Papillary cystic and solid tumor of the pancreas

The papillary cystic and solid tumor of the pancrease (PCSTP) is a primary pancreatic neoplasm of unknown etiology occurring most commonly in young women and regularly containing hemorrhagic areas. Clinical symptoms are non-specific. Although these tumors reach an average diameter of 10 cm, they are often discovered by accident. Because patients with surgically resected PCSTP have very good prognoses, it is important to distinguish these tumors from other growths in the pancreas, for example mucinous cystadenoma. Whereas, due to the variable proportion of fluid components, these tumors offer non-characteristic structure at ultrasonography, computed tomography (CT) possesses high specificity for PCSTP, particularly when calcifications are present. Angiography distinguishes these tumors from hypervascular neoplasms, such as the endocrinologically inactive islet cell tumor. Magnetic resonance tomography (MRT) is especially suited for imaging the hemorrhagic areas in solid tumor formations, as well as hemorrhagic debris in the fluid portions and layer phenomena are frequently observed.     

Performance of low-upper-shelf material under pressurized-thermal-shock loading

The second pressurized-thermal-shock experiment (PTSE-2) of the Heavy-Section Steel Technology Program was conceived to investigate fracture behavior of steel with low ductile-tearing resistance. The experiment was performed in the pressurized-thermal-shock test facility at the Oak Ridge National Laboratory. PTSE-2 was designed primarily to reveal the interaction of ductile and brittle modes of fracture and secondarily to investigates the effects of warm prestressing, A test vessel was prepared by inserting a cracklike flaw of well-defined geometry on the outside surface of the vessel. The flaw was 1 m long by ≈ 15 mm deep. The instrumented vessel was placed in the test facility in which it was initially heated to a uniform temperature and was then concurrently cooled on the outside and pressurized on the inside. These actions produced an evolution of temperature, toughness, and stress gradients relative to the prepared flaw that was appropriate to the planned objectives. The experiment was conducted in twoseparate transients, each one starting with the vessel nearly isothermal. The first transient induced a warm-prestressed state, during which K_I, first exceeded K_Ic. This was followed by repressurization until a cleavage fracture propagated and arrested. The final transient was designed to produce and investigate a cleavage crack propagation followed by unstable tearing. During this transient, the fracture events occurred as had been planned.     

Spectroscopic evaluation of CaYA1O4 doped with trivalent Er, Tm, Yb and Ho for eyesafe laser applications

Spectroscopic properties of relevance for laser applications have been studied for rare earths in CaYA1O₄. Fitting of a theoretical model to observed energy levels yields crystal field parameters and unobserved levels. Structural disorder leads to broad linewidths,but cross sections are larger than in many common hosts. Tm-Tm cross relaxation rates are comparable to those in Tm: YAG, and Yb-Er transfer rates are comparable to those in Yb, Er:phosphate glass. Room temperature Yb-Er upconversion is stronger than in YAG, but modeling shows that neither unconversion nor population of Er⁴I_13/2 is very efficient upon pumping Yb. The host's yellow color intensifies upon annealing in air, a potential problem for visible laser operation. Tm or Ho 2 μm laser operation, or Er 1.5 μ operation upon direct excitation of Er⁴I_13/2, are more promising.     

Example calculations illustrating methods for analyzing ductile flaw stability in nuclear pressure vessels

This paper contains example calculations of ductile flaw instability stresses for hypothetical flaws in nuclear pressure vessels. For comparison, three different methods of estimating upper shelf toughness as a function of Charpy impact energy were used, namely a power law R-curve correlation, the Rolfe-Novak correlation, and the Paris J₅₀ correlation. All three methods were used in LEFM calculations including a plastic zone size correction, and gave similar results, with the Paris J₅₀ method being the most conservative at low Charpy upper shelf energy levels. Safety factors based on the tearing modulus ratio $\text{T}{}_{\mathrm{<mtext>mat</mtext>}}\text{T}{}_{\mathrm{<mtext>appl</mtext>}}$ can exceed those based on load by considerable amounts and use of them at this time is not recommended. The use of resistance curve data obtained from actual vessel material test specimens is recommended over the use of correlations. Furthermore, evaluation of a recently proposed modified crack extension adjustment procedure for R-curve data, which is not over-conservative, is recommended.     

Modeling the dynamics of ant colony optimization

The dynamics of Ant Colony Optimization (ACO) algorithms is studied using a deterministic model that assumes an average expected behavior of the algorithms. The ACO optimization metaheuristic is an iterative approach, where in every iteration, artificial ants construct solutions randomly but guided by pheromone information stemming from former ants that found good solutions. The behavior of ACO algorithms and the ACO model are analyzed for certain types of permutation problems. It is shown analytically that the decisions of an ant are influenced in an intriguing way by the use of the pheromone information and the properties of the pheromone matrix. This explains why ACO algorithms can show a complex dynamic behavior even when there is only one ant per iteration and no competition occurs. The ACO model is used to describe the algorithm behavior as a combination of situations with different degrees of competition between the ants. This helps to better understand the dynamics of the algorithm when there are several ants per iteration as is always the case when using ACO algorithms for optimization. Simulations are done to compare the behavior of the ACO model with the ACO algorithm. Results show that the deterministic model describes essential features of the dynamics of ACO algorithms quite accurately, while other aspects of the algorithms behavior cannot be found in the model.