Phosphate glass samples with various Yb2O3 and Er2O3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spect...Phosphate glass samples with various Yb2O3 and Er2O3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy. The absorption, emission spectra and fluorescence decay studies were carried out both at low and room temperatures. Results showed the existence of several sites occupied by the rare earth ions in the phosphate glass. Up-conversion and cooperative fluorescence were also discussed.展开更多
In many real-time resource-constrained embedded systems, highly-predictable system behavior is a key design requirement. The “time-triggered co-operative” (TTC) scheduling algorithm provides a good match for a wide ...In many real-time resource-constrained embedded systems, highly-predictable system behavior is a key design requirement. The “time-triggered co-operative” (TTC) scheduling algorithm provides a good match for a wide range of low-cost embedded applications. As a consequence of the resource, timing, and power constraints, the implementation of such algorithm is often far from trivial. Thus, basic implementation of TTC algorithm can result in excessive levels of task jitter which may jeopardize the predictability of many time-critical applications using this algorithm. This paper discusses the main sources of jitter in earlier TTC implementations and develops two alternative implementations – based on the employment of “sandwich delay” (SD) mechanisms – to reduce task jitter in TTC system significantly. In addition to jitter levels at task release times, we also assess the CPU, memory and power requirements involved in practical implementations of the proposed schedulers. The paper concludes that the TTC scheduler implementation using “multiple timer interrupt” (MTI) technique achieves better performance in terms of timing behavior and resource utilization as opposed to the other implementation which is based on a simple SD mechanism. Use of MTI technique is also found to provide a simple solution to “task overrun” problem which may degrade the performance of many TTC systems.展开更多
Nano-composite silica-phosphate system (SiO2- P2O5) co-doped with Al2O3 as a host material and prepared by sol gel technique in two forms monolith and thin film using multilayer spin-coating method were activated by E...Nano-composite silica-phosphate system (SiO2- P2O5) co-doped with Al2O3 as a host material and prepared by sol gel technique in two forms monolith and thin film using multilayer spin-coating method were activated by Er3+ and Yb3+ ions as in the formula;[SiO2: 11P2O5: 3 Al2O3: (1.2) Er: (1.2, 1.8 and 3) Yb]. The prepared samples have been synthesized using tetra-ethyl-orthosilicate (TEOS) and triethyl-phosphate (TEP) as precursor sources of silica and phospho-rus oxides. The microstructure and crystallinity of the prepared samples will be characterized by using x-ray diffraction (XRD) which, imply that the crystallite sizes of [SiO2: 11P2O5: 3 Al2O3: (1.2) Er: (1.2) Yb] at 500oC for both thin film and monolith forms of the prepared samples were found to be equal to 35 and 33 nm, respectively. The refractive index will be evaluated by measuring the normal transmission and specular reflection of the prepared samples. The photolu-minescence properties have analyzed in the visible wavelength range between 500 and 800 nm as a function of sample composition.展开更多
One of the challenging tasks in cognitive radio(CR) networks is to agree on a common control channel to exchange control information. This paper presents a novel medium access control(MAC) protocol for CR network whic...One of the challenging tasks in cognitive radio(CR) networks is to agree on a common control channel to exchange control information. This paper presents a novel medium access control(MAC) protocol for CR network which efficiently and intelligently establishes a common control channel between CR nodes. The proposed protocol is the first CR MAC protocol which is hybrid in nature and lies between global common control channel(GCCC) and non-GCCC family of MAC protocols. The dynamic nature of the protocol makes the CR nodes converge on a newly found control channel quicker whenever the interference from a licensed user is sensed. The analytical results show that the dynamic, hybrid and adaptive nature of proposed protocol yields higher throughputs when compared with other CR MAC protocols.展开更多
文摘Phosphate glass samples with various Yb2O3 and Er2O3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy. The absorption, emission spectra and fluorescence decay studies were carried out both at low and room temperatures. Results showed the existence of several sites occupied by the rare earth ions in the phosphate glass. Up-conversion and cooperative fluorescence were also discussed.
文摘In many real-time resource-constrained embedded systems, highly-predictable system behavior is a key design requirement. The “time-triggered co-operative” (TTC) scheduling algorithm provides a good match for a wide range of low-cost embedded applications. As a consequence of the resource, timing, and power constraints, the implementation of such algorithm is often far from trivial. Thus, basic implementation of TTC algorithm can result in excessive levels of task jitter which may jeopardize the predictability of many time-critical applications using this algorithm. This paper discusses the main sources of jitter in earlier TTC implementations and develops two alternative implementations – based on the employment of “sandwich delay” (SD) mechanisms – to reduce task jitter in TTC system significantly. In addition to jitter levels at task release times, we also assess the CPU, memory and power requirements involved in practical implementations of the proposed schedulers. The paper concludes that the TTC scheduler implementation using “multiple timer interrupt” (MTI) technique achieves better performance in terms of timing behavior and resource utilization as opposed to the other implementation which is based on a simple SD mechanism. Use of MTI technique is also found to provide a simple solution to “task overrun” problem which may degrade the performance of many TTC systems.
文摘Nano-composite silica-phosphate system (SiO2- P2O5) co-doped with Al2O3 as a host material and prepared by sol gel technique in two forms monolith and thin film using multilayer spin-coating method were activated by Er3+ and Yb3+ ions as in the formula;[SiO2: 11P2O5: 3 Al2O3: (1.2) Er: (1.2, 1.8 and 3) Yb]. The prepared samples have been synthesized using tetra-ethyl-orthosilicate (TEOS) and triethyl-phosphate (TEP) as precursor sources of silica and phospho-rus oxides. The microstructure and crystallinity of the prepared samples will be characterized by using x-ray diffraction (XRD) which, imply that the crystallite sizes of [SiO2: 11P2O5: 3 Al2O3: (1.2) Er: (1.2) Yb] at 500oC for both thin film and monolith forms of the prepared samples were found to be equal to 35 and 33 nm, respectively. The refractive index will be evaluated by measuring the normal transmission and specular reflection of the prepared samples. The photolu-minescence properties have analyzed in the visible wavelength range between 500 and 800 nm as a function of sample composition.
文摘One of the challenging tasks in cognitive radio(CR) networks is to agree on a common control channel to exchange control information. This paper presents a novel medium access control(MAC) protocol for CR network which efficiently and intelligently establishes a common control channel between CR nodes. The proposed protocol is the first CR MAC protocol which is hybrid in nature and lies between global common control channel(GCCC) and non-GCCC family of MAC protocols. The dynamic nature of the protocol makes the CR nodes converge on a newly found control channel quicker whenever the interference from a licensed user is sensed. The analytical results show that the dynamic, hybrid and adaptive nature of proposed protocol yields higher throughputs when compared with other CR MAC protocols.
