Simulations of solid-state transformation kinetics were carried out calculating temperature and conversion degree for non-isothermal experiments with different heating rates. Simulations were divided in two parts: with constant and with variable activation energy. Simulations were analyzed with widely used model-based and model-free activation energy determination methods, frequency factor and kinetic model determination methods. Much of the attention was devoted to the calculation of kinetic models and frequency factors, as a more difficult and less developed step. For simulations where activation energy did not change all activation energy determination methods were found to give correct results. However, much attention should be devoted to frequency factor determination, because incorrect results would lead to problems in determination of kinetic models. For simulations where activation energy changes, correct activation energy can be determined only by differential methods or integral methods using numerical integration over small intervals. Isokinetic relationship coefficients b and c were more accurately determined with the average linear integral method. Correct kinetic model determination was possible only when coefficients b and c were accurate, and only by analyzing results of all available methods.
A. Bērziņš and A. Actiņš
K. Krūkle-Bērziņa, A. Actiņš and A. Bērziņš
Hydration of Xylazine Hydrochloride Polymorphic Forms A, Z and M
In this work, the hydration of Xylazine hydrochloride polymorphic forms A, Z and M was monitored by gravimetry. A solid state kinetic model of hydration was defined, and rate constants were calculated for different temperatures and humidity conditions. Activation energy values were obtained from the Arrhenius plots of the rate constants in the co-ordinates ln k - T -1.
D. Bērziņš, A. Fedotovs and U. Rogulis
We have investigated the samples of thermally treated oxyfluoride glass ceramics 50SiO2-25LiO2-20YF3-3ErF3-2YbF2 by means of electron paramagnetic resonance (EPR) techniques. After irradiation of the samples with X-rays, in the EPR spectra a hyperfine structure characteristic of F-centres could be observed in different fluoride crystals. The structure of F-centre in the oxyfluoride glass ceramics containing LiYF4 crystallites is discussed.
R. Joffe, N. Jēkabsons, A. Bērziņš, M. Klapers and S. Upnere
The main objective of the work was to analyze the operation of the large radio telescope RT-32 at the Ventspils International Radio Astronomy Centre (VIRAC). The analysis has been performed in order to evaluate dimensional changes in the RT- 32 structural base due to reorientation of the antenna mirror. Three different orientations of the dish were considered, and the dimensional changes in the load carrying substructure were measured. The measurements were made to estimate possible effect of the geometrical changes of the antenna due to gravitational loads on the overall performance of the radio telescope with respect to the obtained astronomical results, their accuracy and validity. Comprehensive mapping and classification of the corrosive damage of steel elements in the antenna have been done. A preliminary numerical analysis by the finite element method was carried out to demonstrate the overall effect of the damaged steel beams on the geometrical distortion of the antenna surface.
M. Bleiders, A. Berzins, N. Jekabsons, K. Skirmante and Vl. Bezrukovs
Irbene RT-32 radio telescope is one of the main instruments operated by Ventspils International Radio Astronomy Center (VIRAC), which is used for participation in VLBI and single-dish mode observations, including European VLBI Network (EVN) and other astronomy projects such as recently started research on small bodies of solar system, which involves weak spectral line detection at L-band. Since start of the operation as a radio telescope, single C-X band receiver has been available at RT-32, but regular demand for L-band frequencies has been received due to its importance in spectral line science. In case of RT-32 geometry, optimum dimensions of L-band feed antenna system are inconveniently large and its installation without significant feed cone rebuilding is complicated. While work is currently ongoing to redesign the feed cone for multiple receiver support and to develop high performance L-band feed system, temporal, compact and low-cost receiver has been built and installed laterally to secondary focus, which in sense of performance and functionality has been proven to be appropriate for most of the current needs. Receiver is based on small parabolic reflector allowing one to use a compact dual circular polarized horn antenna, which together with a Cassegrain antenna forms a three-mirror system. Front-end is uncooled that allows reducing operational and maintenance costs, while still providing acceptable noise performance. Practical tests show average overall sensitivity of 750 Jy at 1650 MHz in terms of system effective flux density (SEFD). The paper describes the development of the receiver and presents the main results of performance characterization obtained at Irbene RT-32.
M. Auzinsh, A. Berzins, R. Ferber, F. Gahbauer, U. Kalnins, R. Rundans and D. Sarkisyan
In this paper we present a device for measuring the magnetic field and its gradient with a spatial resolution of several hundred nanometres. This device is based on caesium metal vapour confined to an extremely thin cell (ETC). To measure magnetic signals, we use absorption and very low laser powers, which might be appealing for modern fabrication techniques. A portable, fully automated device was constructed.
A. Kons, A. Bērziņš, K. Krūkle-Bērziņa and A. Actiņš
The paper reports the investigation of three umifenovir molecular complexes with dicarboxylic acids, prepared to improve the bioavailability of this drug. All three molecular complexes were investigated by powder X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. The solubility and thermal properties were determined as well. Polymorph and solvate screening of umifenovir molecular complexes were performed by recrystallization from various solvents, as well as neat and solvent-drop grinding
Vl. Bezrukovs, I. Shmeld, M. Nechaeva, J. Trokss, D. Bezrukovs, M. Klapers, A. Berzins, A. Lesins and N. Dugin
Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC.
One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others.
During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methanol maser single dish observations.
The apparatus system of RT-32 is equipped with two independent VLBI data acquisition systems: TN-16, and DBBC in combination with MK5b. Both systems are employed in interferometric observations depending on the purpose of experiment and the enabled radiotelescopes.
The current status of RT-32, the availability of its receiving and data acquisition units for VLBI observations and the previous VLBI sessions are discussed.
Ilze Radoviča, Rūdolfs Bērziņs, Gustavs Latkovskis, Dāvids Fridmanis, Liene Ņikitina-Zaķe, Kārlis Ventiņš, Guna Ozola, Andrejs Ērglis and Jānis Kloviņš
Familial hypercholesterolemia (FH) is one of the most common single gene disorders, which is mostly inherited as an autosomal dominant trait. The physical signs of FH are elevated low density lipoprotein cholesterol (LDL-C), elevated total cholesterol (TC) levels and tendon xantomas. Identification and early treatment of affected individuals is desirable and in lack of physical symptoms DNA-based diagnosis provides confirmation of diagnosis and enables early patient management. The majority of FH cases are caused by mutations in four genes (APOB, LADLR, PCSK9, and LDLRAP1). There are commercial kits available for testing of the 20 most common FH causing mutations, but the spectrum of disease-causing mutations is quite diverse in various populations and these tests cover only a minority of disease-causing genetic variants. There is therefore a need to determine the full spectrum of mutations in LDLR, APOB, PCSK9, and LDLRAP1 genes in each population. Here we report mutations found in 16 patients with suspected FH in a sample from the Genome Database of the Latvian population enrolled at the Latvian Centre of Cardiology. We used the next generation sequencing approach to determine the full spectrum of mutations in coding regions of LDLR, APOB, PCSK9, and LDLRAP1. In total we found 22 missense mutations, from which only rs5742904 (Arg3527Gln) in APOB gene had been previously described as a FH-causing mutation confirming FH in one patient. Possible FH-causing mutations however, were identified in the majority of patients. The conclusion is that the most commonly employed commercial mutation panel is not sufficient for diagnosis of FH patients and NGS can help to identify FH-causing mutations in the Latvian population.