12,180 research outputs found
The Optimal Design of Fallible Organizations: Invariance of Optimal Decision Criterion and Uniqueness of Hierarchy and Polyarchy Structures
We present a general framework to study the project selection problem in an organization of fallible decision-makers. We show that when the organizational size and the majority rule for project acceptance are optimized simultaneously, the optimal quality of decision-making, as determined by the decision criterion, is invariant, and depends only on the expertise of decision-makers. This result clarifies that the circumstances under which the decision-making quality varies with the organizational structure are situations where the organizational size or majority rule is restricted from reaching the optimal level. Moreover, in contrast to earlier findings in the literature that the hierarchy and the polyarchy are suboptimal structures, we show that when the size, structure and decision criterion are simultaneously optimized, the hierarchy and the polyarchy are in fact the only possible optimal organizational structures when decision-making costs are present.organizational decision-making, structure, quality, hierarchy, polyarchy
Distributed NEGF Algorithms for the Simulation of Nanoelectronic Devices with Scattering
Through the Non-Equilibrium Green's Function (NEGF) formalism, quantum-scale
device simulation can be performed with the inclusion of electron-phonon
scattering. However, the simulation of realistically sized devices under the
NEGF formalism typically requires prohibitive amounts of memory and computation
time. Two of the most demanding computational problems for NEGF simulation
involve mathematical operations with structured matrices called semiseparable
matrices. In this work, we present parallel approaches for these computational
problems which allow for efficient distribution of both memory and computation
based upon the underlying device structure. This is critical when simulating
realistically sized devices due to the aforementioned computational burdens.
First, we consider determining a distributed compact representation for the
retarded Green's function matrix . This compact representation is exact
and allows for any entry in the matrix to be generated through the inherent
semiseparable structure. The second parallel operation allows for the
computation of electron density and current characteristics for the device.
Specifically, matrix products between the distributed representation for the
semiseparable matrix and the self-energy scattering terms in
produce the less-than Green's function . As an illustration
of the computational efficiency of our approach, we stably generate the
mobility for nanowires with cross-sectional sizes of up to 4.5nm, assuming an
atomistic model with scattering
Extremely high room-temperature two-dimensional hole gas mobility in Ge/Si0.33Ge0.67/Si(001) p-type modulation-doped heterostructures
To extract the room-temperature drift mobility and sheet carrier density of two-dimensional hole gas (2DHG) that form in Ge strained channels of various thicknesses in Ge/Si0.33Ge0.67/Si(001) p-type modulation-doped heterostructures, the magnetic field dependences of the magnetoresistance and Hall resistance at temperature of 295 K were measured and the technique of maximum entropy mobility spectrum analysis was applied. This technique allows a unique determination of mobility and sheet carrier density of each group of carriers present in parallel conducting multilayers semiconductor heterostructures. Extremely high room-temperature drift mobility (at sheet carrier density) of 2DHG 2940 cm2 V–1 s–1 (5.11×1011 cm–2) was obtained in a sample with a 20 nm thick Ge strained channel
Fracture Toughness of Fibrous Membranes
Random fibrous networks exist in both natural biological and engineering materials. While the nonlinear deformation of fibrous networks has been extensively studied, the understanding of their fracture behaviour is still incomplete. To study the fracture toughness of fibrous materials, the near-tip region is crucial because failure mechanisms such as fibril rupture occur in this region. The consideration of this region in fracture studies is, however, a difficult task because it involves microscopic mechanical responses at a small length scale. This paper extends our previous finite element analysis by incorporating the microscopic responses into a macroscopic domain by using a submodeling technique. The detailed study of microstructures at crack tips show a stochastic toughness of membranes due to the random nature of fibrous networks. Further, the sizes of crack tip region, which are sufficient to provide a reasonable prediction of fracture behaviour in a specific type of fibrous network, were presented. Future work includes improving the current linear assumption in the macroscopic models to become nonlinear
Effects of microstructure architecture on the fracture of fibrous materials
Fibrous materials is one of the potential scaffolds used for tissue engineered constructs. One of prerequisite properties for tissue engineered construct is fracture property. The work here study the relationship between microstructure architecture and fracture behavior of fibrous networks by using finite element analysis. The result shows that fibrous networks are toughened by either reducing the fiber density or cross-link percentage of networks. Such implementation increases the degree of non-affine deformation and produces a more compliant response at the crack-tip region. The non-affine deformation in fibrous networks involves fiber movement like fiber rearrangement and reorientation, where such mechanisms allow stress delocalization to occur at the crack-tip region and results in a better fracture toughness of fibrous networks. The findings form this work provide the design guideline of fibrous materials with enhanced toughness for multiple applications
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