Initial Conditions for Bubble Universes

The "bubble universes" of Coleman and De Luccia play a crucial role in string cosmology. Since our own Universe is supposed to be of this kind, bubble cosmology should supply definite answers to the long-standing questions regarding cosmological initial conditions. In particular, it must explain how an initial singularity is avoided, and also how the initial conditions for Inflation were established. We argue that the simplest non-anthropic approach to these problems involves a requirement that the spatial sections defined by distinguished bubble observers should not be allowed to have arbitrarily small volumes. Casimir energy is a popular candidate for a quantum effect which can ensure this, but [because it violates energy conditions] there is a danger that it could lead to non-perturbative instabilities in string theory. We make a simple proposal for the initial conditions of a bubble universe, and show that our proposal ensures that the system is non-perturbatively stable. Thus, low-entropy conditions can be established at the beginning of a bubble universe without violating the Second Law of thermodynamics and without leading to instability in string theory. These conditions are inherited from the ambient spacetime.Comment: Further clarifications; 28 pages including three eps files. This is the final [accepted for publication] versio

Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA

Combined U-Pb, O and Hf isotope data in zircon allows discrimination between juvenile and reworked crust, and is therefore a useful tool for understanding formation and evolution of the continental crust. The crustal evolution of basement rocks in central North America (Laurentia) is poorly constrained, as it is almost entirely overlain by Palaeozoic cover. In order to improve our understanding of the evolution of this region we present U-Pb, O and Hf isotope data from zircon in drill-core samples from the subsurface basement of Ohio. The Hf isotope data suggests juvenile crust formation at similar to 1650 Ma followed by continued reworking of a single reservoir. This similar to 1650 Ma reservoir was tapped at similar to 1450 Ma during the formation of the Granite-Rhyolite Province and subsequently reworked again during the Grenvillian orogeny. The similar to 1650 Ma crust formation model age for the suite of samples along with the presence of similar to 1650 Ma magmatic rocks suggests an eastward extension of the Mazatzal Province (or Mazatzal-like crust) and makes it a possible protolith to the subsurface basement of Ohio and surrounding Mesoproterozoic (i.e. Grenville-age) rocks. The eastward extension of this similar to 1650 Ma crustal reservoir into Ohio requires a revision of the crustal boundary defined by Nd isotopic data to be located further east, now overlapping with the Grenville front magnetic lineament in Ohio. In fact, the easternmost sample in this study is derived from a more depleted reservoir. This limits the extent of >1.5 Ga basement in subsurface Ohio and constrains the location of the crustal boundary. Further, syn-orogenic magmatism at similar to 1050 Ma suggests a potential extrapolation of the Interior Magmatic Belt into Ohio. Oxygen isotopic data in zircon suggests that during Grenvillian metamorphism, zircon recrystallisation occurred in the presence of heavy delta O-18 fluids resulting in zircon with elevated delta O-18 values. (C) 2015 Elsevier B.V. All rights reserved

Pore performance: artificial nanoscale constructs that mimic the biomolecular transport of the nuclear pore complex

The nuclear pore complex is a nanoscale assembly that achieves shuttle-cargo transport of biomolecules: a certain cargo molecule can only pass the barrier if it is attached to a shuttle molecule. In this review we summarize the most important efforts aiming to reproduce this feature in artificial settings. This can be achieved by solid state nanopores that have been functionalized with the most important proteins found in the biological system. Alternatively, the nanopores are chemically modified with synthetic polymers. However, only a few studies have demonstrated a shuttle-cargo transport mechanism and due to cargo leakage, the selectivity is not comparable to that of the biological system. Other recent approaches are based on DNA origami, though biomolecule transport has not yet been studied with these. The highest selectivity has been achieved with macroscopic gels, but they are yet to be scaled down to nano-dimensions. It is concluded that although several interesting studies exist, we are still far from achieving selective and efficient artificial shuttle-cargo transport of biomolecules. Besides being of fundamental interest, such a system could be potentially useful in bioanalytical devices

Electromagnetism in terms of quantum measurements

We consider the question whether electromagnetism can be derived from quantum physics of measurements. It turns out that this is possible, both for quantum and classical electromagnetism, if we use more recent innovations such as smearing of observables and simultaneous measurability. In this way we justify the use of von Neumann-type measurement models for physical processes. We apply operational quantum measurement theory to gain insight in fundamental aspects of quantum physics. Interactions of von Neumann type make the Heisenberg evolution of observables describable using explicit operator deformations. In this way one can obtain quantized electromagnetism as a measurement of a system by another. The relevant deformations (Rieffel deformations) have a mathematically well-defined "classical" limit which is indeed classical electromagnetism for our choice of interaction

Coral Reefs Will Transition to Net Dissolving Before End of Century

Ocean acidification refers to the lowering of the ocean’s pH due to the uptake of anthropogenic CO2 from the atmosphere. Coral reef calcification is expected to decrease as the oceans become more acidic. Dissolving calcium carbonate (CaCO3) sands could greatly exacerbate reef loss associated with reduced calcification but is presently poorly constrained. Here we show that CaCO3 dissolution in reef sediments across five globally distributed sites is negatively correlated with the aragonite saturation state (Ωar) of overlying seawater and that CaCO3 sediment dissolution is 10-fold more sensitive to ocean acidification than coral calcification. Consequently, reef sediments globally will transition from net precipitation to net dissolution when seawater Ωar reaches 2.92 ± 0.16 (expected circa 2050 CE). Notably, some reefs are already experiencing net sediment dissolution

Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification-like conditions

Spiny lobsters rely on multiple biomineralized exoskeletal predator defenses that may be sensitive to ocean acidification (OA). Compromised mechanical integrity of these defensive structures may tilt predator-prey outcomes, leading to increased mortality in the lobsters’ environment. Here, we tested the effects of OA-like conditions on the mechanical integrity of selected exoskeletal defenses of juvenile California spiny lobster, Panulirus interruptus. Young spiny lobsters reside in kelp forests with dynamic carbonate chemistry due to local metabolism and photosynthesis as well as seasonal upwelling, yielding daily and seasonal fluctuations in pH. Lobsters were exposed to a series of stable and diurnally fluctuating reduced pH conditions for three months (ambient pH/stable, 7.97; reduced pH/stable 7.67; reduced pH with low fluctuations, 7.67 ± 0.05; reduced pH with high fluctuations, 7.67 ± 0.10), after which we examined the intermolt composition (Ca and Mg content), ultrastructure (cuticle and layer thickness), and mechanical properties (hardness and stiffness) of selected exoskeletal predator defenses. Cuticle ultrastructure was consistently robust to pH conditions, while mineralization and mechanical properties were variable. Notably, the carapace was less mineralized under both reduced pH treatments with fluctuations, but with no effect on material properties, and the rostral horn had lower hardness in reduced/high fluctuating conditions without a corresponding difference in mineralization. Antennal flexural stiffness was lower in reduced, stable pH conditions compared to the reduced pH treatment with high fluctuations and not correlated with changes in cuticle structure or mineralization. These results demonstrate a complex relationship between mineralization and mechanical properties of the exoskeleton under changing ocean chemistry, and that fluctuating reduced pH conditions can induce responses not observed under the stable reduced pH conditions often used in OA research. Furthermore, this study shows that some juvenile California spiny lobster exoskeletal defenses are responsive to changes in ocean carbonate chemistry, even during the intermolt period, in ways that can potentially increase susceptibility to predation among this critical life stage

Polymer Brushes on Silica Nanostructures Prepared by Aminopropylsilatrane Click Chemistry: Superior Antifouling and Biofunctionality

In nanobiotechnology, the importance of controlling interactions between biological molecules and surfaces is paramount. In recent years, many devices based on nanostructured silicon materials have been presented, such as nanopores and nanochannels. However, there is still a clear lack of simple, reliable, and efficient protocols for preventing and controlling biomolecule adsorption in such structures. In this work, we show a simple method for passivation or selective biofunctionalization of silica, without the need for polymerization reactions or vapor-phase deposition. The surface is simply exposed stepwise to three different chemicals over the course of ∼1 h. First, the use of aminopropylsilatrane is used to create a monolayer of amines, yielding more uniform layers than conventional silanization protocols. Second, a cross-linker layer and click chemistry are used to make the surface reactive toward thiols. In the third step, thick and dense poly(ethylene glycol) brushes are prepared by a grafting-to approach. The modified surfaces are shown to be superior to existing options for silica modification, exhibiting ultralow fouling (a few ng/cm2) after exposure to crude serum. In addition, by including a fraction of biotinylated polymer end groups, the surface can be functionalized further. We show that avidin can be detected label-free from a serum solution with a selectivity (compared to nonspecific binding) of more than 98% without the need for a reference channel. Furthermore, we show that our method can passivate the interior of 150 nm 7 100 nm nanochannels in silica, showing complete elimination of adsorption of a sticky fluorescent protein. Additionally, our method is shown to be compatible with modifications of solid-state nanopores in 20 nm thin silicon nitride membranes and reduces the noise in the ion current. We consider these findings highly important for the broad field of nanobiotechnology, and we believe that our method will be very useful for a great variety of surface-based sensors and analytical devices

After-Sensations and Lingering Pain following Examination in Patients with Fibromyalgia Syndrome.

Fibromyalgia syndrome (FMS) is a chronic widespread pain condition with mixed peripheral and central contributions. Patients display hypersensitivities to a spectrum of stimuli. Patients' blunt pressure pain thresholds are typically reduced, and sometimes (∼15%) gentle brushstroke induces allodynia. However, after-sensations following these stimuli have not, to our knowledge, been reported. We examined the perception of blunt pressure and 'pleasant touch' in FMS. Patients were first interviewed and completed standard psychometric questionnaires. We then measured their sensitivity to blunt pressure and perception of pleasant touch including after-sensations; patients were followed for five days evaluating lingering pain from blunt pressure. We recruited 51 FMS patients and 16 pain-free controls (HC) at a UK Pain Management Centre. Forty-four patients completed the after-sensation protocol. Most patients reported pain after application of less mechanical pressure than HCs; median arm and leg thresholds were 167 kPa and 233 kPa. Eighty-four percent (31/37) of patients reported ongoing pain at the site of pressure application one day after testing, and 49% (18/37) still perceived pain at five days. After-sensations following brushstroke were common in the FMS group, reported by 77% (34/44) compared to 25% (4/16) of HCs; 34% (15/44) patients, but no HCs, perceived these after-sensations as uncomfortable. For FMS patients who experienced after-sensations, brushstroke-pleasantness ratings were reduced, and skin was often an important site of pain. Pain after blunt pressure assessment typically lingers for several days. After-sensations following brushstroke stimulation is a previously unreported FMS phenomenon. They are associated with tactile anhedonia and may identify a clinically distinct subgroup

Beta: an experiment in funded undergraduate start up

This paper reports on an evaluation of a funded undergraduate project designed to enable student business start-up. The programme, entitled 'Beta', provides undergraduate students with £1,500 of seed-corn funding. The key objective of the project is for the participants to exit it with a viable and legal business entity through which they can start trading on completion of the course. The study adopts a case study approach and evaluates all aspects of the Beta programme, the actors involved and its processes and practices. The authors examine the development of the project and the challenges and hurdles that were identified and overcome to realize the project's goals

Deactivation of a Vanadium-Based SCR Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation

We have investigated how the exhaust gases from a heavy-duty Euro VI engine, powered with biogas impact a vanadium-based selective catalytic reduction (SCR) catalyst in terms of performance. A full Euro VI emission control system was used and the accumulation of catalyst poisons from the combustion was investigated for the up-stream particulate filter as well as the SCR catalyst. The NO(x)reduction performance in terms of standard, fast and NO2-rich SCR was evaluated before and after exposure to exhaust from a biogas-powered engine for 900 h. The SCR catalyst retains a significant part of its activity towards NO(x)reduction after exposure to biogas exhaust, likely due to capture of catalyst poisons on the up-stream components where the deactivation of the oxidation catalyst is especially profound. At lower temperatures some deactivation of the first part of the SCR catalyst was observed which could be explained by a considerably higher surface V4+/V(5+)ratio for this sample compared to the other samples. The higher value indicates that the reoxidation of V(4+)to V(5+)is partially hindered, blocking the redox cycle for parts of the active sites