We used the aerosol particle mass analyzer (APM) to measure the mass of mobility-classified diesel exhaust particles. This information enabled us to determine the effective density and fractal dimension of diesel particles as a function of engine load. We found that the effective density decreases as particle size increases. TEM images showed that this occurs because particles become more highly agglomerated as size increases. Effective density and fractal dimension increased somewhat as engine load decreased. TEM images suggest that this occurs because these particles contain more condensed fuel and/or lubricating oil. Also, we observed higher effective densities when high-sulfur EPA fuel (approximately 360 ppm S) was used than for Fischer-Tropsch fuel (approximately 0 ppm S). In addition, the effective density provides the relationship between mobility and aerodynamic equivalent diameters. The relationship between these diameters enables us to intercompare, in terms of a common measure of size, mass distributions measured with the scanning mobility particle sizer (SMPS) and a MOUDI impactor without making any assumptions about particle shape or density. We show that mass distributions of diesel particles measured with the SMPS-APM are in good agreement with distributions measured with a MOUDI and a nano-MOUDI for particles larger than approximately 60 nm. However, significantly more mass and greater variation were observed by the nano-MOUDI for particles smaller than 40 nm than by the SMPS-APM.

SELF-SIMILAR NETWORK TRAFFIC: AN OVERVIEWto the shape of the whole, i.e., it is self-similar. Of course, this is not too surprising since the constructive process-by its recursive action-endows the limiting object with the scale-invariance property.The 1-dimensional Cantor set, e.g., as obtained by projecting the 2-D Cantor set onto the line, can be given an interpretation as a traffic series Xt 2 f 0; 1g-call it "Cantor traffic"-where Xt = 1 means that there is a packet transmission at time t. This is depicted in Figure 1. 1.2 (left). If the constructive process is terminated at iteration n 0, then the contiguous line segments of length 1=3 n may be interpreted as on-periods or packet trains of duration 1=3 n , and the segments between successive on-periods as off-periods or absence of traffic activity. Nonuniform traffic intensities may be imparted by generalizing the constructive framework via the use of probability measures. For example, for the 1-dimensional Cantor set, instead of letting the left and right components after scaling have identical "mass," they may be assigned different mass, subject to the constraint that the total mass be preserved at each stage of the iterative construction. This modification corresponds to defining a probability measure on the Borel subsets of 0; 1 and distributing the measure at each iteration nonuniformly left and right. Note that the classical Cantor set construction-viewed as a map-is not measure-preserving. Figure 1shows such a construction with weights L = 2 =3, R = 1 =3 for the left and right components, respectively. The probability measure is represented by "height"; we observe that scale-invariance is exactly preserved. In general, the traffic patterns producible with fixed weights L , R are limited, but one can extend the framework by allowing possibly different weights associated with every edge in the weighted viii SELF-SIMILAR NETWORK TRAFFIC: AN OVERVIEW processes which are nondecreasing processes whose differences-also called increment process-constitute the original process. For example, for the on/off Cantor traffic construction (cf. Figure 1.1.2 (left)), let us assign the interpretation that time is discrete such that at step n 0, it ranges over the values t = 0; 1=3 n ; 2=3 n ; : : : ; 3 n , 1=3 n ; 1. Thus we can equivalently index the discrete time steps by i = 0; 1; 2; : : : ; 3 n . With a slight abuse of notation, let us redefine X as Xi = 1 if, and only if, in the original process Xi=3 n = 1 and Xi=3 n , " = 1 for all 0 " 1=3 n . That is, for i values for which an on-period in the original process Xt begins at t = i=3 n , Xi is defined to be zero. Thus, in the case of n = 2 , we have

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Denial of service (DoS) attack on the Internet has become a pressing problem. In this paper, we describe and evaluate route-based distributed packet filtering (DPF), a novel approach to distributed DoS (DDoS) attack prevention. We show that DPF achieves proactiveness and scalability, and we show that there is an intimate relationship between the effectiveness of DPF at mitigating DDoS attack and powerlaw network topology.The salient features of this work are two-fold. First, we show that DPF is able to proactively filter out a significant fraction of spoofed packet flows and prevent attack packets from reaching their targets in the first place. The IP flows that cannot be proactively curtailed are extremely sparse so that their origin can be localized-i.e., IP tracebackto within a small, constant number of candidate sites. We show that the two proactive and reactive performance effects can be achieved by implementing route-based filtering on less than 20% of Internet autonomous system (AS) sites. Second, we show that the two complementary performance measures are dependent on the properties of the underlying AS graph. In particular, we show that the power-law structure of Internet AS topology leads to connectivity properties which are crucial in facilitating the observed performance effects.

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Surface passivation of unpassivated Al nanoparticles has been realized using self-assembled monolayers (SAMs). Nanoscale Al particles were prepared in solution by catalytic decomposition of H 3 Al‚NMe 3 or H 3 Al‚N(Me)Pyr by Ti(O i Pr) 4 and coated in situ using a perfluoroalkyl carboxylic acid SAM. Because the Al particles are prepared using wet chemistry techniques and coated in solution, they are free of oxygen passivation. This SAM coating passivates the aluminum and appears to prevent the oxidation of the particles in air and renders the composite material, to some extent, soluble in polar organic solvents such as diethyl ether. Characterization data including scanning electron microscopy , transmission electron microscopy, thermogravimetric analysis, and attenuated total reflectance-Fourier transform infrared spectroscopy of prepared materials are presented.