Electron flow enhancement with a diamond membrane

Secondary electron emission from 2.5-to 5.0-μm thick diamond films (membranes) is considered. The process is studied in the reflection regime, where secondary electrons leave the front surface of the membrane exposed to primary electrons, and in the transmission regime, where primary electrons cause secondary emission from the opposite surface. The secondary emission coefficient is determined based on the behavior of 0.1-to 30-keV electrons in the solid. In the reflection regime, the secondary emission coefficient may be higher than 100 for electron energies of about 3 keV; in the transmission regime, it is no more than 5 even for 30-keV electrons. The emissivity of the membranes in the transmission regime can be improved, specifically, by using porous membranes, which allow one to obtain characteristics similar to those in the reflection regime. Experimental data obtained agree with calculations. The production of diamond films, including porous membranes, is described.     

Direct contact ultrasound for fouling control and flux enhancement in air-gap membrane distillation

Air Gap Membrane distillation (AGMD) is a thermally driven separation process capable of treating challenging water types, but its low productivity is a major drawback. Membrane fouling is a common problem in many membrane treatment systems, which exacerbates AGMD’s low overall productivity. In this study, we investigated the direct application of low-power ultrasound (8–23 W), as an in-line cleaning and performance boosting technique for AGMD. Two different highly saline feedwaters, namely natural groundwater (3970 μS/cm) and RO reject stream water (12760 μS/cm) were treated using Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes. Theoretical calculations and experimental investigations are presented, showing that the applied ultrasonic power range only produced acoustic streaming effects that enhanced cleaning and mass transfer. Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that ultrasound was capable of effectively removing silica and calcium scaling. Ultrasound application on a fouled membrane resulted in a 100% increase in the permeate flux. Cleaning effects accounted for around 30–50% of this increase and the remainder was attributed to mass transfer improvements. Contaminant rejection percentages were consistently high for all treatments (>99%), indicating that ultrasound did not deteriorate the membrane structure. Scanning Electron Microscopy (SEM) analysis of the membrane surface was used to confirm this observation. The images of the membrane surface demonstrated that ultrasound successfully cleaned the previously fouled membrane, with no signs of structural damage. The results of this study highlight the efficient and effective application of direct low power ultrasound for improving AGMD performance.     

Multibubble sonoluminescence enhancement by fluid flow

Forced fluid flow can cause the enhancement of multibubble sonoluminescence (SL) under suitable conditions. The effect of directional flow with a circulator is similar to that of rotating flow with a stirrer. The mechanism of the enhancement is that both flows prevent cavitation bubbles from coalescing and clustering, which are responsible for the quenching of SL. The intensity of sonochemiluminescence (SCL) in an aqueous luminol solution increases with flow speed at higher ultrasonic powers more significantly than that of SL in distilled water. However, in the range of low ultrasonic power, the intensities of SL and SCL decrease with flow speed. Therefore, an optimum flow speed exists in relation to ultrasonic power and frequency.     

Sensitivity enhancement in pulse EPR distance measurements

Established pulse EPR approaches to the measurement of small dipole-dipole couplings between electron spins rely on constant-time echo experiments to separate relaxational contributions from dipolar time evolution. This requires a compromise between sensitivity and resolution to be made prior to the measurement, so that optimum data are only obtained if the magnitude of the dipole-dipole coupling is known beforehand to a good approximation. Moreover, the whole dipolar evolution function is measured with relatively low sensitivity. These problems are overcome by a variable-time experiment that achieves suppression of the relaxation contribution by reference deconvolution. Theoretical and experimental results show that this approach leads to significant sensitivity improvements for typical systems and experimental conditions. Further sensitivity improvements or, equivalently, an extension of the accessible distance range can be obtained by matrix deuteration or digital long-pass filtering of the time-domain data. Advantages and limitations of the new variable-time experiment are discussed by comparing it to the established analogous constant-time experiment for measurements of end-to-end distances of 5 and 7.5 nm on rod-like shape-persistent biradicals and for the measurement of a broadly distributed transmembrane distance in a doubly spin-labeled mutant of plant light harvesting complex II.     

Sensitivity enhancement in thermal lens laser spectrometry

A novel experimental configuration for thermal lens detection is described. The method makes use of optical filtering of the probe beam by means of a circular aperture. This considerably reduces noise associated with intensity fluctuations of the probe beam. The technique provides an enhancement of the signal-to-noise ratio by almost one order of magnitude as compared to other thermal lens laser spectrometers. A theoretical calculation of the signal enhancement associated with optical filtering of the probe beam is presented. Furthermore, experiments on methyl blue dissolved in ethylalcohol are described which verify the theoretical predictions.     

Sensitivity enhancement of AZO-based ethanol sensor decorated by Au nano-islands

Detecting the hazardous gases for monitoring air pollution and medical diagnosis make highly sensitive gas sensors appeal to many researches. In this paper, benefiting from unique properties of noble metals, Al-doped ZnO based Ethanol sensors were fabricated and characterized in three structures including Al: ZnO thin film, Silver and Gold nano-islands on Al: ZnO thin film. The Silver and Gold thin films turn to nano-islands after a simple annealing process. The XRD analysis of the sputtered Al: ZnO layer indicates the wurtzite crystal structure of the layer with a peak at (002) plane. Moreover, the sensitivity study reveals that Nano-islands of noble metals substantially affects the sensitivity of the sensors. The decorated Gold nano-island Al: ZnO Ethanol sensor has the highest response showing an amount of 45. The response of Al: ZnO and Silver decorated Al: ZnO sensors are virtually identical to all concentrations of Ethanol, whereas the Al: ZnO gas sensor with Gold nano-islands has the substantial sensitivity for different concentrations. In addition, the response times of the sensors are 85, 70 and 90 s for Al: ZnO, Al: ZnO with Ag islands and Al: ZnO decorated by Au islands, respectively. The recovery time of Al: ZnO sensor decorated by Au islands is about 23s, while the recovery time of the Al: ZnO and Al: ZnO decorated by Silver islands are 360 and 370s, respectively. Hence, the simple annealing process on the sputtered gas sensor with a thin layer of Gold makes nano-islands on the sensor which elevates the performance of Ethanol sensing due to the high sensitivity and sensitivity of the sensor.     

Experimental investigation of flow boiling heat transfer enhancement under ultrasound fields in a minichannel heat sink

Ultrasound is considered to be an effective active heat transfer enhancement method, which is widely used in various fields. But there is no clear understanding of flow boiling heat transfer characteristics in micro/mini-channels under ultrasonic field since the studies related are limited up to now. In this paper, a novel minichannel heat exchanger with two ultrasonic transducers inside the inlet and outlet plenum respectively is designed to experimentally investigate the impacts of ultrasound on flow boiling heat transfer enhancement in a minichannel heat sink. Flow visualization analyses reveal that ultrasound can promote rapid bubble motion, bubble detachment from heating wall surface and thereby new bubble generation, and decrease the length of confined bubble. Furthermore, the flow boiling experiments are initiated employing working fluid R141b at different ultrasonic parameters (e.g., frequency, power, angle of radiation) and heat flux under three types of ultrasound excitations: no ultrasound (NU), single inlet ultrasound (IU), inlet and outlet ultrasound (IOU). The results indicate that ultrasound has obvious augmentation effects on flow boiling heat transfer even though the intensification effects will be limited with the heat flux increases. The higher ultrasonic power, the lower ultrasonic frequency and the higher ultrasonic radiation angle, the better intensification efficiency. The maximum enhancement ratio of h_ave in the saturated boiling section reaches 1.88 at 50 W, 23 kHz and 45° under the experimental conditions. This study will be beneficial for future applications of ultrasound on flow boiling heat transfer in micro/mini-channels.     

Sensitivity enhancement in quadrupolar nuclei double resonance detection

NMR imaging of quadrupolar nuclei in liquid system has received less attention than the imaging ofS=1/2 nuclei due to difficulties associated with the quadrupolar interaction. The¹⁰B spatial distribution in Na₂ ¹⁰B₁₂H₁₁SH in phantom has been obtained using an indirect J-coupling Double Resonance method. This procedure allows one to localize the quadrupolar nuclei by observing the protons J-coupled with them. The sensitivity gain in the indirect spatial localization of the¹⁰B nuclei with respect to to the direct one, is here computed and verified on the Na₂ ¹⁰B₁₂H₁₁SH images.     

Sensitivity enhancement in optical waveguide sensors using metamaterials

In this paper, we show negative differential resistance (NDR) in CdSe quantum dot/MEH-PPV based nanocomposite multi-layer heterostructures at room temperature. The four-layer structure exhibited a maximum peak-to-valley ratio of current of 1190 at room temperature, while two-layer structures show a value of 4. Two-, three- and four-layer structures are studied. Each device configuration exhibits different kind of negative differential resistance. The possible mechanism is explained on the basis of tunneling phenomena.     

Sensitivity enhancement of HCACO by using an HMQC magnetization transfer scheme

Previous theoretical calculations have demonstrated that the multiquantum relaxation rate of (1)H(alpha)-(13)C(alpha)(R(MQ)) is, on average, 1.3 +/- 0.4 or 1.7 +/- 0.6 times slower than the single-quantum relaxation rate of (13)C(alpha)(R(C)) for a sample with or without, respectively, amide protons. By taking advantage of this fact and by using the PEP sensitivity enhancement scheme, an HMQC version of the HCACO experiment has been developed. We demonstrate that this new experiment is 23 and 55% more sensitive than the original HSQC version of the HCACO experiment, at constant times of 7 and 27 ms, respectively, for a sample of the BC domain of the ciliary neurotrophic factor receptor protein dissolved in D(2)O at 20 degrees C.     

功率超声强化溶液冻结机理的研究进展

功率超声波强化溶液结晶是一种新型的结晶技术,由于其具有促进溶液冻结、控制晶体粒径分布和提高冻结产品质量的作用,近年来受到越来越多的关注。从过冷溶液的一次冰晶成核、二次冰晶成核以及树枝状冰晶体的生长速度等方面对超声波强化溶液结晶的机理进行了综述,并对超声结晶机理研究的发展方向提出了建议。     

Mass transfer enhancement in supercritical fluids extraction by means of power ultrasound

The use of high-intensity ultrasound represents an efficient manner of producing small scale agitation, enhancing mass transfer on supercritical fluids (SF) extraction processes. In this way, a supercritical CO(2) extraction of oil from particulate almonds using power ultrasound was studied. To examine the effect of the acoustic waves all experiments were performed with and without ultrasound. A power ultrasonic transducer for a working frequency of about 20 kHz was constructed and installed inside a high-pressure 5 l SF extractor. The experimental tests were carried out with CO(2) at 280 bar and 55 degrees C. Grounded almonds with an oil content of about 55%, in an amount of 1500 g were deposited inside the SF reactor where the solvent was introduced at a flow rate of 20 kg/h. The results show that the kinetics and the extraction yield of the oil were enhanced by 30% and 20% respectively, when a power of about 50 W was applied to the transducer. The average time of each extraction process was of about 8 h and 30 min. In addition, the transducer was also used as a sensitive probe capable to detect the phase behavior of supercritical fluids when it was driven with low power signals.     

Sensitivity enhancement in structural measurements by solid state NMR through pulsed spin locking

Free induction decay (FID) signals in solid state NMR measurements performed with magic angle spinning can often be extended in time by factors on the order of 10 by a simple pulsed spin locking technique. The sensitivity of a structural measurement in which the structural information is contained in the dependence of the integrated FID amplitude on a preceding evolution period can therefore be enhanced substantially by pulsed spin locking in the signal detection period. We demonstrate sensitivity enhancements in a variety of solid state NMR techniques that are applicable to selectively isotopically labeled samples, including 13C-15N rotational echo double resonance (REDOR), 13C-13C dipolar recoupling measurements using the constant-time finite-pulse radio-frequency-driven recoupling (fpRFDR-CT) and constant-time double-quantum-filtered dipolar recoupling (CTDQFD) techniques, and torsion angle measurements using the double quantum chemical shift anisotropy (DQCSA) technique. Further, we demonstrate that the structural information in the solid state NMR data is not distorted by pulsed spin locking in the detection period.     

Tailoring the properties of polyamide thin film membrane with layered double hydroxide nanoclay for enhancement in water separation

This current paper presented a new candidate and potentially to improve the current membrane materials in water filtration process. With that, the primary materials used in this research study is layered double hydroxides (LDH) nanoclay which can be obtained from earth minerals and self-synthesized from inorganic salts were discussed thoroughly to help a better understanding of these materials. However, the current technologies of water separation were still lagging behind and ineffective especially in removal of divalent metal ions and multivalent salts. Infeasibility of reverse osmosis membrane make it not a viable option for divalent salts filtration. With that, nanofiltration (NF) membrane offered as an alternative to substitute available method. In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating layered double hydroxides (LDH) nanoclay. The LDH nanoclay with different loading ratio of 0, 0.05, 0.1, 0.15 and 0.2 were impregnated into polyamide layer on top of polysulfone substrates. The fabricated TFN were characterized in terms of physicochemical properties (SEM and FTIR) and membrane hydrophilicity (contact angle). After the addition of LDH, the morphological structures of TFN membranes were changed and the surface hydrophilicity was enhanced significantly. FESEM images displayed a typical ridge and valley morphology with nodule-like structures. As the LDH loading was increased, the contact angle decreased from 34.56° to 15.76° showing the surface hydrophilicity of membrane is improved. The separation performance of membrane was evaluated in terms of salt rejection ability by cross flow filtration system. The best performance NF membrane was found to be TFN 0.05 with high water flux and MgCl₂ rejection with values of 24.18 L/m².h and 91% respectively. This study has experimentally validated the potential of LDH materials in membrane process for improvement in water separation process.     

Staggered car-following induced by lateral separation effects in traffic flow

This Letter develops a new staggered car-following model taking into consideration lateral separation effects. Time-to-collision, calculated using visual angle variables, is introduced to describe the lateral separation distance and improve the optimal velocity model. The analytical and numerical results show that the stability of traffic flow can gradually be enhanced with the increase of lateral separation effects. The asymmetry property of traffic flow is also investigated using the new model. The results imply that incorporating lateral separation effects into the car-following model leads to the suppression of traffic jams and greatly enhances the realism of the model.     

Visualization of blood flow by ultrasound speckle interferometry

A new method for the visualization of flowing liquids is suggested. The method makes it possible to obtain images of dynamic objects located in an inhomogeneous medium. The main requirement for the realization of this method is the stability of the field during two successive measurements. The dimensions of the irradiating beam depend on the value of the spatial correlation interval characterizing the inhomogeneities of the medium, while the amplitude distribution in the beam can be arbitrary. A numerical modeling of the method is performed, and images of the models of blood vessels lying under an inhomogeneous layer are presented.     

Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to 'remote detection' described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time.     

Sensitivity enhancement in multiple-quantum NMR experiments with CPMG detection

We present a modified multiple-quantum (MQ) experiment, which implements the Carr-Purcell-Meiboom-Gill (CPMG) detection scheme in the static MQ NMR experiment proposed by W. S. Warren et al. (1980, J. Chem. Phys.73, 2084-2099) and exploited further by O. N. Antzutkin and R. Tycko (1999, J. Chem. Phys.110, 2749-2752). It is demonstrated that a significant enhancement in the sensitivity can be achieved by acquiring echo trains in the MQ experiments for static powder samples. The modified scheme employing the CPMG detection was superior to the original MQ experiment, in particular for the carbonyl carbon with a very large chemical shift anisotropy.     

Phase separation in a chaotic flow

The phase separation between two immiscible liquids advected by a bidimensional velocity field is investigated numerically by solving the corresponding Cahn-Hilliard equation. We study how the spinodal decomposition process depends on the presence-or absence-of Lagrangian chaos. A fully chaotic flow, in particular, limits the growth of domains, and for unequal volume fractions of the liquids, a characteristic exponential distribution of droplet sizes is obtained. The limiting domain size results from a balance between chaotic mixing and spinodal decomposition, measured in terms of Lyapunov exponent and diffusivity constant, respectively.