Promising Antimicrobial Properties of Bioactive Compounds from Different Honeybee Products

Bee products have been known for centuries for their versatile healing properties. In recent decades they have become the subject of documented scientific research. This review aims to present and compare the impact of bee products and their components as antimicrobial agents. Honey, propolis, royal jelly and bee venom are bee products that have antibacterial properties. Sensitivity of bacteria to these products varies considerably between products and varieties of the same product depending on their origin. According to the type of bee product, different degrees of activity were observed against Gram-positive and Gram-negative bacteria, yeasts, molds and dermatophytes, as well as biofilm-forming microorganisms. Pseudomonas aeruginosa turned out to be the most resistant to bee products. An analysis of average minimum inhibitory concentration values for bee products showed that bee venom has the strongest bacterial effectiveness, while royal jelly showed the weakest antibacterial activity. The most challenging problems associated with using bee products for medical purposes are dosage and safety. The complexity and variability in composition of these products raise the need for their standardization before safe and predictable clinical uses can be achieved.     

The general form of representation of wall region of a turbulent boundary layer

On the basis of a formal similarity between turbulent momentum, heat/mass flux and probability function a concept of turbulent flux density distribution has been proposed. It has been shown that the characteristic bell shape of this distribution is almost the same, irrespective of the turbulence model from which it was calculated, and can reveal the structure of the turbulent boundary layer, especially the influence of molecularPr orSc number. This concept may also be used to test consistency and to compare differently formulated models of turbulent transport.     

Effect of carbon substitution on low magnetic field AC losses in MgB2 single crystals

The DC magnetization and AC magnetic susceptibilities were measured for MgB₂ single crystals, unsubstituted and carbon substituted with the composition of Mg(B_0.94C_0.06)₂. AC magnetic losses were derived from the AC susceptibility data as a function of the AC amplitude and the DC bias magnetic field. From the DC magnetization loops critical current densities were derived as a function of temperature and DC field. Results show that the substitution with carbon decreases critical current densities at low external magnetic fields, in contrast to the well known effect of an increase of the critical current densities at higher magnetic fields.     

Weak itinerant ferromagnetism and clean superconductivity in Y9Co7

We present low-temperature magnetic properties for a high-quality polycrystalline sample of the first ferromagnetic superconductor Y₉Co₇. The results of susceptibility and magnetization measurements show the coexistence of a weak itinerant ferromagnetic order with a Curie temperature of T_C ? 4.5 K and superconductivity below T_S = 3 K. Several electronic quantities and parameters characterizing the superconducting and normal state are calculated within the Ginzburg–Landau–Abrikosov–Gorkov theory. The data reveal clean limit superconductivity in Y₉Co₇ due to the good chemical purity and structural order of the specimen.     

Influence of the carbon substitution on the critical current density and AC losses in MgB<Subscript>2</Subscript> single crystals

The DC magnetization and AC complex magnetic susceptibilities were measured for MgB₂ single crystals, unsubstituted and carbon substituted with the composition of Mg(B_0.94C_0.05)₂. The measurements were performed in AC and DC magnetic fields oriented parallel to the c-axis of the crystals. From the DC magnetization loops and the AC susceptibility measurements, critical current densities (J _c were derived as a function of temperature and the DC and AC magnetic fields. Results show that the substitution with carbon decreases J _c ) at low magnetic fields, opposite to the well known effect of an increase of J _c at higher fields. AC magnetic losses were derived from the AC susceptibility data as a function of amplitude and the DC bias magnetic field. The AC losses were determined for temperatures of 0.6 and 0.7 of the transition temperature T _c , so close to the boiling points of LH₂ and LNe, potential cooling media for magnesium diboride based composites. The results are analyzed and discussed in the context of the critical state model.     

Single crystals of LnFeAsO1−xFx (Ln = La,Pr, Nd,Sm, Gd) and Ba1−xRbxFe2As2: Growth,structure and superconducting properties

A review of our investigations on single crystals of LnFeAsO_1?xF_x (Ln = La, Pr, Nd, Sm, Gd) and Ba_1?xRb_xFe₂As₂ is presented. A high-pressure technique has been applied for the growth of LnFeAsO_1?xF_x crystals, while Ba_1?xRb_xFe₂As₂ crystals were grown using a quartz ampoule method. Single crystals were used for electrical transport, structure, magnetic torque and spectroscopic studies. Investigations of the crystal structure confirmed high structural perfection and show incomplete occupation of the (O, F) position in superconducting LnFeAsO_1?xF_x crystals. Resistivity measurements on LnFeAsO_1?xF_x crystals show a significant broadening of the transition in high magnetic fields, whereas the resistive transition in Ba_1?xRb_xFe₂As₂ simply shifts to lower temperature. The critical current density for both compounds is relatively high and exceeds 2 × 10⁹ A/m² at 15 K in 7 T. The anisotropy of magnetic penetration depth, measured on LnFeAsO_1?xF_x crystals by torque magnetometry is temperature dependent and apparently larger than the anisotropy of the upper critical field. Ba_1?xRb_xFe₂As₂ crystals are electronically significantly less anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the existence of two energy gaps in LnFeAsO_1?xF_x. Scanning Tunneling Spectroscopy reveals in addition to a superconducting gap, also some feature at high energy (～20 meV).     

Transport properties of MgB2 single crystals doped with electrons and holes

The thermoelectric power of C, Mn, C:Li, and Al:Li substituted MgB₂ single crystals has been investigated in the temperature range 10-300 K. Both the in-plane (S_ab) and the out-of-plane (S_c) thermopowers are positive for the non-substituted crystal and both S_ab and S_c change a sign for crystals doped with electrons where C is substituted for B in the amount larger than 5 at%. When Li is substituted for Mg, the π band rather than the σ band is doped with holes and the doping effects are much more subtle. The anisotropy ratio of the non-substituted crystal S_ab/S_c≈3 and this ratio is strongly reduced by the substitution of C. Isovalent magnetic Mn ions, which substitute for Mg with a drastic reduction of T_c, do not influence the values and temperature dependences of both S_ab and S_c.