High Differential Group Index of Dispersion Compensating Fibers for OCDMA Encoder/Decoder

We report the LPG pair device that can be used as a pulse duplicator or an OCDMA encoder/decoder. Due to the ring core region of dispersion compensating fiber (DCF), we can shorten the device length by a third and obtain surrounding insensitive LPG devices.

Urbanization between compactness and dispersion:designing a spatial model for measuring 2D binary settlement landscape configurations

Measuring spatial patterns is a crucial task in spatial sciences.Multiple indicators have been developed to measure patterns in a quantitative manner.However,most comparative studies rely on relative comparisons,limiting their explanatory power to specific case studies.Motivated by advancements in earth observation providing unprecedented resolutions of settlement patterns,this paper suggests a measurement technique for spatial patterns to overcome the limits of relative comparisons.We design a model spanning a feature space based on two metrics-largest patch index and number of patches.The feature space is defined as‘dispersion index’and covers the entire spectrum of possible two-dimensional binary(settlement)patterns.The model configuration allows for an unambiguous ranking of each possible pattern with respect to spatial dispersion.As spatial resolutions of input data as well as selected areas of interest influence measurement results,we test dependencies within the model.Beyond,common other spatial metrics are selected for testing whether they allow unambiguous rankings.For scenarios,we apply the model to artificially generated patterns representing all possible configurations as well as to real-world settlement classifications differing in growth dynamics and patterns.

Use of probabilistic and deterministic measures to identify unfavorable earthquake records

This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function (PSDF) of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records.

Understanding Broad Polydispersity in Step-growth Polymerization via Catalyst Competition Mechanism

Conjugated polymers are mainly synthesized by cross-coupling polymerizations catalyzed with transition metal(Pd,Ni)catalysts through step-growth polymerization(SGP)mechanism.According to the classical theory of SGP,the polymer dispersion index(D)of the synthesized polymers will never be higher than 2.However,the cases where conjugated polymers synthesized with D value far exceeding 2 are very common in reality,which severely limits their processing property,performance and applications.To investigate the reason behind the D value deviation from the theoretical value of SGP,direct arylation polycondensation(DArP)of 2-bromo-3-hexylthiophene(3HT)was chosen as the model reaction,and the reaction process was tracked using gel permeation chromatography analysis.When Pd(OAc)_(2) was used as the catalyst,the D value linearly increased with the increase of the weight-average molecular weight(M_(w))of polymer(P3HT)after a short period and reached up to 7.2 at prolonged reaction time.Scanning transmission electron microscopic images of the reaction mixture showed the fibril-like aggregation of P3HT and assembling of Pd species in P3HT aggregates.A catalyst competition mechanism was thus proposed,together with numerical calculation,giving a good fitting to the experimental results,which is believed to have far-reaching significance for guiding the design,synthesis and processing of conjugated polymers.