Magnetization driven metal - insulator transition in strongly disordered Ge:Mn magnetic semiconductors

We report on the temperature and field driven metal-insulator transition in disordered Ge:Mn magnetic semiconductors accompanied by magnetic ordering, magnetoresistance reaching thousands of percents and suppression of the extraordinary Hall effect by a magnetic field. Magnetoresistance isotherms are shown to obey a universal scaling law with a single scaling parameter depending on temperature and fabrication. We argue that the strong magnetic disorder leads to localization of charge carriers and is the origin of the unusual properties of Ge:Mn alloys.Comment: 10 pages, 5 figure

Comparison of the methods of the correction of the venous thromboembolism in bariatric surgery using the low-frequency thromboelastography: our experience

Introduction. In the world of obesity and its complications annually dies about 2.8 million people. Obesity is an independent factor of the risk of venous thromboembolism (VTE), as it interferes with the internal and external pathways of coagulation, as well as in anticoagulant mechanisms, which leads to a hypercoagulation state. Reducing excess body weight in patients with morbid obesity by bariatric surgery is becoming increasingly popular, as barium therapy is an effective means of treating obesity and related concomitant diseases. Advantages of bariatric surgery are undeniable, as well as risks. Despite many blood coagulation studies, cases of thromboembolism in such patients are becoming more frequent, especially during surgical interventions and in the postoperative period, given that the operation is a trigger factor in the development of thromboembolism. Materials and methods. A hemostasis system was studied in 63 patients with BMI> 35 kg / m2. All patients were divided into 3 groups. 1 group (n=20) - patients who received combined therapy: Enoxaparin sodium 0.1% 0.2 ml / kg 2 times a day every 12 hours and Pentoxifylline 100 mg 2 times a day every 12 hours; The 2nd group (n= 17) - patients treated with: Enoxaparin sodium 0.1% 0.2 ml / kg 2 times daily for every 12 hours; Group 3 (control): 26 people with obesity, BMI> 35, not subject to bariatric surgery. The study of the hemostasis system was carried out using low-frequency piezoelectric thromboelastography (LPTEG) immediately after hospitalization and on 1,3,5 days after bariatry. The following blood coagulation constants were checked: Contact Coagulation Intensity; intensity of coagulation drive; maximum bunch density; Fibrinolytic activity is the index of retraction and lysis of the clot. Results. In patients of group 1 (anticoagulants + antiplatelet agents) the risk of thrombotic complications is lower, since this therapy has reduced the value at all stages of hemocoagulation to the reference values; Patients in group 2 (anticoagulants), despite the normalization of the coagulation unit, had an increase in the values of aggregation and fibrinolysis, relative to the norm, which means the risk of thrombotic complications remains high. Conclusions. The instrumental method of NPTEG allowed to adequately estimate the system of hemocoagulation in dynamics in patients with morbid obesity, with BMI ≥ 35 kg / m2; This category of patients has shown a high risk of VTE; It has been proved that for an adequate prevention of VTE in obese patients undergoing bariatric surgery, the combination of anticoagulants and antiplatelet agents is more effective than monotherapy with anticoagulants

Geology, geochemistry and gold-ore potential assessment within Akimov ore-bearing zone (the Altai Territory)

The article considers the geological setting of ore-bearing zone. Geochemical zoning of secondary dispersion haloes within Akimov ore-bearing zone was analyzed. Based on analytical data, distribution of gold mineralization trace-elements was examined. Geochemical associations were identified, analyzed and geometrized. The structure of abnormal geochemical field associated with gold-silver mineralization was determined. Three promising areas for exploration activities were identified

Divergent Perturbation Series

Various perturbation series are factorially divergent. The behavior of their high-order terms can be found by Lipatov's method, according to which they are determined by the saddle-point configurations (instantons) of appropriate functional integrals. When the Lipatov asymptotics is known and several lowest order terms of the perturbation series are found by direct calculation of diagrams, one can gain insight into the behavior of the remaining terms of the series. Summing it, one can solve (in a certain approximation) various strong-coupling problems. This approach is demonstrated by determining the Gell-Mann - Low functions in \phi^4 theory, QED, and QCD for arbitrary coupling constants. An overview of the mathematical theory of divergent series is presented, and interpretation of perturbation series is discussed. Explicit derivations of the Lipatov asymptotic forms are presented for some basic problems in theoretical physics. A solution is proposed to the problem of renormalon contributions, which hampered progress in this field in the late 1970s. Practical schemes for summation of perturbation series are described for a coupling constant of order unity and in the strong-coupling limit. An interpretation of the Borel integral is given for 'non-Borel-summable' series. High-order corrections to the Lipatov asymptotics are discussed.Comment: Review article, 45 pages, PD

Large Magnetoresistance of a Dilute pp-Si/SiGe/Si Quantum Well in a Parallel Magnetic Field

We report the results of an experimental study of the magnetoresistance $\rho_{xx}$ in two samples of $p$-Si/SiGe/Si with low carrier concentrations $p$=8.2$\times10^{10}$ cm$^{-2}$ and $p$=2$\times10^{11}$ cm$^{-2}$. The research was performed in the temperature range of 0.3-2 K in the magnetic fields of up to 18 T, parallel to the two-dimensional (2D) channel plane at two orientations of the in-plane magnetic field $B_{\parallel}$ against the current $I$: $B_{\parallel} \perp I$ and $B_{\parallel} \parallel I$. In the sample with the lowest density in the magnetic field range of 0-7.2 T the temperature dependence of $\rho_{xx}$ demonstrates the metallic characteristics ($d \rho_{xx}/dT>$0). However, at $B_{\parallel}$ =7.2 T the derivative $d \rho_{xx}/dT$ reverses the sign. Moreover, the resistance depends on the current orientation with respect to the in-plane magnetic field. At $B_{\parallel} \cong$ 13 T there is a transition from the dependence $\ln(\Delta\rho_{xx} / \rho_{0})\propto B_{\parallel}^2$ to the dependence $\ln(\Delta\rho_{xx} / \rho_{0})\propto B_{\parallel}$. The observed effects can be explained by the influence of the in-plane magnetic field on the orbital motion of the charge carriers in the quasi-2D system.Comment: revised: included AC conductivity experiments to study the role of localized state in transport; total 6 pages, 7 figures. Accepted PRB; to appear vol.79, Issue 2

Elastic properties of Gd5Si2Ge2 studied with an ultrasonic pulse-echo technique

We present the results of a study of the elastic properties of Gd5Si2Ge2, an alloy with giant magnetocaloric, magnetostrictive, and colossal magnetoresistive properties. Sound wave velocities measured in a number of different geometries allowed us to determine the whole elastic tensor for the monoclinic phase of this material. The anisotropy of the crystal is explored using the polar plots of the variations in the main crystallographic planes of the sound speed, the Young’s modulus, the shear modulus, and the linear compressibility. The effect of hydrostatic pressure on the Gd5Si2Ge2 properties is clarified. The acoustical axes are determined. The bulk modulus is estimated as 68.5 GPa; the Debye temperature is 250 K

Fractional quantum Hall states in a Ge quantum well

Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a SiGe/(001)Si substrate in the quantum Hall regime are reported. We analyse the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarised Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required