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This work experimentally studied the formation process of the ramjet mode occurring in a cavity-based combustor operating at a high-enthalpy supersonic flow. The ramjet mode is featured by the phenomenon that the incoming supersonic inflow is decelerated to be subsonic before it enters the combustor, which is caused by the strong heat release under a high equivalence ratio. In the experiments, the ignition is performed after a steady fuel mass flow rate has been achieved. According to the flame behavior and the flowfield structure, the formation process of the ramjet mode can be divided into three stages, among which stage 1 (from ignition to the cavity shear-layer mode) is shortest, while stage 3 (from the lifted shear-layer mode to the ramjet mode) consumes the longest time. In stage 2, flashback occurs and shock–shock interactions are found to be strongly coupled with the local combustion which have an influence on the propagation velocity of the backpressure. A thickening boundary layer upstream of the separation shock is observed when the separation shock has interwoven with the jet-induced bow-shock. The thickening process could be extremely short (in 100 μs) before the thickened boundary layer separates, during which the propagation velocity of the backpressure can be apparently decelerated. The same phenomena shown in the supplementary experiments confirm that the thickening boundary layer and its deceleration effect on the propagation of the backpressure are not accidental but more likely to be inherent to the flashback occurring under a supersonic flow. [ABSTRACT FROM AUTHOR]

The variegated cardinalfish Fowleria variegata produces grunt and hoot calls during agonistic and courtship interactions. Both sounds are tonal and occur as single and multiunit calls. Grunts are of short duration with variable frequency spectra. Hoots are longer, have a higher fundamental frequency, and a more developed harmonic structure. Agonistic grunt calls and short hoot calls (1–2 hoots) are produced during chases and when striking an individual or a mirror. Grunts are produced primarily in male-female and mirror-image encounters, and short hoot calls are produced primarily in male-male interactions. During the reproductive period, long hoot calls (three and four hoots) are the main sound type in a mix-sexed tank and at Dongsha Atoll. These are likely produced by males because isolated females are silent, and isolated males emit long hoot calls. Courtship interactions are mostly silent, and males are silent after capturing eggs for oral brooding. Tank sounds peak at dusk to early evening with a smaller peak at noon, although there are dusk and dawn peaks at Dongsha Atoll. Tank sounds exhibit a semilunar rhythm with peaks at the new and full moon. Other cardinalfish species from the atoll produce grunts but not hoot calls. [ABSTRACT FROM AUTHOR]

Large-eddy simulations and nanoparticle-based planar laser scattering experiments are conducted to investigate various physical aspects of transverse sonic jets injected into a Ma-3.0 supersonic crossflow through a circular pipe. Configurations with one jet and two opposite jets are compared. For the single jet, a separation shock is generated by the recirculation zone on the opposite wall, and this intersects with the jet shear layer to push several jet plumes into the near-wall region. For the two jets, the bow shocks interact with each other, forming an oblique shock train. All of the shocks promote vortex breakage in jet wakes. A counter-rotating vortex pair is generated in the jet near-field region, enhancing the local mixing. A near-wall region in the jet lee between the counter-rotating vortex pair branches exhibits a low fuel mass fraction. The jet fluid in the downstream near-wall region is entrained by the crossflow upstream of the jet. The interaction between the bow shocks and shear layers of the two jets induces recirculation zones in the lee of the jet, which enhance the fuel mixing. This explains the phenomenon whereby the total pressure recovery coefficient and mixing efficiency of two jets are higher than those of the single jet. [ABSTRACT FROM AUTHOR]

This study investigates the characteristics of a turbulent boundary layer in a curved circular pipe under an inflow of Ma = 3.0. The pipe consisted of a straight part and a curved part with a turning angle of 36° and a radius of curvature, γ = R/Rc, of γ = 0.0825. The nanoparticle-based planar laser scattering technique was applied to visualize the structure of the instantaneous flow field, and a large eddy simulation was conducted to uncover the physical aspects of development of the turbulent boundary layer. The distributions of density and vorticity, baroclinic pressure caused by the density and pressure gradients, and other physical quantities were analyzed. The asymmetry of the turbulent boundary layer in the curved part of the pipe, as influenced by curvature, secondary flow, and oblique shock, was obtained as the boundary layer on the inner wall gradually thickened while that on the outer wall gradually thinned. The secondary flow took the mainstream outer bend of the curved pipe and drew the low-energy fluid in the boundary layer to its inner bend, which led to the gradual thickening of the turbulent boundary layer from the outer to the inner bend along the circumferential direction. A low-speed region was formed in the downstream region of the inner part. The intersection between the oblique shock wave and the shear layer led to a high baroclinic pressure that promoted the generation of the vortex and forced the boundary layer to turn and inhibit the separation in the inner part. [ABSTRACT FROM AUTHOR]

The high-strain-rate dynamic response of a hydroxyl-terminated polyether (HTPE) propellant during impact loading is essential for assessing the structural reliability and impact safety of HTPE propellant. In this study, a modified split Hopkinson pressure bar (SHPB) apparatus has been developed to research the stress–strain behavior of the HTPE propellant over strain rates ranging from 470 to 5910 s−1 at room temperature, and the validity of the SHPB test is analyzed in detail. Meanwhile, the evolution of deformation to failure of the HTPE propellant was recorded by a high-speed digital camera synchronized with the SHPB test, which revealed the correlation between mechanical response and failure mode. Scanning electron microscopy was applied to investigate the microscopic failure mechanism of the post-test HTPE propellant, which indicated two characteristic failure modes: cracking propagates along the (1) debonding surface and (2) transgranular damage path. Finally, based on the stress–strain plots derived from the SHPB tests, the ultimate stress, strain energy density, and adiabatic temperature-rise effect of the HTPE propellant were seen to show strong strain rate dependence by following an empirical power law function. [ABSTRACT FROM AUTHOR]

Using high-pressure infrared methods, we have investigated close interactions of charge-enhanced C-H-O type in ionic liquid/dimethyl sulfoxide (DMSO) mixtures. The solvation and association of the 1-butyl-3-methylimidazolium tetrafluoroborate (BMI+BF4-) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMM+BF4-) in DMSO-d6 were examined by analysis of C-H spectral features. Based on our concentration-dependent results, the imidazolium C-H groups are more sensitive sites for C-H-O than the alkyl C-H groups and the dominant imidazolium C-H species in dilute ionic liquid/DMSO-d6 should be assigned to the isolated (or dissociated) structures. As the dilute mixtures were compressed by high pressures, the loss in intensity of the bands attributed to the isolated structures was observed. In other words, high pressure can be used to perturb the association-dissociation equilibrium in the polar region. This result is remarkably different from what is revealed for the imidazolium C-H in the BMM+BF4-/D2O mixtures. DFT-calculations are in agreement with our experimental results indicating that C4-H-O and C5-H-O interactions seem to play non-negligible roles for BMM+BF4-/DMSO mixtures. [ABSTRACT FROM AUTHOR]

We have probed under high pressure the C–H hydrogen bonds formed by N,N′-disubstituted imidazolium ions having PF6- and Br- counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N–H...F unit) in the infrared spectrum of the PF6- salt indicates that conventional N–H...O and N–H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C2–H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N–H hydrogen bonds in the PF6- salt. This finding is consistent with the pressure-dependent results, which reveal that the C2–H...F interaction is enhanced upon increasing the pressure. In contrast to the PF6- salt, the imidazolium C–H bonds of the Br- salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br- and PF6- ions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The hydrophobic hydration of dimethylsulfoxide (DMSO)/D[sub 2]O was explored using a combination of the high-pressure method and ab initio calculations. The frequencies of the C-H stretching vibration of DMSO increase as the mole fraction of D[sub 2]O increases, while no appreciable changes in spectral shapes are observed upon dilution. Interestingly, the infrared spectra of DMSO/D[sub 2]O observed under high-pressure exhibits dramatic changes, while the new spectral features locating at ∼2942 and ∼3033 cm[sup -1] appear. The spectral changes were attributed to the combined effect of C-H-O hydrogen bonding between C-H in DMSO and oxygen atom in D[sub 2]O, a phase change, pressure increase, etc. Ab initio calculation results, forecasting the frequency shift of the C-H stretching vibration as C-H-O is interacting via hydrogen bonding, are discussed. The reorganization of the hydrogen-bond network or geometry may be responsible for spectral changes as the pressure was elevated. [ABSTRACT FROM AUTHOR]

This study provides the evidence for hydrophobic hydration of CH[sub 3]COOD as its aqueous solution was compressed by high pressure. On going from neat CH[sub 3]COOD to diluted CH[sub 3]COOD/D[sub 2]O mixtures, the C-H vibration absorption bands do not reveal the solvent shift in frequency upon dilution, while the C-H absorption bands are altered into one prominent band at ∼2955 cm[sup -1] as the pressure was applied above 0.3 GPa. The possible explanation is the enhancement of C-H-O interactions between C-H and D[sub 2]O under the condition of high pressure. Ab initio calculations predict that the CH[sub 3] stretching frequencies and intensities of acetic acid are hardly affected by the presence of water, if the methyl group does not participate in the complex formation. Nevertheless, the strongest absorption peak at ∼2928 cm[sup -1] is predicted in several low-energy (acetic acid)-(water)[sub χ]complexes with the participation of C-H-O hydrogen bond. The reorganization of hydrogen-bond network or geometry is suggested to be responsible for the formation of C-H-O hydrogen bond. [ABSTRACT FROM AUTHOR]

C-H—O interactions of a self-assembled triple helix based on the 1-acetamido-3(2-pyrazinyl)-imidazolium cation has been probed by high pressure. The infrared spectroscopic profiles and ab initio calculations allow us to make a vibrational assignment of this compound. The C-H bonds forming C-H—O interactions shorten as the pressure was elevated, while free C-H vibration modes show low sensitivity to high pressure. The pressure-dependent results can be attributed to the strengthening of C-H—O electrostatic-dispersion interactions upon increasing pressure. The appearance of the free-NH infrared absorption indicates that the conventional NH—O hydrogen bond does not dominate the inter-strand packing in the compound. It is proposed that the charge-enhanced C-H—O interactions, forming a helical hydrogen-bonding network, disturb the formation of inter-strand N-H—O hydrogen-bonding in order to form a maximum number of hydrogen bonds. Applying high-pressure seems not to change the C=O bond length in contrast to the trend of blue-shift in frequency of C-H vibrations. London dispersion energy is suggested to be required for understanding the pressure-dependent results, although more additional terms, such as the effect in the presence of charge, are needed for the correct explanation. This work demonstrates that high-pressure studies may have the potential to provide insight into the C-H—O structural properties of biological related systems. [ABSTRACT FROM AUTHOR]

The infrared spectroscopic profiles of HCOOD/D[sub 2]O mixtures were measured as a function of pressure and concentration. The C–H bond of HCOOD shortens as the pressure is elevated, while the increase in C–H bond length upon diluting HCOOD with D[sub 2]O was observed. Based on the experimental results, the shift in frequency of C–H stretching band is concluded to relate to the mechanism of the hydration of the C–H group and the water structure in the vicinity of the C–H group. The pressure-dependent results can be attributed to the strengthening of C–H---O electrostatic/dispersion interaction upon increasing pressure. The observations are in accord with ab initio calculation forecasting a blueshift of the C–H stretching mode via C–H---O interaction in HCOOD-water/(HCOOD)[sub 2]-(D[sub 2]O) complexes relative to the noninteracting monomer/dimer. Hydrogen-bonding nonadditivity and the size of water clusters are suggested to be responsible to cause the redshift in C–H stretching mode upon dilution HCOOD with D[sub 2]O. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

C–H–O interaction of acetone and deuterium oxide has been probed by high pressure. High-pressure study provides the first experimental evidence for the enhancement of hydrophobic hydration of acetone as its aqueous solution was compressed to high-pressure ices. Based on the results, we conclude that the C–H–O interaction may be a distinct possibility to understand the origin of the spectral feature located at ∼2950 cm-1, being sensitive to concentration and pressure dependence. Ab initio calculation results, forecasting the frequency red shift of the C–H stretching vibration as C–H–O is interacted via hydrogen bonding, are discussed. This study demonstrates that high pressure can be used as a valuable means of triggering and investigating C–H–O hydrogen-bonding interaction. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effects of alkyl side-chain length on the interactions between imidazolium ionic liquids (ILs) and β-cyclodextrin (β-CD) were studied at ambient pressure and up to 2.5GPa. No noticeable changes in the C-H band frequencies of 1-methyl-3-propylimidazolium hexafluorophosphate ([MPIM][PF6]) were observed upon β-CD addition under ambient pressure. Nevertheless, β-CD addition inhibited the formation of the [MPIM][PF6] aggregated structure under pressures of ≤0.7 GPa. As the pressure was raised to 1.1–2.5 GPa, [MPIM][PF6] aggregated and formed self-associated configurations. This pressure-induced dissociation was not detected in the 1-butyl-3-methylimidazolium hexafluorophosphate and β-CD mixture ([BMIM][PF6]-β-CD) due to the long side chain in the [BMIM] cation. This indicates that the alkyl side-chain length of the imidazolium ILs plays a non-negligible role in controlling the order and strength of IL-β-CD interactions. It is well known that the validity of infrared spectroscopy for detecting the inclusion complexation is questionable in the literature. However, this study demonstrates that the combination of high pressure and IR spectroscopy may provide a suitable way to monitor the IL-β-CD interactions. [ABSTRACT FROM AUTHOR]

The radiative lifetimes and total cross sections for deactivation of K(7 2S ) and K(5 2D ) by collisions with H2 have been studied. In the sample vapor, the K atoms were prepared in either the 7 2S or the 5 2D state by two-photon absorption using a dye laser. The decay signal of the time-resolved fluorescence from the 7 2S–4 2P1/2 or 5 2D–4 2P3/2 transition was then monitored. Based on the Stern–Volmer equation, the radiative lifetimes are (157±5) ns for the 7 2S state and (569±12) ns for the 5 2D state. The total cross sections for deactivation of excited K atoms by means of collisions with H2 are (150±2) A2 for the 7 2S state and (39±4) A2 for the 5 2D state. The radiative lifetimes in the absence of H2 collisions agree with those previously reported. The cross sections for quenching by H2 have been measured for the first time and are interpreted in terms of the harpoon mechanism. The cross section for the transition 7 2S–5 2D has been measured; this transition has been proved to be the predominant channel for the depopulation of the 7 2S state. [ABSTRACT FROM AUTHOR]

By using a pump-and-probe technique, we have observed for the first time the product KH formed by reaction of K*(7S) with H2 in a single collision under bulk conditions. In contrast, no detectable laser-induced fluorescence (LIF) signal of KH was detected as the K*(7S) was replaced by the K*(5D), a state having 88 cm-1 less energy. These experiments demonstrate for the first time the possibility for an alkali atom to undergo with the H2 molecule a state-selective reaction. This reaction can be satisfactorily understood in terms of the harpoon mechanism. Measurements of the temperature dependence of the rate constant confirm the proposed mechanism. [ABSTRACT FROM AUTHOR]

High-performance organic field-effect transistor nonvolatile memories have been achieved using sputtered C nanoparticles as the nano-floating-gate. The sputtered C nano-floating-gate is prepared with low-cost material and simple process, forming uniform and discrete charge trapping sites covered by a smooth and complete polystyrene layer. The devices show large memory window, excellent retention capability, and programming/reading/erasing/reading endurance. The sputtered C nano-floating-gate can effectively trap both holes and electrons, and it is demonstrated to be suitable for not only p-type but also n-type organic field-effect transistor nonvolatile memories. [ABSTRACT FROM AUTHOR]

Pentacene-based organic field-effect transistor nonvolatile memories employing nano-floating-gate show high performance in vacuum, typically with field-effect mobility of 0.6 cm2/Vs, memory window of 45 V, reading ON/OFF ratio over 106, and excellent retention ability and programming/erasing endurance. The memory performance is unstable in air, which is demonstrated to result mainly from the device operation instability in O2. The O2-induced acceptor-like trap states reduce the electron supply in pentacene during programming, limiting the electron trapping into the nano-floating-gate and thus suppressing the positive threshold voltage shift. The corresponding hole trapping during erasing is not effectively influenced by the ambient gas effects. [ABSTRACT FROM AUTHOR]

The authors describe an electroless deposition method for thin films, based on the irradiation by an x-ray beam emitted by a synchrotron source. Specifically, Ni–P films were deposited at room temperature. This synthesis is a unique combination of photochemical and electrochemical processes. The influence of the pH value on the formation and structural properties of the films was examined by various characterization tools including scanning electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Real time monitoring of the deposition process by coherent x-ray microscopy reveals that the formation of hydrogen bubbles leads to a self-catalysis effect without a preexisting catalyst. The mechanisms underlying the deposition process are discussed in details. [ABSTRACT FROM AUTHOR]

High performance organic field-effect transistor nonvolatile memory is achieved by integrating gold nanoparticles and graphene oxide sheets as the hybrid nano-floating-gate. The device shows a large memory window of about 40 V, high ON/OFF ratio of reading current over 104, excellent programming/erasing endurance, and retention ability. The hybrid nano-floating-gate can increase the density of charge trapping sites, which are electrically separate from each other and thus suppress the stored charge leakage. The memory window is increased under illumination, and the results indicate that the photon-generated carriers facilitate the electron trapping but have almost no effect on the hole trapping. [ABSTRACT FROM AUTHOR]

The microscopic features of binary mixtures formed by an ionic liquid (EMI(+)TFSA(-) or EMI(+)FSA(-)) and a molecular liquid (acetonitrile or methanol) have been investigated by high-pressure infrared spectroscopy. On the basis of its responses to changes in pressure and concentration, the imidazolium C-H appears to exist at least in two different forms, i.e., isolated and associated structures. The weak band at approximately 3102 cm(-1) should be assigned to the isolated structure. CD(3)CN can be added to change the structural organization of ionic liquids. The compression of an EMI(+)TFSA(-)/CD(3)CN mixture leads to the increase in the isolated C-H band intensity. Nevertheless, the loss in intensity of the isolated structures was observed for EMI(+)FSA(-)/CD(3)CN mixtures as the pressure was elevated. In other words, the associated configuration is favored with increasing pressure by debiting the isolated form for EMI(+)FSA(-)/CD(3)CN mixtures. The stronger C-H...F interactions in EMI(+)FSA(-) may be one of the reasons for the remarkable differences in the pressure-dependent results of EMI(+)TFSA(-) and EMI(+)FSA(-).

High-pressure infrared measurements were carried out to observe the microscopic structures of two imidazolium-based ionic liquids, i.e., 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide [EMI(+)(CF(3)SO(2))(2)N(-), EMI(+)TFSA(-)] and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [EMI(+)(FSO(2))(2)N(-), EMI(+)FSA(-)]. The results obtained at ambient pressure indicate that the imidazolium C-H may exist in two different forms, i.e., isolated and network structures. As the sample of pure EMI(+)FSA(-) was compressed, the network configuration is favored with increasing pressure by debiting the isolated form. For EMI(+)TFSA(-)/H(2)O mixtures, the imidazolium C-H peaks split into four bands at high pressures. The new spectral features at approximately 3117 and 3190 cm(-1), being concentration sensitive, can be attributed to the interactions between the imidazolium C-H and water molecules. The alkyl C-H absorption exhibits a new band at approximately 3025 cm(-1) under high pressures. This observation suggests the formation of a certain water structure around the alkyl C-H groups. The O-H stretching absorption reveals two types of O-H species, i.e., free O-H and bonded O-H. For EMI(+)TFSA(-)/H(2)O mixtures, the compression leads to a loss of the free O-H band intensities, and pressure somehow stabilizes the bonded O-H configurations. The results also suggest the non-negligible roles of weak hydrogen bonds in the structure of ionic liquids.

The structural organization in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)])/water or methanol was studied by infrared spectroscopy. No drastic change in the concentration dependence of the alkyl C-H band frequency was observed at high concentration of the ionic liquid. This behavior indicates a clustering of the ionic liquid in alkyl regions. Nevertheless, the presence of methanol significantly perturbs the ionic liquid-ionic liquid associations in the imidazolium region. On the basis of the responses to change in pressure and concentration, two different types of O-H species, i.e., free O-H and bonded O-H, were observed in the O-H stretching region. For [bmim][BF(4)]/water mixtures, the compression leads to loss of the free O-H band intensity. It is likely that free O-H is switched to bonded O-H as high pressures are applied. For [bmim][BF(4)]/methanol mixtures, the free O-H is still stable under high pressures.

Complete active space self-consistent-field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with atomic natural orbital basis sets were performed to investigate the S-loss direct dissociation of the 1 2Pi(X 2Pi), 2 2Pi(A 2Pi), 1 2Sigma+(B 2Sigma+), 1 4Sigma-, 1 2Sigma-, and 1 2Delta states of the OCS+ ion and the predissociations of the 1 2Pi, 2 2Pi, and 1 2Sigma+ states. Our calculations indicate that the S-loss dissociation products of the OCS(+) ion in the six states are the ground-state CO molecule plus the S+ ion in different electronic states. The CASPT2//CASSCF potential energy curves were calculated for the S-loss dissociation from the six states. The calculations indicate that the dissociation of the 1 4Sigma- state leads to the CO + S+ (4Su) products representing the first dissociation limit; the dissociations of the 1 2Pi, 1 2Sigma-, and 1 2Delta states lead to the CO + S+(2Du) products representing the second dissociation limit; and the dissociations of the 2 2Pi and 1 2Sigma+ states lead to the CO + S+(2Pu) products representing the third dissociation limit. Seams of the 1 2Pi-1 4Sigma-, 2 2Pi-1 4Sigma-, 2 2Pi-1 2Sigma-, 2 2Pi-1 2Delta, and 1 2Sigma(+)-1 4Sigma- potential energy surface intersections were calculated at the CASPT2 level, and the minima along the seams were located. The calculations indicate that within the experimental energy range (15.07-16.0 eV) the 2 2Pi(A 2Pi) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 1 2Pi followed by the direct dissociation of 1 2Pi forming S+(2Du) and that within the experimental energy range (16.04-16.54 eV) the 1 2Sigma+(B 2Sigma+) state can be predissociated by 1 4Sigma- forming the S+(4Su) ion and can undergo internal conversion to 2 2Pi followed by the predissociation of 2 2Pi by 1 2Sigma- and 1 2Delta forming the S+(2Du) ion. These indications are in line with the experimental fact that both the 4Su and 2Du states of the S+ ion can be formed from the 2 2Pi and 1 2Sigma+ states of the OCS+ ion.

We have probed under high pressure the C-H hydrogen bonds formed by N,N(')-disubstituted imidazolium ions having PF(6) (-) and Br(-) counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N-H...F unit) in the infrared spectrum of the PF(6) (-) salt indicates that conventional N-H...O and N-H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C(2)-H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N-H hydrogen bonds in the PF(6) (-) salt. This finding is consistent with the pressure-dependent results, which reveal that the C(2)-H...F interaction is enhanced upon increasing the pressure. In contrast to the PF(6) (-) salt, the imidazolium C-H bonds of the Br(-) salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br(-) and PF(6) (-) ions., ((c) 2004 American Institute of Physics.)