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Papers by mojgan kouhnavard

Various types of neurons exhibit subthreshold resonance oscillation (preferred frequency response... more Various types of neurons exhibit subthreshold resonance oscillation (preferred frequency response) to fluctuating sinusoidal input currents. This phenomenon is well known to influence the synaptic plasticity and frequency of neural network oscillation. This study evaluates the resonant properties of pacemaker pyloric dilator (PD) neurons in the central pattern generator network through mathematical modeling. From the pharmacological point of view, calcium currents cannot be blocked in PD neurons without removing the calcium-dependent potassium current. Thus, the effects of calcium (𝐼Ca) and calcium-dependent potassium (𝐼KCa) currents on resonant properties remain unclear. By taking advantage of Hodgkin-Huxley-type model of neuron and its equivalent RLC circuit, we examine the effects of changing resting membrane potential and those ionic currents on the resonance. Results show that changing the resting membrane potential influences the amplitude and frequency of resonance so that the strength of resonance (Q-value) increases by both depolarization and hyperpolarization of the resting membrane potential. Moreover, hyperpolarization- activated inward current (𝐼h) and 𝐼Ca (in association with 𝐼KCa) are dominant factors on resonant properties at hyperpolarized and depolarized potentials, respectively. Through mathematical analysis, results indicate that 𝐼h and 𝐼KCa affect the resonant properties of PD neurons. However, 𝐼Ca only has an amplifying effect on the resonance amplitude of these neurons.

Subthreshold resonance oscillations are observed in many excitatory/inhibitory neurons in our br... more Subthreshold resonance oscillations are observed in many excitatory/inhibitory neurons in our brain. Although they have been thought to play an important role in behavioral or perceptual states in animals, detail properties of these phenomena have not been clarified, yet. It is necessary to understand first these oscillatory features to clarify the contribution of these rhythmic oscillations to higher brain function, such as short-term memory, the working memory, long-term potentiation and long-term depression. Among various voltage-dependent channels thought to be involved in the generation of these oscillations, hyperpolarization-activated potassium channel (h channel) and persistent inactivating sodium channel (NaP) are considered, because these two voltage-dependent channels are closely related to the sustained oscillatory activity observed in Entorhinal cortex and other Neocortex regions. This feature article considers a compartmental neuron model with an h-channel and a NaP-channel. The NaP-channel contribution to the property of subthreshold resonance oscillation is examined by computer simulation of this neuron model.

ABSTRACT Quantum dot-sensitized solar cells (QDSSCs) are renowned energy devices known for their ... more ABSTRACT Quantum dot-sensitized solar cells (QDSSCs) are renowned energy devices known for their distinct qualities, including (i) the ability to harvest sunlight that generates multiple electron–hole pairs, (ii) simplicity in fabrication, and (iii) low cost. The power conversion efficiency (η) rates of many QDSSCs are lower than those of dye-sensitized solar cells, reaching a maximum of 12% as a result of narrow absorption ranges and of the charge recombination occurring at the QD– and TiO2–electrolyte interfaces. New types of sensitizers are necessary to be developed to further increase the η of QDSSCs. Semiconductor QDs are the most applicable material for photosensitization because of their high absorption and the obtained emission spectra that can be manipulated by varying dot sizes.
This paper presents an overview of recent studies on QDSSC photosensitization and provides suggestions to improve QDSSCs by explicitly comparing different sensitizers. Particular focus is directed on the behavior of several important types of semiconductor nanomaterials (sensitizers such as CdS, Ag2S, CdSe, CdTe, CdHgTe, InAs, and PbS) and other nanomaterials that are TiO2, ZnO, and carbon-based species. These materials are developed to enhance the electron transfer efficiency of QDSSCs. Understanding the mechanism of various photosensitization processes can provide design guidelines for future successful applications.

International Conference on experimental Mechanics, ICEM, Dec 2010

International Conference on Enabling Science and Nanotechnology, Dec 2010

ICEM Conference 2010, Nov 2010

ICEM Conference 2010, Oct 2010

Nova Science Publisher, 2011

Applied Mechanics and Material, Jul 2011

MASAUM Journal of Basic and Applied Sciences , Sep 2009

The limitations on carrier (holes and electrons) drift due to high-field streamlining also rand... more The limitations on carrier (holes and electrons)
drift due to high-field streamlining also randomly velocity vector
in equilibrium is reported. Asymmetrical distribution function
that converts randomness in zero-field to streamlined one in a
very high electric field is employed. The ultimate drift velocity is
found to be appropriate thermal velocity for a given
dimensionality for non-degenerately doped nanostructure.
However, the ultimate drift velocity is the Fermi velocity for
degenerately doped nanostructures. Quantum and high-field
effects controlling the transport of carrier in nanostructures are
described. The results obtained are applied to the modeling of a
nanowire transistor.

ACEEE ,International Journal of Recent Trends in Engineering, Nov 2009

The presented model based on the quantum confinement and high electric filed effect illustrates... more The presented model based on the quantum
confinement and high electric filed effect illustrates velocity
approach to the modeling of a P-type silicon nanowire
transistor. It has been clarified that the intrinsic velocity of
nanowire and other hetero-structure field-effect transistors
(FETs) is governed by the transit time of holes (electrons).
The length of the channel for ballistic channel is equal to
mean free path. However, it does not affect the velocity
saturation in high electric field that is always ballistic. In
high electric field, the carriers are in a coordinated relay
race, each carriers passing its velocity to the next at each
virtual probe. The saturation velocity is thus always ballistic
whether or not device length is smaller or larger than the
mean free path. The ballistic saturation velocity is always
independent of scattering-limited low-field mobility that
may be degraded by the gate electric field. After discussing
the quantum nature of carriers, the transport mechanism is
presented and applied to the modeling of p-type silicon
nanowire field effect transistor.

International Conference on Enabling Science and Nanotechnology (ESciNano), , Dec 2010

Two designed systems are proposed consisting of series of micro ring resonator (MRR) and an add/d... more Two designed systems are proposed consisting of series of micro ring resonator (MRR) and an add/drop filter in which the optical dark and bright soliton pulse propagating within the nonlinear waveguides can be amplified which can be used in long communication system. The dark or bright soliton is input into designed systems and travels within the waveguide. A continuous soliton pulse is sliced into smaller pulses by the nonlinear effect which is known as chaos. The power amplification occurs when the soliton propagates along the MRRs or add/drop filter systems

Applied Mechanics and Materials, Jul 2011

We propose a new optical system that can be used to form the multi-soliton pulses within the micr... more We propose a new optical system that can be used to form the multi-soliton pulses within the micro-ring resonators. The system consists of two micro-ring resonators and an add/drop multiplexer that can be integrated into a single system. The large bandwidth signal is generated by using a soliton pulse propagating in a Kerr-type nonlinear medium. The tuned soliton pulses in either spatial or temporal modes are obtained by using the add/drop multiplexer. Results show the generation of multi-soliton pulses within the micro-ring resonator can be achieved for long distance communication. This results in an increase in the number of channels and spaces with a large free spectrum range (FSR) of 650 pm for dense wavelength division multiplexing (DWDM).

nternational Conference on Enabling Science and Nanotechnology (ESciNano), , 2010

A system for continuous variable quantum key distribution via a wavelength router is proposed. Th... more A system for continuous variable quantum key distribution via a wavelength router is proposed. The Kerr type of light in the nonlinear microring resonator (NMRR) induces the chaotic behavior. In this proposed system chaotic signals are generated by an optical soliton or Gaussian pulse within a NMRR system. The parameters, such as input power, MRRs radii and coupling coefficients can change and plays important role in determining the results in which the continuous signals are generated spreading over the spectrum. Large bandwidth signals of optical soliton are generated by the input pulse propagating within the MRRs, which is allowed to form the continuous wavelength or frequency with large tunable channel capacity. The continuous variable QKD is formed by using the localized spatial soliton pulses via a quantum router and networks. The selected optical spatial pulse can be used to perform the secure communication network. Here the entangled photon generated by chaotic signals has been analyzed. The continuous entangled photon is generated by using the polarization control unit incorporating into the MRRs, required to provide the continuous variable QKD. Results obtained have shown that the application of such a system for the simultaneous continuous variable quantum cryptography can be used in the mobile telephone hand set and networks. In this study frequency band of 500 MHz and 2.0 GHz and wavelengths of 775 nm, 2,325 nm and 1.55 μm can be obtained for QKD use with input optical soliton and Gaussian beam respectively.

Conference Presentations by mojgan kouhnavard

Stellate Cells (SCs) of layer II of medial entorhinal cortex show both subthreshold oscillations ... more Stellate Cells (SCs) of layer II of medial entorhinal cortex show both subthreshold oscillations (STOs) and mixed-mode oscillations (MMOs) at theta frequencies (8-12 Hz) under increased injection of depolarizing current. The conductance-based model of fully SCs model consists of seven-dimensional nonlinear equations, which imitate many properties of the oscillatory patterns observed in experimental data. Recently, the reduced model of fully SCs model is introduced, which is three-dimensional system with a threshold and reset value for voltage. In this paper, we examine the effects of external current, Iapp, on MMOs pattern in this reduced model. Specifically, by taking advantage of canard phenomenon, we show that only the specific range of values of Iapp can generates the MMOs in this model. Our method provides a geometrical framework to predict the dynamic properties, which can be resulted in MMO patterns.