Late- to post-Variscan structures on the coast between Penzance and Pentewan, south Cornwall

The occurrence of two generations (D1/D2) of folds and cleavage, compatible with a top to the north-north-west sense of shear during Variscan convergence is confirmed. A subsequent change in the stress regime (sigma(1) approximate to vertical, sigma(3) approximate to north-north-west-south-south-east) brought about the extensional reactivation of convergence-related features. The resultant D3 structures are diverse and include zones of distributed shear within the footwall of the Carrick Thrust, together with detachments and high angle brittle extensional faults within the hangingwall. D3 deformation probably initiated during the Stephanian, prior to lamprophyre intrusion, but persisted into the early Permian and was partially synchronous with granite emplacement and high temperature mineralization. Changes in the stress regime during the Permian (sigma(1) approximate to east-north-east-west-south-west, sigma(3) approximate to north-north-west-south-south-east to sigma(1) approximate to north-north-west-south-south-east, sigma(3) approximate to east-north-east-west-south-west) resulted in strike-slip faulting and the formation of steeply dipping cleavages. Triassic rift-related extension is also recognised (sigma(1) approximate to vertical, sigma(3) approximate to east-north-east-west-south-west). Low temperature base metal mineralization was in part synchronous with Permian and Triassic faulting. This study demonstrates that the Variscan basement in south Cornwall preserves a valuable record of the late Palaeozoic to Mesozoic tectonic evolution of the region

A re-interpretation of the internal structure of the Lizard complex ophiolite, south Cornwall.

publication-status: PublishedPrevious models for the tectonic-stratigraphy of the Lizard complex ophiolite have proposed three thrust-bounded units. However, our studies indicate that post-obduction extensional faulting may have exerted a hitherto unrecognised effect on the present distribution of lithologies. Field and previously published geophysical evidence suggest that the uppermost tectonic unit (the Crousa Downs Unit) represents the downfaulted upper levels of the Goonhilly Downs Unit. Deformed lithologies previously thought to be part of the Goonhilly Downs Unit are reassigned to the underlying Basal Unit. A revised model for the tectonic-stratigraphy is presented. The Basal Nappe is underlain by the Basal Thrust and comprises the Traboe schists, the Landewednack schists and the Old Lizard Head Series. The Goonhilly Downs Nappe, underlain by the Goonhilly Downs Thrust, structurally overlies the Basal Nappe and comprises serpentinised peridotite, Trelan and Crousa Gabbro and the Porthoustock Sheeted Dyke Complex. This work highlights the importance of late- to post-Variscan extensional deformation in south Cornwall

Alteration and vein mineralisation within the Lizard complex, south Cornwall: Constraints on the timing of serpentinisation.

Two distinct episodes of serpentinisation have been identified within the peridotites of the Lizard complex. The first episode (primary serpentinisation) is represented by the complex and pervasive hydration of the Lizard peridotite. The second (later) episode is characterised by a pale to dark green, pseudo-fibrous mixture of lizardite and chrysotile that is restricted to fractures (vein serpentine). Mineralised north-north-west and east-north-east trending fault zones contain fragments of vein serpentine generated during this second episode. Faults with similar orientations and mineralogy within the gabbro unit contain adularia which have been previously elated by Ar-10-Ar-39 and K-Ar methods at 210-220 Ma (Triassic). Stable isotope ratios indicate that the mineralisation within the gabbro and peridotite is genetically similar. The primary and secondary serpentinisation episodes are therefore interpreted as pre-Triassic in age. A latest Carboniferous to early Permian age is proposed for the formation of vein serpentine and a late Devonian to Carboniferous age is proposed for the primary serpentinisation episode. This is envisaged to have taken place post-obduction but a pre-obduction initiation of serpentinisation cannot be discounted

Quantum feedback control of a solid-state qubit

We have studied theoretically the basic operation of a quantum feedback loop designed to maintain a desired phase of quantum coherent oscillations in a single solid-state qubit. The degree of oscillations synchronization with external harmonic signal is calculated as a function of feedback strength, taking into account available bandwidth and coupling to environment. The feedback can efficiently suppress the dephasing of oscillations if the qubit coupling to the detector is stronger than coupling to environment.Comment: Extended version of cond-mat/0107280 (5 pages, 5 figures); to be published in PRB (RC

Policy Insights from Comparing Carbon Pricing Modeling Scenarios

Carbon pricing is an important policy tool for reducing greenhouse gas pollution. The Stanford Energy Modeling Forum exercise 32 convened eleven modeling teams to project emissions, energy, and economic outcomes of an illustrative range of economy-wide carbon price policies. The study compared a coordinated reference scenario involving no new policies with policy scenarios that impose a price on all fossil fuel-related carbon dioxide (CO2) emissions in the U.S. The CO2 price scenarios begin in 2020 at $25/ton or$50/ton and rise each year over inflation at one percent or five percent. The scenarios also vary by the use of the revenue from the carbon pricing policy; scenarios include rebates to households and deficit neutral reductions in marginal tax rates on capital and labor income. Across all models and policy scenarios, the study finds that carbon pricing leads to significant reductions in CO2 emissions, the majority of which occur in the electricity sector via the reduction of coal use. Policy effects on other energy sources vary by model, for example owing to different technology cost assumptions (e.g., cost of natural gas vs. wind generation). Some models translate energy shifts into changes in conventional air pollutants, reporting declines consistent with substantial air quality benefits from the policy scenarios. The economic costs of the policies are expected to be modest – allowing for nearly identical economic growth– but vary across models. These costs are offset by benefits from avoided climate damages (which are not modeled in this study) and health benefits from reductions in conventional air pollution. The study finds that the CO2 taxes generate significant revenue; a $25/ton price would generate roughly$1.4 trillion over the first decade and all models reported that emissions reductions do not significantly depend on the use of the revenue. Using revenues to reduce capital or labor taxes reduces economy-wide costs in most models relative to household rebates, but the estimated size of the cost reductions varies significantly across models. Across all models that estimated impacts across households, devoting at least some revenue to household rebates improves outcomes for low income households relative to applying all revenue to reductions in other taxes. We focus here on results through 2030, concluding that beyond a decade model uncertainties are too large to make quantitative results useful for near-term policy design

A probabilistic model to recover individual genomes from metagenomes

Shotgun metagenomics of microbial communities reveal information about strains of relevance for applications in medicine, biotechnology and ecology. Recovering their genomes is a crucial but very challenging step due to the complexity of the underlying biological system and technical factors. Microbial communities are heterogeneous, with oftentimes hundreds of present genomes deriving from different speci

Sentiment Analysis of Text Guided by Semantics and Structure

As moods and opinions play a pivotal role in various business and economic processes, keeping track of one's stakeholders' sentiment can be of crucial importance to decision makers. Today's abundance of user-generated content allows for the automated monitoring of the opinions of many stakeholders, like consumers. One challenge for such automated sentiment analysis systems is to identify whether pieces of natural language text are positive or negative. Typical methods of identifying this polarity involve low-level linguistic analysis. Existing systems predominantly use morphological, lexical, and syntactic cues for polarity, like a text's words, their parts-of-speech, and negation or amplification of the conveyed sentiment. This dissertation argues that the polarity of text can be analysed more accurately when additionally accounting for semantics and structure. Polarity classification performance can benefit from exploiting the interactions that emoticons have on a semantic level with words – emoticons can express, stress, or disambiguate sentiment. Furthermore, semantic relations between and within languages can help identify meaningful cues for sentiment in multi-lingual polarity classification. An even better understanding of a text's conveyed sentiment can be obtained by guiding automated sentiment analysis by the rhetorical structure of the text, or at least of its most sentiment-carrying segments. Thus, the sentiment in, e.g., conclusions can be treated differently from the sentiment in background information. The findings of this dissertation suggest that the polarity of natural language text should not be determined solely based on what is said. Instead, one should account for how this message is conveyed as well

The chronology and kinematics of late Palaeozoic deformation in the NW contact metamorphic aureole of the Land's End Granite

A structural investigation of coastal exposures between Cape Cornwall and Pendeen Watch, in the NW contact metamorphic aureole of the Land’s End Granite, has confirmed a similar deformation chronology as in a reference section around Porthleven. D1 deformation is represented by an ubiquitous bedding-parallel S1 cleavage although F1 folds have not been recognised. D2 deformation is more localised and characterised by open F2 folds that verge WSW to NW and are associated with an ENE to SE dipping S2 crenulation cleavage. These structures are commonly obscured by later deformation and contact metamorphism and have not been described previously. A set of steeply inclined NNW-SSE trending, and subordinate set of moderately SE dipping, post-D2 metamorphic quartz veins formed coevally during an episode of strike-slip deformation prior to, or during, the early stages of D3 deformation. D3 deformation is widespread and represented by F3 folds and a WNW to NW dipping S3 crenulation cleavage; it has been recorded previously as D2 deformation. Two orders of F3 folds are developed; first order folds have a wavelength of up to 50 m, verge ESE, and result in vertical or steeply inclined bedding and S1 cleavage on their short limbs. Second order folds usually have a wavelength of 1 m or less and usually verge ESE, unless on the short limb of first order folds, where they verge WNW. Previously published data, indicating a dominant NW to WNW vergence of F3 folds on the northern flank of the Land’s End Granite are incorrect. D3 structures are consistent with formation during the extensional reactivation of large-scale thrust faults. Granite emplacement post-dates all three episodes of ductile deformation but granites and their host rocks are deformed by a late brittle expression of D3 deformation. The Land’s End pluton has been accommodated, at the current exposure level, primarily by roof uplift that has resulted in the tilting of D3 and earlier structures to the NW by 40-50º; this may have been accompanied by differential vertical axis rotations of the host rock. The last significant Palaeozoic deformation episode formed F4 folds and S4 cleavage and was a consequence of Mid- to Late Permian ENE-WSW shortening