Improvement of tribological properties of stainless steel by alloying its surface layer with rare earth elements using high intensity pulsed plasma beams

Austenitic stainless steels are widely used in numerous industrial applications due to their excellent corrosion resistance. However some applications are limited in cases when due to low hardness and poor tribological properties of stainless steel wear is responsible for the durability of a given engineering component.In the present work we have undertaken an attempt to improve the wear resistance of AISI 316L steel by alloying its near surface region with rare earth elements—REE using high intensity pulsed plasma beams in so called deposition by pulse erosion (DPE) mode. Power density of pulses was 10⁶–10⁷ W/cm² with the pulse duration in μs range. Heating and cooling processes were of non-equilibrium type. The near surface layer—thickness in μm range—was melted and simultaneously doped with cerium and lanthanum. Various parameters of the process were set up to get level of doping between 0.3 and 2.8 at.% REE.An improvement of tribological properties—linear wear and scratch resistance—with increasing REE concentration as compared to the initial material was observed.     

Nanocomposite Fe-Al Intermetallic Coating Obtained by Gas Detonation Spraying of Milled Self-Decomposing Powder

The nanocomposite structure of Fe-Al intermetallic coating, created in situ during gas detonation spraying (GDS) of as-milled self-decomposing powder and containing disordered 8 nm FeAl nanocrystals, was analyzed using scanning electron microscopy (SEM) with energy-dispersive x-ray (EDX) spectroscopy, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and x-ray diffraction methods. It is found that the Fe-Al coating is characterized by a sublayer morphology consisting of flattened and partially melted splats containing a wide Al range from about 26 to 52 at.%, as well as Al₂O₃ oxides, created in situ at the internal interfaces of splats during the GDS process. The complex oxide films, identified as amorphous Al₂O₃, which are formed in the nanocrystalline Fe-Al matrix of the GDS coating behave like a composite reinforcement in the intermetallic Fe-Al coating. The combined presence of nanosized subgrains in the Fe-Al matrix and the Al₂O₃ nanoceramic dispersoids significantly increases the microhardness of the coating.     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

Particle morphology of various SiC-based nanocomposite powders made by the aerosol-assisted synthesis method

Herein, we present a part of a study on the preparation of SiC-based composite nanopowders by the two-stage Aerosol-Assisted Vapor Phase Synthesis (AAVS) method from organosilicon precursors (neat hexamethyldisiloxane, neat tetramethoxysilane, ethanol solutions of polydimethylsiloxane). Upon generation, liquid aerosol droplets were transported in a stream of argon through a ceramic reactor tube maintained at 1200 degrees C. The resulting solid by-products were collected on a nylon filter as bulk powders. Each raw powder was, subsequently, pyrolyzed in a furnace reactor heated to 1650 degrees C under a flow of argon. After the final pyrolysis at 1650 degrees C, mostly nanocrystalline silicon carbide powder with small quantities of free excess carbon was obtained from the neat hexamethyldisiloxane system, composite powder of not fully converted silica and SiC was prepared from the neat tetramethoxysilane system, and C-rich/SiC composite was made from the ethanol/polydimethylsiloxane solution system. The prevailing phase of the SiC component was the regular beta-SiC polytype. Most of the powders were composed of spheroidal particles--morphology imprinted during aerosol generation at 1200 degrees C and not much affected by the second-stage bulk pyrolysis at 1650 degrees C. The specifics of spheroidal morphology were characteristic of the applied precursor system.     

Does Melatonin Homeostasis Play a Role in Continuous Epigastric Pain Syndrome?

Two clinical forms of functional dyspepsia (FD) are listed in the Rome III criteria: postprandial distress syndrome (PDS) and epigastric pain syndrome (EPS), differing in the recurrence of ailments depending on the diet. Continuous EPS (CEPS) is observed in some EPS patients, also at night, but its cause is still unknown. We showed previously that melatonin (MEL) homeostasis may be associated with FD. In the present work we evaluated selected components of melatonin homeostasis in patients with CEPS. The study included 30 patients with CEPS, 21 women and nine men, aged 21–49 years and 30 control subjects (EPS excluded); organic and mental diseases, as well as Helicobacter pylori infection, were excluded in both groups. The average severity of abdominal pain in the last three months was estimated in a 10-point scale (Visual Analog Scale). The levels of mRNA expression of arylalkylamine-N-acetyltransferase (AANAT) and hydroxyindole-O-methyltransferase (HIOMT), the main components of MEL homeostasis, were determined in gastric mucosa with real time PCR. The fasting serum level of MEL (at 09:00 a.m.) and circadian urine excretion of 6-sulfatoxymelatonin (6-HMS) were determined with ELISA. AANAT expression in antral mucosa of control subjects was 1.76 ± 0.41, in the gastric body 1.35 ± 0.38, and in the dyspeptic group 1.42 ± 0.38 (p < 0.05) and 0.92 ± 0.55 (p < 0.05), respectively. HIOMT expression in the control was 2.05 ± 0.70 in the antrum and 1.57 ± 0.69 in the body and in the CEPS group, it was: 1.51 ± 0.57 (p < 0.05) and 0.74 ± 0.31 (p < 0.001), respectively. MEL concentration (pg/mL) was 9.41 ± 3.09 in the control group and 5.62 ± 1.34 (p < 0.01) in the CEPS group. Urinary 6-HMS excretion (μg/24 h) was 11.40 ± 4.46 in the controls and 7.68 ± 2.88 (p < 0.05) in the CEPS. Moreover, a negative correlation was found between the tested parameters and severity of epigastric pain. These results indicate that patients with CEPS may display low level of AANAT and HIOMT expression in gastric mucosa, resulting in decreased MEL synthesis.     

KNOWLEDGE MANAGEMENT BASED ON FORMAL MODELS OF SOFTWARE PROJECT MANAGEMENT

The objective of this paper is to present a complete conception of decision support systems for software project management. The idea is founded on dynamic and self-adjusting fuzzy models. Specifically, the propsed approach is founded on the knowledge-based methodology and the theories of dynamic systems and fuzzy sets. The presented method can be used in manufacturing of knowledge-based Information Technology (IT) products. A preliminary design of a fuzzy model can take advantage of experience from managing projects. Relevant experimental data resulting from such projects can then be utilized for adjusting the membership functions of the fuzzy model applied in the knowledge-based decistion-support system.     

An approximate algorithm for estimating treatment lags from right censored data

The problem of likelihood estimate of a function, given limited data and a set of constraints, finds many practical applications. One of them is the lag function estimation for treatment effects in clinical trials. However, searching for the global optimum in such problems often turns out to be prohibitively complex. In this paper, we present an algorithm that can be effectively used to approximate such solutions. This algorithm modifies standard genetic algorithms, which model the natural processes of information inheritance and selective pressure. The most important modifications deal with the complex strong constraints imposed on the sought solution. We present few experiments with a simplified version of the problem and discuss possible future extensions that relax the restrictions.