2,680 research outputs found
Bound states on the lattice with partially twisted boundary conditions
We propose a method to study the nature of exotic hadrons by determining the
wave function renormalization constant from lattice simulations. It is
shown that, instead of studying the volume-dependence of the spectrum, one may
investigate the dependence of the spectrum on the twisting angle, imposing
twisted boundary conditions on the fermion fields on the lattice. In certain
cases, e.g., the case of the bound state which is addressed in detail, it
is demonstrated that the partial twisting is equivalent to the full twisting up
to exponentially small corrections
Acidificación do Mar: Unha consecuencia das emisións de CO2
16 páginas, 10 figuras.-- Discurso de ingreso en la Real Academia Galega de Ciencias,
Santiago de Compostela, 18 junio 2015O océano absorbe unha parte significativa de dióxido de carbono (CO2) das actividades
humanas, o que equivale a cerca dun terzo das emisións totais durante o perÃodo industrial
(Khatiwala e col., 2013; Le Quéré e col., 2015). A absorción de CO2 polo océano no só
modera o ritmo do cambio climático, senón que provoca cambios sen precedentes na
quÃmica do océano, diminuÃndo o pH pola disolución adicional de CO2 en auga do mar
dende a atmosfera. AsÃ, a superficie do océano aumentou nun 30% a concentración de ións
de hidroxeno (Raven e col., 2005) desde o principio da Revolución Industrial, o que
equivale a un descenso de 0,1 unidades de pH que non é algo irrelevante a respeito dos
cambios naturais. O actual episodio de acidificación ocorre unhas 100 veces máis
rápidamente do que calquera outro cambio de acidez nos últimos 50 millóns de anos da
historia da terra (Pelejero e col., 2010)Peer reviewe
Long-Lived Non-Equilibrium Interstitial-Solid-Solutions in Binary Mixtures
We perform particle resolved experimental studies on the heterogeneous
crystallisation process of two compo- nent mixtures of hard spheres. The
components have a size ratio of 0.39. We compared these with molecular dynamics
simulations of homogenous nucleation. We find for both experiments and
simulations that the final assemblies are interstitial solid solutions, where
the large particles form crystalline close-packed lattices, whereas the small
particles occupy random interstitial sites. This interstitial solution
resembles that found at equilibrium when the size ratios are 0.3 [Filion et
al., Phys. Rev. Lett. 107, 168302 (2011)] and 0.4 [Filion, PhD Thesis, Utrecht
University (2011)]. However, unlike these previous studies, for our system sim-
ulations showed that the small particles are trapped in the octahedral holes of
the ordered structure formed by the large particles, leading to long-lived
non-equilibrium structures in the time scales studied and not the equilibrium
interstitial solutions found earlier. Interestingly, the percentage of small
particles in the crystal formed by the large ones rapidly reaches a maximum of
around 14% for most of the packing fractions tested, unlike previous
predictions where the occupancy of the interstitial sites increases with the
system concentration. Finally, no further hopping of the small particles was
observed
Global ocean storage of anthropogenic carbon
48 páginas, 7 figuras, 7 tablas. -- S. Kathiwala ... et al.-- Proyecto CarbochangeThe global ocean is a significant sink for anthropogenic carbon (Cant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of Cant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of Cant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data based estimates of the distribution and inventory of Cant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data-assimilation techniques which combine ocean interior estimates of Cant with numerical ocean circulation models. Such methods are especially useful for estimating the air-sea flux and interior transport of Cant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate Cant. Our review also highlights the importance of repeat measurements of hydrographic and biogeochemical parameters to estimate the storage of Cant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based Cant estimates provide important constraints on ocean forward models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of Cant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 Pg C with an uncertainty of ±20%. This estimate includes a broad range of values suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.Peer reviewe
Lifetimes of ultralong-range strontium Rydberg molecules in a dense BEC
The lifetimes and decay channels of ultralong-range Rydberg molecules created
in a dense BEC are examined by monitoring the time evolution of the Rydberg
population using field ionization. Studies of molecules with values of
principal quantum number, , in the range to that contain tens
to hundreds of ground state atoms within the Rydberg electron orbit show that
their presence leads to marked changes in the field ionization characteristics.
The Rydberg molecules have lifetimes of s, their destruction
being attributed to two main processes: formation of Sr ions through
associative ionization, and dissociation induced through -changing
collisions. The observed loss rates are consistent with a reaction model that
emphasizes the interaction between the Rydberg core ion and its nearest
neighbor ground-state atom. The measured lifetimes place strict limits on the
time scales over which studies involving Rydberg species in cold, dense atomic
gases can be undertaken and limit the coherence times for such measurements.Comment: 9 pages, 8 figure
Annotated checklist of marine fishes from the Sanctuary of BahÃa Chamela, Mexico with occurrence and biogeographic data.
An annotated checklist of marine fishes of the Sanctuary of Islands and Islets of BahÃa Chamela in the central Mexican Pacific is presented. Records of fish species were obtained by different methods including visual census, sampling with anesthetics, fisherman-nets, and trawling with a biological dredge. Additional records were obtained from natural history collections and publications. The list comprises 196 species in 64 families and 141 genera. The Carangidae is the most speciose family with 11 species, followed by the Labridae with 10 and the Pomacentridae with nine. Fourteen species are endemic in Mexican Pacific waters, but none is restricted to BahÃa Chamela. The most dominant species recorded during underwater surveys were Epinephelus labriformis, Stegastes flavilatus, and Halichoeres dispilus. Most species are of tropical affinities distributed throughout the tropical eastern Pacific (123), eastern Pacific (23), and Mexican Pacific (14). Other species are known from the eastern and Indo-Pacific regions (18), eastern Pacific and western Atlantic oceans (2), and some are circumtropical (9). A new record of the Gulf Brotula Ogilbia ventralis is provided for the BahÃa Chamela and its geographical distribution is extended to Mexican central Pacific
Seasonal patterns and long-term trends in an estuarine upwelling ecosystem (Ria de Vigo, NW Spain)
16 páginas, 10 figuras, 4 tablasThermohaline properties, nutrient salts, chlorophyll a and meteorological variables have been intensively monitored since
February 1987 in the RÃa de Vigo (NW Spain), in order to examine the temporal variability and the relationships between
these variables over different time scales. In this paper, the seasonal and the long-term components of the 1987–92 time
series are analysed. The seasonal changes in thermohaline properties are forced by meteorological factors, but whereas
temperature shows a well-defined annual cycle, salinity presents a higher frequency variation pattern due to the influence
of upwelling–downwelling events and runoff. Nutrient concentrations change in a regular way through the seasons, so
that characteristic and well-defined cycles are observed, but they are different for each nutrient and, for a given nutrient,
exhibit a marked contrast between surface and bottom layers. The seasonal changes of nutrients are not explainable by
advection and water column processes alone; fractionation of nutrients during recycling and, presumably, sedimentary
processes should also play an important role. The annual cycle of chlorophyll a shows a bimodal pattern, which
corresponds with the development of the spring and autumn blooms; even though the seasonal cycle accounts for an
important amount of the observed temporal variability, variation at lower time scales is also important. Long-term trends,
as a change in the mean level of the analysed time series, have been observed for most of the variables. Salinity increased
and temperature decreased both for surface and bottom series. The largest trend, in terms of the percentage to the
observed variability it represents, was an increase in bottom salinity. In relation to nutrient salts, there was no evidence
of increasing eutrophication, although surface dissolved inorganic nitrogen, and surface and bottom phosphate increased
slightly. Chlorophyll a concentration showed a decreasing trend, especially at the surface. The observed long-term trends
could be attributed to changes of the meteorological factors that operate through an increase in the estuarine residual
circulation.Support for this work came from CICYT project
AMB 92-0165 and EC MAST project CT90-
0017.Peer reviewe
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