Search

The synthesis of MAX phase Ti2AlN from several mixtures of Ti, Al, TiN, and AlN powders by vacuum sintering of greensamples in the form of dense compacts, bulk powder in silica tubes, and plain layer in a closed rectangular molybdenum boat was studied upon variation in charge composition and sintering temperature Ts. The sintering of 2 : 1 Ti–AlN mixture was carried out at 1100, 1200, 1300, 1400, and 1500 °С with exposure time of 60 min. The largest MAX phase content (94 wt.%) was reached at Ts = 1400 °С. The sintering of 1 : 1 TiAl : TiN composition at the same temperature gave 93 wt.% Ti2AlN. The best result (singlephase Ti2AlN in a 100-% yield) was achieved upon the sintering of 1 : 1 : 1 Ti–Al–TiN composition at Ts = 1400 °С. The scalability of our process was checked by the fabrication of a large (0.5 kg) and uniform cake of single-phase Ti2AlN. In experiments we used green samples with shielded lateral surface (bulk powder in silica tubes, plain layer in a closed molybdenum boat) and without shield (dense compacts). It has been shown that shielding of Ti–Al–TiN samples restricts the escape of Al vapor from a sintered mixture, thus providing more favorable conditions for the synthesis of single-phase Ti2AlN. Our process can be readily recommended for practical implementation.

TiAl intermetallic was prepared through thermal coupling of highly exothermic Fe2O3–Al reaction (donor) and low-caloric Ti–Al reaction (acceptor). Green compacts represented three-layer ‘donor–acceptor–donor’ sandwich-type structures. The combustion process was video taped and combustion temperatures in the bulk of donor and acceptor layers and at the interfaces were monitored with a set of thermocouples. The results of video filming and thermocouple measurements allowed us to establish which mode of thermally coupled SHS reaction took place in our conditions. The combustion product was found to contain the TiAl intermetallic with small admixture of Ti3Al and unreacted Al.

The ZrB2–CrB composites with a ceramic bond content of 80 wt.% and a relative density of 0.85 – 0.90 were obtained by the method of electrothermal explosion under pressure. It is shown that the mechanical activation of the source powder mixture decreases its heterogeneity and increases its reactivity.We also obtained a finely divided ceramic composite with homogeneous microstructure containing needle-like ZrB2 grains.

Medical clearance is an essential part for participation is recreational and professional sports events, including participation in the Russian physical culture training system “Ready for labour and defence” («Gotov k Trudu i Oborone» - abbreviated as GTO, in Russian). The Order № 134 of the Ministry of Health of Russia, dated March 1, 2016, defines the procedures for medical clearance of athletes, including those with disabilities. However some questions remaining the assessment of the health condition of the latter still remain open. There is no consensus agreement on contraindications for medical clearance giving and the terms of the validity of such clearance. In this paper we discuss the optimal terms for medical assessment of the disabled athletes, legal procedures, as well as give recommendation on medical clearance for athletes of different disability groups.

The dependence of MAX-phase synthesis on phase composition of the initial mixture and heat treatment terms in the electric furnace was investigated. Using Ti and AlN powders with the molecular ratio 2:1 as an example, the sequence of phase composition changes with increasing exposure temperature was tracked. It was established that the maximum amount of Ti2AlN MAX-phase in the end products is obtained at 1400°C. At this temperature a single phase product (100% wt Ti2AlN) was obtained for the initial mixture Ti:Al:TiN = 1:1:1. The principal possibility of scaling for obtaining a single-phase product of Ti2AlN by vacuum sintering was experimentally shown on the example of the mixture of this composition weighing 500 g at a certain mode of thermal vacuum treatment.

Tubal factor accounts for 25-30% of cases of female infertility. Laparoscopy "Gold Standard" for tubal evaluation. However, it is known that during the initial infection of the fallopian tube mucosal damage occurs, a condition which plays a decisive role in reproduction.In this prospective randomized study, 468 infertile women with evidence of fallopian tube disease were included. In this, for 256 patients (group 1) after laparoscopic salpingolysis, salpingostomy we performed an additional step operation transcervical falloposcopy tubal dilatation (TFTD). 212 patients (group 2) produced only laparoscopic salpingolysis, salpingostomy.As a result, TFTD patency of the fallopian tubes for coaxial catheter was restored in 50 (78%) of 64 tubes with bilateral total occlusion, in 238 (93%) of 254 with partial occlusion of the bilateral, in 14 (58%) of 24 total unilateral occlusion and 26 (92%) of 28 with partial unilateral occlusion. Total number of pregnancies for one year in the first group of patients was 152 (59.3%), in the second 57 (27.1%), of which in the first group 147 -intrauterine pregnancies (57.4%) and in the second - 46 (21.7%).Falloposcopy surgeon provides good opportunities for the diagnosis and treatment of intralumen lesions. Significant increase in the frequency of uterine pregnancy in the case of an additional step - TFTD during salpingolysis, salpingostomy in patients with tubal factor infertility.

17 The first experiments on combustion of compacted metal powder samples in a gaseous nitrogen atmo� sphere exhibited two qualitatively different combus� tion modes: a layer mode and a surface mode [1]. In the layer mode, the combustion front is flat and extends over all the cross section of the sample. In the surface mode, the combustion front is strongly curved, and the leading edge of the reaction front propagates within the surface regions of the sample, whereas the reaction in the core part of the sample either occurs far from the leading edge of the front or is absent. The external patterns of combustion in both modes are identical; therefore, a conclusion on the combustion mode is made based on visual observation of cross sec� tions of burnt samples (the formed nitride and the ini� tial metal powder differ in color) and on chemical analysis of samples taken from the burnt samples. The combustion mode was proposed to quantita�

We present intensive optical, infrared, and radio monitoring observations of the BL Lac object OJ 287, taken between the years 1993-1998. Two large optical outbursts were detected at the predicted times in November 1994 and December 1995. The detection of these outbursts supports the binary black hole model for OJ 287. Optical and radio polarisation observations show large variability in the degree of polarisation and position angle, very similar to those observed during the 1983/84 outburst in OJ 287. The polarisation position angles show very similar behaviour during these observations, indicating that, at least, the magnetic field orientations in radio and optical bands are related in OJ 287. Optical and infrared light curves show continuous variability in time scales ranging from tens of minutes to years. In the radio bands we have observed some of the lowest ever measured flux levels. During the first optical outburst in November 1994 the observed radio flux was very low, but during the second optical outburst radio bands also showed high flux levels. This is a puzzling observation, which can hopefully be used for discriminating between different outburst models. On top of the large outbursts OJ 287 has displayed flaring activity in time scales from days to weeks and shorter time scale flickering.

The aim of the study was to investigate allelic distribution of calcineurin gene (CNB; 5I/5D polymorphism) in athletes of cyclic sports (n = 673) and controls (n = 1073), and to find interrelation between genotypes and risk of left ventricular hypertrophy and physical performance of athletes. Genotyping was performed by restriction fragment length polymorphism. Echocardiography was performed by ultrasound scanner Aloka-3500. Physiological parameters were evaluated by spiroergometry using MetaMax 3B Gas Analyzer. The frequency of CNB D allele was significantly lo- wer in athletes than in controls (5.5 vs. 8.8 %; p = 0.0005), and decreased with the growth of skills. We found that CNB D allele was associated with increased left ventricular mass index and low values of physical performance (when maximal power production capacity and maximal oxygen consumption were measured). Thus, CNB gene 5I/5D polymorphism is associated with the risk of left ventricular hypertrophy and physical performance of athletes.

Heparin binding protein (HBP) is an inactive serine protease homologue with important implications in host defense during infections and inflammations. Two mutants of human HBP, [R23S,F25E]HBP and [G175Q]HBP, have been produced to investigate structure-function relationships of residues in the putative lipid A/lipopolysaccharide (LPS) binding site and BPTI (bovine pancreatic trypsin inhibitor) binding site. The X-ray structures have been determined at 1.9 A resolution for [G175Q]HBP and at 2.5 A resolution for the [R23S,F25E]HBP mutant, and the structures have been fully refined to R-factors of 18.2 % and 20.7 %, respectively. The G175Q mutation does not alter the overall structure of the protein, but the ability to bind BPTI has been eliminated, and the mutant mediates only a limited stimulation of the LPS-induced cytokine release from human monocytes. The lipid A/LPS binding property of [G175Q]HBP is comparable with that of native HBP. The R23S,F25E mutations do not affect the binding of lipid A/LPS and BPTI or the LPS-induced cytokine release from human monocytes. This shows that two diverse ligands, lipid A/LPS and BPTI, do not share binding sites. Previously, there was convincing evidence for the proposed lipid A/LPS binding site of HBP. Unexpectedly, the extensive structural changes introduced by mutation of Arg23 and Phe25 do not affect the binding of lipid A/LPS, indicating that another not yet identified site on HBP is involved in the binding of lipid A/LPS.

We present the lightcurve of 3C 345 (1641+399, z = 0.595) in Johnson R. The data until summer 1992 are analysed and discussed in detail in Schramm et al. (A&A, Nov. 1993). The more recent lightcurve is almost flat (R ≃ 16.9), giving new constraints on variability models, see Camenzind, this proceedings.

Ultrafast phenomena is a term commonly being used to designate processes that are too fast to be time-resolved by ordinary electronic measuring techniques. Very roughly speaking, the present limit of electronic time resolution is about 10-10 s. On the other hand, it is now possible to generate laser pulses with durations corresponding to only a few optical cycles. The shortest laser pulses available today are just a few femtoseconds ( l0-15 s) in duration. The remarkable progress in the generation of ultrashort laser pulses has coincided with the development of new experimental methods of time-resolved spectroscopy. Today optical measurements can be per­ formed with a time resolution limited only by the duration of the available laser pulses. Time resolution of 10-14 s is of great importance in solid-state physics. There is a large variety of interesting ultrafast processes, including phenomena such as cooling of a gas of photoexcited excitons (10-10 s), damping of lattice vibrations (10-12 s), and scattering of electrons and holes out of excited band states, which may be as fast as 10-14 s. The ability to measure these ultrafast solid-state phenomena directly as a function of time often provides a chance to obtain new information that may be hard to determine with other experimental techniques. In this article applications of ultrafast laser spectroscopy to the study of solids are considered. The first section gives an overview of fast exciton phenomena. Dynamics of photoexcited carriers and of lattice vibrations are discussed in the second and third sections. The final part of the article

Die niedrigsten Arbeitstemperaturen der Hartlote fallen in ein Gebiet, das bei rd. 620° C beginnt und bis zu etwa 1100° C reicht, wahrend die obere Grenze des Weichlotens bei etwa 300° C liegt. In dem Temperaturbereich zwischen Weichloten und Hartloten gibt es keine brauchbaren Lote fur die Seh wer met alle. Man hat zwar versucht, auf Zinkbasis und mit anderen Legierungen die bestehende Lucke auszufullen, aber trotz aller Vorteile, die ein solches Lot fur die Anwendung des Lotens bringen wurde, hat sich keine Legierung auf die Dauer durchsetzen konnen.

Unter den Leichtmetallen lassen sich nur das Aluminium und die meisten seiner Legierungen loten.

Den ersten Anstos hierzu gab ein Preisausschreiben fur eine Kuhlanlage zum Auskristallisieren von Paraffin. Es erfaste mich sofort der Gedanke, das hier eine noch ungeklarte Aufgabe der mechanischen Warmelehre vorliege. Dieser Eindruck verstarkte sich, als ein Studium der technischen Literatur uber kunstliche Kuhlung zwar bereits das Vorhandensein der drei heutigen Systeme von Kaltemaschinen aufwies, jedoch jeden Masstab zu einer Vergleichung ihrer Leistungen in thermodynamischer Hinsicht vermissen lies. Sofort ging ich daran, diese Grundlage fur eine Theorie der Kaltemaschinen aufzusuchen. Zunachst handelte es sich darum, festzustellen, 1. welches Verhaltnis zwischen entzogener Warmemenge (Kalteproduktion) und aufgewendeter Energie als das naturgesetzlich hochst erreichbare zu betrachten, 2. welcher Arbeitsvorgang zur Erreichung solcher Hochstleistung auszufuhren sei, und 3. wie sich die verschiedenen bestehenden Kaltemaschinen hierzu verhalten. Die Beantwortung dieser Fragen legte ich (1870) in einer Abhandlung im Bayerischen Industrie-und Gewerbeblatt nieder: „Uber die Warmeentziehung bei niedrigen Temperaturen durch mechanische Mittel“. Die ersten beiden Fragen fanden darin ihre allgemeine Losung2), und die Wirkungsgrade der Kaltluftmaschinen, der Kompressions-Kaltdampfmaschinen und der Absorptionsmaschinen wurden rechnerisch ermittelt.

Das Loten ist durch mancherlei Umstande langer ein Stiefkind der Technik geblieben als andere Verbindungsarten. Es wird vielfach auch heute noch als eine Angelegenheit des Handwerks angesehen und unter den industriellen Verfahren nicht voll anerkannt.

Zum Weichloten der Schwermetalle werden fast ausschlieslich Lote verwendet, die im wesentlichen aus Blei 1 und Zinn zusammengeschmolzen — legiert — sind. Solche Lote werden, auch wenn sie in der Mehrzahl der Falle mehr Blei als Zinn enthalten, als Lotzinn angesprochen und nach ihrem Gewichtsanteil an Zinn bezeichnet. Eine Blei-Zinn-Legierung mit 40 Gewichtschtsprozent Zinn heist nach den DIN-Normen (Tabelle 1) Zinnlot 40 oder LSn 40. Auch im Auslande wird der Zinngehalt bei der Benennung meist vorangestellt.

We present results from a two year intensive monitoring of BL Lac object 3C 66A (PKS 0219+428). This object was observed in outburst during these two years. It reached the brightest ever observed magnitude on V =13.59 (1.2.1995) and on K =10.59 (15.2.1994). The optical and infrared light curves are characterised by randomly distributed fast flares, lasting a few days and well defined outbursts lasting a week or two. On top of these flares we can occasionally see small amplitude microvariability. No clear correlation can be found between the spectral behaviour and the occurrence of these flares. In the radio bands 3C 66A was quite faint and very stable compared to the optical variations. The light curves will be presented with preliminary analysis and discussions on the possible causes for the observed variations.