Persistent Action Research Articles

Amygdala stimulation transforms short-term memory into remote memory by persistent activation of atypical protein kinase C in the anterior cingulate cortex.

Although many studies have addressed the role of the amygdala in modulating long-term memory, it is not known whether weak training plus amygdala stimulation can transform a short-term memory into a remote memory. Object place recognition (OPR) memory after strong training remains hippocampus-dependent through the persistent action of protein kinase Mzeta (PKMζ) for at least 6 days, but it is unknown whether weak training plus amygdala stimulation can transform short-term memory into an even longer memory, and whether such memory is stored through more persistent action of PKMζ in hippocampus. We trained male rats (150 total in our study) to acquire OPR and 15 min or 5 h later induced a brief pattern of electrical stimulation in basolateral amygdala (BLA). Our results reveal that a short-term memory lasting < 4h can be converted into remote memory lasting at least 3 weeks if the BLA is activated 15 min, but not 5 h after learning. To examine how this remote memory is maintained, we injected ZIP, an inhibitor of atypical protein kinase Cs (aPKCs), PKMζ and PKCι/λ, into either hippocampal CA1, dentate gyrus (DG), or anterior cingulate cortex (ACC). Our data reveal amygdala stimulation produces consolidation into remote memory, not by persistent aPKC activation in the hippocampal formation, but in ACC. Our data establish a powerful modulating role of the BLA in forming remote memory and open a path in the search for neurological restoration of memory, based on enhancing synaptic plasticity in aging or neurodegenerative disorders such as Alzheimer's disease.

Playful programming, Social Resilience, and Persistent Actions as Drivers of Preservice Early Childhood Teachers’ Engagement in Computer Science

In this qualitative study, preservice early childhood education teachers created block-based code to control robots and used the robots in field experience at local preschools. The study is grounded in a conceptual framework that weaves together playful programing and resilience, interlocking concepts that can explain sustained engagement during times of challenge. We investigated how and why preservice early childhood teachers exhibit resilience during collaborative programing. We analyzed their debugging processes, reflections, and interviews using a phenomenological lens. We conducted open and axial coding and analysis of discourse and actions during debugging episodes. Results suggest that teachers exhibited resilience due to the following three reasons: through playful coding, preservice early childhood teachers (a) learned that computer science is approachable and fun, (b) engaged in adaptive attribution, and (c) engaged in joint celebration when they observed each other’s successes during collaborative tinkering. These findings provide potential insights for teacher learning of computing but also for novices learning to program.

The differential effect of optogenetic serotonergic manipulation on sustained motor actions and waiting for future rewards in mice.

Serotonin is an essential neuromodulator that affects behavioral and cognitive functions. Previous studies have shown that activation of serotonergic neurons in the dorsal raphe nucleus (DRN) promotes patience to wait for future rewards. However, it is still unclear whether serotonergic neurons also regulate persistence to act for future rewards. Here we used optogenetic activation and inhibition of DRN serotonergic neurons to examine their effects on sustained motor actions for future rewards. We trained mice to perform waiting and repeated lever-pressing tasks with variable reward delays and tested effects of optogenetic activation and inhibition of DRN serotonergic neurons on task performance. Interestingly, in the lever-pressing task, mice tolerated longer delays as they repeatedly pressed a lever than in the waiting task, suggesting that lever-pressing actions may not simply be costly, but may also be subjectively rewarding. Optogenetic activation of DRN serotonergic neurons prolonged waiting duration in the waiting task, consistent with previous studies. However, its effect on lever presses was nuanced, and was detected only by focusing on the period before premature reward check and by subtracting the trends within and across sessions using generalized linear model. While optogenetic inhibition decreased waiting, it did not affect lever pressing time or numbers. These results revealed that the necessity of motor actions may increase motivation for delayed rewards and that DRN serotonergic neurons more significantly promote waiting rather than persistent motor actions for future rewards.

Islamic Environmental Ethics: Preserving the Sacred Balance

Islamic environmental ethics derive from the theological underpinnings of Islam, highlighting the interconnections of all the elements in the universe. Rooted in the concept of Tawhid, a central tenet in Islamic theology, these ethics underscore the belief in the Oneness of God as the creator of the entire universe. Currently, we find ourselves in a world where persistent human actions are causing detrimental impacts on our environment. Anthropogenic activities, including water pollution, air pollution, and land pollution, coupled with inhumane treatment towards other living beings, contribute to the widespread destruction of numerous species, organisms, water bodies, land areas, the ozone layer, and various natural resources. This collective behavior poses a significant threat to the delicate balance of our ecosystems. Environmental challenges have become unavoidable, exacerbated by a general lack of public awareness and the escalating environmental harm caused by irresponsible actions. Islamic environmental ethics offer a framework of principles and moral standards aimed at ensuring the preservation and wellbeing of the natural environment. This paper aims to explore the Islamic perspective on the environment, encompassing both biotic and abiotic components. It will delve into the principles of environmental ethics in Islam, elucidating the role assigned to human beings in this perspective. Furthermore, it will examine Islam's attitude towards the environment, addressing issues related to natural resources and emphasizing the responsibility of humans to act as conscientious stewards of the Earth.

Altered neural anticipation of reward and loss but not receipt in adolescents with obsessive-compulsive disorder

BackgroundObsessive-compulsive disorder (OCD) is characterized by persistent, unwanted thoughts and repetitive actions. Such repetitive thoughts and/or behaviors may be reinforced either by reducing anxiety or by avoiding a potential threat or harm, and thus may be rewarding to the individual. The possible involvement of the reward system in the symptomatology of OCD is supported by studies showing altered reward processing in reward-related regions, such as the ventral striatum (VS) and the orbitofrontal cortex (OFC), in adults with OCD. However, it is not clear whether this also applies to adolescents with OCD.MethodsUsing functional magnetic resonance imaging, two sessions were conducted focusing on the anticipation and receipt of monetary reward (1) or loss (2), each contrasted to a verbal (control) condition. In each session, adolescents with OCD (n1=31/n2=26) were compared with typically developing (TD) controls (n1=33/ n2=31), all aged 10-19 years, during the anticipation and feedback phase of an adapted Monetary Incentive Delay task.ResultsData revealed a hyperactivation of the VS, but not the OFC, when anticipating both monetary reward and loss in the OCD compared to the TD group.ConclusionsThese findings suggest that aberrant neural reward and loss processing in OCD is associated with greater motivation to gain or maintain a reward but not with the actual receipt. The greater degree of reward ‘wanting’ may contribute to adolescents with OCD repeating certain actions more and more frequently, which then become habits (i.e., OCD symptomatology).

Endotoxin Inflammatory Action on Cells by Dysregulated-Immunological-Barrier-Linked ROS-Apoptosis Mechanisms in Gut-Liver Axis.

Our study highlighted the immune changes by pro-inflammatory biomarkers in the gut-liver-axis-linked ROS-cell death mechanisms in chronic and acute inflammations when gut cells are exposed to endotoxins in patients with hepatic cirrhosis or steatosis. In duodenal tissue samples, gut immune barrier dysfunction was analyzed by pro-inflammatory biomarker expressions, oxidative stress, and cell death by flow cytometry methods. A significant innate and adaptative immune system reaction was observed as result of persistent endotoxin action in gut cells in chronic inflammation tissue samples recovered from hepatic cirrhosis with the A-B child stage. Instead, in patients with C child stage of HC, the endotoxin tolerance was installed in cells, characterized by T lymphocyte silent activation and increased Th1 cytokines expression. Interesting mechanisms of ROS-cell death were observed in chronic and acute inflammation samples when gut cells were exposed to endotoxins and immune changes in the gut-liver axis. Late apoptosis represents the chronic response to injury induction by the gut immune barrier dysfunction, oxidative stress, and liver-dysregulated barrier. Meanwhile, necrosis represents an acute and severe reply to endotoxin action on gut cells when the immune system reacts to pro-inflammatory Th1 and Th2 cytokines releasing, offering protection against PAMPs/DAMPs by monocytes and T lymphocyte activation. Flow cytometric analysis of pro-inflammatory biomarkers linked to oxidative stress-cell death mechanisms shown in our study recommends laboratory techniques in diagnostic fields.

Fenomenologi Klaster Pariwisata: Media Digital sebagai Langkah Persistensi

Since the travel warning due to the coronavirus disease 2019 pandemic was issued, business actors in the tourism cluster on Lombok Island have experienced business ups and downs. After this pandemic, the number of tourist visits has not reached its target. This research aims to identify the perceived meaning and behavioral patterns of business actors in the tourism cluster on Lombok Island through persistent actions during the pandemic which caused travel warnings. The research method used is a qualitative-phenomenological method with samples randomly taken from various types of businesses in the tourism cluster and analyzed through data coding. The results show that persistence can be achieved if it is combined with resilience, and business actors can uniformly persist by implementing digital media to offer tourism services. This research can be a reference and recommendation basis for tourism business actors in Lombok to use digital media as the main marketing tool.

D-mannose is a rapid inducer of ACSS2 to trigger rapid and long-lasting antidepressant responses through augmenting BDNF and TPH2 levels

The potentiation of synaptic plasticity and serotonin generation by brain-derived neurotrophic factor (BDNF) and tryptophan hydroxylase 2 (TPH2) is well characterized to facilitate rapid and long-lasting antidepressant actions. Therefore, the identification of the key protein that simultaneously controls both BDNF and TPH2 is important for the treatment of depression. We show here that a lack of acetyl-CoA synthetase short-chain family member 2 (ACSS2) causes impairments in BDNF-dependent synaptic plasticity and tryptophan hydroxylase 2 (TPH2)-mediated serotonin generation, thereby contributing to spontaneous and chronic restraint stress (CRS)-induced depressive-like behavior in mice. Conversely, D-mannose is identified as a rapid ACSS2 inducer and thus mediates rapid and long-lasting antidepressant-like effects. Mechanistically, acute and chronic D-mannose administration inhibits the phosphorylation of EF2 to increase BDNF levels and reverse the reduction of TPH2 histone acetylation and transcription. We reveal that ACSS2 promotes TPH2 histone acetylation and transcription with the requirement of AMPK activation. To elevate nuclear ACSS2 levels, D-mannose can rapidly and persistently activate AMPK via Ca2+-CAMKK2 and the lysosomal AXIN-LKB1 pathway to facilitate its fast-acting and persistent antidepressant responses. Taken together, the results presented here reveal that ACSS2 functions as a novel target to link rapid and persistent antidepressant actions and further suggest that D-mannose is a potential therapeutic agent to resist depression through its augmentation of the ACSS2 dependent BDNF and TPH2 pathways.

A role of splenic heme biosynthesis pathway in the persistent prophylactic actions of arketamine in lipopolysaccharide-treated mice

Relapse is common in remitted patients with major depressive disorder (MDD). Arketamine, an (R)-enantiomer of ketamine, has persistent prophylactic actions in an inflammatory model of depression. However, the precise mechanisms underlying these prophylactic actions remain unknown. Given the role of the brain–spleen axis in depression, we sought to identify splenic molecular targets that play a role in the prophylactic actions of arketamine. Lipopolysaccharide (LPS) (1.0 mg/kg) was administered 6 days after a single injection of arketamine (10 mg/kg) or saline. RNA-sequencing analysis found altered expression in the heme biosynthesis II pathway. Quantitative RT-PCR revealed that pretreatment with arketamine blocked increased expression of genes involved in the heme biosynthesis II pathway in LPS-treated mice, namely, 5-aminolevulinase synthase 2 (Alas2), ferrochelatase (Fech), hydroxymethylbilane synthase (Hmbs). Interestingly, there were positive correlations between the expression of these genes and spleen weight or plasma levels of pro-inflammatory cytokines. We also found higher expression of ALAS2 and FECH in the spleen from MDD patients. Pretreatment with a key intermediate precursor of heme, 5-aminolaevulinic acid (300 mg/kg/day for 3 days), caused splenomegaly, higher plasma levels of pro-inflammatory cytokines, and depression-like behavior in low-dose LPS (0.1 mg/kg)-treated mice. Interestingly, pretreatment with a heme biosynthesis inhibitor, succinyl acetone (120 mg/kg/day for 3 days), had prophylactic effects in LPS (1.0 mg/kg)-treated mice. These data suggest a novel role for the heme biosynthesis II pathway in the spleen for inflammation-related depression. Therefore, the heme biosynthesis pathway could be a new target for the prevention of relapse in MDD patients.

Chemical Composition of the Essential Oil of Catha edulis Forsk from Djibouti and Its Toxicological Investigations In Vivo and In Vitro

This work aimed to evaluate the chemical composition of essential oils from Catha edulis Forsk collected in the Day Forest of the Republic of Djibouti. Additionally, in vivo toxicity studies, biochemical profiling, and hematological tests were conducted to determine the biological activity of the investigated essential oils. Finally, in vitro tests were performed to investigate the antibacterial activity of the essential oils. The essential oils were obtained at yields of 0.75%. Chromatographic analysis identified 39 compounds, of which cathinone (81.4%) and cathine (10.55%) were determined as the two major components, representing 91.95% of the total composition. Catha edulis essential oil had a rat LD50 of 2500 mg/kg, indicating very low toxicity. Chronic exposure studies revealed that use of the essential oil in rats resulted in persistent stimulant action at dosages of 100 and 200 mg/kg, whereas the weight gain of control rats was faster than that of the essential oil-treated rats. Hematological parameters showed a significant increase in red blood cell counts, hemoglobin, hematocrit, and platelets in treated rats, which could indicate blood hyperviscosity that may increase the risk of blood clots and cardiovascular diseases. Furthermore, the investigated essential oil exhibited antimicrobial activity against several bacterial strains.

Prediction of Bay-Shaped Shorelines between Detached Breakwaters with Various Gap Spacings

Detached breakwaters are widely used for shore protection. The planforms of tombolos or salients behind structures have also been used to provide a recreational and sustainable coastal environment. In this study, the comprehensive XBeach model was used to numerically simulate the evolution of wave transformation, nearshore current, and morphological changes in tombolo planforms behind detached breakwaters. Given various gap spacings between consecutive breakwaters, the numerical results indicated that both equilibrium bay-shaped shorelines and bottom profiles form in the lee of detached breakwaters after long-term persistent wave action. These equilibrium shorelines and bottom profiles were verified using well-known empirical formulas. Post-wave-action retreat displacement to the initial shoreline was analyzed, and an empirical relationship was proposed for predicting the equilibrium bay-shaped shoreline. By associating the empirical formula with a parabolic bay-shape equation, some actual beaches were evaluated to validate the predictions of equilibrium shorelines behind detached breakwaters. In conclusion, to appropriately plan the layouts of breakwaters, bay-shaped shorelines of tombolo planforms in the lee of detached breakwaters can be predicted at the design stage by using the proposed relationship.

Botulinum Neurotoxin Injections in Children with Self-Injurious Behaviors

Self-injurious behaviors are repetitive, persistent actions directed toward one's body that threaten or cause physical harm. These behaviors are seen within a broad spectrum of neurodevelopmental and neuropsychiatric conditions, often associated with intellectual disability. Injuries can be severe and distressing to patients and caregivers. Furthermore, injuries can be life-threatening. Often, these behaviors are challenging to treat and require a tiered, multimodal approach which may include mechanical/physical restraints, behavioral therapy, pharmacotherapy, or in some cases, surgical management, such as tooth extraction or deep brain stimulation. Here, we describe a series of 17 children who presented to our institution with self-injurious behaviors in whom botulinum neurotoxin injections were found helpful in preventing or lessening self-injury.

Graphene quantum dots/NiTi layered double hydroxide heterojunction as a highly efficient De-NOx photocatalyst with long persistent post-illumination action

Persistent photocatalysis is an attractive process to broaden the spectrum of environmental applications. Herein, blue luminescent graphene quantum dots (GQD) are incorporated into NiTi-based layered double hydroxide nanosheets (NiTi-LDH) by a facile impregnation method. The enhanced performance of GQD/NiTi-LDH leads to excellent NO photo-removal activity (61 %) and insignificant NO2 release (< 0.6 %), beating the standard TiO2 P25 (48 % and 14.2 %, respectively). Interestingly, after the end of light irradiation period, GQD/NiTi-LDH maintained a NO removal efficiency higher than 20 % for up to 75 min regardless of the previous irradiation time. This De-NOx post-photocatalytic process is the most effective reported at present. The dark/light mechanism is explained by the electron storage capacity of NiTi-LDH under light excitation, which is assisted by the electron migration from GQD to NiTi-LDH. Once the light is shut off, electrons are released and take part in the superoxide radical generation.

Efficacy Evaluation of Oregano Essential Oil Mixed with Bacillus thuringiensis israelensis and Diflubenzuron against Culex pipiens and Aedes albopictus in Road Drains of Italy.

Mosquito management programs in the urban environment of Italian cities mainly rely on larval control with conventional insecticides, primarily targeting the road drains that constitute the principal mosquito breeding sites encountered in public. The repeated utilization of synthetic insecticides may have adverse effects on non-targets and lead to resistance development issues, while the performance of biopesticides encounters limitations in field use. Botanical insecticides as single larval control agents or in binary mixtures with conventional insecticides have been extensively studied in the laboratory as an effective and eco-friendly alternative mosquito control method with promising results. The study herein concerns the investigation, for the first time under realistic conditions in the field, of the joint action of a carvacrol-rich oregano Essential Oil (EO) with two conventional insecticides, namely, the insect growth regulator diflubenzuron and the bio-insecticide Bacillus thuringiensis israelensis (B.t.i.), in road drains in Crevalcore city, Italy, against Culex pipiens and Aedes albopictus. According to the obtained results, the application of both plain EO and its mixtures with diflubenzuron and B.t.i. exerted very high efficacy in terms of immature mosquito population reduction over a two-week period. Three weeks after treatment, the performance of the oil and its mixtures diminished but remained high, while the addition of diflubenzuron potentiated the persistent action of the oil against Cx. pipiens. These findings are indicative of the potential of mixing carvacrol-rich EO with diflubenzuron and B.t.i. as an efficient eco-friendly alternative to mono-insecticide applications in road drains against Cx. pipiens and Ae. albopictus larvae.

Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians

Success stories are rare in conservation science, hindered also by the research-implementation gap, where scientific insights rarely inform practice and practical implementation is rarely evaluated scientifically. Amphibian population declines, driven by multiple stressors, are emblematic of the freshwater biodiversity crisis. Habitat creation is a straightforward conservation action that has been shown to locally benefit amphibians, as well as other taxa, but does it benefit entire amphibian communities at large spatial scales? Here, we evaluate a landscape-scale pond-construction program by fitting dynamic occupancy models to 20 y of monitoring data for 12 pond-breeding amphibian species in the Swiss state Aargau, a densely populated area of the Swiss lowlands with intensive land use. After decades of population declines, the number of occupied ponds increased statewide for 10 out of 12 species, while one species remained stable and one species further declined between 1999 and 2019. Despite regional differences, in 77% of all 43 regional metapopulations, the colonization and subsequent occupation of new ponds stabilized (14%) or increased (63%) metapopulation size. Likely mechanisms include increased habitat availability, restoration of habitat dynamics, and increased connectivity between ponds. Colonization probabilities reflected species-specific preferences for characteristics of ponds and their surroundings, which provides evidence-based information for future pond construction targeting specific species. The relatively simple but landscape-scale and persistent conservation action of constructing hundreds of new ponds halted declines and stabilized or increased the state-wide population size of all but one species, despite ongoing pressures from other stressors in a human-dominated landscape.

A key role of miR-132-5p in the prefrontal cortex for persistent prophylactic actions of (R)-ketamine in mice

(R,S)-ketamine is known to elicit persistent prophylactic effects in rodent models of depression. However, the precise molecular mechanisms underlying its action remain elusive. Using RNA-sequencing analysis, we searched for novel molecular target(s) that contribute to the prophylactic effects of (R)-ketamine, a more potent enantiomer of (R,S)-ketamine in chronic restraint stress (CRS) model. Pretreatment with (R)-ketamine (10 mg/kg, 1 day before CRS) significantly ameliorated body weight loss, increased immobility time of forced swimming test, and decreased sucrose preference of sucrose preference test in CRS-exposed mice. RNA-sequencing analysis of prefrontal cortex (PFC) revealed that several miRNAs such as miR-132-5p might contribute to sustained prophylactic effects of (R)-ketamine. Methyl CpG binding protein 2 (MeCP2) is known to regulate brain-derived neurotrophic factor (BDNF) expression. Quantitative RT-PCR confirmed that (R)-ketamine significantly attenuated altered expression of miR-132-5p and its regulated genes (Bdnf, Mecp2, Tgfb1, Tgfbr2) in the PFC of CRS-exposed mice. Furthermore, (R)-ketamine significantly attenuated altered expression of BDNF, MeCP2, TGF-β1 (transforming growth factor β1), and synaptic proteins (PSD-95, and GluA1) in the PFC of CRS-exposed mice. Administration of agomiR-132-5p decreased the expression of Bdnf and Tgfb1 in the PFC, resulting in depression-like behaviors. In contrast, administration of antagomiR-132-5p blocked the increased expression of miR-132-5p and decreased expression of Bdnf in the PFC of CRS-exposed mice, resulting in antidepressant-like effects. In conclusion, our data show a novel role of miR-132-5p in the PFC underlying depression-like phenotypes in CRS model and the sustained prophylactic effects of (R)-ketamine.

The Africanness of African Literatures and New Patterns in Human Civilization

The explosion of African literatures in 2021 is not a coincidence, but is dictated by the continent’s decolonial, diasporic and hybrid cultural manifestations, its more than a hundred years of struggle for cross-regional integration, its spirit of vigorous and persistent action, and the unique attraction of an Africanness that upholds its selfhood, bridges the gaps, and remembers its history but looks to the future. The diasporic characteristic of attending to, absorbing and squarely facing the tension of heterogeneous cultures means that indigenous African literatures contain a distinctive world consciousness and rational philosophy. They have given rise to diverse civilizations marked by dialogue, inclusiveness and the contemporary spirit of African nations, enabling African literatures to participate effectively in the dialogue of world literature and in new patterns of civilization, displaying as they do a strong vitality, creativity and influence in the positive-sum game with Western culture. This will provide positive encouragement to the mutual learning, integration, harmony, symbiosis and coexistence of civilizations.

“Light Cavalry” of Komsomol in Mid-1930s: a Change of Priorities

The activities of the youth movement of young controllers “light cavalry” in the mid-1930s are analyzed. On the basis of archival documents and publications of the 1930s, the features of the solution of new tasks in production by the “light cavalry”, the participation of detachments in the organization of the Stakhanov movement were revealed. The specificity of the work of special youth associations in railway transport, in rural areas is shown. It is revealed that thanks to the efforts of the “light cavalry” to organize the Stakhanov movement, persistent actions aimed at increasing the efficiency of industrial and transport enterprises, protecting collective farm crops and property, its solid creative potential is demonstrated. Particular attention is paid to the attempts of the “light cavalry” since 1934 to restructure the work, strengthening the implementation of educational functions and the exchange of experience. It is noted that by the end of the period under study, the activity of the “light cavalry” was more understood as a school for educating a new person. It is concluded that the widespread opposition to many undertakings of the members of the organization, coupled with a lack of material interest and a workload of other assignments, leveled the decisive attitude not only of many activists, but also of those who were called upon to follow their example.

Свобода вибору країни проживання: рееміґрація з Канади в Українську РСР (1955–1960-ті роки)

The article examines the peculiarities of the Soviet policy of return-to-the-homeland campaign from Canada to the Ukrainian SSR, which since 1955 was conducted by the Committee for Repatriation to the Motherland. The Ukrainian Diaspora in Canada occupied a special place in the committee’s efforts. The propaganda campaign for re-emigration was aimed at forming a positive images of the Soviet Union / Ukrainian SSR, in particular their economic achievements. The emotional component that was used to stir up nostalgia among the Diaspora was also fully used. The Ukrainian pro-communist press published numerous letters by Ukrainians who had lived in Canada but returned to their native land as evidence of the wonderful life in Ukraine. The return-to-the-homeland campaign was helped by leftist Canadian organizations (such as Association of United Ukrainian Canadians) through their own newspapers. It regularly published letters to friends in Canada from recent returnees. The return-to-the-homeland campaign was conducted in the context of the Cold War and the difficult relationship between Canada and the Soviet Union. However, re-emigration from Canada did not become so massive, as hoped for by its organizers, and by its scale was inferior to reminiscences from other countries (for example, from Argentina). The hundreds of Canadians who resettled in the Soviet Union in the second half of the 1950s represented only a small part of the Ukrainian origin community in Canada. But even in this situation, the Canadian government’s position on the return-to-the-homeland campaign was clearly considered too passive by members of the Ukrainian Canadian Committee. Canadians who returned to the U.S.S.R. felt duped and were not easily integrated into Soviet life. Those who succumbed to the manipulation of Soviet propaganda were quickly disappointed with the realities of life in the Ukrainian SSR and began to appeal for a return. Such persons immediately fell within the sight of the Committee of State Security, whose staff conducted “preventive conversations” with them. From the Canadian government’s perspective, there were no problems for people who had been born in Canada and they were eligible for Canadian citizenship. From the Soviet point of view, such steps were equivalent to political betrayals and were completely prevented. Separate cases of successful returns to the ocean were fixed at the beginning of the 1970s, which became possible due to the detente of international tensions during the Cold War and more persistent actions by Canadian authorities. A small number of repatriates managed with considerable difficulty to return to Canada. Some of them (N. Demydenko, E. Lenko) have been seeking permission to go to Canada for several years.

Modeling of bottom currents for estimating their erosional-depositional potential in the Southwest Atlantic

Contourites are sediments deposited or substantially reworked by the persistent action of bottom currents which are capable of forming a wide range of erosional and depositional features on the seafloor. The study of contourites is a multidisciplinary topic linking physical oceanography and marine geology. While near-bottom circulation is an important subject itself due to different dynamic aspects and climatic estimates of abyssal water transports, it becomes especially important for studies of lateral sedimentation. The precise direct data on bottom currents on the South American continental rise and adjacent abyssal plains remain extremely rare. Numerical modeling can appear helpful for filling the gaps in our knowledge on bottom circulation in the region. This work describes an approach for mapping erosion- and deposition-dominated areas based on the modeled circulation in the bottom layers. The model domain covers the regions with different seabed topography and velocities of bottom currents: the Vema Channel, the Santa Catarina Plateau, the Rio Grande Rise, and parts of the Argentine and Brazil basins. The high vertical resolution used in the model allowed us to study the near-bottom circulation in the deep ocean, while high horizontal resolution enabled modeling currents in narrow underwater passages such as the Vema Channel. The equations that encompass the bottom current velocities and data on surface sediment grain-size are well-known; in this study, we estimate the erosional-depositional potential of bottom currents using these equations. This approach allowed identification of the regions of dominant erosion (to the northeast of the northern exit from the Vema Channel), deposition (northern part of the Santa Catarina Plateau), and non-deposition under the influence of bottom currents. The results were validated by the analysis of echo-facies distribution in the study area and variations in the surface sediment grain-size. This study embraces the transition zone between the Argentine and Brazil basins, which is crucial for understanding the deep and bottom circulation in the western South Atlantic under modern conditions and in the geological past. The presented technique can improve our knowledge on how bottom currents shape the seafloor and control sediment distribution in the Southwest Atlantic.