during infection, in the initiation of immune response, and serves as a receptor for a variety of bacteriophage. We have used (15)N nuclear magnetic resonance relaxation measurements to probe the backbone dynamics of an N-terminally truncated monomeric pilin from P. aeruginosa strain K122-4. (15)N-T(1), -T(2), and [(1)H]-(15)N nuclear Overhauser enhancement measurements were carried out at three magnetic field strengths. The measurements were interpreted using the Lipari-Szabo model-free analysis, which reveals the amplitude of spatial restriction for backbone N-NH bond vectors with respect to nano- to picosecond time-scale motions. Regions of well-defined secondary structure exhibited consistently low-amplitude spatial fluctuations, while the terminal and loop regions showed larger amplitude motions in the subnano- to picosecond time-scale. Interestingly, the C-terminal disulfide loop region that contains the receptor binding domain was found to be relatively rigid on the pico- to nanosecond time-scale but exhibited motion in the micro- to millisecond time-scale. It is notable that this disulfide loop displays a conserved antigenic epitope and mediates binding to the asialo-GM(1) cell surface receptor. The present study suggests that a rigid backbone scaffold mediates attachment to the host cell receptor, and also maintains the conformation of the conserved antigenic epitope for antibody recognition. In addition, slower millisecond time-scale motions are likely to be crucial for conferring a range of specificity for these interactions. Characterization of pilin dynamics will aid in developing a detailed understanding of infection, and will facilitate the design of more efficient anti-adhesin synthetic vaccines and therapeutics against pathogenic bacteria containing type IV pili.

Generalized interframe vertex-based shape encoding scheme for video sequences

The efficiency of shape coding is an important problem concerning content-based image manipulations and object-based coding of the video sequences. In order to encode the shape information of an object, the boundary is approximated by a polygon which can be encoded with the smallest number of bits for maximum allowable distortion. The conventional boundary coding schemes, however, does not successfully remove the temporal redundancy of the video sequences. This paper proposes a new boundary encoding scheme by which the temporal redundancy between two successive frames is efficiently removed, resulting in lower bit-rate than the conventional algorithms. The interframe vertex selection problem is solved by finding the path with the minimum cost in the directed acyclic graph (DAG) and its fast version using a simplified graph is introduced to reduce the computational load. The vertices were selected from both the current frame to be encoded and the previous frame already encoded, and thus, the temporal redundancy was effectively removed.

Structural and functional implications of a proline residue in the antimicrobial peptide gaegurin

Although it is commonly known as a helix breaker, proline residues have been found in the alpha-helical regions of many peptides and proteins. The antimicrobial peptide gaegurin displays alpha-helical structure and has a central proline residue (P14). The structure and activity of gaegurin and its alanine derivative (P14A) were determined by various spectroscopic methods, restrained molecular dynamics, and biological assays. Both P14 and P14A exhibited cooperative helix formation in solution, but the helical stability of P14 was reduced substantially when compared to that of P14A. Chemical-shift analysis indicated that both of the peptides formed curved helices and that P14 showed diminished stability in the region around the central proline. However, hydrogen-exchange data revealed remarkable differences in the location of stable amide protons. P14 showed a stable region in the concave side of the curved helix, while P14A exhibited a stable region in the central turn of the helix. The model structure of P14 exhibited a pronounced kink, in contrast to the uniform helix of P14A. Both peptides showed comparable binding affinities for negatively charged lipids, while P14 had a considerably reduced affinity for a neutral lipid. With its destabilized alpha-helix, P14 exhibited greater antibacterial activity than did P14A. Hence, electrostatic interaction between helical peptides and lipid membranes is believed to be the dominant factor for antibacterial activity. Moreover, helical stability can modulate peptide binding to membranes that is driven by electrostatic interactions. The observation that P14 is a more potent antibacterial agent than P14A implies that the helical kink of P14 plays an important role in the disruption of bacterial membranes.

Matrix GLA protein is a developmental regulator of chondrocyte mineralization and, when constitutively expressed, blocks endochondral and intramembranous ossification in the limb

Matrix GLA protein (MGP), a gamma-carboxyglutamic acid (GLA)-rich, vitamin K-dependent and apatite-binding protein, is a regulator of hypertrophic cartilage mineralization during development. However, MGP is produced by both hypertrophic and immature chondrocytes, suggesting that MGP's role in mineralization is cell stage-dependent, and that MGP may have other roles in immature cells. It is also unclear whether MGP regulates the quantity of mineral or mineral nature and quality as well. To address these issues, we determined the effects of manipulations of MGP synthesis and expression in (a) immature and hypertrophic chondrocyte cultures and (b) the chick limb bud in vivo. The two chondrocyte cultures displayed comparable levels of MGP gene expression. Yet, treatment with warfarin, a gamma-carboxylase inhibitor and vitamin K antagonist, triggered mineralization in hypertrophic but not immature cultures. Warfarin effects on mineralization were highly selective, were accompanied by no appreciable changes in MGP expression, alkaline phosphatase activity, or cell number, and were counteracted by vitamin K cotreatment. Scanning electron microscopy, x-ray microanalysis, and Fourier-transform infrared spectroscopy revealed that mineral forming in control and warfarin-treated hypertrophic cell cultures was similar and represented stoichiometric apatite. Virally driven MGP overexpression in cultured chondrocytes greatly decreased mineralization. Surprisingly, MGP overexpression in the developing limb not only inhibited cartilage mineralization, but also delayed chondrocyte maturation and blocked endochondral ossification and formation of a diaphyseal intramembranous bone collar. The results show that MGP is a powerful but developmentally regulated inhibitor of cartilage mineralization, controls mineral quantity but not type, and appears to have a previously unsuspected role in regulating chondrocyte maturation and ossification processes.

Structural characteristics of tenecin 3, an insect antifungal protein

Tenecin 3, an antifungal protein, previously isolated from the insect Tenebrio molitor, inhibits growth of the fungus Candida albicans. However, the antifungal mechanism and functions of tenecin 3 remain unknown. As an initial step to study the mechanism and functions, physical and structural properties of tenecin 3 were examined by circular dichroism (CD) analysis and 2D nuclear overhauser effect spectroscopy. These analyses suggest that tenecin 3 has a propensity of random structure with very loose turn-like elements. The CD results also indicate that this random structural propensity is not significantly affected by temperature, pH, and by the presence of organic solvents or sodium dodecyl sulfate (SDS) micelles. However, the hydrodynamic studies suggest that tenecin 3 is not in extended form in spite of its random structural feature.

Unusually stable helical kink in the antimicrobial peptide--a derivative of gaegurin

The structure of an active analog of the antibacterial peptide gaegurin was investigated by CD and NMR spectroscopy. The NOE connectivities showed that 21 out of 24 residues formed an a-helix despite the presence of a central proline. CD and NMR analysis indicates that the helix is in fast equilibrium with random coil. From chemical shift analysis of the amide protons, the distances of hydrogen bonding in the helix were calculated, and manifested obvious periodicity which implied a kink in the middle of the helix. 1D amide proton exchange experiments provided further evidence of an exceptionally stable kink. It is inferred that this kink is important not only to the function of the peptide but also to the early stage of the folding as a nucleation site.

Serum levels of antioxidant vitamins in relation to coronary artery disease: a case control study of Koreans

With the changes in trends of disease pattern from infectious to chronic degenerative disease, cardiovascular disease has been considered as the major cause of death in Korea. Numerous studies have been done on the antioxidant effects of some vitamins in the prevention of chronic illness, but not many in relation to the cardiovascular disease. Therefore, the relation between antioxidant vitamins, mainly alpha-tocopherol (alpha-T) and beta-carotene (beta-C), and coronary artery disease (CAD) such as angina pectoris and myocardial infarction has been investigated in this study. The blood samples were obtained from the CAD patients who were angiographically diagnosed within a month (100 case group). Patients who had an experience of PTCA or CABG were excluded from the study. Control subjects were healthy adults who had normal EKG values, no chest pain and no past history of cardiac disease (100 control group). All subjects were free for serum lipid lowering drugs. Serum alpha-T and beta-C were analysed using HPLC. In addition to antioxidant vitamins, serum lipids (total cholesterol, HDL, TG) were also measured. Each case and control was matched in terms of age and sex. And all the CAD risk factors such as blood pressure, smoking, alcohol, serum lipid profile and BMI were adjusted to determine pure effect(s) of alpha-T and beta-C on the CAD. The concentrations of both alpha-T and beta-C were significantly lower in the CAD group than those in control group (P < 0.05); in CAD group, mean values of alpha-T and beta-C were 11.9 +/- 7.2 (micrograms/ml), 35.8 +/- 3.1 (micrograms/dl) respectively. As for the levels of beta-C, it shows inverse relation with age, but not for the alpha-T levels. Serum levels of both vitamins did not show any significant differences in terms of sex, but men have a tendency o higher levels of beta-C, but lower levels of alpha-T.

Structures of revertant signal sequences of Escherichia coli ribose binding protein

Recently we reported (Yi et al., 1994) that the alpha-helical content of the signal peptide of Escherichia coli ribose binding protein, when determined by circular dichroism (CD) and two-dimensional NMR in trifluoroethanol/water solvent, is higher than that of its nonfunctional mutant signal peptide. In the present investigation, the structures of the signal peptides of two revertant ribose binding proteins in the same solvent were also determined with CD and two-dimensional 1H NMR spectroscopy. According to the CD results, both of these revertant signal peptides showed an intermediate helicity between those of wild-type and mutant signal peptides, the helical content of the revertant peptide with higher recovery of the translocation capability being higher. On the other hand, the alpha-helix regions of the wild-type and the revertant peptides as determined by NMR were shown to be the same. This discrepancy may be due to the difference in stability between identical alpha-helical stretches in wild-type and revertant peptides. A good correlation was observed between the helical content of these four ribose binding protein signal peptides in TFE/water as studied by CD and their in vivo translocation activities. It appears, therefore, that both the proper length of the helix and the stability are of functional significance.