Interconversion Scheme Research Articles

Flexible All-Optical 8QAM Signal Format Conversion Using Pump Assisted Nonlinear Optical Loop Mirror

A flexible all-optical format interconversion scheme based on a pump assisted nonlinear optical loop mirror (NOLM) is proposed and numerically simulated for the first time to our knowledge. In this scheme, input multi-Gbps 8QAM signals are divided into clockwise (CW) and counter-clockwise (CCW) components by a 3-dB optical coupler (OC), which also couples light from the input pump into the NOLM from the CCW direction. The numerical model of the pump assisted NOLM with CW and CCW optical paths is simplified using a nonlinear Mach-Zehnder interferometer (MZI). Optical signals in the upper MZI arm will be mainly affected by the self-phase modulation (SPM) effect when traversing the highly nonlinear fiber (HNLF) and those in the lower MZI arm are impacted by cross-phase modulation (XPM) in addition to SPM when they experience the HNLF with the input pump light. When the upper-arm optical signal with SPM phase shift and the lower arm optical signal with SPM and XPM phase shifts are coherently mixed, a new converted 8QAM signal can be obtained. The power transfer function (PTF) of the pump assisted NOLM and the relative phase shift (RPS) between the input and the output optical signals are theoretically provided and verified. By only changing the input power of the 8QAM signal and the pump light, all-optical format interconversion of square-, standard- and star-shaped 8QAM signals can be achieved. Furthermore, the proposed scheme can achieve format conversion from the 30 Gbps square-shaped 8QAM signal to a 20 Gbps quadrature phase shift keying (QPSK) signal. The scheme performance is analyzed via constellation diagrams, eye diagrams, the error vector magnitude (EVM) and the bit error rate (BER) of the optical signals. The scheme developed can be deployed in optical gateways to connect different optical networks by dynamically selecting their appropriate modulation formats.

Programmed Pore-Shape Fixing in a Soft Porous Molecular Crystal-Navigating the Phase Interconversion Landscape.

Pore-shape fixing effects (PSFEs) in soft porous crystals are a relatively unexplored area of materials chemistry. We report the PSFE in the prototypical dynamic van der Waals solid p-tert-butylcalix[4]arene (TBC4). Starting with the high-density guest-free phase, two porous shape-fixed phases were programmed using the stimuli of CO2 pressure and temperature. A suite of complementary in situ techniques, including variable-pressure (VP) single-crystal X-ray diffraction, VP powder X-ray diffraction, VP differential scanning calorimetry, volumetric sorption analysis, and attenuated total reflectance Fourier-transform infrared spectroscopy was used to track dynamic guest-induced transformations, providing molecular-level insight into the PSFE. The interconversion between the two metastable phases is particle size dependent, making this the second example of the PSFE by crystal downsizing, and the first example involving a porous molecular crystal: larger particles undergo reversible transitions while smaller particles remain fixed in the metastable phase. A complete phase interconversion scheme was constructed for the material, thus allowing navigation of the phase interconversion landscape of TBC4 using the easily applied stimuli of CO2 pressure and thermal treatment.

Programmed Pore‐Shape Fixing in a Soft Porous Molecular Crystal—Navigating the Phase Interconversion Landscape

AbstractPore‐shape fixing effects (PSFEs) in soft porous crystals are a relatively unexplored area of materials chemistry. We report the PSFE in the prototypical dynamic van der Waals solid p‐tert‐butylcalix[4]arene (TBC4). Starting with the high‐density guest‐free phase, two porous shape‐fixed phases were programmed using the stimuli of CO2 pressure and temperature. A suite of complementary in situ techniques, including variable‐pressure (VP) single‐crystal X‐ray diffraction, VP powder X‐ray diffraction, VP differential scanning calorimetry, volumetric sorption analysis, and attenuated total reflectance Fourier‐transform infrared spectroscopy was used to track dynamic guest‐induced transformations, providing molecular‐level insight into the PSFE. The interconversion between the two metastable phases is particle size dependent, making this the second example of the PSFE by crystal downsizing, and the first example involving a porous molecular crystal: larger particles undergo reversible transitions while smaller particles remain fixed in the metastable phase. A complete phase interconversion scheme was constructed for the material, thus allowing navigation of the phase interconversion landscape of TBC4 using the easily applied stimuli of CO2 pressure and thermal treatment.

Optical format interconversion nodes between OOK and QPSK enabled by a reconfigurable two-dimensional vector mover.

An optical format interconversion scheme between on-off keying (OOK) and quadrature phase shift keying (QPSK) is proposed and verified in this paper. The conversion system mainly consists of a coherent vector combiner and a reconfigurable two-dimensional (2D) vector mover. As a key element of the proposed conversion system, the 2D vector mover is implemented by a non-degenerate phase-sensitive amplifier (PSA). The operating principle and theoretical derivations of the PSA-based 2D vector mover are fully introduced. The reconfigurable transfer characteristics of the vector mover are analyzed under different parameter settings to exhibit the flexible 2D moving function. The signal constellations, eye diagrams, spectrum, error vector magnitudes, and bit error ratios are estimated and depicted to validate the proposed idea. With the input signal-to-noise ratios of 20 dB and 25 dB, error-free conversions are achieved between 50G Baud OOK and QPSK. The scheme proposed in this paper fills the lack of the one-to-one interconversion between OOK and QPSK, and has potential applications in optical interconnect nodes, across-dimensional optical transmissions, and flexible optical transceivers.

A Combined Exponential-Power-Law Method for Interconversion between Viscoelastic Functions of Polymers and Polymer-Based Materials.

Understanding and modeling the viscoelastic behavior of polymers and polymer-based materials for a wide range of quasistatic and high strain rates is of great interest for applications in which they are subjected to mechanical loads over a long time of operation, such as the self-weight or other static loads. The creep compliance and relaxation functions used in the characterization of the mechanical response of linear viscoelastic solids are traditionally determined by conducting two separate experiments—creep tests and relaxation tests. This paper first reviews the steps involved in conducting the interconversion between creep compliance and relaxation modulus in the time domain, illustrating that the relaxation modulus can be obtained from the creep compliance. This enables the determination of the relaxation modulus from the results of creep tests, which can be easily performed in pneumatic equipment or simple compression devices and are less costly than direct relaxation tests. Some existing methods of interconversion between the creep compliance and the relaxation modulus for linear viscoelastic materials are also presented. Then, a new approximate interconversion scheme is introduced using a convenient Laplace transform and an approximated Gamma function to convert the measured creep compliance to the relaxation modulus. To demonstrate the accuracy of the fittings obtained with the method proposed, as well as its ease of implementation and general applicability, different experimental data from the literature are used.

A New Viscoelasticity Dynamic Fitting Method Applied for Polymeric and Polymer-Based Composite Materials.

The accurate analysis of the behaviour of a polymeric composite structure, including the determination of its deformation over time and also the evaluation of its dynamic behaviour under service conditions, demands the characterisation of the viscoelastic properties of the constituent materials. Linear viscoelastic materials should be experimentally characterised under (i) constant static load and/or (ii) harmonic load. In the first load case, the viscoelastic behaviour is characterised through the creep compliance or the relaxation modulus. In the second load case, the viscoelastic behaviour is characterised by the complex modulus, , and the loss factor, . In the present paper, a powerful and simple implementing technique is proposed for the processing and analysis of dynamic mechanical data. The idea is to obtain the dynamic moduli expressions from the Exponential-Power Law Method (EPL) of the creep compliance and the relaxation modulus functions, by applying the Carson and Laplace transform functions and their relationship to the Fourier transform, and the Theorem of Moivre. Reciprocally, once the complex moduli have been obtained from a dynamic test, it becomes advantageous to use mathematical interconversion techniques to obtain the time-domain function of the relaxation modulus, , and the creep compliance, . This paper demonstrates the advantages of the EPL method, namely its simplicity and straightforwardness in performing the desirable interconversion between quasi-static and dynamic behaviour of polymeric and polymer-composite materials. The EPL approximate interconversion scheme to convert the measured creep compliance to relaxation modulus is derived to obtain the complex moduli. Finally, the EPL Method is successfully assessed using experimental data from the literature.

Three-Input Molecular Keypad Lock Based on a Norbornadiene-Quadricyclane Photoswitch.

The photo- and acidochromic properties of a new generation norbornadiene derivative have been harnessed for the realization of a three-input keypad lock, where a specific sequence of inputs induces a unique output. Reversible quadricyclane/norbornadiene photoisomerization is reported, and this rare feature allows the first example of a norbornadiene-based molecular logic system. The function of this system is clearly rationalized in terms of the interconversion scheme and the absorption spectra of the involved species.

Cluster rearrangement of isonido-ruthenacarboranes [1-(η6-1,4-Me2C6H4)-3(6)-Cl-isonido-1,2,4-RuC2B8H9] under thermal conditions

The heating of the isomeric [1-(η6-1,4-Me2C6H4)-3-Cl-isonido-1,2,4-RuC2B8H9] (1) or [1-(η6-1,4-Me2C6H4)-6-Cl-isonido-1,2,4-RuC2B8H9] (2) complexes (i) in a 1,4-Me2C6H4 solution at 85 °C as well as (ii) in a melt at 165 °C afforded mixtures of isomeric isonido- and closo-ruthenacarboranes, which differ in the positions of the chlorine substituent and the carbon atoms in the cage ligand. Structures of all new isomeric complexes have been established on the basis of analytical and multinuclear NMR data and were characterized by single-crystal X-ray diffraction studies. Also presented are the results of the quantum chemical calculations for the ground and the transition states of the reaction (i), which proved to be basis for the suggestion of interconversion scheme for these isomers.

Observation of Secondary Nucleation on Specific Aβ 42 Fibril Type

Amyloid-β (Aβ) fibril formation is the pivotal phenomenon in Alzheimer's disease (AD). However, the understanding of amyloid fibril mechanism has been hindered by its heterogeneous morphology. Further, recent studies point out the existence of new growth sites on pre-existing fibrils, called secondary nucleation, but there is no report of secondary nucleation for Aβ 42. Here we present a detailed inter-conversion scheme of Aβ42 from the study of Aβ fibrillogenesis by means of electron microscopy and atomic force microscopy. We indentified that the secondary nucleation events occur more favorably on specific fibril type during monomer fibrillization. Further, we proved the stability of the most homogeneous and stable Aβ42 fibril type and analyzed the structural elastic properties by using the statistical theory of semi-flexible polymer. The result suggests that lateral association mechanism gives the most structural stability to certain fibril type with a twisted ribbon structure. The extracted elastic modulus of fibrils is ∼ 1.4 GPa on mica and highly ordered pyrolytic graphite. We suggest that elucidation of secondary nucleation events and elastic modulus value will help progress in our understanding of the aggregation mechanism of Aβ 42 fibrillogenesis in AD.

On the Inter-Conversion Between Hermite and Laguerre Local Image Expansions

The nice relationship existing among the Hermite-Gauss and the Laguerre-Gauss image expansions, whose basis functions span the same signal space, is investigated. As a result, a novel efficient method for Cartesian to polar coordinate inter-conversion, especially suited for dedicated hardware realization, is proposed. Applications to local image rotation, based on the simple steerability of the Laguerre-Gauss expansion, and to local image analysis, based on Gaussian derivatives, are considered in detail. A possible fixed-point realization of the proposed inter-conversion scheme is discussed.

Principal Component Analysis Based Interconversion between Infrared and Near-Infrared Spectra for the Study of Thermal-Induced Weak Interaction Changes of Poly(N-Isopropylacrylamide)

The use of a novel spectral interconversion scheme, principal component analysis (PCA) based spectral prediction, to probe weak molecular interactions of a polymer film is reported. A PCA model is built based on a joint data matrix by concatenating two related spectral data matrices (such as infrared (IR) and near-infrared (NIR) spectra) along the variable direction, then the obtained loading matrix of the model is split into two parts to predict the desired spectra. For a better PCA-based prediction, it is suggested that the samples whose spectra are to be predicted should be as similar as possible to those used in the model. Based on the PCA model, the thermal-induced changes in the weak interaction of poly(N-isopropylacrylamide) (PNiPA) film is revealed by the interconversion between selected spectral ranges measured between 40 and 220 degrees C. The thermal-induced weak interaction changes of PNiPA, expressed as either the band shift or intensity changes at a specific region, have been probed properly. Meanwhile, the robustness of the spectral prediction is also compared with that achieved by a partial least squares (PLS2) model in detail, illustrating its advantages in predicting more subtle structural changes such as C-H groups.

Multivariate Prediction of the Thermal-Induced Weak Interaction Changes of Poly(N-Isopropylacrylamide) Film by the Interconversion between Middle and Near-Infrared Spectra

The use of a novel spectral interconversion scheme to probe weak molecular interactions of a polymer system is reported. Based on the multivariate regression model using partial least squares (PLS), the thermally induced changes in the weak interaction of poly(n-isopropylacrylamide) (PNiPA) film was studied by the interconversion between mid-infrared (MIR) and near-infrared (NIR) spectra measured at temperatures between 40 and 220 degrees C. It was demonstrated that not only NIR spectra but also well-resolved MIR spectra of PNiPA film, either in narrow or wide spectral ranges, can be predicted from each other based on the proposed scheme. The thermally induced weak interaction changes of PNiPA, expressed as either the band shift or intensity changes at a specific region, can be probed properly. Meanwhile, the effect of several important factors such as the selected spectral range, correlation between the specific bands, and especially the multiple scattering corrections (MSC) on the accuracy of the spectral prediction were also investigated in detail. This study provides a novel method for the analysis of weak interactions in complex systems.

Rich Pseudopolymorphic Behavior of the Tetranuclear [Ni4(dpyatriz)2(NO3)8] Complex

Reaction of nickel(II) nitrate with the dpyatriz ligand, namely 2,4,6-tris(bis(pyridin-2-yl)amino)-1,3,5-triazine, in acetonitrile produces a tetranuclear NiII coordination compound, [Ni4(dpyatriz)2(NO3)8(CH3CN)2(H2O)2].2CH3CN (1), the crystal structure of which has been determined by X-ray diffraction using a synchrotron source. 1 has been characterized by IR and UV-vis spectroscopy, elemental and thermogravimetric analyses, and magnetic susceptibility measurements. Its solid-state structure exhibits remarkable anion...pi interactions between coordinated nitrate ions and the triazine rings. In addition, a thorough X-ray powder diffraction study has revealed a number of pseudopolymorphic phases (2-5), resulting from various degrees of hydration/solvation of the [Ni4(dpyatriz)2] core. The interconversion scheme among the different phases has been determined using controlled heating, and the basic structural features of the different pseudopolymorphs have been assessed through ab initio powder diffraction methods.

Interconversion behavior of the C-H bond in the CH4+ radical cation: ab initio molecular dynamics study.

Thermal motion of CH4+ is investigated by performing an ab initio molecular dynamics method with the second-order Møller-Plesset (MP2)/6-311G** force field. In the trajectories obtained at 400 K, we have observed rapid interconversion behavior of the geometrical parameters of CH4+ with the frequency of 0.6/ps, where the C-H pair forming the small angle around 55 degrees is switched to another pair on subpicosecond time scale. The switching patterns are found to be classified into the following two types. Type 1: one C-H of the small angled C-H pair is switched to one C-H of the other C-H pair. Type 2: the small angled C-H pair is switched to the other C-H pair, which has been newly observed in the present ab initio MD calculation. The four C-H bonds of CH4+ are characterized by the long and short C-H bonds in a time region of the trajectories, and also for the time-evolution of C-H bonds such interconversion behavior is observed. The switching patterns of the geometrical parameters are compared with those in the interconversion scheme between six equivalent C2v symmetry structures of CH4+ [Paddon-Row, M. N. et al., J Am Chem Soc 1985, 107, 7696]. We have also investigated the electronic energy fluctuation due to thermal motion of CH4+. The standard deviation of total electronic energy at 400 K is evaluated to be 1.2 kcal/mol.

Synthesis and Conformation Studies of a Dodecaazanonacyclotetratetracontane

A multicyclic molecule (illustrated here) was prepared by self-assembly of 1,3,5-pentanetriamine and formaldehyde in quantitative yield. This molecule can exist in four diamond-lattice conformations of symmetries D2d, S4, C2v and D2d. A conformation interconversion scheme is proposed. It involves also two less populated quasi-diamond-lattice intermediates; one of which forms a clathrate with dioxane.

Interconversion between Relaxation Modulus and Creep Compliance for Viscoelastic Solids

Methods of interconversion between relaxation modulus and creep compliance for linear viscoelastic materials are discussed and illustrated using data from asphalt concrete. Existing methods of approximate interconversion are reviewed and compared for their approximating schemes. A new approximate interconversion scheme that uses the local log-log slope of the source function is introduced. The new scheme is based on the concept of equivalent time determined by rescaling the physical time. The rescaling factor, which can be interpreted as a shift factor on a logarithmic time axis, is dictated by the local slope of the source function on log-log scales. The unknown target function at a given time is obtained by taking the reciprocal of the source function evaluated at an equivalent time. Although the method is developed using a mathematical relationship based on the power-law representations of relaxation modulus and creep compliance, the method is not limited to material functions characterized by power-laws but can be applied to general, non-power-law material functions as long as the relevant material behaviors are broadband and smooth on logarithmic scales. The new method renders good results especially when the log-log slope of the source function varies smoothly with logarithmic time.

Conformations and conformational interconversions of enantholactam

AbstractThe conformational properties of enantholactam (1‐azacyclooctane‐2‐one) in solution were studied by 1H and 13C NMR at various temperatures. Only the cis‐isomer is present and it occurs in two different conformations in the ratio 3:2, as observed by 13C NMR at − 133°C. In the temperature range − 50 to − 140°C, two conformational processes were observed. A low energy process was visible in both the 1H and the 13C NMR spectra with coalescence temperature ca. − 110°C and a free energy of activation of 30 kJ mol−1, identified as interconversion between the two conformations. A higher energy process was visible in the 1H but not in the 13C NMR spectrum with coalescence temperature ca. − 96°C and free energy of activation 35 kJ mol−1. This process was identified as geminal 1H exchange. A conformational interconversion scheme for partial and full site exchange of protons and carbon atoms, explaining the variable‐temperature NMR results, is proposed.

Mercerization of cellulose. I. X‐ray diffraction evidence for intermediate structures

AbstractA study of the mercerization of ramie cellulose was begun using x‐ray diffraction, in order to determine the types of alkali–cellulose structures that occur as intermediates during the conversion of cellulose I to cellulose II. A total of five unique alkali–celluloses (Na–celluloses) could be generated reproducibly, depending only on the alkali concentration used. The reproducibility was enhanced by slowing down the mercerization process, by laterally compressing the fibers in capillary tubes. The five structures, named Na–celluloses I, IIA, IIB, III, and IV, were of two types based on their crystallographic fiber repeats. The first type was represented by Na–celluloses I, III, and IV, all exhibiting a ca. 10 Å repeat. The second type was represented by Na–celluloses IIA and IIB, with a ca. 15 Å repeat. The latter structures are possibly based on a threefold helical chain conformation, which has not been seen in crystalline celluloses. All Na–cellulose structures exhibited a reasonable degree of crystallinity and high degree of fibrous orientation. They formed a definite interconversion scheme, marked by crystalline‐to‐crystalline phase transformations.

Application of a constitutive equation to polymer melts

AbstractYamamoto's integral constitutive equation in which the memory function is dependent on the second invariant of the rate of deformation tensor at past times has been found to be successful in predicting many of the nonlinear viscoelastic functions from the linear viscoelastic data for melts of linear polyethylenes, polypropylenes, and polystryene but not for those of branched polyethylenes with high level of long‐chain branching. A specific functional form for the rate‐dependent relaxation spectrum is used and is based on the physical meaning resulting from the molecular entanglement theory of Graessley on steady shearing flow. No arbitrary constant is involved in such an interconversion scheme. The data examined are dynamic storage modulus and loss modulus, steady flow viscosity, first normal stress difference, and parallel superimposed small oscillations on steady shear flow. The theory predicts that in such parallel superimposed experiments, storage modulus G′(ω,\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) divided by the square of frequency shows a maximum under finite shear and that G′(ω,\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) would itself become negative at a frequency whose value is about one third the superimposed rate of shear. The experiments are in line with such predictions. Possible reasons for the failure of the theory for branched polyethylenes are considered, and a possible approach is suggested so that the interconversion scheme may be successful for such resins.

SWITCHING LANGUAGES FOR INDEXING

The paper describes some properties of simple interconversion devices which enable material intially subject indexed by a particular indexing system to be made available to other institutions using different indexing languages in such a form as to be readily integrated into their indexes. Reference is made to the outline Intermediate Lexicon which is the germinal form of a switching language for the field of information science. Difficulties and problems in effecting satisfactory information transfer through such an interconversion scheme are explored, and suggestions made for the lines upon which further research needs to be undertaken. The author was the Classification Research Group representative on the international working party concerned with the Intermediate Lexicon.