Maximum Allowable Density Research Articles

Hardening of high-energy self-ion irradiated FeCrAl ODS alloys evaluated by micro- and nano-hardness tests

Hardening of two kinds of FeCrAl ODS alloys irradiated by high-energy heavy ions to about 0.8 dpa at nominal 200 °C is investigated. A damage layer of 24 μm in thickness produced by the ion irradiation in the specimens makes possible both the micro- and the nano-hardness tests. Nix-Gao model is used to eliminate the indentation size effect (ISE) from the hardness data of the damage plateau so as to obtain the equivalent bulk hardness values. Results of the hardness tests show that the FeCrAl ODS alloy with 0.8 wt% Hf addition exhibits better resistance to irradiation hardening than that with 0.6 wt% Zr addition. A correlation between the micro- and the nano-hardness data is established as HV0=74.5H0 (HV0 in unit of kgf/mm2, H0 in unit of GPa) for the ODS alloys. A modified Nix-Gao model which includes a maximum allowable density of the geometrically necessary dislocation (GND) and a non-uniform distribution of GNDs can fit well the nano-hardness data in the entire indentation depth range, including the near surface region with a damage ramp.

Effective fitting of nanohardness data in two different ferritic steels irradiated with He ions

A damage plateau (4000 appm/0.25 dpa) was produced in T92 and MA956 by multi-energy He ion irradiation. Nanoindentation was used to characterize the irradiation hardening effect. For the pristine samples, the hardness at the region shallower than 200 nm deviated evidently from the relation predicted by the Nix-Gao model. The hardness of the damaged layer produced by ion irradiation also located in this region. Therefore, a modified model by introducing a maximum allowable density of GNDs proposed by Ruiz-Moreno was used to analyze the hardness data. The fitted result indicated that the hardness of the damaged layer was overestimated by 28.5% for T92 and 48.4% for MA956 in contrast to that obtained from the Nix-Gao model, and a hardening fraction of 64.5% for MA956 and 103.6% for T92 was also obtained. A lower hardening fraction of MA956 was considered to be related to the existence of oxide particles in the matrix.

Free Energy and the Equation of State of a System of Solid Spheres in Narrow Cylindrical Pores

In this work, the free energy and the equation of state of a system of solid spheres in narrow cylindrical pores are determined using the combined method of accelerated convergence of series. This method includes the Euler method and a method based on taking the behavior of the system into account at high densities near the dense packing and on the idea of the effective number of the nearest neighbors. The results are compared with the data of a computer experiment for three different values of pore size and in all cases good agreement between theory and experiment was obtained. These are much better than the results of virial expansion, and when the transverse pore sizes increase, better than the results found on the basis of a series in powers of pressure as well. The method makes it possible to estimate the limits of applicability of the method of convergence acceleration, based on the transition from a series in density to a series in terms of pressure. To do this, the density with close packing and the maximum allowable density found by the method of Euler are compared. If these densities are close, then only the Euler method can be used. In the case of a significant difference, a combined method of accelerated convergence is required.

Measurements on the fly– Introducing mobile micro-sensors for biotechnological applications

The application of standard sensor electrodes is often limited to stirred tank reactors due to their wired nature and their large space requirement. For other cultivation systems, sensors require a great technical effort to be implemented. Here we propose a new concept of sensors: miniaturized, mobile, wireless, and self-contained spherical sensors with diameters of only 7.9 mm. The micro-probes send their data wirelessly at a frequency band of about 433 MHz to a base station during the process run and are easily deployable for many biotechnological applications and reactor types, without any need to modify the cultivation system, as the probes are nearly non-invasive due to their small size. The system consists of a platform that can accommodate various sensor types, e.g., temperature as shown in this work. The sensor spheres are reusable and can be charged by induction before being deployed in a biotechnological application. Furthermore, redundancy can easily be realized by adding several sensors into a single reactor, since each base station can coordinate up to 24 spheres. From computational fluid dynamics (CFD) simulations we could infer the maximum allowable density of spheres that would still enable them to be homogeneously distributed within a reactor as 1.1 g/cm3. We could demonstrate the practical applicability of our concept by deploying the spheres in shaking flasks, lab-scale stirred tank reactors, and tube reactors in typical lab environments. In all cases, the spheres showed reliable data transmission despite the potentially shielding technical environment.

Connectivity of Cognitive Device-to-Device Communications Underlying Cellular Networks

Providing direct communications among a rapidly growing number of wireless devices within the coverage area of a cellular system is an attractive way of exploiting the proximity among them to enhance coverage and spectral and energy efficiency. However, such device-to-device (D2D) communications create a new type of interference in cellular systems, calling for rigorous system analysis and design to both protect mobile users (MUs) and guarantee the connectivity of devices. Motivated by the potential advantages of cognitive radio (CR) technology in detecting and exploiting underutilized spectrum, we investigate CR-assisted D2D communications in a cellular network as a viable solution for D2D communications, in which devices access the network with mixed overlay-underlay spectrum sharing. Our comprehensive analysis reveals several engineering insights useful to system design. We first derive bounds of pivotal performance metrics. For a given collision probability constraint, as the prime spectrum-sharing criterion, we also derive the maximum allowable density of devices. This captures the density of MUs and that of active macro base stations. Limited in spatial density, devices may not have connectivity among them. Nevertheless, it is shown that for the derived maximum allowable density, one should judiciously push a portion of devices into receiving mode in order to preserve the connectivity and to keep the isolation probability low. Furthermore, upper bounds on the cellular coverage probability are obtained incorporating load-based power allocation for both path-loss and fading-based cell association mechanisms, which are fairly accurate and consistent with our in-depth simulation results. Finally, implementation issues are discussed.

Indentation size effect and micromechanics characterization of intermetallic compounds in the Au–Sn system

The indentation size effect and the micromechanics characterization of intermetallic compounds in the Au–Sn system have been investigated by nanoindentation, using continuous multi-cycle loading mode and load-control mode, respectively. An analytic model based on the enlarged plastic zone and the maximum allowable density of geometrically necessary dislocation was established to describe the relationship between the indentation hardness and depth. Our new model gives better predictions of the indentation hardness of Au5Sn, AuSn and AuSn2 for small indentation depths compared to the Nix–Gao model. Pop-in events in the load–displacement curves corresponding to the peaks in the normalized velocity–load curves represent the elastic–plastic or harden-yield transition during indentation. A viscoplastic creep equation was employed to evaluate the creep behavior of the Au–Sn intermetallics. The stress exponents (n) can be well defined into two stress regimes: the high stress regime (HSR) and the low stress regime (LSR). In the HSR, dislocation motion is the dominant creep mechanism with n>5, while in the LSR, grain boundary sliding dominates the creep of Au5Sn and AuSn2 with n≈2, and dislocation viscous glide dominates the creep of AuSn and AuSn4 with n around 3.

Transmission capacity for dual-hop relaying in wireless ad hoc networks

Abstract To account for randomly distributed nodes in a wireless ad hoc network, the transmission capacity is defined as the number of successful transmissions taking place in the network per unit area under an outage constraint. In this paper, we analyze the transmission capacity for dual-hop relaying in a wireless ad hoc network in the presence of both cochannel interference and thermal noise, where interferers are spatially distributed following a Poisson distribution. Specifically, we first present the exact outage probability for amplify-and-forward and decode-and-forward protocols in a Poisson field of interferers without neglecting noise at all nodes. We then derive the transmission capacity of such networks, which determines the maximum allowable density of transmitting nodes for each relay strategy at a specified outage probability and data rate. Numerical results demonstrate that the dual-hop relaying is still beneficial in terms of the transmission capacity in wireless ad hoc Poisson networks.

A model of size effects in nano-indentation

The indentation hardness–depth relation established by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 46, 411–425] agrees well with the micro-indentation but not nano-indentation hardness data. We establish an analytic model for nano-indentation hardness based on the maximum allowable density of geometrically necessary dislocations. The model gives a simple relation between indentation hardness and depth, which degenerates to Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 46, 411–425] for micro-indentation. The model agrees well with both micro- and nano-indentation hardness data of MgO and iridium.

Transport Simulations of a Density Limit in Radiation-Dominated Tokamak Discharges II

The procedures developed previously to simulate the radiatively induced tokamak density limit are used to examine in more detail the scaling of the density limit. It is found that the maximum allowable density increases with auxiliary power and decreases with impurity concentration. However, it is demonstrated that there is little dependence of the density limit on plasma elongation. These trends are consistent with experimental results. Our previous work used coronal equilibrium impurities; the primary result of that paper was that the maximum density increases with current when peaked profiles are assumed. Here, this behavior is shown to occur with a coronal nonequilibrium impurity as well. 26 refs., 4 figs.

Effect of Biological Clogging on Infiltration Rate in Soil Treatment Systems

Effect of biomass on the soil hydraulic conductivity was clarified on andosol soil. The approximate value of the maximum allowable density of biomass was determined, which corresponds to the minimum hydraulic conductivity of the clogged andosol soil. On the basis of these values and the mass balance of the substrate, the relation among substrate concentration, thickness of clogged zone and the percolation rate was discussed. In addition, a numerical model was constructed, and the biomass growth and the change of permeability were simulated. Calculated results were compared with the results of two-dimensional infiltration flow experiments. By using the model, the conditions to avoid infiltration failure were determined.

The perception of dimensions of space and levels of infrastructure and its application in landscape planning

Three different examples of analysis of spatial and functional elements in the landscape are briefly described and compared. The three vary in location, scope and objective. The first is an American report concerning the setting up to a classification system for water-oriented landscapes. The other two are published and situated in The Netherlands. One of them deals with the concept of openness and enclosure in a rural landscape in which recreational land-use is planned. The other sets up guidelines for the planning of electric power lines in the (flat) Dutch landscape. The three share the notion that levels of dimension and/or function that are interrelated in a particular way result in aesthetic satisfaction. This notion is supported in general terms in literature on environmental perception. Attempts to “validate” the notion by means of design and planning studies are illustrated here. They result in proposals for a maximum allowable density of occupation in a recreational area and in criteria for the location and alignment of electric power lines.