USING STATED PREFERENCES (SP) TO ANALYZE THE SERVICE QUALITY OF PUBLIC TRANSPORT

In order to determine the level of satisfaction of the public transport services, the passengers jointly evaluate the various attributes that represent the different aspects of the level of service. From a methodological viewpoint this means finding the weighting that individuals use to evaluate those attributes within what is considered as the level of global satisfaction or utility. In this paper we obtain indicators that permit the aggregate measurement of the quality of the public transport bus services on Gran Canaria in Spain. The analysis focuses on obtaining the preferences using designs of Stated Preferences (SP) that give the individual the choice between the current service and a hypothetical service defined, from a combination of the most relevant variables. With this information multinomial logit models are estimated that permit us to obtain a linear representation of the utility function parameters, from which a measure of the global quality of the service is obtained. The results of the analysis demonstrate that passengers have clearly different behaviour, depending on whether they are urban or interurban users; this is especially relevant in their perception of certain attributes such as frequency, and to some extent the willingness to pay relative to the components of total travelling time.

Circular dichroism simulated spectra of chiral gold nanoclusters: A dipole approximation

Circular dichroism (CD) spectra of chiral bare and thiol-passivated gold nanoclusters have been calculated within the dipole approximation. The calculated CD spectra show features that allow us to distinguish between clusters with different indexes of chirality. The main factor responsible of the differences in the CD lineshapes is the distribution of interatomic distances that characterize the chiral cluster geometry. These results provide theoretical support for the quantification of chirality and its measurement, using the CD lineshapes of chiral metal nanoclusters.Comment: 3 pages + 4 figure

Schmidt's Conjecture and Star Formation in Molecular Clouds

We investigate Schmidt's conjecture (i.e., that the star formation rate scales in a power-law fashion with the gas density) for four well-studied local molecular clouds (GMCs). Using the Bayesian methodology we show that a local Schmidt scaling relation of the form Sigma*(A_K) = kappa x (A_K)^{beta} (protostars pc^{-2}) exists within (but not between) GMCs. Further we find that the Schmidt scaling law, by itself, does not provide an adequate description of star formation activity in GMCs. Because the total number of protostars produced by a cloud is given by the product of Sigma*(A_K) and S'(> A_K), the differential surface area distribution function, integrated over the entire cloud, the cloud's structure plays a fundamental role in setting the level of its star formation activity. For clouds with similar functional forms of Sigma*(A_K), observed differences in their total SFRs are primarily due to the differences in S'(> A_K) between the clouds. The coupling of Sigma*(A_K) with the measured S'(> A_K) in these clouds also produces a steep jump in the SFR and protostellar production above A_K ~ 0.8 magnitudes. Finally, we show that there is no global Schmidt law that relates the star formation rate and gas mass surface densities between GMCs. Consequently, the observed Kennicutt-Schmidt scaling relation for disk galaxies is likely an artifact of unresolved measurements of GMCs and not a result of any underlying physical law of star formation characterizing the molecular gas.Comment: 34 pages, 8 figures, and 2 tables; accepted for publication in ApJ on Sept 23, 201

Ecological conditions leading to the seep of antibiotic resistance genes in the model-type bacterium Escherichia coli

In antibiotic therapy design, conventional wisdom holds that higher antibiotic dosages always leads to the observation of fewer bacterial cells, resulting in a monotonic decay in cell number as a function of increasing antibiotic dose; accordingly, throughout this thesis, we will call this phenomenon a monotone dose-response profile. When we analysed the evolution of antibiotic resistance mediated by the multi-drug efflux pump AcrAB-TolC in Escherichia coli to study if such a monotone dose-response is maintained at all times, our analysis showed that higher dosages can, in fact, lead to higher bacterial loads. This is because selection for drug resistance is mediated by the duplication of the genes, AcrAB-TolC, that encode the aforementioned efflux pump. As explained in detail below, our work highlights the idea that Darwinian selection on additional copies of AcrAB-TolC is a non-linear function of antibiotic dose and that the observed transition from monotone to non-monotone dose-response is a consequence of AcrAB-TolC being strongly selected at very specific dosages. We term this phenomenon an ‘evolutionary hotspot’. Next, we extended the above experimental system to solid media to study how selection on resistance mediated by AcrAB-TolC leads to a ‘spatio-genomic patterning’ effect that we call a ‘bullseye’. Using a bespoke culture device developed as part of this PhD, we show that spatial selection on resistance also depends non-linearly on the distance of the cell from an antibiotic source, and that the non-linearity can be multi-modal as a function of distance, and therefore also of antibiotic dose. This result also contradicts the aforementioned principle that higher antibiotic dosages necessarily lead to fewer bacterial cells. Following on from this, we then studied the ability of microbial competitors for resources to modulate the antibiotic sensitivity of a particular strain of E. coli, namely Tets , using a range of multi-species experiments. We measured the sensitivity to antibiotics of Tets both with, and without, one bacterial or fungal competitor. When that competitor was equally sensitive to the antibiotic, we observed that Tets was less sensitive to it, in part due to an ‘antibiotic sinking’ effect carried out by the competitor strain. However, when the competitor was not sensitive to the antibiotic, Tets was, accordingly, more sensitive than in the absence of competition. In this latter case, the competitor seemed to reduce the growth of Tets by carbon theft as part of a phenomenon known as ‘competitive suppression’. Moreover, this ecological effect is one that synergises with the action of the antibiotic. Finally, we turned to a study of an ecological trade-off motivated by ribosome-binding antibiotics. So, by manipulating the content of ribosomal RNA in the E. coli cell, a large and essential molecule that is bound by antibiotics such as tetracycline or erythromycin, we could subsequently manipulate what is known as a metabolic trade-off between growth rate and growth yield. The latter is the number of cells produced per molecule of carbon found in the extracellular environment of the bacterial population. Using glucose as carbon source we therefore constructed an empirical fitness landscape that shows how the optimum number of ribosomal rRNA operons depends on extracellular glucose concentration. Whilst this study does not relate directly to the presence of an antibiotic, it does show that by altering the number of operons in a manner that is known to affect antibiotic susceptibility, we can also mediate important growth parameters like cell yield, aka efficiency, and growth rate.Engineering and Physical Sciences Research Council (EPSRC

Hydrocracking of long paraffins over Pt-Pd/WO3-ZrO2 in the presence of sulfur and aromatic impurities

The hydrocracking of long paraffins in the presence of sulfur and aromatic impurities using Pt–Pd/WO3–ZrO2 was assessed. The catalysts were tested for n-hexadecane hydrocraking in the presence and absence of several poisons, benzothiophene, quinolein, carbon disulfide, benzene, and naphthalene. At small impurity levels, aromatics are beneficial for the hydrocracking of long paraffins because they increase the liquid yield and reduce the cracking to light gases. Sulfur compounds were strong poisons of the activity. Benzothiophene was the strongest, producing the highest decline in activity and being more strongly chemisorbed than basic quinolein. Sulfur poisoning drastically affected the hydrocracking activity, indicating that acid isomerization cracking on WO3–ZrO2 follows a bifunctional mechanism with a big influence of the metal function. Incorporation of Pd to Pt/WO3–ZrO2 reduced the sulfur poisoning, with Pt–Pd (3:1)/WO3–ZrO2 being the best catalyst for stable hydrocracking of long paraffins in the presence of sulfur. This catalyst retained most of the activity of the Pt/WO3–ZrO2 parent material while being less affected by sulfur.Fil: Busto, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Grau, Javier Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Sepulveda, Jorge H.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Tsendra, Oksana. National Academy of Sciences. Chuiko Institute of Surface Chemistry; UcraniaFil: Vera, Carlos Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentin