Persistent currents through a quantum impurity: Protection through integrability

We consider an integrable model of a one-dimensional mesoscopic ring with the conduction electrons coupled by a spin exchange to a magnetic impurity. A symmetry analysis based on a Bethe Ansatz solution of the model reveals that the current is insensitive to the presence of the impurity. We argue that this is true for any integrable impurity-electron interaction, independent of choice of physical parameters or couplings. We propose a simple physical picture of how the persistent current gets protected by integrability.Comment: 5 pages, minor update

Subpopulations of Mononuclear Cells in Microscopic Lesions of Psoriatic Patients. Selective Accumulation of Suppressor/Cytotoxic T Cells in Epidermis During the Evolution of the Lesion

The age of microscopic lesions in psoriatic subjects was assessed from the stacking characteristics in the horny layer and related to type and density (cells/tissue volume) of mononuclear cells in the epidermis and the dermis determined by immunoperoxidase methods using monoclonal antibodies. Pan T cells (Lyt-2+, Lyt-3+, Leu-4+, OKT3+), T helper cells (Leu-3a+, OKT4+), T suppressor/cytotoxic cells (Leu-2a+, OKT8+), Ia+ cells and monocytes (OKM2+, BRL αmono+) were determined in epidermis and dermis. The psoriatic lesion was divided into regions underneath a parakeratotic and an orthohyperkeratotic/hypergranular portion of the horny layer and contrasted with perilesional and uninvolved psoriatic skin as well as with healthy skin. In the various regions and skin layers, the cell density was highest in parakeratosis and decreased toward normality with decreasing histologic abnormality. The relation between epidermal and dermal cell densities of the T-cell subsets was modified in the involved psoriatic skin with a selective preponderance of T suppressor/cytotoxic cells in the epidermis. The accumulation was present in the youngest lesion found (3 days) and cell densities were unchanged in older lesions. The finding suggests that the altered relationship in the subsets of T cells has an important role during the induction and progress of the psoriatic process in the skin

Dynamic platform modeling for concurrent product-production reconfiguration

To meet a wide range of customer needs, a variety of product concepts can be modeled employing a platform approach. Whereas frequent market changes can be accommodated by dynamically modifying product concepts in iterations, capabilities in production are seldom well incorporated as part of design iterations. In this paper, a dynamic platform modeling approach that supports concurrent product-production reconfiguration is presented. The approach builds on Set-Based Concurrent Engineering (SBCE) processes and a function modeling technique is used to represent product-production variety streams inherent in a production operation model. To demonstrate the approach, a comprehensive case from the aerospace industry is presented. Conceptual representations of a set of aero engine sub-systems and a variety of welding configurations, including their inherent constraints, are mutually modeled and assessed. The results show that a set of product-production alternatives can be dynamically controlled by integrating product-production constraints using a production operation model. Following SBCE processes, inferior alternatives can be put aside until new information becomes available and a new set of alternatives can be reconfigured. The dynamics and concurrency of the approach can potentially reduce the risk of late and costly modifications that propagate from design to production

Describing and evaluating functionally integrated and manufacturing restricted product architectures

Within manufacturing companies, the architectural description of how a product is built is typically well defined while the architecture of the product from a functional view describing how the functional requirements are met in the product is often less articulated. For products composed of many components (modular products) such descriptions are clear, whereas few representation schemes are available that treat highly functionally integrated components, where all the functions are satisfied by one integral, homogenous physical structure. In this paper, an approach to describe the architecture for integrated components in the aerospace industry is described. Different regions of the component, termed as sections, are assumed to satisfy the functions required of the structure which are often manufactured by joining (welding) different segments. By assigning sectional and functional information to different manufactured segments of the structure, graphs are created that link the functional requirements and sections. Two different methods, one based on set compositions and other on creating an enhanced function-means (EF-M) tree are used to link the functions to the sections of the component, resulting in different graphs for different types of manufacturing splits for the same component. Comparison of the methods is then carried out using properties of the graphs produced. The method that utilises set compositions performs well for entire component descriptions while the method that uses an EF-M tree to create a graph describes sections (regions) of the component well so that functional relationships can be better described (integration of already existing design knowledge). The product descriptions created can help designers to identify how alternative manufacturing splits impact the functionally defined product architecture which in turn enables both improved manufacturing and improved design decisions

Pareto-optimal alloys

Large databases that can be used in the search for new materials with specific properties remain an elusive goal in materials science. The search problem is complicated by the fact that the optimal material for a given application is usually a compromise between a number of materials properties and the price. In this letter we present a database consisting of the lattice parameters, bulk moduli, and heats of formation for over 64,000 ordered metallic alloys, which has been established by direct first-principles density-functional-theory calculations. Furthermore, we use a concept from economic theory, the Pareto-optimal set, to determine optimal alloy solutions for the compromise between low compressibility, high stability and price.Comment: 5 pages, 2 figures, To be published in Appl. Phys. Let

Simulation-Driven Manufacturing Planning for Product-Production Variety Coordination

Ambitious manufacturers are challenged to satisfy a broad range of customers while ensuring that the emerging product variety can be produced. Current practice suggests that products and production systems are modeled separately until the late stages of development when the designs are fixed and modifications are costly. In this paper, both product and production varieties are modeled, assessed, and evaluated using discrete-event simulation during preliminary stages. An illustrative example from the aerospace industry is used to demonstrate the approach. The simulation software Simio is used to model a sequence of operations and a set of input data related to a variety of aerospace sub-systems and a variety of welding resources. Through the simulations, the average utilization rate, the average throughput time, and the average work in process are generated. These outputs are used to evaluate the sets of product-production alternatives during the early stages of platform development when the cost to adjust the design of the products, production resources and operations are trifling

Cost effectiveness of disc prosthesis versus lumbar fusion in patients with chronic low back pain: randomized controlled trial with 2-year follow-up

This randomized controlled health economic study assesses the cost-effectiveness of the concept of total disc replacement (TDR) (Charité/Prodisc/Maverick) when compared with the concept of instrumented lumbar fusion (FUS) [posterior lumbar fusion (PLF) /posterior lumbar interbody fusion (PLIF)]. Social and healthcare perspectives after 2 years are reported. In all, 152 patients were randomized to either TDR (n = 80) or lumbar FUS (n = 72). Cost to society (total mean cost/patient, Swedish kronor = SEK, standard deviation) for TDR was SEK 599,560 (400,272), and for lumbar FUS SEK 685,919 (422,903) (ns). The difference was not significant: SEK 86,359 (−45,605 to 214,332). TDR was significantly less costly from a healthcare perspective, SEK 22,996 (1,202 to 43,055). Number of days on sick leave among those who returned to work was 185 (146) in the TDR group, and 252 (189) in the FUS group (ns). Using EQ-5D, the total gain in quality adjusted life years (QALYs) over 2 years was 0.41 units for TDR and 0.40 units for FUS (ns). Based on EQ-5D, the incremental cost-effectiveness ratio (ICER) of using TDR instead of FUS was difficult to analyze due to the “non-difference” in treatment outcome, which is why cost/QALY was not meaningful to define. Using cost-effectiveness probabilistic analysis, the net benefit (with CI) was found to be SEK 91,359 (−73,643 to 249,114) (ns). We used the currency of 2006 where 1 EURO = 9.26 SEK and 1 USD = 7.38 SEK. It was not possible to state whether TDR or FUS is more cost-effective after 2 years. Since disc replacement and lumbar fusion are based on different conceptual approaches, it is important to follow these results over time