3,819 research outputs found
Cold-water coral <em>Lophelia pertusa</em> as a high-resolution archive of paleo-environmental conditions in the central Mediterranean
Field-theoretic functional renormalization group formalism for non-Fermi liquids and its application to the antiferromagnetic quantum critical metal in two dimensions
To capture the universal low-energy physics of metals within effective field
theories, one has to generalize the usual notion of scale invariance and
renormalizable field theory due to the presence of intrinsic scales (Fermi
momenta). In this paper, we develop a field-theoretic functional
renormalization group formalism for full low-energy effective field theories of
non-Fermi liquids that include all gapless modes around the Fermi surface. The
formalism is applied to the non-Fermi liquid that arises at the
antiferromagnetic quantum critical point in two space dimensions. In the space
of coupling functions, an interacting fixed point arises at a point with
momentum-independent couplings and vanishing nesting angle. In theories
deformed with non-zero nesting angles, coupling functions acquire universal
momentum profiles controlled by the bare nesting angles at low energies before
flowing to superconducting states in the low-energy limit. The superconducting
instability is unavoidable because lukewarm electrons that are coherent enough
to be susceptible to pairing end up being subject to a renormalized attractive
interaction with its minimum strength set by the nesting angle. Despite the
inevitable superconducting instability, theories with small bare nesting angles
and bare four-fermion couplings that are repulsive or weakly attractive must
pass through the region with slow RG flow due to the proximity to the non-Fermi
liquid fixed point. The bottleneck region controls the scaling behaviours of
the normal state and the quasi-universal pathway from the non-Fermi liquid to
superconductivity. In the limit that the nesting angle is small, the non-Fermi
liquid scaling dictates the physics over a large window of energy scale above
the superconducting transition temperature.Comment: 109 page
Neuromodulation and ablation with focused ultrasound – toward the future of noninvasive brain therapy
The influence of seawater pH on U / Ca ratios in the scleractinian cold-water coral Lophelia pertusa
The increasing pCO2 in seawater is a serious threat for marine calcifiers and alters the biogeochemistry of the ocean. Therefore, the reconstruction of past-seawater properties and their impact on marine ecosystems is an important way to investigate the underlying mechanisms and to better constrain the effects of possible changes in the future ocean. Cold-water coral (CWC) ecosystems are biodiversity hotspots. Living close to aragonite-undersaturation, these corals serve as living laboratories as well as archives to reconstruct the boundary conditions of their calcification under the carbonate system of the ocean.
We investigated the reef-building CWC Lophelia pertusa as a recorder of intermediate ocean seawater pH. This species-specific field calibration is based on a unique sample set of live in-situ collected L. pertusa and corresponding seawater samples. These data demonstrate that uranium speciation and skeletal incorporation for azooxanthellate scleractinian CWCs is pH dependent. However, this also indicates that internal pH up-regulation of the coral does not play a role in uranium incorporation into the majority of the skeleton of L. pertusa. This study suggests L. pertusa provides a new archive for the reconstruction of intermediate water mass pH and hence may help to constrain tipping points for ecosystem dynamics and evolutionary characteristics in a changing ocean
The influence of seawater pH on U / Ca ratios in the scleractinian cold-water coral Lophelia pertusa
The increasing pCO2 in seawater is a serious threat for marine calcifiers and alters the biogeochemistry of the ocean. Therefore, the reconstruction of past-seawater properties and their impact on marine ecosystems is an important way to investigate the underlying mechanisms and to better constrain the effects of possible changes in the future ocean. Cold-water coral (CWC) ecosystems are biodiversity hotspots. Living close to aragonite-undersaturation, these corals serve as living laboratories as well as archives to reconstruct the boundary conditions of their calcification under the carbonate system of the ocean.
We investigated the reef-building CWC Lophelia pertusa as a recorder of intermediate ocean seawater pH. This species-specific field calibration is based on a unique sample set of live in-situ collected L. pertusa and corresponding seawater samples. These data demonstrate that uranium speciation and skeletal incorporation for azooxanthellate scleractinian CWCs is pH dependent. However, this also indicates that internal pH up-regulation of the coral does not play a role in uranium incorporation into the majority of the skeleton of L. pertusa. This study suggests L. pertusa provides a new archive for the reconstruction of intermediate water mass pH and hence may help to constrain tipping points for ecosystem dynamics and evolutionary characteristics in a changing ocean
Environmental boundary conditions of cold-water coral mound growth over the last 3 million years in the Porcupine Seabight, Northeast Atlantic
IODP Expedition 307 made it for the first time possible to investigate the entire body of a cold-water coral carbonate mound. Here we provide new insights into the long-term history of Challenger Mound on the European continental margin off Ireland. This study is based on age determinations (230Th/U, 87Sr/86Sr) and geochemical signals (Mg/Li and Ba/Ca) measured in the scleractinian cold-water coral Lophelia pertusa from IODP Site 1317 in the Porcupine Seabight. The paleoceanographic reconstructions reveal that coral growth in the Porcupine Seabight was restricted to specific oceanographic conditions such as enhanced export of primary production and Bottom-Water Temperatures (BWT) between ∼8 and 10 °C, related to the water mass stratification of the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Water (ENAW). The geochemical signals from the coral skeletons can be explained by the close interaction between cold-water coral growth, sea-surface productivity and the surrounding water masses – the boundary layer between MOW and ENAW. Enhanced sea-surface productivity and the build-up of a stable water mass stratification between ENAW and MOW caused enhanced nutrient supply at intermediate water depths and facilitated a steady mound growth between ∼3.0 and 2.1 Ma. With the decrease in sea-surface productivity and related reduced export productivity the food supply was insufficient for rapid coral mound growth between ∼1.7 and 1 Ma. During the late Pleistocene (over the last ∼0.5 Myr) mound growth was restricted to interglacial periods. During glacials the water mass boundary between ENAW/MOW probably was below the mound summit and hence food supply was not sufficient for corals to grow
Comparación de las propiedades del concreto f´c=210 kg/cm con adición de mucilago de tuna y sábila, Los Olivos, Lima 2022
En la presente investigación tiene como objetivo realizar la comparación de las
propiedades físicas y mecánicas del concreto con aditivo a base de Mucilago de
Tuna y Mucilago de Sábila, en Los Olivos, Lima-2022. Se realizaron probetas de
concreto usando materiales provenientes de la cantera. Para este proyecto de
investigación se utilizó la metodología, de tipo aplicada con un diseño cuasi
experimental y un enfoque cuantitativo. Se realizó la muestra patrón y muestras
modificadas con Mucilago de Tuna y Mucilago de Sábila con dosificaciones de
0.4%,0.85 y 1.2% de ambos tipos. Según los resultados obtenidos con el diseño
patrón con la adición de 1.2 % de Tuna se obtiene EC(T)1.2%=107.6kg/cm2,
ET(T)1.2%=23.04kg/cm2, EF(T)1.2%=34.93kg/cm2 y Slump(T)1.2%=9.5cm. y
con 1.2% de Mucilago de Sábila se obtiene EC(S)1.2%=109.86kg/cm2,
ET(S)1.2%=22.98kg/cm2, EF(S)1.2%=35.06kg/cm2 y Slump(S)1.2%=9.7 cm.
Se concluye en la investigación que las mezclas con adición de mucilago de
Nopal de la Tuna adicionado al 1.2% aumenta la resistencia a la tracción en
1.52kg/cm2 y aumentado los centímetros 3.53 cm referente al ensayo de SLUMP:
Y en el caso de la mezcla con aditivo de mucilago de Sábila al 1.2% aumentando
la resistencia a la compresión en 7.76kg/cm2 y aumentando la resistencia a la
flexión en 3.53kg/cm2, la adición de ambos productos al concreto contribuye de
manera eficaz a la mezcla , favoreciendo las propiedades Físico y Mecánicas de
acuerdo a las normal E060
Environmental constraints on Holocene cold‐water coral reef growth off Norway: Insights from a multiproxy approach
High-latitude cold-water coral (CWC) reefs are particularly susceptible due to enhanced CO₂ uptake in these regions. Using precisely dated (U/Th) CWCs (Lophelia pertusa) retrieved during research cruise POS 391 (Lopphavet 70.6°N, Oslofjord 59°N) we applied boron isotopes (δ¹¹B), Ba/Ca, Li/Mg, and U/Ca ratios to reconstruct the environmental boundary conditions of CWC reef growth. The sedimentary record from these CWC reefs reveals a lack of corals between ~6.4 and 4.8 ka. The question remains if this phenomenon is related to changes in the carbonate system or other causes. The initial postglacial setting had elevated Ba/Ca ratios, indicative of meltwater fluxes showing a decreasing trend toward cessation at 6.4 ka with an oscillation pattern similar to continental glacier fluctuations. Downcore U/Ca ratios reveal an increasing trend, which is outside the range of modern U/Ca variability in L. pertusa, suggesting changes of seawater pH near 6.4 ka. The reconstructed bottom water temperature at Lopphavet reveals a striking similarity to Barent sea surface and subsea surface temperature records. We infer that meltwater pulses weakened the North Atlantic Current system, resulting in southward advances of cold and CO₂-rich Arctic waters. A corresponding shift in the δ¹¹B record from ~25.0‰ to ~27.0‰ probably implies enhanced pH up-regulation of the CWCs due to the higher pCO₂ concentrations of ambient seawater, which hastened mid-Holocene CWC reef decline on the Norwegian margin
Modeling of Unsteady Friction and Viscoelastic Damping in Piping Systems
In real systems, the phenomena, such as pipe-wall viscoelasticity, unsteady friction or fluid structure interaction induce additional damping and dispersion of transient pressure waves than that defined by classical waterhammer. In this paper, unsteady friction models and viscoelastic damping models will be presented and a theoretical formulation of the viscoelastic damping in piping systems without cavitation will be developed. Firstly, the friction factor will be presented as the sum of the quasi-steady part and the unsteady part related to the instantaneous local acceleration and instantaneous convective acceleration. This unsteady friction model has been incorporated into the method of characteristic algorithm (MOC). Secondly, the damping will be defined in terms of viscoelastic effect attributed to a second viscosity µ’. This model is solved using the Finite Difference Method. Finally, numerical results from the unsteady friction and viscoelastic models are compared with results of laboratory measurements for waterhammer cases with low Reynolds number turbulent flows. This comparison validates the new viscoelastic model
- …