Dispersion Length Research Articles

Terahertz emission from ZnGeP_2: phase-matching, intensity, and length scalability

Collinear phase-matched optical rectification is studied in ZnGeP$_{2}$ pumped with near-infrared light. The pump-intensity dependence is presented for three crystal lengths (0.3, 1.0 and 3.0 mm) to determine the effects of linear optical absorption, nonlinear optical absorption and terahertz free-carrier absorption on the generation. Critical parameters such as the coherence length (for velocity matching), dispersion length (for linear pulse broadening) and nonlinear length (for self-phase modulation) are determined for this material. These parameters provide insight into the upper limit of pulse intensity and crystal length required to generate intense terahertz pulse without detriment to the pulse shape. It is found that for 1-mm thick ZnGeP$_{2}$(012), pumped at 1.28 micron with intensity of ~15 GW/cm2 will produce intense undistorted pulses, whereas longer crystals or larger intensities modify the pulse shape to varying degrees. Moreover, phase-matching dispersion maps are presented for the terahertz generation over a large tuning range (1.1-2.4 micron) in longer (3 mm) crystal, demonstrating the phase-matching bandwidth and phase mismatch that leads to fringing associated with multi-pulse interference. All observed results are simulated numerically showing good qualitative agreement.

The DiskMass Survey

We present ionized-gas (OIII) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as much as three disk scale lengths (h_R). These data have been derived from PPak IFU spectroscopy (4980-5370A), observed at a mean resolution of R=7700 (sigma_inst=17km/s). These data are a fundamental product of our survey and will be used in companion papers to, e.g., derive the detailed (baryonic+dark) mass budget of each galaxy in our sample. Our presentation provides a comprehensive description of the observing strategy, data reduction, and analysis. Along with a clear presentation of the data, we demonstrate: (1) The OIII and stellar rotation curves exhibit a clear signature of asymmetric drift with a rotation difference that is 11% of the maximum rotation speed of the galaxy disk, comparable to measurements in the solar neighborhood in the Milky Way. (2) The e-folding length of the stellar velocity dispersion is two times h_R on average, as expected for a disk with a constant scale height and mass-to-light ratio, with a scatter that is notably smaller for massive, high-surface-brightness disks in the most luminous galaxies. (3) At radii larger than 1.5 h_R, the stellar velocity dispersion tends to decline slower than the best-fitting exponential function, which may be due to an increase in the disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter halo. (4) A strong correlation exists between the central vertical stellar velocity dispersion of the disks and their circular rotational speed at 2.2 h_R, with a zero point indicating that galaxy disks are submaximal. Moreover, weak but consistent correlations exist such that disks with a fainter central surface brightness in bluer and less luminous galaxies of later morphological types are kinematically colder with respect to their rotational velocities.

Characterization of LPGs via Correlation Analysis of an Analytical Solution With Observed Transmission Spectra

In this paper, we describe a technique to characterize long period fiber gratings (LPG) by use of a correlation between the measured transmission spectrum and a theoretical model. The model is robust enough to require only a-priori knowledge of the fiber design and the inscription period. We demonstrate the application of this technique on an example LPG resulting in the calculation of the dispersive core index, length, and strength of the grating to better than experimental error. The technique is further expanded to allow for the modeling of metal jacketed long period gratings by use of an extended version of Erdogan's model.

Equivalence of chain conformations in the surface region of a polymer melt and a single Gaussian chain under critical conditions

In the melt polymer conformations are nearly ideal according to Flory's ideality hypothesis. Silberberg generalized this statement for chains in the interfacial region. We check the Silberberg argument by analyzing the conformations of a probe chain end-grafted at a solid surface in a sea of floating free chains of concentration φ by the self-consistent field (SCF) method. Apart from the grafting, probe chain and floating chains are identical. Most of the results were obtained for a standard SCF model with freely jointed chains on a six-choice lattice, where immediate step reversals are allowed. A few data were generated for a five-choice lattice, where such step reversals are forbidden. These coarse-grained models describe the equilibrium properties of flexible atactic polymer chains at the scale of the segment length. The concentration was varied over the whole range from φ = 0 (single grafted chain) to φ = 1 (probe chain in the melt). The number of contacts with the surface, average height of the free end and its dispersion, average loop and train length, tail size distribution, end-point and overall segment distributions were calculated for a grafted probe chain as a function of φ, for several chain lengths and substrate∕polymer interactions, which were varied from strong repulsion to strong adsorption. The computations show that the conformations of the probe chain in the melt do not depend on substrate∕polymer interactions and are very similar to the conformations of a single end-grafted chain under critical conditions, and can thus be described analytically. When the substrate∕polymer interaction is fixed at the value corresponding to critical conditions, all equilibrium properties of a probe chain are independent of φ, over the whole range from a dilute solution to the melt. We believe that the conformations of all flexible chains in the surface region of the melt are close to those of an appropriate single chain in critical conditions, provided that one end of the single chain is fixed at the same point as a chain in the melt.

Ultraweak long-range interactions of solitons observed over astronomical distances

We report what we believe is the weakest interaction between solitons ever observed. Our experiment involves temporal optical cavity solitons recirculating in a coherently-driven passive optical fibre ring resonator. We observe two solitons, separated by up to 8,000 times their width, changing their temporal separation by a fraction of an attosecond per round-trip of the 100 m-long resonator, or equivalently 1/10,000 of the wavelength of the soliton carrier wave per characteristic dispersive length. The interactions are so weak that, at the speed of light, they require an effective propagation distance of the order of an astronomical unit to fully develop, i.e. tens of millions of kilometres. The interaction is mediated by transverse acoustic waves generated in the optical fibre by the propagating solitons through electrostriction.

In-Line Visualisation of Polymer Plastication in an Injection Moulding Screw

In injection moulding or in extrusion, plastication is the step during which polymer pellets are melted by the means of mechanical dissipation provided by a rotating screw and by thermal conduction coming from a heated metallic barrel. This step is crucial for melt thermal homogeneity, charge dispersion and fibre length preservation. Although there have been a large number of theoretical and experimental studies of plastication during the past decades, mostly on extrusion and mostly using the screw extraction technique, extremely few of them have dealt with trying to visualise plastication, let alone measuring the plastication profile in real-time. As a matter of fact, designing such an equipment is an arduous task. We designed an industry-sized metallic barrel, featuring 3 optical glass windows, each window possessing 3 plane faces itself to allow for visualisation and record by synchronised cameras and lightening by lasers. The laser can be used in a laser induced fluorescence or in a particle imaging velocity measurement framework. The images recorded can be further analysed by digital image processing. Preliminary results confirm the plastication theory and show a compacted solid bed and a melt pool side by side. The total plastication length is a direct function of screw rotation frequency as it is obvious from results on the melt pool width, which increases when the screw rotation frequency decreases. However, some evidence of solid bed breakage has been recorded, whereby the solid bed does not diminish continuously along the screw but is fractured in the compression zone These experimental findings are compared to predictions by a one-dimensional model of plastication

Overcoming temporal polarization instabilities from the latent birefringence in all-normal dispersion, wave-breaking-extended nonlinear fiber supercontinuum generation.

The intrinsic weak birefringence in all-normal dispersion highly nonlinear fiber, particularly ultra-high-numerical-aperture fiber, generates supercontinuum with long term polarization instabilities, even for seed pulses launched along the perceived slow axis of the fiber. Highly co/anti-correlated fluctuations in energy between regions of power spectral density mask the extent of the spectral noise in total integrated power measurements. The instability exhibits a seed pulse power threshold above which the output polarization state of the supercontinuum seeds from noise. Eliminating this instability through the utilization of nonlinear fiber with a large designed birefringence, encourages the exploration of compression schemes and seed sources. Here, we include an analysis of the difficulties for seeding supercontinuum with the highly attractive ANDi-type lasers. Lastly, we introduce an intuitive approach for understanding supercontinuum development and evolution. By modifying the traditional characteristic dispersion and nonlinear lengths to track pulse properties within the nonlinear fiber, we find simple, descriptive handles for supercontinuum evolution.

Effects of semantic predictability and dialect variation on vowel production in clear and plain lab speech

Speech addressed to a non-native or hearing impaired listener features longer, more peripheral vowels. In addition, more extreme dialect-specific forms are produced in semantically predictable contexts, and less extreme forms (more standard forms) in unpredictable contexts. This study investigated the interactions between predictability and speaking style on Southern American English monophthongization of the vowel /aj/. The Midland dialect of American English served as the comparison. Participants read a set of sentences with monosyllabic target words in sentence-final position. Target words varied in semantic predictability based on the preceding sentential context. Each set of sentences was produced twice by each participant—first as if talking to a friend (“plain” speech) and again as if talking to a non-native or hearing impaired listener (“clear” speech). The duration, dispersion, and trajectory length of the vowel in each target word were measured. Preliminary results suggest that, as expected, Southern /aj/ has a shorter trajectory length than Midland /aj/, and in both dialects, /aj/ has a shorter trajectory length in clear speech than plain speech. However, these processes do not interact with each other or with semantic predictability, suggesting that style and predictability effects are independent of the realization of some dialect variants.

A porous media theory for characterization of membrane blood oxygenation devices

A porous media theory has been proposed to characterize oxygen transport processes associated with membrane blood oxygenation devices. For the first time, a rigorous mathematical procedure based a volume averaging procedure has been presented to derive a complete set of the governing equations for the blood flow field and oxygen concentration field. As a first step towards a complete three-dimensional numerical analysis, one-dimensional steady case is considered to model typical membrane blood oxygenator scenarios, and to validate the derived equations. The relative magnitudes of oxygen transport terms are made clear, introducing a dimensionless parameter which measures the distance the oxygen gas travels to dissolve in the blood as compared with the blood dispersion length. This dimensionless number is found so large that the oxygen diffusion term can be neglected in most cases. A simple linear relationship between the blood flow rate and total oxygen transfer rate is found for oxygenators with sufficiently large membrane surface areas. Comparison of the one-dimensional analytic results and available experimental data reveals the soundness of the present analysis.

Hydrodynamic and dispersion behavior in a non-porous silica monolith through fluid dynamic study of a computational mimic reconstructed from sub-micro-tomographic scans

An analysis of the transport properties of the bulk homogeneous core of a commercially available silica monolith (Chromolith®) is presented via direct numerical simulations in a topological model reconstructed from 3D nanotomographic scans at isotropic resolutions of 390nm, 290nm and 190nm. The pore and skeleton size distributions were calculated from image analysis and a representative unit cell from each resolution was reconstructed to simulate the hydrodynamic transport properties using Computational Fluid Dynamics (CFD). A 30μm×30μm×30μm unit cell extracted at 190nm resolution was found to be representative of hydrodynamic permeability. Numerical peak parking simulations yielded an axial external obstruction factor (γe) of 0.8. Mass transfer characteristics of a large non-penetrating molecule (BSA) were evaluated under non-retained conditions so as to elucidate the eddy dispersion contribution to total HETP. Transverse and axial dispersion length scales in the reconstructed model were resolved and related to the structural heterogeneities in the silica monolith. Deviations of simulated HETP from experimental measurements were attributed to a transcolumn dispersion contribution, which amounted to about 90% of the total HETP. The presented approach provides great scope to analyze the contributions of pore network topology to separation performance of silica monoliths (and other porous media) in HPLC applications. A significant reduction in simulation time and memory resources has been observed due to the lower scanning resolution, without significant loss in prediction accuracy.

Characteristics comparison of the ZDSFs based on the triangular graded index and step index single-mode optical fibers

In this paper, the zero-dispersion shifted single-mode optical fibers based on the triangular graded index and step index profiles are successfully designed by applying the method outlined by Oskoui et al. (Journal of Applied Optics, 46 (2007) 6330) and the optimal values for the structural parameters are evaluated. Simulation results indicate that in order to shift the zero-dispersion wavelength near to 1.55μm, the larger core radius is required in the triangular graded index optical fiber compared to the step index one which is useful from fiber fabrication view points. Also, the dispersion and dispersion slope values in the triangular graded index structure are smaller than ones in the step index type and this fact make a great enlargement in the dispersion and higher order dispersion lengths. However, the nonlinear behavior of the step index ZDSF is superior due to larger effective area, but owing to smaller higher order dispersion length, the transmission distance will be restricted with dispersion slope influence instead of nonlinear effects. Meanwhile, the thermal coefficients of the designed graded index are lower than the structure based on the step index and as a result this kind of fiber has better sustainable behavior against temperature variances.

Realization of the Viterbi Algorithm in MLSE with Intersymbol Interference

Optimum receiver model for channels with Intersymbol Interference (ISI) and Additive White Gaussian Noise (AWGN) are introduced to deduce the Viterbi algorithm in the Maximum-Likelihood Sequence Estimation (MLSE). Finally, we use Matlab to simulate the algorithm in three different channels and analyze the experiment results. Analyses show that the Viterbi algorithm is applicable for any channel which is optimum from a probability of error viewpoint; the MLSE for channels with ISI has a computational complexity that grows exponentially with the length of channels time dispersion L; the loss of performance is negligible when the decoding delay achieves 5L.

Semiconductor Nanorod Self-Assembly at the Liquid/Air Interface Studied by in Situ GISAXS and ex Situ TEM

We study the self-assembly of colloidal CdSe/CdS nanorods (NRs) at the liquid/air interface combining time-resolved in situ grazing-incidence small angle X-ray scattering (GISAXS) and ex situ transmission electron microscopy (TEM). Our study shows that NR superstructure formation occurs at the liquid/air interface. Short NRs self-assemble into micrometers long tracks of NRs lying side by side flat on the surface. In contrast, longer NRs align vertically into ordered superstructures. Systematic variation of the NR length and initial concentration of the NR dispersion allowed us to tune the orientation of the NRs in the final superstructure. With GISAXS, we were able to follow the dynamics of the self-assembly. We propose a model of hierarchical self-organization that provides a basis for the understanding of the length-dependent self-organization of NRs at the liquid/air interface. This opens the way to new materials based on NR membranes and anisotropic thin films.

A thermal conductivity model for low concentrated nanofluids containing surfactants under various dispersion types

Various thermal conductivity models for nanofluid have been proposed, however, none have included the effect of the surfactant. In this paper, a thermal conductivity model which includes the effects of the interfacial layer formed by the surfactant and liquid molecules is proposed by upgrading Leong et al.'s model (2006). Based on the analysis of dispersion types, the thickness of the interfacial layer is defined by the length of the surfactant molecule for nanofluid under monolayer adsorption dispersion and double lengths of the surfactant molecule for nanofluid under electric double layer (EDL) adsorption dispersion. The length of the surfactant molecule is obtained by analyzing the stereo-chemical structure and assuming it is fully extended when adsorbed on the surface of the nanoparticle. The present model was compared with some experimental data for low concentrated nanofluid containing surfactants. The comparison results show the present model, in general, produces higher accuracies and precisions.

A comparison between in-field and in-laboratory 50 km ultralong Erbium-doped fiber lasers actively mode-locked

We present a comparison between an in-field and in-laboratory 50 km ultralong Erbium fiber lasers actively mode-locked with repetition rate varying from 1 to 10 GHz generating pulses from 35.2 to 68.7 ps. The pulse widths generated at higher frequencies are in agreement with Kuizenga-Siegman theory. However, for lower frequencies the pulses have higher intracavity peak power which allows the soliton effect to take place. Depending on the pump power level, the repetition rate and the cavity length both lasers can operate in active mode-locking or under the influence of the soliton regime that locks the pulse duration according to the dispersion and cavity length. Due to the soliton robustness, this condition eliminates most of the environmental influence in the in-field mode-locking regime and makes both lasers very similar.

Determination of the optimum launch conditions in counter-Raman amplification using the method of moments

In the regime of counter Raman amplification we used the method of moments in order to obtain optimum launch conditions for different relationships between the pumping stage spacing and the dispersion length. The effects of the peak power signal and prechirping of solitons on propagation are numerically investigated in a system with distributed Raman amplification. The numerical results of the nonlinear Schrödinger equation using the split-step method show that the optimum power control of the injected solitons largely determines the quality of the power-RMS width of the pulses that propagate in those systems.

Characterization of the granular jet in a coaxial gas stream

The granular jet can behave macroscopically like a liquid jet and its dispersion process is similar to the breakup of the liquid jet by an annular air jet. In this paper, the particle dispersion characteristics of a granular jet by an annular air jet, such as the undisturbed length, the dispersion length and the dispersion angle, have been investigated experimentally with a high-speed camera. The results showed that the air jet velocity and granular jet mass flux are the main influencing factors on the undisturbed length and dispersion length of the granular jet. The particle diameter has few effects on the undisturbed length and dispersion length of the granular jet. The empirical equations of the undisturbed length, dispersion length and dispersion angle are obtained.

Detailed theoretical investigation on improved quasi-lossless transmission using third-order Raman amplification based on ultralong fiber lasers

An alternative structure using third-order Raman amplification based on ultralong fiber lasers (UL-FLs) is investigated numerically to further improve the quasi-lossless transmission performance. The performance comparisons on flatness of signal distribution, optical signal–noise ratio (OSNR), and noise figure (NF) among first-order, second-order, and third-order Raman pumping based on UL-FLs are discussed numerically. The results display that the gain distribution is pushed more uniformly along UL-FLs using third-order Raman pumping, which is very useful to further extend the quasi-lossless midspan distance. For transparency transmission, enhanced quasi-lossless transmission could be achieved without sacrifice to OSNR and NF. We also analyze the transmission dynamics of loss-managed fundamental solitons for different pumping configurations. The amplifier span and transmission quality are improved considerably, even for lower dispersion lengths, by employing the proposed scheme.

Investigation of Pre-, Post- and Symmetric-Dispersion Compensation Techniques (DCF) using Different Modulation Formats over High-Speed Optical Link

The focus of this paper is to report a detailed investigation of dispersion compensated optical communication system of different optical pulses such as RZ super Gaussian, NRZ and RZ pulses using pre-, post- and symmetrical-dispersion compensation techniques. The dispersion compensated optical communication system consists of standard single-mode fiber (SSMF) of 16 ps/nm/km after, whose dispersion is compensated using different DCF compensation schemes with proportionate length of dispersion compensated fiber of −80 ps/nm/km. The performance of these three compensation schemes is compared by computing Q-parameter, Eye-closer penalty and required optical power at sensitivity at varied values of Laser line width from 100 MHz to 100 KHz to underscore the best possible performance. A relationship among the attributes laser line width, different optical pulses and different DCF schemes implemented at high transmission rate.

Migration Behaviour of Lanthanides in Compacted Bentonite with Iron Corrosion Product Using Electrochemical Method

ABSTRACTAfter the closure of a high-level waste repository, corrosion of the carbon steel overpack will occur. The corrosion products can then migrate into bentonite and affect the migration behavior of radionuclides in bentonite. Therefore, electrochemical experiments, with Fe2+ supplied by anodic corrosion of carbon steel, were carried out to study trivalent lanthanides in compacted bentonite. The interface between a carbon steel coupon and bentonite (dry density, 1.5 Mg/m3) was spiked with a tracer solution containing Nd(NO3)3, Eu(NO3)3, Dy(NO3)3, and Er(NO3)3. The carbon steel coupon was connected as the working electrode to a potentiostat and held at a constant potential between -550 and 0 mV (vs. Ag/AgCl reference electrode) for 7 days. A model using dispersion and electromigration could explain the measured profiles in the bentonite specimens. The best-fit electromigration velocity was related to the applied electric potential and was 1.0–3.8 nm/s for Nd, Eu, Dy, and Er ions. For these lanthanides, the best-fit dispersion coefficient was also related to the applied potential and was 0.8–1.6 μm2/s, and the dispersion length was calculated as 0.2 mm from the linear relationship between the dispersion coefficient and electromigration velocity. Finally, the apparent diffusion coefficient for these lanthanides was estimated as 0.6–0.9 μm2/s.