Online Optimization of Complex Transportation Systems

This paper discusses online optimization of real-world transportation systems. We concentrate on transportation problems arising in production and manufacturing processes, in particular in company internal logistics. We describe basic techniques to design online optimization algorithms for such systems, but our main focus is decision support for the planner: which online algorithm is the most appropriate one in a particular setting? We show by means of several examples that traditional methods for the evaluation of online algorithms often do not suffice to judge the strengths and weaknesses of online algorithms. We present modifications of well-known evaluation techniques and some new methods, and we argue that the selection of an online algorithm to be employed in practice should be based on a sound combination of several theoretical and practical evaluation criteria, including simulation

Online k-server routing problems

In an online k-server routing problem, a crew of k servers has to visit points in a metric space as they arrive in real time. Possible objective functions include minimizing the makespan (k-Traveling Salesman Problem) and minimizing the sum of completion times (k-Traveling Repairman Problem). We give competitive algorithms, resource augmentation results and lower bounds for k-server routing problems in a wide class of metric spaces. In some cases the competitive ratio is dramatically better than that of the corresponding single server problem. Namely, we give a 1+O((log¿k)/k)-competitive algorithm for the k-Traveling Salesman Problem and the k-Traveling Repairman Problem when the underlying metric space is the real line. We also prove that a similar result cannot hold for the Euclidean plane

Tax Mimicking in the Short- and the Long-Run: Evidence from German Reunification

This paper uses the quasi-experiment of Germany's reunification to identify local tax mimicking by municipalities in Eastern-Germany. After reunification, East-German municipalities were allowed to independently set, for the first time in decades, local business and property tax rates. I explore whether the tax rates chosen by East-German border municipalities were influenced by the tax rates of adjacent West-German municipalities. To obtain causal estimates, I rely on instrumental variables regressions within the spatial lag framework, using West-German border municipalities' tax rates in 1989 as instruments for their post-reunification tax rates. The results suggest that East-German municipalities mimicked business tax rates immediately after reunification, but not in later years. I find no evidence of mimicking for property taxes. These results indicate that mimicking is not an important determinant of local tax policy

Combination therapy with oral treprostinil for pulmonary arterial hypertension. A double-blind placebo-controlled clinical trial

Rationale: Oral treprostinil improves exercise capacity in patients with pulmonary arterial hypertension (PAH), but the effect on clinical outcomes was unknown. Objectives: To evaluate the effect of oral treprostinil compared with placebo on time to first adjudicated clinical worsening event in participants with PAH who recently began approved oral monotherapy. Methods: In this event-driven, double-blind study, we randomly allocated 690 participants (1:1 ratio) with PAH to receive placebo or oral treprostinil extended-release tablets three times daily. Eligible participants were using approved oral monotherapy for over 30 days before randomization and had a 6-minute-walk distance 150 m or greater. The primary endpoint was the time to first adjudicated clinical worsening event: death; hospitalization due to worsening PAH; initiation of inhaled or parenteral prostacyclin therapy; disease progression; or unsatisfactory long-term clinical response. Measurements and Main Results: Clinical worsening occurred in 26% of the oral treprostinil group compared with 36% of placebo participants (hazard ratio, 0.74; 95% confidence interval, 0.56–0.97; P = 0.028). Key measures of disease status, including functional class, Borg dyspnea score, and N-terminal pro–brain natriuretic peptide, all favored oral treprostinil treatment at Week 24 and beyond. A noninvasive risk stratification analysis demonstrated that oral treprostinil–assigned participants had a substantially higher mortality risk at baseline but achieved a lower risk profile from Study Weeks 12–60. The most common adverse events in the oral treprostinil group were headache, diarrhea, flushing, nausea, and vomiting. Conclusions: In participants with PAH, addition of oral treprostinil to approved oral monotherapy reduced the risk of clinical worsening. Clinical trial registered with www.clinicaltrials.gov (NCT01560624)

Does Fiscal Decentralisation Foster Regional Investment in Productive Infrastructure?

The aim of this paper is to analyze the effect of revenue decentralization on the provision of infrastructure at the sub-national level. We estimate the effects of revenue decentralization and earmarked grant financing on the level of sub-national infrastructure investment in 20 European countries over the period 1990-2009. The results are interpreted in light of the predictions of the theory on fiscal federalism. We find that it is sub-national infrastructure investment that increases after revenue decentralization and not investment in redistribution. However, the effect of revenue decentralization is lower the higher the use of earmarked grants to fund infrastructure investment

Identifying Local Tax Mimicking: Administrative Borders and a Policy Reform

This paper exploits an exogenous reform of the local fiscal equalization scheme in the German State of North Rhine-Westphalia to identify tax mimicking by municipalities in the neighboring state of Lower Saxony. The spatial lag regressions provide no evidence for the existence of strategic interactions in municipal business and property taxes. In contrast, traditional spatial lag regressions that rely on variation in neighbors' demographic, political, or economic characteristics for identification provide strong evidence for strategic interactions. This pattern of results indicates that most of the extant literature overestimates the importance of local tax mimicking

Euler is standing in line dial-a-ride problems with precedence-constraints

AbstractIn this paper we study algorithms for “Dial-a-Ride” transportation problems. In the basic version of the problem we are given transportation jobs between the vertices of a graph and the goal is to find a shortest transportation that serves all the jobs. This problem is known to be NP-hard even on trees. We consider the extension when precedence relations between the jobs with the same source are given. Our results include a polynomial time algorithm on paths and approximation algorithms for general graphs and trees with performances of 9/4 and 5/3, respectively