Structural and spectroscopic investigation of the N-methylformamide–water (NMF···3H2O) complex

In this work, theoretical studies on the structure, molecular properties, hydrogen bonding, and vibrational spectra of the N-methylformamide–water (NMF···3H₂O) complex will be presented. The molecular geometry was optimised by using Hartree–Fock (HF), second Møller–Plesset (MP2), and density functional theory methods with different basis sets. The harmonic vibrational frequencies are computed by using the B3LYP method with 6-311++G(d,p) as a basis set and then scaled with a suitable scale factor to yield good coherence with the observed values. The temperature dependence of various thermodynamic functions (heat capacity, entropy, and enthalpy changes) was also studied. A detailed analysis of the nature of the hydrogen bonding, using natural bond orbital (NBO) and topological atoms in molecules theory, has been reported.     

Anomalies of the natural convection of water near 3.98°C

Natural convection of water in a cylindrical cavity with an open surface at a temperature of about 3.98°C (temperature of the maximum water density) is accompanied by typical anomalies on time dependences of temperatures of water layers. In particular, stabilization of temperature T_st is observed in the bottom region of the cavity and duration of such stabilization t_st may reach several hours depending on the experimental conditions. The results for solutions of sodium chloride and ethanol at a relatively low rate of water cooling show that temperature T_st coincides with temperature T_max corresponding to the maximum density of solutions.     

Experimental evidence of the ferroelectric nature of the λ-point transition in liquid water

We studied the dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by pore sizes 3–10 nm. Freezing temperature suppression in nanopores helps keep the water samples in liquid form at temperatures well below 0°C and thus effectively study the properties of supercooled liquid water. We report the first direct measurements of the dielectric constant by the dielectric spectroscopy method and demonstrate very clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the λ-point in the supercooled bulk water in full agreement with the recently developed model of the polar liquid.     

High-resolution inverse Raman spectroscopy of the ν1 band of water vapor

The Raman spectrum of the ν₁ band of water vapor at 7 Torr and 296 K, and at 84 Torr and 404 K, has been measured using high-resolution inverse Raman spectroscopy. The frequencies and relative intensities of the observed transitions are compared to a spectral model based on infrared data. Self-broadening coefficients have been determined for 22 lines from J = 0 to J = 8.     

Estimating the sound speed of the surface layer of the seabed using ocean ambient noise in shallow water

To improve the inversion efficiency, a method for quickly and directly estimating the sound speed of the surface layer of the seabed is proposed. According to the energy flux theory, the ocean ambient noise data received by the vertical line array can be used to extract the bottom loss(BL) passively. The BL curve has an effect on the critical angle, which is used to estimate the sound speed of the surface layer of the seabed. Based on the ray model,the difference between the BL calculated from t...     

Receiving response of towed line array to the noise of the tow ship in shallow water

The receiving response of towed line array to the noise radiated from the tow ship is investigated through normal mode modeling and computer simulation.The phenomenon that the maximum output of the towed line array is away from the endfire direction towards the tow ship is explained.The result is important for the understanding of the phenomenon and also for the application research concerning the suppression of the noise from the tow ship as well as adequate application of towed array techniques in shallow water.     

The directionality of the sound generated by laser-induced liquid breakdown in water The directionality of the sound generated by laser-induced liquid breakdown in water

The directionality of the sound generated by laser-induced liq-uid breakdown in water is investigated both theoretically and experimen-tally.The theoretical analysis is based on the following model.A seriesof small spherical cavities including plasma are homogeneously distributedon a short straight line segment and every such cavity may be consideredas a point source radiating acoustic impulse.Theoretical expressions ofthe relations between the amplitude and width of acoustic impulse and thereceiving direction are given.Experimental results are in agreement withtheoretical predictions.     

Effect of temperature on the morphology of nanobubbles at mica/water interface

The great implication of nanobubbles at a solid/water interface has drawn wide attention of the scientific community and industries. However, the fundamental properties of nanobubbles remain unknown as yet. In this paper, the temperature effects on the morphology of nanobubbles at the mica/water interface are explored through the combination of AFM direct image with the temperature control. The results demonstrate that the apparent height of nanobubbles in AFM images is kept almost constant with the increase of temperature, whilst the lateral size of nanobubbles changes significantly. As the temperature increases from 28℃ to 42℃, the lateral size of nanobubbles increases, reaching a maximum at about 37℃, and then decreases at a higher temperature. The possible explanation for the size change of nanobubbles with temperature is suggested.     

Laser-accelerated self-assembly of colloidal particles at the water–air interface

We experimentally demonstrate that optical tweezers can be used to accelerate the self-assembly of colloidal particles at a water–air interface in this Letter. The thermal flow induced by optical tweezers dominates the growth acceleration at the interface. Furthermore, optical tweezers are used to create a local growth peak at the growing front, which is used to study the preferential incorporation positions of incoming particles.The results show that the particles surfed with a strong Marangoni flow tend to fill the gap and smoothen the steep peaks. When the peak is smooth, the incoming particles incorporate the crystal homogeneously at the growing front.     

Force-field dependence on the interfacial structure of oil–water interfaces

We investigate the performance of different force-fields for alkanes, united (TraPPE) and all atom (OPLS-AA) models, and water (SPC/E and TIP4P-2005), in the prediction of the interfacial structure of alkane (n-octane, and n-dodecane)–water interfaces. We report an extensive comparison of the interfacial thermodynamic properties as well as the interfacial structure (translational and orientational). We use the recently introduced intrinsic sampling method, which removes the averaging effect of the interfacial capillary waves and provides a clear view of the interface structure. The alkane interfacial structure is sensitive to the environment, i.e. alkane–vapour or alkane–water interfaces, showing a stronger structure when it is in contact with the water phase. We find that this structure is fairly independent of the level of detail, full or united atom, employed to describe the alkane phase. The water surface properties show a small dependence on the water model. The dipole moment of the SPC/E model shows asymmetric fluctuations, with a tendency to point both towards the alkane and water phases. On the other hand the dipole moment of the TIP4P-2005 model shows a tendency to point towards the water phase only. Analysis of the intrinsic electrostatic field indicates that the surface water potential is confined to an interfacial region of about 8 Å. Overall we find that the intrinsic structure of alkane–water interfaces is a robust interfacial property, which is independent of the details of the force-field employed. Hence, it should provide a good reference to interpret experimental data.     

What determines the sticking probability of water molecules on ice?

We present both experimental and theoretical studies of the sticking of water molecules on ice. The sticking probability is unity over a wide range in energy (0.5 eV-1.5 eV) when the molecules are incident along the surface normal, but drops as the angle increases at high incident energy. This is explained in terms of the strong orientational dependence of the interaction of the molecule with the surface and the time required for the reorientation of the molecule. The sticking probability is found to scale with the component of the incident velocity in the plane of the surface, unlike the commonly assumed normal or total energy scaling.     

The numerical simulation of the average reverberation intensities in shallow water

A reverberation model for estimating the average reverberation inten-sity in layered shallow water is presented.The reverberation intensity is calculated interms of ray theory for short range and normal mode theory for long range.Thecalculation accuracy has been improved by taking into account the effect of complexeigenvalues on the incident normal mode field.From the comparison between dif-ferent scattering models it has been shown that the separable bistatic-backscatteringmodel is acceptable.This makes it possible to calculate reverberation by using onlythe monostatic-backscattering coefficient and to save greatly the computing time.     

New insights into the mechanisms of ultrasonic emulsification in the oil–water system and the role of gas bubbles

Ultrasonic emulsification (USE) assisted by cavitation is an effective method to produce emulsion droplets. However, the role of gas bubbles in the USE process still remains unclear. Hence, in the present paper, high-speed camera observations of bubble evolution and emulsion droplets formation in oil and water were used to capture in real-time the emulsification process, while experiments with different gas concentrations were carried out to investigate the effect of gas bubbles on droplet size. The results show that at the interface of oil and water, gas bubbles with a radius larger than the resonance radius collapse and sink into the water phase, inducing (oil–water) blended liquid jets across bubbles to generate oil-in-water-in-oil (O/W/O) and water-in-oil (W/O) droplets in the oil phase and oil-in-water (O/W) droplets in the water phase, respectively. Gas bubbles with a radius smaller than the resonance radius at the interface always move towards the oil phase, accompanied with the generation of water droplets in the oil phase. In the oil phase, gas bubbles, which can attract bubbles nearby the interface, migrate to the interface of oil and water due to acoustic streaming, and generate numerous droplets. As for the gas bubbles in the water phase, those can break neighboring droplets into numerous finer ones during bubble oscillation. With the increase in gas content, more bubbles undergo chaotic oscillation, leading to smaller and more stable emulsion droplets, which explains the beneficial role of gas bubbles in USE. Violently oscillating microbubbles are, therefore, found to be the governing cavitation regime for emulsification process. These results provide new insights to the mechanisms of gas bubbles in oil–water emulsions, which may be useful towards the optimization of USE process in industry.     

IR spectroscopic investigation of the structure of water–fuel microemulsion for diesel engines

The structures of a microemulsion formed by a surfactant (ammonium oleate), water drops of a linear size of 1–3 µm, and a diesel fuel has been investigated using IR spectroscopy. It has been found that ammonium oleate molecules in the microemulsion are dissociated on the positive NH₄⁺ ion and the negative ion of the remaining part of the molecule, which forms the hydrogen bond with water molecules. This increases the rate of water, evaporation and leads to the more complete combustion of the diesel fuel. As a result, the concentration of harmful nitrogen oxides and soot particles in the exhaust gas of the diesel engine decreases.     

Effects of water vapor in high vacuum chamber on the properties of HfO_2 films

The influence of water vapor content in high vacuum chamber during the coating process on physical properties of HfO_2 films was investigated.Coatings were deposited on BK7 substrates by electron beam evaporation and photoelectric maximum control method.An in situ residual gas analyzer(RGA)was used to monitor the residual gas composition in the vacuum chamber.The optical properties,microstructure, absorption and laser-induced damage threshold(LIDT)of the samples were characterized by Lambda 900 spectrophotometer,X-ray diffraction(XRD),surface thermal lensing(STL)technique and 1064-nm Q- switched pulsed laser at a pulse duration of 12 ns respectively.It was found that a cold trap is an effective equipment to suppress water vapor in the vacuum chamber during the pumping process,and the coatings deposited in the vacuum atmosphere with relatively low water vapor composition show higher refractive index and smaller grain size.Meanwhile,the higher LIDT value is corresponding to lower absorbance.