Variations in the Thermomechanical and Structural Properties during the Cooling of Shape-Memory R-PETG.

One of the useful features of 3D-printed specimens of recycled polyethylene terephthalate glycol (R-PETG) is the ability to repetitively develop free recovery as well as the work-generating, shape-memory effect. This behavior is enabled by the R-PETG's capacity to stiffen during cooling, thus allowing for a new temporary shape to be induced. Aiming to devise an explanation for the polymer's stiffening, in this study, the variation in some of the R-PETG's parameters during cooling are emphasized and discussed. The evolution of an R-PETG filament's shape was monitored during room-temperature-bending heating-cooling cycles. Straight-shape recovery and the complete loss of stiffness were observed at the start and the end of heating, respectively, followed by the forced straightening of the filament, performed by the operator, around 40 °C, during cooling. The tests performed by dynamic mechanical analysis disclosed the rise of the storage modulus (E') after 100 °C heating followed by either liquid-nitrogen- or air-cooling to room temperature, in such a way that E' was always larger after cooling than initially. Static tests emphasized a peculiar stress variation during a heating-cooling cycle applied in air, within the heating chamber of the tensile testing machine. Tensile-failure tests were performed at -10 °C at a rate of 100 mm/min, with specimens printed at various deposition directions between 10 and 40° to the transversal direction. The specimens printed at 40°, which had the largest ultimate strains, were broken with tensile rates between 100 and 500 mm/min. Deformation rate increase favored the shift from crazing to delamination failure modes. The correlation between the structural changes, the sharp E' increase on heating, and the stiffening induced by cooling represents a novel approach that enables the use of 3D-printed R-PETG for the fabrication of the active parts of low-priced lightweight resettable actuators.

Exploring the Association between COVID-19 and Femoral Head Necrosis: A Comprehensive Review.

This study investigates the correlation between COVID-19 and avascular necrosis of the femoral head, considering the potential contribution of medication-induced effects. This research spans the period from August 2022 to January 2024 and includes 32 patients diagnosed with avascular necrosis. While steroid usage, particularly in high doses, is known to predispose individuals to this condition, this study aims to discern if COVID-19 itself plays a role beyond the influence of medication. Notably, COVID-19 is associated with disturbances in the coagulation system, potentially leading to thromboembolic complications. Of the patients, six did not have COVID-19, while seven had the virus but did not receive steroid treatment. However, 19 patients with COVID-19 exhibited severe pulmonary involvement and were administered both high-dose steroids and antiviral medication. Among the observed patients, 14 were female and 18 were male. Notably, three patients presented bilateral necrosis, all of whom had COVID-19 and significant pulmonary involvement. Diagnostic assessments included frontal and profile X-rays, as well as MRI scans for all patients.

On the Thermomechanical Behavior of 3D-Printed Specimens of Shape Memory R-PETG.

From commercial pellets of recycled polyethylene terephthalate glycol (R-PETG), 1.75 mm diameter filaments for 3D printing were produced. By varying the filament's deposition direction between 10° and 40° to the transversal axis, parallelepiped specimens were fabricated by additive manufacturing. When bent at room temperature (RT), both the filaments and the 3D-printed specimens recovered their shape during heating, either without any constraint or while lifting a load over a certain distance. In this way, free-recovery and work-generating shape memory effects (SMEs) were developed. The former could be repeated without any visible fatigue marks for as much as 20 heating (to 90 °C)-RT cooling-bending cycles, while the latter enabled the lifting of loads over 50 times heavier than the active specimens. Tensile static failure tests revealed the superiority of the specimens printed at larger angles over those printed at 10°, since the specimens printed at 40° had tensile failure stresses and strains over 35 MPa and 8.5%, respectively. Scanning electron microscopy (SEM) fractographs displayed the structure of the successively deposited layers and a shredding tendency enhanced by the increase in the deposition angle. Differential scanning calorimetry (DSC) analysis enabled the identification of the glass transition between 67.5 and 77.3 °C, which might explain the occurrence of SMEs in both the filament and 3D-printed specimens. Dynamic mechanical analysis (DMA) emphasized a local increase in storage modulus of 0.87-1.66 GPa that occurred during heating, which might explain the development of work-generating SME in both filament and 3D-printed specimens. These properties recommend 3D-printed parts made of R-PETG as active elements in low-price lightweight actuators operating between RT and 63 °C.

Heat Treatment and Dynamic Mechanical Analysis Strain Sweep Effects on the Phase Structure and Morphology of an Fe-28Mn-6Si-5Cr Shape Memory Alloy.

Fe-Mn-Si-based shape memory alloys (SMAs) have been extensively investigated since 1982 for various useful properties that enhance the development of different applications such as anti-seismic dampers for very tall buildings, pipe joints, or rail fasteners. In particular, the Fe-28Mn-6Si-5Cr (mass. %) alloy has been mainly used in vibration mitigation or self-adjustable axial displacement applications. Dynamic mechanical analysis (DMA), performed by strain sweeps (SS), enables the monitoring of the evolution of storage modulus and internal friction variations with increasing strain amplitudes at different constant frequencies and temperatures. Thus, applying dynamic bending with various frequencies and amplitudes that actually represents an isothermal mechanical treatment. In the present paper, an Fe-28Mn-6 Si-5Cr (mass. %) SMA was cast by ingot metallurgy, hot-rolled, and water quenched in order to obtain thermally induced martensite and avoid the occurrence of cooling cracks. The influence of the holding time, between 2 and 10 h, at 1050 °C and the effects of DMA-SS performed at three different frequencies were analyzed by a differential scanning calorimetry, an X-ray diffraction, and a scanning electron and atomic force microscopy. The effects of the holding time and mechanical treatment on the structure and morphology of martensite plates were corroborated with the results of the thermal analysis.

Structural-Functional Changes in a Ti50Ni45Cu5 Alloy Caused by Training Procedures Based on Free-Recovery and Work-Generating Shape Memory Effect.

Active elements made of Ti50Ni45Cu5 shape memory alloy (SMA) were martensitic at room temperature (RT) after hot rolling with instant water quenching. These pristine specimens were subjected to two thermomechanical training procedures consisting of (i) free recovery shape memory effect (FR-SME) and (ii) work generating shape memory effect (WG-SME) under constant stress as well as dynamic bending and RT static tensile testing (TENS). The structural-functional changes, caused by the two training procedures as well as TENS were investigated by various experimental techniques, including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and atomic force microscopy (AFM). Fragments cut from the active regions of trained specimens or from the elongated gauges of TENS specimens were analyzed by DSC, XRD, and AFM. The DSC thermograms revealed the shift in critical transformation temperatures and a diminution in specific absorbed enthalpy as an effect of training cycles. The DMA thermograms of pristine specimens emphasized a change of storage modulus variation during heating after the application of isothermal dynamical bending at RT. The XRD patterns and AMF micrographs disclosed the different evolution of martensite plate variants as an effect of FR-SME cycling and of being elongated upon convex surfaces or compressed upon concave surfaces of bent specimens. For illustrative reasons, the evolution of unit cell parameters of B19' martensite, as a function of the number of cycles of FR-SME training, upon concave regions was discussed. AFM micrographs emphasized wider and shallower martensite plates on the convex region as compared to the concave one. With increasing the number of FR-SME training cycles, plates' heights decreased by 84-87%. The results suggest that FR-SME training caused marked decreases in martensite plate dimensions, which engendered a decrease in specific absorbed enthalpy during martensite reversion.

Dual Sensory Impairment: The Correlation between Age Related Macular Degeneration and Sensorineural Hearing Loss.

The pathogeneses of age-related macular degeneration (AMD) and age-related hearing impairment are not yet fully understood. If AMD and age-related hearing impairment are correlated, the cause of both may be a result of a common vulnerability. The aim of this study was to assess the interrelation between age-related macular degeneration and age-related hearing loss. MATERIAL AND METHODS: In our case-control analysis, the hearing conditions of 40 subjects with AMD were compared with 40 age-matched healthy controls. In all patients, retinal changes were certified by clinical examinations, optical coherence tomography (OCT), and fluorescein angiography (FA). All subjects were inspected with pure tone audiometry (PTA), impedance audiometry, and speech audiometry. RESULTS: A significant correlation (p < 0.001) was identified between age-related macular degeneration and age-related hearing impairment. The predominant hearing impairment in this case was sensorineural (SNHL). Of the patients diagnosed with AMD, SNHL was found in 88.89% of those with exudative macular degeneration and in 67.74% of those with atrophic macular degeneration. In contrast, we found that a significant proportion of the control group had normal hearing. CONCLUSION: One possible explanation for the association between retinal and cochlear impairment may be due to a melanin disorder.

E, K, B5, B6, and B9 vitamins and their specific immunological effects evaluated by flow cytometry.

It has been proven that vitamins play an essential role in preventing certain diseases since ancient times. It is thus fruitless to approach the roles of vitamins without making reference to the techniques used in evaluating the effects of these micronutrients. Therefore, the aim of this paper was to summarize the immunological effects of E, K, B5, B6, and B9 vitamins evaluated by flow cytometry. Some of these significant effects were presented and discussed: (a) The role of vitamins E in the prevention and treatment of different types of cancer. (b) The properties of K vitamins in the development and maintenance of pheochromocytoma Cell Line 12 (PC12) cells in Parkinson's disease; (c) The improvement effect of vitamin B5 on the loss of bone mass in low estrogen conditions; (d) The anticancer role of vitamins B6. (e) The role of Vitamin B9 in the regulation of Treg cells. As such, the flow cytometry technique used to assess these properties is essential to evaluate the immunomodulatory effects of certain vitamins. The technique undergoes constant improvement which makes it possible to determine several parameters with a role in the modulation of the immune function and at the same time increase the accuracy of the methods that highlight them.

Effects of cigarette smoking on sensorineural hearing impairment and age related macular degeneration.

INTRODUCTION: Cigarette smoking has been causally associated with various diseases, and among the numerous harmful effects of smoking is included its impact on the senses of vision and hearing. The purpose of this study is to evaluate the impact of cigarette smoking on the visual and auditory functions. METHODS: In this analytic study, hearing and smoking status of 40 patients with agerelated macular degeneration (AMD) were analyzed with 40 age-matched control subjects without AMD. In all subjects (n=80), retinal status was investigated by optical coherence tomography (OCT), with analyses of thickness central subfield (TCS) and thickness average cube (TAC) of the macula. All participants were examined with pure tone audiometry. Audiometric trials comprised pure tone bone and air conduction. The smoking history of all the subjects was recorded in detail. RESULTS: A significant correlation was found between smoking status and visual (p<0.001) and hearing impairment (p<0.05). Cigarette smoking was found to be highly correlated with sensorineural hearing impairment and exudative macular degeneration. CONCLUSIONS: Cigarette smoking damage anti-oxidative systems and tissue metabolism. We have underlined a clear correlation between the risk of sensorineural hearing impairment, exudative macular degeneration and cigarette smoking. Our findings may result in future screening of smokers to identify any hearing and vision impairment and for improving smoking cessation interventions.

Leukemic retinopathy, the first expression in a case of chronic myelomonocytic leukemia - a case report.

A 68-year-old male addressed to our clinic complaining of gradual loss of visual acuity and perceptual distortions. He had a history of extrathoracic hematoma and essential hypertension. The clinical assessment revealed bilateral retinal hemorrhages and white-green foveal and extrafoveal areas. The complete blood count (CBC) suggested a hematologic disorder.

Photoprotection role of melanin in the human retinal pigment epithelium. Imaging techniques for retinal melanin.

The human eye is made up of multiple layers of pigmented tissues that have in componence melanin. In the eye, one can separate melanosomes from various embryonic origins. The pigment-producing cells in the stroma of the iris, ciliary body and the choroid (uveal melanocytes) are neural crest derivatives. On the other hand, ciliary, iris and retinal pigment epithelial cells are developed from the neural ectoderm. One universally accepted role of melanin is to react as neutral-density filter in scattering light. Melanin acts as a free radical stabilizer and has the ability to absorb near-infrared, visible light and UV radiation. This paper reviews the current knowledge on ocular melanin, including ocular melanogenesis, roles of melanin in retinal metabolic processes and some imaging techniques that identify melanin in the retina.

[Multidrug resistant tuberculosis in Romania in the last years (2004-2007)--an extremely important social phenomenon]. / Tuberculoza multidrog rezistenta în România în ultimii ani (2004-2007)--un fenomen social de maxima importanta.

The emergence of resistance to drugs used to treat tuberculosis (TB), and particularly multidrug resistant (MDR-TB) strains, has become a significant public health problem in a number of countries and an obstacle to effective global TB control. In many other countries, the extent of drug resistance is unknown and the management of the patients with MDR-TB is inadequate. In countries where drug resistance has been identified, specific measures need to be taken within TB control programmes to address the problem through appropriate management of patients and adoption of strategies to prevent the propagation and dissemination of drug resistant TB, including MDR-TB. In Romania there are two centers for the management of MDR-TB cases: one in Bucharest at The National Pneumology Institute "Marius Nasta" and the other at Bisericani (Neamt district). The comparative analysis of MDR-TB cases and under treatment evolution was done, in the two excellence centers Bucharest and Bisericani from 2004 to 2007. This is a retrospective study of MDR-TB patients enrolled in Romania between 2004-2007. All patients evaluated were managed under The National Tuberculosis Programme approved protocols and had the opportunity to receive more than 24 months of treatment. In addition, follow-up data on successfully treated patients were collected at the beginning of 2007. This study is based on an MDR register, and a software collecting information on MDR-TB cases. In order to be accepted in one of the two MDR centers, patients need to fulfill certain criteria to improve the treatment results. A total number of 305 MDR-TB patients were registered at the beginning of 2007 in Bucharest MDR center; this study used a number of 170 MDR-TB patients from Bucharest who fulfilled the study's criteria in oppose to the 294 MDR-TB patients from Bisericani. 184 patients from the first cohort of DOTS-Plus project were evaluated until the end of the study: 55 were completed treatment and 54 cured, which means 59,23% succes rate. The conversion rate of culture at 4 months (for the first cohort) in MDR excellence centers was: Bucharest--72,5% and Bisericani--64%.

Feynman diagrams and Wick products associated with q-Fock space.

It is shown that if one keeps track of crossings, Feynman diagrams can be used to compute the q-Wick products and usual operator products in terms of each other.