Pulse Response Method Research Articles

Feed scheduling for time-dependent machining processes by optimization of bulk removal and NC blocks

Time-dependent processes such as CNC fluid jet polishing require feed-rate scheduling through deconvolution of a target removal profile and tool influence function. The dynamic constraints associated with the machine tool driving the process should be considered when solving this numerical problem. This research investigates how material bulk removal affects the scheduled feed-rate and acceleration both in the spatial and time domain, and proposes a method for matching exactly the maximum acceleration with the machine tool limit. Furthermore, the influence of CNC interpolator dynamics is investigated by means of the controller pulse response method. An optimization method for NC blocks is then proposed in order to achieve feed-rates that best match the intended profile. The benefit of bulk removal and NC blocks optimization is validated by fabrication, with and without optimization, of cylindrical Fresnel lenses. Both the shape accuracy and optical performance of the optimally fabricated lens are shown to substantially improve, suggesting that the proposed optimization method has strong potential for industrial application.

Pulse response method for the Wiener-type nonlinear process identification

The Wiener-type nonlinear process where a nonlinear static block follows a linear dynamic subsystem is widely used to describe the dynamics of chemical processes. The present study proposes a new Wiener-type process identification method based on a narrow pulse response to cope with the relatively long process excitation requirement in the previous methods. The proposed identification method is developed based on the property of the Wiener-type nonlinear process that outputs of a linear dynamic subsystem is the same at two points when process outputs are equivalent at those points. The proposed method requires a relatively short process excitation (a single pulse response) but almost exactly estimates the Wiener-type nonlinear process. The simulation and experimental studies show the outstanding performance of the proposed method.

Synthesis and characterization of supermacroporous cryogel with immobilized p-aminobenzenesulfonamide as affinity ligand for the purification of lactoperoxidase from whey.

This study proposed the development of a monolithic supermacroporous affinity column for direct capture of lactoperoxidase, a glycoprotein present in milk, whey, and colostrum, with several applications due to its wide antimicrobial activity. A poly(acrylamide)-based cryogel was produced by radical co-polymerization of monomers in frozen aqueous solution and activated with p-aminobenzenesulfonamide as a ligand for specific interaction with the lactoperoxidase. The axial liquid dispersion coefficients at different liquid flow rates were determined by measuring residence time distributions using the tracer pulse-response method. The axial dispersion coefficient was low and the height equivalent to theoretical plate was not dependent on the flow velocity. The adsorptive capacity of affinity cryogel was studied as a function of flow velocity and the best condition was 0.9cm/min. The response surface methodology was applied to optimize the capture of the enzyme, as a function of pH and salt concentration. Higher purification factor value was found at a salt concentration of 80mmol/L and pH of 8.0 (p<0.05). There was no influence of the variables under study on the yield (p>0.05). The results indicated that affinity cryogel is a promising chromatography support for the use in high-throughput one-step purification of lactoperoxidase from whey.

Effects of baffle designs on damping acoustic oscillations in a solid rocket motor

The baffle is a practical and promising passive damping method of dissipating acoustic energy and increasing acoustic losses in a solid rocket motor (SRM). In this study, numerical studies were conducted conjunction with the acoustic pulse response method (PRM) to evaluate the acoustic damping performance of a full-scale SRM with a baffle. The forced pulse function was imposed according to the frequency of the longitudinal acoustic mode. We comparatively evaluated the acoustic damping performance of the SRM with and without a baffle. The performances were characterized by (1) acoustic growth rate, (2) damping rate, and (3) acoustic energy. The PRM was first validated using data available in the literature. Several numerical investigations were conducted to develop geometry design criteria, which were subsequently used to ensure the effective operation of the baffle to suppress combustion-driven acoustic modes in the SRM. The effects of 1) the baffle axial location (x/L) and 2) the relative diameter (d/D) on acoustic damping performance were examined in detail. The results indicated that the baffle is effective in suppressing acoustic oscillations only when placed at 1/4⩽x/L⩽1/2. Furthermore, when the baffle was placed at x/L=1/2, a relative improvement of approximately 51% and 15.3% in the growth and damping rates, respectively, was achieved compared with those in the SRM without a baffle. In addition, an annular baffle with a smaller inner diameter was observed to have a good design. A baffle with d/D=1/2 was observed to be associated with a favorable damping effect. This research elucidates the effective design of a baffle in stabilizing combustion in a SRM.

Particle residence time distributions in a vortex-based solar particle receiver-reactor: An experimental, numerical and theoretical study

We report a joint experimental, numerical and theoretical study of particle residence times in a novel vortex-based vessel for thermal processing of suspended particles. The tracer pulse-response method, in which the particle phase itself is employed as the tracer, is used to measure the particle residence time distribution (RTD) within a laboratory-scale model of a class of Solar Expanding Vortex Receiver-Reactor (SEVR). The operating parameters of particle size, gas volumetric flow rate and inlet velocity were systematically varied to assess their influence on the particle RTD and to determine the mechanisms controlling the behaviour of the two-phase flow in the SEVR. The particle RTD behaviour is also described by a compartment model consisting of a small plug flow reactor followed by a series of two interconnected continuously-stirred tank reactors (CSTRs).

Particle residence time distributions in a vortex-based solar particle receiver-reactor: The influence of receiver tilt angle

We present the first experimental assessment of the influence of receiver tilt angle on the particle residence time distribution (RTD) of a two-phase solar particle receiver. The tracer pulse response method is used to measure the particle RTD within a laboratory-scale vortex-based solar particle receiver, with the particle phase itself used as the tracer. The experimental parameters of particle size, transporting gas inlet velocity and a range of receiver tilt angles – spanning 180° from vertically upward to downward facing – were systematically varied to determine the influence of key controlling parameters on the particle RTD within the receiver. It was found that the Stokes number of the two-phase flow evaluated at the receiver outlet, Skout, has a controlling influence on the residence time and that the influence of the receiver tilt angle is significant for large particles (Skout > 10) but weak for small particles (Skout ~ 1). This implies that it is preferable to operate tower-mounted systems (i.e. with downward facing receiver tilt angles) with Skout ~ 1. Furthermore, a preliminary scale-up assessment suggests that the influence of tilt angle on the residence time of particles 200 µm and smaller will be insignificant for a nominal 50 MW-scale receiver, which will provide flexibility in the design of industrial-scale devices. Finally, the residence time behaviour for the range of tilt angles assessed can be well described by an analytical compartment model consisting of a small plug flow reactor, followed by two continuously-stirred tank reactors in parallel with a second plug flow reactor.

Analysis of Langmuir Probe Characteristics for Measurement of Plasma Parameters in RF Discharge Plasmas

A simple method for measuring RF plasma parameters by means of a DC-biased Langmuir probe is developed. The object of this paper is to ensure the reliability of this method by using the other methods with different principles. First, Langmuir probe current response on RF voltage superimposed to DC biased probe was examined in DC plasmas. Next, probe current response of DC biased probe in RF plasmas was studied and compared with the first experiment. The results were confirmed by using an emissive prove method, an ion acoustic wave method, and a square pulse response method. The method using a simple Langmuir probe is useful and convenient for measuring electron temperature , electron density , time-averaged space potential , and amplitude of space potential oscillation in RF plasmas with a frequency of the order of .

Hydrothermal flow-through treatment of wheat-straw: Detailed characterization of fixed-bed properties and axial dispersion

The present study focuses on the hydrothermal flow-through treatment of lignocellulosic biomass in a fixed-bed 3L reactor. In combination with a sequential enzymatic hydrolysis, this process enables selective separation of the lignocellulose in its major constituents in minimal equipment.The aim of this work was to acquire detailed knowledge on the particle and bed structure, biomass degradation and non-ideal flow effects during the hydrothermal treatment. Correlations between the hemicellulose solubilization progress and changing fixed-bed characteristics were identified. This information is essential for the development of a realistic process model that considers hemicellulose reaction kinetics as well as mass and heat transfer separately.Hydrothermally pretreated wheat straw beds were analyzed using the tracer pulse response method at ambient conditions. Non-ideal flow was modeled by means of the dispersion model. Additionally, the effective porosity could be calculated from the residence time distribution curves. It was shown that the axial dispersion coefficient as well as the effective porosity were constant after 15min of pretreatment. A linear relationship between the axial dispersion coefficient and the interstitial fluid velocity was found. These results allow simplifying the model by assuming constant values of the corresponding variables. The model can further be used to support the development of biorefinery plants at lab and production scale.

A Measuring Method of Liquid Food Conductivity Based on Pulse Response Measurement Method

The food conductivity is one of impact factors on pulsed electric field sterilization. Abnormal breakdown of high conductivity liquid is also one of the bottlenecks in pulsed electric field sterilization technology. The conductivity of liquid food should be accurate calculated for searching the mechanism of abnormal breakdown deeply. An accurate measuring method of conductivity of liquid food is proposed based on pulse response method. Conductivity can be calculated by data recorded from oscilloscope with electrical pulse treating on the conductance cell. This method can decrease the impact of stray capacitance and polarization phenomenon on measured results.

Experimental evaluation of flow and dialysis performance of hollow-fiber dialyzers with different packing densities

The dialyzer housing structure should be designed in such a way that high dialysis performance is achieved. To achieve high dialysis performance, the flow of the dialysis fluid and blood should be uniform, without channeling and dead spaces. The objective of this study was to evaluate the effect of fiber packing density on the flow of dialysis fluid and blood, and on the dialysis performance of a hollow-fiber dialyzer at defined flow rates for blood (Q (B) = 200 mL/min), dialysis fluid (Q (D) = 500 mL/min), and filtrate (Q (F) = 0 mL/min). We measured Q (D), Q (B), and solute clearance for 3 test dialyzers with dialyzer housing different diameters. To evaluate the flow of dialysis fluid and blood, we measured the residence time of the dialysis fluid and blood in the test dialyzers by use of the pulse-response method. We also measured the clearances of urea, creatinine, vitamin B(12), and lysozyme to evaluate the dialysis performance of the test dialyzers. At packing densities ranging from 48 to 67%, higher packing densities and lower housing diameters of the dialyzer resulted in higher dialysis performance because the dialysis fluid and blood entered the hollow-fiber bundle smoothly and, hence, increased contact area between the dialysis fluid and the blood led to better dialysis performance.

Evaluation of Dialyzer Jacket Structure and Hollow‐Fiber Dialysis Membranes to Achieve High Dialysis Performance

The objective of this study was to determine the optimum dialyzer jacket structure and hollow-fiber dialysis membrane, both of which are indispensable factors for achieving high dialysis performance, by clarifying the relationship between the dialysis performance and the flow of dialysate and blood in a hollow-fiber dialyzer. We evaluated the clearance, dialysate, and blood flow for four commercially available hollow-fiber dialyzers, namely, the APS-15S, APS-15SA, TS-1.6UL, and CX-1.6U. To evaluate dialysate and blood flow, we measured the residence-time distribution of dialysate and blood flow of these dialyzers by the pulse-response method. We also determined the clearances of urea, creatinine, vitamin B(12), and lysozyme to evaluate the dialysis performance of these dialyzers. While the baffle and taper structures allow effective supply of dialysate into the dialyzer jacket, the hollow-fiber shape, inner diameter, and packing density significantly influence the dialysate flow. In dialyzers with long taper-holding slits, the slit area is a key design parameter for achieving optimum dialysate flow. Similarly, the blood flow is significantly influenced by the structure of the inflowing and outflowing blood ports at the header of a dialyzer, and the shape and inner diameter of the hollow fibers. Hollow fibers with smaller inner diameters cause an increase in blood pressure, which causes blood to enter the hollow fibers more easily. The hollow-fiber shape hardly affects the blood flow. While improved dialysate and blood flow cause higher clearance of low molecular-weight substances, higher membrane area and pure-water permeability accelerate internal filtration, thereby causing an increase in the clearance of large molecular-weight substances.

Interpreting the difference between conventional and bi-directional plate-height measurements in liquid chromatography

An experimental and theoretical study was conducted of the column characterization technique in which plate heights determined using the conventional pulse-response method are compared with those determined using a bi-directional method where an eluite sample is introduced into one end of a chromatographic column and elution occurs at the same end after the flow direction is reversed inside the column. Experiments are presented for a micropellicular HPLC column before and after its performance has been degraded by repeated sample injections, for a low-pressure column containing nonporous glass particles, and for an HPLC column containing particles with 300 Å pores. The results obtained are interpreted in terms of several different theories which apply in various Fourier number ranges. It was shown that the transcolumn contribution to convective dispersion in a chromatographic column is largely responsible for the difference observed between conventional and bi-directional plate-height measurements and that a collocation method can be employed to develop a useful analytical expression for this contribution.

Preparation of Supermacroporous Composite Cryogel Embedded with SiO 2 Nanoparticles

Supermacroporous composite cryogels embedded with SiO 2 nanoparticles were prepared by radical cryogenic copolymerization of the reactive monomer mixture of acrylamide (AAm) and N, N-methylene-bis-acrylamide (MBAAm) containing SiO 2 nanoparticles (mass ratios of nanoparticles to the monomer AAm from 0.01 to 0.08) under the freezing-temperature variation condition in glass columns. The properties of these composite cryogels were measured. The height equivalent to theoretical plate (HETP) of the cryogel beds at different liquid flow rates was determined by residence time distribution (RTD) using tracer pulse-response method. The composite cryogel matrix embedded with the mass fraction of SiO 2 nanoparticles of 0.02 presented the best properties and was employed in the following graft polymerization. Chromatographic process of lysozyme in the composite cryogel grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) was carried out to evaluate the protein breakthrough and elution characteristics. The chromatography can be carried out at relatively high superficial velocity, i.e., 15 cm·min −1, indicating the satisfactory mechanical strength due to the embedded nanoparticles.

Optimal estimation of the surface fluxes of methyl chloride using a 3-D global chemical transport model

Abstract. Methyl chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. Large uncertainties in estimates of its source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of the surface fluxes of CH3Cl. The Model of Atmospheric Transport and Chemistry (MATCH), driven by NCEP interannually varying meteorological data, is then used to simulate CH3Cl mole fractions and quantify the time series of sensitivities of the mole fractions at each measurement site to the surface fluxes of various regional and global sources and sinks. We then implement the Kalman filter (with the unit pulse response method) to estimate the surface fluxes on regional/global scales with monthly resolution from January 2000 to December 2004. High frequency observations from the AGAGE, SOGE, NIES, and NOAA/ESRL HATS in situ networks and low frequency observations from the NOAA/ESRL HATS flask network are used to constrain the source and sink magnitudes. The inversion results indicate global total emissions around 4100 ± 470 Gg yr−1 with very large emissions of 2200 ± 390 Gg yr−1 from tropical plants, which turn out to be the largest single source in the CH3Cl budget. Relative to their a priori annual estimates, the inversion increases global annual fungal and tropical emissions, and reduces the global oceanic source. The inversion implies greater seasonal and interannual oscillations of the natural sources and sink of CH3Cl compared to the a priori. The inversion also reflects the strong effects of the 2002/2003 globally widespread heat waves and droughts on global emissions from tropical plants, biomass burning and salt marshes, and on the soil sink.

Influence of microwave irradiation on the intraparticle diffusion of an insulin variant in reversed-phase liquid chromatography under linear conditions

The influence of microwave irradiation on the mass transfer kinetics of an insulin variant in reversed-phase liquid chromatography (RPLC) was investigated. The elution band profiles of insulin were obtained by the pulse-response method, under linear conditions. The RPLC column was placed in a microwave oven and the incremental change in the temperature of the column effluent stream at various microwave energies and mobile phase flow rates were measured. The microwave energy dissipated in the column was set at 15 and 30 W and the mobile phase flow rate was varied from 1.0 to 2.5 mL/min at a mobile phase composition of acetonitrile, water, and trifloroacetic acid (31:69:0.1, v/v/v). The experimental data were analyzed using the conventional method of moment analysis and the lumped pore diffusion model. Regardless of mobile flow rates, the effluent temperatures measured at 15 and 30 W microwave power input were 25 ± 1 and 30 ± 1 °C, respectively. The effect of microwave irradiation on the mass transfer of the variant insulin was determined by comparing the band profiles obtained under the same experimental conditions, at the same column temperature, with and without irradiation. The calculated intraparticle diffusion coefficient, D e, at 30 W (30 ± 1 °C) microwave irradiation was ca. 20% higher than without irradiation at 30 ± 1 °C. These preliminary results suggest that microwave irradiation may have a significant influence on the intraparticle diffusion of insulin in RPLC.

In-situ graft-polymerization preparation of cation-exchange supermacroporous cryogel with sulfo groups in glass columns

Graft polymerization of monomer chains with expected functional groups onto the matrix pore surfaces by initiator is an effective approach for introducing ion-exchange groups to cryogel matrix to get anion- or cation-exchange supermacroporous cryogels. In this work, a novel cation-exchange cryogel with sulfo binding groups was prepared by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogels in glass columns. The grafting polymerization was achieved in an in-situ manner which was performed by pumping the initiator and the reactive solution of graft monomer with sulfo binding groups directly through a cryogel bed pre-produced in a glass column under frozen condition. The axial liquid dispersion characteristics within the monolithic cryogel beds before and after the in-situ polymerization were compared by measuring residence time distributions (RTDs) at various liquid flow rates using tracer pulse-response method. Microstructure morphology of pores within cryogels was analyzed by scanning electron microscopy (SEM). Chromatography of lysozyme was carried out to reveal the protein breakthrough and elution characteristics in the obtained cryogel beds.

Technical Evaluation of Dialysate Flow in a Newly Designed Dialyzer

Rexeed was developed by Asahi Kasei Medical using wave-shaped hollow fibers, a full baffle, and a short taper housing to improve dialysate flow. The present study is clarifies improvement in dialysate flow with Rexeed-15 compared with that of a conventional dialyzer. Dialysate flow was evaluated by the pulse-response method. Dialysate pressure and tracer concentration were measured at a blood-side flow rate (QBeta) of 200 ml/min, a dialysate-side flow rate (QD) of 500 ml/min, and a net filtration rate (QF) of 0 ml/min using needles placed in the test dialyzer. Dialyzer performance was evaluated by measuring urea and vitamin B12 clearance at QB = 200 and 400 ml/min, QD = 300-800 ml/min, and QF = 0 ml/min. In the conventional dialyzer, dialysate channeling was observed. In contrast, Rexeed-15 had a uniform dialysate flow. Urea and vitamin B12 clearance with Rexeed-15 was slightly sensitive to QD. The overall mass transfer coefficient for urea with Rexeed-15 was more than 50% higher than that of the conventional dialyzer, indicating the possibility of reduced dialysate usage with Rexeed. Rexeed has a highly optimal dialysate flow, due to the wave-shaped hollow fibers and the new housing, and gives increased clearance for lower-molecular-weight substances.

Characterization of a novel continuous supermacroporous monolithic cryogel embedded with nanoparticles for protein chromatography

A novel continuous supermacroporous monolithic cryogel embedded with nanometer-size particles was prepared by the radical cryogenic co-polymerization of acrylamide (AAm), N, N′-methylene-bis-acrylamide (MBAAm), allyl glycidyl ether (AGE) and the dispersed surfactant-stabilized Fe 3O 4 nanoparticles under the freezing-temperature variation condition in a glass column. This special separation matrix has interconnected supermacropores with pore size of 10–50 μm, which permit the free-passage of microbial cells or cell debris in the culture fluids and then is interest in downstream processes. The axial liquid dispersion coefficients of the new continuous supermacroporous monolithic bed at different liquid flow rates were obtained by measuring residence time distributions (RTDs) using tracer pulse-response method. The experimental results showed that the axial liquid dispersion within the bed was weak in a wide water flow rate of 0.5–15 cm/min. The axial dispersion coefficient was found to be increased exponentially with the increase of liquid flow rate. Chromatographic process of bovine serum albumin (BSA) in the cryogel monolithic bed was carried out to reveal the protein breakthrough and elution characteristics. Compared with other reported cryogel beds in literature, the protein adsorption capacity of the present cryogel bed was improved due to the embedded nano-sized solid adsorbents in the gel matrix. Microstructure morphology of the embedded nanoparticles in the cryogel and the gel matrix structure were also analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in this paper.

Direct characterization of the spatial effective refractive index profile in Bragg gratings

We propose a pulse response method to directly characterize the phase of the spatial index modulation, including the dc refractive index distribution (distributed phase shift), discrete phase, and chirp of fiber Bragg gratings (FBGs). This method is based on the observation that the spatial phase of gratings is directly related to the temporal phase of its pulse response. Therefore, the phase of the spatial index modulation can be characterized directly by measuring the temporal phase of the pulse response of FBGs. This method is then used to characterize an FBG with a current-induced phase shift.

Influence of Microwave Irradiation on the Mass-Transfer Kinetics of Propylbenzene in Reversed-Phase Liquid Chromatography

The effect of microwave irradiation on the kinetics of mass transfer in reversed-phase liquid chromatography (RPLC) was studied by measuring its influence on the band profile of propylbenzene in a C18-silica column eluted with an aqueous solution of methanol and placed inside a microwave oven. The elution peaks were measured by the pulse-response method, under linear conditions. The amount of microwave energy induced into the column was varied based on the microwave input power. The experimental data were analyzed using the conventional method of moment analysis and the lumped pore diffusion model. With input powers of 15 and 30 W, the effluent temperatures were 25 ± 1 and 30 ± 1 °C, respectively. The effect of microwave irradiation on the mass transfer of the studied solute was determined by comparing the band profiles obtained under the same experimental conditions, at the same temperature, with and without irradiation. The values of the intraparticle diffusion coefficient, De, measured with microwave i...