Experimental Observation of the Slow Squirting Mode in Solid/Fluid/Solid Trilayers

The problem of guided waves in solid/fluid/solid trilayers has been investigated in great detail both theoretically and experimentally. Lloyd and Redwood were the first to investigate guided wave propagation in a layered plate composed of two solids with perfect contact, slip, or a fluid layer at their interface [1]. Rokhlin et al. studied the elastic interface wave guided by a thin film between two solids and utilized it in predicting the strength of adhesive bonds [2,3]. Couchman et al. [4] and Guyott and Cawley [5] reported on the phenomenon of resonance splitting in the vicinity of classical Lamb modes in symmetrical trilayers. Laperre and Thys investigated elastic wave dispersion in both symmetric and asymmetric trilayers composed of two solid plates separated by a fluid layer [6]. A number of papers have appeared on the use of trilayers as antireflection coating [7–9]

Feasibility of Fatigue Crack Detection in Fluid-Filled Cylindrical Holes Using Circumferential Creeping Waves

Recently, the development of a novel ultrasonic inspection technique that detects radial fatigue cracks on the far side of so-called “weep” holes in thin airframe stiffeners was reported [1]. These cracks tend to be located on the upper part of the weep hole (at 12 o’clock position) therefore are not readily detectable by conventional ultrasonic inspection techniques from the lower skin of the wing. The new technique utilizes circumferential creeping waves propagating around the inner surface of the hole to perform the inspection. However, the wet wing has to be emptied and dried out before inspection because even a small amount of fluid fuel trapped in these rather small (approximately 6–7 mm in diameter) holes would strongly affect the propagation of circumferential creeping waves. We have searched the literature for published results on circumferential creeping wave propagation around fluid-filled cylindrical cavities in elastic media. Surprisingly, although the analytical solution of this canonical problem can be readily constructed from existing building blocks, very little was found in terms of numerical results that could be used to gain better understanding of the phenomenon. This motivated us to attack the problem by numerically solving the dispersion equation and constructing the corresponding dispersion and attenuation curves for a specific case of interest, namely, for that of a water-filled cylindrical hole in aluminum

Hall Coefficient Measurement for Residual Stress Assessment in Precipitation Hardened IN718 Nickel-base Superalloy

We investigated the feasibility of residual stress assessment based on Hall coefficient measurements in precipitation hardened IN718 nickel-base superalloy. As a first step, we studied the influence of microstructural variations on the magnetogalvanic properties of IN718 nickel-base superalloy. We found that the Hall coefficient of IN718 increases from ≈8.1×10-11 m3 /C in its fully annealed state of 15 HRC Rockwell hardness to ≈9.8×10-11 m3 /C in its fully hardened state of 45 HRC. Second, we studied the influence of cold work, i.e., plastic deformation at room temperature, and found that cold work had negligible effect on the Hall coefficient of fully annealed IN718, but significantly reduced it in the hardened state of the material. For example, measurements conducted on fully hardened IN718 specimens showed that the Hall coefficient decreased more or less linearly with cold work from its peak value of ≈9.8×10-11 m3 /C in its intact state to ≈9.3×10-11 m3 /C in its most deformed state of 22% plastic strain. Third, we studied the influence of applied stress, and found that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain was measured as a unitless gauge factor F that is defined as the ratio of the relative change of the Hall coefficient ΔRH/RH divided by the axial strain ε = σ/E, where σ is the applied uniaxial stress and E is the Young’s modulus of the material, i.e., ΔRH = RH (1 + F ε). We determined that the galvanomagnetic gauge factor of IN718 is F ≈ 2.5-3 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements will not happen in this case

Validation of a method to elute viruses from different types of face masks

Due to the SARS-CoV-2 pandemic, it is crucial to study the efficiency of face masks in retaining viruses for the upcoming years. The first objective of this study was to validate a method to elute viruses from polyester and cotton face masks. We observed that deionized water followed by 3% beef glycine (pH 9.5 or pH 7.2) was significantly more efficient (p < 0.05) in eluting the bacteriophage phiX174 virus from polyester (4.73% ± 0.25% to 28.67% ± 1.89%), polyester/cotton (3% ± 0.33%), and cotton (1.7% ± 0.21%) face masks than 3% beef glycine only (pH 9.5 or pH 7.2) as a single eluent (3.4% ± 0.16% to 21.33% ± 0.94% for polyester, 1.91% ± 0.08% for polyester/cotton, and 1.47% ± 0.12% for cotton face masks). Also, deionized water was significantly less efficient as a single eluent for eluting bacteriophage phiX174 from all the studied face mask types. The polyethylene glycol (PEG) precipitation method was substantially more efficient (p < 0.05) as a second step concentration method for the viruses in the eluates than the organic flocculation (OF) method. Higher viral loads were eluted from polyester face masks than cotton ones. We also found varying viral loads in the eluate solutions from different commercial polyester face masks, with the highest percentage seen for the N95 face mask. The second objective was to apply the validated method to study the effect of autoclaving on the different face mask materials. Results of the study did not show any significant differences in the viral loads eluted from the studied face masks before and after one and five autoclaving cycles. Moreover, a scanning electron microscope (SEM) analysis revealed no changes in the yarns, elongation, tensile strength, and contact angle measurements of the polyester or cotton materials after one or five autoclaving cycles

Status of FAA Studies in Thermal Acoustics

As with many aerospace applications, commercial jet engine components are operated in demanding environments, often at extreme temperature and stress conditions. The predominant used surface inspection method used on these components is fluorescent penetrant inspection. Research has been ongoing for a number of years on a new technology using a short burst of low frequency ( ∼ 20 KHz) ultrasound to “heat up” cracks and make them visible in the infrared range. The basic premise of the Thermal Acoustic method is to use an energy source with recent efforts using an ultrasonic horn originally intended for use in ultrasonic welding to excite the component. The energy source causes an increase in local heating, which is detectable with infrared cameras typically used in Thermographic inspection. While considerable research is underway, additional information on the sensitivity and applicability of this technique to engine components and alloys is needed prior to widespread use in the aviation industry. The purpose of this program is to provide additional data to determine applicability of this method to engine components

Primary School Teachers’ Perspectives on ADHD in Alkadrow, Khartoum, Sudan

Background: Attention deficit hyperactivity disorder, which is a prevalent neurodevelopmental condition, commonly manifests during early childhood and has the potential to adversely affect an individual’s social, academic, and occupational performance in multiple settings. Students with ADHD may struggle with attention, focus, listening, and completing schoolwork. Additionally, they may exhibit restless or disruptive behavior in class and may have learning disabilities that affect their academic performance. The aim of this study was to explore the perspectives of primary school teachers on ADHD in Alkadrow, Khartoum, Sudan. Methods: A descriptive cross-sectional study was conducted in Alkadrow-Bahri locality, Sudan, over a period of three to six months in 2022. The study population included primary school teachers who had taught for at least one year and encountered at least one student with ADHD. A convenience sampling technique was used to select a minimum of 59 participants, and data were collected using a self-administered questionnaire with closed-ended questions. SPSS version 23 was used to analyze the data, including descriptive statistics and inferential statistics such as chi-square tests and logistic regression analysis. Results: The study had 59 participants, with the majority being female and in the age group of 41–45 years. The participants were mostly married and had obtained psychology courses, with a bachelor’s degree being the most common level of education. Many participants had over 20 years of teaching experience. Regarding the attitude toward attention deficit hyperactivity, most participants strongly agreed that they did have a negative/positive attitude toward it, and a majority agreed or were neutral toward ADHD. However, in the case of attention deficit hyperactivity, a significant percentage of participants disagreed or strongly disagreed with the statement. Conclusion: The study found that most participants had a negative attitude toward student referrals for medical care and believed that most symptoms of ADHD can be lowered by aging. Additionally, more than half strongly disagreed that punishment has a positive effect on ADHD

Prevalence of smoking cigarettes and beliefs regarding smoking habits among medical students: a cross-sectional study in Sudan

BackgroundSmoking is a common problem in university students worldwide. Smoking is one of the most dangerous social phenomena and has a significant impact on public health. This study investigated the beliefs and attitudes of medical students toward smoking in Sudan.MethodsA cross-sectional study was conducted among medical students at Al Neelain University, Sudan, from March to June 2022 using a web-based questionnaire. The questionnaire consisted of eight items on demographic characteristics and 13 on the beliefs and attitudes toward smoking. Other data included smoking status, smoking habits, the number of cigarettes smoked per day, and smoking duration. Data analysis was performed descriptively, and chi-square test and logistic regression were conducted using SPSS version 24. Statistical significance was set at 0.05.ResultsA total of 336 students participated in this study, and the smoking prevalence was 48.8% (41.1% in men and 7.7% in women). In total, 76.8% reported smoking daily at a rate of 5–10 cigarettes per day. In terms of students’ beliefs about smoking, 86.8% disagreed with selling cigarettes at the university. Of the respondents, 68.4% did not approve smoking on campus. There was a relationship between smoking habits and the age group of 22–25 years, which was the highest smoking category among students (p-value = 0.01).ConclusionThe prevalence of cigarette smoking among medical students is disturbing, particularly as they are future doctors. There is a need to include plans to reduce smoking among students that can be incorporated into courses and special programs

Feasibility of Fatigue Crack Detection in Fluid-Filled Cylindrical Holes Using Circumferential Creeping Waves

Recently, the development of a novel ultrasonic inspection technique that detects radial fatigue cracks on the far side of so-called “weep” holes in thin airframe stiffeners was reported [1]. These cracks tend to be located on the upper part of the weep hole (at 12 o’clock position) therefore are not readily detectable by conventional ultrasonic inspection techniques from the lower skin of the wing. The new technique utilizes circumferential creeping waves propagating around the inner surface of the hole to perform the inspection. However, the wet wing has to be emptied and dried out before inspection because even a small amount of fluid fuel trapped in these rather small (approximately 6–7 mm in diameter) holes would strongly affect the propagation of circumferential creeping waves. We have searched the literature for published results on circumferential creeping wave propagation around fluid-filled cylindrical cavities in elastic media. Surprisingly, although the analytical solution of this canonical problem can be readily constructed from existing building blocks, very little was found in terms of numerical results that could be used to gain better understanding of the phenomenon. This motivated us to attack the problem by numerically solving the dispersion equation and constructing the corresponding dispersion and attenuation curves for a specific case of interest, namely, for that of a water-filled cylindrical hole in aluminum.</p

Experimental Observation of the Slow Squirting Mode in Solid/Fluid/Solid Trilayers

The problem of guided waves in solid/fluid/solid trilayers has been investigated in great detail both theoretically and experimentally. Lloyd and Redwood were the first to investigate guided wave propagation in a layered plate composed of two solids with perfect contact, slip, or a fluid layer at their interface [1]. Rokhlin et al. studied the elastic interface wave guided by a thin film between two solids and utilized it in predicting the strength of adhesive bonds [2,3]. Couchman et al. [4] and Guyott and Cawley [5] reported on the phenomenon of resonance splitting in the vicinity of classical Lamb modes in symmetrical trilayers. Laperre and Thys investigated elastic wave dispersion in both symmetric and asymmetric trilayers composed of two solid plates separated by a fluid layer [6]. A number of papers have appeared on the use of trilayers as antireflection coating [7–9].</p

Senolytics in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes. DR is characterized by damage to retinal vasculature resulting in vision impairment and, if untreated, could eventually lead to blindness. The pathogenic mechanism of DR is complex; emerging studies suggest that premature senescence of retinal cells and subsequent secretion of inflammatory cytokines exacerbate DR disease state by stimulating paracrine senescence, pathological angiogenesis, and reparative vascular regeneration. Senolytics are a new class of drugs that can selectively clear out senescent cells from the retina, thus holding a significant promise in DR treatment and prevention. In this review, we discuss the critical role of cellular senescence in DR’s pathogenesis; A literature review was conducted in September of 2021 to explore the therapeutic potential of senolytics in the treatment of DR. Studies that were relevant to the research topic were selected through multiple keyword searches in the search engine, PubMed and thoroughly reviewed using abstracts and full-text articles. We present evidence from animal models for studying cellular senescence in DR and discuss multiple pathogenic mechanisms in cellular senescence and its involvement in DR. We also discuss the current state of pharmaceutical development at preclinical and clinical stages focusing on the senolytic drugs navitoclax, 17-DMAG, piperlongumine, UBX-1325, dasatinib quercetin, and fisetin. In particular, UBX-1325 holds a promising prospect for DR treatment based on the positive outcome of early clinical studies in individuals with diabetic macular edema (DME) and wet age-related macular degeneration