Steady-state Fashion Research Articles

UKAEA capabilities to address the challenges on the path to delivering fusion power.

Fusion power could be one of very few sustainable options to replace fossil fuels as the world's primary energy source. Fusion offers the potential of predictable, safe power with no carbon emissions and fuel sources lasting for millions of years. However, it is notoriously difficult to achieve in a controlled, steady-state fashion. The most promising path is via magnetic confinement in a device called a tokamak. A magnetic confinement fusion (MCF) power plant requires many different science, technology and engineering challenges to be met simultaneously. This requires an integrated approach from the outset; advances are needed in individual areas but these only bring fusion electricity closer if the other challenges are resolved in harmony. The UK Atomic Energy Authority (UKAEA) has developed a wide range of skills to address many of the challenges and hosts the JET device, presently the only MCF facility capable of operating with both the fusion fuels, deuterium and tritium. Recently, several major new UKAEA facilities have been funded and some have started operation, notably a new spherical tokamak (MAST Upgrade), a major robotics facility (RACE), and a materials research facility (MRF). Most recently, work has started on Hydrogen-3 Advanced Technology (H3AT) for tritium technology and a group of Fusion Technology Facilities.This article is part of a discussion meeting issue ‘Fusion energy using tokamaks: can development be accelerated?’

Fully coupled wellbore-reservoir simulation of supercritical CO2 injection from fossil fuel power plant for heat mining from geothermal reservoirs

Abstract The concept of injecting supercritical CO2 (sCO2) into a geothermal reservoir was computationally investigated to assess its performance in terms of the benefit of using CO2 captured from fossil power plants for geothermal heat mining. A coupled wellbore-reservoir system was simulated considering the flow of pure sCO2 in an injection well, the interaction of sCO2 and water in a permeable reservoir, and the flow of the two-phase mixture of sCO2 and water in a production well. Results of simulations indicate that this CO2 application is capable of providing a good source of renewable energy. It was found that for a reservoir with a 0.08 km3 volume, about 8–9 MWth could be extracted in a steady state fashion for a 30-year lifetime operation. This is approximately equivalent to 100 MWth/km3. A sensitivity analysis provided information on the impact of certain parameters on the performance of the integrated system. The injection flowrate, the distance between the production and injection wellbores and the penetrating depth of the production wellbore into the reservoir have a first order impact on the pressure management of the reservoir. Additionally, CO2 injection temperature has a large effect on the thermosiphon characteristics of the system.

Capturing the photo-signaling state of a photoreceptor in a steady-state fashion by binding a transition metal complex.

Binding a small molecule to proteins causes conformational changes, but often to a limited extent. Here, we demonstrate that the interaction of a CO-releasing molecule (CORM3) with a photoreceptor photoactive yellow protein (PYP) drives large structural changes in the latter. The interaction of CORM3 and a mutant of PYP, Met100Ala, not only trigger the isomerization of its chromophore, p-coumaric acid, from its anionic trans configuration to a protonated cis configuration, but also increases the content of β-sheet at the cost of α-helix and random coil in the secondary structure of the protein. The CORM3 derived Met100Ala is found to highly resemble the signaling state, which is one of the key photo-intermediates of this photoactive protein, in both protein local conformation and chromophore configuration. The organometallic reagents hold promise as protein engineering tools. This work highlights a novel approach to structurally accessing short lived intermediates of proteins in a steady-state fashion.

Jet Flight Patterns of Linear Shaped Charges

A typical jet flight pattern of linear shaped charges (LSCs) is studied, and analytical expressions are built for two important parameters of the angle of liner collapse line φ and jet projection angle ω. In order to simplify the nonlinear nature of the liner collapse behavior of LSCs, important assumptions are made, including (1) a constant jet projection velocity at the given standoff distance and (2) the liner collapse occurs in a steady-state fashion, generating a single straight collapse line during the detonation. Based on the assumptions, analytical expressions are derived and the result is compared with side-view images of LSC jet flight to evaluate accuracy and applicability. The analytical approach delivers reasonable accuracy in a given range and is applicable to a short range of standoff distances.

The application of controlled variable magnetic eddy current damping to the study of vortex-induced vibrations

A powerful variable magnetic eddy current damping system has been constructed and utilized in an experimental study of vortex-induced vibrations (VIV). This damping system allows us to impose precise values of nearly ideal viscous damping over a wide range of damping values of interest. This new damping system offers improvements over previously utilized damping methods. Unlike most studies of VIV, where the damping cannot be independently controlled, we are able to impose our system damping independent of the other system parameters. Also, because the system only requires that a thin conductive plate be attached to the oscillating system, the overall mass of the system does not increase dramatically and still allows the investigation of very low mass systems. Finally, the system can operate in a steady-state fashion, supplying a constant damping value for an extended period of time, or in a transient fashion, where the damping value is intentionally varied over time. With this damping system, we have systematically explored both steady and transient damping effects on VIV behavior and provide a brief overview of some sample results.

Tank-Tread Frequency of the Red Cell Membrane: Dependence on the Viscosity of the Suspending Medium

Single human red cells were suspended in media with viscosities ranging from 12.9 to 109 mPa s and subjected to shear flow ranging from 1/s to 290/s in a rheoscope. This is a transparent cone-plate chamber adapted to a microscope. The motion of the membrane around red cells oriented in a steady-state fashion in the shear field (tank-tread motion) was videotaped. The projected length and width of the cells as well as the frequency of tank-tread motion were measured. One-thousand eight-hundred seventy-three cells of three blood donors were evaluated. The frequency increased with the mean shear rate in an almost linear fashion. The slope of this dependence increased weakly with the viscosity of the suspending medium. No correlation was found between the frequency and four morphological red cell parameters: the projected length and width of the cells as well as the ratio and the square root of the product of these quantities. The energy dissipation within the red cell membrane was estimated based on the measured parameters and compared to the energy dissipation in the undisturbed shear flow. At constant mean shear rate the rise of the energy dissipation with viscosity is slower whereas at constant viscosity the rise with the shear rate is steeper than in the undisturbed shear flow. A fit of the data collected in this work to a theoretical red cell model might allow one to determine intrinsic mechanical constants in the low deformation regime.

Flood magnitude–frequency and lithologic control on bedrock river incision in post-orogenic terrain

Mixed bedrock–alluvial rivers–bedrock channels lined with a discontinuous alluvial cover–are key agents in the shaping of mountain belt topography by bedrock fluvial incision. Whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes, the present study investigates river incision processes in a post-orogenic (cratonic) landscape undergoing extremely low rates of incision (< 5 m/Ma). River incision processes are examined as a function of substrate lithology and the magnitude and frequency of formative flows along Sandy Creek gorge, a mixed bedrock–alluvial stream in arid SE-central Australia. Incision is focused along a bedrock channel with a partial alluvial cover arranged into riffle-pool macrobedforms that reflect interactions between rock structure and large-flood hydraulics. Variations in channel width and gradient determine longitudinal trends in mean shear stress ( τ b) and therefore also patterns of sediment transport and deposition. A steep and narrow, non-propagating knickzone (with 5% alluvial cover) coincides with a resistant quartzite unit that subdivides the gorge into three reaches according to different rock erodibility and channel morphology. The three reaches also separate distinct erosional styles: bedrock plucking (i.e. detachment-limited erosion) prevails along the knickzone, whereas along the upper and lower gorge rock incision is dependent upon large formative floods exceeding critical erosion thresholds ( τ c) for coarse boulder deposits that line 70% of the channel thalweg (i.e. transport-limited erosion). The mobility of coarse bed materials (up to 2 m diameter) during late Holocene palaeofloods of known magnitude and age is evaluated using step-backwater flow modelling in conjunction with two selective entrainment equations. A new approach for quantifying the formative flood magnitude in mixed bedrock–alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials; in this case the d 84 size fraction. A 350 m 3/s formative flood fully mobilises the coarse alluvial cover with τ b∼200–300 N/m 2 across the upper and lower gorge riffles, peaking over 500 N/m 2 in the knickzone. Such floods have an annual exceedance probability much less than 10 − 2 and possibly as low as 10 − 3. The role of coarse alluvial cover in the gorge is discussed at two scales: (1) modulation of bedrock exposure at the reach-scale, coupled with adjustment to channel width and gradient, accommodates uniform incision across rocks of different erodibility in steady-state fashion; and (2) at the sub-reach scale where coarse boulder deposits (corresponding to τ b minima) cap topographic convexities in the rock floor, thereby restricting bedrock incision to rare large floods. While recent studies postulate that decreasing uplift rates during post-orogenic topographic decay might drive a shift to transport-limited conditions in river networks, observations here and elsewhere in post-orogenic settings suggest, to the contrary, that extremely low erosion rates are maintained with substantial bedrock channel exposure. Although bed material mobility is known to be rate-limiting for bedrock river incision under low sediment flux conditions, exactly how a partial alluvial cover might be spatially distributed to either optimise or impede the rate of bedrock incision is open to speculation. Observations here suggest that the small volume of very stable bed materials lining Sandy Creek gorge is distributed so as to minimise the rate of bedrock fluvial incision over time.

Velocity field in the spiral-wave pattern observed in rotating shallow-water experiments

The paper presents the first quantitative results of a laboratory study of the velocity field in a two-arm spiral-wave pattern generated in a steady-state fashion by a hydrodynamical instability in a differentially rotating, thin layer of liquid. The liquid layer has a free surface, and the rotational profile includes an interval where the velocity drops abruptly, as in the gaseous disks of spiral galaxies. The properties of anticyclonic vortices observed between the arms of this pattern at the corotation radius are considered.

A steady-state combustion modelling of composite solid propellants

By depicting the transfer of heat and combustion reaction to take place within thin gas layers close to the propellant surface burning in a steady-state fashion, a mathematical equation has been deduced to describe the burning rate of solid propellant as a function of initial grain temperature and chamber pressure. It has been also assumed that chemical reaction could take place in premixing-diffusing zone but were carried out mainly in the reaction-flame zone. All these phenomena taken place in each zone of combustion have been assumed to be steady-state. In the present investigation, the equation, γ=k·(1/R(T i +C))n. exp (-E a/R(T i +C)(P/z) is being presented and it is compared with experimental data. The proposed model has been tested and evaluated vis-a-vis strand burner data for three different propellants based on CTPB, and it has been found that the deviation of the computed burning rates from the measured rates ranged up to 2%.

The interaction of a plume with a rheological boundary: A comparison between two‐ and three‐dimensional models

The discrete nature of volcanic hot spot chains, whose origin is believed to be related to mantle plumes, is suggestive that the plumes feeding them may be pulsating. A possible origin of the pulsations is the interaction of mantle plumes with a rheological interface in the transition zone. We have studied the time‐dependent, three‐dimensional interaction of an upwelling mantle plume with a rheological interface that separates a Newtonian lower mantle from a Newtonian upper mantle with a lower viscosity. Previous two‐dimensional (2‐D) work demonstrates that when a hot plume enters a non‐Newtonian layer with lower viscosity, the hot material is carried from the interface in pulsating, diapiric events. A purely Newtonian analog to this model mimics this behavior in a qualitative manner if the viscosity contrast across the interface is larger than 2 orders of magnitude. In this work, we have used this Newtonian model to make three‐dimensional (3‐D) modeling feasible. A combined spectral/finite difference code has been employed to solve the 2‐D and 3‐D convection equations in Cartesian coordinates. We have varied the Rayleigh number (scaled to the constant viscosity of the lower mantle) between 104 and 105 and the viscosity contrast of the layers between 10 and 1000. In 2‐D situations with low viscosity contrasts, a plume thins in a steady state fashion as it enters the upper layer. At moderate and higher viscosity contrasts (above 50), the plume shows a pulsating behavior. This transition from “thinning” to “pulsating” is found to be strongly dependent on viscosity contrast and only moderately dependent on Rayleigh number. The frequency of the pulsations is linearly dependent on Rayleigh number and viscosity contrast. In three dimensions, the plume thins less and is therefore less susceptible to disruption by shear and the plume moves through the upper layer in a steady state fashion. This disappearance of pulsating behavior in three dimensions indicates a case where conclusions about plume dynamics in two dimensions do not apply to 3‐D situations.

Magnetoelectric tunnel effects in paramagnets

Abstract A number of new magnetoelectric effects in crystals with tunneling paramagnetic centers involving the enhancement of the magnetization by an electric field are discussed. The experiments are performed for [AlO4]0 and Ge3+ (Na) centers on quartz by the EPR technique. Experiments show that the tunneling paramagnetic centers in crystals can be cooled in a steady-state fashion below the lattice temperature by means of low frequency, nonresonant external electric fields, and that the rate of spin-lattice relaxation for the tunneling centers can be controlled by electric fields.

Continuous inversion angiography.

A subtractive time-of-flight technique for magnetic resonance angiography is described. In this approach, the arterial supply to an organ is inverted in a steady-state fashion by applying off-resonance irradiation in the presence of a linear magnetic field gradient. An angiogram is formed by subtracting an image acquired with arterial inversion from a control image acquired with no arterial inversion. A single coil is used to apply both the inversion and observation pulses. Intracranial angiograms obtained from normal volunteers using a two-dimensional projective implementation of this technique at 1.5 T illustrate excellent small vessel detail and background suppression.

Studies on NADH(NADPH)-cytochrome c reductase (FMN-containing) from yeast: Steady-state kinetic properties of the flavoenzyme from top-fermenting ale yeast

A study of the steady-state kinetics of NADH(NADPH)-cytochrome c reductase (FMN-containing) from ale yeast ( M. S. Johnson and S. A. Kuby (1985) J. Biol. Chem. 260, 12341–12350) has led to a postulated three-substrate random-ordered hybrid mechanism, where NAD(P)H and FMN add randomly and very likely in a steady-state fashion, followed by an ordered addition of cytochrome c. Kinetic parameters have been derived from this mechanism. Arrhenius plots showed large differences between NADH and NADPH, as the substrate-reductant. Menadione accelerated cytochrome c reduction and also O 2 uptake, but vitamin K 1 and coenzyme Q 10 were ineffective as electron mediators, possibly as a result of their insolubility. With NADPH as the substrate-reductant, the order of the rate of reduction of electron acceptors was ferricyanide > DCIP > cytochrome c > oxygen; with menadione, the specificity sequence was cytochrome c > ferricyanide > DCIP > oxygen. With NADH, the order was ferricyanide > cytochrome c > oxygen > DCIP, which changed to cytochrome c > ferricyanide > oxygen > DCIP on addition of menadione. Cytochrome b 5 was also reduced in the absence of oxygen. No transhydrogenase activity was observed, but the reduced thionicotinamide analogs of NADH and NADPH acted as substrates. Superoxide dismutase inhibited cytochrome c reduction in air by 50%, but O ⪰ 2 was not necessary for cytochrome c reduction, as evidenced by the increase in rate in the absence of O 2. The product of the reaction with oxygen appeared to be H 2O 2.

Mechanism of oxygen plasma etching of polydimethyl siloxane films

We have used x-ray photoelectron spectroscopy and multiple internal reflection infrared spectroscopy to study the etching of polysiloxane films in an rf oxygen plasma. The results indicate that a structurally strained SiO2 layer, ∼1 nm thick, is formed on the film exposed to oxygen plasma. For a given rf power input this oxidized overlayer recedes with the etching front in a steady state fashion, acting as a protective layer for the underlying polysiloxane film. The etching mechanism is effectively a combination of two competitive processes, namely, ion sputtering and oxidation.

Continental freeboard, sedimentation rates and growth of continental crust

To understand how the Earth has evolved requires a model for the timing and nature of the formation of the continental crust. Of the two contrasting models, the first and most popular is that the continental crust of the Earth has grown throughout geological time. Models of linear or exponential increasing growth with time1,2 are not currently accepted, and it is now generally held that much of the crust was in place by 2,500 Myr with a particularly active period of crustal growth and differentiation between about 3,200 and 2,500 Myr (refs 3–13). The second model argues that the present mass of the continental crust formed very early in Earth history (>4,000 Myr) and has subsequently been recycled through the mantle in a steady-state fashion such that the mass of the crust has not changed during most of Earth history14–16. Resolving these conflicting views is not simple because interpretation of the isotopic evidence is non-unique. The resolution of this debate lies in the interpretation of the record of continental freeboard17–19 and in the plausibility of large scale crustal recycling through the mantle via sediment subduction. We point out here that although the record of continental freeboard is consistent with either limited growth or no-growth models, recent sedimentation rates appear insufficient to support no-growth models. Note that evidence against a no-growth model is not necessarily evidence against minor sediment subduction.

A system for exposing animals to smoke generated in a steady-state fashion

A new method for exposing laboratory animals to polymer pyrolysis products is described. This method is advantageous in that dose may be accurately determined because the concentrations of pyrolysis products in the animal exposure chamber remain constant during exposure. Further, this apparatus was constructed from readily available materials.

Effects of interface kinetics on the growth rate of dendrites

The effects of linear interface kinetics and of square law interface kinetics on the growth of dendrites are investigated theoretically. From interface stability considerations, a simple relationship is discussed which allow the dendrite tip to grow in a stable, steady state fashion. It is found that the slope of the dimensionless velocity versus dimensionless undercooling plot changes when linear kinetics become important, whereas the square law kinetics effect simply displaces the curve to the right without any change in slope at any given velocity.

Primary and Secondary Antibody Response in Rats to Bacterial and Sheep Erythrocyte Antigens

Summary The response of rats to primary and secondary stimulation with bacterial and sheep erythrocyte antigens has been examined. Response to RBC and Str consists of a rapid rise and fall both after primary and secondary injection. The bacterial antigens elicit a rise of titer similar to that produced by RBC and Str. This titer, however, persists for a long period of time in a steady state fashion and second injection leads to a titer rise not very much higher than the steady state level. Cellular proliferation after first and second injection of all antigens shows a similar sequence of events differing only in degree of magnitude but showing essentially the same cell types.