声波的“漩涡”——声学轨道角动量的产生、操控与应用

具有螺旋形相位位错的声涡旋场近来受到了大量关注,因为其所携带的声学轨道角动量具有重要的理论意义与显著的应用价值。当声涡旋与物体相互作用时可以实现角动量的传递,产生可以远程局域或者旋转物体的力矩,这种力学效应对粒子操控等领域意义重大。产生声学轨道角动量的传统方法需要使用由大量独立操控的换能器组成的有源声阵列或是具有不平整厚度及螺旋形结构的无源材料,限制了其在实际中的应用潜力。为利用平面状的小尺寸器件来高效产生声学轨道角动量,发展了基于共振原理的角动量生成技术。最近,声学轨道角动量被拓展至用于开辟新的多路复用信道,以实现高容量的声学通信。文章详细介绍声学轨道角动量的产生、操控及应用方面的最新研究进展。     

Compensating for a bite block in /s/ and /t/ production: palatographic, acoustic, and perceptual data

Electropalatography was used to monitor linguapalatal contact patterns in /s/ and /t/. Talkers often compensated incompletely for a bite block, both immediately after its insertion (sample B1) and after 10 min of practice (sample B2). Significant differences in the number of sensors contacted were noted between normal and bite-block samples for both /s/ and /t/. Differences in length of constriction in /t/, and the A-P location and width of the groove in /s/ were also noted. The two native English subjects compensated better than three Arabic subjects, perhaps because English /s/ and /t/ are formed more posteriorily and with a smaller contact area than their Arabic counterparts. A significant correlation existed between the area and A-P location of linguapalatal contact. All five subjects formed a groove for /s/ in sample B2, but two often did not produce /t/ with complete constriction. This suggests a groove is critical for /s/, but complete constriction is not critical for /t/. The contact patterns in sample B2 more closely resembled normal speech than those in sample B1 in some instances, while in other instances the reverse was true. The conclusion that subjects sometimes overcompensated in sample B2 was supported by the results of detailed acoustic and perceptual analyses for one subject. Taken together, the results suggest that compensation for a bite block is not instantaneous, and that specific parameter values may be encoded in central phonetic representations.     

Sources of acoustic variation: implications for production specificity and call categorization in chacma baboon (Papio ursinus) grunts

Elucidating the information content of vocal signals is fundamental to the understanding of animal communication. Acoustically distinct calls produced in specific contexts allow listeners to predict future events and choose adequate responses. However, the vocal repertoires of most terrestrial mammals consist of a limited number of call types that vary within and between categories. These "graded signaling systems" are thought to be rich in information, at the cost of increasing uncertainty regarding call categorization. In this study, patterns of acoustic variation in grunts of wild chacma baboons (Papio ursinus) were assessed in relation to different contexts, callers' arousal, the presence of listeners, and individual identity. Although overall production specificity was low, and sensitive to the number of contexts under consideration, grunts given in three contexts could be statistically distinguished from each other. Contextual differences remained when controlling for caller arousal, suggesting that these differences cannot be explained by variation in arousal. No audience effect was detected, but individual identity was found to have an influence on acoustic structure. Overall, these results support the view that, in comparison to other signaling systems associated with hazardous conditions, lower production specificity might evolve under relaxed circumstances where unambiguous signaling is less important.     

Cavitation based cleaner technologies for biodiesel production and processing of hydrocarbon streams: A perspective on key fundamentals,missing process data and economic feasibility – A review

The present review emphasizes the role of hydrodynamic cavitation (HC) and acoustic cavitation in clean and green technologies for selected fuels (of hydrocarbon origins such as gasoline, naphtha, diesel, heavy oil, and crude oil) processing applications including biodiesel production. Herein, the role of cavitation reactors, their geometrical parameters, physicochemical properties of liquid media, liquid oxidants, catalyst loading, reactive oxygen species, and different types of emulsification and formation of radicals, formation as well as extraction of formed by-products are systematically reviewed. Among all types of HC reactors, vortex diode and single hole orifices revealed more than 95 % desulfurization yield and a 20 % viscosity reduction in heavy oil upgrading, while multi-hole orifice (100 holes) and slit Venturi allowed obtaining the best biodiesel production processes in terms of high (%) yield, low cost of treatment, and short processing time (5 min; 99 % biodiesel; 4.80 USD/m³). On the other hand, the acoustic cavitation devices are likely to be the most effective in biodiesel production based on ultrasonic bath (90 min; 95 %; 6.7 $/m³) and desulfurization treatment based on ultrasonic transducers (15 min; 98.3 % desulfurization; 10.8 $/m³). The implementation of HC-based processes reveals to be the most cost-effective method over acoustic cavitation-based devices. Finally, by reviewing the ongoing applications and development works, the limitations and challenges for further research are addressed emphasizing the cleaner production and guidelines for future scientists to assure obtaining comprehensive data useful for the research community.     

A unified treatment of electromagnetic decays,electroproduction, and pair production in e+e− annihilation for hadrons of arbitrary spin

We gather together in a unified notation formulas for electromagnetic decay rates of resonances and cross sections for electroproduction and e⁺e^? annihilation for all those processes which can be expressed in terms of matrix elements of the electromagnetic current between single particle (or resonant) helicity states. We show in complete generality how to decompose such helicity matrix elements into form factors which are free of all kinematic singularities and constraints simultaneously at both physical thresholds, and relate them to the familiar multipole moments and to some others which have been used in data analysis. Tables are given of the form factor decomposition of the helicity matrix elements for many cases of actual and potential practical interest.     

Thermosonication as an alternative method for processing,extending the shelf life,and conserving the quality of pulque: A non-dairy Mexican fermented beverage

The aim of this study was to evaluate thermosonication as an alternative method for the pasteurization of pulque in order to improve its shelf life and retain its quality parameters.Thermosonication was carried out at 50 °C using amplitudes of 75% (for 6 and for 9 min), 85% (for 4 and for 6 min), and 95% (for 3 and for 5 min). These were the optimal conditions found for processing pulque by thermosonication. Physicochemical (acidity, color, alcohol content, and sensory analysis) and microbiological (lactic acid bacteria and yeasts) parameters were determined during 30 days for storage at 4 ± 1 °C. Conventional pasteurization (63 °C, 30 min) and raw pulque were used as controls. According to the results, the shelf life of pulque was extended up to 24 days storage at 4 °C. After this time, the quality of beverage decreased, due that the microbial load increases. Thermosonication treatments at 75% and 85% showed a higher content of LAB (6.58–6.77 log CFU/mL) and yeasts (7.08–7.27 log CFU/mL) than conventional pasteurization (3.64 log CFU/mL of LAB and 3.97 log CFU/mL of yeasts) at 24 days of storage. Raw pulque demonstrated up to 7.77 log CFU/mL of yeasts and 7.51 log CFU/mL of LAB. Pulque processed by thermosonication exhibited greater lightness, sensory acceptance, a maximal acidity of 0.83 g/lactic acid, and an alcohol content of 4.48–4.95% v/v. The thermosonication process preserves sensory and physicochemical properties better than conventional pasteurization. Lactic acid bacteria such as Lactobacillus kefiri, Lactobacillus acidophilus, and Lactobacillus hilgardii and yeasts such as Saccharomyces cereviasiae were identified in thermosonicated pulque.     

Installation for supercritical drying: Construction, operation experience, and production of low-density polymer aerogels

Experience of constructing an original installation for supercritical drying of polymer gels and operating it are described in detail. A particular attention is paid to the preparation of anhydrous carbon monoxide. The effectiveness of the designed equipment in producing aerogel samples of different chemical natures is demonstrated.     

A transient testing technique for the determination of matrix parameters of acoustic systems,I: Theory and principles

A transient testing technique has been developed for rapid testing of components in acoustic systems. Fourier transforms of transient pressure data are utilized to provide system characteristics in the frequency domain. The approach is applicable to field testing situations where short duration testing with a minimum of portable instrumentation is desirable and no special apparatus such as anechoic terminations are available. Derivations of matrix parameters expressed in terms of the transforms of pairs of pressure data are presented for a variety of testing conditions and system types. Analytical expressions for theoretical matrix parameters for selected known systems are also included for comparison with experimental results.     

A transient testing technique for the determination of matrix parameters of acoustic systems,II: Experimental procedures and results

This paper deals with the application of a transient testing technique for the determination of matrix parameters of acoustic systems. Experiments were conducted for six systems of various geometrical configurations such as (1) a section of pipe, (2) a small expansion chamber, (3) a large expansion chamber, (4) partition pipes, (5) partition chambers and (6) an expansion chamber with insertion pipes. Two series of results were obtained for these systems, one concerned with the evaluation of matrix parameters for blockable and reciprocal cases and the other for the non-blockable and reciprocal types. Excellent agreement between experimental and theoretical results is illustrated by some typical results obtained for systems (1) and (3).     

Method for measuring the frequency shifts of interference maxima in monitoring of dispersion media: Theory,implementation, and prospects

A theory and implementation of the approach to reconstruction of inhomogeneities in dispersion media, based on measuring the frequency shifts of interference maxima (FSIMs) of wave field, are reported. The possibilities of the new approach are compared with the potential of the conventional technique, which is based on measuring the propagation times of pulsed signals. Specific methods for measuring FSIMs in time-dependent media are described, and the noise immunity of these methods is evaluated. The reconstruction (via FSIM monitoring) of typical oceanic inhomogeneities is described and analyzed. Possible applications of this approach in the infra- and ultrasonic ranges are shown.     

Raman spectroscopic study of the sulfite‐bearing minerals scotlandite,hannebachite and orschallite: implications for the desulfation of soils

The structures of the naturally occurring sulfite‐bearing minerals scotlandite, hannebachite and orschallite have been studied by Raman spectroscopy. Raman bands are observed for scotlandite PbSO₃ at 935, 880, 622 and 474 cm⁻¹ and are assigned to the (SO₃)²⁻ν₁(A₁), ν₃(E), ν₂(A₁) and ν₄(E) vibrational modes, respectively. For hannebachite (CaSO₃)₂·H₂O these bands are observed at 1005, 969 and 655 cm⁻¹ with multiple bands for the ν₄(E) mode at 444, 492 and 520 cm⁻¹. The Raman spectrum of hannebachite is very different from that of the compound CaSO₃·2H₂O. It is proposed, on the basis of Raman spectroscopy, that in the mineral hannebachite, the sulfite anion bonds to Ca through the sulfur atom. The Raman spectrum of the mineral orschallite Ca₃[SO₄](SO₃)₂·12H₂O is complex resulting from the overlap of sulfate and sulfite bands. Raman bands at 1005 cm⁻¹, 1096 and 1215 cm⁻¹ are assigned to the (SO₄)²⁻ν₁ symmetric and ν₃ asymmetric stretching modes. The two Raman bands at 971 and 984 cm⁻¹ are attributed to the (SO₃)²⁻ν₃(E) and ν₁(A₁) stretching vibrations. The formation of sulfite compounds in nature offers a potential mechanism for the removal of sulfates and sulfites from soils. Copyright © 2008 John Wiley & Sons, Ltd.     

B-, N-doped and BN codoped C60 heterofullerenes for environmental monitoring of NO and NO2: a DFT study

ABSTRACT

Using density functional theory calculations, we investigate the gas sensing performance of B-, N-doped and BN-codoped C₆₀ fullerenes towards NO and NO₂ molecules. The calculated adsorption energies and net charge-transfer values indicate that NO and NO₂ molecules have a stronger interaction with the BN-codoped fullerenes compared to the B- or N-doped ones. It is also found that the electronic properties of the BN-codoped C₆₀ exhibit a larger sensitivity towards NO and NO₂ molecules. An increase in the concentration of doped/co-doped B and N atoms tends to weaken the gas sensing ability of these systems.