Performance evaluation of digital pulse position modulation for wavelength division multiplexing FSO systems impaired by interchannel crosstalk

Wavelength division multiplexing (WDM) has been proposed for fibre, intersatellite, free space and indoor optical communication systems. Digital pulse position modulation (DPPM) is a more power efficient modulation format than on-off keying (OOK) and a strong contender for the modulation of free-space systems. Although DPPM obtains this advantage in exchange for a bandwidth expansion, WDM systems using it are still potentially attractive, particularly for moderate coding levels. However, WDM systems are susceptible to interchannel crosstalk and modelling this in a WDM DPPM system is necessary. Models of varying complexity, based on simplifying assumptions, are presented and evaluated for the case of a single crosstalk wavelength. For a single crosstalk, results can be straightforwardly obtained by artificially imposing the computationally convenient constraint that frames (and thus slots also) align. Multiple crosstalk effects are additionally investigated, for the most practically relevant cases of modest coding level, and using both simulation and analytical methods. In general, DPPM maintains its sensitivity advantage over OOK even in the presence of crosstalk while predicting lower power penalty at low coding level in WDM systems

Elastogenic Protein Expression of a Highly Elastic Murine Spinal Ligament: The Ligamentum Flavum

Spinal ligaments, such as the ligamentum flavum (LF), are prone to degeneration and iatrogenic injury that can lead to back pain and nerve dysfunction. Repair and regeneration strategies for these tissues are lacking, perhaps due to limited understanding of spinal ligament formation, the elaboration of its elastic fibers, maturation and homeostasis. Using immunohistochemistry and histology, we investigated murine LF elastogenesis and tissue formation from embryonic to mature postnatal stages. We characterized the spatiotemporal distribution of the key elastogenic proteins tropoelastin, fibrillin-1, fibulin-4 and lysyl oxidase. We found that elastogenesis begins in utero with the microfibril constituent fibrillin-1 staining intensely just before birth. Elastic fibers were first detected histologically at postnatal day (P) 7, the earliest stage at which tropoelastin and fibulin-4 stained intensely. From P7 to P28, elastic fibers grew in diameter and became straighter along the axis. The growth of elastic fibers coincided with intense staining of tropoelastin and fibulin-4 staining, possibly supporting a chaperone role for fibulin-4. These expression patterns correlated with reported skeletal and behavioral changes during murine development. This immunohistochemical characterization of elastogenesis of the LF will be useful for future studies investigating mechanisms for elastogenesis and developing new strategies for treatment or regeneration of spinal ligaments and other highly elastic tissues

A Contribution of Thermoelectric Properties of the Quaternary Chalcogenide Compound Tl_2GaInSe_4 Crystal

Thermoelectric transport measurements were made on single crystal samples of $Tl_2GaInSe_4$. The crystal was prepared by a special design based on the Bridgman technique. Measurements of thermoelectric power were carried out in a special high vacuum-tight calorimeter when the direction of temperature gradient is perpendicular to the cleavage plane. The measurements covered a temperature range extending from 300 to 725 K. The results indicate P-type conductivity for our investigated samples. At room temperature the value of thermoelectric power was 735 μV/deg. The electron to hole mobility ratio was found to be 1.35. The effective mass of holes at room temperature was evaluated as $4.635 \times 10^{-29}$ kg, while for electron was equal to $8.468 \times 10^{-31}$ kg. The relaxation time of majority and minority carriers was estimated as $\tau_p= 2.968 \times 10^{-10}$ s and $\tau_n= 7.326 \times 10^{-12}$ s, respectively. Also, the diffusion coefficient of holes and electrons at room temperature was calculated and found to be 265.132 $cm^2$/s and 358.139 $cm^2$/s, respectively. The diffusion length of holes and electrons are found to be $L_p=2.805 \times 10^{-4}$ cm and $L_n=5.122 \times 10^{-5}$ cm. In addition to these pronounced parameters, the efficiency of thermoelectric element (figure of merit) was evaluated which leads to better applications in many fields

Mutual interference in multichannel optical fibre communication system

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Interpretation of Switching Properties of InGaSe2InGaSe_2 Single Crystal

The goal of this paper is to present experimental results of the switching effect and analyze qualitatively the influence of various factors, such as temperature, light illumination and sample thickness on switching behavior of the high quality ternary chalcogenide semiconductor $InGaSe_2$. Current-controlled negative resistance of $InGaSe_2$ single crystals has been observed for the first time. It has been found that indium gallium diselenide single crystals exhibit bistable or memory switching. The switching process takes place with both polarities on the crystal and has symmetric shapes. Current-voltage characteristics of $Ag-InGaSe_2-Ag$ structures exhibit two distinct regions, high resistance OFF state and low-resistance ON state having negative differential resistance. $InGaSe_2$ is a ternary semiconductor exhibiting S-type I-V characteristics. The specimen under test showed threshold switching with critical field of the switching being $10^3$ V/cm at room temperature

Interpretation of Switching Properties of InGaSe 2

The goal of this paper is to present experimental results of the switching effect and analyze qualitatively the influence of various factors, such as temperature, light illumination and sample thickness on switching behavior of the high quality ternary chalcogenide semiconductor $InGaSe_2$. Current-controlled negative resistance of $InGaSe_2$ single crystals has been observed for the first time. It has been found that indium gallium diselenide single crystals exhibit bistable or memory switching. The switching process takes place with both polarities on the crystal and has symmetric shapes. Current-voltage characteristics of $Ag-InGaSe_2-Ag$ structures exhibit two distinct regions, high resistance OFF state and low-resistance ON state having negative differential resistance. $InGaSe_2$ is a ternary semiconductor exhibiting S-type I-V characteristics. The specimen under test showed threshold switching with critical field of the switching being $10^3$ V/cm at room temperature

Preparation and Switching Behavior Characterization οf Some Quaternary Thallium Chalcogenide Compounds

Investigation of the switching phenomenon on TlGaSSe single crystal revealed that it is typical for a memory switch. The switching process takes place with both polarities on the crystal and have symmetrical shapes. Current-voltage characteristics (CVC) of symmetrical Ag/TlGaSSe/Ag structures exhibit two distinct regions, high resistance "OFF" state and low resistance "ON" state having negative differential resistance. In addition, TlGaSSe is a quarternary semiconductor exhibiting S-type I-V characteristics. The experimental results indicate that the phenomenon in our sample is very sensitive to temperature; light intensity and sample thickness. The switching parameters were checked under the influence of different factors of the ambient condition. The present investigation is the first one on switching phenomenon of TlGaSSe