Stationary soliton on a charged surface of liquid helium and hydrogen films

A change in the shape of a charged surface of liquid hydrogen and helium — the formation of a solitary wave (a positively charged hump for hydrogen and a negatively charged dimple for helium)-is observed in an electric field exceeding a critical value under conditions of total compensation of the applied field by the surface charge. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 547–552 (10 April 1997)     

Polar Red‐Emitting Rhodamine Dyes with Reactive Groups: Synthesis,Photophysical Properties,and Two‐Color STED Nanoscopy Applications

The synthesis, reactivity, and photophysical properties of new rhodamines with intense red fluorescence, two polar residues (hydroxyls, primary phosphates, or sulfonic acid groups), and improved hydrolytic stability of the amino‐reactive sites (NHS esters or mixed N‐succinimidyl carbonates) are reported. All fluorophores contain an N‐alkyl‐1,2‐dihydro‐2,2,4‐trimethylquinoline fragment, and most of them bear a fully substituted tetrafluoro phenyl ring with a secondary carboxamide group. The absorption and emission maxima in water are in the range of 635–639 and 655–659 nm, respectively. A vastly simplified approach to red‐emitting rhodamines with two phosphate groups that are compatible with diverse functional linkers was developed. As an example, a phosphorylated dye with an azide residue was prepared and was used in a click reaction with a strained alkyne bearing an N‐hydroxysuccinimid (NHS) ester group. This method bypasses the undesired activation of phosphate groups, and gives an amphiphilic amino‐reactive dye, the solubility and distribution of which between aqueous and organic phases can be controlled by varying the pH. The presence of two hydroxyl groups and a phenyl ring with two carboxyl residues in the dyes with another substitution pattern is sufficient for providing the hydrophilic properties. Selective formation of a mono‐N‐hydroxysuccinimidyl ester from 5‐carboxy isomer of this rhodamine is reported. The fluorescence quantum yields varied from 58 to 92 % for free fluorophores, and amounted to 18–64 % for antibody conjugates in aqueous buffers. The brightness and photostability of these fluorophores facilitated two‐color stimulated emission depletion (STED) fluorescence nanoscopy of biological samples with high contrast and minimal background. Selecting a pair of fluorophores with absorption/emission bands at 579/609 and 635/655 nm enabled two‐color channels with low cross‐talk and negligible background at approximately 40 nm resolution.     

Quasiadiabatic decay of capillary turbulence on the charged surface of liquid hydrogen

We study the free decay of capillary turbulence on the charged surface of liquid hydrogen. We find that decay begins from the high frequency end of the spectral range, while most of the energy remains localized at low frequencies. The apparent discrepancy with the self-similar theory of nonstationary wave turbulent processes is accounted for in terms of a quasiadiabatic decay wherein fast nonlinear wave interactions redistribute energy between frequency scales in the presence of finite damping at all frequencies. Numerical calculations based on this idea agree well with experimental data.     

Role of parallel reformable bonds in the self-healing of cross-linked nanogel particles

We develop a hybrid computational approach to examine the mechanical properties and self-healing behavior of nanogel particles that are cross-linked by both stable and labile bonds. The individual nanogels are modeled via the lattice spring model (LSM), which is an effective method for probing the response of materials to mechanical deformation. The cross-links between the nanogels are simulated via the hierarchical Bell model (HBM), which allows us to capture the rupturing of multiple parallel bonds as the result of an applied force. Because the labile bonds are relatively reactive, they can reform after they have been ruptured. To incorporate the possibility of bonds reforming, we modify the HBM formalism and validate the modified HBM by considering a system of two surfaces, which are connected by multiple parallel bonds. We then use our hybrid HBM/LSM to simulate the behavior of the cross-linked nanogels under a tensile deformation. In these simulations, each labile linkage between the nanogels contains at most N parallel bonds. We vary the fraction of labile linkages and the value of N in these linkages to determine the optimal conditions for improving the robustness of the material. Although numerous parallel bonds within a linkage enhance the strength of the material, these bonds diminish the ductility and the ability of the material to undergo the structural rearrangements that are necessary for self-repair. For a relatively low fraction of labile bonds and N ≤ 4, however, we can significantly improve the strength of the material and preserve the self-healing properties. For instance, a sample with 30% labile linkages and N = 4 per linkage is roughly 200% stronger than a sample that is cross-linked solely by stable bonds and can still undergo self-repair in response to the tensile deformation. The results reveal how mechanical stress can lead not only to the appearance of cavities within the material but also to bond formation that "heals" these cavities and thus prevents the catastrophic failure of the material.     

Wave formation with the combustion of condensed substances in a turbulent flow

The surface of samples of powder burning in a flow in the presence of erosion is spotted with roughnesses of almost-periodic structure [1]. Such roughnesses are also observed with the combustion of some ablating materials in a flow [2]. It has been observed that, with the unstable (resonance) combustion of powders, different acoustical modes correspond to the structure of the roughnesses [3]. One of the possible mechanisms of the formation of waves on the surface, developed in [4, 5], has still not received sufficient experimental confirmation. The present article discusses the laws governing the formation of a wave structure on the surface of various condensed substances, burning in a turbulent flow of the combustion products of ballistic powder N.     

Biocompatibility of the Ti<Subscript>81</Subscript>Nb<Subscript>13</Subscript>Ta<Subscript>3</Subscript>Zr<Subscript>3</Subscript> Alloy

Titanium-based alloy with low-toxic metals such as niobium, tantalum and zirconium (TiNbTaZr) was manufactured. The primary weight percentages of elements used for fusion were: titanium, 65%; niobium, 20%, tantalum, 10%; and zirconium, 5%. The TiNbTaZr alloy had a yield strength of about 550 MPa, a tensile strength of about 700 MPa, and a Young’s modulus of about 50 GPa, that is, it was comparable with Nitinol. A primary study of the biocompatibility of the TiNbTaZr alloy using the SH-SY5Y cells showed that the alloy did not have significant short-term toxicicity towards the cells incubated on the alloy surface. The number of non-viable cells was 2.5 times lower on the TiNbTaZr alloy than on Nitinol. The biocompatibility of TiNbTaZr was more pronounced than that of the Nitinol reference sample.     

Selective modification of bifunctional heterocyclic compounds containing amino and thioamide groups in acetic acid medium

In acetic acid medium, 2‐chloro‐4,6‐dimorpholin‐4‐yl‐[1,3,5]triazine undergoes amination by bifunctional heterocyclic compounds containing both amino and thioamide groups. The reactions are high‐yielding and selective; the thioamide functions are unaffected under the requisite conditions. The reactions do not proceed in satisfactory yields in other solvents and, thus, require acetic acid. The resulting thioamides, consisting of multiple biologically relevant residues, are easily alkylated at the sulfur (thiolthione) centers to furnish new thioethers in subsequent steps.     

Nanocluster magnetic gel in superfluid He-II

The first results of the study of the structure of an impurity oxygen gel in superfluid He-II and in normal liquid helium have been obtained by the small-angle neutron scattering (SANS) method with cold neutrons. The angular dependence of the neutron scattering intensity I(q) indicates that the characteristic sizes of nanocluster aggregates forming a dispersive system (backbone) of an oxygen gel sample are distributed from 1 to ≈100 nm. According to the estimates made, if the working cell with superfluid helium cooled below 1.8 K is placed in a magnetic field of H ≥ 200 G, the magnetic structure of the nanocluster sample of oxygen gel, which is formed at the condensation of the flow of gaseous ⁴He with the impurity of O₂ vapor on the surface of He-II, will be close to ferromagnetic.