Towards Physical Hybrid Systems

Some hybrid systems models are unsafe for mathematically correct but physically unrealistic reasons. For example, mathematical models can classify a system as being unsafe on a set that is too small to have physical importance. In particular, differences in measure zero sets in models of cyber-physical systems (CPS) have significant mathematical impact on the mathematical safety of these models even though differences on measure zero sets have no tangible physical effect in a real system. We develop the concept of "physical hybrid systems" (PHS) to help reunite mathematical models with physical reality. We modify a hybrid systems logic (differential temporal dynamic logic) by adding a first-class operator to elide distinctions on measure zero sets of time within CPS models. This approach facilitates modeling since it admits the verification of a wider class of models, including some physically realistic models that would otherwise be classified as mathematically unsafe. We also develop a proof calculus to help with the verification of PHS.Comment: CADE 201

Acute Marjolin Ulcer From A Dog Bite

Marjolin ulcers are cancers, usually of squamous cell carcinoma pathology, that occur in scars or wounds. They are classically described in burn victims but can occur with other types of trauma and are rarely seen in association with bite wounds. Marjolin ulcers typically have a latent period of many years post-injury until the development of malignancy, but there are a few case reports of an exceedingly rare acute form. We present a case of a 78-year-old female who developed a Marjolin ulcer one month after sustaining a dog bite to the left index finger

Factorization in graviton interactions

The study of factorization in the linearized gravity is extended to the graviton scattering processes with a massive scalar particle, with a massless vector boson and also with a graviton. Every transition amplitude is shown to be completely factorized and the physical implications of their common factors are discussed.Comment: 5 pages, Revtex 3.0, SNUTP 93-7

Global convergence of a non-convex Douglas-Rachford iteration

We establish a region of convergence for the proto-typical non-convex Douglas-Rachford iteration which finds a point on the intersection of a line and a circle. Previous work on the non-convex iteration [2] was only able to establish local convergence, and was ineffective in that no explicit region of convergence could be given

Quantification of Ophthalmic Changes After Long-Duration Spaceflight, and Subsequent Recovery

A subset of crewmembers are subjected to ophthalmic structure changes due to long-duration spaceflight (>6 months). Crewmembers who experience these changes are described as having Spaceflight Associated Neuro-Ocular Syndrome (SANS). Characteristics of SANS include optic disk edema, cotton wool spots, choroidal folds, refractive error, and posterior globe flattening. SANS remains a major obstacle to deep-space and planetary missions, requiring a better understanding of its etiology. Quantification of ocular, structural changes will improve our understanding of SANS pathophysiology. Methods were developed to quantify 3D optic nerve (ON) and ON sheath (ONS) geometries, ON tortuosity, and posterior globe deformation using MR imaging

Effects of Surface Coatings on the Joint Formation During Magnetic Pulse Welding in Tube-to-Cylinder Configuration

Magnetic Pulse Welding (MPW) is a joining technique favorable for the generation of strong atomic bonded areas between different metals, e.g. aluminum and steel. Brittle intermetallic phases can be avoided due to the high-speed collision and the absence of external heat. The demand for the use of this technique in industries like automotive and plant engineering rises. However, workpieces used in these fields are often coated, e.g. in order to improve the corrosion resistance. Since the weld quality depends on the material’s behavior at the collision zone, surface layers in that region have to be taken into account as well. This work investigates the influences of different coating types. Aluminum to steel welding is used as an example system. On the inner steel part (C45) coatings like zinc, nickel and chrome are applied, while the aluminum flyer tubes (EN AW-6060) are anodized, chromated and passivated. Welding tests are performed using two different welding systems with varying discharging frequencies and four geometrical part setups. For all combinations, the flyer velocity during the process is measured by Photon Doppler Velocimetry (PDV). By using the uncoated material combination as a reference, the removal of surface layers due to jetting is analyzed. Finally, the weld quality is characterized in peel tests, shear-push tests and by the help of metallographic analysis. It is found that certain coatings improve the joint formation, while others are obstructive for the performance of MPW. Some coatings have no influence on the joining process at all

Finite-dimensional analogs of string s <-> t duality and pentagon equation

We put forward one of the forms of functional pentagon equation (FPE), known from the theory of integrable models, as an algebraic explanation to the phenomenon known in physics as st duality. We present two simple geometrical examples of FPE solutions, one of them yielding in a particular case the well-known Veneziano expression for 4-particle amplitude. Finally, we interpret our solutions of FPE in terms of relations in Lie groups.Comment: LaTeX, 12 pages, 6 eps figure

Land use and soil development in Southern chile: Effects on physical properties

Different physical properties of volcanic ash soils were investigated along a transect of 120 km from the western slope of the Central Cordilleras (40°20’S, 72°06’W) to the eastern slope of the Costal Cordillera (39°39’S, 73°11’W) in southern Chile with respect to the degree of soil development (Arenosol versus Andosol stage; Arenosol: young volcanic ash soil, free of clay, tephric properties, Andosol: older volcanic soil, clayey). The Andosols show a higher total pore volume and a higher field capacity, especially due to an increase in fine pores, than the Arenosols. Furthermore, the precompression stress (Pc) as a parameter for the mechanical soil strength is higher for Andosols despite of a lower bulk density. A land use (cropland, meadow, forest) dependent variation of the investigated parameters was less distinct for Andosols. A reduction of macropores and saturated hydraulic conductivity (ks) due to agriculture could be determined in the field, but in general the values are still on a high level with ks-values >100 cm d-1. However, at higher stresses using an oedometer test the ks-values of the Andosols are highly negatively affected with values <10 cm d-1. Aggregation is of major importance for soil stability of Andosols, whereas a homogenization of soil structure will lead to a distinct decrease of Pc of approx. 50%.DFG/HO 911/45-1DFG/BA 1359/12-