4,605 research outputs found
Quantum computers can search rapidly by using almost any transformation
A quantum computer has a clear advantage over a classical computer for
exhaustive search. The quantum mechanical algorithm for exhaustive search was
originally derived by using subtle properties of a particular quantum
mechanical operation called the Walsh-Hadamard (W-H) transform. This paper
shows that this algorithm can be implemented by replacing the W-H transform by
almost any quantum mechanical operation. This leads to several new applications
where it improves the number of steps by a square-root. It also broadens the
scope for implementation since it demonstrates quantum mechanical algorithms
that can readily adapt to available technology.Comment: This paper is an adapted version of quant-ph/9711043. It has been
modified to make it more readable for physicists. 9 pages, postscrip
Particle aggregation, pH changes and metal behaviour during estuarine mixing: review and integration
Estuaries are dynamic mixing zones where river water interacts with seawater, resulting in large and complex geochemical changes. How two key factors, particle aggregation and pH, affect metal behaviour in estuaries is reviewed and integrated in this paper. Riverine particles are coated with organic matter and electrostatic repulsive forces restrict aggregation. In estuaries, increased concentrations of divalent cations reduce the repulsive forces between particles at low salinities, resulting in their rapid coagulation and removal of particulate-associated metals (e.g. Fe and Pb). However, truly dissolved metals may mix conservatively, and metals associated more with colloidal and dissolved organic material (e.g. Cu and Zn) can show variable behaviour. In many field studies and modelling of river inputs with different compositions, pH decreases slightly at low salinity. Geochemical model simulations of dissolved metal speciation indicated that Zn would be desorbed from iron oxide binding surfaces due to these pH and cation concentration changes, with Cu also showing less binding to dissolved organic matter (DOM). DOM, pH and particle surfaces can influence individual metal behaviour at various spatial and temporal scales. Further integrated field and laboratory research in estuaries where key geochemical processes affecting metal concentrations are measured and modelled is needed.Luke M. Mosley and Peter S. Lis
Estimating oceanic primary production using vertical irradiance and chlorophyll profiles from ocean gliders in the North Atlantic
An autonomous underwater vehicle (Seaglider) has been used to estimate marine primary production (PP) using a combination of irradiance and fluorescence vertical profiles. This method provides estimates for depth-resolved and temporally evolving PP on fine spatial scales in the absence of ship-based calibrations. We describe techniques to correct for known issues associated with long autonomous deployments such as sensor calibration drift and fluorescence quenching. Comparisons were made between the Seaglider, stable isotope (13C), and satellite estimates of PP. The Seaglider-based PP estimates were comparable to both satellite estimates and stable isotope measurements
Bubble-Mediated Gas Transfer and Gas Transfer Suppression of DMS and CO2
Direct dimethyl sulfide (DMS) flux measurements using eddy covariance have shown a suppression of gas transfer at medium to high wind speed. However, not all eddy covariance measurements show evidence of this suppression. Processes, such as wave-wind interaction and surfactants, have been postulated to cause this suppression. We measured DMS and carbon dioxide eddy covariance fluxes during the Asian summer monsoon in the western tropical Indian Ocean (July and August 2014). Both fluxes and their respective gas transfer velocities show signs of a gas transfer suppression above 10 m/s. Using a wind-wave interaction, we describe a flow separation process that could be responsible for a suppression of gas transfer. As a result we provide a Reynolds number-based parameterization, which states the likelihood of a gas transfer suppression for this cruise and previously published gas transfer data. Additionally, we compute the difference in the gas transfer velocities of DMS and CO2 to estimate the bubble-mediated gas transfer using a hybrid model with three whitecap parameterizations
Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT
The gravitational spectrometer GRANIT will be set up at the Institut Laue
Langevin. It will profit from the high ultracold neutron density produced by a
dedicated source. A monochromator made of crystals from graphite intercalated
with potassium will provide a neutron beam with 0.89 nm incident on the source.
The source employs superthermal conversion of cold neutrons in superfluid
helium, in a vessel made from BeO ceramics with Be windows. A special
extraction technique has been tested which feeds the spectrometer only with
neutrons with a vertical velocity component v < 20 cm/s, thus keeping the
density in the source high. This new source is expected to provide a density of
up to 800 1/cm3 for the spectrometer.Comment: accepted for publication in Proceedings International Workshop on
Particle Physics with Slow Neutron
Isolation and characterization of centroacinar/terminal ductal progenitor cells in adult mouse pancreas
The question of whether dedicated progenitor cells exist in adult vertebrate pancreas remains controversial. Centroacinar cells and terminal duct (CA/TD) cells lie at the junction between peripheral acinar cells and the adjacent ductal epithelium, and are frequently included among cell types proposed as candidate pancreatic progenitors. However these cells have not previously been isolated in a manner that allows formal assessment of their progenitor capacities. We have found that a subset of adult CA/TD cells are characterized by high levels of ALDH1 enzymatic activity, related to high-level expression of both Aldh1a1 and Aldh1a7. This allows their isolation by FACS using a fluorogenic ALDH1 substrate. FACS-isolated CA/TD cells are relatively depleted of transcripts associated with differentiated pancreatic cell types. In contrast, they are markedly enriched for transcripts encoding Sca1, Sdf1, c-Met, Nestin, and Sox9, markers previously associated with progenitor populations in embryonic pancreas and other tissues. FACS-sorted CA/TD cells are uniquely able to form self-renewing 'pancreatospheres' in suspension culture, even when plated at clonal density. These spheres display a capacity for spontaneous endocrine and exocrine differentiation, as well as glucose-responsive insulin secretion. In addition, when injected into cultured embryonic dorsal pancreatic buds, these adult cells display a unique capacity to contribute to both the embryonic endocrine and exocrine lineages. Finally, these cells demonstrate dramatic expansion in the setting of chronic epithelial injury. These findings suggest that CA/TD cells are indeed capable of progenitor function and may contribute to the maintenance of tissue homeostasis in adult mouse pancreas
Air–sea exchange of acetone, acetaldehyde, DMS and isoprene at a UK coastal site
Volatile organic compounds (VOCs) are ubiquitous in the atmosphere and are important for atmospheric chemistry. Large uncertainties remain in the role of the ocean in the atmospheric VOC budget because of poorly constrained marine sources and sinks. There are very few direct measurements of air–sea VOC fluxes near the coast, where natural marine emissions could influence coastal air quality (i.e. ozone, aerosols) and terrestrial gaseous emissions could be taken up by the coastal seas.
To address this, we present air–sea flux measurements of acetone, acetaldehyde and dimethylsulfide (DMS) at the coastal Penlee Point Atmospheric Observatory (PPAO) in the south-west UK during the spring (April–May 2018). Fluxes of these gases were measured simultaneously by eddy covariance (EC) using a proton-transfer-reaction quadrupole mass spectrometer. Comparisons are made between two wind sectors representative of different air–water exchange regimes: the open-water sector facing the North Atlantic Ocean and the terrestrially influenced Plymouth Sound fed by two estuaries.
Mean EC (± 1 standard error) fluxes of acetone, acetaldehyde and DMS from the open-water wind sector were −8.0 ± 0.8, −1.6 ± 1.4 and 4.7 ± 0.6 µmol m−2 d−1 respectively (“−” sign indicates net air-to-sea deposition). These measurements are generally comparable (same order of magnitude) to previous measurements in the eastern North Atlantic Ocean at the same latitude. In comparison, the Plymouth Sound wind sector showed respective fluxes of −12.9 ± 1.4, −4.5 ± 1.7 and 1.8 ± 0.8 µmol m−2 d−1. The greater deposition fluxes of acetone and acetaldehyde within the Plymouth Sound were likely to a large degree driven by higher atmospheric concentrations from the terrestrial wind sector. The reduced DMS emission from the Plymouth Sound was caused by a combination of lower wind speed and likely lower dissolved concentrations as a result of the estuarine influence (i.e. dilution).
In addition, we measured the near-surface seawater concentrations of acetone, acetaldehyde, DMS and isoprene from a marine station 6 km offshore. Comparisons are made between EC fluxes from the open-water and bulk air–sea VOC fluxes calculated using air and water concentrations with a two-layer (TL) model of gas transfer. The calculated TL fluxes agree with the EC measurements with respect to the directions and magnitudes of fluxes, implying that any recently proposed surface emissions of acetone and acetaldehyde would be within the propagated uncertainty of 2.6 µmol m−2 d−1. The computed transfer velocities of DMS, acetone and acetaldehyde from the EC fluxes and air and water concentrations are largely consistent with previous transfer velocity estimates from the open ocean. This suggests that wind, rather than bottom-driven turbulence and current velocity, is the main driver for gas exchange within the open-water sector at PPAO (depth of ∼ 20 m)
Cognitive Information Processing
Contains reports on four research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA28-043-AMC-02536(E)National Institutes of Health (Grant 1 PO1 GM-14940-01
Разработка модели контейнера для сбора компактных люминесцентных ламп
Предложена конструкция контейнера для сбора у населения компактных люминесцентных ламп. Разработан и создан демонстрационный макет контейнера. Проверена его работоспособность.A container design is proposed for collecting compact fluorescent lamps from the city residents. A demonstration mock-up of the container was developed and created. It is checked up its working capacity
Understanding Shale Gas: Recent Progress and Remaining Challenges
Because of a number of technological advancements, unconventional hydrocarbons, and in particular shale gas, have transformed the US economy. Much is being learned, as demonstrated by the reduced cost of extracting shale gas in the US over the past five years. However, a number of challenges still need to be addressed. Many of these challenges represent grand scientific and technological tasks, overcoming which will have a number of positive impacts, ranging from the reduction of the environmental footprint of shale gas production to improvements and leaps forward in diverse sectors, including chemical manufacturing and catalytic transformations. This review addresses recent advancements in computational and experimental approaches, which led to improved understanding of, in particular, structure and transport of fluids, including hydrocarbons, electrolytes, water, and CO2 in heterogeneous subsurface rocks such as those typically found in shale formations. The narrative is concluded with a suggestion of a few research directions that, by synergistically combining computational and experimental advances, could allow us to overcome some of the hurdles that currently hinder the production of hydrocarbons from shale formations
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