Uncertainty and Intelligence in Computational Stochastic Mechanics

Classical structural reliability assessment techniques are based on precise and crisp (sharp) definitions of failure and non-failure (survival) of a structure in meeting a set of strength, function and serviceability criteria. These definitions are provided in the form of performance functions and limit state equations. Thus, the criteria provide a dichotomous definition of what real physical situations represent, in the form of abrupt change from structural survival to failure. However, based on observing the failure and survival of real structures according to the serviceability and strength criteria, the transition from a survival state to a failure state and from serviceability criteria to strength criteria are continuous and gradual rather than crisp and abrupt. That is, an entire spectrum of damage or failure levels (grades) is observed during the transition to total collapse. In the process, serviceability criteria are gradually violated with monotonically increasing level of violation, and progressively lead into the strength criteria violation. Classical structural reliability methods correctly and adequately include the ambiguity sources of uncertainty (physical randomness, statistical and modeling uncertainty) by varying amounts. However, they are unable to adequately incorporate the presence of a damage spectrum, and do not consider in their mathematical framework any sources of uncertainty of the vagueness type. Vagueness can be attributed to sources of fuzziness, unclearness, indistinctiveness, sharplessness and grayness; whereas ambiguity can be attributed to nonspecificity, one-to-many relations, variety, generality, diversity and divergence. Using the nomenclature of structural reliability, vagueness and ambiguity can be accounted for in the form of realistic delineation of structural damage based on subjective judgment of engineers. For situations that require decisions under uncertainty with cost/benefit objectives, the risk of failure should depend on the underlying level of damage and the uncertainties associated with its definition. A mathematical model for structural reliability assessment that includes both ambiguity and vagueness types of uncertainty was suggested to result in the likelihood of failure over a damage spectrum. The resulting structural reliability estimates properly represent the continuous transition from serviceability to strength limit states over the ultimate time exposure of the structure. In this section, a structural reliability assessment method based on a fuzzy definition of failure is suggested to meet these practical needs. A failure definition can be developed to indicate the relationship between failure level and structural response. In this fuzzy model, a subjective index is introduced to represent all levels of damage (or failure). This index can be interpreted as either a measure of failure level or a measure of a degree of belief in the occurrence of some performance condition (e.g., failure). The index allows expressing the transition state between complete survival and complete failure for some structural response based on subjective evaluation and judgment

Size induced metal insulator transition in nanostructured Niobium thin films: Intragranular and intergranular contributions

With a reduction in the average grain size in nanostructured films of elemental Nb, we observe a systematic crossover from metallic to weakly-insulating behavior. An analysis of the temperature dependence of the resistivity in the insulating phase clearly indicates the existence of two distinct activation energies corresponding to inter-granular and intra-granular mechanisms of transport. While the high temperature behavior is dominated by grain boundary scattering of the conduction electrons, the effect of discretization of energy levels due to quantum confinement shows up at low temperatures. We show that the energy barrier at the grain boundary is proportional to the width of the largely disordered inter-granular region, which increases with a decrease in the grain size. For a metal-insulator transition to occur in nano-Nb due to the opening up of an energy gap at the grain boundary, the critical grain size is ~ 8nm and the corresponding grain boundary width is ~ 1.1nm

Efficacy of proximal femoral nail augmentation in unstable intertrochanteric fracture

Background: To assess the short term functional and radiological outcome of unstable intertrochanteric fracture fixation using proximal femoral nail with augmentation using Cannulated Cancellous (CC) screw or Stainless Steel (SS) wiring.Methods: A prospective study was conducted with 20 cases of unstable intertrochanteric femoral fractures from May 2017 to March 2019. Six females and fourteen male patients in the age group between 40 and 80 years were included in this study. There were 8 cases of AO31A2 and 12 cases of AO31 A3. Fracture were fixed by proximal femoral nail with augmentation by an additional CC screw or encirclage with SS wires to strengthen the lateral trochanteric wall.Results: Fracture union was achieved in all cases with a mean period of 15.4 weeks. Patients were followed up for a period of 6 months. At the end of follow up the Modified Harris Hip Score was found to be more than 90 % in 16 cases.Conclusion: Augmentation of proximal femoral nail in unstable intertrochanteric fracture with additional screw or cerclage wire increases the efficacy and stability of construct, aiding union and expedition of time to union

Strategic implementation of infrastructure priority projects: case study in Palestine

A strategy was developed for implementation and management of multisector urban infrastructure projects. The strategy includes risk-based analytical hierarchy process (AHP) for project prioritization that is based on project deliverables and project life-cycle and implementation guidelines. The expert-opinion elicitation process used for this study consists of a variation of the Delphi technique, scenario analysis, civil works, and nuclear industry recommendations. The AHP methodology utilizes a multicriteria decision-making technique that allows the consideration of both objective and subjective factors in obtaining cardinal priority ranking of infrastructure projects. The methodology, which deals with different fields of infrastructure, can incorporate uncertainty in the process and can be implemented using simple spreadsheet format. The methodology was developed for a group of players (methodology implementers

Mutagenic analysis of the HIV restriction factor shiftless

The interferon-induced host cell protein shiftless (SFL) was reported to inhibit human immunodeficiency virus (HIV) infection by blocking the –1 programmed ribosomal frameshifting (–1PRF) required for expression of the Gag-Pol polyprotein. However, it is not clear how SFL inhibits –1PRF. To address this question, we focused on a 36 amino acids comprising region (termed required for antiviral activity (RAA)) that is essential for suppression of –1PRF and HIV infection and is missing from SFL short (SFLS), a splice variant of SFL with unknown function. Here, we confirm that SFL, but not SFLS, inhibits HIV –1PRF and show that inhibition is cell-type-independent. Mutagenic and biochemical analyses demonstrated that the RAA region is required for SFL self-interactions and confirmed that it is necessary for ribosome association and binding to the HIV RNA. Analysis of SFL mutants with six consecutive amino-acids-comprising deletions in the RAA region suggests effects on binding to the HIV RNA, complete inhibition of –1PRF, inhibition of Gag-Pol expression, and antiviral activity. In contrast, these amino acids did not affect SFL expression and were partially dispensable for SFL self-interactions and binding to the ribosome. Collectively, our results support the notion that SFL binds to the ribosome and the HIV RNA in order to block –1PRF and HIV infection, and suggest that the multimerization of SFL may be functionally important

Upper critical field in nanostructured Nb: Competing effects of the reduction in density of states and the mean free path

We show that the upper critical field in nanometer-sized Nb particles is governed by the changes in the effective Ginzburg-Landau coherence length occurring due to two competing factors: (i) the decrease in the grain size and consequent increase of disorder, and (ii) the effective decrease in the density of states at the Fermi level due to the formation of a Kubo gap. As a result, the upper critical field (HC2) and irreversibility fields (Hirr) in nanostructured Nb show non-monotonic grain size dependences. Between 60nm to 20nm, HC2 is found to increase by 2.5times while there is no appreciable decrease in the superconducting transition temperature (TC) from its bulk value of 9.4K. This can be ascribed to a decrease in the coherence length due to a reduction in the mean free path with decreasing size. Below 20 nm, however, HC2 decreases with decreasing size. In this size range (<20 nm), there also occurs a decrease in the TC as well as the superconducting energy gap. The decrease in HC2 in this regime can be ascribed to the decrease in the density of states at the Fermi level due to a quantization in the electronic energy levels

Mass selection in laser-plasma ion accelerator on nanostructured surfaces

When an intense laser pulse interacts with a solid surface, ions get accelerated in the laser-plasma due to the formation of transient longitudinal electric field along the target normal direction. However, the acceleration is not mass-selective. The possibility of manipulating such ion acceleration scheme to enhance the energy of one ionic species (either proton or carbon) selectively over the other species is investigated experimentally using nanopore targets. For an incident laser intensity of approximately 5×1017 W/cm2, we show that the acceleration is optimal for protons when the pore diameter is about 15-20 nm, while carbon ions are optimally accelerated when the pore diameter is close to 40-50 nm. The observed effect is due to tailoring targetry by the pulse pedestal of the laser prior to the arrival of the main pulse

Hot ion generation from nanostructured surfaces under intense, femtosecond irradiation

We present the effect of a nanostructured surface on the emission of ions and electrons from intense (5-36 Petwatt per sq.cm) femtosecond laser produced plasmas. Electrons from optically polished copper targets coated with copper nanoparticles (CuNP) are observed to be hotter than those from uncoated polished targets. A nearly two-fold enhancement is observed for ions in the range 14-74 keV, while ion yield decreases by a factor of 2 in the 74-2000 keV range. The total ion yields measured using a large area Faraday cup are more from CuNP targets than those from polished Cu targets, indicating increased ion beam divergence due to surface modulations.Comment: 14 pages, 4 figure

Non-monotonic size dependence of the elastic modulus of nanocrystalline ZnO embedded in a nanocrystalline silver matrix

We present the first high pressure Raman study on nanocrystalline ZnO films with different average crystallite sizes. The problem of low Raman signals from nano sized particles was overcome by forming a nanocomposite of Ag and ZnO nanoparticles. The presence of the nanodispersed Ag particles leads to a substantial surface enhancement of the Raman signal from ZnO. We find that the elastic modulus of nanocrystalline ZnO shows a non-monotonic dependence on the crystallite size. We suggest that the non-monotonicity arises from an interplay between the elastic properties of the individual grains and the intergranular region.Comment: 10 pages, 6 figure

From Reliability-Based Design to Resilience-Based Design

Abstract Reliability-based design has been a widely used methodology in the design of engineering structures. For example, the structural design standards in many countries have adopted the load and resistance factor design (LRFD) method. In recent years, the concept of resilience-based design has emerged, which additionally takes into account the posthazard functionality loss and recovery process of a structure. Under this context, the following questions naturally arise: can we establish a linkage between reliability-based design and resilience-based design? Does there exist a simple resilience-based design criterion that takes a similar form of LRFD? This paper addresses these questions, and the answer is “yes”. To this end, a new concept of structural resilience capacity is proposed, which is a generalization of structural load bearing capacity (resistance). The probabilistic characteristics (mean value, variance, probability distribution function) of resilience capacity are derived. Applying the concept of resilience capacity, this paper explicitly shows the relationship between the following four items: time-invariant reliability-, time-invariant resilience-, time-dependent reliability-, and time-dependent resilience-based design methods. Furthermore, an LRFD-like design criterion is proposed for structural resilience-based design, namely, load and resilience capacity factor design (LRCFD), whose applicability is demonstrated through an example. The LRCFD method can also be used, in conjunction with LRFD, to achieve reliability and resilience goals simultaneously of the designed structure.</jats:p