A note on the null distribution of the local spatial heteroscedasticity (LOSH) statistic

Recently, Ord and Getis (Ann Reg Sci 48:529–539, 2012) developed a local statistic \(H_i\) , called local spatial heteroscedasticity statistic, to identify boundaries of clusters and to describe the nature of heteroscedasticity within clusters. Furthermore, in order to implement the hypothesis testing, Ord and Getis suggested a chi-square approximation method to approximate the null distribution of \(H_i\) , but they said that the validity of the chi-square approximation remains to be investigated and some other approximation methods are still worthy of being developed. Motivated by this suggestion, we propose in this paper a bootstrap procedure to approximate the null distribution of \(H_i\) and conduct some simulation to empirically assess the validity of the bootstrap and chi-square methods. The results demonstrate that the bootstrap method can provide a more accurate approximation than the chi-square method at the cost of more computation time. Moreover, the power of \(H_i\) in identifying boundaries of clusters is empirically examined using the proposed bootstrap method to compute \(p\)  values of the tests, and the multiple comparison issue is also discussed.     

Effect of Wind on Smoldering Combustion Limits of Moist Pine Needle Beds

We studied moist pine needle beds burning under the effect of wind, in order to determine the upper moisture limit for which there is fire propagation for different wind velocities. For this purpose we built a wind tunnel that allowed us to burn a 600 mm by 150 mm by 40 mm bed under wind velocities between 0.5 m/s and 5.0 m/s and controlled air temperature. Results show an increase in moisture limit from 54% to approximately 140%, for the velocity range indicated. Combustion at limiting conditions proceeds mainly by smoldering with some periods of flaming combustion. It was observed that, for conditions close to extinction, the smoldering front is not quenched at the surface. Additionally, it was also observed that a strong flow of hot gases exit from the fuel bed at the free surface. These two observations lead to the conclusion that the main heat sink is moisture evaporation and that heat losses to the surroundings is reduced by the blowing effect of the hot gases coming off the bed. A dimensional analysis suggests a correlation between moisture limit and wind velocity of the form M = A ? B/ \( {v} \) _w ² , where M is moisture limit for fire propagation, A and B are constants, and \( {v} \) _w is wind speed. Two dimensionless numbers helped to plot the smoldering temperature and fire propagation velocity in a more meaningful way. They are \( \Uppi_{1} = {{T_{sml} c_{p,g} } \mathord{\left/ {\vphantom {{T_{sml} c_{p,g} } {v_{w}^{2} }}} \right. \kern-0pt} {v_{w}^{2} }} \) and \( \Uppi_{2} = {{Mh_{fg} } \mathord{\left/ {\vphantom {{Mh_{fg} } {v_{w}^{2} }}} \right. \kern-0pt} {v_{w}^{2} }} \) , where T _sml is smoldering temperature, c _p,g is the gas specific heat, M is fuel moisture content and h _fg is the latent heat of water evaporation. A relatively high moisture limit at 5 m/s wind velocity is possible due to the relatively high air flow into the smoldering front and the efficient heat feedback produced in forward smoldering.     

Radiant Ignition of Polyurethane Foam: The Effect of Sample Size

Although smouldering ignition of upholstery items remains a leading cause of residential fire deaths, relatively little research is conducted on the topic. An experimental investigation of the effect of sample size on the ignition and spread of smouldering and flaming in polyurethane foam under natural flow conditions is reported here. Polyurethane foam samples are used because this is a common material in modern, residential environments and one for which there exists significant quantities of previous experimental data in the literature. Samples of different square cross-section size and a fixed height of 150 mm are insulated on all sides except the top which is exposed to a radiant heat flux and is open to the air. Samples with side lengths of 50 mm, 100 mm, and 140 mm are studied. Ignition and spread dynamics are diagnosed using thirteen thermocouples located along the vertical centre line. The onset of smouldering ignition (13  $\hbox{kW}\, \hbox{m}^{-2}$ , 8  $\hbox{kW}\, \hbox{m}^{-2}$ and $7\,\hbox{kW}\, \hbox{m}^{-2}$ for 50 mm, 100 mm and 140 mm sample sizes respectively) is observed at significantly lower heat fluxes that flaming (45  $\hbox{kW}\,\hbox{m}^{-2}$ , 32  $\hbox{kW}\,\hbox{m}^{-2}$ and $30\,\hbox{kW}\,\hbox{m}^{-2}$ respectively). Critical heat fluxes for smouldering and flaming ignition increase with decreasing sample size, with smouldering ignition being significantly more sensitive to sample size than flaming ignition under the size range studied. Smouldering spread rates are measured in the range from 3  $\hbox{mm}\, \hbox{min}^{-1}$ to $25\,\hbox{mm}\, \hbox{min}^{-1}$ and found to be a strong function of the heat flux and depth of the smoulder front. The effect of sample size on smouldering has been theoretically proposed before but this is the first time that this effect has been demonstrated experimentally for ignition. The fact that large samples result in the lowest critical heat flux could have implications for testing procedures and translation of results from small-scale testing to real-scale in the built environment.     

The neighborhood or the region? Reassessing the density–wage relationship using geocoded data

I analyze the effects of sub-city-level density of economic activity on wages. Using a geocoded dataset on employment and wages in the city areas of Sweden, the analysis is based on squares representing “neighborhoods” ( $0.0625\,\hbox {km}^{2})$ , “districts” ( $1\,\hbox {km}^{2})$ , and “agglomerations” ( $10\,\hbox {km}^{2})$ . The wage-density elasticity depends on spatial resolution, with the elasticity being highest in neighborhood squares, where a doubling of density is associated with wage increases of 1.2 %, or roughly the size of the elasticity for region density. Moving from a mean-density neighborhood to the densest neighborhood would on average increase wages by 9 %. The results are consistent with (i) the existence of a localized density spillover effect and (ii) quite sharp attenuation of human capital spillovers. An implication of the findings is that if the data source is not sufficiently disaggregated, analyses of the density–wage link risk understating the benefits of working in dense parts of regions, such as the central business districts.     

A modified empirical criterion for strength of transversely anisotropic rocks with metamorphic origin

A modified empirical criterion is proposed to determine the strength of transversely anisotropic rocks. In this regard, mechanical properties of intact anisotropic slate obtained from three different districts of Iran were taken into consideration. Afterward, triaxial rock strength criterion introduced by Rafiai was modified for transversely anisotropic rocks. The criterion was modified by adding a new parameter $ \alpha $ for taking the influence of strength anisotropy into consideration. The results obtained have shown that the parameter $ \alpha $ can be considered as the strength reduction parameter due to rock anisotropy. The modified criterion was compared to the modified Hoek–Brown (Saroglou and Tsiambaos) and Ramamurthy criteria for different anisotropic rocks. It was concluded that the criterion proposed in this paper is a more accurate and precise criterion in predicting the strength of anisotropic rocks.     

Economic growth in Italian NUTS 3 provinces

This paper analyzes the conditional \(\beta \) -convergence hypothesis for NUTS 3 Italian provinces. A methodology for the simultaneous treatment of spatial dependence and spatial heterogeneity is developed. Spatial dependence is introduced in the economic model by assuming a spatial Durbin model specification. The absence of data experienced by some economic variables at the NUTS 3 level is addressed through a modified version of the Bayesian interpolation method introduced by Palma and Benedetti (J Geogr Syst 5:199–220, 1998). Spatial heterogeneity is taken into account by identifying convergence clubs. For this purpose, we use the modified simulated annealing algorithm introduced by Postiglione et al. (Comput Econ 42:151–174, 2013). The methodology is compared with the heteroscedastic approach proposed by Kelejian and Prucha (J Econom 157:53–67, 2010).     

Impact d’une galerie étanche peu profonde sur l’écoulement d’une nappe

While many studies have been achieved on the interactions between groundwater and deep tunnels, in order to identify the evolution of pore pressure around the structure and to characterize the flow to its leaky parts, few studies have dealt with the impact of the carrying out of an impervious gallery in a shallow aquifer. The induced change in the piezometric level of the aquifer and the one in the hydraulic gradient of the flow however can, in this case, have significant consequences, in particular when the linear structure is located in an urban environment. This paper investigates, in steady state, the case of a straight tunnel having a horizontal axis perpendicular to the direction of the regional groundwater flow and a circular or square cross section. The aim is to determine the additional lost head Δh _s due to the tunnel (i.e. additional to that resulting from the regional flow, supposed to be uniform with a hydraulic gradient i ₀). In the context of a horizontal confined aquifer having a thickness 2B and of a tunnel of radius R located in the middle part of the aquifer, an analogy can be established with the flow above a hydraulic threshold resulting from a local rise of the elevation of the base of an aquifer, having a thickness B, on a width 2R and with a vertical maximum amplitude R. When neglecting the vertical component of the hydraulic gradient compared to its horizontal component, analytical solutions are developed for various hydraulic threshold shapes (rectangular, triangular and circular), based on the equivalence with a local change in the transmissivity of an aquifer keeping a constant thickness. The corresponding formulas take the form: $ {\frac{{\Updelta h_{s} - \Updelta h_{0} }}{{\Updelta h_{0} }}} = f(a) $ , with $ a = {\frac{R}{B}} $ and Δh ₀ = 2Ri ₀. The use of these formulas shows that the additional lost head Δh _s due to the hydraulic threshold is proportional to i ₀ and that, for values of the ratio a < 0.5, the change in the piezometric surface is small. These conclusions are therefore limited by the fact that the vertical conductivity is supposed to be very large. In order to remove this hypothesis, numerical simulations are achieved using the MODFLOW code. It is considered a confined aquifer of length 2L = 110 m and thickness B = 10 m, a ratio $ a = {\frac{R}{B}} = 0.25 $ and a horizontal hydraulic conductivity $ K_{H} = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . In the case of an isotropic medium ( $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} = 1 $ ), the simulations allow to check the linearity of the relationship between Δh _s and i ₀, with therefore a homogeneous variation in the proportionality coefficient compared to analytical solutions. Simulations also reveal that, in the case considered, the width of influence upstream and downstream L _i , corresponding to a value of the vertical component of the hydraulic gradient <1% of i ₀, is below 5.5R for the three hydraulic threshold shapes, and that it was few influenced by the hydraulic gradient i ₀. In the case of an anisotropy of the horizontal and vertical hydraulic conductivities, simulations reveal the significant importance of the anisotropy ratio $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} $ when it is more than 1, the most common case, and indicate that the proposed analytical solutions give an asymptotic value of $ {\frac{{\Updelta h_{s} }}{{\Updelta h_{0} }}} $ for the isotropic case and for the values of the component α < 1. In the context of an unconfined aquifer, the hydraulic threshold model is not directly applicable. The model studied, using the Dupuit-Forchheimer assumption, is the one of a water table aquifer with a sloped base (slope value: p ₀). The simulations focus on an aquifer of length 2L = 85 m, with a tunnel of circular cross section having a diameter 2R = 5 m, bottom of which is located 5 m above the base of the aquifer, the isotropic hydraulic conductivity being equal to $ K = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . The definitions of water heights d ₀ and d between the water table and the top of the tunnel are given in Fig. 7. The water table can be located above (fully submerged tunnel) or below (partially emerged tunnel) the top of the tunnel. The difference d ₀ ? d represents the half of the additional lost head Δh _s due to the tunnel. Simulations are performed for various values of p ₀ and d ₀. They provide the values of i ₀, d and Δh _s . In the case of a fully submerged tunnel (d > 0), a significant rise of the water table upstream of the tunnel is obtained only for high values of the hydraulic gradient (5 and 10%), but, even in this case, it remains less than the tenth of the wetted height of the aquifer h _m . It is also highlighted that the ratio $ {\frac{{\Updelta h_{s} }}{{i_{0} }}} $ varies as a linear function of (R + d) and that, in the studied case, there is no influence of the tunnel for d ≥ 4R. In the case of a partially emerged tunnel (d < 0), the aquifer is locally confined under the tunnel. It is suggested that an equivalence is possible with the case of a confined aquifer having a thickness equal to the wetted height in the unconfined aquifer. This is verified with one of the simulations. In the case of a partially emerged tunnel, the change in the water table due to the tunnel remains low.     

Fire Whirl Experimental Facility with No Enclosure of Solid Walls: Design and Validation

In this work, a fire whirl facility with no enclosure of solid walls was designed, for experimental simulation of fire whirls in open field. Air curtains were used to produce the generating eddy of fire whirl. Tests were conducted to evaluate the capability of the new facility. It was found that there was an optimal tilt angle for the air curtains to produce stable fire whirls. Experiments of fire whirls under different pool diameters showed that the mass loss rate \( \dot{m} \) depended on the circulation \( \varGamma \) by \( \dot{m}\sim \varGamma^{1.18} \) and the dimensionless flame height satisfied \( H^{*} \sim \varGamma^{*0.71} \) (where the asterisks denote dimensionless variables). It was also found that the ratio of the continuous flame height to the whole flame height for different pool diameters was 0.67. The centerline temperatures varied with the normalized height \( Z \) by \( Z^{0.08} \), \( Z^{ - 1.30} \) and \( Z^{ - 2.18} \), respectively in the regions of the continuous flame, intermittent flame and plume. The radiative fraction was calculated to be close to 44%. All these results fit well with literature data, thereby the capability of the new facility for producing stable fire whirls was fully validated. Some potential applications of the new facility were discussed in detail. Especially, instruments such as infrared camera can be used to investigate the flame radiation of fire whirls by the new facility.     

Are small communities at risk of population loss?

Small communities almost universally worry about out-migration and the negative effects of out-migration on community viability. Using Oregon community-level data and applying the threshold estimation method of Hansen (Econometrica 68(3):575–603, 2000), we are able to identify population thresholds that distinguish small communities from their larger counterparts based on significant structural differences in factors affecting net migration. Our results suggest that smaller communities are more at risk of population decline than larger ones. After controlling for spatial spillovers from neighboring communities, the average net migration rate is 3 % in the larger communities (roughly above 5,000 population), 2 % in the mid-sized communities (roughly between 1,250 and 5,000) and $-3$  % in the smallest communities (roughly less than 1,250). Other things equal, geographic isolation from large cities and low wage rates provide some protection from net out-migration for the smallest communities, but even for the smallest places, a larger population base lowers the risk of net out-migration.     

Hydrogeochemie von Eisenausfällungen an Grundwasseraustritten der Abraumkippe Berrenrath (Rheinisches Braunkohlenrevier)

Groundwater at the abandoned lignite mine in Berrenrath (Germany) is acidic and highly mineralised. Average iron concentrations of 588 mg/l indicate a high potential for acidification. Furthermore, investigations revealed a complete depletion of the carbonate buffer capacity (CaCO₃ and $\mathrm{HCO}_{3}^{-}$ ) during chemical groundwater evolution. Over the next few decades, no decrease of dissolved pyrite oxidation products is expected. On the contrary, within the drainage ditches at the edges of the dump, an intense precipitation of iron oxides is occurring. However, despite oxygen saturation, precipitation of iron oxides is incomplete due to strong acidification of the surface water (pH<3.0). The main contamination of the iron sludge is caused by high nickel concentrations. This element is only loosely bound to the iron oxides and is easily mobilised. Because of high nickel- and sulphate-concentrations, the excavated material has to be deposited in a controlled landfill (German dump category of 2 to 3).     

Spatial competition with quadratic transport costs and one online firm

d’Aspremont (Econometrica 47:1145–1150 , 1979) showed that a Hotelling (Econ J 39:41–57 , 1929) duopoly model with quadratic transport costs yields maximal differentiation. However, the introducing of an online firm ensures that the duopolist will never be located at the end points of the market. In other words, an online firm can raise a market effect that induces two firms to be finitely differentiated. The implication of the socially optimal solution is derived. The results herein can be extended to allow multiple firms. Finally, a free-entry equilibrium and the Stackelberg equilibrium are also discussed.     

Numerical Investigation of Back-Layering Length and Critical Velocity in Curved Subway Tunnels with Different Turning Radius

Curved tunnels are inevitable subjected to the city underground geological conditions. Due to the catastrophic consequence of tunnel fires with high population density, the related researches on fire safety of curved tunnel are full of significance. Therefore, a series of curved subway tunnels with turning radius of 300–1000 m were investigated numerically by FDS 5.5.3 in terms of the smoke back-layering length and critical ventilation velocity under the heat release rate of 5–10 MW. Theoretical analysis shows that the curved tunnel with the local resistance has an advantage of preventing smoke spreading compared with straight tunnel. The simulation results also indicated that both the smoke back-layering length and the critical ventilation velocity increased with the rising turning radius, and the straight tunnel has the largest values. In fact, the local resistance impact factor for the smoke back-layering length in the curved tunnel, \( k_{f} \), was controlled by turning radius \( R \) and ventilation velocity \( V \). The dimensionless critical velocity increased slightly from \( 0.638Q^{*1/3} \) to \( 0.669Q^{*1/3} \) when the turning radius increased from 300 m to 1000 m. Without considering the influence of turning radius (local resistance), previous models cannot be applied to the curved tunnel. The improved prediction models about smoke back-layering length and critical velocity with the factor of turning radius could provide a technical guideline for the tunnel ventilation designs.     

Measurement of the Thermal Parameters of Composite Materials During Fire Tests with Quantitative Infrared Imaging

A fire resistance test, as performed on plates of carbon fibre reinforced polymer composites, is conceptually analogous to a step heating, and can be modelled by the one-dimensional heat equation. Thus modelled, the plate operates as a linear system with an impulse response function that relates temperatures at the front face (the one exposed to fire) and the rear face, and depends on two parameters, namely thermal diffusivity (\(\alpha \)) and effective Biot number (Bi). Taking as input the time evolution of temperature at the front face, the output of the model for each (\(\alpha \), Bi) couple is a predicted temperature for the rear side of the plate. At each point of the plate, \(\alpha \) and Bi can be retrieved by fitting the predicted temperature to the experimental one. These parameters are good quantitative indicators of thermal damage, and therefore its measurement has a particular interest to understand degradation processes associated with fire action. To perform their retrieval as described, temperature measurement for both faces of the plate during the experiment are made with a specifically developed infrared imaging system, composed by two synchronized infrared cameras that image both sides of the sample during the fire test and provide surface temperature maps, spatially co-registered and with the flame effects filtered out. Applying the fitting procedure described to these temperature maps makes possible, for the first time, to measure \(\alpha \) and Bi in situ during the fire test. The value of \(\alpha \) obtained by this procedure (varying from \(\approx 0.5 \times 10^{-7} \, \mathrm{m}^{2} \, \mathrm{s}^{-1}\) in the region most affected by fire, to \(\approx 7 \times 10^{-7} \, \mathrm{m}^{2} \, \mathrm{s}^{-1}\) near sample edges) has been compared to those measured after the test, on samples at room temperature, with the classical flash method. A good general agreement has been found, with differences that can be attributed to the temperature dependence of diffusivity. From this comparison a critical temperature of \(T = 450^{\circ }\)C has been identified, that separates two different regimes, probably related to different degradation states, with slopes of \(-\,1.5 \times 10^{-9} \, \mathrm{m}^{2} \, \mathrm{s}^{-1} \, \mathrm{K}^{-1}\) for \(T<450^{\circ }\)C and \(3 \times 10^{-10} \, \mathrm{m}^{2} \, \mathrm{s}^{-1} \, \mathrm{K}^{-1}\) for \(T>450^{\circ }\)C.     

CFD Simulations of Pool Fires in a Confined and Ventilated Enclosure Using the Peatross–Beyler Correlation to Calculate the Mass Loss Rate

The aim of this paper is to analyse the application of the Peatross–Beyler (P&B) correlation (Fire and safety science—Proceedings of the fifth international symposium, 1997) to calculate the Mass loss rate (MLR) for a pool fire in a confined and ventilated enclosure for a range of conditions.The experimental references considered are the PRISME-SI-D1, D2 and D6 tests (Prétrel et al. in 9th International seminar on fire safety in nuclear power plants and installations, 2005), conducted by the Institut de Radioprotection et de Sûreté Nucléaire.The dimensions of the enclosure used in the experiment are 5 m in length, 6 m in width and 4 m in height. A pool fire, \(0.4\,\hbox {m}^2\) hydrogenated tetrapropylene (TPH, \(\hbox {C}_{12}\hbox {H}_{26}\)), is located in the center of the room. The compartment is connected to the outside through an inlet and outlet. The P&B correlation is implemented as a boundary condition in computational fluid dynamics calculations. The MLR outcome depends on the average \(\hbox {O}_2\) concentration in a predefined volume and the characteristics of the fuel. The influence of the size and location of the predefined volume, the ventilation branch position (at 1 m and 3.65 m from the floor) and the Renewal Rate (\(R_r\)) (\(4.7\,\hbox {h}^{-1}\) and \(8.4\,\hbox {h}^{-1}\)) are studied. Two types of \(\hbox {O}_2\) predefined volumes have been tested: layer and ring. The layer volume is located in the low part of the compartment, the base of the volume spanning the compartment floor. The ring is a volume around the pit. It is assumed for both approaches that the measured \(\hbox {O}_2\) is representative of the available oxygen for the flame. The P&B boundary condition predicts the influence of the vitiation on the MLR. Other methods, such as imposing the MLR expected in open condition, overpredict the amount of injected fuel. The results show that the P&B correlation provides good agreement with the experimental data. The deviation between experimental data and numerical prediction for the average MLR in the best case is ?5.0% with absolute values of 0.004 kg/s and 0.0038 kg/s for the experiment and the simulation respectively for case PRS-SI-D1. The MLR calculation is influenced by the position of the ventilation opening and the \(R_r\). The temperature and \(\hbox {O}_2\) concentration profiles are significantly influenced by the ventilation configuration. These differences are related to the transport of the injected air from the inlet to the floor by density difference.     

Reactions entre granulats calcaires et pate de ciment alumineux

As it has been pointed out about Portland cement, the aluminous cement reactsd with calcite. This reaction has been studied by X-ray diffraction with two types of specimen: the interfacial zone between cement paste and aggregate is investigated with a “double-specimen” model, the contact zone and the bulk are studied with mortars. The hydration reactions of the aluminous cement largely changed in the interfacial zone by the calcareous nature of the aggreagate. Calcite reacts with the two calcium aluminate hydrates CAH₁₀ et C₂AH₈ to form calcium hydrocarboaluminate. This reaction occurs in two steps: firstly C₄A.1/2 \(\bar C\) .12H₂O and secondly C₃A.CaCO₂.11H₂O. As we know, this reaction retards the conversion of the hexagonal aluminates in the cubic form C₃AH₆, which is responsible for damages on aluminous concretes. This retard of the conversion is studied for calcareous and siliceous concretes. The rate of the conversions depends on the nature of the hydrates; it decreases in the following order: C₂AH₈?CAH₁₀?C₃A.CaCO₃.11H₂O The physico-chemical study of the interfacial zone between aggregate and aluminous cement paste is a step in explaining the mechanical comportment of concretes made with aluminous binders.     

Combination of Kriging methods and multi-fractal analysis for estimating spatial distribution of geotechnical parameters

Spatial variability (randomness, correlation, and singularity) within the geotechnical parameters of complicated geological movements influences the estimation quality that depends on how well mathematical tools can account for variability through limited observations of a spatial field. Classical statistical methods depict randomness well, but cannot account for the problems associated with spatial correlations. Geostatistical methods such as ordinary Kriging (OK), universal Kriging (UK), and co-Kriging (CK) can produce predictions based on spatial auto-correlation and cross-correlation, but are always accompanied by average smoothing effects; a local singularity created by nonlinear geo-processes, therefore, requires special methods to be properly evaluated. In this study, a shallow load-bearing stratum of silt clay (length = 525 m, width = 80 m) at the former 2010 Expo Park in Shanghai was explored by performing 42 borehole laboratory experiments, which provided the key geotechnical parameters: the cohesion coefficient (\( C \), in kPa), the friction angle (\( \varphi \), in ^o), and the compression modulus (\( E_{\text{S}} \), in MPa). First, Kriging methods such as OK, UK, and CK estimated these geotechnical parameters, then a multi-fractal analysis was employed to measure the local singularity. Cross-validation illustrates that multi-fractal analysis has the ability to depict a local anomaly, and further that the auxiliary information utilized in CK improves spatial estimation accuracy.     

Sous-produits industriels comme granulats routiers

Relation between the characteristics of the aggregates and the properties of some materials—Experimental research works (laboratory or site). Industrial by-products used are as follows:

- as an aggregate:

? stone and gravel pit refuse

? crushed blast furnace slag

? incenerator waste slag

- as a binder:

? hydraulic and non-hydraulic fly ash

? granulated blast furnace slag

? hydrated and carbide lime refuse.

Pavement layers applied are as follows:

- unbound base courses: mechanical stabilisation using stone pit refuse, crushed blast furnace slag, waste incinerator slag

- with hydraulic binder: (cement, fly-ash, granulated slag):

? lean concrete with crushed blast furnace slag and stone pit refuse

? hydraulically bound crushed blast furnace slag, waste incinerator slag, and sand obtained as refuse at sieving

- with hydrocarbon binder:

? bituminous stone pit refuse, bituminous crushed blast furnace slag, and bituminous mixture of gravel and sand and waste incinerator slag

? rolled asphalt with crushed blast furnace slag.

     

Hotelling was right with decreasing returns to scale and a coalition-proof refinement

This paper provides a simple, realistic, and very slightly modified version of the production technology in Hotelling’s (Econ J 39:41–57, 1929) spatial model with linear transportation costs to overcome the nonexistence problem of equilibrium—decreasing returns to scale. It is shown that a pure strategy Nash equilibrium in price competition always exists for all location pairs and guarantees uniqueness if we utilize a coalition-proof refinement introduced by Bernheim et al. (J Econ Theory 42:1–12, 1987). Decreasing returns to scale reduce the profit a firm can capture through price undercutting and stabilize the price equilibrium due to the increasing average production cost of firms. As a consequence, duopoly firms agglomerating at the center of a line are shown to be at the unique location equilibrium. This paper confers a new validity to the so-called principle of minimum differentiation, in some sense, with the least deviation from the original Hotelling (Econ J 39:41–57, 1929) model.     

Caractérisation minéralogique et géotechnique des argiles marneuses gonflantes de la région de Médéa,Algérie

This paper presents the approach followed for the geological, mineralogical, and geotechnical characterization of swelling marly clays in the Médéa region. This investigation is conducted in order to estimate the swelling potential of this marly clay layer. The studied sites, located at about 80 km south of Algiers, Algeria, cover an area of approximatively 400 hectares. Five sites are considered. In the first step, the geological, tectonic, climatic, and hydrological contexts of the region are described. According to the geological map of Médéa, most of the formations encountered in the area are composed of Miocene layers represented by marly clays (Fig. 2). This region is characterized by its high and low temperature in summer and winter, respectively, and variable humidity (Fig. 3). In a second step, the results of geotechnical studies, X-ray diffraction tests, chemical analyses, and scanning electron microscope (SEM) observations are presented (Figs. 3, 4, 5, 6, 7, 8, 9). The soils contain quartz (20–26 %), calcium carbonates (11–55 %), kaolinite (8–13 %), illite (6–14 %) and Montmorillonite (18–26 %). The study of their microstructure by means of SEM indicates that these soils are formed by a compact marly clay matrix that is relatively homogeneous and oriented in the dip direction of bedding. A grain size analysis shows that the clay content varies between 17 and 70 %. The water content of all samples varies between 8 and 30 %. The values of the liquidity limit (LL) and plasticity index (PI) vary between 28–76 % and 16–36 % respectively, indicating a highly plastic soil; this is also confirmed by a specific surface varying between 99 and 179 m²/g. The dry density γ _d varies between 15 and 19 kN/m³. The swelling potential of the marly clay samples is evaluated firstly using various indirect methods. In literature, a number of empirical classifications are proposed by different authors (BRE 1980; Chen 1988; Komornik and David 1969; Seed et al. 1962; Snethen 1984; Vijayvergiya et Ghazzaly 1973 et Williams and Donaldson 1980). The swelling potential is related to certain physical properties of soils, such as consistency limits, clay content, methylene blue value, etc. In general, these methods indicate that all the tested soils have a high swelling potential, which confirms the results of mineralogical analysis. Secondly, direct measurements of swelling parameters are performed. Swelling tests are carried out using a standard slaved one-dimensional odometer using two methods: free swell and constant volume, according to standard ASTM D 4546-90 and AFNOR (1995). The swell pressure, the swell percentage and the swell index are given in Fig. 16. It is noted that the soils develop very significant swell pressures which vary between 25 and 900 kPa. This is in agreement with the results obtained by empirical methods. This investigation clearly shows that the marly clays of the Médéa region have a high swelling potential. Therefore, taking into account the phenomenon of soil swelling in structure design is essential.     

Floatation extraction of thinly-emulsified tributyl phosphate stabilized by silicic acid

We have studied regularities of floatation extraction of fine-emulsion tributyl phosphate stabilized by silicic acid. Most completely the floatation process occurs at pH 5–6. At the concentration of silicic acid 500–550 mg/dm³ the degree of floatation extraction of tributyl phosphate (α) reaches 70% (floatation time of tributyl phosphate is 10 min). In the presence of HNO₃ (1–5 mol/dm³) the value α passes through the maximum at \(C_{HNO_3 } \)= 3 mol/dm³. A conclusion was made about an important role in the studied floatation process of not only electrical, but also structural-mechanical properties of the surface of the air drops and bubbles.