This paper analyses the recent developments in public space policy in the city of Hanoi, Vietnam. It has three aims. The first is to look at a potentially progressive urban policy in contrast to most work on ‘policies in motion’ that has primarily been concerned with neoliberal policies. The second is to put the process of public space policymaking in Hanoi in historical and cultural perspective. We therefore describe public space in Hanoi as historically constituted by different layers of meaning and physical urban patterns. The paper's third aim is to analyse the translocal connections involved in a policy that is still in the making, and therefore characterized by a series of ‘loose threads’. We show how different types of connections – policy mobility, topological relations and inter‐referencing – relate Hanoi to multiple locales elsewhere. The conclusion reflects on the ‘politics of reception’ showing how analysing a policy in the making develops a critical analysis of policies in motion. 相似文献
The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4. 相似文献
The paper gives a brief review of the geology of the Iullemmeden Basin of northwestern Nigeria and how the stratigraphic sequence produces complex geotechnical problems. Mineralogical analysis showed the clay shale to be predominantly attapulgite. Detailed geotechnical properties of the clay showed the liquid limit to be greater than 200% and it depended significantly on treatment before testing. Very low maximum dry densities of 1137 kg/m3 (71 pcf), a high optimum moisture content of 41%, and a high compression index of 0.23 were obtained. The results presented also indicated that the attapulgite has very critical potential volume change. Results of the shear strength characteristics showed the effective cohesion to be zero in all the tests and a loss of strength of about 50% occurred as a result of decrease in the rate of strain. 相似文献
The physical properties of bentonite-based buffer materials for nuclear waste repositories have been investigated by a number of different laboratory tests. These tests have yielded a material model that is valid for conditions close to water saturation and is useful for describing: (a) the stress, strain and volume change behaviour; (b) the pore pressure and flow of water; and (c) the thermal and thermomechanical response.
The material model is based on the Drucker-Prager Plasticity model and a Porous Elastic Model. The effective stress concept and Darcy's law are applied and the swelling/consolidation and thermomechanical processes are coupled according to the separate mechanical properties of the pore water, the solids and the clay skeleton. The model can be used by the finite-element program ABAQUS.
The model has been tested in several laboratory and field verification tests. Comparison between measured and calculated behaviour shows that the general behaviour is described properly and several calculations of different scenarios have been made for the Swedish KBS 3 concept. However, certain processes, like the hysteresis effect at consolidation/swelling, the curved stress-strain relation at shearing, and the curved failure envelope, are not modelled in a perfectly accurate way and an improved material model is proposed here. It combines the behaviour of the Cam-clay model on the wet side with the more relevant plastic behaviour of a modified Drucker-Prager model with a curved failure envelope and the possibility to introduce strain softening after failure.
The paper presents some laboratory results that are the basis of the first model. It also shows the application of the model to finite-element calculations of some laboratory tests. Comparisons between the calculations and measured results expose some disadvantages of the model and a concept for an improved model is suggested. 相似文献
The use of precise post-processed satellite orbits and satellite clock corrections in absolute positioning, using one GPS
receiver only, has proven to be an accurate alternative to the more commonly used differential techniques for many applications
in georeferencing.
The absolute approach is capable of centimeter accuracy when using state-of-the-art, dual-frequency GPS receivers. When using
observations from single-frequency receivers, however, the accuracy, especially in height, decreases. The obvious reason for
this degradation in accuracy is the effect of unmodeled ionospheric delay.
This paper discusses the availability of some empirical ionospheric models that are publicly available and quantifies their
usefulness for absolute positioning using single-frequency GPS receivers. The Global Ionospheric Model supplied by International
GPS Service (IGS) is the most accurate one and is recommended for absolute positioning using single-frequency GPS receivers.
Using high-quality single-frequency observations, a horizontal epoch-to-epoch accuracy of better than 1 m and a vertical accuracy
of approximately 1 m is demonstrated. ? 2002 Wiley Periodicals, Inc. 相似文献
Lithology and Mineral Resources - Several barite deposits have been reported to occur in Nigeria within the Benue Trough, one of the West Central African Rift Systems (WCARS) considered variously... 相似文献
Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used
to examine the profile stability functions of momentum, φm, and sensible heat, φh, in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover
different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five
levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φm and φh in detail and includes ample data for the very stable case. New parameterizations for φm (ζ) and φh (ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter
ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ m follows a ζ 1/3 dependence, whereas φh initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects
of self-correlation, which occur in plots of φm and φh versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging. 相似文献
Turbulent and mean meteorological data collected at five levels on a 20-m tower over the Arctic pack ice during the Surface
Heat Budget of the Arctic Ocean experiment (SHEBA) are analyzed to examine different regimes of the stable boundary layer
(SBL). Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime
to very stable stratification. Scaling arguments and our analysis show that the SBL can be classified into four major regimes:
(i) surface-layer scaling regime (weakly stable case), (ii) transition regime, (iii) turbulent Ekman layer, and (iv) intermittently
turbulent Ekman layer (supercritical stable regime). These four regimes may be considered as the basic states of the traditional
SBL. Sometimes these regimes, especially the last two, can be markedly perturbed by gravity waves, detached elevated turbulence
(‘upside down SBL’), and inertial oscillations. Traditional Monin–Obukhov similarity theory works well in the weakly stable
regime. In the transition regime, Businger–Dyer formulations work if scaling variables are re-defined in terms of local fluxes,
although stability function estimates expressed in these terms include more scatter compared to the surface-layer scaling.
As stability increases, the near-surface turbulence is affected by the turning effects of the Coriolis force (the turbulent
Ekman layer). In this regime, the surface layer, where the turbulence is continuous, may be very shallow (< 5 m). Turbulent
transfer near the critical Richardson number is characterized by small but still significant heat flux and negligible stress.
The supercritical stable regime, where the Richardson number exceeds a critical value, is associated with collapsed turbulence
and the strong influence of the earth’s rotation even near the surface. In the limit of very strong stability, the stress
is no longer a primary scaling parameter. 相似文献
Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov similarity theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov similarity theory in stable conditions is limited by the inequalities Ri < Ricr and Rf < Rfcr. However, it is found that Rfcr = 0.20–0.25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin–Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson–Kolmogorov cascade) have been filtered out. 相似文献