Lost in Abstraction: Monotonicity in Multi-Threaded Programs (Extended Technical Report)

Monotonicity in concurrent systems stipulates that, in any global state, extant system actions remain executable when new processes are added to the state. This concept is not only natural and common in multi-threaded software, but also useful: if every thread's memory is finite, monotonicity often guarantees the decidability of safety property verification even when the number of running threads is unknown. In this paper, we show that the act of obtaining finite-data thread abstractions for model checking can be at odds with monotonicity: Predicate-abstracting certain widely used monotone software results in non-monotone multi-threaded Boolean programs - the monotonicity is lost in the abstraction. As a result, well-established sound and complete safety checking algorithms become inapplicable; in fact, safety checking turns out to be undecidable for the obtained class of unbounded-thread Boolean programs. We demonstrate how the abstract programs can be modified into monotone ones, without affecting safety properties of the non-monotone abstraction. This significantly improves earlier approaches of enforcing monotonicity via overapproximations

Impedance generalization for plasmonic waveguides beyond the lumped circuit model

We analytically derive a rigorous expression for the relative impedance ratio between two photonic structures based on their electromagnetic interaction. Our approach generalizes the physical meaning of the impedance to a measure for the reciprocity-based overlap of eigenmodes. The consistence with known cases in the radiofrequency and optical domain is shown. The analysis reveals where the applicability of simple circuit parameters ends and how the impedance can be interpreted beyond this point. We illustrate our approach by successfully describing a Bragg reflector that terminates an insulator-metal-insulator plasmonic waveguide in the near-infrared by our mpedance concept

Degrees of Lookahead in Regular Infinite Games

We study variants of regular infinite games where the strict alternation of moves between the two players is subject to modifications. The second player may postpone a move for a finite number of steps, or, in other words, exploit in his strategy some lookahead on the moves of the opponent. This captures situations in distributed systems, e.g. when buffers are present in communication or when signal transmission between components is deferred. We distinguish strategies with different degrees of lookahead, among them being the continuous and the bounded lookahead strategies. In the first case the lookahead is of finite possibly unbounded size, whereas in the second case it is of bounded size. We show that for regular infinite games the solvability by continuous strategies is decidable, and that a continuous strategy can always be reduced to one of bounded lookahead. Moreover, this lookahead is at most doubly exponential in the size of a given parity automaton recognizing the winning condition. We also show that the result fails for non-regular gamesxwhere the winning condition is given by a context-free omega-language.Comment: LMCS submissio

Labor Mobility and Patenting Activity

We measure the quantitative importance of labor mobility as a vehicle for the transmission of knowledge and skills across firms. For this purpose we create a unique data set that matches all applications of Danish firms at the European Patent Office to linked employer-employee register data for the years 1999-2002. The Danish workforce is split into "R&D workers", who hold a bachelor's or a master's degree in a technical field, and "non{R&D workers". We find that mobile R&D workers ("R&D joiners"') contribute more to patenting activity than immobile R&D workers. Furthermore, R&D workers who have previously been employed by a patenting firm ("patent exposed workers") have a larger effect on patenting activity than R&D workers without this experience. Patent exposed R&D joiners constitute the most productive group of workers: for firms that patented prior to 1999, one additional worker of this type relates to an increase in the number of patent applications of the new employer by 0.0646. This corresponds to a 14 percent increase in the mean number of yearly patent applications. We also find that mobility of R&D workers increases the joint patenting activity of the donor and recipient firms, confirming the importance of labor mobility for innovation in the economy.labor mobility; dynamic count data; patents

Labor Mobility, Social Network Effects, and Innovative Activity

We study the mapping between labor mobility and industrial innovative activity for the population of R&D active Danish firms observed between 1999 and 2004. Our study documents a positive relationship between the number of workers who join a firm and the firm's innovative activity. This relationship is stronger if workers join from innovative firms. We also find evidence for positive feedback from workers who leave for an innovative firm, presumably because the worker who left stays in contact with their former colleagues. This implies that the positive feedback ("social network effects") that has been found by other studies not only exists but even outweighs the disruption and loss of knowledge occurring to the previous employer from the worker leaving. Summing up the effects of joining and leaving workers, we find ample evidence for mobility to be associated with an increase in total innovative activity of the new and the old employer.labor mobility, innovation, social network

The value-added of investable hedge fund indices

This paper empirically investigates the risk and performance of three types of alternative beta products over the January 2002 to September 2009 time period: funds of hedge funds (FHFs), investable hedge fund indices (IHFIs), and hedge fund replication strategies (HFRS). We show that IHFIs are true alternative beta products with high correlations and beta to noninvestable hedge fund indices. Our results further suggest that, in a best case scenario, IHFIs outperform FHFs and HFRS on a risk-adjusted basis. However, in the worst case scenario, IHFIs underperform both investments. If we take the average of all IHFIs, we find they perform equally well as FHFs. Hence, IHFIs constitute a solid alternative to FHF investments, while costing substantially less, and offering generally more transparency and liquidity. We propose that fee-sensitive investors especially should consider taking a core-satellite approach to their hedge fund portfolio, with the core represented by cheap passive hedge fund beta through IHFIs, and the satellite represented by more expensive and actively managed alphagenerating FHFs. --Hedge funds,investable hedge fund indices,alternative beta,funds of hedge funds,hedge fund replication,Omega ratio

Regulation of Pharmaceutical Prices: Evidence from a Reference Price Reform in Denmark

On April 1, 2005, Denmark changed the way references prices, a main determinant of reimbursements for pharmaceutical purchases, are calculated. The previous reference prices, which were based on average EU prices, were substituted to minimum domestic prices. Novel to the literature, we estimate the joint effects of this reform on prices and quantities. Prices decreased more than 26 percent due to the reform, which reduced patient and government expenditures by 3.0 percent and 5.6 percent, respectively, and producer revenues by 5.0 percent. The prices of expensive products decreased more than their cheaper counterparts, resulting in large differences in patient benefits from the reform.pharmaceutical markets; regulation; co-payments; reference pricing; asymmetric welfare effects