In this paper, the effects of Nb addition (5–20 wt %) on the microstructure, mechanical properties, corrosion behavior, and cytotoxicity of Ti-Nb alloys were investigated with the aim of understanding the relationship between phase/microstructure and various properties of Ti-xNb alloys. Phase/microstructure was analyzed using X-ray diffraction (XRD), SEM, and TEM. The results indicated that the Ti-xNb alloys (x = 10, 15, and 20 wt %) were mainly composed of α + β phases with precipitation of the isothermal ω phase. The volume percentage of the ω phase increased with increasing Nb content. We also investigated the effects of the alloying element Nb on the mechanical properties (including Vickers hardness and elastic modulus), oxidation protection ability, and corrosion behavior of Ti-xNb binary alloys. The mechanical properties and corrosion behavior of Ti-xNb alloys were found to be sensitive to Nb content. These experimental results indicated that the addition of Nb contributed to the hardening of cp-Ti and to the improvement of its oxidation resistance. Electrochemical experiments showed that the Ti-xNb alloys exhibited superior corrosion resistance to that of cp-Ti. The cytotoxicities of the Ti-xNb alloys were similar to that of pure titanium.
The LaFe(13)-(x)Si(x) (1.0 < or = x < or = 5.0) series is studied experimentally and theoretically to gain possible understanding for the relationships among geometrical structure, chemical composition, magnetic behavior, and physical properties as related to the magnetocaloric effect in these compounds. As the Si concentration increases, LaFe(13)-(x)Si(x) exhibits a structural transformation from the cubic NaZn(13) structure type to a tetragonal derivative due primarily to preferential ordering of Fe and Si atoms. At room temperature, LaFe(13)-(x)Si(x) crystallize in the cubic structure for the range 1 < or = x < or = 2.6 and in the tetragonal for 3.2 < or = x < or = 5. In the range 2.6 < or = x < or = 3.2, it shows a two-phase mixture. Temperature-dependent single-crystal X-ray diffraction experiments near the corresponding Curie temperatures were performed on the room-temperature cubic phases to examine the origin of the large isothermal magnetic entropy changes. A thorough statistical and structural analysis of the data indicates that the noncentrosymmetric F43c space group provides a more adequate atomic arrangement than the centrosymmetric Fm3c space group. This change in space group leads to divergence for specific sets of Fe-Fe distances below the Curie temperature that arises from tilting of Fe-centered [Fe(12)-(x)Si(x)] icosahedra. The noncentrosymmetric space group also agrees with the predominance of icosahedral clusters lacking local inversion symmetry. From extended Hückel and tight-binding linear muffin-tin orbital (TB-LMTO) electronic structure calculations on various model structures, the F43c model is more energetically favorable than the Fm3c model. Extended Hückel calculations on various icosahedral [Fe(12)-(n)Si(n)] (n = 1-5) clusters and TB-LMTO calculations on "LaFe(13)," LaFe(11)Si(2), and LaFe(9)Si(4) have also been carried out to study the effects of a main group element (Si) on stabilizing the cubic NaZn(13)-type structure, influencing the transformation between cubic and tetragonal symmetries, and to study relationships among their chemical bonding and magnetic properties.
In vitro cytotoxicity test is an initial step to identify the harmful effects of new dental materials. Aim of this study was to develop a stable human cell line derived from normal gingival fibroblasts (hNOF) and to assess its feasibility in in vitro cytotoxicity testing. Immortalized human gingival fibroblasts (hTERT-hNOF) were successfully established with human telomerase reverse transcriptase gene transfection, preserving its phenotypical characteristics, replicative potential and biological properties. Utilizing standard cytotoxicity test modeling and dental materials, hTERT-hNOF were evaluated for their feasibility in cytotoxicity testing, compared with hNOF and L929 cells. Similar pattern of cytotoxic response was observed among hNOF, hTERT-hNOF and L929 cells. Cytotoxicity response of hTERT-hNOF was significantly similar to hNOF, moreover hTERT-hNOF and hNOF were found to be more sensitive towards the tested dental materials compared to L929 cells. This study suggested that hTERT-hNOF is an effective cytotoxic test model for dental materials.
We report the design and characterization of a CMOS pixel direct charge sensor, Topmetal-II -, fabricated in a standard 0.35 µm CMOS Integrated Circuit process. The sensor utilizes exposed metal patches on top of each pixel to directly collect charge. Each pixel contains a low-noise charge-sensitive preamplifier to establish the analog signal and a discriminator with tunable threshold to generate hits. The analog signal from each pixel is accessible through time-shared multiplexing over the entire array. Hits are read out digitally through a column-based priority logic structure. Tests show that the sensor achieved a < 15 e − analog noise and a 200 e − minimum threshold for digital readout per pixel. The sensor is capable of detecting both electrons and ions drifting in gas. These characteristics enable its use as the charge readout device in future Time Projection Chambers without gaseous gain mechanism, which has unique advantages in low background and low rate-density experiments.
Human plasma high density lipoproteins (HDL), the primary vehicle for reverse cholesterol transport, are the target of serum opacity factor (SOF), a virulence determinant of Streptococcus pyogenes that turns serum opaque. HDL comprise a core of neutral lipids-cholesteryl esters and some triglyceridesurrounded by a surface monolayer of cholesterol, phospholipids, and specialized proteinsapolipoproteins (apos) A-I and A-II. HDL is an unstable particle residing in a kinetic trap from which it can escape via chaotropic, detergent or thermal perturbation. Recombinant (r) SOF catalyzes the transfer of nearly all neutral lipids of ~100,000 HDL particles (D ~ 8.5 nm) into a single, large cholesteryl ester-rich microemulsion (CERM; D >100 nm) leaving a new HDL-like particle-neo HDL (D ~5.8 nm) while releasing lipid-free (LF) apo A-I. CERM formation and apo A-I release have similar kinetics suggesting parallel or rapid consecutive steps. By using complementary physico-chemical methods, we have refined the mechanistic model for HDL opacification. According to size exclusion chromatography, HDL containing non-labile apo A-I resists rSOFmediated opacification. Based on kinetic cryo electron microscopy, rSOF (10 nM) catalyzes the conversion of HDL (4 μM) to neo HDL via a step-wise mechanism in which intermediate-size particles are seen. Kinetic turbidimetry revealed opacification as a rising exponential reaction with a rate constant k = (4.400 ± 0.004) × 10 −2 min −1 . Analysis of the kinetic data using transition state theory gave an enthalpy, entropy and free energy of activation of ΔH ‡ = 73.9 kJ/mol, ΔS ‡ = −66.87 J/°K, and ΔG ‡ = 94.6 kJ/mol respectively. The free energy of activation for opacification is nearly identical to that for the displacement of apo A-I from HDL by guanidine hydrochloride. We conclude that apo A-I lability is required for HDL opacification, LF apo A-I desorption is the rate-limiting step, and nearly all HDL particles contain at least one labile copy of apo A-I.
KeywordsSerum opacity factor; electron cryomicroscopy; HDL remodeling; lipid fusion; apolipoprotein A-I; Streptococcus pyogenes Cardiovascular disease (CVD) is a major source of mortality and morbidity and identification of therapies that address its underlying causes is an important public health priority.
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