A comparison of radioactive waste from first generation fusion reactors and fast fission reactors with actinide recycling

Limitations of the fission fuel resources will presumably mandate the replacement of thermal fission reactors by fast fission reactors that operate on a self-sufficient closed fuel cycle. This replacement might take place within the next one hundred years, so the direct competitors of fusion reactors will be fission reactors of the latter rather than the former type. Also, fast fission reactors, in contrast to thermal fission reactors, have the potential for transmuting long-lived actinides into short-lived fission products. The associated reduction of the long-term activation of radioactive waste due to actinides makes the comparison of radioactive waste from fast fission reactors to that from fusion reactors more rewarding than the comparison of radioactive waste from thermal fission reactors to that from fusion reactors. Radioactive waste from an experimental and a commercial fast fission reactor and an experimental and a commercial fusion reactor has been characterized. The fast fission reactors chosen for this study were the Experimental Breeder Reactor 2 and the Integral Fast Reactor. The fusion reactors chosen for this study were the International Thermonuclear Experimental Reactor and a Reduced Activation Ferrite Helium Tokamak. The comparison of radioactive waste parameters shows that radioactive waste from the experimental fast fission reactor may be less hazardous than that from the experimental fusion reactor. Inclusion of the actinides would reverse this conclusion only in the long-term. Radioactive waste from the commercial fusion reactor may always be less hazardous than that from the commercial fast fission reactor, irrespective of the inclusion or exclusion of the actinides. The fusion waste would even be far less hazardous, if advanced structural materials, like silicon carbide or vanadium alloy, were employed

Photosynthesis and light-dependent proton pumps increase boundary layer pH in tropical macroalgae: A proposed mechanism to sustain calcification under ocean acidification

Ocean acidification (OA) projections predict ocean pH to decline between 0.2 and 0.4 by 2100 with potential negative consequences for marine calcifiers without acclimation or adaption strategies to accomodate greater H+ in seawater. Biotic control of calcified reef macroalgae thalli surface diffusive boundary layer (DBL) chemistry may overcome low pH in seawater as one strategy to accommodate OA conditions. To investigate this strategy, we examined surface DBL O2 and pH dynamics in five calcifying macroalgae (Halimeda, Udotea, Jania, Neogoniolithon, crustose coralline algae CCA) from the Florida Reef Tract under ambient (8.1) and low (7.65) pH using microsensors (100�μm) at the thalli surface in a flow-through flume. The role of photosynthesis and photosystem II (PSII)-independent proton pumps in controlling DBL pH were examined. Four of the five macroalgae exhibited a strong positive linear relationship between O2 production and increasing pH in the first 15�30�s of irradiance. Once a quasi-steady-state O2 concentration was reached (300�s), all species had DBL pH that were higher (0.02�0.32) than bulk seawater. The DBL pH increase was greatest at low pH and dependent on PSII. Some evidence was found for a light-dependent, but PSII-independent, proton pump. High DBL � pH upon illumination was likely in response to carbon concentrating mechanisms (CCMs) for photosynthesis. CCMs may be a HCO3��H+ symport, OH� antiport or other DIC transport system, accompanied by proton efflux. HCO3� dehydration by external carbonic anhydrase (CAext) also produces OH� that can neutralize H+ in the DBL. CO2 or HCO3� uptake for photosynthesis may also engage H+/OH� fluxes as part of intracellular acid-base regulation changing DBL pH. A higher � pH within the DBL at low pH could be accounted for by greater CO2 diffusion and/or lower efficiencies in exporting cellular H+ across a lower concentration gradient, and/or a more efficient removal of H+ by CAext-driven dehydration of HCO3�. In the dark, � pH was less than in the light as these dynamics were primarily due to photosynthesis. We present a conceptual model of inorganic carbon uptake and ion transport pathways, as well as other processes associated with photosynthesis that drive DBL � pH and sustain tropical macroalgal calcification in the light under OA. In the dark, unless PSII-independent proton pumps are present, which do not appear to be ubiquitous amongst species, acidification processes likely dominate, resulting in CaCO3 net dissolution, particularly under OA conditions

Production of Metal Prototypes Using a High Powered Laser Machining Centre

The established commercially available rapid prototyping techniques are now well known throughout the manufacturing community. They are able to produce high quality, accurate prototypes, but are limited largely to processing polymer, wax or paper materials. Where a metal part is required, then a further process step, such as investment casting using the prototype part as a pattern is required. As a further point most of the above systems are high capital cost dedicated pieces of equipment. This paper describes the use of laser machining centres as rapid prototyping tools in the areas of, laminated prototyping, using both paper and metal, and laser forming.Mechanical Engineerin

Theory of Stellar Oscillations

In recent years, astronomers have witnessed major progresses in the field of stellar physics. This was made possible thanks to the combination of a solid theoretical understanding of the phenomena of stellar pulsations and the availability of a tremendous amount of exquisite space-based asteroseismic data. In this context, this chapter reviews the basic theory of stellar pulsations, considering small, adiabatic perturbations to a static, spherically symmetric equilibrium. It starts with a brief discussion of the solar oscillation spectrum, followed by the setting of the theoretical problem, including the presentation of the equations of hydrodynamics, their perturbation, and a discussion of the functional form of the solutions. Emphasis is put on the physical properties of the different types of modes, in particular acoustic (p-) and gravity (g-) modes and their propagation cavities. The surface (f-) mode solutions are also discussed. While not attempting to be comprehensive, it is hoped that the summary presented in this chapter addresses the most important theoretical aspects that are required for a solid start in stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Serum (1 → 3)-β-d-glucan measurement as an early indicator of Pneumocystis jirovecii pneumonia and evaluation of its prognostic value

AbstractPneumocystis jirovecii (carinii) pneumonia (PJP) is a major cause of disease in immunocompromised individuals. However, until recently no reliable and specific serological parameters for the diagnosis of PJP have been available. (1 → 3)-β-d-Glucan (BG) is a cell wall component of P. jirovecii and of various other fungi. Data from the past few years have pointed to serum measurement of BG as a promising new tool for the diagnosis of PJP. We therefore conducted a retrospective study on 50 patients with PJP and 50 immunocompromised control patients to evaluate the diagnostic performance of serum BG measurement. Our results show an excellent diagnostic performance with a sensitivity of 98.0% and a specificity of 94%. While the positive predictive value was only 64.7%, the negative predictive value was 99.8% and therefore a negative BG result almost rules out PJP. BG levels were already strongly elevated in an average of 5 days and up to 21 days before microbiological diagnosis demonstrating that the diagnosis could have been confirmed earlier. BG levels at diagnosis and maximum BG levels during follow-up did not correlate with the outcome of patients or with the P. jirovecii burden in the lung as detected by Real-Time PCR. Therefore, absolute BG levels seem to be of no prognostic value. Altogether, BG is a reliable parameter for the diagnosis of PJP and could be used as a preliminary test for patients at risk before a bronchoalveolar lavage is performed

Multidimensional continued fractions, dynamical renormalization and KAM theory

The disadvantage of `traditional' multidimensional continued fraction algorithms is that it is not known whether they provide simultaneous rational approximations for generic vectors. Following ideas of Dani, Lagarias and Kleinbock-Margulis we describe a simple algorithm based on the dynamics of flows on the homogeneous space SL(2,Z)\SL(2,R) (the space of lattices of covolume one) that indeed yields best possible approximations to any irrational vector. The algorithm is ideally suited for a number of dynamical applications that involve small divisor problems. We explicitely construct renormalization schemes for (a) the linearization of vector fields on tori of arbitrary dimension and (b) the construction of invariant tori for Hamiltonian systems.Comment: 51 page

On collisional capture rates of irregular satellites around the gas-giant planets and the minimum mass of the solar nebula

We investigated the probability that an inelastic collision of planetesimals within the Hill sphere of the Jovian planets could explain the presence and orbits of observed irregular satellites. Capture of satellites via this mechanism is highly dependent on not only the mass of the protoplanetary disk, but also the shape of the planetesimal size distribution. We performed 2000 simulations for integrated time intervals $\sim 2$ Myr and found that, given the currently accepted value for the minimum mass solar nebula and planetesimal number density based upon the \citet{Nesvorny2003} and \citet{Charnoz2003} size distribution $dN \sim D^{-3.5} dD$, the collision rates for the different Jovian planets range between $\sim 0.6$ and \gtrsim 170 \, \Myr^{-1} for objects with radii, 1 \, \km \le r \le 10 \, \km. Additionally, we found that the probability that these collisions remove enough orbital energy to yield a bound orbit was $\lesssim 10^{-5}$ and had very little dependence on the relative size of the planetesimals. Of these collisions, the collision energy between two objects was $\gtrsim 10^3$ times the gravitational binding energy for objects with radii $\sim 100$ km. We find that, capturing irregular satellites via collisions between unbound objects can only account for $\sim 0.1$ of the observed population, hence can this not be the sole method of producing irregular satellites.Comment: 11 pages 4 figures 1 table; This replaces a prior submission, which contained some minor contradictions within the text accepted by MNRAS in pres

Dislocations and the critical endpoint of the melting line of vortex line lattices

We develop a theory for dislocation-mediated structural transitions in the vortex lattice which allows for a unified description of phase transitions between the three phases, the elastic vortex glass, the amorphous vortex glass, and the vortex liquid, in terms of a free energy functional for the dislocation density. The origin of a critical endpoint of the melting line at high magnetic fields, which has been recently observed experimentally, is explained.Comment: 4 pages, 1 figur

Maximally-localized Wannier functions for entangled energy bands

We present a method for obtaining well-localized Wannier-like functions (WFs) for energy bands that are attached to or mixed with other bands. The present scheme removes the limitation of the usual maximally-localized WFs method (N. Marzari and D. Vanderbilt, Phys. Rev. B 56, 12847 (1997)) that the bands of interest should form an isolated group, separated by gaps from higher and lower bands everywhere in the Brillouin zone. An energy window encompassing N bands of interest is specified by the user, and the algorithm then proceeds to disentangle these from the remaining bands inside the window by filtering out an optimally connected N-dimensional subspace. This is achieved by minimizing a functional that measures the subspace dispersion across the Brillouin zone. The maximally-localized WFs for the optimal subspace are then obtained via the algorithm of Marzari and Vanderbilt. The method, which functions as a postprocessing step using the output of conventional electronic-structure codes, is applied to the s and d bands of copper, and to the valence and low-lying conduction bands of silicon. For the low-lying nearly-free-electron bands of copper we find WFs which are centered at the tetrahedral interstitial sites, suggesting an alternative tight-binding parametrization.Comment: 13 pages, with 9 postscript figures embedded. Uses REVTEX and epsf macro

Response to “Comment on ‘optimal exposure biomarkers for nonpersistent chemicals in environmental epidemiology’”

We appreciate the opportunity to respond to the letter from Stahlhut et al. regarding our Brief Communication. We stressed the importance of biospecimen integrity and the potential danger of unrecognized contamination of convenience samples, particularly with ubiquitous environmental chemicals such as bisphenol A (BPA) and phthalates