Unoccupied Topological States on Bismuth Chalcogenides

The unoccupied part of the band structure of topological insulators Bi$_2$Te$_{x}$Se$_{3-x}$ ($x=0,2,3$) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly-dispersing surface states are found at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi$_2$Se$_3$ and Bi$_2$Te$_2$Se. In Bi$_2$Te$_3$ small structural variations can change the character of the local energy gap depending on which an unoccupied Dirac state does or does not exist. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state

Electronic properties and phase transitions in low-dimensional semiconductors

We present the first review of the current state of the literature on electronic properties and phase transitions in TlX and TlMX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi- and photoconductivity, non-linear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of TlX and TlMX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor-metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. Electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.Comment: 70 pages, 38 figure

CARDIAC ARRHYTHMIA AND CONDUCTION DISTURBANCES IN PATIENTS WITH SYSTEMIC SCLEROSIS

Aim: To assess prevalence of certain cardiac arrhythmias and conduction disturbances in the Russian population of systemic sclerosis patients using standard 12-lead and 24-hour electrocardiography (ECG); to estimate correlation between cardiac arrhythmia and clinical features of systemic sclerosis. Materials and methods: 80 systemic sclerosis patients and 60 sex- and age-matched controls were included. All patients underwent standard 12-lead and 24-hour ECG. Results: Arrhythmias on standard 12-lead ECG were demonstrated in 14 patients (17.5%) including sinus arrhythmia in 2 cases and premature beats in 13 cases (16%). Supraventricular (SV) and ventricular (V) ectopic beats were recorded in 5 (6%) and 7 (9%) patients, respectively; in one patient both SV and V ectopic beats were found. ECG signs of focal fibrosis were demonstrated in 9 patients (11%). In 24-hour ECG, frequencies of SV and V ectopic beats were 40 and 65%, respectively. Compared to the controls, systemic sclerosis patients had significantly higher prevalence and severity of cardiac arrhythmia. 36% of patients had high grade ventricular premature beats, associated with potential risk of life-threatening arrhythmia and sudden cardiac death. Conclusion: Cardiac arrhythmias and conduction disturbances are found in the majority of patients with systemic sclerosis. Standard ECG does not reflect true prevalence of cardiac arrhythmia in systemic sclerosis. In systemic sclerosis patients, 24-hour ECG is recommended as obligate method for initial examination and treatment efficacy control

TRADITIONAL RISK FACTORS FOR CARDIOVASCULAR DISEASES IN SYSTEMIC SCLEROSIS AND THEIR RELATIONSHIP TO STRUCTURAL CHANGES OF THE HEART

<p><strong>Objective:</strong> to determine the frequency of traditional risk factors (TRFs) for cardiovascular diseases (CVD) in patients with systemic sclerosis (SS) and to analyze their relationship to the clinical manifestations of SS, as well as to structural changes, as evidenced by echocardiography (EchoCG).<br /><strong></strong></p><p><strong>Subjects and methods.</strong> The investigation enrolled 125 patients with SS and 50 sex- and age-matched, apparently healthy individuals included in a control group. Standard electrocardiography was performed in all and EchoCG – in 121 patients. The Systematic Coronary Risk Evaluation (SCORE) scale was used to assess the risk of fatal CVD in 100 patients with SS and in 47 control individuals within 10 years.<br /><strong></strong></p><p><strong>Results and discussion.</strong> The frequency of TFRs in patients with SS was not significantly different from that in the control group, except for the occurrence of hypercholesterolemia and increased body mass index (BMI). In SS, BMI &gt;25 kg/m2 was observed significantly more often and the frequency of hypercholesterolemia was lower than in the controls (p &lt;0.018). Hypertension and diabetes mellitus were slightly more frequently encountered in SS patients than in the controls, but this difference was insignificant. Taking into account the Russian Society of Cardiology (RSC) guidelines, the cardiovascular risk (CVR) was assessed with the SCORE scale. A very high CVR was much more common in SS and a moderate CVR was much more frequently seen in the control group. There were no substantial differences in the frequency of low and high CVRs. SS is characterized by the increased frequency of high total CVD risk as compared to the controls. Hypertension, overweight, and over 50 years of age were associated with more obvious structural heart disease.<br /><strong></strong></p><p><strong>Conclusion.</strong> TRFs make a substantial contribution to the formation of a high CVR in patients with SS, promoting the development of atherosclerosis and its complications. Assessment of TGFs in SS patients will facilitate identifying patients at high risk for cardiovascular death and timely prescribing therapy. Hypertension is an important TGF that in SS is associated with considerable structural changes in the heart; therefore adequate blood pressure control is of importance in improving SS prognosis especially in patients older than 50 years.</p

STRUCTURAL AND FUNCTIONAL CHANGES EVALUATED BY ECHOCARDIOGRAPHY IN PATIENTS WITH SYSTEMIC SCLEROSIS AND HEART RATE VARIABILITY

Objective: to estimate heart rate variability (HRV) in patients with systemic sclerosis (SS) and to investigate their relationship to echocardiographic structural and functional changes in the heart.Subjects and methods. The investigation enrolled 125 patients with SS and 50 gender- and age-matched apparently healthy individuals who made up a control group. In addition to clinical examinations, 73 patients underwent HRV assessment from 24-hour Holter electrocardiogram (ECG) monitoring results and 121 patients had echocardiography (EchoCG). 24-hour Holter ECG monitoring was carried out in all control individuals.Results and discussion. Examination of the main parameters of time-domain HRV in patients with SS revealed a significant decline in all temporal and spectral indices, except for the mean R–R interval duration (meanNN), as compared with the control group. EchoCG detected a variety of changes, primarily the induration and calcification of aortic and mitral valves in most patients. Left ventricular diastolic dysfunction was encountered in almost half of the patients with SS. Eight patients had a lower left ventricular ejection fraction (LVEF), which was &lt;55%. Studying the association of HRV values with separate EchoCG parameters revealed significant inverse correlations of the mean standard deviation of R–R intervals in 5-minute recording segments during 24 hours with the thickness of the interventricular septum (r = -0.18; p &lt; 0.05) and with the induration of the aortic valve (r = -0.18; p &lt; 0.05); the square root mean squared of successive differences (RMSSD, ms) for R–R intervals and the percentage of adjacent R–R intervals that varied by more than 50 ms (pNN50) correlated with the induration of the aortic valve (r = -0.23; p&lt;0.05 and r = -0.25; p &lt; 0.05, respectively), with the presence of pericarditis (r = -0.24; p &lt; 0.05 and r = -0,27; p &lt; 0.05, respectively), and with the level of pulmonary artery systolic pressure (r = -0.23; p &lt; 0.05 and r = -0.27; p &lt; 0.05, respectively). There was also a direct correlation of rMSSD and pNN50 with LVEF (r = 0.27; p &lt; 0.05 and r = 0.29, respectively; p &lt; 0.05). A significant decrease in rMSSD and pNN50 was ascertained in hypertensive patients as compared to non-hypertensive patients (18.1±4.8 and 24.9±13.3; 2.3±1.8 and 5.7±6.5, respectively; p &lt; 0.05). Conclusion. Comprehensive examination using EchoCG and 24-hour Holter ECG monitoring revealed the high frequency and severity of significant cardiac changes in SS. The temporal spectrum analysis of HRV could confirm a significant reduction in the function of both the sympathetic and parasympathetic parts of the autonomic nervous system. Decreased HRV was associated with SS severity and activity, traditional cardiovascular risk factors, and cardiac structural changes