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In the water bodies of Ukraine, 6 new species of naked amoebae were found: Saccamoeba sp., Ripella sp., Vannella lata Page, 1988, The camoeba sp., Acanthamoeba sp., Vahlkampfia sp. According to the current taxonomy, they belong to 3 classes, 4 orders, 5 families and 6 genera. New localities and original descriptions of the species are presented, along with brief characteristics of the corresponding genera. The camoeba sp. and Acanthamoeba sp. are first reported from the territory of Ukraine.

The biotopic and seasonal distributions of the naked amoeba species related to the specific morphotypes were analyzed on the territory of Zhytomyr and Volyn Polissya. It was demonstrated that the polytactic and, to some extent, rugose and branched morphotypes of naked amoebas have the adaptive significance and could have emerged as a result of adaptation to characteristic conditions of oligotrophic lakes. In turn, the formation of lanceolate morphotype may be associated with the adaptation to low water temperatures, whereas the formation of flamellian morphotype may be an adaptation to high temperatures.

Taxonomy of naked amoebae and specifics of their distribution in water bodies of Sumy Region are presented. Our research identified 12 species of naked amoebae of 11 morphotypes. We established their ecological groups relative to abiotic aquatic factors: euryoxidic, stenooxidic, stenobiotic and those that survive in a wide range of organic matter content. According to the species composition, swamp and riparian species complexes of naked amoebae were identified. It was found that species complexes of amoeba are influenced by such factors as temperature, concentration of dissolved oxygen and organic compounds.

The species Rhzamoeba sp., Thecamoeba quadrilineata Carter, 1856, Thecamoeba verrucosa Ehrenberg, 1838, Flamella sp., and Penardia mutabilis Cash, 1904 are first reported in the fauna of Ukraine and described based on original material.

New Gymnamoebae Species (Gymnamoebia) in the Fauna of Ukraine Information is given on new in the fauna of Ukraine gymnamoebae species: [Saccamoeba stagnicola] Page, 1974; [Mayorella] sp.; [Korotnevella] sp.; [Paradermamoeba levis] Smirnov et Goodkov, 1994; [Paradermamoeba valamo] Smirnov et Goodkov, 1993 and [Stenamoeba stenopodia] Smirnov, Nassonova, Chao et Cavalier-Smith, 2007.

Biotopic Distribution of Naked Amoebas (Protista) in Ukrainian Polissya Area Forty-one species of naked amoebas were found in the different types of waterbodies of Zhytomyr and Volyn' parts of Ukrainian Polissya region. The major part of species of naked amoebas in this region demonstrated the prevalence to living in a certain type of water body that possible depends on the hydrochemical and trophic parameters of water. The limnetic and floodplain species complexes of amoebas are distinguished in Ukrainian Polissya.

The atomic nucleus is made of protons and neutrons (nucleons), which are themselves composed of quarks and gluons. Understanding how the quark–gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification—known as the EMC effect—was first observed over 35 years ago, there is still no generally accepted explanation for its cause 1 – 3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4 , 5 . Here we report simultaneous, high-precision measurements of the EMC effect and SRC abundances. We show that EMC data can be explained by a universal modification of the structure of nucleons in neutron–proton SRC pairs and present a data-driven extraction of the corresponding universal modification function. This implies that in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have distorted quark structure. This universal modification function will be useful for determining the structure of the free neutron and thereby testing quantum chromodynamics symmetry-breaking mechanisms and may help to discriminate between nuclear physics effects and beyond-the-standard-model effects in neutrino experiments. Simultaneous high-precision measurements of the EMC effect and short-range correlated abundances for several nuclei reveal a universal modification of the structure of nucleons in short-range correlated neutron–proton pairs.

The atomic nucleus is one of the densest and most complex quantum-mechanical systems in nature. Nuclei account for nearly all the mass of the visible Universe. The properties of individual nucleons (protons and neutrons) in nuclei can be probed by scattering a high-energy particle from the nucleus and detecting this particle after it scatters, often also detecting an additional knocked-out proton. Analysis of electron- and proton-scattering experiments suggests that some nucleons in nuclei form close-proximity neutron–proton pairs 1 – 12 with high nucleon momentum, greater than the nuclear Fermi momentum. However, how excess neutrons in neutron-rich nuclei form such close-proximity pairs remains unclear. Here we measure protons and, for the first time, neutrons knocked out of medium-to-heavy nuclei by high-energy electrons and show that the fraction of high-momentum protons increases markedly with the neutron excess in the nucleus, whereas the fraction of high-momentum neutrons decreases slightly. This effect is surprising because in the classical nuclear shell model, protons and neutrons obey Fermi statistics, have little correlation and mostly fill independent energy shells. These high-momentum nucleons in neutron-rich nuclei are important for understanding nuclear parton distribution functions (the partial momentum distribution of the constituents of the nucleon) and changes in the quark distributions of nucleons bound in nuclei (the EMC effect) 1 , 13 , 14 . They are also relevant for the interpretation of neutrino-oscillation measurements 15 and understanding of neutron-rich systems such as neutron stars 3 , 16 . Electron-scattering experiments reveal that the fraction of high-momentum protons in medium-to-heavy nuclei increases considerably with neutron excess, whereas that of high-momentum neutrons decreases slightly, in contrast to shell-model predictions.

The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of quantum chromodynamics. However, as these equations cannot be solved directly, nuclear interactions are described using simplified models, which are well constrained at typical inter-nucleon distances 1 – 5 but not at shorter distances. This limits our ability to describe high-density nuclear matter such as that in the cores of neutron stars 6 . Here we use high-energy electron scattering measurements that isolate nucleon pairs in short-distance, high-momentum configurations 7 – 9 , accessing a kinematical regime that has not been previously explored by experiments, corresponding to relative momenta between the pair above 400 megaelectronvolts per c ( c , speed of light in vacuum). As the relative momentum between two nucleons increases and their separation thereby decreases, we observe a transition from a spin-dependent tensor force to a predominantly spin-independent scalar force. These results demonstrate the usefulness of using such measurements to study the nuclear interaction at short distances and also support the use of point-like nucleon models with two- and three-body effective interactions to describe nuclear systems up to densities several times higher than the central density of the nucleus. High-energy electron scattering that can isolate pairs of nucleons in high-momentum configurations reveals a transition to spin-independent scalar forces at small separation distances, supporting the use of point-like nucleon models to describe dense nuclear systems.

Particle knockout scattering experiments1,2 are fundamental for mapping the structure of atomic nuclei2–6, but their interpretation is often complicated by initial- and final-state interactions of the incoming and scattered particles1,2,7–9. Such interactions lead to reduction in the scattered particle flux and distort their kinematics. Here we overcome this limitation by measuring the quasi-free scattering of 48 GeV c–112C ions from hydrogen. The distribution of single protons is studied by detecting two protons at large angles in coincidence with an intact 11B nucleus. The 11B detection suppresses the otherwise large distortions of reconstructed single-proton distributions induced by initial- and final-state interactions. By further detecting residual 10B and 10Be nuclei, we also identified short-range correlated nucleon–nucleon pairs9–13 and provide direct experimental evidence for separation of the pair wavefunction from that of the residual many-body nuclear system9,14. All measured reactions are well described by theoretical calculations that include no distortions from the initial- and final-state interactions. Our results showcase the ability to study the short-distance structure of short-lived radioactive nuclei at the forthcoming Facility for Antiproton and Ion Research (FAIR)15 and Facility for Rare Isotope Beams (FRIB)16 facilities, which is relevant for understanding the structure and properties of nuclei far from stability and the formation of visible matter in the Universe.Initial- and final-state interactions distort the kinematics in particle knockout scattering experiments, complicating their interpretation. These effects are suppressed by detecting 11B nuclei in quasi-free scattering of 12C ions from hydrogen.