Social Public Purchasing: Addressing A Critical Void in Public Purchasing Research

2021 ◽  
Author(s):  
Fatima Hafsa ◽  
Nicole Darnall ◽  
Stuart Bretschneider
Keyword(s):  
Critical Void

scholarly journals Fatal Void Size Comparisons in Via-Below and Via-Above Cu Dual-Damascene Interconnects

2004 ◽  
Vol 812 ◽  
Author(s):  
Z. -S. Choi ◽  
C. L. Gan ◽  
F. Wei ◽  
C. V. Thompson ◽  
J. H. Lee ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Failure Mechanisms ◽  
Simulation Tool ◽  
Void Size ◽  
Dual Damascene ◽  
Preferential Nucleation ◽  
Failure Correlation ◽  
Void Volumes ◽  
Damascene Interconnects ◽  
Critical Void

AbstractThe median-times-to-failure (t50's) for straight dual-damascene via-terminated copper interconnect structures, tested under the same conditions, depend on whether the vias connect down to underlaying leads (metal 2, M2, or via-below structures) or connect up to overlaying leads (metal 1, M1, or via-above structures). Experimental results for a variety of line lengths, widths, and numbers of vias show higher t50's for M2 structures than for analogous M1 structures. It has been shown that despite this asymmetry in lifetimes, the electromigration drift velocity is the same for these two types of structures, suggesting that fatal void volumes are different in these two cases. A numerical simulation tool based on the Korhonen model has been developed and used to simulate the conditions for void growth and correlate fatal void sizes with lifetimes. These simulations suggest that the average fatal void size for M2 structures is more than twice the size of that of M1 structures. This result supports an earlier suggestion that preferential nucleation at the Cu/Si3N4 interface in both M1 and M2 structures leads to different fatal void sizes, because larger voids are required to span the line thickness in M2 structures while smaller voids below the base of vias can cause failures in M1 structures. However, it is also found that the fatal void sizes corresponding to the shortest-times-to-failure (STTF's) are similar for M1 and M2, suggesting that the voids that lead to the shortest lifetimes occur at or in the vias in both cases, where a void need only span the via to cause failure. Correlation of lifetimes and critical void volumes provides a useful tool for distinguishing failure mechanisms.

Critical Void Dimension of Carbon Frameworks to Accommodate Insoluble Products of Lithium–Oxygen Batteries

2021 ◽  
Author(s):  
Chihyun Hwang ◽  
Myung-Jun Kwak ◽  
Jinhyeon Jeong ◽  
Kyungeun Baek ◽  
Ki-Yong Yoon ◽  
...  
Keyword(s):  
Lithium Oxygen Batteries ◽  
Critical Void

Rain impact soil crust. IV. Packing of sand and silt fractions by raindrops

Soil Research ◽  
1991 ◽  
Vol 29 (2) ◽  
pp. 331 ◽  
Author(s):  
AJ Moss
Keyword(s):  
Void Ratio ◽  
Packed Bed ◽  
Stress Waves ◽  
Soil Crust ◽  
Structural Element ◽  
Loose Packing ◽  
Impact Events ◽  
Underlying Soil ◽  
Silt Layer ◽  
Critical Void

Comparison of resistance to fast and slow deformation by rain-packed and artificially prepared sand and silt fractions showed that, whereas sands are left in loosely packed states after accrual under rain impact, silts are left more densely packed, i.e. below critical void ratio. This contrast is attributed mainly to the declining importance of hydraulic penetration with pore size. Rain-packed silt is dilatant and cannot deform without expansion which, in turn, requires water entry at a rate compatible with the required deformation. In the short duration of rain-impact events, hydrodynamic time lagging occurs because water can move only slowly through the small silt pores. Consequently, densely packed silt remains essentially rigid. However, drop-outflow sheets are able to entrain silt and distribute it over the surface as densely packed bed-load deposits, thus maintaining its dilatancy. Sand, its larger pores invaded by hydraulic penetration jets which maintain loose packing, cannot behave in this manner. Relative stability of the silt layer on soil surfaces, and its suppression of hydraulic penetration, allow transmission of drop-generated stress waves which cause the immediately underlying soil to become compacted into the main structural element of the rain-impact soil crust.

Effect of Critical Void Volume Fraction fF on Results of Ductile Fracture Simulation for S235JR Steel under Multi-Axial Stress States

2014 ◽  
Vol 598 ◽  
pp. 113-118 ◽  
Author(s):  
Paweł Grzegorz Kossakowski ◽  
Wiktor Wciślik
Keyword(s):  
Volume Fraction ◽  
Axial Stress ◽  
Material Model ◽  
Model Parameters ◽  
Material Microstructure ◽  
Fracture Simulation ◽  
Critical Volume Fraction ◽  
Stress States ◽  
The Impact ◽  
Critical Void

The article describes an example of the GTN material model parameters determination and application. The main objective of the study was to determine experimentally the value of the critical volume fraction of voids fFfor S235JR steel and to assess the impact of this parameter on the numerical force-elongation curve under the multi-axial stress state. Value of fFwas obtained by the quantitative analysis of the material microstructure at fracture surfaces. For a sake of comparison, two other values of fF, described in the literature, were also used in numerical simulations.

Concept of critical void ratio used in estimating dynamic stability of sands

2009 ◽  
Vol 64 (2) ◽  
pp. 116-122
Author(s):  
E. S. Kushnareva ◽  
E. A. Voznesensky
Keyword(s):  
Dynamic Stability ◽  
Void Ratio ◽  
Critical Void

scholarly journals Experimental determination of the void volume fraction for S235JR steel at failure in the range of high stress triaxialities

2017 ◽  
Vol 62 (1) ◽  
pp. 167-172 ◽  
Author(s):  
P. G. Kossakowski
Keyword(s):  
Volume Fraction ◽  
High Stress ◽  
Material Model ◽  
Tensile Tests ◽  
Void Volume Fraction ◽  
Void Volume ◽  
Advanced Technique ◽  
Quantitative Image ◽  
Critical Void

Abstract This paper is concerned with the critical void volume fraction fF representing the size of microdefects in a material at the time of failure. The parameter is one of the constants of the Gurson-Tvergaard-Needleman (GTN) material model that need to be determined while modelling material failure processes. In this paper, an original experimental method is proposed to determine the values of fF. The material studied was S235JR steel. After tensile tests, the void volume fraction was measured at the fracture surface using an advanced technique of quantitative image analysis The material was subjected to high initial stress triaxialities T0 ranging from 0.556 to 1.345. The failure processes in S235JR steel were analysed taking into account the influence of the state of stress.

Investigation of Transition From Annular to Intermittent Flow in Pipes

2000 ◽  
Vol 122 (1) ◽  
pp. 22-28 ◽  
Author(s):  
Avni Serdar Kaya ◽  
X. Tom Chen ◽  
Cem Sarica ◽  
James P. Brill
Keyword(s):  
Liquid Film ◽  
Void Fraction ◽  
Entire Range ◽  
Annular Flow ◽  
Intermittent Flow ◽  
Boundary Equation ◽  
Inclination Angles ◽  
Conservation Of Momentum ◽  
Transition Models ◽  
Critical Void

A new unified model is proposed for the transition from annular to intermittent flow patterns for the entire range of pipe inclination angles. Experimentally, it has been observed that the transition from annular flow takes place at a critical void fraction. To obtain a transition boundary equation, conservation of momentum equations for gas and the liquid film are combined and solved with the critical void fraction. The new model captures the correct transition characteristics, agrees favorably with experimental flow pattern data, and performs the best when compared with previous transition models. [S0195-0738(00)00601-4]

scholarly journals Norm-Conserving Pseudopotentials and Basis Sets to Explore Actinide Chemistry in Complex Environments

2021 ◽  
Author(s):  
Jun-Bo Lu ◽  
David Cantu ◽  
Cong-Qiao Xu ◽  
Manh-Thuong Nguyen ◽  
Han-Shi Hu ◽  
...  
Keyword(s):  
Oxidation States ◽  
Basis Sets ◽  
Complex Environments ◽  
Large Core ◽  
Generalized Gradient ◽  
Gaussian Basis Sets ◽  
Exchange Correlation ◽  
Generalized Gradient Approximation ◽  
Core Set ◽  
Critical Void

We have developed a new set of norm-conserving pseudopotentials and companion Gaussian basis sets for the actinide (An) series (Ac - Lr) using the Goedecker, Teter and Hutter (GTH) formalism with the Perdew, Burke and Ernzerhof (PBE) exchange-correlation functional of generalized gradient approximation (GGA). To test the accuracy and reliability of the newly parameterized An-GTH pseudopotentials and basis sets, a variety of benchmarks on actinide-containing molecules are carried out and compared to all-electron and available experimental results. The new pseudopotentials include both medium- ([Xe]4f14) and large-core ([Xe]4f145d10) options that have successfully reproduced structures and energetics, particularly redox processes. The medium-core size set, in particular, reproduce all-electron calculations over multiple oxidation states from 0 to VII, whereas the large-core set is suitable only for the early series elements and low oxidation states. The underlying reason for these transferability issues are discussed in detail. This work fills a critical void in the literature for studying the chemistry of 5f-block elements in condensed phase.

Collapse of cohesive overburden following removal of support

1990 ◽  
Vol 27 (3) ◽  
pp. 355-364 ◽  
Author(s):  
W. H. Craig
Keyword(s):  
Critical Diameter ◽  
Extraction Process ◽  
Void Size ◽  
Critical Stability ◽  
Constant Acceleration ◽  
Turn On ◽  
Centrifuge Models ◽  
Critical Void ◽  
Bound Analysis ◽  
Material Extraction

Model tests have been performed in a large centrifuge to investigate the conditions for critical stability of a circular cavity formed by removal of underlying support strata beneath a soft to very soft cohesive overburden. Initial tests used a fixed geometry and were subjected to increasing self-weight by the "gravity turn-on" technique, while later tests utilized a dynamic material extraction process at constant acceleration levels. The mechanics of failure are described and a simple upper-bound analysis is found to predict the critical void size within acceptable limits for a range of the ratio of overburden depth to critical diameter from 0.5 to 1.5. Key words: cohesive overburden, stability, centrifuge, models, voids.

Sign in / Sign up

Export Citation Format

Share Document