Effects of MRI on sex hormones and other fertility parameters in adult male rats

زمینه و هدف: از بهترین تکنیک های دنیای پزشکی در تشخیص بیماری ها استفاده از تصویربرداری رزونانس مغناطیسی (MRI) است. برای تولید تصاویر در MRI از سه نوع میدان الکترومغناطیسی متفاوت استفاده می شود. هدف از این مطالعه بررسی اثرات میدان های MRI بر ترشح هورمون های جنسی و سایر پارامترهای باروری در موش های صحرایی نر بالغ بوده است. مطالعات متعددی در مورد اثرات هر یک از این میدان ها بر سیستم های زیستی وجود دارد. روش بررسی: در این مطالعه تجربی 40 سر موش صحرایی نر بالغ نژاد ویستار به صورت تصادفی به چهار گروه 10 تایی (دو گروه آزمایشی و دو گروه کنترل) تقسیم شدند. گروه های آزمایش به مدت 25 دقیقه در کویل دستگاه MRI با شدت میدان مغناطیسی 35/0 تسلا قرار گرفتند. سپس حیوانات دوره اول آزمایش و کنترل را به سرعت در هولدر قرار داده و دمای پوست اسکرتوم آنها با دما سنج دیجیتالی اندازه گیری شد. این حیوانات به آزمایشگاه منتقل و پس از خونگیری و تهیه نمونه های سرم، کشته شدند. بیضه ها از بدن آنها خارج و با ترازوی دیجیتالی وزن شد. 96 ساعت بعد از MRI همین مراحل برای حیوانات دوره دوم آزمایش و کنترل انجام شد. هورمون های تستوسترون، هورمون تحریک کننده فولیکول (FSH) و هورمون لوتئیزه کننده (LH) به روش رادیوایمنواسی (RIA) اندازه گیری و در گروه های مختلف با هم مقایسه شدند. یافته ها: در مرحله اول که پس از انجام MRI صورت گرفت، افزایش معناداری در هورمون FSH (003/0=P) و کاهش معنی داری در میزان هورمون تستوسترون گروه آزمایش نسبت به کنترل مشاهده شد (001/0=P) اما تغییرات میزان هورمون LH، وزن بیضه ها و دمای پوست اسکرتوم معنی دار نبود. در مورد دوره دوم که 96 ساعت بعد از انجام MRI صورت گرفت فقط افزایش معنی دار هورمون FSH در گروه آزمایش نسبت به کنترل که مشابه نتایج دوره اول بود مشاهده شد (04/0=P). نتیجه گیری: میدان های MRI می توانند باعث اختلال در ترشح برخی از هورمون های جنسی موش صحرایی نر بالغ شوند

Fluctuation of mean free path and transition temperature induced vortex pinning in (Ba,K)Fe2As2 superconductors

The vortex pinning mechanisms of Ba0.72K0.28Fe2As2 single crystal have been studied systematically as a function of temperature and magnetic field. The temperature dependence of the critical current density, Jc(T), was analysed within the collective pinning model at different magnetic fields. It was found that both the dl pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation, and the dTc pinning mechanism, which is associated with spatial fluctuations of the transition temperature, coexist in the Ba0.72K0.28Fe2As2 single crystal in fields smaller than 4 T. Their contributions are strongly temperature and magnetic field dependent. At lower temperature and

Iron based superconductors: Superconducting and flux pinning properties

Discovered in 2008, iron based superconductors are the latest high temperature superconductors which have aroused enormous attention in the scientific community. Finding superconductivity in compounds containing iron, after two decades of intensive research on the high temperature cuprates was a surprise to the scientists in this field, as they thought that the magnetic nature of iron would disrupt the pairing of electrons in the superconducting state. These materials exhibit high upper critical field, high critical current density, very high intrinsic pinning potential and low anisotropy compared with MgB2 and other conventional superconductors, and even cuprate superconductors. Iron based superconductors would be good candidates for use in electricity generators, cheaper medical imaging scanners, and extremely fast levitating trains

Study of supercoducting and magneto transport properties of REFeAsO1-xFx (RE=La and Ce)

Iron-based superconductors are the most recently discovered superconductors which could be suitable for a variety of applications. The high upper critical fields and relatively high critical current density in this group are good evidence that these compounds can be competitive with MgB2 and even high critical temperature (Tc) cuprates. Moreover, the first high temperature superconductors, cuprates, have been studied intensively for more than 20 years, but scientists still don’t know exactly how these materials work. Finding the first non-cuprate high temperature superconductors can help to unveil the mystery of superconductivity. It is possible that the clues to how these materials work could lead to the design of room temperature superconductors. The first iron-based superconductor compound, LaFeAsO1-xFx, shows superconductivity at 26 K. However, the transition temperature is increased by replacing La by other rare earth elements with smaller atomic radii, such as Ce, Sm, Nd, Pr, and Gd, resulting in an increase of up to 56 K for GdFeAsO1-xFx compound. The parent compounds show antiferromagnetic spin density wave order, and superconductivity appears by introducing charge carriers, either through electron or hole doping. Six families of iron based superconductors have been discovered so far. The first family has the formula REOFeAs, in which RE stands for rare earth element. These compounds have a tetragonal layered ZrCuSiAs structure with the P4/nmm space group. The second family has the formula AFe2As2, in which A is alkali- rear elements. They have the ThCr2Si2 structure with space group I4/mmm. The next family is LiFeAs, which has an infinite layered structure and crystallizes into the CuPb-type tetragonal structure. The next category, FeSe, presents a tetragonal structure, the simplest crystal structure among the iron-based superconductors. The latest families discovered so far are (Ca,Sr) FFeAsand Sr4Sc2Fe2As2O6. (Ca,Sr)FFeAs has the ZrCuSiAs type structure with P4/nmm space group. Sr4Sc2Fe2As2O6 has a layered structure with the space group I4/mmm. For practical application of the Fe-based superconductors, two of the most important parameters are the upper critical field, Hc2, and the critical current density, Jc. The upper critical field is an intrinsic property, which has been approximated to be higher than 55 or 64 T in LaFeAs O0.9F0.1, 70 T in PrFeAsO0.85F0.15, over 100 T in SmFeAsO0.85F0.15,and 230 T in high-pressure (HP) fabricated NdFeAsO0.82F0.18. The Jc is sample dependent and controlled by the flux pinning behaviour. However, the available data for critical current density and pinning force in LaFeAsO1-xFx compound are very limited so far. As La is non-magnetic, LaFeAsO1-xFx was selected for study in this thesis, as it should be an ideal sample to study the flux pinning related properties. This is because all the other RE compounds contain a magnetic RE. Compared to LaFeAsO1-xFx, where Fe is the only possible ion carrying a significant magnetic moment, a rare earth oxypncictide with a paramagnetic ion such as Ce+3 in CeFeAsO1-xFx also offered a unique opportunity to study the interplay between the rare-earth element and the Fe magnetic ions. Our results show that the critical current density for both compounds, LaFeAsO1-xFx and CeFeAsO1-xFx, depends on the level of fluorine doping. For LaFeAsO1-xFx compound, with increasing fluorine doping from x = 0.05 to x = 0.15, Jc is increased. After that, with further increases in x, the Jc is reduced. For CeFeAsO1-xFx, Jc is decreased with increasing fluorine doping. Both compounds show a superior Jc field dependence at low temperature. A peak effect was observed in the CeFeAsO1-xFx samples with x = 0.1 at T = 20 K. The peak effect was also detected at 5 K, 10 K and 15 K for LaFeAsO0.85F0.15 compound. Jc shows weak magnetic field dependence at T \u3c 20 K for both compounds. By using the Ginzburg-Landau equation and the Werthamer-Helfand-Hohenberg (WHH) theory, we estimate Hc2ab(0) = 122 T and 185 T for LaFeAsO0.85F0.15 and CeFeAsO0.9F0.1, respectively. The pinning potential scales as Uo/kB B-n, where Uo is the pinning potential energy, kB= Boltzmann’s constant, and n = 0.2 for B \u3c 3 T and n = 0.7 for B \u3e 3 T for CeFeAsO0.9F0.1, and n = 0.13 for B \u3c 1 T and n = 0.68 for B \u3e 1 for LaFeAsO0.85F0.15.So, it is expected that single-vortex pinning may coexist with collective creep in lowfield. The value of Uo for the CeFeAsO0.9F0.1 doped sample is two times higher than for the LaFeAsO0.95F0.05. The Hc2 values of these compounds have the potential to be increased even more, through proper chemical doping and physical approaches, due to the two-gap superconductivity in the new iron-based superconductors. As the Jc values are still considerably lower than those of individual grains, the challenge is to produce these materials with more texture and connectivity, in order to allow these new superconductors to carry a high critical current density in low and high magnetic fields

Study on newly discovered iron-based superconductors

Discovered in 2008, iron pnictides are the latest high temperature superconductors which have aroused enormous attention in the scientific community. The discovery of iron based superconductors (FBSs) marked the foundation of a new era in the field of superconductivity by replacing the Copper Age by the Iron Age. This discovery has given scientists the chance to study the superconducting and magnetic properties in a different family of high temperature superconductors, as understanding the nature of superconductivity in unconventional superconductor is crucial for designing new materials with higher critical temperature (Tc). These materials would be good candidates for use in electricity generators, cheaper medical imaging scanners, and extremely fast levitating trains because superconducting materials with higher Tc would not require expensive coolants to reach the superconducting transition temperature. Therefore, the discovery of FBSs was a significant achievement in the condensed matter community. The main focus and novelty of this work is twofold: firstly, the pinning potential, thermally activated flux flow behaviour and superconducting properties of iron based superconductors, mostly hole doped BaFe2As2 pnictides and arsenic free FeSe1-xTex chalcogenides was investigated in details. Secondly, the magnetic and transport properties of parent compound BaFe2As2 and non superconducting Ba(Fe1-xCrx)2As2 was studied using magnetic, magnetoresistance and neutron diffraction measurements. Understanding the vortex pinning mechanism in FBSs is crucial for practical applications and fundamental study due to the relatively high critical temperature, high upper critical field (Bc2), high critical current density, very high intrinsic pinning potential, and nearly isotropic superconductivity of these compounds, and also due to the possibilities for the fabrication of superconducting wire. In order to understand the pinning mechanisms in these systems, scaling analysis of the normalized pinning force as a function of reduced field was performed. Analysis using the Dew-Hughes model has suggested that point pins alone cannot explain the observed field variation of the pinning force density. According to the collective flux pinning model, the field dependence of the magnetization shows that the flux pinning in Ba(Fe1-xNix)2As2 is dominated by the spatial variation in the charge carrier mean free path. Irradiation has been employed in order to increase the pinning potential, and as a result, the critical current density in BaFe1.9Ni0.1As2 single crystal. The C4+irradiation cause little change in the superconducting critical temperature, but it can enhance infield critical current density (Jc) by a factor of up to 1.5, with enhanced flux jumping at 2 K. Also, the magnetic optical imaging results confirm the enhancement of Jc in the irradiated samples. These results suggest that light C4+ ion irradiation is an effective method for the enhancement of Jc in FBSs compared to heavy ion irradiation and neutron irradiation. In addition, The angular dependence of the upper critical field and the pinning potential of underdoped BaFe1.9Co0.1As2 single crystals have been investigated by measuring magneto-transport at different magnetic fields and angles. Furthermore, by scaling the angular dependence of the resistance, based on the anisotropic Ginzburg-Landau (GL) theory, an anisotropy value of less than 2.1 was determined for different temperatures below the superconducting transition temperatures. Based on these results, the pinning potential is strongly angle dependent for θ ≤ 45° and almost angle independent for θ ≥ 45°, while Bc2 increase monotonically with increasing angle. Also, the thermally activated flux flow (TAFF) behaviour of arsenic free Fe1.06Te0.6Se0.4 single crystals were analysed using the conventional Arrhenius relation and modified TAFF model. It was found that the Arrhenius curve slopes are directly related to, but not equal to, the activation energies of Fe1.06Te0.6Se0.4 single crystals. Therefore, the use of a modified TAFF model, ρ(T, B) = ρ0f exp(-U/T), is suggested, where the temperature dependence of the prefactor ρ0f = 2ρcU/T and the nonlinear relation of the thermal activation energy are considered. Furthermore, a detailed investigation was carried out to understand the magnetic and magnetoresistance behaviour of non-superconducting Ba(Fe1-xCrx)2As2. It should be noted that understanding the antiferromagnetic order of iron ions itself is also important for both fundamental study and practical application. It is very interesting to design new magnetic device based on spin dependent transport properties of pnictide materials. Ba(Fe1-xCrx)2As2 is the first doped compound with no superconductivity phase and magnetic phases is the only competitor as Cr concentration increases. Transport and magnetic measurements show an interesting two fold symmetry in non superconducting Ba(Fe1-xCrx)2As2 (x = 0.303) compound which depend on temperature and magnetic field. In order to understand the temperature and magnetic field response of iron pnictide at atomic level, neutron diffraction studies were performed for Ba(Fe1-xCrx)2As2 (x=0.303)

Progress in research on the stability of organometal perovskite solar cells

Organometal lead halides based perovskite solar cells (PSC) are a recent discovery in photovoltaic technology that have demonstrated impressive power conversion efficiency achieved by cost-effective solution method (e.g. roll-to-roll production) from readily available raw materials. Nevertheless, the PSC devices have shown limited operating life-times due to degradation of the perovskite materials. Since long operational durability is essential for this new and promising PV technology to fulfil its mission to deliver clean, low cost renewable energy, this review presents the most recent research on understanding of the factors that may cause the degradation process in perovskite materials and PSC devices. Strategies that may improve the stability of PSCs through optimization of the device architectures and development of new materials are also discussed

Synthesis of magnesium nickel boride aggregates via borohydride autogenous pressure

We demonstrate synthesis of the ternary intermetallic MgNi3B2 using autogenous pressure from the reaction of NaBH4 with Mg and Ni metal powder. The decomposition of NaBH4 to H2 and B2H6 commences at low temperatures in the presence of Mg and/or Ni and promotes formation of Ni-borides and MgNi3B2 with the increase in temperature. MgNi3B2 aggregates with Ni-boride cores are formed when the reaction temperature is >670 °C and autogenous pressure is >1.7 MPa. Morphologies and microstructures suggest that solid–gas and liquid–gas reactions are dominant mechanisms and that Ni-borides form at a lower temperature than MgNi3B2. Magnetic measurements of the core-shell MgNi3B2 aggregates are consistent with ferromagnetic behaviour in contrast to stoichiometric MgNi3B2 which is diamagnetic at room temperature.