Study of pyro-carbon coated alumina kernel using mixed contrast transfer based X-ray phase retrieval technique

We have used the contrast transfer function based X-ray phase retrieval technique for phase retrieval studies on a two-component system. Pyro-carbon coated alumina matrix was chosen as a two-component system for these studies. Simulations as well as experimental results are presented. This paper shows that X-ray phase contrast along with phase retrieval can become an alternative tool for non-destructive characterization of these materials. We have also attempted to retrieve the spatial distribution of the projected thickness map of the two different elements.     

The double ended queue with mixed-Erlangian arrival distribution and limited waiting space

The steady state solution of the double-ended queue involving taxis and customers at a taxi stand has been considered under the assumption that there is limited waiting space both for taxis and for customers. Taxis arrive according to mixed Erlangian input, the mean times of stay in the various phases which comprise the arrival channel not being the same. The arrivals of customers are assumed to be Poisson distributed. We obtain an expression for the probabilities that there aren units in the queue. The cases of exponential and 2-Erlang arrival distributions for taxis have been considered as particular cases. For the 2-Erlang arrival distribution for taxis, we have evaluated the probabilities that the waiting space for customers or taxis is full; their values are also shown by means of graphs. Paper presented at the Fourth Annual Convention of Operational Research Society of India, 2nd–4th, March 1972, held at Madras.     

Independent and Simultaneous Monitoring of Chromatic and Polarization-Mode Dispersion in OOK and DPSK Transmission

We propose and demonstrate a novel technique for a simultaneous chromatic and first-order polarization-mode-dispersion (PMD) monitoring method using a partial bit delay Mach-Zehnder interferometer (MZI) with radio-frequency (RF) clock tone monitoring. RF clock tones at the output of the two branches of the MZI behave oppositely with increasing chromatic dispersion (CD) which improves the sensitivity of the measurement. The technique increases CD monitoring sensitivity over standard clock tone methods by a factor of two for a nonreturn-to-zero intensity modulation format and a factor of five for a differential-phase-shift-keying modulation format. The accuracy of PMD monitoring is also enhanced. Moreover, the partial bit delay allows the signal to pass through the constructive branch of the MZI with no observable degradation of the signal quality, allowing it to be normally detected by a receiver     

An Acknowledgment-Based Approach for the Detection of Routing Misbehavior in MANETs

We study routing misbehavior in MANETs (mobile ad hoc networks) in this paper. In general, routing protocols for MANETs are designed based on the assumption that all participating nodes are fully cooperative. However, due to the open structure and scarcely available battery-based energy, node misbehaviors may exist. One such routing misbehavior is that some selfish nodes will participate in the route discovery and maintenance processes but refuse to forward data packets. In this paper, we propose the 2ACK scheme that serves as an add-on technique for routing schemes to detect routing misbehavior and to mitigate their adverse effect. The main idea of the 2ACK scheme is to send two-hop acknowledgment packets in the opposite direction of the routing path. In order to reduce additional routing overhead, only a fraction of the received data packets are acknowledged in the 2ACK scheme. Analytical and simulation results are presented to evaluate the performance of the proposed scheme     

Transparent hashing in the encrypted domain for privacy preserving image retrieval

Search through a database of encrypted images against a crumpled and encrypted query will remain privacy preserving only if comparisons between selective features derived from these images is executed in the encrypted domain itself. To facilitate this, the encryption process must remain transparent to specific image statistics computed in the spatial or transform domain. Consequently, the perceptual hash formed by quantizing the image statistics remains the same before and after the encryption process. In this paper, we propose a transparent privacy preserving hashing scheme tailored to preserve the DCT-AC coefficient distributions, despite a constrained inter-block shuffling operation. These DCT distributions can be mapped onto a generalized Gaussian model characterized by shape and scale parameters, which can be quantized and Gray-coded into a binary hash matrix. The encryption scheme has been shown to be perceptually secure and does not impair the search reliability and accuracy of the hashing procedure. Experimental results have been provided to verify the robustness of the hash to content-preserving transformations, while demonstrating adequate sensitivity to discriminate between different images.     

Dissolution of bioactive glasses: The effects of crystallinity coupled with stress

Fixing the chemical composition of bioactive ceramic glass does not dictate biological response. Processing history can alter the microstructure, phase composition, degree of crystallinity, and residual stress—all of which can contribute to mechanical performance and bioactive response. This paper discusses effects of thermal and mechanical processing performed on bioactive glass 45S5 with regard to the micro-structural changes that occur during in vitro immersion, and how such changes can be related to bioactivity with respect to implant materials. The underlying theme is the relationship between mechanical properties, stress, microstructure, and bioactivity, and how to achieve optimization.     

Design of Minimum Seepage-Loss Nonpolygonal Canal Sections

Analytical solutions exist for the problem of determination of seepage loss from polygonal sections such as a triangle, a rectangle, and a trapezoid. In this investigation, seepage from circular and exponential sections has been calculated by a finite-difference-based numerical solution of the differential equation governing the seepage flow. The phreatic boundaries of the flow domain were described in terms of two parameters that are estimated by a minimization process. Such seepage computations were performed for a large number of independent dimensionless variables of the section geometry. Subjecting the computed seepage to regression analyses explicit equations for seepage loss from canals having circular and exponential cross sections have been obtained. Using these seepage-loss equations, the design variables for minimum seepage loss of circular and exponential canal sections have been obtained. The use of the design equations has been illustrated by design examples.     

Certainty equivalence and the minimax principle in self-tuning control

The majority of the published treatments of self-tuning controllers employ a certainty equivalence assumption whereby at each step, identification is performed first and then a control is devised by treating parameter estimates as if they were the correct values. This note demonstrates that when knowledge of parameter estimate uncertainty is used to minimize the maximum one-step-ahead cost, the optimal regulator gains for a class of self-tuning regulators will be either zero or the certainty equivalence gain.     

Microstructural aspects of superplasticity

The microstructural aspects of the superplastic phenomenon are reviewed. The experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity. It is shown, that in spite of often conflicting evidence in the literature, a common pattern of microstructural behaviour emerges for all the materials and conditions investigated to date.     

Carotid artery repair for radiation-associated atherosclerosis is a safe and durable procedure

OBJECTIVE: The development of carotid atherosclerosis after neck irradiation is well documented. There has been concern about the safety and durability of carotid artery repair through a radiated field. The objective of this report is to describe the immediate and long-term results of a series of cases collected in a 13-year interval. METHODS: From 1984 to 1997, 24 patients underwent 26 carotid artery operations. All the patients had undergone prior radiation therapy at a mean interval of 17 years, with an average radiation dose of 6300 rad. Severe scarring of the skin or radiation fibrosis were present in two thirds of the patients, with 4 patients having permanent tracheostomies. The indications for carotid surgery included cerebral or monocular transient ischemic attack (58%), asymptomatic high-grade stenosis (27%), prior stroke (12%), and tumor invasion of the carotid artery (4%). General anesthesia was used with selective shunting on the basis of carotid artery back pressure or electroencephalography monitoring. Patch angioplasty closure was used in 79% of the patients. The operations included standard carotid endarterectomy (n = 20), external carotid endarterectomy (n = 2), carotid patch angioplasty alone (n = 2), aortocarotid bypass grafting (n = 1), and carotid interposition grafting (n = 1). Four patients required skin grafting or myocutaneous flaps. RESULTS: No deaths or strokes occurred within 30 days of the operations. Six patients had transient cranial nerve palsy, and two had wound infections. The patients were followed from 1 to 156 months, with six patients being followed for longer than 18 months. No strokes were seen at late follow-up examination. Duplex scan examination documented one occlusion, in a patient with primary closure, and two restenoses, one of which necessitated reoperation. The remainder of the grafts were widely patent. CONCLUSIONS: Carotid surgery after neck irradiation is safe and durable. The long-term patency rates and the protection against subsequent neurologic events are similar to the results obtained in the absence of radiation therapy. Problems of wound healing were not found in this series.