Keeping the Edge: Managing Defense for the Future

This book “addresses a need widely rec- ognized but long neglected: to adapt and modernize the system by which the United States manages the largest and most successful security establishment in history.” Do not be misled into thinking that the word “managing” in the title suggests a dry treatment of managerial practices requiring extensive change. Keeping the Edge deals with that, but it primarily examines many key organiza- tional strategy issues; these studies will have comprehensive value to anyone within academia or the national security environment wishing to improve what the authors regard as management and organizational shortfalls that impede im- plementation of wise strategy and policy choices

Spontaneous thermal runaway as an ultimate failure mechanism of materials

The first theoretical estimate of the shear strength of a perfect crystal was given by Frenkel [Z. Phys. 37, 572 (1926)]. He assumed that as slip occurred, two rigid atomic rows in the crystal would move over each other along a slip plane. Based on this simple model, Frenkel derived the ultimate shear strength to be about one tenth of the shear modulus. Here we present a theoretical study showing that catastrophic material failure may occur below Frenkel's ultimate limit as a result of thermal runaway. We demonstrate that the condition for thermal runaway to occur is controlled by only two dimensionless variables and, based on the thermal runaway failure mechanism, we calculate the maximum shear strength $\sigma_c$ of viscoelastic materials. Moreover, during the thermal runaway process, the magnitude of strain and temperature progressively localize in space producing a narrow region of highly deformed material, i.e. a shear band. We then demonstrate the relevance of this new concept for material failure known to occur at scales ranging from nanometers to kilometers.Comment: 4 pages, 3 figures. Eq. (6) and Fig. 2a corrected; added references; improved quality of figure

Zipf's law in Multifragmentation

We discuss the meaning of Zipf's law in nuclear multifragmentation. We remark that Zipf's law is a consequence of a power law fragment size distribution with exponent $\tau \simeq 2$. We also recall why the presence of such distribution is not a reliable signal of a liquid-gas phase transition

Mixing and Accretion in lambda Bootis Stars

Strong evidence for deep mixing has been uncovered for slowly rotating F, and A stars of the main sequence. As the accretion/diffusion model for the formation of lboo stars is heavily dependent on mixing in superficial regions, such deep mixing may have important repercussions on our understanding of these stars. It is shown that deep mixing at a level similar to that of FmAm stars increases the amount of matter that needs to be accreted by the stars with respect with the standard models by some three orders of magnitude. It is also shown that significantly larger accretion rates have to be maintained, as high as $10^{-11}$~M_\sun yr^{-1}, to prevent meridional circulation from canceling the effect of accretion. The existence of old ($\approx 1$~Gyr) is not a likely outcome of the present models for accretion/diffusion with or without deep mixing. It is argued that lboo stars are potentially very good diagnostics of mixing mechanisms in moderately fast rotators.Comment: To appear in Astrophysical Journal Letters. 4 pages, 2 fgure

Relation Between First Arrival Time and Permeability in Self-Affine Fractures with Areas in Contact

We demonstrate that the first arrival time in dispersive processes in self-affine fractures are governed by the same length scale characterizing the fractures as that which controls their permeability. In one-dimensional channel flow this length scale is the aperture of the bottle neck, i.e., the region having the smallest aperture. In two dimensions, the concept of a bottle neck is generalized to that of a minimal path normal to the flow. The length scale is then the average aperture along this path. There is a linear relationship between the first arrival time and this length scale, even when there is strong overlap between the fracture surfaces creating areas with zero permeability. We express the first arrival time directly in terms of the permeability.Comment: EPL (2012)

Scaling Analysis and Evolution Equation of the North Atlantic Oscillation Index Fluctuations

The North Atlantic Oscillation (NAO) monthly index is studied from 1825 till 2002 in order to identify the scaling ranges of its fluctuations upon different delay times and to find out whether or not it can be regarded as a Markov process. A Hurst rescaled range analysis and a detrended fluctuation analysis both indicate the existence of weakly persistent long range time correlations for the whole scaling range and time span hereby studied. Such correlations are similar to Brownian fluctuations. The Fokker-Planck equation is derived and Kramers-Moyal coefficients estimated from the data. They are interpreted in terms of a drift and a diffusion coefficient as in fluid mechanics. All partial distribution functions of the NAO monthly index fluctuations have a form close to a Gaussian, for all time lags, in agreement with the findings of the scaling analyses. This indicates the lack of predictive power of the present NAO monthly index. Yet there are some deviations for large (and thus rare) events. Whence suggestions for other measurements are made if some improved predictability of the weather/climate in the North Atlantic is of interest. The subsequent Langevin equation of the NAO signal fluctuations is explicitly written in terms of the diffusion and drift parameters, and a characteristic time scale for these is given in appendix.Comment: 6 figures, 54 refs., 16 pages; submitted to Int. J. Mod. Phys. C: Comput. Phy

Nontrivial temporal scaling in a Galilean stick-slip dynamics

We examine the stick-slip fluctuating response of a rough massive non-rotating cylinder moving on a rough inclined groove which is submitted to weak external perturbations and which is maintained well below the angle of repose. The experiments presented here, which are reminiscent of the Galileo's works with rolling objects on inclines, have brought in the last years important new insights into the friction between surfaces in relative motion and are of relevance for earthquakes, differing from classical block-spring models by the mechanism of energy input in the system. Robust nontrivial temporal scaling laws appearing in the dynamics of this system are reported, and it is shown that the time-support where dissipation occurs approaches a statistical fractal set with a fixed value of dimension. The distribution of periods of inactivity in the intermittent motion of the cylinder is also studied and found to be closely related to the lacunarity of a random version of the classic triadic Cantor set on the line.Comment: 7 pages including 6 figure

Évaluation de l'impact de l'assainissement urbain sur la qualité des eaux du bassin versant de la rivière Chaudière à l'aide du système de modélisation intégrée GIBSI

Le programme d'assainissement des eaux de Québec (PAEQ), mis en place à la fin des années 1970, s'est d'abord attaqué au problème de la pollution ponctuelle d'origine urbaine. Plusieurs stations de traitement des eaux usées municipales ont été construites dans le cadre de ce programme réduisant de façon importante les charges de polluants d'origine urbaine. La question demeure toutefois de savoir dans quelle mesure les charges urbaines rejetées avant et l'après l'instauration de ce programme peuvent entraîner des dépassements de différents critères de l'eau. La présente étude a pour objectif d'examiner cette problématique pour le bassin versant de la rivière Chaudière en utilisant le système de modélisation intégrée GIBSI (Gestion Intégrée par Bassin versant à l'aide d'un Système Informatisé). Deux scénarios d'assainissement urbain ont été examinés, l'un représentatif de la période avant la mise en place du programme, le début des années 1980, et un autre représentatif de la période plus récente. Deux chroniques météorologiques ont été utilisées (années 1983 et 1994). L'estimation des probabilités de dépassement de différents critères de l'eau montre une nette réduction de ces probabilités après mise en place du programme. Pour la DBO5 et l'azote total, les charges urbaines rejetées actuellement n'entraînent pas de dépassement des critères de qualité de l'eau pour les deux années retenues. Toutefois, les résultats montrent que les charges en phosphore total d'origine urbaine peuvent à elles seules entraîner des probabilités de dépassement importantes lors d'étiage.In 1978, the Québec Government put in place a provincial municipal clean water program, referred to as the Programme d'assainissement des eaux du Québec (PAEQ), to restore the province's rivers to their natural state. The program focussed primarily on the problem of municipal waste loads and, hence, a large number of wastewater treatment plants (WWTP) were constructed during the 1980's and the 1990's. At the beginning of the 1980's, only a few percent of the population had their waste water treated, but this figure had increased to over 95% by 1997 (Figure 1). In the Chaudière river watershed, this program resulted in the construction of more than 35 WWTP over an 18-year period. Although an impressive effort was devoted to reduce municipal waste loads, a question remains: how does this reduction translate into terms of overall improvement of water quality at the watershed level?The Chaudière river watershed was considered for this application. This watershed covers an area of 6682 km2 and is located south of Quebec City. Land use is dominated by forest (62%) followed by agricultural land (33%), urban area (3.6 %), and water (1.7 %). The total population in 1996 was 173129 and was mainly located in the northern part (i.e., the downstream region) of the watershed. A total of 44 municipal point loads were identified (see Figure 2 and Table 1), most of them corresponding to WWTP. Characteristic data on municipal WWTP for year 1995 were obtained from the Quebec Department of the Environment (MINISTERE DE L'ENVIRONNEMENT ET DE LA FAUNE DU QUEBEC, 1997) and used to estimate average concentrations of total phosphorus and the biological oxygen demand (BOD). Data included affluent and effluent concentrations at various WWTP. Since no data were available for nitrogen, a concentration of 40 mg-N/l was used (TCHOBANOGLOUS et SCHOEDER, 1985; NOVOTNY et CHESTERS, 1981). Nitrogen removal efficiency for different types of treatment was estimated from available data compiled by the Environment Quebec (Table 2). An average, per capita, daily wastewater volume of 0.73 m3 was derived. This large value indicates a large infiltration capacity in the sewer network and, on average, a poor structural state.Results were analysed at four locations distributed along the river. These points corresponded to the locations of the four major water quality monitoring stations (Figure 3). Total annual loads within the sub-watersheds defined by these points were estimated (Table 3). Affluent characteristics were considered for the simulation of the pre-PAEQ period. Figure 4 represents the evolution of total phosphorus loads at station 2340012 (water intake for the town of Charny, the most downstream point). It shows that an important reduction occurred in 1986. For the same sub-watershed, the overall reduction for the 1982-1999 period was 38% for total phosphorus, 37% for total nitrogen and 83% for BOD.Assessment of the impact of the PAEQ was done using the integrated modelling system GIBSI ("Gestion Intégrée par Bassin versant à l'aide d'un Système Informatisé") (ROUSSEAU et al., 2000; MAILHOT et al., 1997 ; VILLENEUVE et al., 1998). Only pollutant loads originating from sewer networks were considered; pollutant loads from industrial plants not connected to a municipal sewer network were not considered in this study. Similarly, diffuse sources of pollution from urban area or agricultural land were not taken into account. Two scenarios were considered: a first scenario associated with the 1983 year corresponding to the pre-PAEQ period; and a second scenario associated with the 1994 year describing the post-PAEQ period (following load reductions). Two hydrological reference years were also selected, namely, years 1983 and 1994. The former corresponded to a significantly drier year than the latter. At station 2340012 (Charny water intake), this difference was even more pronounced when considering that the cumulative summer flow was 6.9 times larger in 1994 than in 1983. Four simulations corresponding to different combinations of representative municipal waste loads and meteorological conditions were performed (Table 5).Simulation results at the four control points were compared with water quality standards (WQS) for total phosphorus (0.03 mg-P/l, aesthetic WQS for prevention of eutrophication in rivers) and BOD (3 mg-BOD5 /l, sanitary WQS for domestic use of water requiring disinfection treatment only). The probabilities of exceeding these WQS were defined (equation 1) as the number of days (daily computational time step) where simulated values exceeded a given value (complementary cumulative distribution function). Table 8 introduces annual probabilities of exceeding WQS at the four control points and for the different simulations whereas Table 9 introduces those for the summer period. At station 2340012 (Charny water intake), for hydrological year 1994, a comparison of pre- and post-PAEQ conditions for total phosphorus shows that post-PAEQ condition lowered the number of days exceeding WQS by 49. Similar reductions were reached at the other control points. For the 1994 summer period, the reduction was not as pronounced since the probability of exceeding WQS was 0.24 for pre-PAEQ situation and it decreased to 0.21 for the post-PAEQ condition. These probabilities worsened under the 1983 summer conditions as concentrations exceeded the WQS 98% of the time at station 2340014

The spatial distribution of coronae on Venus

Coronae on Venus are large, generally circular surface features that have distinctive tectonic, volcanic, and topographic expressions. They range in diameter from less than 200 km to at least 1000 km. Data from the Magellan spacecraft have now allowed complete global mapping of the spatial distribution of coronae on the planet. Unlike impact craters, which show a random (i.e., Poisson) spatial distribution, the distribution of coronae appears to be nonrandom. We investigate the distribution here in detail, and explore its implications in terms of mantle convection and surface modification processes