Novel combinatorial constructions of optical orthogonal codes for incoherent optical CDMA systems

Three novel classes of optical orthogonal codes (OOCs) based on combinatorial designs are proposed. They are applicable to both synchronous and asynchronous incoherent optical code-division multiple access (OCDMA) and compatible with spectral-amplitude-coding (SAC), fast frequency hopping, and time-spreading schemes. Simplicity of construction, larger codeword families, and larger flexibility in cross-correlation control make the proposed OOC families interesting candidates for future OCDMA applications. A novel balanced SAC receiver for multiuser interference cancellation that can handle unequal in-phase cross correlation of OOC is also proposed. The upper bound on the bit-error rate as a function of the number of users in SAC schemes is given for all proposed OOC classes.     

Plasma surface modifications for improved biocompatibility of commercial polymers

This report describes work using low pressure gas plasma techniques for the fabrication of surfaces designed for compatibility with biological tissue and fluids. The smoothness of the surfaces was investigated using scanning tunnelling microscopy (STM) and the wettability was assessed by measurement of air/water contact angles. Plasma surface treatment rendered fluorocarbon polymers wettable by polar liquids, but the wettability decreased with time during storage of the samples in air. Plasma polymerization, on the other hand, allowed the deposition of thin coatings which were more stable with time. STM of plasma polymers, which were coated with a sputtered film of platinum or gold, showed that these coatings were smooth and continuous. The attachment and growth of human umbilical artery endothelial cells was used to assess the biocompatibility of several plasma polymer surfaces. There was some correlation between the ability of a surface to grow cells and the wettability of that surface with polar liquids, but significant differences in cell growth on surfaces with very similar hydrophilicity indicated that other factors are at least as important.     

An airborne radiometer for stratospheric water vapor measurements at 183 GHz

The Airborne Millimeter- and Submillimeter Observing System (AMSOS) is a total-power radiometer for observations of the 183.3-GHz water vapor rotational line, operated onboard a Learjet aircraft of the Swiss Air Force. The radiometer is also used to observe the 175.45-GHz ozone line in the other sideband. The neatly designed quasi optics provide a regular and narrow output beam with a half-power beam-width angle of 1.2/spl deg/ and efficient sideband switching. A /spl lambda//4-quasi-optical isolator is used for baseline reduction securing attenuation of internal reflections by more than 30 dB. A low noise temperature of the ambient-temperature-operating system (1900 K) and excellent target pointing (better than 0.1/spl deg/) provide a good duty cycle and reliable calibration. A reliable control over the radiometer's operational parameters, like system stability and system temperatures, and higher automatization were required to come up with high demands of an onboard operation. The measured spectra look typical for the region and time where they were observed.     

100-gb/s transmission using orthogonal frequency-division multiplexing

The possibility of 100-Gb/s transmission over 25-GHz bandwidth using orthogonal frequency-division multiplexing (OFDM) is demonstrated. It is shown that 100-Gb/s transmission over 3840 km can be achieved using single-sideband quadrature-phase-shift keying OFDM transmission and low-density parity-check codes.     

Capacity of channels with redundant multitrack (d,k) constraints:the k<d case

Run-length-limited or (d,k) recording codes are widely used in digital storage systems with peak detection. The channel capacities of the redundant multitrack (d,k) constraint are calculated and tabulated for k相似文献   

Projective-plane iteratively decodable block codes for WDM high-speed long-haul transmission systems

Low-density parity-check (LDPC) codes are excellent candidates for optical network applications due to their inherent low complexity of both encoders and decoders. A cyclic or quasi-cyclic form of finite geometry LDPC codes simplifies the encoding procedure. In addition, the complexity of an iterative decoder for such codes, namely the min-sum algorithm, is lower than the complexity of a turbo or Reed-Solomon decoder. In fact, simple hard-decoding algorithms such as the bit-flipping algorithm perform very well on codes from projective planes. In this paper, the authors consider LDPC codes from affine planes, projective planes, oval designs, and unitals. The bit-error-rate (BER) performance of these codes is significantly better than that of any other known foward-error correction techniques for optical communications. A coding gain of 9-10 dB at a BER of 10/sup -9/, depending on the code rate, demonstrated here is the best result reported so far. In order to assess the performance of the proposed coding schemes, a very realistic simulation model is used that takes into account in a natural way all major impairments in long-haul optical transmission such as amplified spontaneous emission noise, pulse distortion due to fiber nonlinearities, chromatic dispersion, crosstalk effects, and intersymbol interference. This approach gives a much better estimate of the code's performance than the commonly used additive white Gaussian noise channel model.     

Engineering geological evaluation of the conditions for constructing a bridge and a tunnel in the zone of the old Petrovaradin Fortress,Serbia

The paper discusses the geotechnical conditions related to the construction of a new bridge over the Danube and a tunnel passing beneath the Petrovaradin Fortress at Novi Sad, Serbia. Analyses showed that both the bridge and the tunnel could be built without causing damage to any of the historical structures and that it would better to build two 8 m wide tunnels than a single 16 m wide structure. One of the two tunnels will involve the widening of an existing one, whereas the other will be newly constructed. The evidence suggests that the new bridge can be built on the reinforced piers of a bridge which was destroyed in World War II.