Experimental Evaluation of the Optical Properties of Porous Silica/Carbon Composite Particles

Light scattering by porous spheroidal silica and several silica/carbon composite particles having different carbon contents was systematically investigated using a laser particle counter coupled with a pulse height analyzer (LPC-PHA). A new and simple method for the measurements of the effective complex refractive index of silica/carbon composite particles using a conventional LPC-PHA system and a differential mobility analyzer was introduced and tested. Challenge particles, from pure silica to silica/carbon compounds having a gradually increasing porous structure, were prepared by spray-drying methods for use in testing of the inversion method. By representing the deviation of the real part of the refractive index of a porous silica particle versus the size on a topographical map, the inversion method for the determination of the real part of the refractive indices was found to have a satisfactory precision. Furthermore, the method can be applied to the measurement of the complex refractive index of silica/carbon composite particles by extending the best fitting method to complex refractive indices. The effective complex refractive index of silica/carbon composite particles as a function of their carbon content is reported. Both the real and imaginary parts of the complex refractive index were increased with increasing carbon content of the composite particles.     

Dielectric response of ionically conducting liquids in thelow-frequency region

The selected dielectric studies are presented of ionically conducting materials (liquid crystal, epoxide resin) in the range of time, 10^-4 to 10⁴ s, or frequency, 10^-4 to 10⁴ Hz. The properties of the space charge at the blocking electrodes were taking into account. Investigations were focused on the time domain dielectric response of the model liquid crystalline pentylcyanobiphenyl. Similar studies were performed also on the epoxide resin Epidian 3. An influence of external parameters like temperature or concentration of impurities were included to interpret the obtained results. This interpretation was established on the principles of the two theoretical models for the space charge polarization     

Get in touch: cooperative decision making based on robot-to-robot collisions

We demonstrate the ability of a swarm of autonomous micro-robots to perform collective decision making in a dynamic environment. This decision making is an emergent property of decentralized self-organization, which results from executing a very simple bio-inspired algorithm. This algorithm allows the robotic swarm to choose from several distinct light sources in the environment and to aggregate in the area with the highest illuminance. Interestingly, these decisions are formed by the collective, although no information is exchanged by the robots. The only communicative act is the detection of robot-to-robot encounters. We studied the performance of the robotic swarm under four environmental conditions and investigated the dynamics of the aggregation behaviour as well as the flexibility and the robustness of the solutions. In summary, we can report that the tested robotic swarm showed two main characteristic features of swarm systems: it behaved flexible and the achieved solutions were very robust. This was achieved with limited individual sensor abilities and with low computational effort on each single robot in the swarm.     

Efficient and inefficient ant coverage methods

Ant robots are simple creatures with limited sensing and computational capabilities. They have the advantage that they are easy to program and cheap to build. This makes it feasible to deploy groups of ant robots and take advantage of the resulting fault tolerance and parallelism. We study, both theoretically and in simulation, the behavior of ant robots for one-time or repeated coverage of terrain, as required for lawn mowing, mine sweeping, and surveillance. Ant robots cannot use conventional planning methods due to their limited sensing and computational capabilities. To overcome these limitations, we study navigation methods that are based on real-time (heuristic) search and leave markings in the terrain, similar to what real ants do. These markings can be sensed by all ant robots and allow them to cover terrain even if they do not communicate with each other except via the markings, do not have any kind of memory, do not know the terrain, cannot maintain maps of the terrain, nor plan complete paths. The ant robots do not even need to be localized, which completely eliminates solving difficult and time-consuming localization problems. We study two simple real-time search methods that differ only in how the markings are updated. We show experimentally that both real-time search methods robustly cover terrain even if the ant robots are moved without realizing this (say, by people running into them), some ant robots fail, and some markings get destroyed. Both real-time search methods are algorithmically similar, and our experimental results indicate that their cover time is similar in some terrains. Our analysis is therefore surprising. We show that the cover time of ant robots that use one of the real-time search methods is guaranteed to be polynomial in the number of locations, whereas the cover time of ant robots that use the other real-time search method can be exponential in (the square root of) the number of locations even in simple terrains that correspond to (planar) undirected trees. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Self-selection Technique for Flooding and Routing in Wireless Ad-hoc Networks

There is a fundamental difference between wireless and wired networks, since the latter employ point-to-point communication while the former use broadcast transmission as the communication primitive. In this paper, we describe an algorithm, called self-selection, which takes advantage of broadcast communication to efficiently implement the basic operation of selecting a node possessing some desired properties among all the neighbors of the requestor. Self-selection employs a prioritized transmission back-off delay scheme in which each node’s delay of transmitting a signal is dependent on the probability of the node’s ability to best perform a pertinent task, and in turn, enables the node to autonomously select itself for the task. We demonstrate the benefits of self-selection in two basic wireless ad hoc network communication algorithms: flooding and routing. By relating back-off delay to the signal strength of a received packet, we design an efficient variant of conventional flooding called Signal Strength Aware Flooding. By using distance-to-destination to derive back-off delay, we design a novel and fault-tolerant wireless ad hoc network routing protocol named Self-Selective Routing.

Minimizing cycle time and group scheduling, using Petri nets a study of heuristic methods

The objective of this paper is a study of minimizing the maximum completion time min F _max, or cycle time of the last job of a given family of jobs using flow shop heuristic scheduling techniques. Three methods are presented: minimize idle time (MIT); Campbell, Dudek and Smith (CDS); and Palmer. An example problem with ten jobs and five machines is used to compare results of these methods. A deterministic t-timed colored Petri net model has been developed for scheduling problem. An execution of the deterministic timed Petri net allows to compute performance measures by applying graph traversing algorithms starting from initial global state and going into a desirable final state(s) of the production system. The objective of the job scheduling policy is minimizing the cycle time of the last job scheduled in the pipeline of a given family of jobs. Three heuristic scheduling methods have been implemented. First, a sub-optimal sequence of jobs to be scheduled is generated. Second, a Petri net-based simulator with graphical user interface to monitor execution of the sequence of tasks on machines is dynamically designed. A deterministic t-timed colored Petri net model has been developed and implemented for flexible manufacturing systems (FMS). An execution of the deterministic timed Petri net into a reachability graph allows to compute performance measures by applying graph traversing algorithms starting from initial global state to a desirable final state(s) of the production system.     

Primary structure of 2S albumin from seeds of Lupinus cosentinii

 The 2S albumin from seeds of Lupinus cosentinii Guss. was purified, and the complete amino acid sequences of the dominating small and large subunit were determined by automated Edman degradation of the reduced and S-pyridylethylated polypeptides and of their enzymatic fragments. The small subunit of the 2S albumin consists of 35 amino acid residues resulting in a molecular mass (M _r) of 4233. The large subunit contains 73 amino acid residues (M _r = 8627). The two polypeptide chains are linked by two interchain disulphide bonds. In addition, the large polypeptide contains two intrachain disulphide bridges and one free sulphydryl group. A high degree of homology (88–89%) exists between the primary structure of the 2S albumin from L. cosentinii and those from other Lupinus species. The positions of the cysteines and of some other amino acids are conserved not only in most of the Dicotyledoneae 2S albumins sequenced so far but also in other storage proteins. Received: 26 May 1997     

Primary structure of 2S albumin from seeds of Lupinus albus

 The 2S albumin from the seeds of white lupin (Lupinus albus L.) was purified by ammonium sulfate precipitation and ultrafiltration followed by anion-exchange and reversed-phase HPLC. The complete amino acid sequences of the large and the dominating small subunit were determined by automated Edman degradation of the reduced and S-pyridylethylated polypeptides and of their enzymatic fragments. The small subunit of the 2S albumin (a) consists of 37 amino acid residues resulting in a molecular mass M _r of 4407. The large subunit (b) contains 75 amino acid residues (M _r=8827). The two polypeptide chains are linked by two interchain disulfide bonds (Cys^a8-Cys^b24 and Cys^a20-Cys^b13 or, more probably, Cys^a20-Cys^b12). In addition, the large polypeptide contains two intrachain disulfide bridges (Cys^b26-Cys^b68 and Cys^b12-Cys^b60 or, more probably, Cys^b13-Cys^b60) and one free sulfhydryl group (Cys^b40). A high degree of homology (88%) exists between the primary structure of the 2S albumin from L. albus and that of a comparable 2S protein from L. angustifolius, designated conglutin δ. Received: 4 April 1996