Significant Quality Degradation Research Articles

Intrabasin variations in age and growth of Barbus bocagei populations

The age and growth of the Iberian cyprinid Barbus bocagei Steindachner 1865, were studied in six different streams in the River Tagus basin. The fish were aged by scale reading and their lengths were back-calculated. Age structures were similar at four sites (R. Ocreza, R. Rio Frio, R. Sever and R. Canha), where six to seven age classes were present. In contrast, 10 age groups were detected in the R. Erges and 11 in the R. Nabao. The slopes (b) of the length–weight regressions did not differ significantly between the six populations. The growth of the populations was compared with that available throughout the study area (another two sites). Classification analysis of the lengths-at-age by sites matrix revealed three major groups (by decreasing order of growth rate): 1, Belver Reservoir; 2, R. Tagus, Nabao and Erges; 3, Rio Frio, Sever, Canha and Ocreza. We hypothesize that highly stressful conditions in the summer diminish growth rates and longevity in the Rio Frio, Canha and Ocreza rivers and that lower temperatures all year round could limit growth in the Sever. Higher growth rates were observed in warm-water streams with more stable environmental conditions (group 2) and in a highly productive lentic system (group 1). Among the sites that were studied, the one that revealed the highest growth performance by B. bocagei was the most polluted, the R. Nabao. This offers evidence of the species plasticity and of its successful adaptation to streams displaying significant degradation in water quality.

Dynamic Response of Non-Pixeled Amorphous Silicon Based Image Sensors

AbstractLarge area hydrogenated amorphous silicon p-i-n structures with low conductivity doped layers were proposed as single element image sensors. This work is focused on the analysis of the dynamic behavior of the sensor. Additionally some sensor parameters like maximum scanning speed, from which depends the maximum achievable frame rate are presented and discussed.In order to evaluate the sensor response to a time varying light excitation the sensor was locally illuminated with a focused chopped light source and the generated photocurrent was measured under different load conditions. Results show that the sensor is mainly capacitive and a signal rise time of approximately 100 νs was measured under a 1 kΩ load. A model for the sensor was created from the experimental data and was used to simulate the dynamic behavior of the sensor. The simulation results obtained are in good agreement with the experimental ones.As conclusion one can expect a trade off between the frame rate and the number of pixels. A frame rate higher than 10 fps was achieved for 100×100 pixels readout without a significant degradation in the image quality.

Incorporation of nitrogen in diamond by using a modulated growth technique

Owing to negative electron affinity (NEA), diamond has emerged as one of the most important materials for a low threshold cold cathode in vacuum microelectronics and in flat-panel display technology [1]. N-type doping of diamond is an important problem to be solved for effective emission of electrons. Nitrogen is one of common impurities in both natural and synthetic diamond. A recent report showed the possibility of nitrogen for n-type doping in the diamond matrix [2]. Substitutional nitrogen produces a deep-lying donor level below the conduction band minimum. The activation energy is roughly 1.7 eV. Therefore, the level is too deep to be ionized at room temperature. A dramatic improvement of field emission characteristics has been reported for a heavily nitrogen-doped diamond [3]. Urea [(NH3)2CO], N2 and melamine [C3H6N6] have been utilized as nitrogen doping sources [4–6]. Specifically, Okano et al. achieved the lowest turn-on field of ∼0.5 V/μm with nitrogen-doped diamond films by employing urea as a doping source [7]. However, a significant degradation of diamond quality has been observed during the nitrogen incorporation [5, 8]. In particular, the nitrogen incorporation substantially affects the surface morphology and thereby results in a spiked surface morphology with very low growth rate. This result means that there is a trade-off between surface morphology and doping density. The trade-off has been a technical hurdle in achieving heavy nitrogen doping while maintaining a reasonable surface morphology. In this paper, we introduce a modulated growth technique to overcome the hurdle. A home-built hot filament chemical vapor deposition (HFCVD) system was used for deposition of diamond films. Twisted W wires (0.45 mm diameter) were used for a filament. Prior to deposition, the filament was carburized at least for 7 h while monitoring the resistivity of W wires. The filament temperature was measured by an optical pyrometer. The separation between the substrate (n-type Si(111), 5× 5 mm2) and filament was 6.5 mm. The substrate surface was scratched with 1 μm diamond suspension. After dipping into a diluted

Contrast Measurement of Reflection Masks Fabricated from Cr and Ta Absorbers for Extreme Ultraviolet Lithography

We chose Cr and Ta metals as new absorbing materials for extreme ultraviolet lithography (EUVL) reflection masks. The transmittances of EUV light for these metals were calculated to be nearly equal to those for W metal at the wavelength of 13.5 nm. Reflection masks were successfully fabricated from Ta metal films by dry-etching and from Cr metal films by the lift-off technique. The mask contrast was measured using an EUV reflectometer system with a synchrotron radiation source. For the Cr absorber mask, measured peak reflectivities at the reflecting and the absorbing part of the processed patterns were 59% and 4.9%, respectively, and the contrast was about 12. The peak reflectivities at the reflecting and absorbing parts of the processed patterns for the Ta absorber mask were 50% and 0.48%, respectively, and the contrast was about 105. The masks, prepared about one year before the reflectivity measurements and stored in air, exhibited no significant degradation of reflectivity or surface quality. However, a 4% reduction in reflectivity was observed after two years' storage in air, even though the top layer of the Mo/Si multilayer for the masks was Si, which has been reported to prevent oxidation.

Regional depressurization and its impact on the sustainability of freshwater resources in an extensive midcontinent variable‐density aquifer

Regional depressurization due to groundwater withdrawal from a large confined midcontinent aquifer may cause significant changes in the regional flow field and solute distributions through time. This study addresses the effects of depressurization in the Silurian‐Devonian carbonate aquifer in the western flank of the Appalachian Basin in Ohio, where salinity‐derived variable‐density flow effects are significant. This complex hydrogeologic environment is examined using an interpretative, transient, numerical flow and transport model to examine the hydrodynamics involved in the salinization process, to simulate changes in the velocity field and solute distributions over the past 100‐year period, and to forecast the effects of three different depressurizing scenarios over the next 100‐year period. The results indicate that large‐scale depressurization can lead to significant changes in the regional flow patterns, resulting in changes in solute distributions and salinization of a portion of the aquifer. Depressurization creates vertical flow gradients within the carbonate aquifer that transport brine from underlying and overlying shale units into the updip freshwater portion of the aquifer. Model results show the development of flow reversals in the downdip portions of the aquifer that facilitate transport of brine from the deeper portions of the carbonate aquifer. These processes result in significant water quality degradation in the updip portion of the aquifer, which is extensively used for municipal, industrial, and domestic water supplies. Our results indicate the need to monitor water levels, pumping rates, and water quality so that future management decisions regarding the sustainability of the resource are based on complete and accurate field data.

Integrated model for performance analysis of all-optical multihop packet switches

The overall performance of an all-optical packet switching system is usually determined by two criteria, i.e., switching latency and packet loss rate. In some real-time applications, however, in which packets arriving later than a timeout period are discarded as loss, the packet loss rate becomes the most dominant criterion for system performance. Here we focus on evaluating the performance of all-optical packet switches in terms of the packet loss rate, which normally arises from the insufficient hardware or the degradation of an optical signal. Considering both aspects, we propose what we believe is a new analysis model for the packet loss rate that reflects the complicated interactions between physical impairments and system-level parameters. On the basis of the estimation model for signal quality degradation in a multihop path we construct an equivalent analysis model of a switching network for evaluating an average bit error rate. With the model constructed we then propose an integrated model for estimating the packet loss rate in three architectural examples of multihop packet switches, each of which is based on a different switching concept. We also derive the bounds on the packet loss rate induced by bit errors. Finally, it is verified through simulation studies that our analysis model accurately predicts system performance.

Pulsewidth control loop in high-speed CMOS clock buffers

In high-speed CMOS clock buffer design, the duty cycle of a clock is liable to be changed when the clock passes through a multistage buffer because the circuit is not pure digital. Signal quality degradation is influenced by temperature and process deviation. In this paper, we propose a pulsewidth control loop to get required pulsewidth. To investigate the loop stability, a linearized small signal analysis model is used. Results of SPICE simulation show that the pulsewidth can be well controlled if the loop parameters are properly chosen. The pulsewidth can be easily adjusted to a desired value by sizing the ratio of transistor sizes in the current mirror of charge pump.

NMR spectroscopy and MRI investigation of a potential bioartificial liver.

NMR feasibility was established for a coaxial hydrophobic-membrane bioreactor containing isolated rat hepatocytes with features designed to mimic the human liver. A novel triple-tuned NMR probe and a perfusion system controlling temperature, gas concentrations, flow-rate, and pH were used. We determined the optimum coaxial interfiber distance (i.e. diffusion distance) for maintaining hepatocyte viability in two bioreactor prototypes. Prototype no. 1 and no. 2 had diffusion distances of 500 microns and 200 microns, respectively. Cell viability was established by 31P NMR and trypan blue exclusion. Only prototype no. 2 maintained cell viability for more than 6 h, indicating the importance of diffusion distance. 31P spectra obtained over this 6 h time period were similar to in vivo spectra of rat liver. The 31P spectra were found to be more sensitive to subacute cell viability than trypan blue exclusion. In the 1H and 31P spectra, 1H2O and inorganic phosphate signals were split in two at all flow-rates, probably due to bulk magnetic susceptibility effects originating from the three bioreactor compartments. MRI was useful for quality control and determining flow dynamics, fiber integrity, and cell inoculate distribution. MRI revealed that the inner fibers were not centered in either prototype. Although an increased flow-rate did not influence spectral resolution or chemical shifts, significant degradation of MRI quality occurred above 50 mL/min. NMR spectroscopy and imaging provide valuable, real-time information on cell biochemistry and flow dynamics which can be used in development and monitoring of bioreactors designed as artificial livers.

Motion estimation for high performance transcoding

Traditionally, the re-use of motion vectors extracted from incoming video bit-stream during transcoding has been widely accepted. However, this simple re-use scheme introduces significant quality degradation in many applications including the situation when the frame-rate conversion is needed. In this paper, we analyzed the quantization errors that cause the extracted motion vectors to be non-optimal and we performed simulations to show the quality degradation due to the inaccurate motion vectors during transcoding. To improve the video quality, we proposed an adaptive motion vector refinement. With a highly reduced computational complexity, the proposed adaptive motion vector refinement achieves significant quality improvement in comparison to the conventional motion vector re-use scheme. In addition, the adaptive motion vector refinement is almost as good as performing a new full-scale motion estimation.

Optimisation of satellite frequency plans with balancedcarriers by simulated annealing

Nonlinear channels suffer from intermodulation distortion degrading signal quality and preventing amplifiers from achieving a good performance. Classically, frequency plans are optimised manually using heuristic rules. This contribution presents an automatic optimisation procedure based on simulated annealing and guided by C/(N+I) maximising criteria. Significant improvements in channel performance are achieved.

Wavefront quality of optimized diffractive lenses

Diffractive lenses can be designed using optimization techniques, such as radially symmetric iterative discrete on-axis (RSIDO) encoding. The wavefront quality of such lenses is evaluated using the point spread function and the modulation transfer function. We find that the wavefront quality is highly dependent on the particular merit function used for optimization. It is found that an optimization based on the diffraction efficiency can lead to a significant degradation in wavefront quality. Whereas optimization based on an image-quality merit function does not lead to a strong decrease of diffraction efficiency.

Optimizing AC‐mode atomic force microscope imaging

AbstractWe have operated an atomic force microscope in ambient air with several oscillating cantilever modes to establish the optimal scanning parameters to maximize image resolution and to minimize probe and sample damage. This was done by scanning a surface in air and correlating scan parameters such as oscillation amplitude and damping with image resolution. We also examined the geometry of the probe with a scanning electron microscope, before and after scanning, in order to determine whether the scanning technique had an effect on the geometry of the probe tip. If the probe is oscillated such that it contacts the surface on each oscillation, substantial damage or “wear” to the probe occurs and significant degradation of image quality was observed. In ambient air, the optimal conditions are achieved when the probe penetrates the contamination layer and reverses direction before touching the surface. Under these “near‐contact” conditions no probe damage is observed and high‐image resolution can be maintained indefinitely.

MO READOUT CHANNEL EVALUATION THROUGH THE SIMULATION OF VARIOUS FORMS OF SIGNAL QUALITY DEGRADATION

A new method for evaluating the readout channel of Pulsed Laser Irradiate Magnetic Field Modulation (PLIMFM) Magneto-Optical (MO) disks is proposed. Almost any form of signal quality degradation can be taken into account. Maximum Likelihood (ML) signal processing can significantly decrease signal detection error rates, especially when residual marks exist.

A new signal quality degradation monitor for digital transmission channels

An innovative approach to the automatic monitoring of signal quality on digital transmission channels such as communication links is presented. A communication channel is said to be experiencing some form of stress when the channel (and hence the signal) is distorted from nominal conditions. The stress may be the result of a variety of sources such as transmitter and receiver equipment errors, ionospheric effects, tropospheric effects, and jamming. A new monitor, the DEGRAD (Digital Eye Gridded Receiver with Arbitrary Degradation) monitor, is developed that is better able to detect and identify channel degradations before a significant change in signal quality is noticed by the end user. >

Morphological Image Coding Based on a Geometric Sampling Theorem and a Modified Skeleton Representation

A new approach for gray-level image coding using binary morphological operations on the image bit-planes is presented. This approach is based on a Geometric Sampling Theorem (GST), and on a modified morphological skeleton. The theorem, which is proved in this paper, states conditions for the reconstruction of the boundary of a continuous two level image from a unique subset of points of its skeleton representation. This set of points, referred to as essential points, is found to play an important role in the skeleton representation of discrete binary images as well. The modified morphological skeleton (MMS) uses an exponentially increasing in size structuring element. The computational advantage of this representation was previously reported. A new approach to its development is presented here, and its advantage in image coding is demonstrated. The coding scheme consists of the following steps: First, the image is preprocessed by an error-diffusion technique in order to reduce the number of bit-planes from 8 to 4 without significant quality degradation. The pixel values are subsequently converted to Gray-code. The bit-planes are represented by the MMS. Redundancy in this representation is reduced using an algorithm motivated by the GST. These reduced modified morphological skeletons are coded with an entropy coding scheme particularly devised for efficient skeleton coding. The possibility of the introduction of geometric errors to reduce the bit-rate is also discussed. Compression ratios of up to 11:1 were obtained for satellite images.

Imaging after titanium cranioplasty.

Titanium cranioplasty has been used in our unit for reconstruction of cranial defects following trauma, tumour resection and bone loss due to postcraniotomy infection. It has previously been assumed that imaging to assess recurrence of disease progression after cranioplasty would be severely compromised in the presence of metallic material. Titanium is a non-ferrous metal of low atomic number, which is relatively radiolucent and allows exceptionally clear images to be obtained without significant degradation of image quality, on CT and magnetic resonance (MR) imaging. Cases are presented that demonstrate the use of CT contrast cisternography and MR imaging after titanium cranioplasty. On the basis of its strength, biocompatibility and excellent handling characteristics, allied to its suitability for all post-operative imaging techniques, we conclude that titanium plate is the material of choice for cranioplasty.

Pitch-synchronous frame-by-frame and segment-based articulatory analysis by synthesis

This paper presents a pitch-synchronous analysis-by-synthesis procedure for estimating model parameters for voiced speech. These model parameters describe the vocal-tract shape and the time derivative of the glottal area function. The excitation waveform is derived from the glottal area function by incorporating source-tract interaction using the current vocal-tract input impedance. The corresponding analysis procedure for estimating the model parameters once every pitch period is outlined. A significant improvement in quality was obtained for the new pitch-synchronous analysis/synthesis procedure relative to the fixed-frame-length-based scheme used previously. It was also found that the new pitch-synchronous articulatory analysis/synthesis scheme achieves lower rms spectral distortion values than the 2.4 kb/s. Federal standard LPC-10E algorithm. A segment-based procedure for estimating the vocal-tract model parameters at a rate much lower than the current pitch is described. In this segment-based analysis-by-synthesis approach, the model parameters are estimated every 50–100 ms. The parameters for the intermediate pitch periods are derived by interpolation. The segments are selected using a maximum likelihood segmentation algorithm that segments an utterance into diphonelike units. A segment-based parameter optimization scheme could lead to a highly economical representation of the speech signal for potential applications in very low bit rate speech coding and speech storage. The above schemes were optimized for a pilot test sentence and then evaluated using eight test sentences for a log area and the Coker articulatory model representation of the vocal tract. Nine listeners were asked to judge the quality of the synthesis in a paired-comparison test and the results were analyzed using a nonparametric one-tailed sign test. For the log-area representation of the vocal tract, we found a significant degradation in speech quality for the segment-based optimization procedure relative to the frame-based procedure. However, for the Coker model representation, the degradation was found to be insignificant. This shows that unlike cross-sectional areas, the movement of various articulators in the vocal tract during speech production can be described with sufficient accuracy by specifying the position of these articulators and by using an interpolation function at time intervals much longer than a pitch period.

Method for error recovery of line spectral frequencies

Corruption of line spectral frequencies results in significant degradation of the speech quality. Usually, FEC is used to protect the LSFs, especially in very noisy channels. The Letter describes an effective error recovery scheme which relies only on the inherent and natural structure of the LSFs.

Application of Optical Disc System to Medical Use -Special Focus on PACS-

Two years of clinical experience with picture archiving and communication system (PACS) at Hokkaido University Hospital is described. Both magnetic and write-once optical discs are indispensable for medical data storage of the PACS. Data compression of medical images is routinely employed without significant degradation of image quality, to reduce data sorage space and data transferring time. Image quality of the work station and data access time are acceptable in clinical use of the PACS.

Management and clinical utilization of computed tomography, magnetic resonance imaging, and angiography in Hokkaido University Hospital picture archiving and communication system

We made a preliminary assessment of the Hokkaido University picture archiving and communication system (HU-PACS). Data access time from either imaging machines or data base to workstations was 1.5 minutes, which is great benefit for data communication in routine examinations. Image quality of the work station was estimated in terms of brain computed tomography (CT) and digitized cerebral angiograms. Cerebral infarction was definitely observed on the cathode-ray tube (CRT) monitor of the work station. Although the picture quality of CRT was acceptable, we had to manipulate window level and width for CRT diagnosis of cerebral angiography. Data compression was routinely used without significant degradation of those image quality. Nevertheless, further improvement of maneuverability of the workstation should be considered.