Microstructure of GaN deposited by lateral confined epitaxy on patterned Si (111)

Lateral confined epitaxy (LCE) is an epitaxial growth method on substrates patterned to form uniform mesas separated by trenches for laterally restricting growth area. In this work, plan view and cross-sectional transmission electron microscopy (TEM) were used in order to characterize the microstructure of GaN films grown by metal-organic chemical vapor deposition on patterned Si (111) using the LCE method. Two kinds of propagation modes of the dislocations were observed. The dislocations in the center of the mesa mainly propagate vertically to the surface. On the other hand, dislocations close (1–2 μm) to the mesa edges tend to bend laterally, allowing dislocation reactions that result in a lower dislocation density. This suggests that the overall material quality improves with decreasing mesa size, which is consistent with the observed increase in photoluminescence band edge peak intensity.     

Maintaining Authenticated Communication in the Presence of Break-Ins

We study the problem of maintaining authenticated communication over untrusted communication channels, in a scenario where the communicating parties may be occasionally and repeatedly broken into for transient periods of time. Once a party is broken into, its cryptographic keys are exposed and perhaps modified. Yet, when aided by other parties it should be able to regain its ability to communicate in an authenticated way. We present a mathematical model for this highly adversarial setting, exhibiting salient properties and parameters, and then describe a practically appealing protocol for solving this problem. A key element in our solution is devising a proactive distributed signature (PDS) scheme in our model. The PDS schemes known in the literature are designed for a model where authenticated communication is available. We therefore show how these schemes can be modified to work in our model, where no such primitives are available a priori. In the process of devising these schemes, we also present a new definition of PDS schemes (and of distributed signature schemes in general). This definition may be of independent interest. Received 22 April 1998 and revised 2 April 1999     

On the equivalence of weak learnability and linear separability: new relaxations and efficient boosting algorithms

Boosting algorithms build highly accurate prediction mechanisms from a collection of low-accuracy predictors. To do so, they employ the notion of weak-learnability. The starting point of this paper is a proof which shows that weak learnability is equivalent to linear separability with ? ₁ margin. The equivalence is a direct consequence of von Neumann’s minimax theorem. Nonetheless, we derive the equivalence directly using Fenchel duality. We then use our derivation to describe a family of relaxations to the weak-learnability assumption that readily translates to a family of relaxations of linear separability with margin. This alternative perspective sheds new light on known soft-margin boosting algorithms and also enables us to derive several new relaxations of the notion of linear separability. Last, we describe and analyze an efficient boosting framework that can be used for minimizing the loss functions derived from our family of relaxations. In particular, we obtain efficient boosting algorithms for maximizing hard and soft versions of the ? ₁ margin.     

Review: Automation and meat quality-global challenges.

The global meat industry has seen significant changes in the methods used to harvest and process fresh meat over the past century. Increased use of automation has led to significant increases in line speed for beef, pork, sheep, poultry and fish operations. For example, currently the fastest line observed has been broilers at 13,500/h. Such developments have required in-depth understanding of the pre and post rigor processes to prevent defects. Procedures such as maturation chilling and electrical stimulation are now common in red meat and poultry processing; allowing shorter time to deboning, while harvesting high quality meat. Robots designed to cut meat are also appearing on the market, and replacing traditional manual operations. This is a challenge, because high speed equipment is not necessarily sensitive to variations in size/quality issues, and requires development of unique sensors and control systems. Also, progress in breeding and genetics is contributing to greater product uniformity and quality; helping in operating automated equipment.     

Finding the dimension of slow dynamics in a rhythmic system

Dynamical systems with asymptotically stable periodic orbits are generic models for rhythmic processes in dissipative physical systems. This paper presents a method for reconstructing the dynamics near a periodic orbit from multivariate time-series data. It is used to test theories about the control of legged locomotion, a context in which time series are short when compared with previous work in nonlinear time-series analysis. The method presented here identifies appropriate dimensions of reduced order models for the deterministic portion of the dynamics. The paper also addresses challenges inherent in identifying dynamical models with data from different individuals.     

Infused design. II. Practice

Infused design, introduced in the preceding paper, is a new methodology for design that opens up new channels of cooperation between designers from different engineering fields. The methodology enables an engineer from one engineering field to infuse his designs with the knowledge and experience of an engineer from some other field. During the infusion, the knowledge of the designers ascends to a common mathematical meta-level, consisting of discrete mathematical models—called combinatorial representations, and then descends to other disciplinary domains. All the domains that can be reached in this fashion are candidates to export knowledge for infusion. This sequel paper is aimed at unfolding the practice of the theory from part I by demonstrating four scenarios dealing with various design activities. The design scenarios studied in this paper expose novel cooperation channels between mechanical and civil engineers, and between mechanical and electrical engineers. Further applications of the proposed approach, including the pedagogical advantages it offers, are thoroughly discussed.

Centralized and Distributed Multi-view Correspondence

A probabilistic algorithm is presented for finding correspondences across multiple images in systems with large numbers of cameras and considerable overlap. The algorithm employs the theory of random graphs to provide an efficient probabilistic algorithm that performs Wide-baseline Stereo (WBS) comparisons on a small number of image pairs, and then propagates correspondence information among the cameras. A concrete mathematical analysis of its performance is given. The algorithm is extended to handle false-positive and false-negative failures of the WBS computations. We characterize the detectability of the existence of such failures, and propose an efficient method for this detection. Based on this, we propose a heuristic method for discarding false matches, and demonstrate its effectiveness in reducing errors. Since in many multi-camera applications cameras are attached to processors that handle local processing and communication, it is natural to consider distributed solutions that make use of the local processors and do not use a central computer. Our algorithm is especially suited to run in a distributed setting. If the local processors are sufficiently powerful, this allows an order of magnitude increase in computational efficiency. More importantly, a distributed implementation provides strong robustness guarantees, and eliminates the existence of a single point of failure that is inherent when the application is coordinated by a central computer. We show how to efficiently overcome processor crashes and communication failures with a minimal reduction in the quality of the algorithm’s results. This paper is an extension of Avidan et al. (2004), which appeared in ECCV-04.     

Chemical transformation of 3-bromo-2,2-bis(bromomethyl)-propanol under basic conditions

The mechanism of the spontaneous decomposition of 3-bromo-2,2-bis(bromomethyl)propanol (TBNPA) and the kinetics of the reaction of the parent compound and two subsequent products were determined in aqueous solution at temperatures from 30 to 70 degrees C and pH from 7.0 to 9.5. TBNPA is decomposed by a sequence of reactions that form 3,3-bis(bromomethyl)oxetane (BBMO), 3-bromomethyl-3-hydroxymethyloxetane (BMHMO), and 2,6-dioxaspiro[3.3]-heptane (DOH), releasing one bromide ion at each stage. The pseudo-first-order rate constant of the decomposition of TBNPA increases linearlywith the pH. The apparent activation energy of this transformation (98+/-2 KJ/mol) was calculated from the change of the effective second-order rate constant with temperature. The pseudoactivation energies of BBMO and BMHMO were estimated to be 109 and 151 KJ/mol, respectively. Good agreement was found between the rate coefficients derived from changes in the organic molecules concentrations and those determined from the changes in the Br- concentrations. TBNPA is the most abundant semivolatile organic pollutant in the aquitard studied, and together with its byproducts they posess an environmental hazard. TBNPA half-life is estimated to be about 100 years. This implies that high concentrations of TBNPA will persist in the aquifer long after the elimination of all its sources.     

Hot‐fillable containers containing PET/PEN copolymers and blends

Bottles and containers made of PET are not suitable for hot filling since the limiting upper‐use temperature of this polymer is about 85°C. In the present study the properties and performance of bottles made from copolymers and blends of PET containing NDC groups and manufactured by the Injection Stretch Blow Molding (ISBM) process were investigated. These compositions possess advanced properties and can be used up to 95°C. The properties of these bottles were found to depend on their composition and microstructure. The glass transition temperature, the degree of crystallinity and the induced strains that were measured by differential scanning calorimetry and differential mechanical thermal analysis are reported. It was concluded that NDC‐containing PET based copolymers and blends could be processed by a one‐stage ISBM process into containers of improved properties and hot‐filling capabilities. Polym. Eng. Sci. 44:1670–1675, 2004. © 2004 Society of Plastics Engineers.     

Case Studies in Security and Resource Management for Mobile Object Systems

Mobile objects have gained a lot of attention in research and industry in the recent past, but they also have a long history. Security is one of the key requirements of mobile objects, and one of the most researched characteristics related to mobility. Resource management has been somewhat neglected in the past, but it is being increasingly addressed, in both the context of security and QoS. In this paper we place a few systems supporting mobile objects in perspective based upon how they address security and resource management. We start with the theoretical model of Actors that supports concurrent mobile objects in a programming environment. Then we describe task migration for the Mach microkernel, a case of mobile objects supported by an operating system. Using the OMG MASIF standard as an example, we then analyze middleware support for mobile objects. Mobile Objects and Agents (MOA) system, is an example of middleware level support based on Java. The active networks project, Conversant, supports object mobility at the communication protocol level. We summarize these projects, comparing their security and resource management, and conclude by deriving a few general observations on how security and resource management have been applied and how they might evolve in the future.