Carbon nanotube sponges as tunable materials for electromagnetic applications.

The microwave conductivity and permittivity of both single-walled and multi-walled carbon nanotube (SWCNT and MWCNT) sponges were measured while compressing the samples. Compression leads to a huge variation of the absorptance, reflectance, and transmittance of the samples. The dependence of the microwave conductivity on the sponge density follows a power-law relation with exponents 1.7 ± 0.1 and 2.0 ± 0.2 for MWCNT and SWCNT sponges, respectively. These exponents can be decreased slightly by the addition of a non-conducting component which partly electrically separates adjacent tubes within the samples. The conductivity of MWCNT sponge was measured in the terahertz range while heating in air from 300 to 513 K and it increased due to an increase of a number of conducting channels in MWCNTs.

Flexible transparent graphene/polymer multilayers for efficient electromagnetic field absorption.

Thanks to its high electrical conductivity, a graphene plane presents a good shielding efficiency against GHz electromagnetic radiations. Several graphene planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties of isolated graphene. Maximum absorption of radiations for frequency around 30 GHz is achieved with six separated graphene planes, which is the optimum number. This remarkable result is demonstrated experimentally from electromagnetic measurements performed in the Ka band on a series of multilayers obtained by piling 1, 2, 3... graphene/PMMA units on a silica substrate. Theoretical calculations convincingly explain the observed absorption and transmission data in the GHz domain. It is concluded that graphene/PMMA multilayers can be used as an efficient optically transparent and flexible shielding media.

Epoxy resin/carbon black composites below the percolation threshold.

A set of epoxy resin composites filled with 0.25-2.0 wt.% of commercially available ENSACO carbon black (CB) of high and low surface area (CBH and CBL respectively) has been produced. The results of broadband dielectric spectroscopy of manufactured CB/epoxy below the percolation threshold in broad temperature (200 K to 450 K) and frequency (20 Hz to 1 MHz) ranges are reported. The dielectric properties of composites below the percolation threshold are mostly determined by alpha relaxation in pure polymer matrix. The glass transition temperature for CB/epoxy decreases in comparison with neat epoxy resin due to the extra free volume at the polymer-filler interface. At room temperature, the dielectric permittivity is higher for epoxy loaded with CBH additives. In contrast, at high temperature, the electrical conductivity was found to be higher for composites with CBL embedded. The established influence of the CB surface area on the broadband dielectric characteristics can be exploited for the production of effective low-cost antistatic paints and coatings working at different temperatures.

Multilayered graphene in K(a)-band: nanoscale coating for aerospace applications.

We report on the experimental study of electromagnetic (EM) properties of multilayered graphene in K(a)-band synthesized by catalytic chemical vapor deposition (CVD) process in between nanometrically thin Cu catalyst film and dielectric (SiO2) substrate. The quality of the produced multilayered graphene samples was monitored by Raman spectroscopy. The thickness of graphene films was controlled by atomic force microscopy (AFM) and was found to be a few nanometers (up to 5 nm). We discovered, that the fabricated graphene, being only some thousandth of skin depth, provided remarkably high EM shielding efficiency caused by absorption losses at the level of 35-43% of incident power. Being highly conductive at room temperature, multilayer graphene emerges as a promising material for manufacturing ultrathin microwave coatings to be used in aerospace applications.

Soft cutting of single-wall carbon nanotubes by low temperature ultrasonication in a mixture of sulfuric and nitric acids.

To decrease single-wall carbon nanotube (SWCNT) lengths to a value of 100-200 nm, aggressive cutting methods, accompanied by a high loss of starting material, are frequently used. We propose a cutting approach based on low temperature intensive ultrasonication in a mixture of sulfuric and nitric acids. The method is nondestructive with a yield close to 100%. It was applied to cut nanotubes produced in three different ways: gas-phase catalysis, chemical vapor deposition, and electric-arc-discharge methods. Raman and Fourier transform infrared spectroscopy were used to demonstrate that the cut carbon nanotubes have a low extent of sidewall degradation and their electronic properties are close to those of the untreated tubes. It was proposed to use the spectral position of the far-infrared absorption peak as a simple criterion for the estimation of SWCNT length distribution in the samples.

Hyperthermic effect of multi-walled carbon nanotubes stimulated with near infrared irradiation for anticancer therapy: in vitro studies.

UNLABELLED: It is proposed to use the novel paradigm of treating cancer with hyperthermic therapy using multi-walled carbon nanotubes (MWCNT) stimulated with near infrared (NIR) irradiation. AIM: To establish the capacity of MWCNT stimulated with NIR irradiation to destroy Erlich ascitic carcinoma (EAC) cells. MATERIALS AND METHODS: EAC cells suspension was irradiated with NIR heating lamp with a wavelength of 0.78-1.40 mm and power density of 3.5 W/cm2 over 1.5 min in the presence of MWCNT (0.1 mg/ml). The changes in the temperature of suspension with the NIR exposure time was measured using the differential cooper-constantan thermocouple. The viability of EAC cells was evaluated by trypan blue staining. RESULTS: The death of 95.2% of EAC cells in the presence of MWCNT was observed after 1.5 min of NIR light irradiation: thermal ablation temperature was approximately 50 degrees C. CONCLUSIONS: It was demonstrated that addition of MWCNT to EAC cell suspension results in the photo-ablative destruction of cells exposed to short time NIR irradiation.

Matter coupling to strong electromagnetic fields in two-level quantum systems with broken inversion symmetry.

We demonstrate theoretically the parametric oscillator behavior of a two-level quantum system with broken inversion symmetry exposed to a strong electromagnetic field. A multitude of resonance frequencies and additional harmonics in the scattered light spectrum as well as an altered Rabi frequency are predicted to be inherent to such systems. In particular, dipole radiation at the Rabi frequency appears to be possible. Since the Rabi frequency is controlled by the strength of the coupling electromagnetic field, the effect can serve for the frequency-tuned parametric amplification and generation of electromagnetic waves. Manifestation of the effect is discussed for III-nitride quantum dots with strong built-in electric field breaking the inversion symmetry. Terahertz emission from arrays of such quantum dots is shown to be experimentally observable.

[Microbial community of the water column of the Selenga River-Lake Baikal biogeochemical barrier].

The microbial communities of the estuarine zone and the mixing zone of river and lake waters in the Selenga River estuary were studied using the fluorescence in situ hybridization (FISH) method. The microorganisms belonging to the phylogenetic group Gammaproteobacteria were found to predominate in the river estuary, constituting up to 17% of the total bacterial community. Among cultivable microorganisms, organotrophic bacteria were predominant (2040 CFU/ml) in this zone, which results in high rates of microbial production (6.0 microg C/(1 day). The microbial community structure changed with distance from the river estuary; representatives of the Alpha-, Beta-, and Gammaproteobacteria were present in equal proportions; psychrotolerant and oligotrophic bacteria were numerous. The rate of heterotrophic carbon dioxide assimilation decreased to 3.8 microg C/(1 day). At 5-7 km from the river estuary, where the hydrologic, physical, and chemical conditions are similar to those of lake waters, members of the Betaproteobacteria, which are typical of the open waters of Lake Baikal, are the major representatives of planktonic microorganisms.

Dipole polarizability of onion-like carbons and electromagnetic properties of their composites.

Onion-like carbons (OLC) obtained by thermal transformation of nanodiamonds are agglomerates of multi-shell fullerenes, often covered by an external graphitic mantle. For the present work, elemental OLC units were constructed on the computer by coalescence of several two-layer fullerenes, in a structure similar to carbon peapods with a corrugated external wall. The electrical polarizability of such pod-of-peas fullerenes has been computed by a classical monopole-dipole atomistic theory. The description of pod-of-peas fullerenes was further simplified by representing them as linear arrays of point-like objects, whose polarizability matches that of the starting molecules. Calculations demonstrated that the static polarizability of spherically shaped assemblies of these arrays, modeling real OLC materials, is weakly dependent on the geometry of its constituent molecules and is chiefly proportional to the volume of the whole cluster. It increases with increasing filling fraction of the pod-of-peas fullerenes in the OLC aggregate. The polarizability so obtained can be used in Maxwell-Garnett theory to predict the permittivity of OLC-based composites, at least for static excitations. Experimental results obtained at GHz frequencies reveal a weak attenuation for OLC- and nanodiamond-based polydimethylsiloxane composites. In these silicone composites, we did not find long chains of coupled OLCs. Quite separated clusters were found instead, which contribute little to the polarizability and to the dielectric properties, in good agreement with our theoretical predictions.

Thermal radiation from carbon nanotubes in the terahertz range.

The thermal radiation from an isolated finite-length carbon nanotube (CNT) is theoretically investigated both in near- and far-field zones. The formation of the discrete spectrum in metallic CNTs in the terahertz range is demonstrated due to the reflection of strongly slowed-down surface-plasmon modes from CNT ends. The effect does not appear in semiconductor CNTs. The concept of a CNT as a thermal nanoantenna is proposed.

Spontaneous decay of excited atomic states near a carbon nanotube.

The spontaneous decay process of an excited atom placed inside or outside a carbon nanotube is analyzed. Calculations have been performed for various achiral nanotubes. The effect of the nanotube surface is shown to increase the atomic spontaneous decay rate by up to 6 orders of magnitude compared with that of the same atom in vacuum. This increase is associated with nonradiative decay via surface excitations in the nanotube.

[The evaluation of the late results of destruction of the atrioventricular junction in patients with drug-resistant atrial fibrillation]. / Otsenka otdalennykh rezul'tatov destruktsii predserdno-zheludochkovogo soedineniia u bol'nykh s rezistentnoi k lekarstvennym sredstvam mertsatel'noi aritmiei.

Atrial fibrillation is a commonly seen form of disordered cardiac rhythm. Catheter-radio frequency ablation of the atrioventricular junction was found out to be an effective approach to control heart rate in continued drug-refractory cardiac fibrillation permitting the quality of the patients' life to be improved. The best results are achievable in patients presenting with chronic cardiac fibrillation.

[The clinical use of the new antioxidant thiotriazoline in ischemic ophthalmopathies]. / Klinicheskoe primenenie novogo antioksidanta tiotriazolina pri ishemicheskikh oftal'mopatiiakh.

The new antioxidant Thiotriazoline was used in the treatment of patients with retinal vascular occlusive processes. The agent improved retinal metabolism by inhibiting free radical oxidation. Thiotriazoline is superior to alpha-tocopherol acetate in its activity. Unlike the latter, it has no vasodilating effect.

Group-velocity dispersion in an all-pass Bragg filter.

On the basis of previously performed theoretical analysis it is shown that a slanted volume grating acts as an all-pass filter with nonlinear dispersion when the diffracted wave is evanescent. An analytical expression for the grating transfer function applicable over a wide angular range of mutual orientation of the initial wave and grating vectors is presented. It is demonstrated that group-velocity dispersion (GVD) in an all-pass Bragg filter is a frequency-dependent quasi-periodic function provided that GVD levels are sufficiently high.

[The role of a 1-day hospital in providing staged treatment and ambulatory care of patients with phlebothrombosis of the retina]. / Rol' odnodnevnogo statsionara pri provedenii étapnogo lecheniia i dispanserizatsii bol'nykh flebotrombozami sechatki.

Foundations for a two-stage dispensarization of patients with phlebothrombosis of the retina are given. The experience of work with one-day hospital at the Office of Ophthalmoendocrinology and Vascular Pathology of the Eye has confirmed efficacy of this new form of ophthalmological aid beyond a hospital system.