Alternative Modes Of Operation Research Articles

Scrape-off layer features of the QH-mode

The quiescent high confinement (QH-mode) and quiescent double barrier (QDB) modes in DIII-D have long-duration H-mode confinement without ELMs, possibly an alternative operating mode in future tokamaks for avoiding damage by ELMs. Instead of ELMs, there is an edge harmonic oscillation (EHO), which is a continuous electromagnetic mode with associated density fluctuations. The edge pedestal is similar to ELMing H-mode, but at very low density to date. We see C 6+ ion temperatures of 3–7 keV in scrape-off layer (SOL), 100 kV/m radial electric fields just inside the separatrix, and a hot area on the divertor baffle whose heating correlates with the presence of the EHO. We attribute the baffle heating to perturbation of trapped ion orbits by the EHO, allowing particles to strike the baffle. The outboard SOL is wider than the inboard, probably for lack of trapped ions on the inside.

Ultrahigh-efficiency power amplifier for space radar applications

This paper describes a broad-band switch mode power amplifier based on the indium phosphide (InP) double heterojunction bipolar transistor (DHBT) technology. The amplifier combines the alternative Class-E mode of operation with a harmonic termination technique that minimizes the insertion loss of matching circuitry to obtain ultrahigh-efficiency operation at X-band. For broad-band Class-E performance, the amplifiers output network employs a transmission line topology to achieve broad-band harmonic terminations while providing the optimal fundamental impedance to shape the output current and voltage waveforms of the device for maximum efficiency performance. As a result, 65% power-added efficiency (PAE) was achieved at 10 GHz. Over the frequency band of 9-11 GHz, the power amplifier achieved 49%-65% PAE, 18-22 dBm of output power, and 8-11 dB gain at 4 V supply. The reported power amplifier achieved what is believed to be the best PAE performance at 10 GHz and the widest bandwidth for a switch-mode design at X-band.

Pore network modelling of affinity chromatography: determination of the dynamic profiles of the pore diffusivity of β-galactosidase and its effect on column performance as the loading of β-galactosidase onto anti-β-galactosidase varies with time

A three-dimensional pore network model for diffusion in porous adsorbent particles was employed in a dynamic adsorption model that simulates the adsorption of a solute in porous particles packed in a chromatographic column. The solution of the combined model yielded the dynamic profiles of the pore diffusion coefficient of β-galactosidase along the radius of porous adsorbent particles and along the length of the column as the loading of β-galactosidase onto anti-β-galactosidase immobilized on the surface of the pores of the particles occurred, and, the dynamic adsorptive capacity of the chromatographic column as a function of the design and operational parameters of the chromatographic system. It was found that for a given column length the dynamic profiles of the pore diffusion coefficient were influenced by (a) the superficial fluid velocity in the column, (b) the diameter of the adsorbent particles, and (c) the pore connectivity of the porous structure of the adsorbent particles. The effect of the magnitude of the pore connectivity on the dynamic profiles of the pore diffusion coefficient of β-galactosidase increased as the diameter of the adsorbent particles and the superficial fluid velocity in the column increased. The dynamic adsorptive capacity of the column increased as (i) the particle diameter and the superficial fluid velocity in the column decreased, and (ii) the column length and the pore connectivity increased. In preparative affinity chromatography, it is desirable to obtain high throughputs within acceptable pressure gradients, and this may require the employment of larger diameter adsorbent particles. In such a case, longer column lengths satisfying acceptable pressure gradients with adsorbent particles having higher pore connectivity values could provide high dynamic adsorptive capacities. An alternative chromatographic system could be comprised of a long column packed with large particles which have fractal pores (fractal particles) that have high pore connectivities and which allow high intraparticle diffusional and convective flow mass transfer rates providing high throughputs and high dynamic adsorptive capacities. If large scale monoliths could be made to be reproducible and operationally stable, they could also offer an alternative mode of operation that could provide high throughputs and high dynamic adsorptive capacities.

Parallel beams from nuclear microprobe lens systems

A nuclear microprobe lens system is normally used to focus a diverging beam into a fine probe. It does this by making the astigmatism terms in the first-order transfer matrix: ( x/ θ) and ( y/ φ) zero. Thus the position of a ray vector in the image plane ( x, y) in the linear approximation will not depend on the divergence of the ray vector in the object plane ( θ, φ). This is accomplished at the expense of magnifying the object divergence by factors ( θ/ θ) and ( φ/ φ) in the xoz and yoz planes, respectively, leading to relatively steep convergence angles at the Gaussian image plane where the specimen is located. An alternative operation mode of the nuclear microprobe lens system is possible where the convergence angle of the beam after the lens system in the linear approximation is made independent of the divergence angle of the beam prior to the lens system. In this case the terms ( θ/ θ) and ( φ/ φ) in the first-order transfer matrix are zero. This mode of the lens system does not produce a focused beam, so is most suitable for crystals without lateral structure. As an example, we present measurements from the 〈0 0 0 1〉 α-Al 2 O 3 axis, which show significant improvement in channeling angular widths for planar channeling mode even when compared to the unfocused mode.

Pore network modelling: determination of the dynamic profiles of the pore diffusivity and its effect on column performance as the loading of the solute in the adsorbed phase varies with time

A three-dimensional pore network model for diffusion in porous adsorbent particles was employed in a dynamic adsorption model that simulates the adsorption of a solute in porous particles packed in a chromatographic column. The solution of the combined model yielded the dynamic profiles of the pore diffusion coefficient of β-galactosidase along the radius of porous ion-exchange particles and along the length of the column as the loading of the adsorbate molecules on the surface of the pores occurred, and, the dynamic adsorptive capacity of the chromatographic column as a function of the design and operational parameters of the chromatographic system. The pore size distribution of the porous adsorbent particles and the chemistry of the adsorption sites were unchanged in the simulations. It was found that for a given column length the dynamic profiles of the pore diffusion coefficient were influenced by: (i) the superficial fluid velocity in the column, (ii) the diameter of the adsorbent particles and (iii) the pore connectivity of the porous structure of the adsorbent particles. The effect of the magnitude of the pore connectivity on the dynamic profiles of the pore diffusion coefficient increased as the diameter of the adsorbent particles and the superficial fluid velocity in the column increased. The dynamic adsorptive capacity of the column increased as: (a) the particle diameter and the superficial fluid velocity in the column decreased, and (b) the column length and the pore connectivity increased. In preparative chromatography, it is desirable to obtain high throughputs within acceptable pressure gradients, and this may require the employment of larger diameter adsorbent particles. In such a case, longer column lengths satisfying acceptable pressure gradients with adsorbent particles having higher pore connectivity values could provide high dynamic adsorptive capacities. An alternative chromatographic system could be comprised of a long column packed with large particles which have fractal pores (fractal particles) that have high pore connectivities and which allow high intraparticle diffusional and convective flow mass transfer rates providing high throughputs and high dynamic adsorptive capacities. If large scale monoliths could be made to be reproducible and operationally stable, they could also offer an alternative mode of operation that could provide high throughputs and high dynamic adsorptive capacities.

Analysis of Manual and Centralised Supervisory Control Operations to Improve Level of Service: A Case Study of Pyramid Hill No 1 Channel, Victoria, Australia

The current challenge facing irrigation inAustralia is tofind ways to improve the operationalperformance of existing systems rather thanconstructing new ones. Unsteady flowsimulation models are often used as keytools to study and test improvedoperational scenarios for existing systems.While these models are generally notrecommended for real-time control, researchhas shown that they are able to simulatecanal response for different test scenariosfor operations planning. This paperpresents the results of two alternativemodes of operation for the Pyramid Hill No.1 Channel in northern Victoria, Australia.The channel is currently under manualoperation. Centralised control is the mostimmediate option considered by theirrigation authority to enable remotesupervision and control of the canal toimprove the channel operation and level ofservice standards. This type of control istermed Supervisory Control and DataAcquisition (SCADA). The two alternativeoperational scenarios were simulated andanalysed using the unsteady flow-simulationmodel DUFLOW. Specific performanceindicators were defined to compare the twomodes of operations based on the simulationresults. The results show that SCADAoperation has considerable potential toclosely match the discharges at thedownstream regulator with those ordered byfarmers while maintaining the water surfaceelevations within allowable fluctuationtolerance throughout the length of thecanal.

Styrene synthesis in a reverse-flow reactor

Multifunctional reactor concepts for thermal coupling of endothermic synthesis reactions with an exothermic auxiliary reaction are presented. The processes are carried out in an autothermal operation mode incorporating regenerative heat exchange within the reactor through periodic flow reversal. Catalytic dehydrogenation of ethylbenzene to styrene is considered as a particular example, where catalytic combustion of the produced hydrogen serves as a heat source. Two alternative operation modes are discussed, the asymmetric operation mode, where the synthesis reaction and the combustion are separated in time and the symmetric operation mode with external combustion and hot gas injection, or with air injection and in situ hydrogen combustion. A lab-scale reactor with an integrated catalytic burner has been set-up and experiments with the symmetric operation mode have been performed. The symmetric operation mode with hot gas injection proves to be an attractive alternative to conventional processes for styrene synthesis: it allows for high conversions and high selectivities, combined with an efficient heat recovery.

Comparison of Various Process Engineering Concepts of Preparative Chromatography

Liquid chromatography utilizing porous solid phases (adsorption chromatography) is one of the most powerful and versatile methods of modern analytical chemistry. Its widespread application is due in part to the development of a broad range of combinations of solid stationary and liquid mobile phases. Normal phase and reverse phase chromatography with pure and chemically modified silica, respectively, affinity chromatography, can be cited as examples. In addition to its use as an analytical method, chromatography is becoming increasingly important in the preparative scale for the isolation of pure substances in the pharmaceutical industry, in biotechnology, and in the production of fine chemicals. In many cases, the required purity criteria can only be met with chromatographic techniques, as in the resolution of racemates. From a process engineering viewpoint, a better understanding of concentration profile deformations caused by intended overloading of separation columns has recently been acquired. In particular, this concerns the description of displacement and entrainment effects associated with the competitive adsorption. A series of alternative operating modes has been developed and used to enhance yields and productivities. In spite of a number of attempted comparative studies, quantitative information about optimizing these processes is lacking. This article will compare four different process engineering concepts of preparative chromatography on the basis of a uniform theoretical model.

Indirect Access — Using Intelligence to Make a Virtue Out of a Necessity

Indirect access using intelligent CPE means that customer dialling habits do not change when they switch to a second operator. This is an essential technology for second operators, in order to reach highly profitable mass-market customers and this paper describes some of the important features they should consider when designing such a service. In particular it highlights the need to consider complete service design rather than just equipment price. Remotely managed intelligent smartboxes and routers can support a range of alternative telco operation modes, such as switchless resellers and aggregators, and the use of indirect access to complement targeted access build is mentioned. Collaborative work on vendor and design analysis is reviewed and the point is made that remote management is a key ingredient that should be developed as a valuable marketing tool. This technology could support mass-market packet or Internet-based voice services and some operating models can be readily shifted to such a network without the customer needing to know. There are great similarities between dial up Internet service propositions and indirect access so the two services can be converged. It is stressed that indirect access is not a 'fallback' for direct access, but a true value add service in itself.

Vergleich verschiedener verfahrenstechnischer Konzepte der präparativen Flüssigchromatographie

AbstractLiquid chromatography utilising porous solid phases (adsorption chromatography) is one of the most powerful and versatile methods of modern analytical chemistry. Its widespread application is due in part to the development of a broad range of combinations of solid stationary and liquid mobile phase. Normal phase and reverse phase chromatography with pure and chemically modified silica gel, respectively, affinity chromatography, and ion chromatography can be cited as examples [1]. In addition to its use as an analytical method, chromatography is becoming increasingly important in the preparative‐scale isolation of pure substances in the pharmaceutical industry, in biotechnology, and in the production of fine chemicals. In many cases, the required purity criteria can only be met with chromatographic techniques, as in the resolution of racemates. From a process engineering viewpoint, a better understanding of concentration profile deformations caused by intended overloading of separation columns has recently been acquired [2]. In particular, this cncerns the description of displacement and entrainment effects associated with the competing adsorption. A series of alternative operating modes has been developed and used [3] for enhancing yields and productivities. In spite of a number of attempted comparative studies [4] there is a lack of quantitative information about optimized process. This article aims to compare four different process engineering concepts of preparative chromatography on the basis of a uniform theoretical model.

Acute pollution of recipients in urban areas

Oxygen and ammonia concentration are key parameters of acute water pollution in urban rivers. These two abiotic parameters are statistically assessed for a historical rain series by means of a simplified deterministic model of the integrated drainage system. Continuous simulation of the system performance indicates that acute water pollution is caused by intermittent discharges from both sewer system and wastewater treatment plant. Neglecting one of them in the evaluation of the environmental impact gives a wrong impression of total system behavior. Detention basins and alternative operational modes in the treatment plant under wet weather loading have a limited positive effect for minimizing acute water pollution.

Use of Continuous Distillation Columns for Batch Separation

Over the last few decades many alternative column configurations and modes of operation have been suggested for batch distillation. This paper addresses the potential use of continuous distillation columns for the batch separation task. It is shown that under certain circumstances the conventional dynamic batch operation (inherent with a batch distillation column) can be replaced by the steady state operation of a continuous column without significant compromise of the recovery and energy consumption. This allows steady state modelling and optimization as opposed to dynamic modelling and optimization. Multi-Pass Sequential Steady State (MPSSS) operation is suggested to achieve high recovery of species in short operation time and low energy cost (meaning high productivity). Multi-pass operation achieves better recovery compared to conventional operation for the same energy consumption and operation time. The performance of a continuous column un dergoing multiple separation duties is also addressed in this work. It is shown that by choosing an optimal feed rate, an existing continuous column can be used effectively for separating multiple binary mixtures with different ‘degrees of difficulty’ of separation.

Finite-element analysis of cyclic heat transfer in a shell-and-tube latent heat energy storage exchanger

The physical module of a shell-and-tube latent heat thermal storage exchanger consists of a tube which is surrounded by an external coaxial cylinder made up of a phase-change material (PCM). A heat-transfer fluid flows through the tube to store or extract thermal energy from the PCM. Two alternative operation modes are possible. One option is to introduce hot and cold fluids (for charge and discharge processes, respectively) from the same end of the tube. The other is to introduce the hot and cold fluids from different ends of the tube. A finite-element model is developed to simulate the inherently cyclic thermal process involved as a result of the alternating melting and freezing processes in the storage exchanger. Computations have been carried out to investigate the effects of the two different operation modes. Numerical results provide guidance for selection of the appropriate mode.

Acute pollution of recipients in urban areas

Oxygen and ammonia concentration are key parameters of acute water pollution in urban rivers. These two abiotic parameters are statistically assessed for a historical rain series by means of a simplified deterministic model of the integrated drainage system. Continuous simulation of the system performance indicates that acute water pollution is caused by intermittent discharges from both sewer system and wastewater treatment plant. Neglecting one of them in the evaluation of the environmental impact gives a wrong impression of total system behavior. Detention basins and alternative operational modes in the treatment plant under wet weather loading have a limited positive effect for minimizing acute water pollution.

The role of reaction calorimetry in the development and scale-up of aromatic nitrations

Abstract A Mettler RC-1 reaction calorimeter was utilized to investigate the thermochemistry of two aromatic nitrations prior to their scaleup. The calorimetry provided data that enabled the evaluation of alternative modes of operation and ultimately to intrinsically safer processes than were originally proposed. The results from this study and how they were used for pilot plant scale-up are discussed.

A framework for an interactive project scheduling system under limited resources

In this paper, we propose a framework for an interactive project scheduling system under limited resources. The framework includes a modelling module ( model) and a scheduling module ( scheduler). The modelling module model allows the Decision Maker (DM) to develop his/her own model with features such as alternative operating modes for activities; renewable, nonrenewable and/or doubly-constrained resource constraints; general cash flow patterns, related to the realization of activities or events; and progress payments distributed over the project span. The performance criteria include the maximization of Net Present Value (NPV), and either the minimization of maximum tardiness (when a project due date exists) or the minimization of the project duration (when there is no project due date). The scheduler is developed on a constraint-based scheduling algorithm, which is called Local Constraint Based Analysis ( lcba) and which has previously been tested and shown to produce near-optimal results with respect to the criterion of minimizing project duration. The decisions taken in the scheduler consist of determining the start times of activities and the specific operating modes in which they are to be realized. The decisions are taken by activating relevant essential conditions in lcba and in cases where resource conflicts are not resolved, the DM reaches a final decision by testing the alternatives proposed by lcba through a what-if routine. The scheduler represents a realistic scheduling system which is useful not only in the planning phase of a project but can also be employed during the progress of a project for updating the project plan, if necessary. An important feature is that the project plan can be updated by performing the least modification of future commitments. It is possible to freeze the activities already scheduled in the near future while admitting the changes in the activity/network information.

Groups for good or Ill

Abstract Groups consist of collections of individuals who act and take decisions together. They are hugely important in economic and social activity, encompassing governments, firms, local organizations and families. Yet much of neo‐classical economics ignores them, focusing on individuals, or treating groups as quasi‐individuals. This paper classifies alternative modes of operation of groups and considers some empirical cases, exploring why some groups help improve incomes and distribution while others are unproductive. It is argued that a trust/reciprocity mode of operation tends to be associated with “good” group behaviour. The mode of operation of particular groups is conditioned by individual motivation and social pressures; these are both dependent on historical circumstances, including the degree of equity within the community and prevalent incentives, constraints and philosophy. A crude market philosophy can encourage individual short‐term maximizing behaviour, undermining good group behaviour. In...

Improving the performance of two-component phase Doppler anemometers

The Gaussian beam defect is now a well documented deficiency of conventional phase Doppler anemometers and leads to significant errors in particle size estimation when the particle size takes on dimensions of the same order as the measurement volume. In the present paper, an alternative operation mode of conventional, two-component phase Doppler anemometry systems is proposed, which removes these errors for many applications. The new approach is analysed theoretically and its improved performance is verified experimentally. Furthermore, the effect of a slit aperture on the trajectory-dependent size measurement has been experimentally investigated.

The Value of Flexibility: The Case of a Dual-Fuel Industrial Steam Boiler

0 It is now widely understood that conventional economic analysis based on discounted cash flow (DCF) methods fails to capture the strategic impact of projects. In particular, DCF methods ignore the flexibilities that give project managers options to revise decisions in response to changing exogenous economic conditions. importance of such operating options becomes critical when the environment is highly volatile and the technology is flexible, thus permitting managerial intervention at little cost. For example, when facing exogenous stochastic prices a project with operating options can protect itself against some of the adverse price movements by switching into an alternative mode of operation that is less affected by the adverse price realizations. In effect, the irreversibility assumption of conventional investment analysis is violated. Real options techniques, by endogenizing the optimal operating rules and explicitly capturing the flexibility and its effects on uncertainty, provide for a consistent treatment of risk in the valuation of flexible projects. growing literature on real options has revealed several important lessons:1 (i) the volatility of prices becomes an important determinant of investment, both in terms of the type of investment (e.g., rigid versus flexible technologies) and in terms of the quantity of investment (in that high volatility increases the value and Tobin's q of flexible systems); (ii) the value of flexibility per se may be determined explicitly, given the dynamics for relative model described in this paper is based on an earlier working paper entitled The Value of Flexibility, MIT-EL 86-014WP. empirical results are extensions of the results from an unpublished research project that I conducted with David Wood, with the assistance of Michael Provance and Yoshiki Ogawa at the Center for Energy Policy Research at the MIT Energy Laboratory. project was interrupted by the untimely death of David Wood. paper would not be possible without his contributions, and hence is really a joint product. However, I am solely responsible for any errors. 1See Pindyck [ 13] for a review of the literature on irreversible investments under uncertainty. Kulatilaka and Marcus [9] provide a more intuitive discussion of real options and their implications. Mason and Merton [10] contains a general technical discussion of issues related to the use of options techniques in capital budgeting.

Absolute phasing of segmented mirrors using the polarization phase sensor

The polarization phase sensor (PPS) is an optical sensor capable of measuring absolute displacements between two segments of a spherical mirror. The sensing apparatus consists of a white light polarization interferometer which forms a set of interference fringes representative of the displacement between the two segments. A detector array senses these fringes and computer software performs an analysis. The result of these calculations is a measurement of the absolute misalignment between the two segments. The sensor, in its current configuration, is capable of measuring ±30 μrad of tilt between the two segments with an accuracy of 3.29 μrad and a precision of 2.27 μrad and ±2 μm of piston between the two segments with an accuracy of 0.00516 μm, and a precision of 0.031 μm. This paper will address the optical design and operating characteristics of this sensor. A conclusion will discuss alternate modes of operation and upgrades to the instrument which will increase piston capture range.