Resolving the Spatial Structures of Bound Hole States in Black Phosphorus.

Understanding the local electronic properties of individual defects and dopants in black phosphorus (BP) is of great importance for both fundamental research and technological applications. Here, we employ low-temperature scanning tunnelling microscope (LT-STM) to probe the local electronic structures of single acceptors in BP. We demonstrate that the charge state of individual acceptors can be reversibly switched by controlling the tip-induced band bending. In addition, acceptor-related resonance features in the tunnelling spectra can be attributed to the formation of Rydberg-like bound hole states. The spatial mapping of the quantum bound states shows two distinct shapes evolving from an extended ellipse shape for the 1s ground state to a dumbbell shape for the 2px excited state. The wave functions of bound hole states can be well-described using the hydrogen-like model with anisotropic effective mass, corroborated by our theoretical calculations. Our findings not only provide new insight into the many-body interactions around single dopants in this anisotropic two-dimensional material but also pave the way to the design of novel quantum devices.

Two-dimensional exciton properties in monolayer semiconducting phosphorus allotropes.

Excitons play a key role in technological applications since they have a strong influence on determining the efficiency of photovoltaic devices. Recently, it has been shown that the allotropes of phosphorus possess an optical band gap that can be tuned over a wide range of values including the near-infrared and visible spectra, which would make them promising candidates for optoelectronic applications. In this work we carry out ab initio many-body perturbation theory calculations to study the excitonic effects on the optical properties of two-dimensional phosphorus allotropes: the case of blue and black monolayers. We elucidate the most relevant optical transitions, exciton binding energy spectrum as well as real-space exciton distribution, particularly focusing on the absorption spectrum dependence on the incident light polarization. In addition, based on our results, we use a set of effective hydrogenic models, in which the electron-hole Coulomb interaction is included to estimate exciton binding energies and radii. Our results show an excellent agreement between the many-body methodology and the effective models.

[Regional intraosseous thrombolytic therapy in comprehensive treatment of patients with diabetic foot syndrome]. / Regionarnaia vnutrikostnaia tromboliticheskaia terapiia v kompleksnom lechenii sindroma diabeticheskoi stopy.

The authors assessed efficacy of regional intraosseous administration of urokinase medac in comprehensive treatment of patients with complicated forms of diabetic foot syndrome by means of analysing therapeutic results in a total of 65 patients presenting with pyonecrotic complications of diabetic foot. The patients were subdivided into 2 groups. The control group was composed of 35 patients receiving basic therapy. The study group comprised 30 patients subjected to comprehensive treatment including regional intraosseous (into the heel bone of the affected limb) administration of urokinase medac at a dose of 100 thousand IU for 5 days. Efficacy of treatment was evaluated by the course of the wound process, indices of haemostasis, free radical oxidation, results of surgical treatment. In patients of the Study Group the terms of wound purification from pyonecrotic masses amounted to 9.8±0.3 days, which was by 4.7 days less than in the Control Group patients (p<0.01), marginal epithelialization of wounds also occurred averagely by 6.4 days faster. On day 22 of using the basic therapy alone, the haemostasis system preserved the condition of coagulation activity. The Study Group patients as early as on day 5 of treatment demonstrated shifts towards normocoagulation. In the Control Group by day 22 of treatment, the level of malonic dialdehyde decreased by 18.5%, the index of catalase activity increased by 24.6% (p<0.05); in the Study Group the level of malonic dialdehyde decreased by 42.6% and catalase activity increased by 69.4% (p<0.01). On the background of using urokinase the number of high amputations decreased by 18% and the number of operations with the supporting function preserved decreased by 12% as compared with basic therapy alone. A conclusion was made that additional use of regional intraosseous administration of urokinase medac as compared with basic therapy alone promoted a more significant decrease in the coagulation activity of blood and the level of free-radical lipid oxidation, stimulation of regenerative processes, as well as improvement of outcomes of surgical treatment.

Multiferroic Two-Dimensional Materials.

The relation between unusual Mexican-hat band dispersion, ferromagnetism, and ferroelasticity is investigated using a combination of analytical, first-principles, and phenomenological methods. The class of material with Mexican-hat band edge is studied using the α-SnO monolayer as a prototype. Such a band edge causes a van Hove singularity diverging with 1/sqrt[E], and a charge doping in these bands can lead to time-reversal symmetry breaking. Herein, we show that a material with Mexican-hat band dispersion, α-SnO, can be ferroelastic or paraelastic depending on the number of layers. Also, an unexpected multiferroic phase is obtained in a range of hole density for which the material presents ferromagnetism and ferroelasticity simultaneously.

[Macular drusen variability: multimodal imaging potential]. / Variabel'nost' makulyarnykh druz: vozmozhnosti mul'timodal'noi vizualizatsii.

Insufficient and controversial knowledge about the macular drusen (MD), a lack of scientifically proven management methods for drusen and their strong correlation with AMD active progression makes MD an important area of research. AIM: The purpose of the study ­ to assess clinical feature of MD using modern digital imaging technologies. MATERIAL AND METHODS: Patients with both hard and soft drusen were studied using fluorescein angiography, swept-source optical coherence tomography (OCT), OCT-angiography, autofluorescence (both short-wavelength and near infra-red), scanning laser ophthalmoscopy in Multicolor mode. The retina, choroid and vitreoretinal interface were assessed on 50 patients with AMD and drusen using different imaging modalities. An additional group of the study was presented by 5 patients with geographic atrophy (GA) formed as a result of soft drusen fading, where retrospective assessment of the OCT scans was performed with special attention to the signs of soft drusen regression associated with atrophy of the overlying RPE. RESULTS: Two types of hard drusen were defined as the reticular pseudodrusen and the cuticular drusen. The qualitative and comparative analysis of data for each type of MD was performed. Vitreoretinal interface evaluation demonstrated the correlation between vitreomacular adhesion and mixed reticular and cuticular drusen. The choroidal thickness assessment in 9 different macular sectors in drusenoid eyes does not reveal a significant difference with control group. All of the analysed drusen-faded-eyes initially had been presented with OCT patterns of "nascent" GA. CONCLUSION: The modern retinal imaging techniques enable new approach to the diagnostic differentiation and description of various macular drusen types. The value of these methods for AMD prognosis is yet to be further investigated.

Tunneling Plasmonics in Bilayer Graphene.

We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At subnanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in the former case but are negligible in the latter. We found through infrared nanoimaging that bilayer graphene supports plasmons with a higher degree of confinement compared to single- and double-layer graphene, a direct consequence of interlayer tunneling. Moreover, we were able to shut off plasmons in bilayer graphene through gating within a wide voltage range. Theoretical modeling indicates that such a plasmon-off region is directly linked to a gapped insulating state of bilayer graphene, yet another implication of interlayer tunneling. Our work uncovers essential plasmonic properties in bilayer graphene and suggests a possibility to achieve novel plasmonic functionalities in graphene few-layers.

[Bioimpedance analysis in medicine].

This review covers the problems of using of bioimpedancemetry in medicine. This method is currently becoming more widely used for diagnostics of various pathological disorders. The advantages and disadvantages of non-invasive and invasive bioelectrical impedance analysis were described. It was revealed that the results of invasive bioimpedancemetry were more accurate in comparison with the results of non-invasive bioimpedancemetry, and changed due to morphological damages of tissues. This review provides an overview of the practicability of more extensive using of invasive bioelectrical impedance analysis in medicine.

Spin-orbit proximity effect in graphene.

The development of spintronics devices relies on efficient generation of spin-polarized currents and their electric-field-controlled manipulation. While observation of exceptionally long spin relaxation lengths makes graphene an intriguing material for spintronics studies, electric field modulation of spin currents is almost impossible due to negligible intrinsic spin-orbit coupling of graphene. In this work, we create an artificial interface between monolayer graphene and few-layer semiconducting tungsten disulphide. In these devices, we observe that graphene acquires spin-orbit coupling up to 17 meV, three orders of magnitude higher than its intrinsic value, without modifying the structure of the graphene. The proximity spin-orbit coupling leads to the spin Hall effect even at room temperature, and opens the door to spin field effect transistors. We show that intrinsic defects in tungsten disulphide play an important role in this proximity effect and that graphene can act as a probe to detect defects in semiconducting surfaces.

Strain-induced gap modification in black phosphorus.

The band structure of single-layer black phosphorus and the effect of strain are predicted using density functional theory and tight-binding models. Having determined the localized orbital composition of the individual bands from first principles, we use the system symmetry to write down the effective low-energy Hamiltonian at the Γ point. From numerical calculations and arguments based on the crystal structure of the material, we show that the deformation in the direction normal to the plane can be used to change the gap size and induce a semiconductor-metal transition.

Tunable phonon polaritons in atomically thin van der Waals crystals of boron nitride.

van der Waals heterostructures assembled from atomically thin crystalline layers of diverse two-dimensional solids are emerging as a new paradigm in the physics of materials. We used infrared nanoimaging to study the properties of surface phonon polaritons in a representative van der Waals crystal, hexagonal boron nitride. We launched, detected, and imaged the polaritonic waves in real space and altered their wavelength by varying the number of crystal layers in our specimens. The measured dispersion of polaritonic waves was shown to be governed by the crystal thickness according to a scaling law that persists down to a few atomic layers. Our results are likely to hold true in other polar van der Waals crystals and may lead to new functionalities.

Experimental study of the diagnostic potentialities of bioimpedance measurement in acute intestinal obstruction.

The dynamics of impedance values of the small and large intestine, parietal peritoneum, and greater omentum was analyzed during different periods of experimental acute intestinal obstruction. The impedance was below the normal, which indicated progressive microcirculatory disorders and necrosis of the intestinal wall. The histomorphological picture of healing of anastomoses created after resection of the intestine with consideration for bioimpedance values and of anastomoses created after resection of the intestine in a priori viable tissues virtually did not differ.

Electronic and plasmonic phenomena at graphene grain boundaries.

Graphene, a two-dimensional honeycomb lattice of carbon atoms of great interest in (opto)electronics and plasmonics, can be obtained by means of diverse fabrication techniques, among which chemical vapour deposition (CVD) is one of the most promising for technological applications. The electronic and mechanical properties of CVD-grown graphene depend in large part on the characteristics of the grain boundaries. However, the physical properties of these grain boundaries remain challenging to characterize directly and conveniently. Here we show that it is possible to visualize and investigate the grain boundaries in CVD-grown graphene using an infrared nano-imaging technique. We harness surface plasmons that are reflected and scattered by the graphene grain boundaries, thus causing plasmon interference. By recording and analysing the interference patterns, we can map grain boundaries for a large-area CVD graphene film and probe the electronic properties of individual grain boundaries. Quantitative analysis reveals that grain boundaries form electronic barriers that obstruct both electrical transport and plasmon propagation. The effective width of these barriers (∼10-20 nm) depends on the electronic screening and is on the order of the Fermi wavelength of graphene. These results uncover a microscopic mechanism that is responsible for the low electron mobility observed in CVD-grown graphene, and suggest the possibility of using electronic barriers to realize tunable plasmon reflectors and phase retarders in future graphene-based plasmonic circuits.

[Intra-arterial thrombolytic therapy of ischaemic complications of lower-limb diabetic angiopathy].

Based on the parameters of haemostasis, free radical oxidation and endogenous intoxication the study was aimed at assessing efficacy of intra-arterial administration of urokinase medac in complicated forms of lower-limb diabetic angiopathy. The authors assessed the outcomes of treating a total of 32 patients with complicated forms of lower-limb diabetic angiopathy on the background of basic therapy and 30 patients whose combined therapy included intra-arterial administration of the thrombolytic agent urokinase medac, also studying the indices of haemostasis, endogenous intoxication, free-radical oxidation and antioxidant defence. At admission to hospital, patients were found to have shifts of the coagulogram towards hypercoagulation. The group of patients receiving intra-arterial administration of urokinase showed that the examined parameters on day 20 of treatment as compared with basic therapy alone increased: those of coagulability by 6% (p<0.05), activated partial thromboplastin time by 14% (p<0.01), thrombin time by 9.2% (p<0.01), antithrombin III by 7% (p<0.001). The fibrinogen level decreased by 9% (p<0.05), malonic dialdehyde concentration dropped by 30% (p<0.001), the concentrations of catalase and superoxide dismutase elevated by 55% (p<0.001) and 42%, respectively (p<0.05). The effective concentration of albumin by day 20 increased up to 42.03±0.36 g/L and was by 5% higher as compared with the basic therapy alone (p<0.005). The toxicity index fell to 0.04+0.1 which was by 50% less than after basic therapy. Conclusion. Intra-arterial administration of urokinase medac in treatment of lower-limb diabetic angiopathy considerably normalizes elevated processes of coagulation, accompanied by decreased intensity of free-radical oxidation and followed by elevated concentration of the antioxidant protection enzymes and a decrease in the degree of endogenous intoxication.

Gate-tuning of graphene plasmons revealed by infrared nano-imaging.

Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such medium--graphene--is amenable to convenient tuning of its electronic and optical properties by varying the applied voltage. Here, using infrared nano-imaging, we show that common graphene/SiO(2)/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nanometres at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and the wavelength of these plasmons by varying the gate voltage. Using plasmon interferometry, we investigated losses in graphene by exploring real-space profiles of plasmon standing waves formed between the tip of our nano-probe and the edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene. Standard plasmonic figures of merit of our tunable graphene devices surpass those of common metal-based structures.

Apparent power-law behavior of conductance in disordered quasi-one-dimensional systems.

The dependence of hopping conductance on temperature and voltage for an ensemble of modestly long one-dimensional wires is studied numerically using the shortest-path algorithm. In a wide range of parameters this dependence can be approximated by a power law rather than the usual stretched-exponential form. The relation to recent experiments and prior analytical theory is discussed.

On the origin of the genetic code: signatures of its primordial complementarity in tRNAs and aminoacyl-tRNA synthetases.

If the table of the genetic code is rearranged to put complementary codons face-to-face, it becomes apparent that the code displays latent mirror symmetry with respect to two sterically different modes of tRNA recognition. These modes involve distinct classes of aminoacyl-tRNA synthetases (aaRSs I and II) with recognition from the minor or major groove sides of the acceptor stem, respectively. We analyze the anticodon pairs complementary to the face-to-face codon couplets. Taking into account the invariant nucleotides on either side (5' and 3'), we consider the risk of anticodon confusion and subsequent erroneous aminoacylation in the ancestral coding system. This logic leads to the conclusion that ribozymic precursors of tRNA synthetases had the same two complementary modes of tRNA aminoacylation. This surprising case of molecular mimicry (1) shows a key potential selective advantage arising from the partitioning of aaRSs into two classes, (2) is consistent with the hypothesis that the two aaRS classes were originally encoded by the complementary strands of the same primordial gene and (3) provides a 'missing link' between the classic genetic code, embodied in the anticodon, and the second, or RNA operational, code that is embodied mostly in the acceptor stem and is directly responsible for proper tRNA aminoacylation.

A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express.

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 microm, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at approximately 115 km and varies with solar zenith angle over a range of approximately 10 km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96 km +/- 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted.

South-polar features on Venus similar to those near the north pole.

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.

A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO.

Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of approximately 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.

[Prevention of complications in combined (laser and extrascleral) treatment of retinal detachment]. / Profilaktika oslozhnenií pri kombinirovannom (lazernom i ékstraskleral'nom) lechenii otsloek setchatki.

The main factors of risk were analyzed and indications for preventive laser coagulation were specified in the paper. An approach was defined to ensure a maximally sparing surgical and stage-based laser treatment in retinal detachment, which is targeted at preventing its relapses and at improving the functional results.