Hydroelastic analysis of water impact of flexible asymmetric wedge with an oblique speed

Current paper deals with hydroelastic impact of asymmetric and symmetric wedge sections with oblique speed into calm water. It is aimed to provide a better insight regarding fluid–structure interaction of the wedge sections of a high-speed craft into water in more realistic condition, in the presence of heel angle and oblique speeds. The defined problem is numerically investigated by coupled Finite Volume Method and Finite Element Method under two-way approach consideration. Accuracy of the proposed model is assessed in different steps. The results of current method are compared against previous experimental, numerical and theoretical methods and good agreement is displayed in these comparisons. Subsequently, the method is used in order to examine the fluid and structure behavior during the elastic impact of the wedge into water. Accordingly, four different physical situations are simulated. In the first part, symmetric impact with no oblique speed is simulated. The results of this part show fluctuations in vertical force and pressure of the midpoint during the impact time. Also, the relation of deadrise with deflection and pressure is observed in this part. In the second part, heel angle is also taken into consideration. It is concluded that the pressure and deflections at the right side of the wedge reduce, but these parameters increase at the left side. Moreover, it is observed that, the pressure at the midpoint of the left side of the wedge with deadrise angle of 10°, becomes negative, when the wall of the flexible wedge reaches its largest deflection. It is also observed that, the pressure at left side of the wedge with deadrise angle of 20°, reaches zero. Such behavior does not occur for the wedges of 30° and 45° deadrise angles. In the third part of simulations, oblique water entry of a flexible wedge of 20° deadrise angle is simulated, and no heel angle is considered. Harmonic behavior is observed for the vertical force, horizontal force, pressure of the midpoint and its deflection. First peaks of all of these variables are larger than the second peak. The obtained results lead us to conclude that an increase in oblique speed yields larger deflection and pressure at the right side. Meanwhile, no significant effect is observed for the left side of the wedge. Also, larger oblique speed is found to yield larger forces and angular moment. Final part of simulations involves the oblique water entry of a flexible wedge of 5° heel angle. Comparison of the results in the final part with that of third part, show that heel angle affects the pressure and deflection at both sides of the wedge. It is also observed that pressure and deflections of the left side increase, while those of right side increase. It is also seen that, similar as in the case of no heel angle, an increase in oblique speed leads to an increase of pressure and deflection at the starboard. It also leads to an increase in frequency of the vibration at right side.     

High-temperature dynamic behavior in bulk liquid water: A molecular dynamics simulation study using the OPC and TIP4P-Ew potentials

Classical molecular dynamics simulations were performed to study the high-temperature (above 300 K) dynamic behavior of bulk water, specifically the behavior of the diffusion coefficient, hydrogen bond, and nearest-neighbor lifetimes. Two water potentials were compared: the recently proposed “globally optimal” point charge (OPC) model and the well-known TIP4P-Ew model. By considering the Arrhenius plots of the computed inverse diffusion coefficient and rotational relaxation constants, a crossover from Vogel–Fulcher–Tammann behavior to a linear trend with increasing temperature was detected at T* ≈ 309 and T* ≈ 285 K for the OPC and TIP4P-Ew models, respectively. Experimentally, the crossover point was previously observed at T* ± 315–5 K. We also verified that for the coefficient of thermal expansion α _P (T, P), the isobaric α _P (T) curves cross at about the same T* as in the experiment. The lifetimes of water hydrogen bonds and of the nearest neighbors were evaluated and were found to cross near T*, where the lifetimes are about 1 ps. For T < T*, hydrogen bonds persist longer than nearest neighbors, suggesting that the hydrogen bonding network dominates the water structure at T < T*, whereas for T > T*, water behaves more like a simple liquid. The fact that T* falls within the biologically relevant temperature range is a strong motivation for further analysis of the phenomenon and its possible consequences for biomolecular systems.     

Werner's Syndrome: A Rare Cause of Hoarseness

Werner's syndrome (WS) is a rare hereditary disorder which is characterized by clinical signs of premature aging. A 31-year-old man presented with a 12-year history of hoarseness. Also noted were diabetes mellitus, cataracts, scleroderma-like skin atrophy, osteoporosis, and hypogonadism. A clinical diagnosis of WS was made. Laryngoscopy revealed bowed vocal folds resulting in a spindle-shaped closure with glottal incompetence during phonation. We used Gortex for medialization of the middle part of vocal fold to correct the glottal gap in this patient. Despite correction of glottal incompetence in patients with WS, quality of voice could not be improved to that of age-matched normal individuals.     

Simultaneous Determination of Ranitidine and Metronidazole at Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

Single‐walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs‐film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10^?8 mol L^?1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10^?8 mol L^?1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.     

Thermochemistry of the Reaction of Solvated Sodium Ion Clusters with Thymine in the Gas Phase: An Example of the Reaction in Microcosmic Environment

The thermochemistry of the reaction of the microsolvated Na⁺ such as [Na(H₂O) _n ; n?=?1?6]⁺, [Na(NH₃) _n ; n?=?1?6]⁺ and [Na(H₂O) _n (NH₃) _m ; n?+?m?=?2?6]⁺ with thymine (Thy), as an example of a reaction in the microcosmic environment, have been studied in this work, theoretically. It was found that the increase of the number of solvent molecules in the structure of microsolvated Na⁺ is accompanied by the decrease of the standard enthalpy (\(\Delta H_{r}^{^\circ }\)) and Gibbs free (\(\Delta G_{r}^{^\circ }\)) energies of the reaction (Thy?+?[Na(X) _n ]⁺→Thy-Na(X) _n ⁺ ; X?=?solvent molecule). Also, the calculations showed that the electronic intermolecular interaction (?E_int) between the Thy and microslovated Na⁺ decreased with the increase of solvent molecules. For the interaction of the [Na(H₂O) _n ; n?=?4, 5 and 6]⁺ ions with the Thy, there was the probability of forming of the hydrogen bond between water molecules in the structure of solvated Na⁺ and the Thy. The gas phase infrared (IR) spectra of the complexes of the microsolvated Na⁺ with the Thy for different values of n were calculated and compared with each other to follow the change in the frequency of the stretching vibration of the interaction path between the C=O group of the Thy and Na (O…Na) with n. Using the calculated values of \(\Delta G_{r}^{^\circ }\) of the reactions, the mole fractions of the complexes of microsolvated Na⁺ ions with the Thy were calculated at different humidity.     

Reaction of tert‐Butyl Isocyanide with Alkyl Propiolates in the Presence of α‐Chloroketones

tert‐Butyl isocyanide reacts with α‐chloroketones in the presence of alkyl propiolates in one pot to afford functionalized γ‐iminolactones as sole product in good yields.     

Effect of MWCNT–Fe3O4/water hybrid nanofluid on the thermal performance of ribbed channel with apart sections of heating and cooling

Journal of Thermal Analysis and Calorimetry - A two-dimensional (2D) numerical simulation is performed to simulate the laminar forced convection of a nanofluid in a ribbed channel with apart...     

The physicochemical properties of polyhydroxyalkanoates with different chemical structures

A set of polyhydroxyalkanoates are synthesized, and a comparative study of their physicochemical properties is performed. The molecular masses and polydispersities of polyhydroxyalkanoates are found to be independent of their chemical structures. It is shown that the temperature characteristics and degrees of crystallinity of polyhydroxyalkanoates are affected by the chemical compositions of the monomers and their quantitative contents in the polymers. The incorporation of 4-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate units into the chain of poly(3-hydroxybutyrate) decreases its melting point and thermal degradation temperature relative to these parameters of a homogeneous poly(3-hydroxybutyrate) sample (175 ± 5°C and 275 ± 5°C, respectively). The higher the content of the second monomer units in the poly(3-hydroxybutirate) chain, the greater the changes. The degrees of crystallinity of polyhydroxyalkanoate copolymers are generally lower than that of poly(3-hydroxybutyrate) (75 ± 5%). The effect on the ratio of the amorphous and crystalline phases of the copolymer samples becomes more pronounced in the series 3-hydroxy-valerate-3-hydroxyhexanoate-4-hydroxybutyrate. The prepared samples exhibit different properties ranging from rigid thermoplastic materials to engineering elastomers.