Synthesis and surface control of colloidal Cr3+-doped SnO2 transparent magnetic semiconductor nanocrystals.

The synthesis of colloidal Cr(3+)-doped SnO(2) nanocrystals prepared under mild conditions via a hydrolysis method is described. We show by means of nanocrystal surface ligand exchange that even under mild reaction conditions a significant fraction of the dopant ions reside on the nanocrystal surfaces. Two different approaches aimed at achieving internal dopant incorporation-surface-bound dopant complexation and isocrystalline shell growth-are described and compared. While free-standing nanocrystals are paramagnetic, the films prepared from the same nanocrystals exhibit ferromagnetic ordering at room temperature. The measured magnetization is associated with structural defects formed at the interfaces of nanocrystals in their films, and discussed in terms of the defect-related itinerant-electron-mediated mechanism. The observed ferromagnetism is compared to ferromagnetism in Cr(3+)-doped In(2)O(3) nanocrystalline films. These results demonstrate the possibility of controlling surface structure and composition of doped oxide nanocrystals using different approaches. Furthermore, this work emphasizes the importance of surface structure and composition in tailoring properties of doped multifunctional transparent conducting oxide nanostructures.

Electronic absorption spectroscopy of cobalt ions in diluted magnetic semiconductor quantum dots: demonstration of an isocrystalline core/shell synthetic method.

This paper reports the application of ligand-field electronic absorption spectroscopy to probe Co(2+) dopant ions in diluted magnetic semiconductor quantum dots. It is found that standard inverted micelle coprecipitation methods for preparing Co(2+)-doped CdS (Co(2+):CdS) quantum dots yield dopant ions predominantly bound to the nanocrystal surfaces. These Co(2+):CdS nanocrystals are unstable with respect to solvation of surface-bound Co(2+), and time-dependent absorption measurements allow identification of two transient surface-bound intermediates involving solvent-cobalt coordination. Comparison with Co(2+):ZnS quantum dots prepared by the same methods, which show nearly isotropic dopant distribution, indicates that the large mismatch between the ionic radii of Co(2+) (0.74 A) and Cd(2+) (0.97 A) is responsible for exclusion of Co(2+) ions during CdS nanocrystal growth. An isocrystalline core/shell preparative method is developed that allows synthesis of internally doped Co(2+):CdS quantum dots through encapsulation of surface-bound ions beneath additional layers of CdS.

[Perforation of acute diverticulitis of the cecum]. / Perforacija akutnog divertikulitisa cekuma.

Two cases of perforations in diverticulitis of the caecum are presented. The disease was manifested with the following complications: inflammation and perforation. Diverticula of the caecum are asymptomatic, accidentally found during surgery undertaken for other reasons. Out two patients were admitted to the hospital as emergency-patients, with the suspicion of acute appendicitis. Symptoms were unusual. Both patients were operated on. Histopathologic findings confirmed the diagnosis of acute perforated diverticulitis of the caecum in both cases.

[Breech presentation in multiple pregnancy]. / Porodaj zatkom u viseplodnoj trudnoci.

A retrospective analysis of the ten-year experience with the delivery of twins in breech presentation was performed in this paper. Out of 17,300 deliveries there were 173 deliveries of twins which accounted for 1%. From that number there were 99 (57.2%) multiple deliveries where one or both of the twins were in breech presentation. Deliveries in this group were more frequently terminated surgically (31.8%) than in the whole population of deliveries of twins (x2 = 26,182; p less than 0.001). In this group of 99 deliveries, out of 198 twins 117 were born with the body mass less than 2,500 g (59.1%) and 56 (56.6%) pregnancies were terminated prior to 37th week of gestation. Perinatal mortality was greater in the group of twins with breech presentation (12.52:9.8%). Breech presentation put the fetus at risk due to two reasons--multiple pregnancy (high prematurity and newborn with the delay in fetal growth and development) on one hand and complications which may arise during the breech presentation on the other.