Interrogating the superconductor Ca10(Pt4As8)(Fe2-xPtxAs2)5 Layer-by-layer.

Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe2As2 layers) and intermediate Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.

Role of antiferromagnetic ordering in the (1×2) surface reconstruction of Ca(Fe(1-x)Co(x))2As2.

Low energy electron diffraction, scanning tunneling microscopy and spectroscopy, and first-principles spin-dependent density functional theory are utilized to investigate the geometric, electronic, and magnetic structures of the stripe-ordered (1×2) surface of Ca(Fe1-xCox)2As2 (x=0, 0.075). The surface is terminated with a 50% Ca layer. Compared to the bulk, the surface Ca layer has a large inward relaxation (∼0.5 Å), and the underneath As-Fe2-As layer displays a significant buckling. First-principles calculations show that the (1×2) phase is stabilized by the bulk antiferromagnetic spin ordering through the spin-charge-lattice coupling. Strikingly, a superconducting gap (∼7 meV at 7.4 K) is observed to spatially coexist with the (1×2) phase (x=0.075 compound). This implies the coexistence of both superconductivity and AFM ordering at the surface.

PdTe: a strongly coupled superconductor.

We report the electrical transport, magnetic, and thermodynamic properties of polycrystalline PdTe which exhibits superconductivity below 4.5 K. Using the measured values for the lower (H(c1)) and upper (H(c2)) critical fields, and the specific heat C(p), we estimate the thermodynamic critical field H(c)(0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ. Compared with band structure calculations, the density of states at the Fermi level is enhanced due to electron-phonon coupling with λ(ep) = 1.4. Furthermore, the large values of ΔC(p)/γ(n)T(c) and 2Δ(0)/k(B)T(c) suggest that PdTe is a strongly coupled superconductor.

Intestinal protozoan parasitic infection among school children.

BACKGROUND: Intestinal protozoan parasitosis is highly prevalent among general population, majority of them are children. The objective of the study is to find out the prevalence of intestinal protozoan infection in school children of Sindhuli. METHODS: Stool samples were collected from school children of Sindhuli in June 2011 and investigated in National Institute of Tropical Medicine and Public Health Research, Laboratory by using formal-ether concentration method. Statistical significance was analyzed by using Chi-Square test. RESULTS: A total of 342 stool samples were collected and 68 (19.8%) protozoan parasites were identified. The prevalence rate of protozoa in boys and girls were 16.9% and 22.0% respectively. Altogether 5 species of protozoan parasites were detected. Of them Entamoeba coli was most common followed by Giardia lamblia, Entamoeba histolytica, Blastocystis hominis and Endolimax nana. Positive rate was highest in Dalit (20.3%), and least in Indo-Aryan (19.6%). CONCLUSIONS: There is a low prevalence of intestinal protozoan parasitosis among children even though this study emphasizes the need for improved environmental hygiene i.e. clean water supplies and enhanced sanitation.

Study on carrier rate of Streptococcus pyogenes among the school children and antimicrobial susceptibility pattern of isolates.

This study was done to investigate the rate of Streptococcus pyogenes or Group A streptococcus (GAS) and antimicrobial susceptibility pattern of isolates in asymptomatic school children in Kathmandu and Sindhuli districts. Pharyngeal swabs were collected and subjected to crystal violet blood agar (CVBA). A total of 468 asymptomatic school aged children were included and 51 (10.8%) were found to be GAS carrier. Among the isolates 23 (12.0%) were from boys where 28 (10.1%) were from girls. The GAS colonization rate was statistically insignificant (P > 0.05) with sex and age sub-group, although the rate was slightly higher among the boys and age sub group 10-12 years. GAS was significantly higher in large family size (p < 0.05). Out of 51 isolates, 100.0% isolates were sensitive to antibiotic penicillin where as 7.8% and 5.8% isolates were resistant to antibiotic ampicillin and erythromycin respectively.

Crystal growth, structure, and physical properties of Ln(Cu,Al)12 (Ln = Y, Ce, Pr, Sm, and Yb) and Ln(Cu, Ga)12 (Ln = Y, Gd-Er, and Yb).

Single crystals of Ln(Cu,Al)12 and Ln(Cu,Ga)12 compounds (Ln = Y, Ce-Nd, Sm, Gd-Ho, and Yb for Al and Ln = Y, Gd-Er, Yb for Ga) have been grown by flux-growth methods and characterized by means of single-crystal x-ray diffraction, complemented with microprobe analysis, magnetic susceptibility, resistivity and heat capacity measurements. Ln(Cu,Ga)12 and Ln(Cu,Al)12 of the ThMn12 structure type crystallize in the tetragonal I4/mmm space group with lattice parameters a approximately 8.59 Šand c approximately 5.15 Šand a approximately 8.75 Šand c approximately 5.13 Šfor Ga and Al containing compounds, respectively. For aluminium containing compounds, magnetic susceptibility data show Curie-Weiss paramagnetism in the Ce and Pr analogues down to 50 K with no magnetic ordering down to 3 K, whereas the Yb analogue shows a temperature-independent Pauli paramagnetism. Sm(Cu,Al)12 orders antiferromagnetically at T(N)approximately 5 K and interestingly exhibits Curie-Weiss behaviour down to 10 K with no Van Vleck contribution to the susceptibility. Specific heat data show that Ce(Cu,Al)12 is a heavy fermion antiferromagnet with T(N) approximately 2 K and with an electronic specific heat coefficient γ0 as large as 390 mJ K2 mol(-1). In addition, this is the first report of Pr(Cu,Al)12 and Sm(Cu,Al)12 showing an enhanced mass (approximately 80 and 120 mJ K(2) mol(-1)). For Ga containing analogues, magnetic susceptibility data also show the expected Curie-Weiss behaviour from Gd to Er, with the Yb analogue being once again a Pauli paramagnet. The antiferromagnetic transition temperatures range over 12.5, 13.5, 6.7, and 3.4 K for Gd, Tb, Dy, and Er. Metallic behaviour is observed down to 3 K for all Ga and Al analogues. A large positive magnetoresistance up to 150% at 9 T is also observed for Dy(Cu,Ga)12. The structure, magnetic, and transport properties of these compounds will be discussed.

NaV2O4: a quasi-1D metallic antiferromagnet with half-metallic chains.

NaV2O4 crystals were grown under high pressure using a NaCl flux, and the crystals were characterized with x-ray diffraction, electrical resistivity, heat capacity, and magnetization. The structure of NaV2O4 consists of double chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic, with the resistivity perpendicular to the chains more than 20 times greater than that parallel to the chains. Magnetically, the intrachain interactions are ferromagnetic and the interchain interactions are antiferromagnetic; 3D antiferromagnetic order is established at 140 K. First-principles electronic structure calculations indicate that the chains are half-metallic. Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was found for half-metallic materials.

[A study of the action of sodium chlorate on strains of nitrate reducing soil bacteria (author's transl)]. / Etude de l'action de chlorate of soude sur des souches de bactéries du sol réductrices du nitrate.

Fours strains of nitrate reducing bacteria isolated from soil were studied for their behavior towards chlorate. They are facultative anaerobes, except for Bacillus megatherium (which is a strict aerobe) and they possess a nitrate reductase A. The growth of three strains of bacteria (Klebsiella pneumoniae, B. licheniformis and Micromonospora globosa) was slowed by sodium chlorate at a concentration of 0.06 to 0.1% while the other strain (B. megatherium) tolerated the CIO3- well. The delay of bacterial growth due to chlorate lasts for a certain period, after which the bacteria multiply again. The lag phase is due to small quantities of chlorite produced from the chlorate; the growth phase which follows is provoked by the multiplication of chlorate resistant mutants, most often nitrate reductase-negative and sometimes positive. Some reverse mutants nitrate reductase positive of K. pneumoniae no longer had the same characteristics as the wild strain: some resisted to chlorate or were different as to gas formation. The reduction of nitrate to ammonia by these bacteria is diminished in the presence of chlorate: the reduction of nitrate to nitrite was inhibited or not inhibited according to the type of strain. The bacteria broke down the chlorate partially or completely, according to the strains and the sustrates.