Current status of existing railway bridges in Vietnam: An overview of steel deficiencies

Currently, the deterioration of bridge conditions is causing many problems. Therefore, the work reported in this paper was carried out to survey the present condition of railway bridges in Vietnam, concentrating on steel deficiencies. Literature reviews were initiated to identify common defects with site inspections and personal interviews to ascertain their validity. Finding the defects draws an overall picture of Vietnamese railway bridges that are in poor physical condition, thus providing poor serviceability. Besides structural failure, local defects were already identified, consisting of corrosion, fatigue, functional obsolescence and aging. New problems that have been identified are human invasions and missing elements. It is widely considered that overload, collision impacts, adverse climate conditions and poor maintenance are the main causes. Additionally, this paper includes previous wars, improper data keeping, and elemental burglary as country-specific causes. It suggests that maintenance efforts should be prioritized to eliminate these deficiencies. Trained maintenance crews need to be established and further research should be carried out to create an adequate maintenance management system in Vietnam.     

Extended Domain of Existence for PSCs in Superconductors

By means of nanosecond pulse techniques, we have studied the current-induced dissipation in one-dimensional superconducting bridges, namely, metallic and high-T _c films. It is well known that narrow strips dissipate through phase-slip centers (PSC) close to T _c, or hot spots (HS) at low T, rather than by flux flow. When driven by step pulses of current, PSC give stable voltages, while HS produce a voltage linearly changing with time. By using two-step pulses of current, we have studied the decay of a HS into another HS, or a PSC, or into a zero-resistance state. It was thus found possible to reach the PSC state at arbitrary low temperatures.     

Carrier Co-doping Method with Size Compensation to Enhance TC of Mn-doped Nitrides

Based on ab initio electronic structure calculations of Mn-doped III–V nitrides (AlN, GaN, InN), a co-doping method with size compensation to enhance the Curie temperature (T_C) of Nitride-based DMS is proposed. Three cases are considered: (1) Single doping: cations are substituted randomly by Mn. (2) One-site co-doping: Cations or anions are substituted by co-dopants. (3) Two-site co-doping: co-dopants are introduced into both cation and anion sites. Be is chosen as co-dopant for (Al, Mn)N and (Ga, Mn)N, and Cd (or C) for (In, Mn)N. Concentrations of co-dopants are chosen as a function of Mn concentration so that the volume distortion caused by Mn doping is reduced. It is found that, by hole co-doping, the ferromagnetism is more stabilized than that in the single doping case. The anti-ferromagnetic super-exchange interaction, which remains dominant for high Mn concentrations in (Al, Mn)N and (Ga, Mn)N due to the small lattice constant, is reduced by co-doping Be into both kinds of sites, resulting in a strong enhancement of T_C in the regime of high Mn-concentrations. Furthermore, as the 3d-partial density of states at the Fermi level gains its maxima, one can expect that T_C reaches its highest value.     

Modelling of heat and mass transfer processes during core melt discharge from a reactor pressure vessel

The objective of this paper is to study the heat and mass trasnfer processes related to core melt discharge from a reactor vessel in a light water reactor severe accident. The phenomenology modelled includes the convection in, and heat transfer from, the melt pool in contact with the vessel lower head wall, the fluid dynamics and heat transfer of the melt flow in the growing discharge hole and multi-dimensional heat conduction in the ablating lower head wall. A research programme is underway at the Royal Institute of Technology (Kungliga Tekniska Högskolan, KTH) to (1) identify the dominant heat and mass transfer processes determining the characteristics of the lower head ablation process: (2) develop and validate efficient analytical/computational models for these processes; (3) apply models to assess the character of the melt discharge process in a reactor-scale situation; (4) determine the sensitivity of the melt discharge to structural differences and variations in the in-vessel melt progression scenarios. The paper also presents a comparison with recent results of vessel hole ablation experiments conducted at KTH with a melt simulant.     

Domain decomposition methods for nonlinear problems in fluid dynamics

The numerical solution of finite element approximations of complicated two- and three-dimensional nonlinear problems can be a most formidable task. In order to overcome this difficulty related to dimensionality, domain-splitting methods can be very effective, particularly in view of obtaining a fast and economical conjugate gradient solver, which can be used to precondition the solution of nonlinear problems by optimization methods via nonlinear least squares or weighted residual formulations. A new technique of this type will be introduced and analysed and its efficiency will be discussed from numerical experiments concerning the numerical simulation of transonic flows for compressible inviscid fluids and incompressible viscous flows modelled by the Navier-Stokes equations.     

Isolation of erythropoietin receptor agonist peptides using evolved phage libraries

Cyclic peptides capable of activating the erythropoietin receptor (EPOR) were isolated from phage display libraries by screening with a novel EPOR-IgG fusion protein reagent. A parental clone ERB1 (EPO Receptor Binder 1) was first isolated from a phage display library displaying 38 random amino acids as an N-terminal fusion with the M13 minor capsid protein, pill. An evolved library was then produced from the parental sequence using an oligonucleotide saturation mutagenesis strategy which yielded EPOR binding sequences with 20 times the relative affinity of ERB1. Two synthetic peptides were constructed from these sequences both of which bind the EPO receptor in specific ELISA, and act as full agonists in EPO dependent cell proliferation assays. These peptides are 18 amino acids in length, disulfide-bonded, and have a minimum consensus sequence of CXXGWVGXCXXW, where X represents positions tolerant of several amino acids.     

Stabilized approximate solutions of certain integral equations of first kind arising in contact problems of elasticity

The paper presents a method of constructing, by successive approximation, stabilized approximate solutions of certain integral equations of first kind in contact problems of elasticity. In these equations, the unknown function is a surface stress under the stamp, which is allowed to have a square root singularity under the edges of the stamp, and is therefore not square integrable. The author shows that it is nevertheless possible to apply the theory of positive operators to the present problem by constructing an appropriate L₂-space which includes functions with square root singularities.

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Résumé On présente une méthode d'élaboration par approximations successives de solutions approchées stables de certaines équations intégrales du premier genre relatives à des problèmes de contact élastique. Dans ces équations, la fonction inconnue est une contrainte de surface sous le point de contact, qui peut présenter une singularité d'ordre 1/2 sous les bords du poin¢on, et qui dès lors n'est pas intégrable par voie quadratique.L'auteur montre qu'il est néanmoins possible d'appliquer la théorie des opérateurs positifs à un tel problème, en construisant un espace de Hilbert incluant des fonctions présentant des singularités d'ordre 1/2.

     

Force control for hydraulic load simulator using self-tuning grey predictor – fuzzy PID

Hydraulic systems play an important role in modern industry for the reason that hydraulic actuator systems have many advantages over other technologies with electric motors, as they possess high durability and the ability to produce large forces at high speeds. Therefore, the hydraulic actuator has a wide range of application fields such as hydraulic punching, riveting, pressing machines, and molding technology, where controlled forces or pressures with high accuracy and fast response are the most significant demands. Consequently, many hybrid actuator models have been developed for studying how to control forces or pressures with best results.This paper presents a kind of hydraulic load simulator for conducting performance and stability testing related to the force control problem of hydraulic hybrid systems. In the dynamic loading process, perturbation decreases control performance such as stability, frequency response, and loading sensitivity decreasing or bad. In order to improve the control quality of the loading system while eliminating or reducing the disturbance, a grey prediction model combined with a fuzzy PID controller is suggested. Furthermore, fuzzy controllers and a tuning algorithm are used to change the grey step size in order to improve the control quality. The grey prediction compensator can improve the system settle time and overshoot problems. Simulations and experiments on the hydraulic load simulator are carried out to evaluate the effectiveness of the proposed control method when applied to hydraulic systems with various external disturbances encountered in real working conditions.