Dielectric environment and/or random disorder effects on free, charged and localized excitonic states in monolayer WS2.

Excitonic effects play an important role on the optoelectronic behavior of atomically thin two-dimensional (2D) crystals of the WS2 transition metal dichalcogenide. In this paper, neutral and charged exciton behaviors in monolayer WS2 are handled within effective-mass approximation for which the critical parameters are ensured from our ab initio calculations. Firstly, we reveal an exciton series with a novel energy dependence on the orbital angular momentum. Considerable control of the dielectric environment on neutral and charged excitons binding energies is elucidated. We demonstrate that for accepted values of effective masses, the negative and positive trion binding energies should be identical. Secondly, localization of neutral exciton center of mass motion by random potential arising from monolayer defects is also studied. The results obtained are in agreement with available experimental work.

Two carriers in vertically coupled quantum dots: magnetic field effect.

We study a two-charge-carrier (two holes or two electrons) quantum dot molecule in a magnetic field. In comparison with the electron states in the double quantum dot, the switching between the hole states is achieved by changing both the inter-dot distance and magnetic field. We use harmonic potentials to model the confining of two charge carriers and calculate the energy difference delta E between the two lowest energy states with the Hund-Mulliken technique, including the Coulomb interaction. Introducing the Zeeman effect, we note a ground-state crossing, which can be observed as a pronounced jump in the magnetization at a perpendicular magnetic field of a few Tesla. The ground states of the molecule provide a possible realization for a quantum gate.

[Non-typhoid Salmonella in pediatric patients in Tunis (Hospital Charles-Nicolle) from 1980 to 1991]. / Salmonelles non typhoïdiques en milieu pédiatrique a Tunis (Hôpital Charles-Nicolle) de 1980 a 1991.

252 nontyphoidic salmonellae strains isolated from pediatrics were identified by using standard laboratory procedures and were serotyped with commercial antisera. Antibiotic susceptibility tests were performed by the agar diffusion method. Mostly isolates obtained from feces (182) and blood (67) and 89% of them from newborns and nursings. S. sér. Wien represented 75% of the isolates. The other serovars were essentially S. sér Typhimurium, S. sér Infantis and S. sér Enteritidis. All the isolates of S. sér Wien and S. sér Typhimurium were resistant to amoxicillin, carbenicillin, cephalothin, streptomycin, chloramphenicol and tetracycline from 1980. From 1987 S. sér Wien isolates developed resistance to cefotaxime and amikacin. Distribution nontyphoidic salmonellae strains according to the year was variable. Maximal isolates were in September and October. Two major epidemics were observed in this study, in 1982 and 1989. 94% of the strains determined nosocomial infections. The source of infection was established during the epidemic of 1989. The application of hygiene measures led to decline the number of isolates in 1990 and their disappearance in 1991, any strains of S. sér Wien was isolated.

[Dermatitis herpetiformis and chronic diarrhea: a case]. / Dermatite herpétiforme et diarrhée chronique: une observation.

We report on a case of dermatitis herpetiformis in an eight-year-old boy presenting diarrhoea, short stature and characteristic skin rash. Jejunal biopsy showed a partial villous atrophy. The diagnosis was confirmed by immunofluorescence which showed granular IgA deposits in the papillary dermis. On a gluten-free diet associated with dapsone, the child gained weight and height, with partial resolution of the rash.