Alexander V. Polyakov

Intercomparison of satellite and ground-based measurements of ozone, NO2, HF, and HCl near Saint Petersburg, Russia

Regular intercomparison of different observing systems is a part of their testing and validation protocol, which gives the estimates of real measurement errors. The main objective of our study is the comparison of satellite and ground-based measurements of atmospheric composition near Saint Petersburg, Russia. Since early 2009, high-resolution Fourier Transform Infrared (FTIR) solar absorption spectra have been recorded at Peterhof station (59.82° N, 29.88° E), located in the suburbs of Saint Petersburg. We derived column amounts of O3, HCl, HF, and NO2 from these spectra using the retrieval codes SFIT2 and PROFFIT. We compared the data retrieved from Bruker 125 HR FTIR measurements with coincident satellite observations of the Microwave Limb Sounding (MLS), Ozone Monitoring Instrument (OMI), Fourier Transform Spectrometer from Atmospheric Chemistry Experiment (ACE-FTS), Global Ozone Monitoring Experiment (GOME and GOME-2), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instruments. The relative differences in ozone columns of FTIR from OMI-TOMS amount within (+3.4 ± 2.9)%, from GOME-2 are (+2.2 ± 3.0)%. The comparison of FTIR and MLS measurements of stratospheric ozone columns gives no mean and 5% of the RMS differences. Measurements of NO2 columns agree with the mean difference of +9% and the RMS differences within 14–16% for FTIR vs. GOME-2, SCIAMACHY, and OMI. FTIR vs. GOME comparison gives (+6 ± 31)%. HCl columns comparison for FTIR vs. MLS shows −4.5% in the mean and 12% in the RMS differences. FTIR vs. ACE-FTS comparison (nine cases) gives −8% and 10% for the mean and the RMS relative differences, respectively. Comparison of HF columns shows (−12 ± 6)% and (−12 ± 11)% for FTIR vs. ACE data v.2.2 and v.3.0, respectively. These figures show that the Peterhof ground-based FTIR measuring system can be used to support the validation of satellite data in the monitoring of stratospheric gases.

Experimental study of thermodynamic and fatigue properties of submicrocrystalline titanium under high cyclic and gigacyclic fatigue regimes

This paper presents an experimental study of the mechanical and thermal behavior of titanium samples (Grade 2 and Grade 4) with different grain sizes under cyclic loading. The self-heating test demonstrates that the structure of the material has a strong effect on the dissipation ability of titanium. The threshold of energy dissipation corresponding to the transition through the fatigue limit is shown for coarse-grained titanium. On contrary, submicrocrystalline samples exhibit the dependence of continuous energy dissipation on the applied stress amplitude. Analysis of the fatigue properties of titanium in a gigacyclic regime provides evidence that grain grinding improves substantially the fatigue properties of the material.

Comparison of different techniques in atmospheric temperature-humidity sensing from space

Numerical closed-loop experiments on retrieving atmospheric temperature and humidity profiles by high-resolution measurements of the outgoing thermal infrared (IR) radiation using a Russian Fourier spectrometer (IRFS-2) were performed. Three techniques were used: multiple linear regression (MLR), the iterative physical-mathematical approach (IPMA), and artificial neural networks (ANNs). The MLR technique gives significant root mean square (RMS) errors in the retrieval of the temperature profile, especially in the troposphere region; these errors may be as great as 2–3 K. The ANN and IPMA techniques are considerably more accurate, giving approximately equal RMS errors of 1.0–1.5 K at altitudes of 2–30 km. For all interpretation techniques, a growth of errors of retrieval of temperature in the lower troposphere is observed and is especially substantial (up to 3 K for the near-surface temperature) in thermal sensing over land. The systematic errors of temperature retrieval for the ANN technique are practically zero, and for the other two techniques, they do not exceed 0.4 K. The differences in thermal sensing of the atmosphere over water and land manifest themselves in the appearance of an additional five determined coefficients of expansion of the spectral dependence of the IR emissivity of land in principal components. This leads to increased errors on thermal sensing in the lower troposphere, up to ~0.5 K for all interpretation techniques. The information content of the IRFS-2 device measurements with regard to the atmospheric humidity profile is relatively small because of the values of the errors of measurements of the outgoing radiation in the shortwave range, and in particular, in the water vapour absorption band 6.3 µm. The ANN technique makes it possible to determine relative humidity in the troposphere with RMS errors of 10–15%. In the case of observations over water, the mean errors of the ANN technique are practically equal to zero, and for the MLR and IPMA techniques, they are of an approximately equal order of magnitude, namely 2–4% of relative humidity. The IPMA and MLR techniques give RMS humidity errors of 15–20% and up to 40%, respectively.

Evolution of Microstructure and Mechanical Properties of Titanium Grade 4 with the Increase of the ECAP-Conform Passes

This work reports on the results of investigation of microstructure change of commercially pure titanium Grade 4 with the increase of the number of ECAP-Conform passes. There has been investigated influence of continuous equal-channel angular pressing by the scheme “Conform” (ECAP-C) on the structure and properties of commercially pure titanium Grade 4. It has been demonstrated that as a result of first two ECAP-C cycles titanium structure is strongly fragmented and deformation bands are formed. With the further increase of ECAP-C passes to 6 the band structure is transformed into ultrafine-grained (UFG) structure with the grain size of about 250 nm. The strength of titanium regularly grows with the increase of the number of ECAP-C passes, while ductility, which settles after first cycle on the level of 12%, is almost not changed with the further strain degree increase. As a result of the subsequent drawing of titanium after ECAP-C its strength additionally increases to 1300 MPa, with retention of ductility about 11%.

Formation of a nanostructure and properties of titanium rods during equal-channel angular pressing CONFORM followed by drawing

Severe plastic deformation by equal-channel angular pressing according to the Conform schedule (ECAP-Conform) is used for the first time to produce long titanium rods in a nanostructured state. As a result of ECAP-Conform followed by drawing, the ultimate strength of Grade 4 titanium increases to 1350 MPa, and its yield strength increases to 1300 MPa at a high retained plasticity. The high efficiency and output of the ECAP-Conform method allow the development (on its basis) of a commercial technology for the production of high-strength nanostructured titanium, which is a promising material for medical implants.

High fatigue strength and enhanced biocompatibility of UFG CP Ti for medical innovative applications

This study is focused on the fatigue properties of the UFG Ti Grade 4 and its biocompatibility. The UFG titanium was produced by ECAP-Conform in combination with subsequent drawing, which allows fabricating rods of up to 3 mm suitable for industrial applications. The endurance limit of smooth and notched samples of UFG Ti is considerably higher than in conventional Ti. The UFG Ti also demonstrates an increased capacity of human osteoblast-like U2OS cells to colonize and, therefore, better osseointegration. Torsional strength of standard Ti-6Al-7Nb products and UFG Ti Grade 4 products was evaluated. An advantage of the UFG titanium over the conventional coarse-grained material was shown.

Physical Simulation of Hot Rolling of Ultra-fine Grained Pure Titanium

Complex thermo-mechanical processing routes are often developed for fabrication of ultra-fine grained (UFG) metallic materials with superior mechanical properties. The processed UFG metallic materials often have to undergo additional metalforming operations for fabrication of complex shape parts or tools that can significantly affect their microstructure and crystallographic texture, thus further changing their mechanical properties. The development of novel thermo-mechanical processing routes for fabrication of UFG metallic materials or for further metalforming operations is very time-consuming and expensive due to much higher cost of the UFG metallic materials. The objective of this work is to perform physical simulation of hot rolling of UFG pure Ti obtained via severe plastic deformation and to analyze the effect of hot rolling on the microstructure, crystallographic texture, and hardness of the material. It is demonstrated that physical simulation of metalforming processes for UFG metallic materials can significantly reduce the amount of material required for development of processing routes as well as to increase the efficiency of experimental work.

Measurements of Trace Gases at Saint-Petersburg State University (SPbSU) in the Vicinity of Saint-Petersburg, Russia

An overview of atmospheric trace gas measurements made using various spectroscopic ground-based instrumentation and measurement techniques at the Department of Physics of Atmosphere, St. Petersburg State University is given. The SPbSU trace-gas retrievals have been compared to independent ground-based and satellite measurements as well as to models. Temporal variations (from diurnal cycles to long-term trends) of trace-gases have been studied on the basis of experimental data.

Atmospheric integrated water vapour measured by IR and MW techniques at the Peterhof site Saint Petersburg, Russia

ABSTRACT Regular comparison of different systems for monitoring atmospheric integrated water vapour (IWV) is part of their testing and validation protocol. We compared coincident measurements of IWV over Saint Petersburg (Russia) from ground-based Fourier-transform spectrometer Bruker IFS 125 HR (FTIR) and microwave radiometer RPG-HATPRO (MW) at the Peterhof site between March 2013 and June 2015. This study is a contribution towards global efforts to make such inter-comparisons at various ground-based sites. Since FTIR measures solar radiance, the vast majority of coincident pairs correspond to the spring and summer seasons. The numbers of measurements in the dry season (from October to April) and in the wet season (from May to September) are almost identical, comprising 616 and 638 pairs, respectively. MW and FTIR data sets demonstrate a high level of agreement: the mean relative difference between MW and FTIR data is less than 3% (0.3 mm), with standard deviation from the means of about 4% (0.4 mm). Notwithstanding the short distance between both instruments (150 m), they can monitor different air masses: MW is a zenith-viewing instrument whereas FTIR follows the sun. We analysed the FTIR observation fields under different solar zenith and azimuth angles, taking into account the location of the Peterhof site between the Gulf of Finland and rural suburbs of Saint Petersburg. Although in general MW measurements slightly overestimated IWV in comparison with the FTIR data, we detected several episodes when FTIR gave higher values than MW. These episodes relate to the FTIR observations directed at the coastal region with more humid air than that above the measurement site. We may conclude at this stage of our investigations that the spatial inhomogeneity of humidity fields in the atmosphere causes the most significant differences between the two data sets. Detailed analysis of variation in spatial IWV, e.g. using a MW radiometer in angular scanning mode, is an issue for future research.

The atmospheric and surface sounding from the Meteor satellite (numerical simulation)

The main characteristics of the instruments onboard «Meteor-3M» satellite (IRFS-2, MTVZA-GYa, MSU-MR) measuring the outgoing radiation in visible, NIR, IR and microwave spectral ranges are presented. Characteristics of the informativity of outgoing radiation measurements (degrees of freedom, the Shannon information content) are analyzed under cloudless and cloudy conditions. Various techniques and software for interpreting the outgoing radiation measurements made by these instruments separately or in combination are developed and described. Mathematical basis of techniques is the Multiple Linear Regression (MLR) analysis and a nonlinear generalization of a method of statistical regularization. Numerical simulation of remote measurements is performed using the ensemble of realizations of the atmosphere and underlying surface state. As a result, potential errors of retrieving the atmospheric and surface parameters are estimated and analyzed under cloudless and cloudy conditions.