Constant Drop Research Articles

Protein adsorption and desorption on lipid bilayers

The protein surface usually exhibits one or a few charged spots. If a lipid bilayer contains a significant amount of lipids with oppositely charged head groups, protein adsorption on a bilayer may be energetically favourable due to the protein-lipid electrostatic interaction. The specifics of this case are that the lipids are highly mobile and the protein adsorption is accompanied by the redistribution of lipids between the areas covered and not covered by protein. We present a kinetic model illustrating that this effect is especially interesting if the fraction of the surface covered by charged lipids is relatively low. In this situation, with increasing protein coverage, the protein desorption rate constant rapidly increases while the adsorption rate constant drops, so that there is critical fraction of the area covered by protein. Adsorption above this fraction is hindered both kinetically and thermodynamically.

Implications of critical flux and cake enhanced osmotic pressure (CEOP) on colloidal fouling in reverse osmosis: Modeling approach

This article describes a predictive model to account for the performance of a reverse osmosis (RO) system under the influence of colloidal fouling (using silica particles as model colloids) in terms of transmembrane pressure increase (δTMP) in constant flux operation or flux drop (δJ v) in constant pressure operation. The predictive model considers the implications of both the critical flux (J crit) and cake enhanced osmotic pressure (CEOP) phenomenon and is based on the membrane retention, concentration polarization, mass transfer, resistance in series and osmotic pressure model, cake resistance, and critical flux concept.

Neuromuscular control in landing from supra-maximal dropping height

The present study utilized high-impact supra-maximal landings to examine the influence of the pre-impact force level on the post-impact electromyographic (EMG) activity and, in particular, on the short latency EMG reflex (SLR) component. Unilateral-leg landings were performed in a sitting position on a sledge apparatus after release from high, but individually constant dropping height. A lower limb guiding device fixed to the front of the sledge seat allowed the subjects to sustain a given pre-set force level up to impact. This force level was either freely chosen or set at 20, 35, and 50% of maximal isometric plantarflexion force. EMG activity was recorded from eight major lower limb muscles. It was expected that the increase in the pre-impact force level would require the intervention of a protective neural strategy during the post-impact phase that would attenuate the SLR amplitude. The ultrasonography recordings confirmed that the soleus fascicles were stretched to induce SLR. The main finding was the similarity across all tested conditions of the impact peak force and post-impact EMG activity, including the SLR response. Both observations are mostly attributed to the similar EMG levels and close force levels reached toward impact. The instruction to maintain a given pre-set force level was indeed overruled when getting close to impact. It is suggested that, in the present supra-maximal landing condition, a protective central neural strategy did occur that took into account the pre-set force level to secure similar impact loads.

Post- to pre-overnight sleep systolic blood pressures are associated with sleep respiratory disturbance, pro-inflammatory state and metabolic situation in patients with sleep-disordered breathing

Objective The aim of the current study was to investigate whether changes in post- to pre-overnight sleep systolic blood pressure (SSBP) are associated with sleep respiratory disturbance, pro-inflammatory state, and metabolic situation in patients with sleep-disordered breathing (SDB). Methods Anthropometry, sleep polysomnography, biochemical markers, and pre- and post-overnight sleep BP were measured from 263 SDB patients. All SDB patients were further subgrouped into MORNING SURGE (% changes from post- to pre-overnight SSBP >+1SD of this cohort), MORNING DROP (% changes <−1SD), CONSTANT HIGH (% changes within ± 1SD, averaged SSBP > 130 mmHg) and CONSTANT LOW (% changes within ± 1SD, averaged SSBP < 130 mmHg). Results BMI, neck circumference, waistline circumference, respiratory disturbance index, arousal index, lowest oxygen saturation, duration of SaO 2 < 90%, blood glucose, hs-CRP, and metabolic syndrome score in MORNING SURGE and CONSTANT HIGH were significantly greater than those in CONSTANT LOW. Except metabolic syndrome score, all other parameters in MORNING DROP were similar to those in CONSTANT LOW. Conclusion Patients with SDB whose post- to pre-overnight SSBPs were elevated or maintained a constant high have more sleep respiratory disturbance, more pro-inflammatory state, and higher metabolic syndrome indices than the rest. Without subdividing into CONSTANT LOW, MORNING DROP, CONSTANT HIGH, and MORNING SURGE, the important pathophysiologic points of SDB patients will possibly be missed.

An Advanced Optimal Approach for High Voltage AC Bushing Design

This paper proposes a new and advanced methodology for finding the optimum electrical design of high voltage ac capacitive graded bushings using an improved genetic algorithm approach as an effective meta-heuristic method. A case study has been conducted on a 145 kV oil impregnated paper (OIP) bushing and the IEC 60137 tests have been performed to evaluate its performance. Condenser-bushings contain concentric conductive foils which are isolated from each other. The partial capacitances between conducting cylinders can be modified by adjusting the number, diameter, place and length of these cylinders as well as the thickness of insulating material between foils. As a result, the voltage drop and also the electrical stress in the core and along the surface will change. This paper finds optimal value of bushing design parameters to achieve well-distributed electric stress with the lowest possible maximum value and also a constant voltage drop for different layers by using an improved genetic algorithm optimization method subject to practical and technological constrains. The proposed method of this research work has been applied to a 145 kV OIP bushing. The performance of optimal designed 145 kV OIP bushing under IEC 60137 tests is very promising.

Effect of the Drop Size Distribution of Fuel Spray on Ignition Phenomenon

The ignition of fuel spray is affected by various factors, i.e., temperature, pressure, equivalence ratio, droplet diameter, number density of droplets, air velocity, ignition energy, and so on. In order to clarify the effects of spray characteristics on spray ignition phenomenon, there have been many researches. However, the effect of drop size distribution on spray ignition has not been studied yet because it is difficult to control drop size distribution independently with other spray characteristics. In this study, it is aimed to clarify the effect of drop size distribution of fuel spray on ignition phenomenon, using drop size distribution control technique developed by the authors The results of this study clearly show that the ignition probability decrease with the increase of standard deviation of drop size distribution under the constant mean drop size and concentration condition. In addition, the decrease ratio of ignition probability decreases by the decrease of average fuel spray concentration. The results also show that flame area decrease with the increase of the standard deviation of drop size distribution.

Piezodielectric Effect of Carbon Fiber—Sulfoaluminate Cement Composites

Carbon fiber—sulfoaluminate cement composites (CFSC) were fabricated by compressing technology. The mechanism of piezodielectric effect of CFSC was discussed. The results show that the relative dielectric constant of CFSC sample decreases when the stress is less than 5 MPa. However, when the stress is in the range of 5—60 MPa, the relative dielectric constant increases linearly. When the stress exceeds 60 MPa, the relative dielectric constant drops dramatically because of the destruction of CFSC under stress. When the content of carbon fiber is 0.5% (by mass), its fractional change of relative dielectric constant corresponds to the cyclic compressive stress even if the cyclic time arrives at thousand and the stress amplitude is enhanced to 40 MPa. CFSC containing 0.5% carbon fiber content has good piezodielectric effect, which is suitable for the application of important buildings such as bridges, dams, and so on to realize real-time, dynamic, and health monitoring.

A scaling law for slow earthquakes

Recently, a series of unusual earthquake phenomena have been discovered, including deep episodic tremor, low-frequency earthquakes, very-low-frequency earthquakes, slow slip events and silent earthquakes. Each of these has been demonstrated to arise from shear slip, just as do regular earthquakes, but with longer characteristic durations and radiating much less seismic energy. Here we show that these slow events follow a simple, unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes. We find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant, with a spectral high-frequency decay of f(-1). This scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category. The observed scale dependence of rupture velocity for these events can be explained by either a constant low-stress drop model or a diffusional constant-slip model. This new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation.

A comparison between spray cooling and film flow cooling during the rewetting of a hot surface

The paper is dealing with a research carried out at the Institute of Thermal-Fluid Dynamics to investigate the rewetting of a hot surface. The rewetting of the hot surface by spray cooling has been analyzed in previous works. After the droplet impingement, the liquid film falls along the surface, and rewetting by falling film takes place. The experiment was characterized by a 1-dimensional liquid spray, i.e., drops having a uniform, constant diameter, impinging on the heated surface. The cooling rate of the hot surface has been detected as a function of wall temperature, drop diameter and velocity, and impact point of the spray. The working feature of the spray is based on the varicose rupture of the liquid jet: imposing a periodic (symmetrical) perturbation with appropriate amplitude and frequency on the jet surface, the flow is “constrained” to break soon after leaving the nozzle, eventually obtaining constant diameter drops, depending on the nozzle diameter and liquid velocity. In this paper, previous results with spray cooling are compared with experimental runs in which the spray injection is replaced with a falling film all along the test section. The rewetting velocity has been calculated from the response of the thermocouples placed on the heated wall and using a digital image system based on the video image registered during the runs.

Acid-salt conversion by means of electrodialysis: Application of the systematic approach to food engineering systems (SAFES) methodology

A study of the acid-salt equilibrium citric acid by means of the SAFES methodology during electrodialysis was performed in order to determined if the fractional composition of the acid forms affects the process due to the predominance of non-dissociated forms. Experiments at constant potential drop, feed and variable current density were performed. Total concentration of acid and its fractional forms were determined. Results showed that even though in the dilution cell, molecules of basic forms, were removed the pH did not decrease. This may indicate that when removing the salt, the acid forms did not predominate and therefore does not affect the process.

Lattice Model Simulation of Penetrant Diffusion along Hexagonally Packed Rods in a Barrier Matrix As Determined by Pulse-Field-Gradient Nuclear Magnetic Resonance

The structural influence on translational diffusion of 2,2,4-trimethylpentane (TMP) through SEBS triblock polymer (poly(styrene)-block -poly(ethene-co-but-1 -ene)-block -poly(styrene)) was studied using pulse field gradient (PFG) NMR coupled with lattice model simulation. Two types of PFG experiments were performed: one observing the time-dependent apparent diffusion constant and another observing the diffusion-induced NMR signal attenuation. TMP is selectively sorbed into the rubbery ethylene/butylenes (EB) phase while the glassy poly(styrene) (PS) phase acts as a barrier to TMP diffusion. The observed apparent diffusion constant drops drastically at the grain boundary, in which the orientation of the minor EB cylinder phase changes from grain to grain. In the lattice model simulation, in order to match the large drop of diffusion constant, the diameter of the EB cylinder at the interface had to be reduced by a factor of about 0.7. This extra restriction in the size of the conductive phase indicates the important role of the grain boundary on diffusion in membrane applications of block copolymers. The simulation also shows that the grain boundary influence on diffusion becomes significant when the solubility and diffusivity of the penetrant are greatly different between the rubber and glass phases. In addition, we extended the lattice model to simulate the diffusion-induced PFG NMR signal attenuation. From the simulation and theoretical fitting, it is obvious that the EB phase at grain boundary is not connected well, which is in agreement with our observation of a drastic apparent diffusion constant drop at the grain boundaries in the PFG experiment.

LC Determination of 4-Bromoaniline in Green Algae Chlamydomonas reinhardtii After Continuous-Flow Microextraction

In this study, the determination of 4-Bromoaniline (4-BA) in green algae Chlamydomonas reinhardtii (C. reinhardtii) was investigated by applying continuous-flow microextraction (CFME) combined with high-performance liquid chromatography (HPLC). Continuous-flow microextraction was conducted in a homemade glass chamber, i.e. the sample solution flowed through a constant volume drop of solvent in the chamber at a constant flow rate. The effects of different factors on extraction efficiencies were also investigated and these factors included the kind of extraction solvent, solvent drop volume, sample flow rate, extraction time and addition amount of salt. Under the optimum extraction conditions (extraction solvent, carbon tetrachloride; solvent drop volume, 3.5 μL; sample flow rate, 1.0 mL min−1; extraction time, 10 min; no addition of salt), the calibration plot was set up by plotting peak area against a series of 4-Bromoaniline concentrations (0.01–10 μg mL−1) in aqueous solution. The correlation coefficient (r) was 0.9990. The limit of detection (LOD) was 0.6 ng mL−1. The precision of this method was obtained by successive five time analyses of 100-ng mL−1 standard solution of 4-Bromoaniline, and the relative standard deviation (RSD) was 3.5%. The concentration factor was calculated by the ratio of peak area of the analyte obtained after and before extraction and found to be 10.6. 4-Bromoaniline residues in Chlamydomonas. reinhardtii cells and tap water samples were satisfactorily analyzed according to the method described above.

What can the braking indices tell us about the nature of pulsars?

As a result of observational difficulties, braking indices of only six rotation-powered pulsars are obtained with some certainty. All these values are remarkably smaller than the value ( n = 3) expected for pure magnetodipole radiation model. Various models have been proposed to explain this phenomenon such as introducing additional torques by particle outflow or accretion disk, changes in inclination angle or magnetic field strength, and field-reconnection process in pulsar magnetosphere. We re-examined the braking index based on previous research and suggest a constant gap potential drop in the open-field line region for pulsars with magnetospheric activity. New constraints on model parameters from observed braking indices are presented.

Noise in cavity ring-down spectroscopy caused by transverse mode coupling

In our continuous wave cavity ring-down spectroscopy (CW-CRDS) experiments, we have often observed that the decay time constant drops to a lower value at some cavity lengths or some intercavity pressures. The resulting instabilities lead to a reduction in the sensitivity of our CRDS system. We have deduced that the cause of this noise is the coupling between the TEM(00) mode that the laser excites, and the higher order transverse modes of the cavity. The coupling will cause anti-crossings as the modes tune with cavity length. A consequence is that the decay of light intensity leaving the cavity is no longer a single exponential decay, but the signal can be quantitatively fit to a two-mode beating model. With a 4mm diameter intra-cavity aperture, the higher order modes are suppressed and the stability of the system improved greatly. One coupling mechanism is scattering from the mirror surfaces. This can explain some features of our data including the strength of this coupling and the relative tuning rate of the coupled modes. Remarkably, a scattering intensity between modes of ~ 10(-12) can produce observable changes in the cavity decay rate. However, the tuning rate between the TEM(00) mode and the higher order modes in a cavity pressure scan is larger than predicted and is still not explained. Images of higher order transverse modes excited at certain cavity conditions were recorded by an Indium Gallium Arsenide (InGaAs) area camera.

A Kinetic Model of the Formation of Organic Monolayers on Hydrogen-Terminated Silicon by Hydrosilation of Alkenes

We have analyzed a kinetic model for the formation of organic monolayers based on a previously suggested free radical chain mechanism for the reaction of unsaturated molecules with hydrogen-terminated silicon surfaces (Linford, M. R.; Fenter, P. M.; Chidsey, C. E. D. J. Am. Chem. Soc 1995, 117, 3145). A direct consequence of this mechanism is the nonexponential growth of the monolayer, and this has been observed spectroscopically. In the model, the initiation of silyl radicals on the surface is pseudo first order with rate constant, ki, and the rate of propagation is determined by the concentration of radicals and unreacted Si-H nearest neighbor sites with a rate constant, kp. This propagation step determines the rate at which the monolayer forms by addition of alkene molecules to form a track of molecules that constitute a self-avoiding random walk on the surface. The initiation step describes how frequently new random walks commence. A termination step by which the radicals are destroyed is also included. The solution of the kinetic equations yields the fraction of alkylated surface sites and the mean length of the random walks as a function of time. In mean-field approximation we show that (1) the average length of the random walk is proportional to (kp/ki)1/2, (2) the monolayer surface coverage grows exponentially only after an induction period, (3) the effective first-order rate constant describing the growth of the monolayer and the induction period (kt) is k = (2ki kp)1/2, (4) at long times the effective first-order rate constant drops to ki, and (5) the overall activation energy for the growth kinetics is the mean of the activation energies for the initiation and propagation steps. Monte Carlo simulations of the mechanism produce qualitatively similar kinetic plots, but the mean random walk length (and effective rate constant) is overestimated by the mean field approximation and when kp >> ki, we find k approximately ki0.7kp0.3 and Ea = (0.7Ei+ 0.3Ep). However the most striking prediction of the Monte Carlo simulations is that at long times, t >> 1/k, the effective first-order rate constant decreases to ki even in the absence of a chemical termination step. Experimental kinetic data for the reaction of undec-1-ene with hydrogen-terminated porous silicon under thermal reflux in toluene and ethylbenzene gave a value of k = 0.06 min(-1) and an activation energy of 107 kJ mol(-1). The activation energy is in reasonable agreement with density functional calculations of the transition state energies for the initiation and propagation steps.

Gate Leakage Reduction by Clocked Power Supply of Adiabatic Logic Circuits

Abstract. Losses due to gate-leakage-currents become more dominant in new technologies as gate leakage currents increase exponentially with decreasing gate oxide thickness. The most promising Adiabatic Logic (AL) families use a clocked power supply with four states. Hence, the full VDD voltage drops over an AL gate only for a quarter of the clock cycle, causing a full gate leakage only for a quarter of the clock period. The rising and falling ramps of the clocked power supply lead to an additional energy consumption by gate leakage. This energy is smaller than the fraction caused by the constant VDD drop, because the gate leakage exponentially depends on the voltage across the oxide. To obtain smaller energy consumption, Improved Adiabatic Logic (IAL) has been introduced. IAL swaps all n- and p-channel transistors. The logic blocks are built of p-channel devices which show gate tunneling currents significantly smaller than in n-channel devices. Using IAL instead of conventional AL allows an additional reduction of the energy consumption caused by gate leakage. Simulations based on a 90nm CMOS process show a lowering in gate leakage energy consumption for AL by a factor of 1.5 compared to static CMOS. For IAL the factor is up to 4. The achievable reduction varies depending on the considered AL family and the complexity of the gate.

Characterization of flow and voltage profiles in planar electrochromatography

Planar electrochromatography (PEC) is a new technology for thin layer chromatography (TLC) where the separation is driven by electroosmotic forces, not capillary action. This allows for much faster and more efficient chromatography in a planar format. Care needs to be taken when performing these experiments because voltage and flow characteristics can change through a single run, due to buffer gradients, temperature changes (Joule heating) and localized plate heterogeneity. We have designed a PEC instrument and cover grid to allow investigation of flow and voltage characteristics as solvent moves across a TLC plate. Our unique cover grid allows monitoring voltage at eight discrete points between the positive and negative reservoirs. A linear relationship between voltage and distance should be seen, giving a constant voltage drop across a plate, but this did not occur. This non-linear function changes over time, following the plate equilibration. Once a plate is equilibrated, voltage and flow characteristics remain fairly constant. Theoretical calculations support the physical observations. Larger plate widths (5 cm) were also briefly investigated and it is concluded that large width plates could be easily implemented to maintain multiple sample capability.

Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: Application to a new microangiographic system

Detector characterization with modulation transfer function (MTF) and detective quantum efficiency (DQE) inadequately predicts image quality when the imaging system includes focal spot unsharpness and patient scatter. The concepts of MTF, noise power spectrum, noise equivalent quanta and DQE were referenced to the object plane and generalized to include the effect of geometric unsharpness due to the finite size of the focal spot and the effect of the spatial distribution and magnitude of x-ray scatter due to the patient. The generalized quantities provide performance characteristics that consider the complete imaging system, but reduce to a description of the detector properties without magnification or scatter. We have evaluated a new neurovascular angiography imaging system based on a region of interest (ROI) microangiographic detector using these generalized quantities. A uniform head-equivalent phantom was used as a filter and x-ray scatter source. This allowed the study of all properties of the detector under clinically relevant x-ray spectra and x-ray scatter conditions. Realistic focal spots (0.8 mm nominal), beam energies (60-100 kVp), and detector exposures (0.8-2.3 mR) were used, and the effects of different scatter fractions (0-0.62) resulting from changing the beam size (0-100 cm2) were investigated. The generalized MTF and DQE were found to have very little dependence on the tube voltage and the detector entrance exposure. Magnification, with the focal spot used, results in a large decrease of the generalized DQE at higher frequencies (about 100-fold at 10 cycles/mm), but a significantly smaller decrease at lower frequencies. Scatter on the other hand, causes a constant drop in the generalized DQE (factor of 3 for scatter fraction 0.3) for all frequencies. Our results show that there are tradeoffs in the choice of the different system parameters; therefore this methodology of studying the imaging system as a whole could provide guidance in system design.

Experimental result on rewetting of hot surfaces by droplet impingement

The paper is dealing with a research carried out at the Institute of Thermal-Fluid Dynamics of ENEA (Casaccia Center) to investigate the rewetting of a hot surface cooled with droplet impingement. After the droplet impingement, the liquid film falls along the surface. The reference situation is the external surface of a tank which, after a fire, is subjected to flames or high temperature anyway, and is cooled with water or an extinguishing liquid. The experiment is characterized by a one-dimensional liquid spray, i.e., droplets having a uniform, constant diameter, impinging on the heated surface. The cooling rate of the hot surface has been detected as a function of wall temperature, droplet diameter and velocity, and point of impact of the spray on the heated surface. The working principle of such a spray is based on the varicose rupture of a liquid jet (Rayleigh–Weber instability): imposing a periodic perturbation of appropriate amplitude and frequency on the jet surface, the flow is “constrained” to break soon after leaving the nozzle, eventually obtaining constant diameter drops, depending, for a given liquid, on the nozzle diameter and liquid velocity. Dimensions of droplets used in the present work range from about 0.3 to 1.5 mm. A digital image system allows to know, for each nozzle, droplet diameter and aspect ratio. Each nozzle disk is manufactured in order to have the same cross flow area independent of the number of nozzles in the disk. The rewetting velocity has been calculated from the response of the thermocouples placed on the heated wall and from a digital image system based on the video image registered during the runs. A comparison of the two methods is provided. Two different locations of the jet impingement on the heated surface are tested. The spray is impinging outside the heated length, just upstream the copper clamp in one series of tests, while in a second series of tests the spray impinges directly on the first wall thermocouple, 25 mm below the beginning of the heated length. Prediction of the rewetting velocity obtained using available correlations has shown a good agreement with experimental data.

Band-gap expansion, core-level shift, and dielectric suppression of porous silicon passivated by plasma fluorination

The effect of plasma fluorination on the band gap, 2p core-level energy, and the dielectric behavior of porous silicon (PS) prepared under constant conditions has been examined using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, photoluminescence, and reflection. It has been found that with increasing extent of fluorination, the band gap expands, and the 2p level and the dielectric constant drop down substantially compared with those of the as-grown PS, being quite similar to the effect of particle size reduction. These findings could be interpreted as the fluorination-induced crystal field enhancement and the valence charge repopulation of silicon. The surface fluorination may provide an effective method for tuning the optical and dielectric properties of nanometric silicon.