Dynamic Behavior in Piezoresponse Force Microscopy

Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM) implemented on a beam-deflection atomic force microscope (AFM) is analyzed using a combination of modeling and experimental measurements. The PFM signal comprises contributions from local electrostatic forces acting on the tip, distributed forces acting on the cantilever, and three components of the electromechanical response vector. These interactions result in the bending and torsion of the cantilever, detected as vertical and lateral PFM signals. The relative magnitudes of these contributions depend on geometric parameters of the system, the stiffness and frictional forces of tip-surface junction, and operation frequencies. The dynamic signal formation mechanism in PFM is analyzed and conditions for optimal PFM imaging are formulated. The experimental approach for probing cantilever dynamics using frequency-bias spectroscopy and deconvolution of electromechanical and electrostatic contrast is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques

Thermodynamic theory of epitaxial ferroelectric thin films with dense domain structures

A Landau-Ginsburg-Devonshire-type nonlinear phenomenological theory is presented, which enables the thermodynamic description of dense laminar polydomain states in epitaxial ferroelectric thin films. The theory explicitly takes into account the mechanical substrate effect on the polarizations and lattice strains in dissimilar elastic domains (twins). Numerical calculations are performed for PbTiO3 and BaTiO3 films grown on (001)-oriented cubic substrates. The "misfit strain-temperature" phase diagrams are developed for these films, showing stability ranges of various possible polydomain and single-domain states. Three types of polarization instabilities are revealed for polydomain epitaxial ferroelectric films, which may lead to the formation of new polydomain states forbidden in bulk crystals. The total dielectric and piezoelectric small-signal responses of polydomain films are calculated, resulting from both the volume and domain-wall contributions. For BaTiO3 films, strong dielectric anomalies are predicted at room temperature near special values of the misfit strain.Comment: 19 pages, 8 figure

Study of Theoretical and Observed Capacities of Bored Cast-Insitu Piles in Tuff, Braccia and Weathered Basalt

The termination depth of bored cast in situ piles poses serious problem to the field engineers particularly on weak weathered rock, stiff clays and dense sands. Some sort of decision making tool is available for driven piles in the form of driving formulae. The first part of paper deals with a simple method based on penetration resistance to the advancement of bore and its relation with end bearing and frictional resistance offered by formation. The second and third parts of paper deal with a newly conceived dynamic method for ascertaining the safe load on pile and its comparison with the safe load value derived from penetration resistance actually observed. The dynamic test proposed is simpler, quicker cost effective and shall be an excellent quality assurance tool for the bored cast-in-situ piles

Deterioration of Bored Cast in Situ Piles Due to Aggressive Water

Most of the data available from the cement industry and the literature exhibits performance of concrete cubes cured in normal water. Even the literature related to the durability of concrete deals mostly with concrete cured in normal water (closer to potable water in characteristics). However, the bored-cast-in-situ piles are cured in the ground water. The development of strength of concrete of bored cast-in-situ piles depends upon the quality of ground water. The effect of sulphates and chloride is well established and most of the codes stipulate permissible limits of pH, sulphates and chlorides contents in the ground water. In the last 20 years, authors have come across a number of situations where inspite of water being certified as satisfactory, from chlorides-sulphate point of view the pile shafts have shown deterioration beyond the conceivable limits. The authors have been working on the problem to establish the effect of quality of water with reference to Ryzner index and Marble test; a parameter that plays a significant role in deciding the quality of water and Marble test as proposed by DIN. The research work involves curing of cubes of same mix in a chemically analyzed ground water as well as normal water. The properties of the concrete like cube strength, elasticity, permeability and setting time are compared. Three types of cement in three grades of concrete are used. The cubes are tested for cube strength for 1, 7, 14, 28, 45 and 90. The findings of the research programme shall be presented into the pape

Evaluation of an anthropometric head surrogate exposed to chisel-nosed fragment simulating projectile impact

Fragment-induced penetrating injuries pose a significant threat in modern combat. Explosions from explosive devices generate metallic fragments that can lethally penetrate various body regions, with the head being particularly most vulnerable to fatality in terms of penetration. Hence, understanding the head’s response to fragment impact is crucial. To this end, this study investigated the ballistic response of an anatomically accurate anthropometric head surrogate to fragment impact. The head surrogate comprised simulants for the three major layers of the head (skin, skull, and brain). Using a pneumatic gas gun, we impacted chisel-nosed fragment simulating projectiles (FSPs) of 1.10-g and 2.79-g on the head surrogate. We analyzed the ballistic response of the head surrogate in terms of ballistic limit velocities (V50), energy densities (E50/A), and failure mechanisms in each layer. The results indicated sensitivity to the FSP size. The 1.10-g FSP had a ∼41% higher V50 and a ∼63% higher E50/A compared to the 2.79-g FSP. Additionally, each head surrogate layer exhibited distinct failure mechanisms. The skin simulant failed due to a combination of shearing and elastic hole enlargement, forming a cavity smaller than the size of the FSP. The skull simulant fractured, creating a cavity at the entry point matching the FSP size. The brain simulant failure involved shearing of the cavity and penetration of fractured skull fragments. We also observed no significant difference in response when introducing a flexible neck attachment on which the head surrogate was mounted. Furthermore, comparisons of an anthropometric (close-shape) head surrogate with a simplified open-shaped head surrogate revealed the minimal influence of the head curvature on the response due to the localized nature of fragment penetration. These findings provide a comprehensive understanding of the head surrogate’s mechanical response to fragment impact. The insights from this work hold significant value in the assessment of penetrating head injury, especially against small fragments. The results can be applied in modern warhead design and forensic investigations

Investigation of dynamic responses of skin simulant against fragment impact through experiments and concurrent computational modeling

Perforation of the skin by fragment impact is a key determinant of the severity of an injury and incapacitation during modern asymmetric warfare. Computational models validated against experimental data are thus desired for simulating the responses of a skin simulant against fragment impact. Toward this end, experiments and concurrent computational modeling were used to investigate the dynamic responses of the skin simulant against fragment impact. Fragment simulating projectiles (FSPs) of masses 1.10 g and 2.79 g were considered herein, and the responses of the skin simulant were investigated in terms of the threshold velocity, energy density, peak displacement, and failure mechanisms. The results illustrate numerous salient aspects. The skin simulant failure involved cavity shearing followed by elastic hole enlargement, and these results were sensitive to the strain rate. The best agreement between the simulated and experimental results was achieved when the input stress–strain curves to the simulation were based on the full spectrum of strain rates. When a single stress–strain curve corresponding to a specific strain rate was used as the input, the threshold velocity and peak displacement of the skin simulant were either underpredicted or overpredicted depending on the strain rate considered. The threshold velocity was also sensitive to the input failure strain; here, the best agreement was obtained when the failure strain was based on the theoretical limiting strain. When the FSP materials were changed to plastics, the threshold velocities increased by up to 33%; however, the energy densities and generated stresses exceeded the contusion and laceration thresholds of the skin

Dynamic Response of Brain Subjected to Blast Loadings: Influence of Frequency Ranges

Blast wave induced a frequency spectrum and large deformation of the brain tissue. In this study, new material parameters for the brain material are determined from the experimental data pertaining to these large strain amplitudes and wide frequencies ranging (from 0.01 Hz to 10 MHz) using genetic algorithms. Both hyperelastic and viscoelastic behavior of the brain are implemented into 2D finite element models and the dynamic responses of brain are evaluated. The head, composed of triple layers of the skull, including two cortical layers and a middle dipole sponge-like layer, the dura, cerebrospinal fluid (CSF), the pia mater and the brain, is utilized to assess the effects of material model. The results elucidated that frequency ranges of the material play an important role in the dynamic response of the brain under blast loading conditions. An appropriate material model of the brain is essential to predict the blast-induced brain injury

Dynamic Response of Brain Subjected to Blast Loadings: Influence of Frequency Ranges

Blast wave induced a frequency spectrum and large deformation of the brain tissue. In this study, new material parameters for the brain material are determined from the experimental data pertaining to these large strain amplitudes and wide frequencies ranging (from 0.01 Hz to 10 MHz) using genetic algorithms. Both hyperelastic and viscoelastic behavior of the brain are implemented into 2D finite element models and the dynamic responses of brain are evaluated. The head, composed of triple layers of the skull, including two cortical layers and a middle dipole sponge-like layer, the dura, cerebrospinal fluid (CSF), the pia mater and the brain, is utilized to assess the effects of material model. The results elucidated that frequency ranges of the material play an important role in the dynamic response of the brain under blast loading conditions. An appropriate material model of the brain is essential to predict the blast-induced brain injury

Food insecurity and its determinants among adults in North and South India.

This is the final version. Available from BMC via the DOI in this record. Availability of data and materials: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.BACKGROUND: Food insecurity is a major public health problem worldwide. In India, there are limited food insecurity assessment studies using a conventionally accepted method like the Food Insecurity Experience Scale (FIES), developed by the Food and Agricultural Organization (FAO). This study aims to measure food insecurity using the FIES and explore its determinants and association with body mass index (BMI) among Indian adults.  METHODS: In a cross-sectional study, we used FIES to measure food security in a sample of 9005 adults residing in North and South India. Using questionnaires, socio-demographic factors, dietary intake and food security data were collected. The dietary diversity scores (FAO-IDDS) and food insecurity scores (FAO-FIES) were calculated. Body size was measured and BMI was calculated.  RESULTS: The mean age of the study participants was 52.4 years (± 11.7); half were women and half resided in rural areas. Around 10% of the participants reported having experienced (mild or moderate or severe) food insecurity between October 2018 and February 2019. Dietary diversity (measured by FAO's Individual Dietary Diversity Scores, IDDS) was low and half of the participants consumed ≤ 3 food groups/day. The mean BMI was 24.7 kg/m2. In the multivariate analysis, a lower IDDS and BMI were associated with a higher FIES. The place of residence, gender and wealth index were important determinants of FIES, with those residing in South India, women and those belonging to the poorest wealth index reporting higher food insecurity. CONCLUSION: Food security is understudied in India. Our study adds important evidence to the literature. Despite having marginal food insecurity, high prevalence of low diet quality, especially among women, is disconcerting. Similar studies at the national level are warranted to determine the food insecurity situation comprehensively in India and plan appropriate policy actions to address it effectively, to attain the key Sustainable Development Goals (SDG).Wellcome TrustEli Lille