366 research outputs found
Neural Signals Related to Outcome Evaluation Are Stronger in CA1 than CA3
No full textWe have shown previously that CA1 conveys significant neural signals necessary to update value of the chosen target, namely chosen value and reward signals. To better understand hippocampal neural processes related to valuation, we compared chosen value- and reward-related neural activity between the CA3 and CA1 regions. Single units were recorded with tetrodes from the dorsal CA3 and CA1 regions of rats performing a dynamic foraging task, and chosen value- and reward-related neural activity was estimated using a reinforcement learning model and multiple regression analyses. Neural signals for chosen value and reward converged in both CA3 and CA1 when a trial outcome was revealed. However, these neural signals were stronger in CA1 than CA3. Consequently, neural signals for reward prediction error and updated chosen value were stronger in CA1 than CA3. Together with our previous finding that CA1 conveys stronger value signals than the subiculum, our results raise the possibility that CA1 might play a particularly important role among hippocampal subregions in evaluating experienced events. © 2017 Lee, Huh, Lee, Ghim, Lee and Jung. © 2017 Lee, Huh, Lee, Ghim, Lee and Jung. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Copyright © 2017 Lee, Huh, Lee, Ghim, Lee and Jung. This is an open-access article
distributed under the terms of the Creative Commons Attribution License (CC BY).
The use, distribution or reproduction in other forums is permitted, provided the
original author(s) or licensor are credited and that the original publication in this
journal is cited, in accordance with accepted academic practice. No use, distribution
or reproduction is permitted which does not comply with these terms.1221Nsciescopu
Estimation of atmospheric CO <sub>2</sub> uptake by silicate weathering in the Himalayas and the Tibetan Plateau: a review of existing fluvial geochemical data
No full textThe fluvial geochemical data of major rivers draining the Himalayas and the Tibetan Plateau (HTP) are compiled from literature and supplemented with data from the author's group to explore the spatial variability in the major element and strontium isotopic compositions and in rates of silicate weathering and concomitant drawdown of atmospheric CO2. The results indicate that carbonate weathering dominates the major element composition of these rivers, and when the silicate contributions are carefully separated, there is spatial variability within the HTP system. Silicate contributions are highest in the rivers of the Himalayan syntaxes and in the Yamuna, Alaknanda-Bhaghirathi and Kosi tributaries of the Ganges. The 87Sr/86Sr ratios are especially radiogenic in the Ganges tributaries but the values do not necessarily correlate with the relative input from silicate weathering. Even in the Yamuna tributary of the Ganges where rates of CO2 consumption by silicate weathering are several times those of the rivers of the eastern Tibetan Plateau, the rates are comparable to the rivers draining the Andes. Thus, the Ganges tributaries supply uniquely radiogenic 87Sr to the ocean but cannot be considered anomalous in terms of silicate weathering rates in comparison to other major rivers draining orogenic zones. © The Geological Society of London 2010.N
Learning how to learn
No full textThis lightning talk presents some learning concepts that could be useful for researchers
wanting to learn a new skill or a new tool, and trainers who wants to create effective
training programmes.Jun will explain some learning related concepts including but not limited to: • The mastery curve • Chunking • Categorising what to understand vs memorise vs practiceABOUT THE AUTHOR(S) Jun Huh comes from a start-up background with focus around providing genuine value to
the users and steering organisations to be more user driven.</div
Corrigendum to “LightSOD : Towards lightweight and efficient network for salient object detection” [J. Comput. Vis. Imag. Underst. 249 (2024) 104148] (Computer Vision and Image Understanding (2024) 249, (S1077314224002297), (10.1016/j.cviu.2024.104148))
No full textThe authors regret that the corresponding author for this article was incorrectly listed as Ngo Thien Thu ([email protected]). The correct corresponding author is Eui-nam Huh. Professor Eui-Nam Huh's contact details are as follows: [email protected] Department Computer Science and Engineering, KyungHee University Global Campus, Deogyeong-daero, Yongin-si, 17104, Gyeonggi-do, Republic of Korea The authors would like to apologise for any inconvenience caused. © 2024 The Author(s)</p
Human coronavirus 229E uses clathrin-mediated endocytosis as a route of entry in huh-7 cells
No full textHuman coronavirus 229E (HCoV-229E) is an endemic coronavirus responsible for approximately one-third of “common cold” cases. To infect target cells, HCoV-229E first binds to its receptor on the cell surface and then can follow different pathways, entering by direct fusion or by taking advantage of host cell mechanisms such as endocytosis. Based on the role of clathrin, the process can be classified into clathrin-dependent or -independent endocytosis. This study characterizes the role of clathrin-mediated endocytosis (CME) in HCoV-229E infection of the human hepatoma cell line Huh-7. Using specific CME inhibitory drugs, we demonstrated that blocking CME significantly reduces HCoV-229E infection. Additionally, CRISPR/Cas9-mediated knockout of the µ subunit of adaptor protein complex 2 (AP-2) further corroborated the role of CME, as KOs showed over a 50% reduction in viral infection. AP-2 plays an important role in clathrin recruitment and the maturation of clathrin-coated vesicles. Our study also confirmed that in Huh-7 cells, HCoV-229E requires endosomal acidification for successful entry, as viral entry decreased when treated with lysomotropic agents. Furthermore, the colocalization of HCoV-229E with early endosome antigen 1 (EEA-1), only present in early endosomes, suggested that the virus uses an endosomal route for entry. These findings highlight, for the first time, the role of CME in HCoV-229E infection and confirm previous data of the use of the endosomal route at a low pH in the experimental cell model Huh-7. Our results provide new insights into the mechanisms of entry of HCoV-229E and provide a new basis for the development of targeted antiviral therapiesThe author(s) declare that financial support was received for the publication of this article. This research was funded by Ministerio de Ciencia e Innovación, Spain (grant number PID2019-110570GB-I00
User journey-driven product management
No full textNeSI was facing challenges around user onboarding. We built a journey map for NeSI
researchers to gain better understanding of the extent of the problem, and focus on where
the biggest issue was. As an organisation, we are striving to be more metric driven, and
using this user journey as a reference for the team members to see things from researchers’
perspective.Jun will share the process NeSI went through, along with the user journey and service
blueprint that maps the journey to internal processes, how looking at the numbers in the
context of the user journey helped us identify problem areas. The process led us to achieve improvements in the account setup process, and have given
us a useful reference point to understand what to focus on next.ABOUT THE AUTHOR(S)Jun Huh, Innovation and Growth at NeSI. Jun comes from a start-up background with focus around providing genuine value to
the users and steering organisations to be more user driven. </div
Interest rate spreads as indicators for monetary policy
No full textMonetary policy - United States ; Interest rates
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PH sensitive polymers for novel conformance control and polymer flooding applications
No full texttextPolymer flooding is a commercially proven technology to enhance oil recovery from mature reservoirs. The main mechanism for improving oil recovery is to increase the viscosity of injection water by adding polymer, thereby creating a favorable mobility ratio for improved volumetric sweep efficiency. However, polymer injection brings on several potential problems: a) a high injection pressure with associated pumping cost; b) creation of unwanted injection well fractures; and c) mechanical degradation of polymers due to high shear near wellbore. The high viscosity of polymer solutions and permeability reduction by polymer retention reduce mobility, and simultaneously increase the pressure drop required for the propagation of the polymer bank. The objective of this dissertation is to develop an improved polymer injection process that can minimize the impact of those potential problems in the polymer flooding process, and to extend this application to conformance control. This objective is accomplished by utilizing the pH sensitivity of partially hydrolyzed polyacrylamide (HPAM), which is the most commonly used EOR polymer. The idea of the “low-pH polymer process” is to inject HPAM solution at low-pH conditions into the reservoir. The polymer viscosity is low in that condition, which enables the polymer solution to pass through the near wellbore region with a relatively low pressure drop. This process can save a considerable amount of pump horse power required during injection, and also enables the use of large-molecular-weight polymers without danger of mechanical degradation while injecting below the fracture gradient. Away from the near wellbore region, the polymer solution becomes thickened with an increase in pH, which occurs naturally by a spontaneous reaction between the acid solution and rock minerals. The viscosity increase lowers the brine mobility and increases oil displacement efficiency, as intended. Another potential application of the low-pH polymer injection process is conformance control in a highly heterogeneous reservoir. As a secondary recovery method, water flooding can sweep most oil from the high-permeability zones, but not from the low-permeability zones. The polymer solution under low-pH conditions can be placed deep into such high-permeability sands preferentially, because of its low viscosity. It is then viscosified by a pH increase, caused by geochemical reactions with the rock minerals in the reservoir. With the thickened polymer solution in the high permeability sands, the subsequently injected water is diverted to the low permeability zone, so that the bypassed oil trapped in that zone can be efficiently recovered. To evaluate the low-pH polymer process, extensive laboratory experiments were systematically conducted. As the first step, the rheological properties of HPAM solutions, such as steady-shear viscosity and viscoelastic behavior, were measured as functions of pH. The effects of various process variables, such as polymer concentrations, salinity, polymer molecular weight, and degree of hydrolysis on rheological properties, were investigated for a wide range of pH. A comprehensive rheological model for HPAM solutions was also developed in order to provide polymer viscosity in terms of the above process variables. As the second step, weak acid (citric acid) and strong acid (hydrochloric acid) were evaluated as pH control agents. Citric acid was shown to clearly perform better than hydrochloric acid. A series of acid coreflood experiments for different process variables (injection pH, core length, flow rate, and the presence of shut-ins) were carried out. The effluent pH and five cations (total Ca, Mg, Fe, Al, and K) were measured for qualitative evaluation of the geochemical reactions between the injected acid and the rock minerals; these measurements also provide data for future history matching simulations to accurately characterize these geochemical reactions. Finally, polymer coreflood experiments were carried out with different process variables: injection pH, polymer concentration, polymer molecular weight, salinity, degree of hydrolysis, and flow rate. The transport characteristics of HPAM solutions in Berea sandstone cores were evaluated in terms of permeability reduction and mobility reduction. Adsorption and inaccessible/excluded pore volume were also measured in order to accurately characterize the transport of HPAM solutions under low-pH conditions. The results show that the proposed “low-pH polymer process” can substantially increase injectivity (lower injection pressures) and allow deeper transport of polymer solutions in the reservoir due to the low solution viscosity. The peak pH’s observed in several shut-ins guarantee that spontaneous geochemical reactions can return the polymer solution to its original high viscosity. However, low-pH conditions increase adsorption (polymer-loss) and require additional chemical cost (for citric acid). The optimum injection formulation (polymer concentration, injection pH) will depend on the specific reservoir mineralogy, permeability, salinity and injection conditions.Petroleum and Geosystems Engineerin
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A Study of a PH-Sensitive Polymer for Novel Conformance Control Applications
No full textUse of pH-sensitive crosslinked poly(acrylic acid) polymer has been proposed as a novel in-depth conformance control system for improved oil recovery. The polymer forms a soft and flexible microgel with a molecular network structure in aqueous solution. When dispersed, it becomes acidic and exists in an unswelled and coiled state. High swelling occurs at neutral pH, accompanied by an increase in viscosity of several orders of magnitude. The objective for developing this system is to propagate microgels under acidic condition deep into the high permeability zone which has been swept by the injected fluid. Once placed, microgels swell as pH-buffering reactions with mineral components occur. The swelled microgels provide resistance to subsequent fluid flow, leading to an improved waterflood profile. New laboratory studies were conducted to develop this novel polymer-gel system, and to investigate its technical feasibility. The development in this thesis is divided into three broad tasks, which include: 1) viscosity measurements of pH-triggered polymer-gel systems at different pH, shear rate, polymer concentration, and ionic strength; 2) geochemical characterization in terms of spatial and temporal change in pH when a dilute hydrochloric acid preflush is injected into a sandstone core; and 3) characterization of polymer microgel transport in porous media in terms of its molecular interaction parameters. Laboratory viscosity measurements indicated that the apparent viscosity of a crosslinked poly(acrylic acid) is strongly dependent on pH, justifying its use as a conformance control agent. The ionic strength, one of the reservoir variables, was found to be inversely proportional to swelling ratio, i.e, the apparent viscosity. Since high ionic strength interrupts the swelling of microgels, it should be kept as low as the salinity of reservoir brine. Apparent viscosity was also observed to be proportional to crosslink density. Therefore, a high crosslink density is preferred over a low crosslink density, because a lower concentration is required to achieve a given viscosity. As a preflush, a 0.1M hydrochloric acid is inefficient because of its weak reactivity with silicate minerals. Core flood experiments showed that the alumino-silicate minerals in Berea sandstone core must be completely dissolved before a low pH environment can be established, which is necessary for good propagation of microgels. Thus, use of more concentrated hydrochloric acid or a highly reactive chemical should be considered for use in a preflush stage. In experiments of microgel transport in pure-silica sandpacks, a poly(acrylic acid) polymer with high crosslink density was found to form more rigid microgel particles than a polymer with low crosslink density. The rigid particles have weaker attractive adsorption characteristics, leading to less retention. Addition of anionic surfactant helps to effectively reduce the inter-particle attraction between microgels by binding hydro-phobically to particles. Retention decreased by approximately 40% over a surfactant free flooding case, but, could not be completely eliminated. It is concluded in this study that an aqueous solution of Carbopol® 934 which has the highest crosslink density available, with the addition of an anionic surfactant, can propagate deep into a porous medium with one order of magnitude permeability reduction. Such a polymer-surfactant combination can be applied in a relatively high permeability zone for improved conformance control.Petroleum and Geosystems Engineerin
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