703 research outputs found
Mathematical Model of the Oxidation of a Uranium Carbide Fuel Pellet Including an Adherent Product Layer
Uranium carbide is a candidate fuel for Generation IV nuclear reactors. However, like any candidate fuel, a reprocessing route should be established before implementation. One proposed method involves a pre-oxidation step, where the carbide fuel is oxidised to an oxide and then reprocessed as normal. A mathematical model has been developed to simulate such an oxidation using finite difference approximations of the heat and mass transfer processes occurring. Available literature was consulted to provide coefficients for the reaction rates and importantly the diffusion of oxygen through the adherent oxide layer that forms on the carbide: the rate limiting step. The transient temperature, oxygen and carbon monoxide distributions through the system are modelled in order to predict oxidation completion times and the temperatures reached. It was found that for a spherical pellet of radius 0.935cm, the oxidation can take between 1 h to 19 h depending on the oxidation conditions and reach temperatures of up to 1556°C. A robust model results that offers increased understanding of a process crucial to the sustainable use of carbide fuels in energy generation
Gold in the Dalradian terrane : a review of previous work
The Dalradian Supergroup comprises a Late Precambrian sequence of marine clastic sedimentary
rocks and minor basic volcanic rocks which was folded and metamorphosed during the early
Palaeozoic Caledonian Orogeny. Intrusive igneous rocks are widespread throughout the
Dalradian terrane. The most important in terms of gold metallogenesis are the post-tectonic
granites which comprise a diverse suite of calc-alkaline intrusions emplaced between 420 and
395 Ma.
Numerous occurrences of gold in bedrock and alluvium are documented in the Dalradian terrane
of Scotland. Mesothermal vein occurrences are the most important and include the Cononish
deposit, near Tyndrum in Perthshire, where planning permission for mining has been granted.
Gold mineralisation of several other styles, including intrusion-related, epithermal, stratiform
and occurrences associated with mafic-ultramafic intrusions, is also present.
This report has been compiled for the BGS Core Programme project ‘Sedimentary Basin
Resources: Gold in orogenic extensional basins – the Dalradian’. This project, carried out
between 1997–2000, was designed to investigate the factors controlling the distribution of gold
in the Dalradian and to develop a predictive metallogenic model for gold mineralisation in this
terrane. This report provides a` review of known gold occurrences and the results of past mineral
exploration activity in the Dalradian terrane. The latter has been compiled from records held in
BGS archives and the available data are summarised in a series of appendices.
Exploration for metalliferous mineralisation has been carried out widely in the Dalradian terrane
by commercial mining companies and by BGS. In the 1970s most work focused on Cu, Pb, Zn,
Ni and Mo, while more recently, from 1981 onwards, precious metals (Au and PGE) were the
prime target. Between 1972 and 1984 the DTI sought to encourage private-sector mineral
exploration by the provision of grants under the Mineral Exploration and Investment Grants Act
(MEIGA). About 150 reports derived from these projects are available on open-file at BGS.
Exploration by BGS was carried out mainly through the DTI-funded Mineral Reconnaissance
Programme (MRP), which ran between 1972 and 1997. Nearly 150 reports and associated data
releases were produced by the MRP. Together the MEIGA and MRP reports have been the major
sources of information used in this report.
The combination of improved genetic models for gold deposits, the increased availability of
multidisciplinary digital geoscience data and the information on previous exploration
summarised in this report provides a sound basis for research on gold mineralisation in the
Dalradian terrane. Potential exists in a range of settings that may host economic gold deposits
Reactive Ion Etching on (Yb,Nb):RbTiOPO<sub>4</sub>/RbTiOPO<sub>4</sub> epitaxial layers for the fabrication of Y-splitters and Mach-Zehnder Interferometers
Rubidium titanyl phosphate RbTiOPO4 (RTP) belongs to a highly diverse and versatile structural family and because of its large non-linear optical coefficients, wide transparency, high laser damage threshold, high chemical stability and low dielectric constants, this material is highly attractive for electro-optic applications such as modulators and Q-switches. RTP has a similar non-linear optical coefficient to KTP but, unlike KTP, it can be doped with Yb3+ ions to obtain a high enough concentration to allow efficient laser action. Because of all these interesting properties, RTP is a strong candidate as a platform material for integrated photonics. Reactive ion etching (RIE) is a commonly used method in etching of semiconductors, but there is little literature available on the plasma-based etching of RTP. Moreover, single-mode rib waveguides have been successfully fabricated in (Yb,Nb):RTP by RIE. In this work, (Yb,Nb):RbTiOPO4/RbTiOPO4 (001) epitaxial layers have been structured by RIE by using a combination of Ar and SF6 gases. The refractive index contrasts between the (Yb,Nb):RbTiOPO4 layer and the RbTiOPO4 substrate at 1.55 microns have been measured
Spectra and energy levels of the trivalent ytterbium ion doped into lithium niobate by thermal indiffusion
An x-cut LiNbO3 substrate has been doped with Yb3+ ions by thermal diffusion from an Yb metal film of thickness 7nm. Polarised absorption and fluorescence spectra of the dopant ion have been measured using Ti-diffused y-propagating channel waveguides prepared in the doped region. Yb is a diode- pumpable laser ion with characteristics which can be compared favourably with those of Nd in some respects; for example the small energy difference between pump and laser photons reduces thermal load facilitating high power operation. A waveguide laser geometry is particularly advantageous for Yb due to the quasi-3-level nature of the laser transition. The simple fabrication technique described here has been used to produce a system which may have the potential to operate as an Yb waveguide laser in an electro-optic host crystal
Star and Planet Formation with ALMA: an Overview
Submillimeter observations with ALMA will be the essential next step in our
understanding of how stars and planets form. Key projects range from detailed
imaging of the collapse of pre-stellar cores and measuring the accretion rate
of matter onto deeply embedded protostars, to unravelling the chemistry and
dynamics of high-mass star-forming clusters and high-spatial resolution studies
of protoplanetary disks down to the 1 AU scale.Comment: Invited review, 8 pages, 5 figures; to appear in the proceedings of
"Science with ALMA: a New Era for Astrophysics". Astrophysics & Space
Science, in pres
A stochastic model for heart rate fluctuations
Normal human heart rate shows complex fluctuations in time, which is natural,
since heart rate is controlled by a large number of different feedback control
loops. These unpredictable fluctuations have been shown to display fractal
dynamics, long-term correlations, and 1/f noise. These characterizations are
statistical and they have been widely studied and used, but much less is known
about the detailed time evolution (dynamics) of the heart rate control
mechanism. Here we show that a simple one-dimensional Langevin-type stochastic
difference equation can accurately model the heart rate fluctuations in a time
scale from minutes to hours. The model consists of a deterministic nonlinear
part and a stochastic part typical to Gaussian noise, and both parts can be
directly determined from the measured heart rate data. Studies of 27 healthy
subjects reveal that in most cases the deterministic part has a form typically
seen in bistable systems: there are two stable fixed points and one unstable
one.Comment: 8 pages in PDF, Revtex style. Added more dat
Survival, pathologic response, and genomics in CALGB 40601 (Alliance), a neoadjuvant Phase III trial of paclitaxel-trastuzumab with or without lapatinib in HER2-positive breast cancer
PURPOSE CALGB 40601 assessed whether dual versus single human epidermal growth factor receptor 2 (HER2) -targeting drugs added to neoadjuvant chemotherapy increased pathologic complete response (pCR). Here, we report relapse-free survival (RFS), overall survival (OS), and gene expression signatures that predict pCR and survival. PATIENTS AND METHODS Three hundred five women with untreated stage II and III HER2-positive breast cancer were randomly assigned to receive weekly paclitaxel combined with trastuzumab plus lapatinib (THL), trastuzumab (TH), or lapatinib (TL). The primary end point was pCR, and secondary end points included RFS, OS, and gene expression analyses. mRNA sequencing was performed on 264 pretreatment samples. RESULTS One hundred eighteen patients were randomly allocated to THL, 120 to TH, and 67 to TL. At more than 7 years of follow-up, THL had significantly better RFS and OS than did TH (RFS hazard ratio, 0.32; 95% CI, 0.14 to 0.71; P 5.005; OS hazard ratio, 0.34; 95% CI, 0.12 to 0.94; P 5.037), with no difference between TH and TL. Of 688 previously described gene expression signatures, significant associations were found in 215 with pCR, 45 with RFS, and only 22 with both pCR and RFS (3.2%). Specifically, eight immune signatures were significantly correlated with a higher pCR rate and better RFS. Among patients with residual disease, the immunoglobulin G signature was an independent, good prognostic factor, whereas the HER2-enriched signature, which was associated with a higher pCR rate, showed a significantly shorter RFS. CONCLUSION In CALGB 40601, dual HER2-targeting resulted in significant RFS and OS benefits. Integration of intrinsic subtype and immune signatures allowed for the prediction of pCR and RFS, both overall and within the residual disease group. These approaches may provide means for rational escalation and de-escalation treatment strategies in HER2-positive breast cancer
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