We spend one third of our life in sleep. The interesting point about the sleep is that the neurons are not quiescent during sleeping and they show synchronous oscillations at different regions. Especially Sharp wave ripples are observed in the hippocampus. Here, we propose a simple phenomenological neural mass model for the CA1-CA3 network of the hippocampus considering the spike frequency adaptation for excitatory neurons. The model consists of one group of identical CA1 excitatory neurons, one group of identical CA1 inhibitory neurons, one group of identical CA3 excitatory neurons, and one group of identical CA3 inhibitory neurons. All the recurrent connections between the neurons of CA3 network are considered. For CA1 neurons the excitatory to inhibitory, inhibitory to excitatory and inhibitory to inhibitory connections are considered. CA1 and CA3 neurons are connected by long-range connections from CA3 excitatory neurons to both CA1 excitatory and inhibitory neurons. We show that this simple model can spontaneously generate the oscillations similar to the Sharp waves in the CA3 network. The duration of the Sharp waves is determined by the slow dynamic of the adaptation process. The excitatory inputs from CA3 network to the CA1 network during these Sharp waves induce ripples in the CA1 network due to the interaction of excitatory and inhibitory neurons. We next show that contrary to intuition and in a very good agreement with the recent experimental findings, reduction of the excitation increases the amplitude of the ripples while decreases the frequency of them. This model can also spontaneously generate ripple doublets. The decrease in the excitation is associated with the increase in the probability of observing ripple doublets. Our results shed light on our understanding of the mechanism underlying the generation of Sharp wave ripples.

Background and Aim: The acquisition and consolidation of new tasks into long-term memory involve the appearance of Sharp-wave ripples in the temporal lobe during resting or sleep, which play a crucial role in memory consolidation. Additionally, Sharp-wave ripples, high-frequency waves in the molecular layer of the hippocampus, are associated with synaptic plasticity and memory consolidation. This study aims to investigate the impact of high-frequency electrical stimulation of the hippocampal Schaffer collateral (SC) pathway on memory consolidation in behaving rats. Methods: Stereotaxic surgery was conducted to implant stimulating electrodes in the SC pathway and recording electrodes in the CA1 region of male Wistar rats. After confirming electrophysiological recording, electrodes were secured to the skull using dental cement. Two hours following each acquisition session rats underwent stimulation of the SC pathway with a frequency of 200 Hz to assess its effect on spatial memory formation. Spatial learning was then conducted using the Morris water maze over three consecutive days. Electrical stimulation occurred two hours post-learning on each day, and spatial memory was evaluated on the fourth day. Results: Stimulation of the SC pathway with high frequency resulted in long-term synaptic strengthening in CA1. However, behavioral testing revealed no significant difference in learning and spatial memory between the group receiving electrical stimulation and the control group. Conclusion: These findings suggest that high-frequency stimulation of the SC pathway does not enhance memory, indicating that synaptic strengthening in the CA1 region does not necessarily translate into memory improvement.

A problem of Raman backscattering of laser beam propagating in a transversely wiggler magnetized plasma is considered in the presence of density ripples. Required dispersion relation of excited upper hybrid wave is derived by using the fluid model and taking into account the coupling between primary upper hybrid wave and density ripples. Using wave equation and nonlinear ponderomotive force and considering the coupling between the sideband wave and the upper hybrid wave, an expression of growth rate of this instability is obtained. The calculations demonstrate that the growth rate decreases by increasing the external magnetic field since the coupling between the scattered wave and upper-hybrid wave is weak and phase matching condition is not well-satisfied for higher external magnetic field. We have observed that instability is suppressed due to the presence of density ripples. Also, the suppression is significant for the case of small wave number density ripples as large faction of energy of upper hybrid electron wave transfers to the secondary hybrid electron wave.

In this study, we have evaluated generation and development of sandy bed ripples under controlled wave conditions using physical modeling.Experiments of this study have been done in experimental flume of Soil Conservation and Watershed Management Research Institute (SCWMRI). wave flume has 20m length, 5.5m width and 2m height that have been separated to three sections by two walls. Our model has been setup in 3 parts with different slopes of 0.01, 0.02 and 0.03.Physical simulation tests were carried out in two different series to investigate the bed changes during the time(in 4 runs) as well as the effects of different heights and periods of waves on ripples (in 8 runs). Results showed that increasing in wave height and period will caused increase of ripples height and wave length. Also increase of wave heights, will caused more amounts of transported sediments. As well as, bed ripples will be become more asymmetrical with increasing in wave period.we suggested relations for predicting ripple's dimension less height and wavelength by using physical model data together with a large existent set of experimental and field data. Calculating statistical indexes shows these relations have more precious in predicting ripples geometry towards existed relations.

The flow field around a Sharp cone model configuration has been investigated by means of Schlieren facility in hypersonic shock tunnel. The time dependent evolution of flow around a cone of angle 11. 38° with base radius of 150mm has been visualized for a flow Mach number M = 6. 5. Experiments have been carried out with Helium as driver gas and air as test gas to visualize the hypersonic flow field. The flow establishment, steady state, and termination process of the hypersonic flow have been visualized for two different angles of attack, namely 0° &5° . Experimentally measured shock angle compares well with the theoretical and the computational study. The measured shock layer thickness compares well with the numerical simulation for both angles of attack.