Effect of Zr content on phase stability, deformation behavior, and Young's modulus in Ti-Nb-Zr alloys

Ti alloys have attracted continuing research attention as promising biomaterials due to their superior corrosion resistance and biocompatibility and excellent mechanical properties. Metastable beta-type Ti alloys also provide several unique properties such as low Young's modulus, shape memory effect, and superelasticity. Such unique properties are predominantly attributed to the phase stability and reversible martensitic transformation. In this study, the effects of the Nb and Zr contents on phase constitution, transformation temperature, deformation behavior, and Young's modulus were investigated. Ti-Nb and Ti-Nb-Zr alloys over a wide composition range, i.e., Ti-(18-40)Nb, Ti-(15-40)Nb-4Zr, Ti-(16-40)Nb-8Zr, Ti-(15-40)Nb-12Zr, Ti-(12-17)Nb-18Zr, were fabricated and their properties were characterized. The phase boundary between the beta phase and the alpha '' martensite phase was clarified. The lower limit content of Nb to suppress the martensitic transformation and to obtain a single beta phase at room temperature decreased with increasing Zr content. The Ti-25Nb, Ti-22Nb-4Zr, Ti-19Nb-8Zr, Ti-17Nb-12Zr and Ti-14Nb-18Zr alloys exhibit the lowest Young's modulus among Ti-Nb-Zr alloys with Zr content of 0, 4, 8, 12, and 18 at.%, respectively. Particularly, the Ti-14Nb-18Zr alloy exhibits a very low Young's modulus less than 40 GPa. Correlation among alloy composition, phase stability, and Young's modulus was discussed.Web of Science132art. no. 47

Institutional Change, Obsolescing Legitimacy, and Multinational Corporations: The Case of the Central American Banana Industry

This paper studies the practice of integration of influential host country actors to a multinational corporation as a strategy to decrease problems of legitimacy to the foreign firm before the host country's society. By developing the concept of obsolescing legitimacy, we argue that this strategy provides legitimacy to the foreign firm only in the absence of institutional changes in the host country. Once these changes take place, an alliance by the multinational to an elite or a political system no longer ruling the host country will become a liability and will generate problems of legitimacy for the multinational. We illustrate our argument with the case of the US multinational United Fruit Company in Central America.

Unintended complication of intracranial subdural hematoma after percutaneous epidural neuroplasty.

Percutaneous epidural neuroplasty (PEN) is a known interventional technique for the management of spinal pain. As with any procedures, PEN is associated with complications ranging from mild to more serious ones. We present a case of intracranial subdural hematoma after PEN requiring surgical evacuation. We review the relevant literature and discuss possible complications of PEN and patholophysiology of intracranial subdural hematoma after PEN

The ganglionated plexus: The upstream triggers of atrial fibrillation

The ganglionated plexuses (GP) are dense epicardial nerves that are implicated in atrial fibrillation (AF). They can be functionally located from the endocardium using high frequency stimulation (HFS) which can locate distinct GP that trigger atrial ectopy/AF (ET-GP) or atrioventricular (AV) dissociating (AVD-GP). Our aim was to map and understand the histological, anatomical and functional properties of the different types of GP and ablate them with or without pulmonary vein isolation (PVI) in patients with AF. We hypothesised that ablating these specific GP sites is feasible, and prevents AF. Firstly, to investigate this, we mapped for AVD-GP and ET-GP using HFS in the left atrium of patients with AF. An automated process was used to merge and transform all patient maps onto one reference left atrial shell. A probability density function was applied at each tested site, including GP and negative HFS response sites, to create a probability distribution atlas of AVD-GP and ET-GP. There were distinct anatomical regions according to each GP sub-type, and ET-GP had preponderance to the PV ostia, roof, and mid-anterior wall. These are the areas that would usually be targeted with circumferential PVI. Therefore, a prospective, randomised, controlled study was performed (GANGLIA-AF) which assessed ET-GP ablation without PVI and PVI alone in patients with paroxysmal AF. Patients were followed-up for 12 months with multiple 48hr Holter monitors. The primary endpoint was any documented atrial arrhythmia >30s, and the secondary endpoints included complications and redo ablations. This showed that there was no statistically significant difference in AF prevention between the two arms, however the GP ablation arm required less ablation on average than the PVI arm. We also performed a smaller pilot study of redo AF ablation patients, assessing for feasibility and safety of GP ablation in addition to redo PVI. The same follow-up and endpoint criteria were used as in the GANGLIA-AF study. Some patients had permanent PVI, and non-PV triggers of AF were identifiable with HFS. We also developed a custom-built high frequency stimulator (Tau-20) that was used to identify ectopy-triggering (ET) sites in Langendorff-perfused porcine hearts. We were able to replicate the HFS responses used in the clinical setting in the porcine atria. Transmural cross-sectional dissections were taken from ET and non-ET sites, and the tissues were stained for parasympathetic and sympathetic nerves using immunohistochemistry methods. This showed that the mean density of nerves was greater in ET sites compare to non-ET sites. The Tau-20 has been successfully trialled in humans in the clinical setting, and with further improvements, it may replace the old Grass S88 stimulator for future GP ablation cases. In conclusion, ET-GP are upstream triggers of AF that can be ablated without PVI to prevent paroxysmal AF. GP ablation can be achieved with less RF energy than PVI implying a more specific technique on mechanistic grounds. The cross-over rate and clinical outcomes for GP ablation needs further improvement but GANGLIA-AF provides evidence that GP ablation may be an alternative or an adjunct technique to PVI. In addition, our ex-vivo evidence of increased nerve density at ET sites may account for the differential functional response of ET-GP stimulation in the clinical setting.Open Acces

On nonparametric likelihood methods for weakly and strongly dependent time series

This dissertation investigates and develops three different nonparametric likelihood methods for time series. For handling dependent data, current statistical methodology often relies on selecting parametric distributional models to accurately represent the data-generating process, which can be challenging. The three nonparametric likelihood methods considered are a blockwise empirical likelihood (EL), a block bootstrap, and a frequency domain bootstrap. Each method differs in form for building a nonparametric likelihood, but all methods involve setting empirical probabilities on observed data. An additional theme of this dissertation is the type or strength of the dependence in a stationary time process. The behavior of statistical methods can change dramatically between SRD and LRD cases, which complicates the development of appropriate resampling methods. The dissertation consists of four chapters. Chatper 1 provides Introduction to explain the relationship about three manuscripts from Chatper 2, 3 and 4. Chapter 2 considers a new blockwise empirical likelihood (BEL) method for stationary, weakly dependent time processes, called a progressive block empirical likelihood (PBEL). Unlike the standard BEL originally proposed by Kitamura~(1997), the PBEL method does not require any block length selections. Because the performance of the standard BEL can depend critically on the block length choice, the PBEL method in contrast enjoys a type of robustness against block selection issues. Chapters 3 and 4 consider different bootstrap problems for stationary, linear time series which could exhibit LRD. Chapter 3 investigates the large-sample properties of a block bootstrap method for estimating the distribution of sample means. The results establish the validity of the block bootstrap under either LRD or SRD. Additionally, for estimating the variance of a sample mean under LRD, explicit expressions are provided for the large-sample bias and variance of block bootstrap estimators along with formulas for the theoretically optimal block sizes under LRD. Perhaps surprisingly, optimal blocks become shorter in length as the strength of the LRD increases. Chapter 4 develops a frequency domain bootstrap (FDB) method for a problem involving Whittle estimation (Whittle, 1953), which is a popular technique for fitting parametric spectral density models to time series. For linear LRD time processes, the resulting Whittle estimators are known to have normal limit laws. However, convergence to normality can be slow under LRD and the finite-sample distributions of Whittle estimators tend to be asymmetric. As a remedy, the FDB method can be used for calibrating confidence intervals in place of a normal approximation

Cytotoxicity and acute toxicity evaluation of hydrogen-rich Gynostemma pentaphyllum Makino distillate

Hydrogen-rich Gynostemma pentaphyllum Makino distillate (HRGD) consists of Gynostemma pentaphyllum Makino steam distillate with hydrogen gas. Although both G. pentaphyllum Makino and hydrogen-rich water are well known for their biological and medical benefits, there is a lack of information on their safety and toxicity in vivo acute oral toxicity test and in vitro cytotoxicity method. The current study aimed to assess the cytotoxicity and acute oral toxicity of HRGD as a part of a safety evaluation using rat and human cell models. HRGD was administered orally once by gavage to male and female Sprague-Dawley rats at doses of 0, 2500, and 5000 mg/kg. Cytotoxicity assay was conducted in vitro at various concentrations in 10 different human normal and cancer cell lines; TK6 (human normal lymphomablastoid cells), Chang (human hepatic cells), 16HBE14o- (human bronchial epithelial cells), URotsa (human urothelium cells), MCF (human breast cancer cells), Hela (human cervical cancer cells), A375 (human malignant melanoma cells), HCT116 (human colon cancer cells), HepG2 (human liver cancer cells) and A549 (human non-small cell lung adenocarcinoma cells). From a 14-day study in rats, we observed no compound-related changes in mortality, clinical signs, body weight, food/water consumption, organ weight and gross pathology in all dose group. The result of in vivo acute toxicity shows that no observed adverse effect level of HRGD was below 5000 mg/kg for both sexes of rats, and the minimal lethal dose was considered to be more than 5000 mg/kg. HRGD also had no in vitro cytotoxicity against all tested cells. The present study data indicated that HRGD may contain bioactive compounds of potential therapeutic significance that are relatively safe from toxic effects