| 1. |
- Jonsson, Thomas, et al.
(författare)
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Differences in the Performance of Safety Performance Functions Estimated for Total Crash Count and for Crash Count by Crash Type
- 2009
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981. ; :2102, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- In recent years the development and use of crash prediction models for roadway safety analyses have received substantial attention. These models, also known as safety performance functions (SPFs), relate the expected crash frequency of roadway elements (intersections, road segments, on-ramps) to traffic volumes and other geometric and operational characteristics. A commonly practiced approach for applying intersection SPFs is to assume that crash types occur in fixed proportions (e.g., rear-end crashes make up 20% of crashes, angle crashes 35%, and so forth) and then apply these fixed proportions to crash totals to estimate crash frequencies by type. As demonstrated in this paper, such a practice makes questionable assumptions and results in considerable error in estimating crash proportions. Through the use of rudimentary SPFs based solely on the annual average daily traffic (AADT) of major and minor roads, the homogeneity-in-proportions assumption is shown not to hold across AADT, because crash proportions vary as a function of both major and minor road AADT. For example, with minor road AADT of 400 vehicles per day, the proportion of intersecting-direction crashes decreases from about 50% with 2,000 major road AADT to about 15% with 82,000 AADT. Same-direction crashes increase from about 15% to 55% for the same comparison. The homogeneity-in-proportions assumption should be abandoned, and crash type models should be used to predict crash frequency by crash type. SPFs that use additional geometric variables would only exacerbate the problem quantified here. Comparison of models for different crash types using additional geometric variables remains the subject of future research.
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| 2. |
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| 3. |
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The Seventeenth Data Release of the Sloan Digital Sky Surveys : Complete Release of MaNGA, MaStar, and APOGEE-2 Data
- 2022
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Ingår i: Astrophysical Journal Supplement Series. - : Institute of Physics (IOP). - 0067-0049 .- 1538-4365. ; 259:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys.
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| 4. |
- Toolan, Daniel T. W., et al.
(författare)
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Insights into the Structure and Self-Assembly of Organic-Semiconductor/Quantum-Dot Blends
- 2022
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Ingår i: Advanced Functional Materials. - : John Wiley & Sons. - 1616-301X .- 1616-3028. ; 32:13
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Tidskriftsartikel (refereegranskat)abstract
- Controlling the dispersibility of crystalline inorganic quantum dots (QD) within organic-QD nanocomposite films is critical for a wide range of optoelectronic devices. A promising way to control nanoscale structure in these nanocomposites is via the use of appropriate organic ligands on the QD, which help to compatibilize them with the organic host, both electronically and structurally. Here, using combined small-angle X-ray and neutron scattering, the authors demonstrate and quantify the incorporation of such a compatibilizing, electronically active, organic semiconductor ligand species into the native oleic acid ligand envelope of lead sulphide, QDs, and how this ligand loading may be easily controlled. Further more, in situ grazing incidence wide/small angle X-ray scattering demonstrate how QD ligand surface chemistry has a pronounced effect on the self-assembly of the nanocomposite film in terms of both small-molecule crystallization and QD dispersion versus ordering/aggregation. The approach demonstrated here shows the important role which the degree of incorporation of an active ligand, closely related in chemical structure to the host small-molecule organic matrix, plays in both the self-assembly of the QD and small-molecule components and in determining the final optoelectronic properties of the system.
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| 5. |
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| 6. |
- Weir, Michael P., et al.
(författare)
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Ligand Shell Structure in Lead Sulfide–Oleic Acid Colloidal Quantum Dots Revealed by Small-Angle Scattering
- 2019
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:16, s. 4713-4719
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystal quantum dots are generally coated with an organic ligand layer. These layers are a necessary consequence of their chemical synthesis, and in addition they play a key role in controlling the optical and electronic properties of the system. Here we describe a method for quantitative measurement of the ligand layer in 3 nm diameter lead sulfide–oleic acid quantum dots. Complementary small-angle X-ray and neutron scattering (SAXS and SANS) studies give a complete and quantitative picture of the nanoparticle structure. We find greater-than-monolayer coverage of oleic acid and a significant proportion of ligand remaining in solution, and we demonstrate reversible thermal cycling of the oleic acid coverage. We outline the effectiveness of simple purification procedures with applications in preparing dots for efficient ligand exchange. Our method is transferrable to a wide range of colloidal nanocrystals and ligand chemistries, providing the quantitative means to enable the rational design of ligand-exchange procedures.
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| 7. |
- Whitehead, Jake, 1989-
(författare)
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Energy Efficient Vehicle Policy: Lessons Learnt : An analysis of the effects of incentive policies on the demand, usage and pricing of energy efficient vehicles.
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Encouraging the uptake of energy efficient vehicles (EEVs) is an aspiration of critical importance in a day and age in which we are confronted with the increasingly dire consequences of human behaviour on our planet, and on the planet for generations to come. The transport sector is one of the highest contributors of anthropogenic greenhouse gas emissions, whilst pollution from this sector is responsible for a large proportion of human deaths each and every year. Given the severity of these issues, it is more important than ever for policy-makers, and researchers alike, to encourage a transition within the community towards more sustainable lifestyles. Transportation is key to this change.As a service that every human being uses, almost every day of his or her life, the transport sector presents a unique opportunity for behavioural change. Through efficient and targeted policies, consumers can be incentivised to make more sustainable transport choices and to consider the consequences of their own actions. Foremost amongst these initiatives is that of encouraging a transition towards energy efficient vehicles.This thesis has been produced in order to shed further light on issues affecting this transition. In particular for policy-makers, this document includes a series of recommendations based on prevailing findings in the current literature, in addition to the novel and significant findings of this research effort. These include the various lessons learnt from government policies that have already been implemented in regions around the globe.As a thesis by publication, this document consists of four research articles that investigate factors affecting the EEV market, specifically in terms of: consumer demand, vehicle usage and product pricing. A number of other demographic and economic factors have also been examined, including the role of economies-of-scale.
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| 8. |
- Whitehead, Jake, 1989-
(författare)
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Making the Transition to a ‘Green’ Vehicle Fleet : An analysis of the choice and usage effects of incentivising the adoption of low-emission vehicles
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Making the transition to a ‘green’ vehicle fleet is a noteworthy endeavour for any policy maker. Under the current global pressures of increasing greenhouse gas emissions there is no doubt that all efforts that can be adopted in order to improve the sustainability of our cities should be explored. In saying this however, it is crucial when designing such policies that proper cost-benefit analyses are performed; taking into account the potentially negative rebound effects of such measures and understanding which individuals are affected by such policies.Comprising of two papers, this thesis analyses the choice and usage effects of an exemption for low-emission vehicles (LEVs) from Stockholm’s congestion charging scheme. The ambition of this study has been to understand: the extent to which this exemption policy influenced the demand for LEVs; which individuals were targeted; whether the policy led to any rebound effects (increased LEV usage); and ultimately what the effect of this policy was in terms of changes in emissions.Paper I employs a MNL model to examine the demographics of those individuals who purchased an LEV in Stockholm during 2008 and the extent to which the exemption policy influenced this demand. It was found that those owners living within the cordon but who commuted across the boundary for work had the highest propensity towards purchasing an exempt LEV. The exemption policy was found to have increased the share of exempt LEVs by 1.9% to 18.9% in total, corresponding to an additional 550 exempt LEV purchases in 2008 due to this policy.In Paper II, the differences in annual usage rates between demographically-similar LEV and conventional vehicle owners are calculated using propensity score matching in order to control for potential self-selection effects. Through this procedure it was found that the direct emissions of vehicle owners who adopted LEVs were reduced by 52.4%. Although the exemption policy was partially responsible for increasing the number of LEVs, it also appears to have encouraged an increase in annual usage, leading to rebound effects that offset the potential reduction in emissions (increase in LEV usage: 12.2% for owners that lived inside / worked outside cordon; 8.5% for owners that lived outside / worked inside cordon).Through the analysis detailed in the two papers of this thesis, the effects of an incentive based policy in Stockholm upon both the demand and usage of LEVs have been highlighted. The benefits, as well as the possible complications of this initiative have also been discussed, in the hope of enlightening policy makers to ensure that potential emissions reductions are maximised for similar policy initiatives in the future. With personal vehicles likely to continue dominating the share of home-work trips over the coming years, cities must continue their efforts in encouraging the transition to a ‘green’ vehicle fleet. It is important, however, that these efforts lead to incentive based policies that are balanced, reasonable, and designed to minimise potentially substantial rebound effects.
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| 9. |
- Whitehead, Jake, 1989-, et al.
(författare)
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The impact of a congestion charging exemption scheme on the demand for low-emission vehicles
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- To stimulate sales of Low-Emission Vehicles (LEVs) it was decided to exempt some of these automobiles from Stockholm’s congestion charge. In this paper the effect this policy had on the demand for LEVs is estimated by simulating different policy scenarios using the results of a multinomial logit model (MNL). This model was based upon owner-specific demographics merged with vehicle registry data for all new private vehicles registered in Stockholm county during 2008. Through this process the characteristics of individuals who had a higher propensity towards purchasing an exempt LEV were identified. The most significant characteristics included inter-cordon residency (positive), distance of home from cordon boundary (negative), and commuting across the cordon boundary (positive). Inter-cordon residents commuting across the boundary had the highest propensity towards purchasing an exempt LEV. Owners under the age of 30 preferred low CO2 petrol/diesel vehicles, whilst those over 30 preferred electric vehicles. In terms of electric vehicles, those living within the cordon had the highest propensity towards this alternative. By calculating vehicle shares from the MNL model, and comparing these with a simulated scenario where the congestion charging exemption was inactive, the policy was found to have a substantial effect, increasing the share of exempt LEVs in Stockholm by 1.9% to a total share of 18.9% (13.1% increase for inter-cordon residents commuting over the boundary; 5.0% increase for outer city residents commuting over the boundary). In other words, the exemption policy was found to have increased LEV purchases in Stockholm, during 2008, by approximately 550 vehicles.
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| 10. |
- Whitehead, Jake, 1989-, et al.
(författare)
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The impact of a congestion pricing exemption on the demand for new energy efficient vehicles in Stockholm
- 2014
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Ingår i: Transportation Research Part A. - : Elsevier. - 0965-8564 .- 1879-2375. ; 70, s. 24-40
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Tidskriftsartikel (refereegranskat)abstract
- As governments seek to transition to more efficient vehicle fleets, one strategy has been to incentivize ‘green’ vehicle choice by exempting some of these vehicles from road user charges. As an example, to stimulate sales of energy efficient vehicles (EEVs) in Sweden, some of these automobiles were exempted from Stockholm’s congestion tax. In this paper the effect this policy had on the demand for new, privately-owned, exempt EEVs is assessed by first estimating a model of vehicle choice and then by applying this model to simulate vehicle alternative market shares under different policy scenarios. The database used to calibrate the model includes owner-specific demographics merged with vehicle registry data for all new private vehicles registered in Stockholm County during 2008. Characteristics of individuals with a higher propensity to purchase an exempt EEV were identified. The most significant factors included intra-cordon residency (positive), distance from home to the CBD (negative), and commuting across the cordon (positive). By calculating vehicle shares from the vehicle choice model and then comparing these estimates to a simulated scenario where the congestion tax exemption was inactive, the exemption was estimated to have substantially increased the share of newly purchased, private, exempt EEVs in Stockholm by 1.8% (±0.3%; 95% C.I.) to a total share of 18.8%. This amounts to an estimated 10.7% increase in private, exempt EEV purchases during 2008, i.e., 519 privately owned, exempt EEVs.
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