Prediction and observation of an antiferromagnetic topological insulator.

Magnetic topological insulators are narrow-gap semiconductor materials that combine non-trivial band topology and magnetic order1. Unlike their nonmagnetic counterparts, magnetic topological insulators may have some of the surfaces gapped, which enables a number of exotic phenomena that have potential applications in spintronics1, such as the quantum anomalous Hall effect2 and chiral Majorana fermions3. So far, magnetic topological insulators have only been created by means of doping nonmagnetic topological insulators with 3d transition-metal elements; however, such an approach leads to strongly inhomogeneous magnetic4 and electronic5 properties of these materials, restricting the observation of important effects to very low temperatures2,3. An intrinsic magnetic topological insulator-a stoichiometric well ordered magnetic compound-could be an ideal solution to these problems, but no such material has been observed so far. Here we predict by ab initio calculations and further confirm using various experimental techniques the realization of an antiferromagnetic topological insulator in the layered van der Waals compound MnBi2Te4. The antiferromagnetic ordering  that MnBi2Te4  shows makes it invariant with respect to the combination of the time-reversal and primitive-lattice translation symmetries, giving rise to a ℤ2 topological classification; ℤ2 = 1 for MnBi2Te4, confirming its topologically nontrivial nature. Our experiments indicate that the symmetry-breaking (0001) surface of MnBi2Te4 exhibits a large bandgap in the topological surface state. We expect this property to eventually enable the observation of a number of fundamental phenomena, among them quantized magnetoelectric coupling6-8 and axion electrodynamics9,10. Other exotic phenomena could become accessible at much higher temperatures than those reached so far, such as the quantum anomalous Hall effect2 and chiral Majorana fermions3.

Band structure engineering in topological insulator based heterostructures.

The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.

Ultrasonic intensification of ozone and electrochemical destruction of 1,3-dinitrobenzene and 2,4-dinitrotoluene.

The removal of nitroaromatics from polluted water is difficult due to their high stability to conventional treatment methods. This paper presents a method for the destruction of 1,3-dinitrobenzene and 2,4-dinitrotoluene in aqueous solutions. The compounds are shown to be stable to reaction with ozone, even under ultrasonic activation. The use of ultrasound enhances the rate of electrochemical reduction but the overall rate of reaction is still slow. However, the simultaneous application of ultrasound and ozonation to the electrochemical reaction allows virtually complete destruction of the compounds in short times. The effect is attributed to the ultrasonic enhancement of the electrochemical process giving intermediates that are susceptible to ozone oxidation. While further analytical work is needed to deduce the exact contributions of the various possible degradation mechanisms, the work demonstrates the synergies that can be gained by using combined techniques for the destruction of these difficult compounds.

[Mathematical simulation of the selection process in a dairy herd]. / Matematicheskaia imitatsiia selektsionnogo protsessa v stade molochnogo skota.

The effect of intensity of selection for parentage and individual performance of cows, according to age structure, genetic gain and average production was studied in a dairy unit per 2000 stable places. The maximum genetic gain was achieved as a result of combined selection of cow dams when 66 per cent of heifers were selected for parentage and 20 per cent of first-calvers were culled for their performance (26.5 replacements). With increase in the selection intensity, the average milk yield increased by 3-6 per cent but the genetic efficiency of cow dams selection decreased by 10-37 per cent.

[Mechanism of inactivation and mutagenesis induced by ethyleneimine in Drosophila germ cells. V. Relation of complete and mosaic mutations during the supplementary action of high temperature]. / Izuchenie mekhanizma inaktivatsii i mutageneza pri deistvii étilenimina na polovye kletki drozofily. Soobshchenie V. Sootnoshenie polynkh i mozaichnykh mutatsii pri dopolnitel'nom deistvii vysokoi temperatury

Supplementary effect of high temperature (37 degrees C) an hour after the treatment of mature sperms of Drosophila with ethylene imine resulted in an increased level of the inactivation (the frequency of dominant lethal mutation). The frequency of complete mutations (recessive sex-linked lethal mutations) increased by the supplementary effect of high temperature at low doses of E1, and it did not change under a comparatively high dose of the mutagen. The frequency of mosaic mutations decreased under the effect of high temperature at both doses of E1. No effect of high temperature was observed in 4 and 24 h after the E1 treatment. The results obtained are discussed in connection with the proportion of inactivation and mutagenesis under the effect of chemical mutagens on Drosophila germ cells.

[A method for covering the subcutaneous fat in the surgery of postoperative ventral hernias]. / Sposob obkladyvaniia podkozhnoi kletchatki v khirurgii posleoperatsionnykh ventral'nykh gryzh.

The authors suggested a method for covering the subcutaneous fat and tested it in 115 operations for postoperative ventral hernias. The method is based on vertical arrangement of gauze napkins covering one another in turn by one third. All of the operated on patients had no inflammatory complications of the postoperative wound. The authors claim this method to be among the elements preventing postoperative inflammatory complications of wounds.

[Surgical treatment of choledochal cyst]. / Khirurgicheskoe lechenie kist kholedokha.

The article analyses experience with the treatment of 5 female patients with a rare disease of the extrahepatic biliary tract--cysts of the choledochus. Errors and complications in surgical tactics are shown. The authors recommend the means for improving the diagnosis and the choice of adequate tactics in various surgical situations in cysts of the choledochus. Cholecystectomy with creation of a +cysto-duodeno-anastomosis and removal of the cause of chronic impairment of duodenal patency is the adequate operation.

[Tactics in cholelithic intestinal obstruction]. / Taktika pri zhelchnokamennoi kishechnoi neprokhodimosti.

Tactical manipulations in cholelithic intestinal obstruction are analysed. The authors had 4 cases with cholelithic intestinal obstruction, in one of them obstruction with a gallstone occurred again on the 23rd postoperative day. Relaparotomy, correction of the obstruction, and cholecystectomy with one-stage removal of a biliodigestive fistula had to be conducted. It is pointed out that in obstruction of the intestine with a gallstone correction of the obstruction is a more sparing operation than one-stage cholecystectomy and removal of a biliodigestive fistula. With the use of this tactics there were no fatal outcomes.

[Cohen's operation in the treatment of vesico-ureteral reflux in children]. / Operatsiia Koéna pri lechenii puzyrno-mochetochnikovogo refliuksa u detei.

The present study is a review of the results of Cohen's operation performed on 43 ureters in 32 children. Treatment results were assessed through the comparison of cystographic and 131I-hippuran renographic findings obtained before and after surgery. Urodynamic recovery in the affected ureter was demonstrated in all children. One year after surgery, there was no improvement in the activity of the resected kidney in 37% of patients. In the remaining patients, secretion improved by 10-13% in the affected kidney. Seventeen children returned for follow-up examination 2 years after surgery. The activity of the affected kidney and the contralateral one improved in 13 of 17 patients. There was no upper urinary retention due to ureteral stricture in any of the children. The rate of recurrent vesico-ureteral reflux (VUR) was 5.3%. Augmentation or persistence of purification deficiency in the affected kidney, detected in 12 patients at first postoperative follow-up, was qualified as a result of aggravated chronic pyelonephritis rather than that of surgical complications related to methodologic specifics. This assumption was verified by the results of the next follow-up examination 2 years after surgery. Therefore, Cohen's method can be recommended for large-scale application in the treatment of VUR in children and is expected to essentially reduce the rate of relapses and improve the standards of surgical care of children with this grave disease.