ATM support in a transparent network

A generic approach to the mapping of various routing modes and packet formats onto different link layers in the plaNET network is discussed. It is argued that the necessary transformations can be performed relatively easily, at little additional cost to the network and, more importantly, without performance degradation. The approach taken and components used in plaNET to provide the simple interfacing with ATM (asynchronous transfer mode) networks and links are described     

Computing shortest paths for any number of hops

In this paper, we introduce and investigate a "new" path optimization problem that we denote the all hops optimal path (AHOP) problem. The problem involves identifying, for all hop counts, the optimal, i.e., minimum weight, path(s) between a given source and destination(s). The AHOP problem arises naturally in the context of quality-of-service (QoS) routing in networks, where routes (paths) need to be computed that provide services guarantees, e.g., delay or bandwidth, at the minimum possible "cost" (amount of resources required) to the network. Because service guarantees are typically provided through some form of resource allocation on the path (links) computed for a new request, the hop count, which captures the number of links over which resources are allocated, is a commonly used cost measure. As a result, a standard approach for determining the cheapest path available that meets a desired level of service guarantees is to compute a minimum hop shortest (optimal) path. Furthermore, for efficiency purposes, it is desirable to precompute such optimal minimum hop paths for all possible service requests. Providing this information gives rise to solving the AHOP problem. The paper's contributions are to investigate the computational complexity of solving the AHOP problem for two of the most prevalent cost functions (path weights) in networks, namely, additive and bottleneck weights. In particular, we establish that a solution based on the Bellman-Ford algorithm is optimal for additive weights, but show that this does not hold for bottleneck weights for which a lower complexity solution exists.     

Optimal multiplexing on a single link: delay and bufferrequirements

This paper is motivated by the need to provide per-session quality of service guarantees in fast packet-switched networks. We address the problem of characterizing and designing scheduling policies that are optimal in the sense of minimizing buffer and/or delay requirements under the assumption of commonly accepted traffic constraints. We investigate buffer requirements under three typical memory allocation mechanisms which represent tradeoffs between efficiency and complexity. For traffic with delay constraints we provide policies that are optimal in the sense of satisfying the constraints if they are satisfiable by any policy. We also investigate the tradeoff between delay and buffer optimality, and design policies that are “good” (optimal or close to) for both. Finally, we extend our results to the case of “soft” delay constraints and address the issue of designing policies that satisfy such constraints in a fair manner. Given our focus on packet switching, we mainly concern ourselves with nonpreemptive policies, but one class of nonpreemptive policies which we consider is based on tracking preemptive policies. This class is introduced and may be of interest in other applications as well     

Smart polymer nanoparticles designed for environmentally compliant coatings

We describe the synthesis, characterization, and film-forming properties of two-component nanoparticles that undergo a reversible morphology transformation in water as a function of pH. The particles consist of a high molecular weight acrylate copolymer and an acid-rich oligomer designed to be miscible with the polymer when its -COOH groups are protonated. Attaching a fluorescence resonance energy transfer (FRET) pair to components inside the nanoparticles enabled us to assess morphology at the molecular level. By inspecting changes in the donor fluorescence decay profile at different pH values, we established miscibility of the components in acidic solution but with charge-induced phase separation when the oligomers were neutralized to their carboxylate form. Complementary titration experiments revealed that the nanoparticles adopt a core-shell structure when the acid groups are deprotonated. We studied the effect of the acid-rich oligomer on the diffusion rate of the high molecular weight polymers following film formation. Our results show that the carboxylated oligomer enhanced the rate of diffusive mixing between high molecular weight molecules by more than 2 orders of magnitude. FRET measurements carried out on partially dried films using a low-resolution microscope showed that the carboxylate oligomer shell can delay coalescence for ca. 30 min after passage of the drying front. This delay is expected to help with increasing the 'open time' of latex paints, a desirable property of solvent-based paints that remains difficult to achieve with (environmentally compliant) waterborne paints. Use of ammonia as a volatile base resulted in synergistic effects: initial retardation of coalescence followed by acceleration of diffusive mixing as the ammonium salts dissociated and ammonia evaporated from the film.     

Guided quasicontinuous atom laser

We report the first realization of a guided quasicontinuous atom laser by rf outcoupling a Bose-Einstein condensate from a hybrid optomagnetic trap into a horizontal atomic waveguide. This configuration allows us to cancel the acceleration due to gravity and keep the de Broglie wavelength constant at 0.5 microm during 0.1 s of propagation. We also show that our configuration, equivalent to pigtailing an optical fiber to a (photon) semiconductor laser, ensures an intrinsically good transverse mode matching.     

Queueing-blocking system with two arrival streams and guardchannels

An approach to the study of a multichannel cutoff priority system for two Poisson arrival streams with distinct arrival rates and the same potential service time distribution is proposed. This approach makes it possible to obtain the state probabilities in simple closed-form expressions. These expressions provide a straightforward way to derive the distribution of the number of busy servers, the queue length distributions, and, above all, a very simple criterion for the stability of the system. The computations can still be carried out for large systems (e.g. 100 servers). The method can easily be extended from the infinite-queue-length case to a system with finite capacity. As applied to cellular radio, the method offers a means of increasing the total carried traffic while improving the perceived service quality     

Current transport characteristics of SiGeC/Si heterojunction diode

The characteristics of heterojunction diodes fabricated from p-type epitaxial Si_0.07Ge_0.91C_0.02 alloy grown by molecular beam epitaxy on n-type Si(100) have been examined by using current-voltage, capacitance-voltage, and Hall effect measurements. The SiGeC/Si heterojunction diode shows good rectification with nearly ideal forward bias behavior and low reverse leakage currents compared to Ge/Si heterojunction diodes. The temperature dependence of the current-voltage behavior indicates that the principle conduction mechanism is by electron injection over a barrier. Reverse breakdown occurs by the avalanche mechanism     

Reliability estimation of aeronautic component by accelerated tests

This article presents a reliability assessment of aeronautic electronic board using the accelerated test approach. The mission profile used is one defined in FIDES for electronic equipment in aircraft. The reliability function is defined taking into account the different phases of product life (Ground, Taxiing, Flying, Dormant). FIDES describes the environment (thermal and humidity, thermal cycling, mechanical, …) for each phase. The paper presents the different accelerated life models used to take into account all environment. A test plan is proposed to estimate the unknown parameters of accelerated life models. The thermal and humidity and thermal cycling tests have been performed and the data are analyzed. Finally, the reliability function is evaluated.     

Alkali metal hydrides: New metallating reagents for germanium and tin

New procedures for the preparation of organogermyl- and stannyl-sodium or -potassium, which undergo coupling reactions with alkyl, allyl, and benzyl halides and α-enones, are reported.