Strategies to maximize carried traffic in dual-mode cellularsystems

Dual-mode cellular systems based on the EIA/TIA IS-54 standard offer the eventual prospect of carrying up to six digital calls in the same bandwidth as a single analog call. During the transition from analog to digital service, however, the call-carrying capacity of such systems will be limited by the presence of existing analog users. In this situation, it is reasonable to ask if there are call-handling strategies that could increase the total traffic carried by providing preferential treatment to digital users. We consider four such strategies for maximizing the total traffic carried by a dual-mode cellular system. For two of these strategies, including the baseline “no-control” strategy we develop closed-form solutions for carried traffic and other related service statistics. The closed-form solution for the no-control case is then extended to provide a tight upper bound on carried traffic for any control strategy. We also present a method for finding the optimal control strategy by applying linear programming (LP) techniques. The strategies are compared for various proportions of analog and digital users and offered traffic levels. The findings show that it is actually quite difficult to obtain gains using strategies that exploit the difference in spectral efficiency between analog and digital calls, even with formally optimal strategies. While this is an unexpected finding, we feel the conclusion has been well validated and is now understood and explained in the paper     

Characterization of wavelength-selective fiber-optic devices usinga modified phase-shift method

We present a novel measurement setup that can be used for the complete characterization of fiber Bragg gratings and wavelength selective fiber-optic devices. Our setup is based on the phase-shift method (PSM), which we have modified to include the measurement of polarization-induced effects such as polarization-dependant loss (PDL) and polarization-mode dispersion (PMD). We measure the spectral response of devices used in transmission and in reflection, the wavelength dependency of the group delays due to chromatic and polarization-mode dispersion, and the wavelength dependency of the polarization-dependent loss. Experimental results are presented and sources of error are discussed. Comparisons with the Jones matrix eigenanalysis method for the measurement of PDL and differential group delay due to PMD have been carried out     

Laterally coupled InP-based single-mode microracetrack notch filter

We demonstrate an InP-based microracetrack notch filter with >25-dB extinction and 19-nm free-spectral range at 1550 nm. The curved section of the resonator has a radius of 2.25 /spl mu/m. To our knowledge, this represents the best extinction and the smallest radius of curvature for such a device to date.     

Engineering implementation of a hybrid optical correlator using SLMs

Optical correlators have been widely used for such applications as automatic target identification, invariant pattern recognition and machine vision. In hybrid optical correlators, Spatial light modulators (SLMs) are used to dynamically update the input and the filter. However, implementation is difficult because of the interference of “ghost” images; rigorous requirements for filter registration, accurate and effective filter sizing and complex valued filtering functions. This paper proposes some practical approaches to handle these issues and provides engineering details of how to build a hybrid optical correlator, where a SLM serves as an updateable intensity filter for real-time pattern recognition.     

Total Synthesis of (+)‐6‐epi‐Ophiobolin A

The ophiobolin sesterterpenes are notable plant pathogens which have recently elicited significant chemical and biological attention because of their intriguing carbogenic frameworks, reactive functionalities, and emerging anticancer profiles. Reported herein is a total synthesis of (+)‐6‐epi‐ophiobolin A in 14 steps, a task which addresses construction of the synthetically challenging spirocyclic tetrahydrofuran motif as well as several other key stereochemical problems. This work demonstrates a streamlined synthetic platform to complex ophiobolins leveraging disparate termination modes of a radical polycyclization cascade for divergent elaboration and functionalization.     

Bridging and Conformational Control of Porphyrin Units through Non-Traditional Rigid Scaffolds

Connecting two porphyrin units in a rigid linear fashion, without any undesired electron delocalization or communication between the chromophores, remains a synthetic challenge. Herein, a broad library of functionally diverse multi-porphyrin arrays that incorporate the non-traditional rigid linker groups cubane and bicyclo[1.1.1]pentane (BCP) is described. A robust, reliable, and versatile synthetic procedure was employed to access porphyrin-cubane/BCP-porphyrin arrays, representing the largest non-polymeric structures available for cubane/BCP derivatives. These reactions demonstrate considerable substrate scope, from utilization of small phenyl moieties to large porphyrin rings, with varying lengths and different angles. To control conformational flexibility, amide bonds were introduced between the bridgehead carbon of BCP/cubane and the porphyrin rings. Through varying the orientation of the substituents around the amide bond of cubane/BCP, different intermolecular interactions were identified through single crystal X-ray analysis. These studies revealed non-covalent interactions that are the first-of-their-kind including a unique iodine-oxygen interaction between cubane units. These supramolecular architectures indicate the possibility to mimic a protein structure due to the sp³ rigid scaffolds (BCP or cubane) that exhibit the essential conformational space for protein function while simultaneously providing amide bonds for molecular recognition.     

Stabilization of hydrated AcIII cation: the role of superatom states in actinium-water bonding

²²⁵Ac-based radiopharmaceuticals have the potential to become invaluable in designated cancer therapy. However, the limited understanding of the solution chemistry and bonding properties of actinium has hindered the development of existing and emerging targeted radiotherapeutics, which also poses a significant challenge in the discovery of new agents. Herein, we report the geometric and electronic structural properties of hydrated Ac^III cations in the [Ac^III(H₂O)_n]³⁺ (n = 4–11) complexes in aqueous solution and gas-phase using density functional theory. We found that nine water molecules coordinated to the Ac^III cation is the most stable complex due to an enhanced hydration Gibbs free energy. This complex adopts a closed-shell 18-electron configuration (1S²1P⁶1D¹⁰) of a superatom state, which indicates a non-negligible covalent character and involves H₂O → Ac^III σ donation interaction between s-/p-/d-type atomic orbitals of the Ac atom and 2p atomic orbitals of the O atoms. Furthermore, potentially existing 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination. These results imply the importance of superatom states in actinide chemistry generally, and specifically in Ac^III solution chemistry, and highlight the conversion mechanism between different coordination numbers.

The stable 9-coordinated complex adopts a closed-shell 18-electron configuration of a 1S²1P⁶1D¹⁰ jellium state, while potential 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination.     

Vortex phase diagram studies in the weakly pinned single crystals of YNi2B2C and LuNi2B2C

We present a study of magnetization measurements performed on the single crystals of YNi₂B₂C and LuNi₂B₂C. For both the compounds, we find flux jumps in magnetisation values in the respective field regions, where the structural transitions in the flux line lattice symmetry have been reported in these systems via the small angle neutron scattering experiments. The magnetisation hysteresis loops and the AC susceptibility measurements show pronounced peak effect as well as second magnetisation peak anomaly for both YNi₂B₂C and LuNi₂B₂C. Based on these results, a vortex phase diagram has been constructed for YNi₂B₂C forH∥c depicting different glassy phases of the vortex matter.     

Size dependence of the Mössbauer effect in one-dimension

Employing a model of coupled harmonic oscillators we analyze the nature of recoilless emission in the Mössbauer effect for a finite sized 1D lattice. We demonstrate explicitly that under certain assumptions, recoilless probability first attains a maximum for a certain lattice size and then decreases with increasing lattice size. Further, we derive a scaling relation for this variation. Our treatment may have relevance to the recoilless probability in finite clusters such as nanocrystals and nanowires.     

Distributed partial-express routing of broad-band transport networkdemands

There are a number of contexts in transport network design where cost savings arise from providing a dedicated transmission system between two nonadjacent nodes. This occurs when the cost to terminate demands at intermediate cross-connecting and grooming nodes exceeds the alternative of providing a dedicated, perhaps only partly filled, system. Today, dedicated end-to-end “express routes” are usually found where large demands flow between major centers or to/from hubbing sites where traffic can be aggregated to warrant an express system. Smaller demand flows are usually terminated at each flexibility point en route to permit remultiplexing with other demands, thereby keeping the fiber system fill high. We consider a new means to find economic express system opportunities among combinations of the smaller co-routed demands. The hypothesis is that certain collections of demand may warrant express treatment over some common portion of their routes. These demands need not share common end nodes or be aggregated at a hub. Rather, they are discovered among the natural pattern of demand flows as a group of demands that travel together over some sequence of spans on which an express system might be cost-effective. The search problem is to detect the maximally coherent subgroups of demands en route that yield the best economic payback. Test results were obtained in four representative transport network topology and demand matrix models. Assuming a 75% level of system fill in the nonexpress baseline case, opportunities worth up to $45 M in equipment savings, relative to conventional design, were obtained using industry-supplied cost data. The concept of distributed partial-express system design may also be applicable to WDM-based networks to assign OC-n level units of demand to various express or nonexpress wavelengths