A note on alternative matrix entry estimation techniques

Estimation of trip tables and other matrices that are subject to constraints is a common practical problem. This note reviews four common estimation methods: (1) minimization of the sum of absolute deviations, (2) the biproportional technique, (3) information minimization and (4) constrained generalized least squares (CGLS) regression. A small example illustrates their application. Computational approaches and burdens as well as implicit error structure assumptions are reviewed. The paper concludes that estimates obtained from the biproportional, information minimization and CGLS regression (with a chi-square type error distribution assumption), are likely to be similar in practice. Choice of an appropriate technique depends upon a priori assumptions of error structures, relative computational burdens and the usefulness of estimate uncertainty measures.     

Comparison of trends in tributyltin concentrations among three monitoring programs in the United States

The results of three national monitoring programs in the United States (U.S.) that measure concentrations of tributyltin (TBT) are compared. Regional and site comparisons are made of changes in TBT concentrations since passage of the Organotin Antifouling Paint Control Act (OAPCA) in 1988. The monitoring programs compared are the U.S. LongTerm Monitoring Program conducted by a consortium of tributyltin manufacturers, the National Oceanic and Atmospheric Administration's National Status and Trends Mussel Watch project, and the U.S. Navy's TBT monitoring program. All of the monitoring results demonstrate declining TBT concentrations over time. These declines have occurred rapidly (within a few years) and are considerable (56%–71% decrease in TBT concentrations in water, 47%–55% decrease in sediments, and 40%–82% decrease in bivalve tissues). Mean TBT concentrations in water are generally below the current U.S. Environmental Protection Agency marine chronic water quality criterion of 10ng/L. These results indicate that the OAPCA has been effective in reducing TBT concentrations in the aquatic environment.     

Air–sea gas exchange at extreme wind speeds measured by autonomous oceanographic floats

Measurements of the air–sea fluxes of N₂ and O₂ were made in winds of 15–57 m s^− 1 beneath Hurricane Frances using two types of air-deployed neutrally buoyant and profiling underwater floats. Two “Lagrangian floats” measured O₂ and total gas tension (GT) in pre-storm and post-storm profiles and in the actively turbulent mixed layer during the storm. A single “EM-APEX float” profiled continuously from 30 to 200 m before, during and after the storm. All floats measured temperature and salinity. N₂ concentrations were computed from GT and O₂ after correcting for instrumental effects. Gas fluxes were computed by three methods. First, a one-dimensional mixed layer budget diagnosed the changes in mixed layer concentrations given the pre-storm profile and a time varying mixed layer depth. This model was calibrated using temperature and salinity data. The difference between the predicted mixed layer concentrations of O₂ and N₂ and those measured was attributed to air–sea gas fluxes F_BO and F_BN. Second, the covariance flux F_CO(z) = wO₂′(z) was computed, where w is the vertical motion of the water-following Lagrangian floats, O₂′ is a high-pass filtered O₂ concentration and (z) is an average over covariance pairs as a function of depth. The profile F_CO(z) was extrapolated to the surface to yield the surface O₂ flux F_CO(0). Third, a deficit of O₂ was found in the upper few meters of the ocean at the height of the storm. A flux F_SO, moving O₂ out of the ocean, was calculated by dividing this deficit by the residence time of the water in this layer, inferred from the Lagrangian floats. The three methods gave generally consistent results. At the highest winds, gas transfer is dominated by bubbles created by surface wave breaking, injected into the ocean by large-scale turbulent eddies and dissolving near 10-m depth. This conclusion is supported by observations of fluxes into the ocean despite its supersaturation; by the molar flux ratio F_BO/F_BN, which is closer to that of air rather than that appropriate for Schmidt number scaling; by O₂ increases at about 10-m depth along the water trajectories accompanied by a reduction in void fraction as measured by conductivity; and from the profile of F_CO(z), which peaks near 10 m instead of at the surface.At the highest winds O₂ and N₂ are injected into the ocean by bubbles dissolving at depth. This, plus entrainment of gas-rich water from below, supersaturates the mixed layer causing gas to flux out of the near-surface ocean. A net influx of gas results from the balance of these two competing processes. At lower speeds, the total gas fluxes, F_BO, F_BN and F_CO(0), are out of the ocean and downgradient.     

Area-wide travel plans—targeting strategies for greater participation in green travel initiatives: a case study of Rouse Hill Town Centre,NSW Australia

Travel planning by employers promoting more sustainable travel has delivered less car dependent behaviour for the commute in many places. Area-wide or precinct travel plans are less common but, where they exist, attempt to provide a more holistic approach through capturing synergies between employers and employees throughout a precinct. Area-based travel planning aimed at influencing employers, employees and residents are new, especially in relation to creating synergies for a single precinct that has more of an origin focus with participants travelling to diverse destinations. This paper examines various strategies that have been employed in order to achieve greener travel and to provide a self-sustaining travel planning environment. The aim of this paper is to assess the community awareness, interest and involvement with a number of green initiatives and to understand how sustainable travel planning has been absorbed by residents within a new regional centre in New South Wales, Australia. The analysis of a resident survey undertaken in 2011 distinguishes between the community awareness and their propensity to take part in each of the greener travel initiatives. The results show that a generic approach is likely to be less effective than segmenting the market so as to more directly target likely participants. Attitudes to greener travel are also highly significant and working to change them should also affect potential take up of sustainable travel initiatives. The conclusions inform the development of successful precinct based travel demand strategies both in Australia and beyond.     

Parameterization of air–sea gas fluxes at extreme wind speeds

Air–sea flux measurements of O₂ and N₂ obtained during Hurricane Frances in September 2004 [D'Asaro, E. A. and McNeil, C. L., 2006. Measurements of air–sea gas exchange at extreme wind speeds. Journal Marine Systems, this edition.] using air-deployed neutrally buoyant floats reveal the first evidence of a new regime of air–sea gas transfer occurring at wind speeds in excess of 35 m s^− 1. In this regime, plumes of bubbles 1 mm and smaller in size are transported down from near the surface of the ocean to greater depths by vertical turbulent currents with speeds up to 20−30 cm s^− 1. These bubble plumes mostly dissolve before reaching a depth of approximately 20 m as a result of hydrostatic compression. Injection of air into the ocean by this mechanism results in the invasion of gases in proportion to their tropospheric molar gas ratios, and further supersaturation of less soluble gases. A new formulation for air–sea fluxes of weakly soluble gases as a function of wind speed is proposed to extend existing formulations [Woolf, D.K, 1997. Bubbles and their role in gas exchange. In: Liss, P.S., and Duce, R.A., (Eds.), The Sea Surface and Global Change. Cambridge University Press, Cambridge, UK, pp. 173–205.] to span the entire natural range of wind speeds over the open ocean, which includes hurricanes. The new formulation has separate contributions to air–sea gas flux from: 1) non-supersaturating near-surface equilibration processes, which include direct transfer associated with the air–sea interface and ventilation associated with surface wave breaking; 2) partial dissolution of bubbles smaller than 1 mm that mix into the ocean via turbulence; and 3) complete dissolution of bubbles of up to 1 mm in size via subduction of bubble plumes. The model can be simplified by combining “surface equilibration” terms that allow exchange of gases into and out of the ocean, and “gas injection” terms that only allow gas to enter the ocean. The model was tested against the Hurricane Frances data set. Although all the model parameters cannot be determined uniquely, some features are clear. The fluxes due to the surface equilibration terms, estimated both from data and from model inversions, increase rapidly at high wind speed but are still far below those predicted using the cubic parameterization of Wanninkhof and McGillis [Wannikhof, R. and McGillis, W.R., 1999. A cubic relationship between air–sea CO₂ exchange and wind speed. Geophysical Research Letters, 26:1889–1892.] at high wind speed. The fluxes due to gas injection terms increase with wind speed even more rapidly, causing bubble injection to dominate at the highest wind speeds.     

Learning from traffic data collected before,during and after a hurricane

Hurricanes harm people and damage property through extreme wind speeds and flooding associated with heavy rains and storm surge. One of the most effective and widely used tactics to protect people from hurricanes is evacuation. Improved knowledge of the behavior of communities before, during and after an evacuation can better support emergency planning and operations, and thus help make evacuations safer and more efficient. The objective of this work is to identify ways to use traffic data to better understand evacuation behavior and to explore ways to integrate traffic data into evacuation planning and response. Traffic data collected in Delaware before, during and after Hurricane Irene in August 2011 using automated traffic recorders are assembled and analyzed. The analysis shows that a significant number of residents and visitors evacuated from the beach communities and the evacuation patterns are very similar to the traffic patterns experienced on summer weekends. These insights suggest that this type of analysis may also be of value for other events in other communities.     

Enhanced, multi criteria based site selection to measure mobile source toxic air pollutants

A multi-criteria-based site selection process that was developed for the Las Vegas near-road study is used to select the most appropriate near-road measurement sites in the Detroit area. The study measures particulate matter with aerodynamic diameters ?2.5 μm and mobile source air toxic compounds, and to document the rationale for selecting or rejecting specific sites. An application of this multi-criteria decision analysis may be the recent US Environmental Protection Agency rule requiring the siting of NO₂ monitors within 50 m of major roads as well as siting for the measurement of community-wide NO₂ concentrations.     

The importance of time in transit and reliability of transit time for shippers,receivers, and carriers

Reliability of transit time is reputed to be the most important variable influencing freight transport today, according to shipper surveys. Average transit time also plays a major role. A model is developed that shows how a cost-minimizing shipper will adjust its economic order quantity as reliability and/or time in transit changes. Such changes impact on average inventory costs, ordering costs, expected shortage costs and expected excess costs. The model is developed for both discrete and continuous transit time distributions. Reliability is defined as the variance of transit time. A matrix is prepared for some sample data, which shows the minimum cost attainable with each mean/variance of transit time distribution. Comparing across rows and columns of the matrix enables one to show the value (reduction in total cost) obtainable by improving reliability and/or mean transit time. In addition, value can be obtained by improving reliability while increasing average transit time. It is suggested that the model can be used for shippers in negotiating service improvements with carriers and by carriers in negotiating service improvements with shippers. In the former case, the carrier can determine how much they are willing to pay for the improvement, whereas in the latter case, the carriers can determine how much they are able to charge for the improvement.     

Nitroglycerin reduces augmentation index and central blood pressure independent of effects on cardiac preload

Objective To determine whether reduction In central pressure augmentation and central systolic blood pressure by nitroglycerine (NTG) results from effects on pre-lead or is due to arterial dilation. Methods We compared effects of NTG with these of lower body negative pressure (LBNP). Hemodyunmic measurements were made at rest, during LBNP (10, 20 and 30 mmHg, each for 15 min) and after NTG (10, 30 and 100μg/min, each dose for 15 min) in ten healthy volunteers. Cardiac pre-lead, stroke volume and cardiac output were assessed by echacardiography. Central pressure an mnentation and central systolic pressure were obtained by radial tonometry using a transfer function. Results LBNP (20 mmHg) and NTG (30μg/min) reduced pre-lead (as measured by the peak velocity of the S wave in the superior vena eava) to a similar degree [by (26. 8 ± 3.8) % and (23.9 ± 3. 4) %, respectively]. Compared to LBNP, NTG reduced systemic vascular resistance [by (32. 9 ± 7.5) %, p< 0. 01], decreased peripheral and central pressure augmentation [by (20. 8 ± 3. 4)% units and (12. 9±2. 9)% units, respectively, each P< 0. 01]. Conclusion These results suggest that a reduction in pre-load does not explain reduction in pressure augmentation and central systolic blood pressure by NTG and that these effects are mediated through arterial dilation.