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The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) flew on May 13$^{\text{th}}$ and 14$^{\text{th}}$ of 2023. Consisting of two novel optical telescopes, the payload utilized next-generation instrumentation for the observations of extensive air showers from near space. One instrument, the fluorescence telescope (FT) searched for Ultra-High Energy Cosmic Rays (UHECRs) by recording the atmosphere below the balloon in the near-UV with a 1~$\mu$s time resolution using 108 multi-anode photomultiplier tubes with a total of 6,912 channels. Validated by pre-flight measurements during a field campaign, the energy threshold was estimated around 2~EeV with an expected event rate of approximately 1 event per 10 hours of observation. Based on the limited time afloat, the expected number of UHECR observations throughout the flight is between 0 and 2. Consistent with this expectation, no UHECR candidate events have been found. The majority of events appear to be detector artifacts that were not rejected properly due to a shortened commissioning phase. Despite the earlier-than-expected termination of the flight, data were recorded which provide insights into the detectors stability in the near-space environment as well as the diffuse ultraviolet emissivity of the atmosphere, both of which are impactful to future experiments.

A hot salt corrosion (HSC) test was performed on the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed via cold Rotary Swaging. The grain size and volume fraction of the recrystallized microstructure in the alloy were varied by choosing appropriate annealing temperatures and times. The microstructure and corrosion resistance of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000 h of annealing at 250C. Metallographic studies were carried out to investigate the effects of annealing on the nature and extent of corrosive damage in the titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the titanium alpha-alloy samples were conducted using X-ray diffraction and electron microscopy. During the HSC testing of the titanium alpha-alloy Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC) and pitting corrosion was observed. To the best of our knowledge, it was shown for the first time that annealing affects the relationship among the IGC, pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged low-temperature annealing at 250C resulted in a more pronounced increase in the uniform corrosion rate than short-term high-temperature annealing for 30 min at 500-700C. An in-depth analysis of the effect of the structure and phase composition of the grain boundaries on the susceptibility of the alpha-alloy Ti-2.5Al-2.6Zr to HSC was conducted., Comment: 37 pages, 2 tables, 17 figures, 69 references

The research results of the microstructure and corrosion resistance of Ti and Ti-Al-V Russian industrial titanium alloys obtained by spark plasma sintering (SPS) are described. Investigations of the microstructure, phase composition, hardness, tensile strength, electrochemical corrosion resistance and hot salt corrosion of Ti-Al-V titanium alloy specimens were carried out. It was shown that the alloy specimens have a uniform highly dense microstructure and high hardness values. The studied alloys also have high resistance to electrochemical corrosion during tests in acidic aqueous solution causing the intergranular corrosion as well as high resistance to the hot salt corrosion. The assumption that the high hardness of the alloys as well as the differences in the corrosion resistance of the central and lateral parts of the specimens are due to the diffusion of carbon from the graphite mold into the specimen surface was suggested., Comment: 28 pages, 3 tables, 13 figures, 61 references

The study focuses on corrosion fatigue processes taking place in an ultrafine-grained (UFG) near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian industrial name PT7M) used in nuclear engineering. UFG structure formed with Rotary Swaging is found to increase resistance to corrosion fatigue. Parameters of the Basquin's equation are defined and the slope of the fatigue curve Sa-lg(N) is shown to depend (nonmonotonic dependence) on the UFG alloy annealing temperature. This effect can be explained with the patterns of microstructural evolution in a UFG alloy PT7M during annealing: (1) reduced density of lattice dislocations, (2) precipitation and dissolution of zirconium nanoparticles, (3) release of a''-phase particles causing internal stress fields along interphase (a-a'')-boundaries, and (4) intensive grain growth at elevated annealing temperatures. It is shown that the fatigue crack closure effect manifested as changing internal stress fields determined using XRD method may be observed in UFG titanium alloys., Comment: 54 pages, 2 tables, 19 figures, 64 referances

The corrosion-fatigue strength in 3% aqueous NaCl solution and the resistance against hot salt corrosion (HSC) of the fine-grained near-a alloy Ti-5Al-2V (Russian analog of Grade 9 titanium alloy with increased aluminum content) has been studied. The properties of the Ti-5Al-2V alloy in the coarse-grained state, in the fine-grained after cold Rotary Swaging (RS), in partly recrystallized state, and in fully recrystallized one have been investigated. The mechanical properties of the alloy were characterized using compression tests and microhardness measurements. The effects of RS and of the annealing temperature and time on the character of corrosion destruction of the surface and on the composition of the products of the HSC were studied. RS was shown to result in an increase in the depth of the intergranular corrosion defects while the recrystallization annealing promotes the increasing of the corrosion resistance of the Ti-5Al-2V titanium alloy. The parameters of the Basquin equation for the corrosion-fatigue curves for the near-a Ti-5Al-2V alloy in the coarse-grained state, in the severely strained one, and after recrystallization annealing were determined for the first time. An effect of nonmonotonous dependencies of the slopes of the corrosion-fatigue curves for the strained near-a Ti-5Al-2V alloy on the recrystallization annealing temperature has been observed., Comment: 46 pages, 1 table, 19 figures, 64 references

The study investigates the density, phase composition, microstructure and mechanical properties (microhardness, fracture toughness) of binderless WC + SiC and WC + SiC + C ceramics obtained by Spark Plasma Sintering (SPS). Nanopowders of a-WC produced by DC arc plasma chemical synthesis were used as raw materials. Powder compositions for sintering contained graphite (0.3, 0.5% wt.) or b-SiC (1, 3, 5% wt.) with 0.3% wt. graphite. It was shown that WC + 1% wt. SiC + 0.3% wt.C ceramics have a homogeneous fine-grained microstructure, high relative density, increased microhardness and Palmquist fracture toughness (Indentation Fracture Resistance). The kinetics of the initial sintering stage of WC + C and WC + C + SiC powder compositions was also analyzed using high-temperature dilatometry at the conventional pressureless sintering (CPS) conditions. The CPS and SPS activation energies of WC + SiC powder at the intensive shrinkage stage were determined using the Young-Cutler model. The CPS activation energies of WC, WC + C and WC + C + SiC powder compositions are close to the activation energy of diffusion of the carbon C along the a-WC grain boundaries. The SPS activation energies of WC + C and WC+ C + SiC powder compositions turn out to be lower than the activation energy of the C of a-WC grain boundary., Comment: 35 pages, 3 tables, 18 figures, 40 references

The paper presents the investigation of ordinary and ternary vanadates with zircon and monazite structures. Vanadates LnVO4 and CaLnZr(VO4)3 , where (Ln = La, Nd, Sm, Eu, Gd, Dy, Yb) and solid solution La0.3Nd0.5Sm0.1Eu0.1VO4, were prepared by precipitation reaction. Bulk ceramic samples were obtained from powders by Spark Plasma Sintering (SPS). The powders and ceramics were examined with several physicochemical methods. The coefficients of thermal expansion at 900{\deg}C were determined. The hydrolytic stability of ceramic materials was studied. The peculiarities of high-rate SPS of powders of ordinary and ternary vanadates were analyzed., Comment: 56 pages, 22 figures, 4 tables, 65 refernces, 1 appendix

Oxide Y2.5Nd0.5Al5O12 (YAG:Nd) with garnet structure was synthesized in the powder and ceramics forms. Fine-grained YAG:Nd ceramics with a relative density of ~99% were obtained by the Spark Plasma Sintering method (SPS). The radiation resistance of ceramics was studied under irradiation with swift Xe-ions (E = 146 MeV). A gradient defect structure is formed in irradiated ceramics, varying from layer to layer. The strained YAG phase formed as a result of Xe ions irradiation is localized in a near-surface layer with a thickness of ~5 {\mu}m. Full amorphization of the samples was observed under irradiation with a fluence of 1x10^13 cm-2. The calculated critical fluence was 6.5x10^12 cm-2, which corresponded to 0.03 dpa. The microhardness of the surface layers of irradiated ceramics is less than the central layers, and, in general, decreases with increasing ion fluence., Comment: 26 pages, 9 figures, 33 references

Mini-EUSO is a wide Field-of-View (FoV, 44$^{\circ}$) telescope currently in operation from a nadia-facing UV-transparent window in the Russian Zvezda module on the International Space Station (ISS). It is the first detector of the JEM-EUSO program deployed on the ISS, launched in August 2019. The main goal of Mini-EUSO is to measure the UV emissions from the ground and atmosphere, using an orbital platform. Mini-EUSO is mainly sensitive in the 290-430 nm bandwidth. Light is focused by a system of two Fresnel lenses of 25 cm diameter each on the Photo- Detector-Module (PDM), which consists of an array of 36 Multi-Anode Photomultiplier Tubes (MAPMTs), for a total of 2304 pixels working in photon counting mode, in three different time resolutions of 2.5 ${\mu}$s, 320 ${\mu}$s, 40.96 ms operation in parallel. In the longest time scale, the data is continuously acquired to monitor the UV emission of the Earth. It is best suited for the observation of ground sources and therefore has been used for the observational campaigns of the Mini-EUSO. In this contribution, we present the assembled UV flasher, the operation of the field campaign and the analysis of the obtained data. The result is compared with the overall efficiency computed from the expectations which takes into account the atmospheric attenuation and the parameterization of different effects such as the optics efficiency, the MAPMT detection efficiency, BG3 filter transmittance and the transparency of the ISS window.

Mini-EUSO (Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory) is a telescope observing the Earth from the International Space Station since 2019. The instrument employs a Fresnel-lens optical system and a focal surface composed of 36 multi-anode photomultiplier tubes, 64 channels each, for a total of 2304 channels with single photon counting sensitivity. Mini-EUSO also contains two ancillary cameras to complement measurements in the near infrared and visible ranges. The scientific objectives of the mission range from the search for extensive air showers generated by Ultra-High Energy Cosmic Rays (UHECRs) with energies above 10$^{21}$ eV, the search for nuclearites and Strange Quark Matter (SQM), up to the study of atmospheric phenomena such as Transient Luminous Events (TLEs), meteors and meteoroids. Mini-EUSO can map the night-time Earth in the near UV range (between 290-430 nm) with a spatial resolution of about 6.3 km (full field of view of 44{\deg}) and a maximum temporal resolution of 2.5 $\mu$s, observing our planet through a nadir-facing UV-transparent window in the Russian Zvezda module. The detector saves triggered transient phenomena with a sampling rate of 2.5 $\mu$s and 320 $\mu$s, as well as continuous acquisition at 40.96 ms scale. In this paper we discuss the detector response and the flat-fielding and calibration procedures. Using the 40.96 ms data, we present $\simeq$6.3 km resolution night-time Earth maps in the UV band, and report on various emissions of anthropogenic and natural origin. We measure ionospheric airglow emissions of dark moonless nights over the sea and ground, studying the effect of clouds, moonlight, and artificial (towns, boats) lights. In addition to paving the way forward for the study of long-term variations of natural and artificial light, we also estimate the observation live-time of future UHECR detectors., Comment: 49 pages, 27 figures, 1 table, published in Remote Sensing of Environment

The creep mechanism in the compression testing of the tungsten carbide with different grain sizes has been studied. The WC samples with high density (96.1-99.2%) were obtained by SPS from nano-, submicron, and micron-grade WC powders. The samples had a coarse-grained (CG) surface layers of ~0.3 mm in thickness and ultrafine-grained (UFG) central parts consisting of WC with a small fraction of W2C. The creep tests were conducted in two regimes: (Mode #1) holding at different temperatures (1300-1375C) at 70 MPa; (Mode #2) tests at different stresses (50, 70, 90 MPa) at 1325C. Tests in Mode #1 were done to determine the effective creep activation energy Qcr while tests in Mode #2 - to determine the coefficient n in the power law creep equation. The increasing of the fraction of the W2C particles from 1.7 up to 4% was found to result in a decrease in the Qcr from 17.5 down to 13 kTm. The coefficient n equals to 3.1-3.7. The Qcr in the WC sintered from nanopowders was shown to be 31 kTm. This value is 1.5-2 times greater than the Qcr in the UFG samples obtained by SPS from commercial powders. The increased fraction of the W2C formed when sintering the nanopowders with increased adsorbed oxygen concentration was suggested to be one of the origins of the increase in the Qcr when testing the UFG samples. The mechanical removing of the CG layers from the surfaces of the tungsten carbide sample was shown to result in an accelerated creep, insufficient decrease in the Qcr and coefficient n to 2.5-2.6. The creep rate of the samples was suggested to be determined simultaneously by the creep process in the CG surface layers and the creep process in the UFG central parts of the samples. The creep rate in the surface CG layers is determined by intensity of carbon diffusion in the WC crystal lattice while the creep rate in the UFG central parts - by the intensity of grain boundary diffusion., Comment: 56 pages, 16 figures, 1 table, 89 refernces

The results of dynamic strength tests of the alumina ceramics with various grain sizes are presented. The ceramics were obtained by Spark Plasma Sintering (SPS) of industrial submicron and fine Al2O3 powders. The heating up was performed with the rate of 10 oC/min; the grain sizes in the ceramics was controlled by varying the SPS temperature and the heating rate as well as by varying the initial sizes of the Al2O3 particles in the powders. The ceramics had a high density (over 98%) and a uniform fine-grained microstructure (the mean grain sizes varied from 0.8 to 13.4 mkm). The dynamic compressing tests were carried out by modified Kolsky method with using split Hopkinson pressure bar. The tests were performed at room temperature using a 20-mm PG-20 gas gun with the strain rate of ~10^3 s-1. The dependence of the dynamic ultimate strength of alumina on the grain size was found for the first time to have a non-monotonous character (with a maximum). The maximum value of the dynamic ultimate compression strength (SY = 1060 MPa) was provided at the mean grain size of ~2.9-3 mkm. The reduction of SY for alumina in the range of submicron grain sizes was shown to originate from the reduction of the relative density of the ceramics sintered at lower SPS temperatures., Comment: 16 pages, 1 table, 6 figures, 28 references

The effect of temperature modes and heating rates (Vh) on the shrinkage kinetics of submicron and fine aluminum oxide powders has been studied. The objects of research comprised (i) submicron alfa-Al2O3 powder, (ii) submicron alfa-Al2O3 powder with an amorphous layer on particle surface, (iii) fine alfa-Al2O3 powder. The alumina ceramic specimens were produced by Spark Plasma Sintering (SPS). Equally fine powders (i) and (ii) were used to analyze the effect of an amorphous layer on sintering kinetics. Powders (i) and (iii) were used to analyze the effect of the initial particle size on shrinkage kinetics. Shrinkage curves were analyzed using the Young-Cutler and Coble models. It has been shown that sintering kinetics is determined by the intensity of grain boundary diffusion for submicron powders and by simultaneous lattice and grain boundary diffusion for fine powders. It has been determined that an amorphous layer on the surface of submicron alfa-Al2O3 powder affects grain boundary migration rate and the Coble equation parameters at SPS final stages. It has been suggested that abnormal characteristics of the alumina ceramics sintered from a submicron powder with an amorphous layer on the particle surface are associated with an increased concentration of defects at grain boundaries that were formed during crystallization of the amorphous layer., Comment: 62 pages, 20 figures, 5 tables, 67 references