Preface to the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 2)'.

As an emerging research field, physics-informed machine learning and its structural integrity applications may bring new opportunities to the intelligent solution of engineering problems. Pure data-driven approaches have some limitations when solving engineering problems due to lack of interpretability and data hungry applications. Therefore, further unlocking the potential of machine learning will be an important research direction in the future.

Preface to the theme issue 'physics-informed machine learning and its structural integrity applications'.

The issue focuses on physics-informed machine learning and its applications for structural integrity and safety assessment of engineering systems/facilities. Data science and data mining are fields in fast development with a high potential in several engineering research communities; in particular, advances in machine learning (ML) are undoubtedly enabling significant breakthroughs. However, purely ML models do not necessarily carry physical meaning, nor do they generalize well to scenarios on which they have not been trained on.

Fatigue crack growth in epoxy polymer nanocomposites.

The present paper describes detailed analyses of experimental data for the cyclic-fatigue behaviour of epoxy nanocomposite polymers. It has been shown that the data may be interpreted using the Hartman-Schijve relationship to yield a unique, 'master', linear relationship for each epoxy nanocomposite polymer. By fitting the experimental data to the Hartman-Schijve relationship, two key materials parameters may be deduced: (i) the term , which may be thought of as the fatigue equivalent to the quasi-static value of the fracture energy, , and (ii) the fatigue threshold value, [Formula: see text], below which no significant fatigue crack growth (FCG) occurs.

Modelling the Variability and the Anisotropic Behaviour of Crack Growth in SLM Ti-6Al-4V.

The United States Air Force (USAF) Guidelines for the Durability and Damage Tolerance (DADT) certification of Additive Manufactured (AM) parts states that the most difficult challenge for the certification of an AM part is to establish an accurate prediction of its DADT. How to address this challenge is the focus of the present paper. To this end this paper examines the variability in crack growth in tests on additively manufactured (AM) Ti-6Al-4V specimens built using selective layer melting (SLM).

High-resolution optical microscopy for characterising microstructural deformation in microtensile testing.

Imaging surface deformation of a coupon specimen in microtensile testing with an optical microscope presents challenges due to the narrow depth of field (DoF) of optical microscopes. Materials being heterogeneous at microscopic length scale, the sample surface deforms into a complex 3D surface texture, evolving continuously as the loading increases. Because of the narrow DoF, the region that is in focus within the field of view (FoV) decreases substantially in size with the increasing out-of-plane heterogeneous deformation.

Further Studies into Crack Growth in Additively Manufactured Materials.

Understanding and characterizing crack growth is central to meeting the damage tolerance and durability requirements delineated in USAF Structures Bulletin EZ-SB-19-01 for the utilization of additive manufacturing (AM) in the sustainment of aging aircraft. In this context, the present paper discusses the effect of different AM processes, different build directions, and the variability in the crack growth rates related to AM Ti-6Al-4V, AM Inconel 625, and AM 17-4 PH stainless steel. This study reveals that crack growth in these three AM materials can be captured using the Hartman-Schijve crack growth equation and that the variability in the various versus curves can be modeled by allowing the terms Δ and to vary.

Requirements and Variability Affecting the Durability of Bonded Joints.

This paper firstly reveals that when assessing if a bonded joint meets the certification requirements inherent in MIL-STD-1530D and the US Joint Services Standard JSSG2006 it is necessary to ensure that: (a) There is no yielding at all in the adhesive layer at 115% of design limit load (DLL), and (b) that the joint must be able to withstand design ultimate load (DUL). Secondly, it is revealed that fatigue crack growth in both nano-reinforced epoxies, and structural adhesives can be captured using the Hartman-Schijve crack growth equation, and that the scatter in crack growth in adhesives can be modelled by allowing for variability in the fatigue threshold. Thirdly, a methodology was established for estimating a valid upper-bound curve, for cohesive failure in the adhesive, which encompasses all the experimental data and provides a conservative fatigue crack growth curve.

Effect of human head morphological variability on the mechanical response of blast overpressure loading.

A methodology is introduced to investigate the effect of intersubject head morphological variability on the mechanical response of the brain when subjected to blast overpressure loading. Nonrigid image registration techniques are leveraged to warp a manually segmented template model to an arbitrary number of subjects following a procedure to coarsely segment the subjects in batch. Finite element meshes are autogenerated, and blast analysis is conducted.

Bright triplet excitons in caesium lead halide perovskites.

Nanostructured semiconductors emit light from electronic states known as excitons. For organic materials, Hund's rules state that the lowest-energy exciton is a poorly emitting triplet state. For inorganic semiconductors, similar rules predict an analogue of this triplet state known as the 'dark exciton'.

Anxiety disorders and obesity.

Anxiety disorders are the most prevalent mental disorders in developed countries. On the other hand, obesity is recognized to be one of the greatest public health problems worldwide.The connection between body weight and mental disorders remains an open issue.

Hospital anxiety and depression scale. A quantitative analysis in medical outpatients, psychiatric outpatients and normal subjects.

Depressive and anxiety symptomatology represent the most common psychiatric manifestations that complicate the management and prognosis of patients with somatic disorders. The Hospital Anxiety and Depression Scale (HADS) is a reliable, valid andpractical screening tool for identifying and quantifying anxiety and/or depression in non-psychiatric out patients. The aim of the present study was to compare the psychometric properties of the HADS among internal medicine outpatients, psychiatric outpatients and the generalpopulation.

[A volumetric study of brain structures in subtypes of depression].

The aim of this study is to compare the volumes of hippocampus, amygdala and subgenual prefrontal cortex among patients with melancholic depression, patients with psychotic depression and normal controls. Thirty nine patients with a diagnosis of major depression (22 with melancholic and 17 with psychotic subtype) and 18 normal controls were included in the study. Hippocampal, amygdala, anterior and posterior subgenual cortex volumes were measured by manual tracings on magnetic resonance volumetric images and compared across the 3 groups.

PM1 and PM2.5 ionic composition and VOCs measurements in two typical apartments in Athens, Greece: investigation of smoking contribution to indoor air concentrations.

During the last decades, the air quality of the city of Athens has been quite aggravated. Scientific interest has been focused on health effects caused by both outdoor and indoor air pollution. The purpose of this study was the presentation of results from air quality measurements in two similar typical Athenian apartments in the same suburban area.

PM2.5 and volatile organic compounds (VOCs) in ambient air: a focus on the effect of meteorology.

PM(2.5) and VOCs (benzene, toluene, m-p-o-xylenes) concentrations were measured in an urban and a suburban site in Athens, Greece, during the period between April and November 2004. This period, which is considered to be the warmer period in Greece, is characterized by the development of sea-breeze over the Attica Basin.

Ions species size distribution in particulate matter associated with VOCs and meteorological conditions over an urban region.

Airborne particulate matter (PM10, PM2.5, PM1) and volatile organic compounds (benzene, toluene, m,p-xylene, o-xylene) samples were collected during winter and summer seasons of 2005 at two sites, representing an urban and a suburban region of the Greater Athens Area. Urban site traffic emissions were the major contributor to the concentration of PM2.

Estimation of selected heavy metals and arsenic in PM10 aerosols in the ambient air of the Greater Athens Area, Greece.

Aerosol samples of PM(10) were collected during summer and winter 2003 at two different sites in the Messogia Basin northeast of Athens, to demonstrate the variations of heavy metals in PM(10) and examine their relationship with both gaseous pollutants and meteorological parameters. Estimated heavy metals during the experimental campaign were mercury (Hg), cadmium (Cd), lead (Pb), nickel (Ni) and arsenic (As). The average heavy metal concentrations for the first site (Spata) constituted 0.

Gas-particle concentration and characterization of sources of PAHs in the atmosphere of a suburban area in Athens, Greece.

Atmospheric polycyclic aromatic hydrocarbons (PAH) were determined in two places in a suburban area of Athens greater area (AGA) during June and November 2003. Fourteen PAHs were quantified in the collected samples. The total concentration in the gas phase ranged between 6.

Temporal variations of PM2.5 in the ambient air of a suburban site in Athens, Greece.

Twenty-three hour measurements of PM(2.5) particulate matter have been carried out during the period between the 1st April and the 13th November 2003 in a suburban area of Athens. The monitoring site was located in the National Research Center "DEMOKRITOS", on the foot of Hemittos Mountain and about 12 km away from the center of Athens.

Effectiveness of combined tamoxifen citrate and testosterone undecanoate treatment in men with idiopathic oligozoospermia.

Objective: To assess the effect of treatment with a combination of the antiestrogen tamoxifen citrate and the androgen testosterone undecanoate on sperm variables and pregnancy incidence in men with idiopathic oligozoospermia and couple subfertility.

Design: Prospective, randomized, placebo-controlled trial.

Setting: Clinical research in a tertiary care academic hospital.

Treatment of recurrent genital herpes with interferon alpha-2alpha.

The purpose of the present study was to evaluate the efficacy and safety of parenteral administration of interferon alpha-2alpha in the treatment of recurrent herpes genitalis. A total of 97 patients (66 males, 31 females, mean age 34.86 +/-16.

Treatment of penile intraepithelial neoplasia (PIN) with interferon alpha-2a, CO2 laser (vaporization) and 5-fluorouracil 5% (5-FU).

This study was undertaken to assess the effectiveness of CO2 laser (vaporization), 5-FU topical application and Interferon (IFN alpha-2a) parenterally in the therapy of penile intraepithelial neoplasia (PIN). From March 1986 to September 1991, 1,372 men, sexual partners of women with condylomata accuminata or flat or cervical intraepithelial neoplasia (CIN), were submitted to peoscopy, of 1,019 men who presented with various lesions caused by human papillomavirus (HPV)-confirmed histologically-208 were treated for PIN. The best treatment modalities irrespective of grade of lesion were found to be the combination of 5-FU plus CO2 laser vaporisation plus IFN alpha-2a (high dose) (96.

Peoscopic diagnosis of flat condyloma and penile intraepithelial neoplasia. Clinical manifestation.

Peoscopy was performed in order to assess penile lesions in the male sexual partners of 326 women with cervical intraepithelial neoplasia (CIN) or flat condyloma (FC). Each patient was submitted to a careful naked-eye inspection, peoscopy and biopsy of any suspicious lesion which was confirmed histologically and immunohistochemically. A brush cytologic examination of the distal portion of the urethra was also performed.

Seminal volume and total sperm number trends in men attending subfertility clinics in the greater Athens area during the period 1977-1993.

The trends for such important parameters of male fertility as seminal volume and total sperm number were assessed in men living permanently in the Greater Athens area over a prolonged period of time. To this end, the records of three andrological laboratories employing the same method for semen evaluation were analysed retrospectively. Out of 23,850 men examined from 1977 to 1993 (17 years) for couple subfertility, a total of 2385 (10%) were selected for evaluation by a randomization procedure.

Treatment of men with flat (FC) or acuminata (CA) condylomata with interferon alpha-2a.

This study was undertaken to assess the effect of CO2 laser vaporization, 5-fluorouracil 5% (5-FU) topical application and Interferon alpha-2a (IFA alpha-2a) in the treatment of C.A. or F.

Comparative study of systemic interferon alfa-2a with oral isotretinoin and oral isotretinoin alone in the treatment of recurrent condylomata accuminata.

Objectives: We attempted to test the hypothesis that the combination of systemic interferon alfa-2a and oral isotretinoin is more effective than isotretinoin alone in the treatment of recurrent condylomata accuminata.

Study Design: Fifty seven women with recurrent condylomata accuminata were randomly assigned in two groups. Group A (n = 24) received isotretinoin alone (Roaccutan, Roche) 1 mg/kgr orally daily for 3 months or until a remission was achieved; Group B (n = 33) received Interferon alfa-2a (Roferon-A, Roche) 3 million units subcutaneously three times for 8 weeks plus isotretinoin 1 mg/Kg orally for 3 months or until a remission was achieved.