Search

Rectangular orthogonal digital filter banks (ODFBs) based on square-root-raised-cosine (SRRC) functions are widely utilised to realise flexible and elastic multi-channel aggregations for fixed and mobile networks. However, long digital filter lengths are required to minimize digital filtering-associated signal distortions. In this paper, based on the extended Gaussian function (EGF), a novel rectangular ODFB with excellent robustness against the short digital filter length-induced truncation effect is proposed. Optimum digital filter parameters of the EGF-based ODFBs are identified and verified in multi-channel hybrid OFDM-digital filter multiple access (DFMA) PONs based on intensity modulation and direct detection (IMDD). By making use of the identified optimum digital filter parameters, extensive comparisons of digital filter characteristics and corresponding multi-channel upstream PON performances are made between the EGF-based ODFBs and the SRRC-based ODFBs. It is shown that to achieve a similar aggregated upstream signal transmission capacity, the EGF-based ODFB reduces the digital filter DSP complexity by a factor of 4. For a digital filter length as short as 8, in comparison with the SRRC-based ODFB, the EGF-based ODFB introduces >1.5 dB (>0.8 dB) improvements in upstream receiver sensitivity for 5-bits (8-bits) DACs/ADCs, increases the aggregated upstream signal transmission capacity by >5.5%, enlarges the ONU launch power dynamic range by >2.5 dB and improves the frequency offset tolerance by a factor of >1.5. In addition, the EGF-based ODFB also enhances upstream performance robustness against ONU symbol timing offsets. [ABSTRACT FROM AUTHOR]

In recent years, flight safety is still one of the main issues for all airlines. En route civil airplanes may encounter adverse weather conditions. Some fatal airplane accidents happened because of the weather disturbance. Moreover, we should also design path to avoid the prohibited area. Therefore a good path planning algorithm plays an increasingly important role in air traffic management. An efficient path planning algorithm can help the plane to avoid severe weather conditions, restricted areas and moving obstacles to ensure the safety of the cabin crews and passengers. Here, we build our algorithm based on the A* search algorithm. Moreover, our algorithm can also find the path with least energy costs. As a result, our algorithm can improve the safety operation of the airplanes and reduce the workload of pilots and air traffic controllers.

In connection with the design of a hard-x-ray telescope for the Constellation X-Ray Observatory we measured the reflectivity of an iridium-coated zerodur substrate as a function of angle at 55, 60, 70, and 80 keV at the National Synchrotron Light Source of Brookhaven National Laboratory. The optical constants were derived from the reflectivity data. The real component of the index of refraction is in excellent agreement with theoretical values at all four energies. However, the imaginary component, which is related to the mass attenuation coefficient, is 50% to 70% larger at 55, 60, and 70 keV than theoretical values. OCIS codes: 340.0340, 340.7470, 310.6860, 310.1620, 350.1260.

Nanoparticles with different core@shell structures (NaGdF4:Yb/Tm@NaLnF4 with Ln=lanthanide) were successfully synthesized for luminescence upconversion from 980 nm to 800 nm. The upconversion luminescence of the core@shell nanoparticles (NaGdF4:Yb/Tm@NaGdF4) has a much stronger infrared emission centered at 800 nm than that of the core-only nanoparticles (NaGdF4:Yb/Tm). This is not only due to the removal of surface defects of the core nanoparticles by the shell, which results in the decrease of the luminescence quenching, but also due to the breaking of the crystal field symmetry around the Tm3+ ion. By replacing the NaGdF4 shell with an NaYF4, the emission could further be enhanced. We suggest that the breaking of the crystal field symmetry plays also in this case a key role for further enhancement of upconversion emission. The importance of this asymmetry was further revealed by investigating the energy transfer between Er3+ ion in the shell and the Tm3+ ion of the core nanoparticle. [ABSTRACT FROM AUTHOR]

Silo honking is an acoustical emission with a fundamental frequency of several hundred Hertz and an intensity often greater than 100 dB. It occurs when a silo is discharging and is similar to the 'honk' of a lorry horn. The high amplitude of the honk makes it a significant noise pollution issue for workers at the site and for neighboring businesses and residents. This paper considers some possible excitation mechanisms that may be responsible for honking and presents measurements obtained from a full scale honking silo detailing the acoustic emissions and the associated vibration of the silo walls. Experimental results are presented which are comprised of simultaneous measurements of the three components of the wall vibrations and the acoustic pressure. The wall vibrations have an initial impulse response with a high amplitude O(100g) and subsequent oscillatory accelerations with amplitude O(10g). The frequency spectra of the acceleration and acoustic pressure measurements comprises a sharp peak at the fundamental acoustic frequency and a harmonic series of peaks at integer multiples of the fundamental frequency. It is shown that the honking is not generated by a resonance inside the silo, as in a flute or organ pipe: the sound is generated by the silo walls acting as large speakers. The interaction between the wall and the sliding pellets is considered as a possible excitation mechanism for the acoustic emissions. Laboratory friction measurements are presented using pellets from the honking silo and a wall sample. The results of these measurements show that the particles exhibit a slip-stick behavior when sheared against the wall material. This slip-stick behavior is characterized under different conditions for pellets that are known to produce honking. Particles that have not been observed to honk were also tested and did not produce slip-stick motion at the wall. CE Database subject headings: Acoustics; Noise; Vibration; Slip: Silos; Particle motion; Particulate media.