Method for calculating the coupling coefficient in step-index optical fibers

A simple method is proposed for determining the mode coupling coefficient D in step-index multimode optical fibers. It only requires observation of the far-field output pattern for one fiber length with the input light launched centrally along the fiber axis (theta(0)=0). For illustration, the coupling coefficient determined by this simple method for a step-index plastic optical fiber was used to calculate the coupling length L(c) at which the equilibrium mode distribution is achieved, and length z(s) at which the steady-state distribution is achieved. Our results are in good agreement with experimental results reported earlier.     

Mode coupling in strained and unstrained step-index plastic optical fibers

Using the power-flow equation, we have examined the state of mode coupling in strained and unstrained step-index plastic optical fibers. The strained fibers show much stronger mode coupling than unstrained fibers of the same types. As a result, the coupling lengths where equilibrium mode distribution is achieved and the lengths of fiber required for achieving a steady-state mode distribution for strained fibers are much shorter than the corresponding lengths for unstrained fibers.     

Cooperative multicast for maximum network lifetime

We consider cooperative data multicast in a wireless network with the objective to maximize the network lifetime. We present the maximum lifetime accumulative broadcast (MLAB) algorithm that specifies the nodes' order of transmission and transmit power levels. We prove that the solution found by MLAB is optimal but not necessarily unique. The power levels found by the algorithm ensure that the lifetimes of the active relays are the same, causing them to fail simultaneously. For the same battery levels at all the nodes, the optimum transmit powers become the same. The simplicity of the solution is made possible by allowing the nodes that are out of the transmission range of a transmitter to collect the energy of unreliably received overheard signals. As a message is forwarded through the network, nodes will have multiple opportunities to reliably receive the message by collecting energy during each retransmission. We refer to this cooperative strategy as accumulative multicast. Cooperative multicast not only increases the multicast energy-efficiency by allowing for more energy radiated in the network to be collected, but also facilitates load balancing by relaxing the constraint that a relay has to transmit with power sufficient to reach its most disadvantaged child. When the message is to be delivered to all network nodes this cooperative strategy becomes accumulative broadcast (Maric and Yates, 2002). Simulation results demonstrate that cooperative broadcast significantly increased network lifetime compared with conventional broadcast. We also present the distributed MLAB algorithm for accumulative broadcast that determines the transmit power levels locally at the nodes.     

Discrete Memoryless Interference and Broadcast Channels With Confidential Messages: Secrecy Rate Regions

We study information-theoretic security for discrete memoryless interference and broadcast channels with independent confidential messages sent to two receivers. Confidential messages are transmitted to their respective receivers while ensuring mutual information-theoretic secrecy. That is, each receiver is kept in total ignorance with respect to the message intended for the other receiver. The secrecy level is measured by the equivocation rate at the eavesdropping receiver. In this paper, we present inner and outer bounds on secrecy capacity regions for these two communication systems. The derived outer bounds have an identical mutual information expression that applies to both channel models. The difference is in the input distributions over which the expression is optimized. The inner bound rate regions are achieved by random binning techniques. For the broadcast channel, a double-binning coding scheme allows for both joint encoding and preserving of confidentiality. Furthermore, we show that, for a special case of the interference channel, referred to as the switch channel, derived bounds meet. Finally, we describe several transmission schemes for Gaussian interference channels and derive their achievable rate regions while ensuring mutual information-theoretic secrecy. An encoding scheme in which transmitters dedicate some of their power to create artificial noise is proposed and shown to outperform both time-sharing and simple multiplexed transmission of the confidential messages.     

Multirate fiber-optic CDMA: system design and performance analysis

In this paper, we discuss possibilities of multirate transmission using fiber-optics code-division multiple-access (CDMA) networks. Two schemes are introduced: the parallel scheme and the serial mapping scheme. The theory of optical CDMA is reviewed and the basic properties of OOC families used in the paper given. Also a new property of optical orthogonal code (OOC) sequences is introduced which greatly increases the number of sequences in the network. Performance analysis of the two systems is done using as the parameter the number of simultaneous different-rate users as a function of the required probabilities of error. It is shown that addition of error correction coding increases the number of users in the network. Examples of the two systems are given and it is shown that a high number of different-rate users can be accommodated in the network with no increase in the complexity of optical processing     

A Novel Approach to Modeling and Simulation of NTC Thick-Film Segmented Thermistors for Sensor Applications

This paper describes the design, modeling, simulation, and fabrication of thick-film segmented thermistors. These thermistors were printed on alumina using negative temperature coefficient 3K3 paste, composed of nanometer powder. Their room temperature resistance was measured versus the number of segments and electrode surface value for the fixed layer thickness and electrode spacing. After that, very large thermistors were printed to serve as both the powerful self-heaters and the heat loss sensors in the thermistor volume air flow meter and anemometer. For an application in AC bridges, impedance Z(f) and insertion loss S21 [dB] of the same largest segmented thermistor were measured using network analyzer HP8752A. Impedance modeling was performed using simple equivalent electrical circuit with circuit parameters estimated by fitting procedure (traditional approach), as well as using a commercial electromagnetic simulation program microwave office (MWO, novel approach). This was followed by the modeling of electrical current distribution over a number of segments done within the MWO. The results obtained from simulations and measurements were mutually compared.     

Estrogen and the neural mediation of female–male mounting in the rat.

Sexually receptive females mount sexually sluggish males to entice them to copulate, and estrogen and male olfactory cues mediate this female–male mounting (FMM) in the rat. This study examined whether brain regions that concentrate steroid hormones and receive olfactory projections were important for the mediation of FMM. Fos induction was observed within the medial amygdala, medial preoptic area, and ventromedial hypothalamus of ovariectomized, hormone-primed rats that displayed FMM compared with rats that did not. Excitotoxic lesions of those regions eliminated FMM, whereas implants of crystalline estradiol benzoate to the ventromedial hypothalamus, but not the medial preoptic area or medial amygdala, restored FMM. These data indicate that the ventromedial hypothalamus is a critical area of convergence of hormonal, olfactory, and somatosensory inputs for FMM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Crystallization and microstructure of metastable water quenched nanostructured 8 mol% yttria-stabilized zirconia using the solution precursor plasma spray method

A t′ tetragonally structured metastable 8 mol% yttria-stabilized zirconia (8 mol% YSZ) nanomaterial was synthesized by means of solution thermal plasma spray with water quenching of reacted species. Synthesis of the 8 mol% YSZ powder involved vaporization of a liquid precursor injected into a plasma jet where individual droplets, depending on their trajectory within the plasma, experienced varied thermal histories. Thus, not all the material produced underwent a complete gel → glass → nanocrystalline transformation sequence. Consequently, the collected powder contained a proportion of gel and glass (amorphous) state material. Additionally, the powder contained nano-scale and small micron-scale rapidly solidified 8 mol% YSZ particles. Following thermal treatment, the gel and the amorphous content transformed to produce (i) densely packed nanograin and (ii) chain-like nanograin aggregates. The nanograin aggregates are suggestive of a strong, yet short-range intergranular attraction, as predicted in computer simulation studies presented in the literature. Interestingly, this mixed morphology powder, after compaction and heat treatment at 1400 °C for 2 h, transformed into 98 % dense material with a homogeneous 200–500 nm grain size. For generating 8 mol% YSZ, the solution precursor plasma spray method offers a high synthesis rate using a low-cost precursor to produce powder that can be consolidated into morphologically homogeneous bulk nanomaterial.