scholarly journals Variance and invariance of neuronal long-term representations

2017 ◽  
Vol 372 (1715) ◽  
pp. 20160161 ◽  
Author(s):  
Claudia Clopath ◽  
Tobias Bonhoeffer ◽  
Mark Hübener ◽  
Tobias Rose
Keyword(s):  
Sensory Input ◽  
Cell Activity ◽  
Population Level ◽  
Cell Types ◽  
Sensory Experience ◽  
Homeostatic Plasticity ◽  
Long Term Stability ◽  
Brain Extracts ◽  
The One

The brain extracts behaviourally relevant sensory input to produce appropriate motor output. On the one hand, our constantly changing environment requires this transformation to be plastic. On the other hand, plasticity is thought to be balanced by mechanisms ensuring constancy of neuronal representations in order to achieve stable behavioural performance. Yet, prominent changes in synaptic strength and connectivity also occur during normal sensory experience, indicating a certain degree of constitutive plasticity. This raises the question of how stable neuronal representations are on the population level and also on the single neuron level. Here, we review recent data from longitudinal electrophysiological and optical recordings of single-cell activity that assess the long-term stability of neuronal stimulus selectivities under conditions of constant sensory experience, during learning, and after reversible modification of sensory input. The emerging picture is that neuronal representations are stabilized by behavioural relevance and that the degree of long-term tuning stability and perturbation resistance directly relates to the functional role of the respective neurons, cell types and circuits. Using a ‘toy’ model, we show that stable baseline representations and precise recovery from perturbations in visual cortex could arise from a ‘backbone’ of strong recurrent connectivity between similarly tuned cells together with a small number of ‘anchor’ neurons exempt from plastic changes. This article is part of the themed issue ‘Integrating Hebbian and homeostatic plasticity’.

scholarly journals Electret Filters—From the Influence of Discharging Methods to Optimization Potential

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 65
Author(s):  
Maximilian Kerner ◽  
Kilian Schmidt ◽  
Stefan Schumacher ◽  
Christof Asbach ◽  
Sergiy Antonyuk
Keyword(s):  
Fine Particles ◽  
Operating Time ◽  
Filtration Efficiency ◽  
Long Term Stability ◽  
Aerosol Filtration ◽  
Charge Decay ◽  
The One ◽  
Testing Standards ◽  
Discharge Efficiency

Electret filters are electrostatically charged nonwovens which are commonly used in aerosol filtration to remove fine particles from gases. It is known that the charge and thus also the filtration efficiency can degrade over time. Thus, many testing standards require to remove the charge by treatment with liquid isopropanol (IPA) or IPA-saturated air. However, the parameters influencing this discharge have not been completely clarified yet. The aim of this work was, on the one hand, to experimentally investigate the influence of the IPA treatment on different electret filters and, on the other hand, to show the optimization potential of electret filters with respect to efficiency and long-term stability by numerical simulations. The experiments revealed that the air permeability is a central influencing parameter. Small pores lead to a reduced discharge efficiency using liquid IPA, while both treatment methods are suitable for larger pores. The simulations showed that a homogeneous charge distribution within the filter depth is advantageous for the initial performance. In contrast, charge penetrating deeper in the filter medium delays the charge decay and thus increases the operating time, with the trade-off of a lower initial performance.

Synthesis of Nanosized Polymer Particles in Nonaqueous Emulsion

2013 ◽  
Vol 1546 ◽  
Author(s):  
Robert Dorresteijn ◽  
Robert Haschick ◽  
Kevin Müller ◽  
Markus Klapper ◽  
Klaus Müllen
Keyword(s):  
Ring Opening ◽  
Continuous Phase ◽  
Size Distributions ◽  
Aqueous Emulsion ◽  
Long Term Stability ◽  
Dispersed Particles ◽  
One Step ◽  
Moisture Sensitive ◽  
The One

ABSTRACTIn nonaqueous emulsion, moisture-sensitive polymerizations are performed in order to generate nanoparticles, which are not accessible by common aqueous emulsion polymerization. A nonaqueous emulsion, consisting of two immiscible aprotic organic solvents, is stabilized by amphiphilic block copolymers, such as PIb-PEO or PIb-PMMA copolymer, and lead to formation of nanosized dispersed droplets. They act as dispersed “nanoreactors” for the one-step synthesis of poly(urethane) nanoparticles in a polyadditon reaction as well as poly(L-lactide) nanoparticles through ring-opening polymerization, catalyzed by a moisture-sensitive catalyst. The well-dispersed particles possess average diameters below 100 nm and have narrow size distributions owing to the long-term stability of the dispersed droplets in the continuous phase.

scholarly journals Co-circulation of SARS-CoV-2 and Influenza under vaccination scenarios

2021 ◽  
Author(s):  
Manuel A. Acuña-Zegarra ◽  
Mayra Núñez-López ◽  
Andreu Comas-García ◽  
Mario Santana-Cibrian ◽  
Jorge X. Velasco-Hernández
Keyword(s):  
Reproduction Number ◽  
Population Level ◽  
Host Population ◽  
Effective Coverage ◽  
Factors Affecting ◽  
Contact Rates ◽  
Effective Contact ◽  
The One ◽  
Transmission Factors

AbstractThe interaction and possibly interference between viruses infecting a common host population is the problem addressed in this work. We model two viral diseases both of the SIRS type that have similar mechanism of transmission and for which a vaccine exists. The vaccine is characterized by its coverage, induced temporal immunity and efficacy. The population dynamics of both diseases considers infected individuals of each disease and hosts that are susceptible to one but have recovered from the other. We do not incorporate coinfection. We postulate two main transmission factors affecting the effective contact rates: i) that the virus with higher reproduction number can superinfect the one with lower reproduction number and ii) that there is some protection induced by vaccination against the weaker virus that reduces the probability of infection by the stronger virus. Our results indicate that coexistence of the viruses is possible in the long term. The time-dependent effective contact rate may induce either alternating outbreaks of each disease or synchronous outbreaks. We also found the existence of bi-stability triggered by a backward bifurcation, conducive to scenarios where, at the population level, vaccine application may promote persistence of both diseases provided the effective coverage and vaccine efficacy are low.

Glutamate Neurotransmission in the Cerebellar Interposed Nuclei: Involvement in Classically Conditioned Eyeblinks and Neuronal Activity

2005 ◽  
Vol 93 (1) ◽  
pp. 44-52 ◽  
Author(s):  
D. P. Aksenov ◽  
N. A. Serdyukova ◽  
J. R. Bloedel ◽  
V. Bracha
Keyword(s):  
Neuronal Activity ◽  
Cerebellar Cortex ◽  
Cell Activity ◽  
Population Level ◽  
Cell Types ◽  
Firing Frequency ◽  
Glutamate Neurotransmission ◽  
Critical Components ◽  
Classically Conditioned

The cerebellar interposed nuclei (IN) are critical components of a neural network that controls the expression of classically conditioned eyeblinks. The IN receive 2 major inputs: the massive, γ-aminobutyric acid (GABA)–mediated input from the Purkinje cells of the cerebellar cortex and the relatively weaker, glutamate-mediated input from collaterals of mossy and climbing fiber cerebellar afferent systems. To elucidate the role of IN glutamate neurotransmission in conditioned response (CR) expression, effects of blocking fast glutamatergic neurotransmission in the IN with γ-d-glutamylglycine (DGG) on the expression of conditioned eyeblinks and on cerebellar nuclear neuronal activity were examined. Surprisingly, blocking fast glutamate receptors in the IN did not abolish CRs. DGG decreased CR incidence and slightly increased CR latency. In contrast, identical amounts of DGG applied to the cerebellar cortex abolished CRs. Similar to the behavioral effects, DGG had unexpectedly mild effects on IN neurons. At the population level, the baseline firing frequency of IN cells was not affected. After DGG injections, the incidence of excitatory modulation of cell activity in the interstimulus interval decreased but was not abolished. A combined block of fast glutamate and GABAA neurotransmission using a mixture of DGG and picrotoxin dramatically reduced CR incidence, increased the firing frequency of all cell types, and virtually abolished all modulation of neuronal activity. These results indicate that fast glutamate neurotransmission in the IN plays only an accessory role both in the expression of behavioral CRs and in the generation of associated neuronal activity in the IN.

scholarly journals Long-term monitoring with spring-based gravimeters: tilt-control benefits and application to the Rochefort Cave Laboratory (Belgium)

2020 ◽  
Author(s):  
Benjamin Fores ◽  
Arnaud Watlet ◽  
Michel Van Camp ◽  
Olivier Francis
Keyword(s):  
Linear Drift ◽  
Term Stability ◽  
Long Term Stability ◽  
New Information ◽  
Non Linear ◽  
Long Term Monitoring ◽  
The One ◽  
Term Monitoring ◽  
Local Hydrology

<p>Spring-based gravimeters are light and easy to install, with a precision around 5 μGal/√Hz. However, they are still not used for long-term gravity monitoring. The main reason for that is the non-linear drift of those instruments, which is very difficult to correct without removing geophysical signals. We will show that when the tilt is actively controlled, a gPhone spring-based gravimeter shows a quasi-linear drift and can reach a long-term stability at the µGal level.</p><p>This allows experiments such as the one in the Rochefort Cave Laboratory (Belgium). Thanks to the size of the gPhone and its low facility requirements, a monitoring from inside a cave was possible. Coupled with another gravity monitoring at the surface, it reveals new information on the local hydrology of this karstic site.</p>

scholarly journals The local help network to the homeless: case study of the city of koper, Slovenia

2014 ◽  
Vol 53 (2) ◽  
pp. 199-208
Author(s):  
Blaž Matija Geršak ◽  
Klara Praprotnik ◽  
Milan Krek
Keyword(s):  
Social Acceptance ◽  
The Other ◽  
Red Cross ◽  
Short Term ◽  
Staff Members ◽  
Long Term Stability ◽  
The One ◽  
The City

Abstract Aim: To present the work of professionals and volunteers of the local help network that revolves around trying to help the homeless and to stimulate readers to critically assess the possible methods aimed towards the successful integration of those people into society. Methods: In the city of Koper, we visited five governmental (GOs) and non-governmental organisations (NGOs): Red Cross Koper, Daybreak Association, Center for Social Work Koper, Diocesan Caritas Koper and Koper Prison; and interviewed 3-10 staff members at each organisation. Results: For each organisation, we described its duties and activities, including its interconnection with other organisations, methods of integrating the homeless into the society and the personal thoughts of its staff members. Conclusions: Both GOs and NGOs are necessary for providing effective assistance to people in need. NGOs excel at quickly responding to immediate needs. Their programs are usually implemented only as short-term resolutions. GOs on the other hand require a longer time to implement their concepts. Nonetheless, in contrast to NGO projects, they provide long-term stability. Even though people from remote parts of the society usually cooperate, the efforts of those who work with them are nothing short of exerting. They strive to achieve a general social acceptance of their ward population, which is the one thing those people need the most. Since only the society is truly capable of offering them a firm stepping stone towards escaping from the vicious circle in which they stray.

Middle East Islamist movements fragment under pressure

2015 ◽  
Keyword(s):  
Political Islam ◽  
The Political ◽  
Islamic State ◽  
Content Type ◽  
Long Term Stability ◽  
Sudden Rise ◽  
The One ◽  
State Group ◽  
Islamist Movements

Significance Almost two years on from Morsi's removal from office in 2013 mainstream Islamist movements in the region find themselves caught between an authoritarian crackdown led by Egypt and the Gulf on the one hand, and the sudden rise of Islamic State group (ISG) on the other. With political participation discredited, these two pressures are forcing Muslim Brotherhood-inspired movements to revise ideology and strategy as they compete to maintain and expand their constituencies. Impacts Mainstream Islamists will remain a significant political force in the region, but take years to regroup. Long-term stability will depend on allowing non-violent Islamists access to the political sphere. Younger Islamists will be increasingly attracted to radical ideologies. Egypt's slide into a more oppressive police state will continue. Saudi Arabia has put aside differences with Qatar and Turkey over political Islam for now -- but the dispute could resurface.

scholarly journals Study of lifetime of Platinum Modified Metal Oxides Electrodes

2020 ◽  
Vol 14 (4) ◽  
pp. 1479-1488
Author(s):  
Lemeyonouin Aliou Guillaume Pohan ◽  
Ollo Kambiré ◽  
Mohamed Berté ◽  
Lassiné Ouattara
Keyword(s):  
Metal Oxides ◽  
Platinum Metal ◽  
Porous Structures ◽  
Term Stability ◽  
Long Term Stability ◽  
Physical Measurements ◽  
Platinum Coating ◽  
The One ◽  
A Current

Pt, IrO2, RuO2, Pt-IrO2 and Pt-RuO2 electrodes have been shown to be effective in their application in various fields. However, it is necessary to study their long-term stability. So, our objective is to prepare them and study their lifetime using intensiostatic measurement. Then they were prepared at 400 °C on titanium plates used as a substrate. Physical measurements (scanning electron microscopy) of these anodes revealed that their surface are rough and porous structures. Lifetime study was carried out in H2SO4 9 N and under a current density of 410 mA /cm2. The long-term stability of Pt improved when coupled to IrO2 in contrast to RuO2. From this study, the performance of the electrode was found to increase in the order: RuO2 < Pt-RuO2 < Pt < Pt-IrO2 < IrO2. For RuO2 and IrO2 pure electrodes, the deactivation would be due to the dissolution of precursors deposited on the titanium. For the Pt pure electrode, deactivation would be due to the detachment of platinum coating. The deactivation of the Pt-IrO2 and Pt-RuO2 electrode would be due, on the one hand to the platinum detachment from IrO2 or RuO2 and on the other hand to the metal oxides (IrO2 or RuO2) dissolution.Keywords: Electrodes, platinum, metal oxides, lifetime.

scholarly journals Study of Long-Term Stability of Ni-Zr0.92Y0.08O2-δ|Zr0.92Y0.08O2-δ|Ce0.9Gd0.1O2-δ |Pr0.6Sr0.4CoO3-δ at SOFC and SOEC Mode

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 824
Author(s):  
Freddy Kukk ◽  
Priit Möller ◽  
Rait Kanarbik ◽  
Gunnar Nurk
Keyword(s):  
Cell Activity ◽  
Solid Oxide ◽  
Electrolysis Cell ◽  
Term Stability ◽  
Long Term Stability ◽  
Electrode Activity ◽  
Solid Oxide Electrolysis Cell ◽  
The Stability ◽  
Solid Oxide Cell

Long term stability is one of the decisive properties of solid oxide fuel cell (SOFC) as well as solid oxide electrolysis cell (SOEC) materials from the commercialization perspective. To improve the understanding about degradation mechanisms solid oxide cells with different electrode compositions should be studied. In this work, Ni-Zr0.92Y0.08O2-δ (Ni-YSZ)| Zr0.92Y0.08O2-δ (YSZ)|Ce0.9Gd0.1O2-δ (GDC)|Pr0.6Sr0.4CoO3-δ (PSC) cells are tested in the SOFC regime for 17,820 h at 650 °C, and in the SOEC regime for 860 h at 800 °C. The SOFC experiment showed a degradation speed of 2.4% per 1000 h at first but decreased to 1.1% per 1000 h later. The electrolysis test was performed for 860 h at 800 °C. The degradation speed was 16.3% per 1000 h. In the end of the stability tests, an electrode activity mapping was carried out using a novel 18O tracing approach. Average Ni grain sizes were measured and correlated with the results of the oxygen isotope maps. Results indicate that Ni coarsening is dependent on solid oxide cell activity. Strontium, chromium and silicon concentrations were also analyzed using the ToF-SIMS method and compared to the electrode activity map, but significant correlation was not observed.

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