Bidirectional transport on a dynamic lattice

Bidirectional variants of stochastic many particle models for transport by molecular motors show a strong tendency to form macroscopic clusters on static lattices. Inspired by the fact that the microscopic tracks for molecular motors are dynamical, we study the influence of different types of lattice dynamics on stochastic bidirectional transport. We observe a transition toward efficient transport (corresponding to the dissolution of large clusters) controlled by the lattice dynamics.Comment: 5 pages, 5 figure

Last but not Least: Additional Positional Effects on Citation and Readership in arXiv

We continue investigation of the effect of position in announcements of newly received articles, a single day artifact, with citations received over the course of ensuing years. Earlier work [arXiv:0907.4740, arXiv:0805.0307] focused on the "visibility" effect for positions near the beginnings of announcements, and on the "self-promotion" effect associated to authors intentionally aiming for these positions, with both found correlated to a later enhanced citation rate. Here we consider a "reverse-visibility" effect for positions near the ends of announcements, and on a "procrastination" effect associated to submissions made within the 20 minute period just before the daily deadline. For two large subcommunities of theoretical high energy physics, we find a clear "reverse-visibility" effect, in which articles near the ends of the lists receive a boost in both short-term readership and long-term citations, almost comparable in size to the "visibility" effect documented earlier. For one of those subcommunities, we find an additional "procrastination" effect, in which last position articles submitted shortly before the deadline have an even higher citation rate than those that land more accidentally in that position. We consider and eliminate geographic effects as responsible for the above, and speculate on other possible causes, including "oblivious" and "nightowl" effects.Comment: 13p, appeared JASIST on-line first (12 Oct 2010

Intracellular transport driven by cytoskeletal motors: General mechanisms and defects

Cells are strongly out-of-equilibrium systems driven by continuous energy supply. They carry out many vital functions requiring active transport of various ingredients and organelles, some being small, others being large. The cytoskeleton, composed of three types of filaments, determines the shape of the cell and plays a role in cell motion. It also serves as a road network for the so-called cytoskeletal motors. These molecules can attach to a cytoskeletal filament, perform directed motion, possibly carrying along some cargo, and then detach. It is a central issue to understand how intracellular transport driven by molecular motors is regulated, in particular because its breakdown is one of the signatures of some neuronal diseases like the Alzheimer. We give a survey of the current knowledge on microtubule based intracellular transport. We first review some biological facts obtained from experiments, and present some modeling attempts based on cellular automata. We start with background knowledge on the original and variants of the TASEP (Totally Asymmetric Simple Exclusion Process), before turning to more application oriented models. After addressing microtubule based transport in general, with a focus on in vitro experiments, and on cooperative effects in the transportation of large cargos by multiple motors, we concentrate on axonal transport, because of its relevance for neuronal diseases. It is a challenge to understand how this transport is organized, given that it takes place in a confined environment and that several types of motors moving in opposite directions are involved. We review several features that could contribute to the efficiency of this transport, including the role of motor-motor interactions and of the dynamics of the underlying microtubule network. Finally, we discuss some still open questions.Comment: 74 pages, 43 figure

Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?

Intracellular transport processes driven by molecular motors can be described by stochastic lattice models of self-driven particles. Here we focus on bidirectional transport models excluding the exchange of particles on the same track. We explore the possibility to have efficient transport in these systems. One possibility would be to have appropriate interactions between the various motors' species, so as to form lanes. However, we show that the lane formation mechanism based on modified attachment/detachment rates as it was proposed previously is not necessarily connected to an efficient transport state and is suppressed when the diffusivity of unbound particles is finite. We propose another interaction mechanism based on obstacle avoidance that allows to have lane formation for limited diffusion. Besides, we had shown in a separate paper that the dynamics of the lattice itself could be a key ingredient for the efficiency of bidirectional transport. Here we show that lattice dynamics and interactions can both contribute in a cooperative way to the efficiency of transport. In particular, lattice dynamics can decrease the interaction threshold beyond which lanes form. Lattice dynamics may also enhance the transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table

The succinctness of first-order logic on linear orders

Succinctness is a natural measure for comparing the strength of different logics. Intuitively, a logic L_1 is more succinct than another logic L_2 if all properties that can be expressed in L_2 can be expressed in L_1 by formulas of (approximately) the same size, but some properties can be expressed in L_1 by (significantly) smaller formulas. We study the succinctness of logics on linear orders. Our first theorem is concerned with the finite variable fragments of first-order logic. We prove that: (i) Up to a polynomial factor, the 2- and the 3-variable fragments of first-order logic on linear orders have the same succinctness. (ii) The 4-variable fragment is exponentially more succinct than the 3-variable fragment. Our second main result compares the succinctness of first-order logic on linear orders with that of monadic second-order logic. We prove that the fragment of monadic second-order logic that has the same expressiveness as first-order logic on linear orders is non-elementarily more succinct than first-order logic

Training marketing by German companies – which training place characteristics are communicated?

Context: Although the German dual system of vocational education and training makes a major contribution to securing the supply of skilled workers for trade and industry, its function has been under scrutiny for several years. Companies are finding it increasingly difficult to recruit trainees, and increasing numbers of training places are vacant. However, such recruitment problems tend to be concentrated in certain occupations rather than occurring across all sectors equally. This has led to a significant increase in competition among companies seeking to secure the services of trainees in various occupations and calls into question the extent to which such fierce rivalry is reflected in the type of training marketing they conduct.  Approach: This paper investigates the training place characteristics companies communicate in their advertisements. Among these characteristics, differences exist in the general conditions of training, requirements for trainees and incentives the companies provide. Latent class analyses were used to investigate the patterns revealed in the training place characteristics and to examine if the frequency with which patterns occur correlates with whether a company is seeking trainees for an occupation with or without recruitment problems and with company size. The analyses were based on data collected from 1,939 small and medium-sized enterprises via standardised telephone interviews conducted at the beginning of 2016. The companies in question had offered training places in one of nine selected dual occupations. Four of the training occupations considered have recruitment problems. There are no recruitment difficulties in the other five.Findings: The single group latent class analysis initially conducted resulted in a model with three latent classes exhibiting clearly differentiated patterns of training place characteristics. As well as focusing on general conditions and the requirements for training, the “aggressive” pattern mainly emphasises the incentives the training place or company offered. The “requirements-oriented” pattern concentrates on the future requirements for trainees. The “basic” pattern communicates only a very few fundamental training place characteristics. A subsequent multi-group latent class analysis revealed evidence that small and medium-sized enterprises offering training are more likely to display an aggressive pattern in occupations with recruitment problems than SMEs providing training in occupations where there are no recruitment difficulties. By the same token, small and medium-sized enterprises with training provisions in occupations with recruitment problems are less likely to exhibit training marketing aligned to the requirements of applicants than firms offering training in occupations without recruitment difficulties, although this is significantly clearer amongst small companies than medium-sized companies. Nevertheless, the class with requirements-oriented marketing constitutes the largest class for all four company groups. Conclusion: The results indicate that conditions in the training market affect the training marketing companies carry out. However, they also show that companies are more likely to use their training marketing to react to recruitment problems that have already occurred rather than take a preventative approach towards such difficulties. For small companies in particular, the limitations in resources available for more elaborate training marketing likely contribute to this approach. Nevertheless, further research is needed to consolidate the outcomes identified here.&nbsp

When Labour and Capital Collude: The Varieties of Welfare Capitalism and Early Retirement in Europe, Japan and the USA. CES Germany & Europe Working Papers, No. 00.4, 2000

The institutionalisation of early retirement has become a universal feature of postwar industrial economies, though there are significant cross-national variations. This paper studies the impact of different types of welfare regimes, production systems and labour relations on early exit from work. After an analysis of the main trends, the paper discusses the costs and benefits of early retirement for the various actors — labour, capital and the state — at different levels. The paper outlines both the "pull” and "push” factors of early exit. It first compares the distinct welfare state regimes and private occupational pensions in their impact on early retirement. Then it looks at the labour-shedding strategies inherent to particular employment regimes, production systems and financial governance structures. Finally, the impact of particular industrial relations systems, and especially the role of unions is discussed. The paper finds intricate "institutional complementarities” between particular welfare states, production regimes and industrial relations systems, and these structure the incentives under which actors make decisions on work and retirement. The paper argues that the "collusion” between capital, labour and the state in pursuing early retirement is not merely following a labour-shedding strategy to ease mass unemployment, but also caused by the need for economic restructuration, the downsizing pressures from financial markets, the maintenance of peaceful labour relations, and the consequences of a seniority employment system