Children were less frequently infected with SARS-CoV-2 than adults during 2020 COVID-19 pandemic in Warsaw, Poland.

Clinical data suggest that during the current COVID-19 pandemic, children are less prone than adults to SARS-CoV-2 infection. Our purpose was to determine the frequency of SARS-CoV-2 in children vs. adults during the 2020 pandemic in Warsaw, Poland, and to investigate whether RSV and/or influenza A/B infections were associated with SARS-CoV-2 infections. We present results of RT-PCR tests for SARS-CoV-2 performed in Warsaw, Poland. Some of the pediatric subjects were also PCR-tested for RSV, and A and B influenza. We compared the test results from the four groups of symptomatic and asymptomatic subjects: 459 symptomatic pediatric patients (children 0-18 years old), 1774 symptomatic adults, 445 asymptomatic children, and 239 asymptomatic adults. 3.26% (15/459) of symptomatic pediatric patients were positive for SARS-CoV-2 in contrast to 5.58% (99/1774) of symptomatic adults (p = 0.0448). There were no SARS-CoV-2 positive cases in the group of asymptomatic children (0/445) and two positive cases in the group of asymptomatic adults (2/239), i.e., 0.83%. In the group of symptomatic pediatric patients, 17.14% (6/35) (p = 0.0002) were positive for RSV, 8.16% (4/49) were positive for influenza A, and 2.04% (1/49), thus 10.20% (5/49) (p = 0.0176) for influenza A/B. Children were less prone to SARS-CoV-2 infection than the adults during the COVID-19 pandemic in Warsaw. Higher percentage of symptomatic children was infected with RSV or influenza A/B than with SARS-CoV-2. This suggests a necessity for the testing for all these viruses for an early identification and isolation of SARS-CoV-2-positive patients for an ensuing 2020 autumn return of COVID-19.

Impact of parental smoking on influenza and others respiratory infections in children.

BACKGROUND: The predisposition of cigarette smokers for the development of respiratory infections, including influenza, have been well documented. As well, those exposed to side stream smoke are prone to viral and bacterial infections of the respiratory tract. AIM: The study aimed to evaluate whether the prevalence of smoking parents is higher among children with respiratory tract infections, including influenza, in comparison to the general population. MATERIAL AND METHODS: Observational, cohort study. The authors surveyed a cohort of patients and their families, hospitalized in the Paediatric University Hospital in Warsaw during 2018 influenza season. Patients were diagnosed with influenza (using PCR) or other respiratory tract infections. A questionnaire on smoking habits was performed. RESULTS: Overall, 72 patients were included in the study, median age 2 years and 9 months (IQR: 1.4 - 7.2), influenza was diagnosed in 43% (n= 31) of patients. The percentage of regularly smoking parents in the whole cohort amounted to 33.3% (44 of 132) and was statistically significantly higher (p < 0.05) than in the general population (22.7%), whereas in the subgroup with influenza and non-influenza infections it reached 32.2% and 34.2%, respectively. CONCLUSIONS: The prevalence of smoking parents of children with acute respiratory tract infections is higher than in the general population: exposing children to tobacco smoke is one of the risk factors for acquiring influenza and others respiratory tract infections. Quitting smoking can decrease the risk of infectious diseases.

The clinical course of gastroenteritis due to nosocomial and community acquired norovirus infections in immunocompromised and immunocompetent children - single center experience.

BACKGROUND: After the introduction of rotavirus vaccines into immunization schedules, noroviruses account for the majority of acute gastrointestinal infections. The aim of the study was to assess the clinical presentation in immunocompromised and immunocompetent children with hospital- and community-acquired norovirus gastroenteritis. MATERIAL AND METHODS: We retrospectively reviewed clinical records of children with noroviral gastroenteritis, hospitalized in the Pediatric Hospital, Medical University of Warsaw, between 2015 and 2018. Acute gastrointestinal tract symptoms and confirmed etiology of noroviral infection were inclusion criteria. The analysis was performed in the subgroups of immunocompetent and immunocompromised patients, during community-acquired and nosocomial infections. RESULTS: A total of 57 children with median age 1.5 year (IQR: 0.7-4.0) were recruited. The majority of patients were immunocompetent (87.7%), and nosocomial infections were predominant (56.1%). Gastrointestinal symptoms included nausea, vomiting and diarrhoea (in approximately 85%), while systemic manifestations such as fever and malaise where observed in only ». Routine laboratory tests were normal in most of the patients. An analysis in the subgroups revealed statistically significant differences in blood pH and serum electrolyte levels - acidosis and electrolyte disturbances were statistically significantly more common in immunocompromised vs immunocompetent patients (p<0.05). CONCLUSIONS: More frequently the clinical presentation includes gastrointestinal symptoms with no differences between immunocompromised and immunocompetent hosts. The median laboratory values were normal in generally healthy children; disturbances were observed only in children with immunodeficiencies. Therefore, prophylactic measures are of particular importance in the latter group, which is especially sensitive to severe and nosocomial infections.

Pediatric Eosinophilic Esophagitis: Results of the European Retrospective Pediatric Eosinophilic Esophagitis Registry (RetroPEER).

OBJECTIVES: Recommendations for diagnosing and treating eosinophilic esophagitis (EoE) are evolving; however, information on real world clinical practice is lacking. To assess the practices of pediatric gastroenterologists diagnosing and treating EoE and to identify the triggering allergens in European children. METHODS: Retrospective anonymized data were collected from 26 European pediatric gastroenterology centers in 13 countries. Inclusion criteria were: Patients diagnosis with EoE, completed investigations prescribed by the treating physician, and were on stable medical or dietary interventions. RESULTS: In total, 410 patients diagnosed between December 1999 and June 2016 were analyzed, 76.3% boys. The time from symptoms to diagnosis was 12 ±â€Š33.5 months and age at diagnosis was 8.9 ±â€Š4.75 years. The most frequent indications for endoscopy were: dysphagia (38%), gastroesophageal reflux (31.2%), bolus impaction (24.4%), and failure to thrive (10.5%). Approximately 70.3% had failed proton pump inhibitor treatment. The foods found to be causative of EoE by elimination and rechallenge were milk (42%), egg (21.5%), wheat/gluten (10.9%), and peanut (9.9%). Elimination diets were used exclusively in 154 of 410 (37.5%), topical steroids without elimination diets in 52 of 410 (12.6%), both diet and steroids in 183 of 410 (44.6%), systemic steroids in 22 of 410 (5.3%), and esophageal dilation in 7 of 410 (1.7%). Patient refusal, shortage of endoscopy time, and reluctance to perform multiple endoscopies per patient were noted as factors justifying deviation from guidelines. CONCLUSIONS: In this "real world" pediatric European cohort, milk and egg were the most common allergens triggering EoE. Although high-dose proton pump inhibitor trials have increased, attempted PPI treatment is not universal.

Values From Three-dimensional High-resolution Anorectal Manometry Analysis of Children Without Lower Gastrointestinal Symptoms.

BACKGROUND & AIMS: Three-dimensional high-resolution anorectal manometry (3DHRAM) provides a topographic image of pressure along the anal canal. We aimed to determine normal 3DHRAM values in children. METHODS: We performed a prospective study of 61 children (34 male; mean age, 8.28 years) without any symptoms arising from the lower gastrointestinal tract who were evaluated at the Department of Pediatric Gastroenterology and Nutrition, Medical University of Warsaw, Poland. Manometry procedures were performed by using a rigid probe without medication. Pressure within the anal canal and 3D images of sphincters were measured. If possible, squeeze pressure and thresholds of sensation were evaluated. The population was divided into age groups of <5 years, 5-8 years, 9-12 years, and older than 12 years. RESULTS: The mean resting and squeeze sphincter pressures were 83 ± 23 mm Hg and 191 ± 64 mm Hg, respectively. The mean length of the anal canal was 2.62 ± 0.68 cm and correlated with age (r = 0.49, P < .0001). The mean rectal balloon volume to elicit rectoanal inhibitory reflex was 15.7 ± 10.9 cm(3). The first sensation, urge, and discomfort were observed at balloon volumes of 24.4 ± 23.98 cm(3), 45.9 ± 34.55 cm(3), and 91.6 ± 50.17 cm(3), respectively. The mean resting pressure of the puborectalis muscle was 69 ± 14 mm Hg, whereas the mean squeeze pressure was 124 ± 33 mm Hg. There was no statistically significant difference in pressure parameters between age groups. We observed a positive correlation between age and balloon volume needed to elicit discomfort (r = 0.49, P < .001). CONCLUSIONS: In a prospective study, we determined normal values from 3DHRAM analysis of children without symptoms arising from the lower gastrointestinal tract. There were no significant differences in pressure results between children of different sexes or ages. ClinicalTrials.gov number: NCT02236507.

Human Immunodeficiency Virus as a Risk Factor for Cardiovascular Disease.

The developments in HIV treatments have increased the life expectancy of people living with HIV (PLWH), a situation that makes cardiovascular disease (CVD) in that population as relevant as ever. PLWH are at increased risk of CVD, and our understanding of the underlying mechanisms is continually increasing. HIV infection is associated with elevated levels of multiple proinflammatory molecules, including IL-6, IL-1ß, VCAM-1, ICAM-1, TNF-α, TGF-ß, osteopontin, sCD14, hs-CRP, and D-dimer. Other currently examined mechanisms include CD4 + lymphocyte depletion, increased intestinal permeability, microbial translocation, and altered cholesterol metabolism. Antiretroviral therapy (ART) leads to decreases in the concentrations of the majority of proinflammatory molecules, although most remain higher than in the general population. Moreover, adverse effects of ART also play an important role in increased CVD risk, especially in the era of rapid advancement of new therapeutical options. Nevertheless, it is currently believed that HIV plays a more significant role in the development of metabolic syndromes than treatment-associated factors. PLWH being more prone to develop CVD is also due to the higher prevalence of smoking and chronic coinfections with viruses such as HCV and HBV. For these reasons, it is crucial to consider HIV a possible causal factor in CVD occurrence, especially among young patients or individuals without common CVD risk factors.

Investigation of Layered Structure Formation in MgB2 Wires Produced by the Internal Mg Coating Process under Low and High Isostatic Pressures.

Currently, MgB2 wires made by the powder-in-tube (PIT) method are most often used in the construction and design of superconducting devices. In this work, we investigated the impact of heat treatment under both low and high isostatic pressures on the formation of a layered structure in PIT MgB2 wires manufactured using the Mg coating method. The microstructure, chemical composition, and density of the obtained superconductive wires were investigated using scanning electron microscopy (SEM) with an energy-dispersive X-ray spectroscopy (EDS) analyzer and optical microscopy with Kameram CMOS software (version 2.11.5.6). Transport measurements of critical parameters were made by using the Physical Property Measurement System (PPMS) for 100 mA and 19 Hz in a perpendicular magnetic field. We observed that the Mg coating method can significantly reduce the reactions of B with the Fe sheath. Moreover, the shape, uniformity, and continuity of the layered structure (cracks, gaps) depend on the homogeneity of the B layer before the synthesis reaction. Additionally, the formation of a layered structure depends on the annealing temperature (for Mg in the liquid or solid-state), isostatic pressure, type of boron, and density of layer B before the synthesis reaction.

Changes in Primary HIV-1 Drug Resistance Due to War Migration from Eastern Europe.

In recent years, especially as a result of war in Ukraine, enormous movements of migration to Poland from eastern European countries have been reported, including people living with Human Immunodeficiency Virus (HIV). We have conducted multi-center, prospective study, which aimed to establish HIV-1 subtype and assess the presence of primary drug resistance mutations to nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and protease inhibitors in antiretroviral treatment naïve patients. The clinical trial recruited 117 individuals during 2 years period (2020-2022). The prevalence of HIV-1 subtype A was statistically significantly more frequent in Ukrainian, and HIV-1 subtype B in Polish patients (p < 0.05). Drug resistance mutations were detected in 44% of all cases and the comparison of presence of mutations in the analyzed groups, as well as in the subgroups of subtype A and B HIV-1 has not revealed any significant differences (p > 0.05), nevertheless Polish patients had multidrug resistance mutations more frequent (p < 0.05). The results from our trial show no increased risk of transmission of multidrug resistant HIV strains in our cohort of Ukrainian migrants.Clinical trials. Gov number NCT04636736; date of registration: November 19, 2020.

Effect of Low Annealing Temperature on the Critical-Current Density of 2% C-Doped MgB2 Wires Used in Superconducting Coils with the Wind-and-React (W&R) Method-High-Field and High-Temperature Pinning Centers.

The use of a low annealing temperature during the production of coils made from superconducting materials is very important because it reduces the production costs. In this study, the morphology, transport critical-current density (Jc), irreversible magnetic field (Birr), and critical temperature (Tc) of straight wires and small 2% C-doped MgB2 coils were investigated. The coils were made using the wind-and-react (W&R) method and annealed at various temperatures from 610 °C to 650 °C for 2-12 h. Critical-current measurements were made for both the coils and straight wires at the temperatures of 4.2 K, 20 K, 25 K, and 30 K. During our research study, we determined the process window that provides the best critical parameters of the coils (annealing at a temperature of 650 °C for 6 h). Moreover, we observed that small coils made with unreacted MgB2 wire and then annealed had morphology and critical parameters similar to those of straight 2% C-doped MgB2 wires. Moreover, small-diameter bending of 20 mm and 10 mm did not lead to transverse cracks, which can cause a large reduction in Jc in the coils. This indicates that the processes of optimization of thermal treatment parameters can be carried out on straight MgB2 wires for MgB2 superconducting coils.

Impact of Combined Antiretroviral Therapy on Metabolic Syndrome Components in Adult People Living with HIV: A Literature Review.

The development of metabolic derangements as a result of HIV treatment has been an important area of research since the introduction of zidovudine in the 1980's. Antiretroviral therapy has intensely evolved in the last three decades, with new drugs gradually incorporated into everyday clinical practice. With the life expectancy of people living with HIV rapidly approaching that of their HIV-negative counterparts, the influence of these antiretrovirals on the development of the components of the metabolic syndrome remains of major interest to clinicians and their patients. In this review, we aimed to discuss the impact of cART on components of the metabolic syndrome, i.e., weight, plasma lipid levels, plasma glucose levels, and blood pressure, describing the influence of cART classes and of individual antiretrovirals. We also aimed to outline the limitations of the research conducted to date and the remaining knowledge gaps in this area.

Excessive laxity of connective tissue in constipated children.

Excessive laxity of the connective tissue refers to a group of inherited abnormalities manifested by disturbances in the functioning of internal organs, including the gastrointestinal tract. Increased susceptibility to stretching of the distal part of the large intestine and abnormal colonic motor function could explain the predisposition to the development of functional constipation in some children. Our aim was to determine whether patients with functional constipation are more likely to be characterized by congenital laxity of connective tissue compared to the population of healthy children. Children diagnosed with functional constipation according to the Rome III criteria were prospectively enrolled in the study (study group, S) and compared to otherwise healthy children (control group, C). Excessive laxity of the connective tissue was evaluated using the Beighton Score (BS) and expressed as median and interquartile range (IQR). The study included 411 patients (median age 7.8 years, min 3 years, max 18 years; 49% male), comprising 211 patients in the S group and 200 children in the C group. The median BS in the S group was significantly higher than in the C group (median: 5 points [IQR: 1-4.5] vs 2 points [IQR: 3-7], respectively; p = 0.000). Furthermore, increased connective tissue laxity was observed more frequently in females (p < 0.05). Increased connective tissue laxity was more frequent in children with functional constipation, especially in girls. Excessive laxity of the connective tissue may be one of the etiological factors of functional constipation in children.

Frailty and prefrailty in people living with HIV, with focus on women living with HIV.

With the increasing lifespan of people living with HIV (PLWH), frailty and prefrailty are becoming topics which require more attention. The reciprocal interactions between chronic inflammation, comorbidities and frailty demonstrate the complex pathophysiology of frailty and its consequences. Female sex, HIV infection without antiretroviral treatment, reduced CD4 cell count, depression and cardiovascular disease are some of the risk factors for frailty among PLWH. Frailty predisposes to falls and can therefore lead to more frequent fractures, hospitalization and death, especially in women with osteoporosis. Continuous antiretroviral treatment, prevention of comorbidities such as depression and diagnosis of prefrailty are crucial interventions to slow the development of frailty. This review summarizes the literature on frailty in people living with HIV and discusses frailty management strategies in order to improve the health outcomes in women living with HIV.

Evaluation of Clinical Biomarkers Related to CD4 Recovery in HIV-Infected Patients-5-Year Observation.

Human Immunodeficiency Virus infection leads to the impairment of immune system function. Even long-term antiretroviral therapy uncommonly leads to the normalization of CD4 count and CD4:CD8 ratio. The aim of this study was to evaluate possible clinical biomarkers which may be related to CD4 and CD4:CD8 ratio recovery among HIV-infected patients with long-term antiretroviral therapy. The study included 68 HIV-infected patients undergoing sustained antiretroviral treatment for a minimum of 5 years. Clinical biomarkers such as age, gender, advancement of HIV infection, coinfections, comorbidities and applied ART regimens were analyzed in relation to the rates of CD4 and CD4:CD8 increase and normalization rates. The results showed that higher rates of CD4 normalization are associated with younger age (p = 0.034), higher CD4 count (p = 0.034) and starting the therapy during acute HIV infection (p = 0.012). Higher rates of CD4:CD8 ratio normalization are correlated with higher CD4 cell count (p = 0.022), high HIV viral load (p = 0.006) and acute HIV infection (p = 0.013). We did not observe statistically significant differences in CD4 recovery depending on gender, HCV/HBV coinfections, comorbidities and opportunistic infections. The obtained results advocate for current recommendations of introducing antiretroviral therapy as soon as possible, preferably during acute HIV infection, since it increases the chances of sufficient immune reconstruction.

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique.

We show that the structure of multifilament MgB2 wires made by the powder-in-tube (PIT) method can be texturized by annealing the structure under high isostatic pressure. Our results show that we obtained continuous fibers with a uniform diameter of 250 nm in all 36 filaments, a small grain size of approximately 50 nm and a high density of the superconducting material. These results contribute to a significant improvement in the critical current density in high magnetic fields, e.g., 100 A/mm2 at 14 T and 4.2 K.

Magnetic Field Influence on the Microwave Characteristics of Composite Samples Based on Polycrystalline Y-Type Hexaferrite.

Here, we report results on the magnetic and microwave properties of polycrystalline Y-type hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave-absorbing material. The reflection losses in the 1-20 GHz range of the Y-type hexaferrite powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in the absence and in the presence of a magnetic field. A permanent magnet was used with a strength of 1.4 T, with the magnetic force lines oriented perpendicularly to the direction of the electromagnetic wave propagation. In the case of using an external magnetic field, an extraordinary result was observed. The microwave reflection losses reached a maximum value of 35.4 dB at 5.6 GHz in the Ku-band without a magnetic field and a maximum value of 21.4 dB at 8.2 GHz with the external magnetic field applied. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the decrease of the reflected wave attenuation. At a fixed thickness, tm, of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field.

Correlation of clinical symptoms, endoscopic features and density of oesophageal eosinophilia in children with newly-diagnosed eosinophilic esophagitis.

INTRODUCTION AND OBJECTIVE: Eosinophilic esophagitis (EoE) is an inflammatory immune-mediated oesophageal disease of growing prevalence. The aim of this study is to characterise the clinical symptoms, endoscopic features and histological findings, as well as their possible correlations, in newly-diagnosed EoE paediatric patients. MATERIAL AND METHODS: Between 2009-2018, the clinical records of patients diagnosed with EoE at the Paediatric Hospital in Warsaw, Poland, were retrospectively reviewed. Inclusion criteria were upper gastrointestinal tract symptoms in association with oesophageal mucosal biopsy specimens containing not less than 15 intraepithelial eosinophils per hpf. The prevalence and the possible correlations between symptoms, endoscopic features and the density of eosinophilic infiltration were analysed; the medical history of the comorbidities were also assessed. RESULTS: The study included 47 children (median age 9.5 years). The most common clinical symptoms were abdominal pain (53%) and GERD-like symptoms (26%). The most common macroscopic changes were white plaques and exudates in 47% and furrows in 34%. A macroscopically normal oesophagus was observed in 28% of the children. The median number of eosinophils was estimated to be 45 eosinophils/hpf (IQR: 30-60), and no significant differences were found between the density of eosinophil infiltration and clinical symptoms or endoscopic features. Moreover, 70% of the children had a history of an allergy disease, older children (>3 years) tended to have pollen allergy more often than younger children (p<0.05). CONCLUSIONS: The density of oesophageal eosinophilia does not correlate with symptoms or endoscopic findings in children with newl-diagnosed EoE.

Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, N-Value, and Engineering Critical Current Density in Mgb2 Wires.

Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (Birr), critical temperature (Tc), upper magnetic field (Bc2), engineered critical current density (Jec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on Birr, Tc, Bc2, Jec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest Birr, Tc, Bc2, Jec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.

Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB2 Wires.

Annealing undoped MgB2 wires under high isostatic pressure (HIP) increases transport critical current density (Jtc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases Jtc by 25% in range magnetic fields from 2 T to 4 T and does not increase Jtc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the Jtc by 40% at 4.2 K in magnetic fields above 6 T and reduces Jtc by one order at 20 K in MgB2 wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB2 material and the number of connections between grains compared to MgB2 wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB2 material and more connections between grains during the liquid-state Mg reaction.

The role of laser biostimulation in early post-surgery rehabilitation and its effect on wound healing.

BACKGROUND: The aim of this paper is to investigate whether laser biostimulation starting on the first day after surgery of the brachial plexus or peripheral nerves has a positive therapeutic effect on wound healing. MATERIAL AND METHODS: Surgical procedures were carried out on 44 male Wistar rats. The animals were divided into a control group (Group 1), where the surgical wounds were allowed to heal spontaneously, and an experimental Group 2, where the wounds were exposed to laser irradiation with the following parameters: wavelength 810 nm, power 100 mW, energy 15 J, laser exposure surface 3 cm(2), single application time 2 min. 30 sec., continuous mode. The results were assessed with pathomorphological tests (gross appearance of the wound, light and electron microscopy studies) and breaking strength examination. Statistical analysis used arithmetic means, standard deviations and Student's t test for independent samples. RESULTS: Low energy infrared laser radiation had a beneficial effect on the covering of the scar with stratified squamous cornifying epithelium and intensified wound healing. CONCLUSIONS: The gross and microscopic findings indicated a beneficial effect of laser stimulation on wound healing. These results underscore the utility of biostimulation lasers in the early post-operative period. Physicomechanical investigations did not reveal an effect of infrared laser biostimulation on the breaking strength of the cutaneous scar.

Structural, Magnetic and Microwave Characterization of Polycrystalline Z-Type Sr3Co2Fe24O41 Hexaferrite.

We report results on the structural and microwave properties and magnetic phase transitions in polycrystalline Sr3Co2Fe24O41 hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave absorbing material. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves revealed a change in the magnetization behavior at 293 K. The reflection losses in the 1-20 GHz range of the Sr3Co2Fe24O41 powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in both the absence and presence of a magnetic field. In the latter case, a dramatic rise in the attenuation was observed. The microwave reflection losses reached the maximum value of 32.63 dB at 17.29 GHz in the Ku-band. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the appearance of new reflection losses maxima. At a fixed thickness tm of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field.