171 research outputs found
Analiza meÄupovrÅ”ine eksplozijski zavarenih ploÄa iz niskougljiÄnog Äelika i titana
On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness approximately 1 to 2 mm. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.Na osnovi eksperimentalnih rezultata utvrÄeno je da pri eksplozijskom zavarivanju dvaju metala na meÄupovrÅ”ini spoja nastaje veoma tanki sloj rastaljenog metala unutar kojeg dolazi do istjecanja neÄistoÄa tijekom taljenja. Velika brzina hlaÄenja nakon sudara dovodi do nastanka sitnozrnate legure drugaÄije strukture s projeÄnom veliÄinom od 1 do 2 mm. Zapaženo nastajanje amorfnog sloja na podruÄju spoja kod razliÄitih kombinacija metalnih materijala predstavlja temeljni mehanizam eksplozijskog zavarivanja metala. Primjenom rezultata metalografske analize u radu je opisan razvoj vrtloga koji su nastali eksplozijskim zavarivanjem ploÄa iz niskougljiÄnog Äelika i titana
Unutarnja oksidacija Cu-Se legura
The purpose of our investigation was to perform the thermodynamic calculation of all possible reactions in the Cu-Se-O system and to explain the oxidation mechanism in various conditions. For such study, a model of copper with one single inclusion and alloy with 1.65 wt. % Se were made. Depending on time, the oxidation has been taking place at two different temperatures and two oxygen partial pressures. The oxidized samples have been investigated by DTA, optical and electron microscopy (SEM).Namjena istraživanja je izraditi termodinamiÄki proraÄun svih moguÄih reakcija u sustavu Cu-Se-O i obrazložiti mehanizme oksidacije u razliÄitim uvjetima. Za takovo izuÄavanje izraÄen je model bakra sa samo jednim ukljuÄkom i legura sa 1,65 mas. % Se. U ovisnosti od vremena, oksidacija se odvijala kod razliÄitih temperatura i kod dviju razliÄitih djelomiÄnih tlakova kisika. Oksidirani uzorci su bili ispitivani metodom DTA, optiÄkom i elektronskom mikroskopijom (SEM)
Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273
Relativistically blueshifted absorption features of highly ionised ions, the
so-called ultra-fast outflows (UFOs), have been detected in the X-ray spectra
of a number of accreting supermassive black holes. If these features truly
originate from accretion disc winds accelerated to more than 10 per cent of the
speed of light, their energy budget is very significant and they can contribute
to or even drive galaxy-scale feedback from active galactic nuclei (AGN).
However, the UFO spectral features are often weak due to high ionisation of the
outflowing material, and the inference of the wind physical properties can be
complicated by other spectral features in AGN such as relativistic reflection.
Here we study a highly accreting Narrow Line Seyfert 1 galaxy PG 1448+273. We
apply an automated, systematic routine for detecting outflows in accreting
systems and achieve an unambiguous detection of a UFO in this AGN. The UFO
absorption is observed in both soft and hard X-ray bands with the XMM-Newton
observatory. The velocity of the outflow is (26900 +- 600) km/s (~0.09c), with
an ionisation parameter of log ({\xi} / erg cm s^-1)=4.03_{-0.08}^{+0.10} and a
column density above 10^23 cm^-2. At the same time, we detect weak warm
absorption features in the spectrum of the object. Our systematic outflow
search suggests the presence of further multi-phase wind structure, but we
cannot claim a significant detection considering the present data quality. The
UFO is not detected in a second, shorter observation with XMM-Newton,
indicating variability in time, observed also in other similar AGN.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 1 tabl
Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1
Ultraluminous pulsars are a definite proof that persistent super-Eddington
accretion occurs in nature. They support the scenario according to which most
Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar
mass rather than sub-Eddington intermediate mass black holes. An important
prediction of theories of supercritical accretion is the existence of powerful
outflows of moderately ionized gas at mildly relativistic speeds. In practice,
the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is
required to resolve their observational signatures in ULXs. Using RGS, outflows
have been discovered in the spectra of 3 ULXs (none of which are currently
known to be pulsars). Most recently, the fourth ultraluminous pulsar was
discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO)
in the X-ray spectrum of the object, with a significance of more than
3{\sigma}, during one of the two simultaneous observations of the source by
XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of
65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This
is the first direct evidence for a UFO in a neutron star ULX and also the first
time that this its evidence in a ULX spectrum is seen in both soft and hard
X-ray data simultaneously. We find no evidence of the UFO during the other
observation of the object, which could be explained by either clumpy nature of
the absorber or a slight change in our viewing angle of the accretion flow.Comment: 10 pages, 4 figures. Accepted to MNRA
Analiza meÄupovrÅ”ine niskougljiÄnog Äelika/tantal nakon eksplozivnog zavarivanja
The article discusses the morphology, microstructure and chemical composition of the boundary layer in explosive welding of low-carbon steel and tantalum plates. Pools of melt composed of both metals and having a heterogeneous chemical composition appear on the boundary layer. This phenomenon is the result of incomplete mixing of both: molten metals due to rapid cooling and solidification. Within the pools of alloy, a large number of non-metallic oxide inclusions, products of deoxidation of molten alloys, can be found. The non-metal inclusions are round (0.1 to 2 Āµm in diameter) and vary in both: size and chemical composition. The main component of the non-metal inclusions is Ta2O5, which also contains iron, manganese, and aluminium oxides. The number of non-metal inclusions is unusually high for low-carbon steel and comparable to the number of non-metal inclusions in welds. Oxygen which causes the large number of deoxidised products does not originate in the low-carbon steel, as this steel is relatively clean. The most probable source of oxygen is the oxide scale from the surface of the low-carbon steel, which was poorly cleaned prior to welding.Älanak raspravlja o morfologiji, mikrostrukturi i kemijskom sastavu pograniÄnog sloja pri eksplozivnom zavarivanju traka niskougljiÄnog Äelika i tantala. PodruÄje zone taljenja sastavljeno je od oba metala i na graniÄnom sloju pojavljuje se heterogeni kemijski sastav. Ova pojava je posljedica nepotpunog mijeÅ”anja oba rastaljena metala, zbog naglog hlaÄenja i oÄvrÅ”Äivanja. Unutar podruÄja spajanja legure može se utvrditi veliki broj nemetalnih oksidnih ukljuÄaka, produkata dezoksidacije rastaljenih legura. Nemetalni ukljuÄci su okrugli (0.1 do 2 Āµm) i variraju u veliÄini i kemijskom sastavu. Glavna komponenta nemetalnih ukljuÄaka je Ta2O5, koji takoÄer sadrži željezne, manganove i aluminijeve okside. Broj nemetalnih ukljuÄaka je neouobiÄajeno velik za niskougljiÄni Äelik i usporediv je s brojem nemetalnih ukljuÄaka u zavarima. Kisik koji dovodi do nastanka velikog broja produkata dezoksidacije ne potiÄe iz niskougljiÄnog Äelika jer je Äelik relativno Äist. Najvjerojatniji izvor kisika je povrÅ”inski oksidni sloj niskougljiÄnog Äelika koji je slabo oÄiÅ”Äen prije procesa zavarivanja
Origin of central abundances in the hot intra-cluster medium - I. Individual and average abundance ratios from XMM-Newton EPIC
The hot intra-cluster medium (ICM) is rich in metals, which are synthesized
by supernovae (SNe) explosions and accumulate over time into the deep
gravitational potential well of clusters of galaxies. Since most of the
elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse
(SNcc) supernovae, measuring their abundances gives us direct information on
the nucleosynthesis products of billions of SNe since the epoch of the star
formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments
onboard XMM-Newton to measure the abundances of 9 elements (O, Ne, Mg, Si, S,
Ar, Ca, Fe and Ni) from a sample of 44 nearby cool-core galaxy clusters,
groups, and elliptical galaxies. We find that the Fe abundance shows a large
scatter (~20-40%) over the sample, within 0.2 and, especially,
0.05. Unlike the absolute Fe abundance, the abundance ratios (X/Fe)
are quite uniform over the considered temperature range (~0.6-8 keV), and with
a limited scatter. In addition to a unprecedented treatment of systematic
uncertainties, we provide the most accurate abundance ratios measured so far in
the ICM, including Cr/Fe and Mn/Fe that we firmly detect (>4{\sigma} with MOS
and pn independently). We find that Cr/Fe, Mn/Fe and Ni/Fe, differ
significantly from the proto-solar values. However, the large uncertainties in
the proto-solar abundances prevent us from making a robust comparison between
the local and the intra-cluster chemical enrichments. We also note that,
interestingly, and despite the large net exposure time (~4.5 Ms) of our
dataset, no line emission feature is seen around ~3.5 keV.Comment: 17 pages, 9 figures, accepted for publication in A&
Influence of the Deep Cryogenic Treatment on AISI 52100 and AISI D3 Steelās Corrosion Resistance
The effect of deep cryogenic treatment (DCT) on corrosion resistance of steels AISI 52100 and AISI D3 is investigated and compared with conventional heat-treated counterparts. DCTās influence on microstructural changes is subsequently correlated to the corrosion resistance. DCT is confirmed to reduce the formation of corrosion products on steelsā surface, retard the corrosion products development and propagation. DCT reduces surface cracking, which is considered to be related to modified residual stress state of the material. DCTās influence on each steel results from the altered microstructure and alloying element concentration that depends on steel matrix and type. This study presents DCT as an effective method for corrosion resistance alteration of steels
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