General quantitative specification theories with modal transition systems

This paper proposes a new theory of quantitative specifications. It generalizes the notions of step-wise refinement and compositional design operations from the Boolean to an arbitrary quantitative setting. Using a great number of examples, it is shown that this general approach permits to unify many interesting quantitative approaches to system design.     

Laminar premixed flame fuel consumption rate modulation by shocks and expansion waves

The main contributing effects leading to premixed laminar flame fuel consumption rate changes following variable strength shock or expansion wave passage were studied analytically and numerically. The effects were separated into two groups: gas compression, or one-dimensional effects, and flame front distortion, or two-dimensional effects. The first group was examined analytically using a one-dimensional flame model and solution of shock and expansion wave refraction. Two-dimensional effects were examined numerically using both shock and expansion wave passage through a sinusoidally perturbed propane-air laminar flame. Flame fuel consumption amplification due to the gas compression increased rapidly (from 1.3 to 24 times for Mach 1.1–1.7 shocks), while flame length amplification peaked (∼15 times) at a given shock strength (∼Mach 1.3). Thus gas compression became the dominant effect for stronger shocks. In contrast to the shocks, a slower reaction kinetic produced by the expansion wave passage allowed for a significantly longer period of flame length growth. This resulted in a temporary burning rate increase above initial values. The negative chemical kinetic effect of the weak expansion wave passage was temporarily offset by the flame length increase. The overall reaction rate amplification was up to four times stronger in fast/slow refractions. Also, the observed values of the flame stretch are reported in the paper.     

Observing Internet Worm and Virus Attacks with a Small Network Telescope

A network telescope is a portion of IP address space dedicated to observing inbound internet traffic. The purpose of a network telescope is to detect and log malicious traffic which originates from internet worms and viruses. In this paper, we investigate the statistical properties of observed traffic from a passive Class C telescope over a total of three months. We observe that only a few IP sources and destination ports are responsible for the majority of the traffic. We also demonstrate various ways to visualise the traffic profile from a telescope. We show that specific profiles can identify and distinguish portscans, hostscans and distributed denial-of-service (DDOS) attacks. Looking at the inter-arrival time of packets, the power spectrum and the detrended fluctuation analysis of the observed traffic, we show that there is very little sign of long-range dependence. This is in stark contrast to other network traffic and presents exciting possibilities for identifying malicious traffic purely from its traffic profile.     

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.     

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.     

Correlations between ion and neutron irradiations: Defect production and stage I recovery

A comparison is made between results of recent neutron- and ion-irradiation experiments on metals. Specifically, lowtemperature defect production and stage-I annealing are discussed. Defect production efficiencies observed for neutron irradiations are shown to be consistent with results for ion irradiations. A phenomenological model describing both defect production and stage-I annealing in terms of thermal-spike induced recombinations is introduced. The stage-I recovery fraction for ion and neutron irradiations is found to correlate with cascade-energy density as represented by an appropriate nuclear stopping power.     

High-performance liquid chromatography-atmospheric pressure photoionization/tandem mass spectrometric analysis for small molecules in plasma

A generic high-performance liquid chromatography (HPLC) system interfaced with an atmospheric pressure photoionization (APPI) source and a tandem mass spectrometer was developed for the quantitative determination of small molecules in plasma in support of exploratory in vivo pharmacokinetics. This report summarizes the effects of variations in reversed-phase mode HPLC conditions such as mobile-phase flow rate, solvent composition, organic modifier content, and nebulizer temperature on the photoionization efficiency of both clozapine and lonafarnib. The matrix ionization suppression effect on this method was investigated using the postcolumn infusion technique. The procedure was used to quantitate plasma levels following oral administration of 42 drug discovery compounds to rats. The pharmacokinetic results of 42 drug discovery compounds in rats evaluated by both APPI and atmospheric pressure chemical ionization interfaces were found to be well correlated.     

Evaluations of the Irwin βIc adjustment for small specimen fracture toughness data

Thickness size effects and large amounts of data scatter often occur in the cleavage fracture toughness testing of steel. It is shown that the Irwin β_Ic equation provides an effective adjustment for thickness size effects as well as reduces data scatter. Examples of applying the Irwin β_Ic adjustment to both static and dynamic toughness data are given. The significance of cleavage microcracking in the initiation of fast fracture is discussed and it is reasoned that this phenomenon is closely related to the sensitivity of the cleavage fracture toughness to triaxiality and strain rate.