Remarks on separating words

The separating words problem asks for the size of the smallest DFA needed to distinguish between two words of length <= n (by accepting one and rejecting the other). In this paper we survey what is known and unknown about the problem, consider some variations, and prove several new results

Local and Global Superconductivity in Bismuth

We performed magnetization M(H,T) and magnetoresistance R(T,H) measurements on powdered (grain size ~ 149 micrometers) as well as highly oriented rhombohedral (A7) bismuth (Bi) samples consisting of single crystalline blocks of size ~ 1x1 mm2 in the plane perpendicular to the trigonal c-axis. The obtained results revealed the occurrence of (1) local superconductivity in powdered samples with Tc(0) = 8.75 \pm 0.05 K, and (2) global superconductivity at Tc(0) = 7.3 \pm 0.1 K in polycrystalline Bi triggered by low-resistance Ohmic contacts with silver (Ag) normal metal. The results provide evidence that the superconductivity in Bi is localized in a tiny volume fraction, probably at intergrain or Ag/Bi interfaces. On the other hand, the occurrence of global superconductivity observed for polycrystalline Bi can be accounted for by enhancement of the superconducting order parameter phase stiffness induced by the normal metal contacts, the scenario proposed in the context of "pseudogap regime" in cuprates [E. Berg et al., PRB 78, 094509 (2008)].Comment: 12 pages including 9 figures and 1 table, Special Issue to the 80th birthday anniversary of V. G. Peschansky, Electronic Properties of Conducting System

Best in Class International Franchising: Report for the UK Retail Sector

Retailing is such a fast-moving industry it is difficult to keep on top of changes in domestic markets, let alone those in geographically and culturally distant foreign markets. Although it is tempting for a UK-based retailer to remain domestic and focus on strengthening their competitive position in the UK before going overseas, the most successful retailers continuously explore what it takes to operate effectively across national borders. UK retailers need to “think bigger” if they are to escape the economic slowdown of Western Europe. There is now a renewed push for internationalisation by UK firms and they are setting adventurous growth targets. Retailing is fast becoming a global industry and it is vital for “UK plc” that our leading retailers are successful in emerging markets. Against this backdrop, we conducted a study of one type of foreign market entry mode, namely franchising. We propose that franchising is to retailing what exporting is to manufacturing. It is a low-risk, low-involvement way for retailers to enter risky foreign markets, but which nevertheless must be professionally executed. In order to shed light on how UK retailers can make franchising work in emerging markets, we focus on the advanced franchising model used by one particular retailer. This model has been developed over decades of steady expansion of its franchising operations overseas. As well as examining their franchising operations, the study gathered a range of other information on international franchising in order to develop a complete picture of good practices. It is unlikely that a firm with a fast-moving, complex product assortment (e.g., general merchandise) will be able to follow the franchising model of dealing with many small franchisees across many foreign markets (i.e., the McDonald’s model). Indeed, the focal retailer uses an area development franchising approach, targeting franchisees that have capabilities sufficient to develop and manage a franchisor-branded store network in their country or region. While not equals, given the franchisor’s ownership of the brand, such relationships operate as partnerships. Franchisees are empowered to exert influence and use their local know-how to help meet the precise needs of foreign customers. Unlike in traditional franchising partnerships, where the franchisor is in control and intensively monitors across its network of franchisees, we observe that cross-border franchising may be optimally developed through openly communicating with and trusting a capable partner. The differences between emerging markets and the UK can be so extreme that it is difficult for the franchisor to control operations there, irrespective of their resource base and experience. In effect, the franchisor is reliant on the franchisee to make and implement decisions in the local marketplace and absorb risks. The overseas franchisees can effectively play a role in building the brand with the franchisor through a form of alliance. Knowledge exchange is crucial not only in the running of the franchise partnership but also for the franchisor’s learning about local market conditions and growth opportunities. When operating in emerging markets the franchisor needs to “learn from their experiences all the time”. UK retail brands resonate strongly amongst aspirational, emerging market customers. Yet, retailers can be slow to go overseas if they perceive differences in, and lack familiarity with, foreign markets. This is where franchising comes in. Far from being a basic business model, best-in-class franchising can be made to play a central role in overseas retailing due to its ability to mitigate threats and seek out growth opportunities. Furthermore, UK retailers can derive flexibility advantages from using franchising in emerging markets as the basis upon which to expand into other, higher-profit equity-based modes (e.g., joint ventures) if and when local circumstances dictate this

Runtime Coordinated Heterogeneous Tasks in Charm++

Effective utilization of the increasingly heterogeneous hardware in modern supercomputers is a significant challenge. Many applications have seen performance gains by using GPUs, but many implementations leave CPUs sitting idle.In this paper, we describe a runtime managed system for coordinating heterogeneous execution. This system manages data transfers to and from GPU devices and schedules work across the computational resources of the system. The programmer need only tag methods and parameters to enable heterogeneous execution.Using this system, we observe improvements in programmer productivity and application performance. For selected benchmarks, when using heterogeneous execution we observe speedups of up to 3.09x relative to using only the host cores or only the device

Quantum Monte Carlo calculations of six-quark states

The variational Monte Carlo method is used to find the ground state of six quarks confined to a cavity of diameter R_c, interacting via an assumed non-relativistic constituent quark model (CQM) Hamiltonian. We use a flux-tube model augmented with one-gluon and one-pion exchange interactions, which has been successful in describing single hadron spectra. The variational wave function is written as a product of three-quark nucleon states with correlations between quarks in different nucleons. We study the role of quark exchange effects by allowing flux-tube configuration mixing. An accurate six-body variational wave function is obtained. It has only ~13% rms fluctuation in the total energy and yields a standard deviation of ~<.1%; small enough to be useful in discerning nuclear interaction effects from the large rest mass of the two nucleons. Results are presented for three values of the cavity diameter, R_c=2, 4, and 6 fm. They indicate that the flux-tube model Hamiltonian with gluon and pion exchange requires revisions in order to obtain agreement with the energies estimated from realistic two-nucleon interactions. We calculate the two-quark probability distribution functions and show how they may be used to study and adjust the model Hamiltonian.Comment: 49 pages, 13 figures, submitted to Phys. Rev.

Extreme alpha-clustering in the 18O nucleus

The structure of the 18O nucleus at excitation energies above the alpha decay threshold was studied using 14C+alpha resonance elastic scattering. A number of states with large alpha reduced widths have been observed, indicating that the alpha-cluster degree of freedom plays an important role in this N not equal Z nucleus. However, the alpha-cluster structure of this nucleus is very different from the relatively simple pattern of strong alpha-cluster quasi-rotational bands in the neighboring 16O and 20Ne nuclei. A 0+ state with an alpha reduced width exceeding the single particle limit was identified at an excitation energy of 9.9+/-0.3 MeV. We discuss evidence that states of this kind are common in light nuclei and give possible explanations of this feature.Comment: 4 pages, 2 figures, 1 table. Resubmission with minor changes for clarity, including removal of one figur

Comparative Performance between Two Photogrammetric Systems and a Reference Laser Tracker Network for Large-Volume Industrial Measurement

This paper determines the capability of two photogrammetric systems in terms of their measurement uncertainty in an industrial context. The first system – V-STARS inca3 from Geodetic Systems Inc. – is a commercially available measurement solution. The second system comprises an off-the-shelf Nikon D700 digital camera fitted with a 28 mm Nikkor lens and the research-based Vision Measurement Software (VMS). The uncertainty estimate of these two systems is determined with reference to a calibrated constellation of points determined by a Leica AT401 laser tracker. The calibrated points have an average associated standard uncertainty of 12·4 μm, spanning a maximum distance of approximately 14·5 m. Subsequently, the two systems’ uncertainty was determined. V-STARS inca3 had an estimated standard uncertainty of 43·1 μm, thus outperforming its manufacturer's specification; the D700/VMS combination achieved a standard uncertainty of 187 μm

The role of secondary Reggeons in central meson production

We estimate the contribution of f_2 trajectory exchange to the central \eta and \eta^\prime production. It is shown that secondary Reggeons may give a large contribution to processes of double diffractive meson production at high energy.Comment: 7 pages, Latex, 5 figure