Sub-100-as timing jitter optical pulse trains from mode-locked Er-fiber lasers

We demonstrate sub-100-attosecond timing jitter optical pulse trains generated from free-running, 77.6-MHz repetition-rate, mode-locked Er-fiber lasers. At -0.002(\pm0.001) ps2 net cavity dispersion, the rms timing jitter is 70 as (224 as) integrated from 10 kHz (1 kHz) to 38.8 MHz offset frequency, when measured by a 24-as-resolution balanced optical cross-correlator. To our knowledge, this result corresponds to the lowest rms timing jitter measured from any mode-locked fiber lasers so far. The measured result also agrees fairly well with the Namiki-Haus analytic model of quantum-limited timing jitter in stretched-pulse fiber lasers.Comment: 4 pages, 2 figures, to appear in Optics Letter

Freight Transport Modal Shift in NZ: Building Understanding of Shippers’ Mode Choice based on RP (revealed preference)/ SP (stated preference) surveys

The main objectives of this study are to identify the constraints on shifting freight in New Zealand (NZ) from road to rail and/or coastal shipping, and to quantify the trade-off between factors affecting shippers’ perceptions, to assist in increasing the share of freight moved by non-road transport modes. This was done by three logistic regression methods. The ranked logit results show that NZ shippers ranked transport time as the most significant constraint upon distributing goods by rail, while accessibility and load size were the most significant constraints upon using coastal shipping. The study also identifies how NZ shippers’ modal shift constraints vary according to the firm’s individual or logistical characteristics (e.g. their use of logistics facilities, lead time, and delivery distance). Mode choice models, consistent with econometric theory and based on transport cost, time, reliability and modal frequency, are developed. Multinomial logit (MNL) and mixed logit (ML) models are estimated, to identify the factors influencing the choice between road, rail and coastal shipping, for domestic inter-island freight flows. Finally, the models are used, with empirical data on transport cost, time and reliability, to estimate the effect (on mode split) of policies to alter the values of these variables

Modal shift for New Zealand shippers for various policy scenarios

Increasing transport problems caused by high dependency on road transport, has brought us to investigate various policy scenarios to promote a greater use of rail and coastal transport for freight transport in New Zealand. For this, we examined how factors associated with freight transport (e.g. cost and reliability) influenced the transport decisions of shippers with various operation types. Online stated preference surveys were developed and mixed-logit models were estimated from the data provided by 233 shippers. These models were used to calculate the base mode shares, and subsequently, to test various hypothetical policy options for promoting greater use of rail and coastal transport. The results show that a substantial improvement in reliability of both the rail and coastal freight transport services will lead to a substantial decline in the share of road transport, especially for shippers with short-haul and long-haul operations, transporting either large or small shipment volume

Analysing freight shippers' mode choice preference heterogeneity using latent class modelling

This paper describes a study to improve understanding of the decision-making process of New Zealand firms, freight shippers and agents when making freight transport mode choice decisions. Such studies, despite their importance, are relatively scarce due to issues related to data confidentiality, restraining firms from taking part in such studies. To achieve the objective, we use latent class (LC) modelling, which postulates that firms’ behaviour depends on two components: 1) some observable attributes, such as travel distance and size of operations; and 2) unobserved latent heterogeneity. The latter is taken into account by sorting firms into a number of classes based on similarities in their characteristics. Subsequently, the behaviour of firms in each class is explained by a set of parameter estimates, which differs from the sets assigned to other classes. In this study, data were gathered using stated preference surveys from 190 NZ firms, freight shippers and agents. Based on their freight operations, participants were grouped into: 1) long-haul and large shipments and 2) long-haul and small shipments. Furthermore, as each participant evaluated 18 choice scenarios, the data set contains 3,420 choice records. The results of the LC modelling allow policy makers to design more appropriate strategies and policies for different segments of the population to improve intermodal transport and to attract the largest latent class for both cases. In addition, the LC model indicates that the potential improvement in modal shift, which can be achieved by applying different policy options, varies with both transport distance and the size of shipments. Furthermore, in order to promote sustainable freight transport, one policy would be to increase the reliability of both the rail and sea freight transport services

Electrochemical behaviour of carbamazepine in acetonitrile and dimethylformamide using glassy carbon electrodes and microelectrodes

The electrochemical reduction of carbamazepine in acetonitrile (ACN) and dimethylformamide (DMF) using a glassy carbon electrode and microelectrodes has been studied. The reduction process is consistent with an Electrochemical-Chemical mechanism (EC) involving a two electron transfer followed by a first order reaction, as shown by the cyclic voltammetry and differential pulse voltammetry. Half-wave potential, number of electron transfer, diffusion coefficient and rate constant of the associated chemical reaction are reported. Detection limits are in DPV: LoD=0.92 and 0.76 μg mL-1 in ACN and DMF, respectively. Precision (%RSD) and recovery (%) values when pharmaceutical compounds (200mg carbamazepine tablets) and spiked plasma samples were tested ranged from 1.09 to 9.04% and % recoveries ranged from 96 to 104.1%

Mode Choice in Freight Transport in New Zealand: Findings of a Revealed Preference (RP) Survey of Shippers

Transport mode choice for freight plays an important role in the logistics process. Mode choice for freight transport is influenced by company’s transportation demand, logistical actives, as well as supply chain characteristics. Due to the great heterogeneity of companies and due to questions of confidentiality and reliability of data, considerably less research have been done on modelling freight transport demand in New Zealand. Freight transport demand characteristics, such as the attributes of the shipper or consigner, the attributes of the commodities to be transported, and the spatial attributes of shipments, strongly influence mode choice. In this paper, we use a revealed preference (RP) experiment to explore the relative importance of six transport mode choice attributes based on a sample of nearly 200 companies across a range of industries in New Zealand. The results show several distinct types of transport mode choice behaviour, and that the preferences for timeliness, cost, accessibility, restitution, customer service, and suitability vary greatly between industry groups and business types. We also tested seven factors that may hinder the use of rail or shipping by companies in New Zealand as transport mode for domestic and international shipments. The practical importance of this research is that we provide a logical starting point for modelling freight transport mode choice in New Zealand

Zakharov simulation study of spectral features of on-demand Langmuir turbulence in an inhomogeneous plasma

We have performed a simulation study of Langmuir turbulence in the Earth's ionosphere by means of a Zakharov model with parameters relevant for the F layer. The model includes dissipative terms to model collisions and Landau damping of the electrons and ions, and a linear density profile, which models the ionospheric plasma inhomogeneity whose length scale is of the order 10--100 km. The injection of energy into the system is modeled by a constant source term in the Zakharov equation. Langmuir turbulence is excited ``on-demand'' in controlled ionospheric modification experiments where the energy is provided by an HF radio beam injected into the overhead ionospheric plasma. The ensuing turbulence can be studied with radars and in the form of secondary radiation recorded by ground-based receivers. We have analyzed spectral signatures of the turbulence for different sets of parameters and different altitudes relative to the turning point of the linear Langmuir mode where the Langmuir frequency equals the local plasma frequency. By a parametric analysis, we have derived a simple scaling law, which links the spectral width of the turbulent frequency spectrum to the physical parameters in the ionosphere. The scaling law provides a quantitative relation between the physical parameters (temperatures, electron number density, ionospheric length scale, etc.) and the observed frequency spectrum. This law may be useful for interpreting experimental results.Comment: 7 pages, 8 figure

Phase Statistics of Soliton

The characteristic function of soliton phase jitter is found analytically when the soliton is perturbed by amplifier noise. In additional to that from amplitude jitter, the nonlinear phase noise due to frequency and timing jitter is also analyzed. Because the nonlinear phase noise is not Gaussian distributed, the overall phase jitter is also non-Gaussian. For a fixed mean nonlinear phase shift, the contribution of nonlinear phase noise from frequency and timing jitter decreases with distance and signal-to-noise ratio.Comment: 8 pages, submitted to JOSA