Spike Timing-Dependent Plasticity in the CA1 Pyramidal Neuron in a Modeled Hippocampal Circuit

Spike timing-dependent plasticity (STDP) plays an important role in sculpting informationstoring circuits in the hippocampus, since motor learning and memory are thought to be closely linked with this classical plasticity. To further understand the information delivery in a hippocampus circuit, we build a computational model to study the potential role of linear changes in the synaptic weight and synaptic number. Several key results have been obtained: (i) Changes in the synaptic weight and numbers lead to different long-term modification; (ii) the first paired spiking from two neurons significantly influences the adjusted subsequent paired spiking; the pre-post spiking pair strengthens the following paired spiking; however, the post-pre spiking pair depresses the subsequent spiking; (iii) when the synaptic weight and synaptic numbers are changed, the interval of the first spiking pair may undergo reduction, and (iv) when we stimulate a stellate neuron weakly or decrease the capacitance of CA1 pyramidal neuron, LTP is more easily produced than LTD; on the contrary, LTD is more easily produced in an opposite situation; increase in the synaptic numbers can promote activation of the CA1 pyramidal neuron.Пластичність, залежна від часу генерування піків (spike timing-dependent plasticity – STDP), відіграє важливу роль у формуванні нейромереж, що накопичують інформацію в гіпокампі; вважається, що моторне навчання та пам’ять тісно пов’язані з пластичністю цього типу. Для глибшого розуміння процесів передачі інформації в гіпокампальній нейромережі ми створили комп’ютерну модель, щоб вивчити потенціальну роль лінійних змін синаптичної ваги та числа синапсів у таких мережах. Було отримано чотири основні результати: 1) зміни ваги та числа синапсів можуть призводити до появи різних феноменів довготривалої модифікації; 2) перша пара потенціалів дії, генерована двома нейронами, істотно впливає на характеристики другої пари піків; генерація пари піків у пре-пост-послідовності полегшує генерацію наступної пари, тоді як пост-прегенерація пари пригнічує генерацію наступної пари; 3) коли вага синапсів та їх кількість змінюються, інтервал у першій парі піків зменшується; 4) коли стимулювати зірчастий нейрон з невеликою інтенсивністю або зменшити ємність пірамідного нейрона CA1, легше індукується довготривала потенціація; у протилежній ситуації легше виникає довготривала депресія; збільшення числа синапсів полегшує активацію пірамідного нейрона CA1

Dimensional Crossover in the Effective Second Harmonic Generation of Films of Random Dielectrics

The effective nonlinear response of films of random composites consisting of a binary composite with nonlinear particles randomly embedded in a linear host is theoretically and numerically studied. A theoretical expression for the effective second harmonic generation susceptibility, incorporating the thickness of the film, is obtained by combining a modified effective-medium approximation with the general expression for the effective second harmonic generation susceptibility in a composite. The validity of the thoretical results is tested against results obtained by numerical simulations on random resistor networks. Numerical results are found to be well described by our theory. The result implies that the effective-medium approximation provides a convenient way for the estimation of the nonlinear response in films of random dielectrics.Comment: 9 pages, 2 figures; accepted for publication in Phys. Rev.

Analysis of long-term depression in the Purkinje cell circuit (a model study)

In the cerebellum, long-term depression (LTD) plays a key function in sculpting neuronal circuits to store information, since motor learning and memory are thought to be associated with such long-term changes in synaptic efficacy. To better understand the principles of transmission of information in the cerebellum, we, in our model, distinguished different types of neurons (type 1- and type 2-like) to examine the neuronal excitability and analyze the interspike interval (ISI) bifurcation phenomenon in these units, and then built a Purkinje cell circuit to study the impact of external stimulation on LTD in this circuit. According to the results of computational analysis, both climbing fiber-Purkinje cell and granule cell-Purkinje cell circuits were found to manifest LTD; the external stimuli would influence LTD by changing both depression time and depression intensity. All of the simulated results showed that LTD is a very significant factor in the Purkinje circuit networks. Finally, to deliver the learning regularities, we simulated spike timing-dependent plasticity (STDP) by increasing the CaP conductance.У мозочку довготривала депресія (ДД) відіграє ключову роль у пристосуванні нейронних мереж до накопичення інформації, оскільки моторне навчання та пам’ять, як вважають, асоційовані з подібними тривалими змінами синаптичної ефективності. Намагаючись краще зрозуміти принципи передачі інформації в мозочку, в перебігу дослідження збудливості нервових клітин та аналізу феномена біфуркації міжімпульсних інтервалів у цих нейронах ми диференціювали в нашій моделі різні види нейронів (першого і другого типів). Потім була сформована модель нервової мережі клітини Пуркін̕ є для дослідження впливів зовнішньої стимуляції на ДД у такій мережі. Відповідно до результатів комп’ютерного аналізу, ДД проявляється і в мережі «ліаноподібне волокно–клітина Пуркін̕ є», і в мережі «гранулярна клітина–клітина Пуркін̕ є». Зовнішня стимуляція може впливати на ДД, змінюючи як час, так і інтенсивність депресії. Згідно з результатами моделювання, ДД є дуже істотним фактором при функціонуванні мереж, котрі містять у собі клітини Пуркін̕ є. Нарешті, ми, щоб виявити закономірності процесу навчання, за допомогою збільшення CaP-провідності моделювали пластичність, залежну від часу генерації піка (STDP)

Self-similarity and novel sample-length-dependence of conductance in quasiperiodic lateral magnetic superlattices

We study the transport of electrons in a Fibonacci magnetic superlattice produced on a two-dimensional electron gas modulated by parallel magnetic field stripes arranged in a Fibonacci sequence. Both the transmission coefficient and conductance exhibit self-similarity and the six-circle property. The presence of extended states yields a finite conductivity at infinite length, that may be detected as an abrupt change in the conductance as the Fermi energy is varied, much as a metal-insulator transition. This is a unique feature of transport in this new kind of structure, arising from its inherent two-dimensional nature.Comment: 9 pages, 5 figures, revtex, important revisions made. to be published in Phys. Rev.

Effective nonlinear optical properties of composite media of graded spherical particles

We have developed a nonlinear differential effective dipole approximation (NDEDA), in an attempt to investigate the effective linear and third-order nonlinear susceptibility of composite media in which graded spherical inclusions with weak nonlinearity are randomly embedded in a linear host medium. Alternatively, based on a first-principles approach, we derived exactly the linear local field inside the graded particles having power-law dielectric gradation profiles. As a result, we obtain also the effective linear dielectric constant and third-order nonlinear susceptibility. Excellent agreement between the two methods is numerically demonstrated. As an application, we apply the NDEDA to investigate the surface plasma resonant effect on the optical absorption, optical nonlinearity enhancement, and figure of merit of metal-dielectric composites. It is found that the presence of gradation in metal particles yields a broad resonant band in the optical region, and further enhances the figure of merit.Comment: 20 pages, 5 figure

Second Harmonic Generation for a Dilute Suspension of Coated Particles

We derive an expression for the effective second-harmonic coefficient of a dilute suspension of coated spherical particles. It is assumed that the coating material, but not the core or the host, has a nonlinear susceptibility for second-harmonic generation (SHG). The resulting compact expression shows the various factors affecting the effective SHG coefficient. The effective SHG per unit volume of nonlinear coating material is found to be greatly enhanced at certain frequencies, corresponding to the surface plasmon resonance of the coated particles. Similar expression is also derived for a dilute suspension of coated discs. For coating materials with third-harmonic (THG) coefficient, results for the effective THG coefficients are given for the cases of coated particles and coated discs.Comment: 11 pages, 3 figures; accepted for publication in Phys. Rev.

Tailoring Passivation Molecular Structures for Extremely Small Open-Circuit Voltage Loss in Perovskite Solar Cells

Passivation of electronic defects at the surface and grain boundaries of perovskite materials has become one of the most important strategies to suppress charge recombination in both polycrystalline and single-crystalline perovskite solar cells. Although many passivation molecules have been reported, it remains very unclear regarding the passivation mechanisms of various functional groups. Here, we systematically engineer the structures of passivation molecular functional groups, including carboxyl, amine, isopropyl, phenethyl, and tert-butylphenethyl groups, and study their passivation capability to perovskites. It reveals the carboxyl and amine groups would heal charged defects via electrostatic interactions, and the neutral iodine related defects can be reduced by the aromatic structures. The judicious control of the interaction between perovskite and molecules can further realize grain boundary passivation, including those that are deep toward substrates. Understanding of the underlining mechanisms allows us to design a new passivation molecule, D-4-tert-butylphenylalanine, yielding high-performance p-i-structure solar cells with a stabilized efficiency of 21.4%. The open-circuit voltage (VOC) of a device with an optical bandgap of 1.57 eV for the perovskite layer reaches 1.23 V, corresponding to a record small VOC deficit of 0.34 V. Our findings provide a guidance for future design of new passivation molecules to realize multiple facets applications in perovskite electronics

Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes

© 2018 The Authors. Published by Elsevier B.V. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.Peer reviewe

Structure of Schlafen13 reveals a new class of tRNA/rRNA- targeting RNase engaged in translational control

Cleavage of transfer (t)RNA and ribosomal (r)RNA are critical and conserved steps of translational control for cells to overcome varied environmental stresses. However, enzymes that are responsible for this event have not been fully identified in high eukaryotes. Here, we report a mammalian tRNA/rRNA-targeting endoribonuclease: SLFN13, a member of the Schlafen family. Structural study reveals a unique pseudo-dimeric U-pillow-shaped architecture of the SLFN13 N'-domain that may clamp base-paired RNAs. SLFN13 is able to digest tRNAs and rRNAs in vitro, and the endonucleolytic cleavage dissevers 11 nucleotides from the 3'-terminus of tRNA at the acceptor stem. The cytoplasmically localised SLFN13 inhibits protein synthesis in 293T cells. Moreover, SLFN13 restricts HIV replication in a nucleolytic activity-dependent manner. According to these observations, we term SLFN13 RNase S13. Our study provides insights into the modulation of translational machinery in high eukaryotes, and sheds light on the functional mechanisms of the Schlafen family

Argon Plasma Treatment to Tune Perovskite Surface Composition for High Efficiency Solar Cells and Fast Photodetectors

The surface composition of perovskite films is very sensitive to film processing and can deviate from the optimal, which generates unfavorable defects and results in efficiency loss in solar cells and slow response speed in photodetectors. An argon plasma treatment is introduced to modify the surface composition by tuning the ratio of organic and inorganic components as well as defect type before deposition of the passivating layer. It can efficiently enhance the charge collection across the perovskite–electrode interface by suppressing charge recombination. Therefore, perovskite solar cells with argon plasma treatment yield enhanced efficiency to 20.4% and perovskite photodetectors can reach their fastest respond speed, which is solely limited by the carrier mobility