Size determination of Acipenser ruthenus spermatozoa in different types of electron microscopy

In this study three types of scanning electron microscopes were used for the size determination of spermatozoa of sterlet Acipenser ruthenus – high vacuum scanning electron microscope (SEM, JEOL 6300), environmental scanning electron microscope (ESEM, Quanta 200 FEG), field emission scanning electron microscope (FESEM, JEOL 7401F) with cryoattachment Alto 2500 (Gatan) and transmission electron microscope (TEM, JEOL 1010). The use of particular microscopes was tied with different specimen preparation techniques. The aim of this study was to evaluate to what degree the type of used electron microscope can influence the size of different parts of spermatozoa. For high vacuum SEM the specimen was prepared using two slightly different procedures. After chemical fixation with 2.5% glutaraldehyde in 0.1 M phosphate buffer and post-fixation by 1% osmium tetroxide, the specimen was dehydrated by acetone series and dried either by critical point method or by means of t-butylalcohol. For ESEM fresh, unfixed material was used, which was dropped on microscopic copper grids. In FESEM working in cryo-mode the specimen was observed in a frozen state. Ultrathin sections from chemically fixed and Epon embedded specimens were prepared for TEM observation. Distinct parts of sterlet spermatozoa were measured in each microscope and the data obtained was statistically processed. Results confirmed that the classical chemical procedure of specimen preparation for SEM including critical point drying method led to a significant contraction of all measured values, which could deviate up to 30% in comparison with values measured on the fresh chemically untreated specimen in ESEM. Surprisingly sperm dimensions determinated on ultrathin sections by TEM are comparable with values obtained in ESEM or FESEM.     

Constant factor approximation for ATSP with two edge weights

We give a constant factor approximation algorithm for the Asymmetric Traveling Salesman Problem on shortest path metrics of directed graphs with two different edge weights. For the case of unit edge weights, the first constant factor approximation was given recently by Svensson. This was accomplished by introducing an easier problem called Local-Connectivity ATSP and showing that a good solution to this problem can be used to obtain a constant factor approximation for ATSP. In this paper, we solve Local-Connectivity ATSP for two different edge weights. The solution is based on a flow decomposition theorem for solutions of the Held–Karp relaxation, which may be of independent interest.     

Winding up of the wave-function phase by an insulator-to-superfluid transition in a ring of coupled Bose-Einstein condensates

We study phase transition from the Mott insulator to superfluid in a periodic optical lattice. Kibble-Zurek mechanism predicts buildup of winding number through random walk of BEC phases, with the step size scaling as a third root of transition rate. We confirm this and demonstrate that this scaling accounts for the net winding number after the transition.     

Neobavaisoflavone May Modulate the Activity of Topoisomerase Inhibitors towards U-87 MG Cells: An In Vitro Study

Despite many advances in therapy, glioblastoma (GB) is still characterized by its poor prognosis. The main reason for this is unsuccessful treatment, which slightly extends the duration of remission; thus, new regimens are needed. One of many types of chemotherapeutics that are being investigated in this field is topoisomerase inhibitors, mainly in combination therapy with other drugs. On the other hand, the search for new anti-cancer substances continues. Neobavaisoflavone (NBIF) is a natural compound isolated from Psoralea corylifolia L., which possesses anti-oxidant, anti-inflammatory, and anti-cancer properties. The aim of this study was to evaluate the effect of NBIF in human U-87 MG glioblastoma cells in comparison to normal human NHA astrocytes, and to examine if it influences the activity of irinotecan, etoposide, and doxorubicin in this in vitro model. We demonstrated that NBIF decreases U-87 MG cells viability in a dose-dependent manner. Furthermore, we found that it inhibits cell growth and causes glutathione (GSH) depletion more intensely in U-87 MG cells than in astrocytes. This study also provides, for the first time, evidence of the potentialization of the doxorubicin effect by NBIF, which was shown by the reduction in the viability in U-87 MG cells.     

Phase transformation in shape memory alloys: a numerical approach for thermomechanical modeling via peridynamics

Meccanica - The work is devoted to the numerical aspects of the modeling tool elaborated to simulate the phenomenon of solid phase transformation in shape memory alloys. Particularly, a nonlocal...     

A general stereoselective method for the synthesis of cyclopropanecarboxylates. A new version of the homologous Horner-Wadsworth-Emmons reaction

The synthesis of alpha-, beta- and gamma-substituted alpha-phosphono-gamma-lactones was accomplished using different ring closure and ring homologation strategies. It was found that the lactones could be selectively transformed into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF. The reported reaction provides an attractive alternative to the classical homologous Horner-Wadsworth-Emmons approach to the construction of cyclopropanes with electron-withdrawing functionalities.     

Stereochemical preference of nucleophillic cleavage in methyl erythrofuranosides explained by density functional theory computations

The nucleophillic substitution is a common method for preparation of saccharide derivatives. For biologically active compounds, it is desirable that the stereochemistry is under control and the amount of byproducts is limited. Therefore, we studied the S_N2 nucleophillic attacks of the azide anion on methyl 2,3-anhydro-α- and -β-l-erythrofuranoside, as well as on their epithio and epimino analogues, which are used as common intermediates in sugar chemistry. Geometry and energetics of the reactions were investigated in the gas phase and in two different solvents using the density functional theory methods. Equilibrium structures of the reactants, reaction-complexes, transition states and products were localized on the computed potential energy surfaces. According to the theory the methoxy group may suppress the substitutions at the 2-position, but detailed reaction rate is influenced by nature of the furanosides and the presence of solvent. Predicted substitution selectivity in the position 2 or 3 of the furanose sugars is in agreement with experimental data.     

Irreversible electrowetting on thin fluoropolymer films

A study was conducted to investigate electrowetting reversibility associated with repeated voltage actuations for an aqueous droplet situated on a silicon dioxide insulator coated with an amorphous fluoropolymer film ranging in thickness from 20 to 80 nm. The experimental results indicate that irreversible trapped charge may occur at the aqueous-solid interface, giving rise to contact angle relaxation. The accumulation of trapped charge was found to be related to the applied electric field intensity and the breakdown strength of the fluoropolymer. On the basis of the data, an empirical model was developed to estimate the amount of trapped charge in the fluoropolymer as well as the voltage threshold for the onset of irreversible electrowetting.     

An Image Encryption Algorithm Using Logistic Map with Plaintext-Related Parameter Values

This paper deals with a plaintext-related image encryption algorithm that modifies the parameter values used by the logistic map according to plain image pixel intensities. The parameter values are altered in a row-wise manner, which enables the usage of the same procedure also during the decryption. Furthermore, the parameter modification technique takes into account knowledge about the logistic map, its fixed points and possible periodic cycles. Since the resulting interval of parameter values achieves high positive values of Lyapunov exponents, the chaotic behavior of the logistic map should be most pronounced. These assumptions are verified by a set of experiments and the obtained numerical values are compared with those reported in relevant papers. It is found that the proposed design that uses a simpler, but well-studied, chaotic map with mitigated issues obtains results comparable with algorithms that use more complex chaotic systems. Moreover, the proposed solution is much faster than other approaches with a similar purpose.