A non-equilibrium analysis and control framework for active queue management

We present a non-equilibrium analysis and control approach for the Active Queue Management (AQM) problem in communication networks. Using simplified fluid models, we carry out a bifurcation study of the complex dynamic queue behavior to show that non-equilibrium methods are essential for analysis and optimization in the AQM problem. We investigate an ergodic theoretic framework for stochastic modeling of the non-equilibrium behavior in deterministic models and use it to identify parameters of a fluid model from packet level simulations. For computational tractability, we use set-oriented numerical methods to construct finite-dimensional Markov models, including control Markov chains and hidden Markov models. Subsequently, we develop and analyze an example AQM algorithm using a Markov Decision Process (MDP) based control framework. The control scheme developed is optimal with respect to a reward function, defined over the queue size and aggregate flow rate. We implement and simulate our illustrative AQM algorithm in the ns-2 network simulator. The results obtained confirm the theoretical analysis and exhibit promising performance when compared with well-known alternative schemes under persistent non-equilibrium queue behavior.     

p53 expression in oral precancer as a marker for malignant potential

The potential of p53 protein expression as a marker for determining which oral precancerous lesions may transform to malignancy with time was assessed. We compared the p53 expression in archival formalin-fixed, paraffin-embedded tissues from 22 baseline biopsies of precancerous lesions that transformed to cancer in 4-25 years against that in 68 similar lesions that did not transform over the same time period. Twenty-nine percent of precancers that transformed were p53-positive at baseline, compared to 31% of the biopsies that did not transform to malignancy. When examined by immunohistochemical methods p53 expression failed to detect potential malignant status of oral precancer. Non-specificity of the assay may account for this result but overexpression of p53 due to DNA damage by tobacco/betel-quid in non-progressive lesions needs further study. Nine precancerous lesions became p53-immunoreactive from precancer to cancer. This may suggest p53 overexpression peaks close to the time of transition from precancer to cancer rather than early in the natural history of oral precancer.     

Malignant epithelial parotid gland tumours: analysis and results in 65 previously untreated patients

BACKGROUND: Optimal management of malignant epithelial parotid tumours requires knowledge of the available therapeutic modalities and the different biological characteristics. The aim of the study was to review the characteristics of patients at presentation, histological classification, disease-free and overall survival rates, and the results of the applied treatment policy regarding the facial nerve and neck. METHODS: Between 1974 and 1995 a total of 65 patients was treated with curative intent for a previously untreated malignant epithelial parotid gland tumour. All patients underwent some type of parotidectomy, 20 of whom had an en bloc radical neck dissection. In selected cases the facial nerve or its branches were peeled off the tumour thus violating the objective of tumour-free margins and relying heavily on the efficacy of postoperative radiotherapy. In total 51 patients received postoperative radiotherapy. None of the patients was lost to follow-up. RESULTS: There were 12 locoregional failures (18 per cent). In only one of these 12 patients was salvage therapy successful; the remaining 11 patients died from the tumour. All but one of the eight patients with distant metastasis only died from the tumour. The estimated 5- and 10-year disease-free rates were 68 and 59 per cent respectively. The corresponding survival rates were 75 per cent and 67 per cent. A significant relationship could be observed between tumour stage and survival. The presence of lymph node metastases proved to be the strongest single prognostic factor. CONCLUSION: In selected cases a conservative approach towards the facial nerve is justified.     

Software architectural support for handheld computing

The authors present a software-architecture-based approach to support computing on distributed, handheld, mobile, resource-constrained devices.     

Seismic performance of chevron braced steel frames with and without viscous fluid dampers as a function of ground motion and damper characteristics

This study is aimed at comparing the seismic performance of steel chevron braced frames (CBFs) with and without viscous fluid dampers (VFDs) as a function of the intensity and frequency characteristics of the ground motion and VFD parameters. For this purpose, comparative nonlinear time history (NLTH) analyses of single and multiple story CBFs with and without VFDs are conducted using ground motions with various frequency characteristics scaled to represent small, moderate and large intensity earthquakes. Additionally, NLTH analyses of single and multiple story CBFs with VFDs are conducted to study the effect of the damping ratio and velocity exponent of the VFD on the seismic performance of the frames. The analysis results revealed that the seismic performance of the CBFs without VFDs is very poor and sensitive to the frequency characteristics and intensity of the ground motion due to brace buckling effects. Installing VFDs into the CBFs significantly improved their seismic performance by maintaining their elastic behavior. Furthermore, VFDs with smaller velocity exponents and larger damping ratio are observed to be more effective in improving the seismic performance of the CBFs. However, VFDs with damping ratios larger than 50% do not produce significant additional improvement in the seismic performance of the CBFs.     

Preparation and characterization of electropolymerized poly(N-substituted maleimide-co-styrene) coatings on copper substrates

poly(N-substituted maleimide-co-styrene) copolymer films were electropolymerized onto copper substrates as possible candidates for electronic applications. The N-substituted moieties that were investigated include phenyi, 3-carboxyphenyl, and 4-carboxyphenyl. Uniform coatings of 25 μm or more thickness were successfully applied using each of the three N-substituted maleimides. The thickness was controlled by manipulating the monomer concentration, current density, and reaction time. Not only did the 3- and 4-carboxyphenylmaleimide (CMI)/styrene copolymers have high glass transition temperatures (220°C) and fairly good thermal stability (≈ 430°C), but they also have rather low dielectric constants (2.55 for 4-CMI/styrene), comparable to those of polyimides. Polymerization of the coatings was observed by in-situ Fourier transform infrared spectroscopy (FTIRS), using a special cell that made the observation of the polymer structure development possible. It was found by FTIRS that all three monomers, when used with styrene, produced alternating copolymers. © 1993 John Wiley & Sons, Inc.     

Acute poisoning in children

This prospective study comprised 120 children brought to the hospital with the history of acute poisoning. Poisonings occurred accidentally in 116 cases (96.7%) and 78 cases (65%) were children aged 1-4 years. Medical aid was sought earliest in case of children with animal bite and in infants. Kerosene and medications accounted for 72 cases (60%) of poisoning exposures. None of the care-takers of children received any instruction regarding prevention of accidents and poisoning prior to the episode, in spite of multiple contacts with health-care providers. Role of health education and other preventive measures are stressed.     

Effect of 1 wt.% yttrium addition on high-temperature sulfidation behavior of Fe-15Cr-4Al alloy

High-temperature sulfidation studies have been carried out on Fe-15Cr-4Al with and without 1% Y in the temperature range 700–1000°C in an H ₂-H₂ S environment over the sulfur pressure range of 10 ^–9–10^–3 atm. Two-layered and three-layered sulfide scales were observed in both alloys at low and high sulfur pressures, respectively. The pegging phenomenon, similar to that occurring in high-temperature oxidation, across the innermost layer and substrate was observed in the case of the yttrium-containing alloy. Yttrium was found to be associated with aluminum and chromium sulfides. The role of yttrium was more evident at low than at high sulfur pressures and was found to reduce the parabolic rate constants by a factor of about one-half to one-seventh, respectively.     

Stability Analysis of Four-Lobe Pressure-Dam Bearings

This paper analyzes the dynamic behavior of a new type of bearing, namely, four-lobe pressure-dam bearing. It is produced by incorporating two pressure dams in the upper two lobes and two relief tracks in the lower two lobes of an ordinary four-lobe bearing. The characteristic curves of this type of bearing show that it is much more stable as compared to an ordinary four-lobe bearing. A study of the performance characteristics of this type of bearing is also undertaken.     

Analysis of tool temperature fluctuation in interrupted cutting

A unidimensional model for temperature distribution in the tool during intermittent cutting is presented. The tool-chip interface heating is approximated by a periodic rectangular heat flux. The effects of cutting time ratio, frequency of temperature fluctuation and thermal diffusivity of the tool material on internal temperature distribution and on thermal stresses developed in the tool have been discussed. With increasing cutting frequency, the temperature gradient in the cutting zone increases, but with higher thermal diffusivity of the tool material, it diminishes. The magnitude of thermal stresses increases with increase in amplitude of temperature fluctuation