921 research outputs found
Towards achieving strong coupling in 3D-cavity with solid state spin resonance
We investigate the microwave magnetic field confinement in several microwave
3D-cavities, using 3D finite-element analysis to determine the best design and
achieve strong coupling between microwave resonant cavity photons and solid
state spins. Specifically, we design cavities for achieving strong coupling of
electromagnetic modes with an ensemble of nitrogen vacancy (NV) defects in
diamond. We report here a novel and practical cavity design with a magnetic
filling factor of up to 4 times (2 times higher collective coupling) than
previously achieved using 1D superconducting cavities with small mode volume.
In addition, we show that by using a double-split resonator cavity, it is
possible to achieve up to 200 times better cooperative factor than the
currently demonstrated with NV in diamond. These designs open up further
opportunities for studying strong and ultra-strong coupling effects on spins in
solids using alternative systems with a wider range of design parameters.Comment: 20 pages, 9 figure
The Origin of Primordial Dwarf Stars and Baryonic Dark Matter
I present a scenario for the production of low mass, degenerate dwarfs of
mass via the mechanism of Lenzuni, Chernoff & Salpeter (1992).
Such objects meet the mass limit requirements for halo dark matter from
microlensing surveys while circumventing the chemical evolution constraints on
normal white dwarf stars. I describe methods to observationally constrain this
scenario and suggest that such objects may originate in small clusters formed
from the thermal instability of shocked, heated gas in dark matter haloes, such
as suggested by Fall & Rees (1985) for globular clusters.Comment: TeX, 4 pages plus 2 postscript figures. To appear in Astrophysical
Journal Letter
Is the Large Magellanic Cloud a Large Microlensing Cloud?
An expression is provided for the self-lensing optical depth of the thin LMC
disk surrounded by a shroud of stars at larger scale heights. The formula is
written in terms of the vertical velocity dispersion of the thin disk
population. If tidal forcing causes 1-5 % of the disk mass to have a height
larger than 6 kpc and 10-15 % to have a height above 3 kpc, then the
self-lensing optical depth of the LMC is , which is
within the observational uncertainties. The shroud may be composed of bright
stars provided they are not in stellar hydrodynamical equilibrium.
Alternatively, the shroud may be built from low mass stars or compact objects,
though then the self-lensing optical depths are overestimates of the true
optical depth by a factor of roughly 3. The distributions of timescales of the
events and their spatial variation across the face of the LMC disk offer
possibilities of identifying the dominant lens population. In propitious
circumstances, an experiment lifetime of less than 5 years is sufficient to
decide between the competing claims of Milky Way halos and LMC lenses. However,
LMC disks can sometimes mimic the microlensing properties of Galactic halos for
many years and then decades of survey work are needed. In this case
observations of parallax or binary caustic events offer the best hope for
current experiments to deduce the lens population. The difficult models to
distinguish are Milky Way halos in which the lens fraction is low (< 10 %) and
fattened LMC disks composed of lenses with a typical mass of low luminosity
stars or greater. A next-generation wide-area microlensing survey, such as the
proposed ``SuperMACHO'' experiment, will be able to distinguish even these
difficult models with just a year or two of data.Comment: 25 pages, 4 figures, The Astrophysical Journal (in press
Large Magellanic Cloud Microlensing Optical Depth with Imperfect Event Selection
I present a new analysis of the MACHO Project 5.7 year Large Magellanic Cloud
(LMC) microlensing data set that incorporates the effects of contamination of
the microlensing event sample by variable stars. Photometric monitoring of
MACHO LMC microlensing event candidates by the EROS and OGLE groups has
revealed that one of these events is likely to be a variable star, while
additional data has confirmed that many of the other events are very likely to
be microlensing. This additional data on the nature of the MACHO microlensing
candidates is incorporated into a simple likelihood analysis to derive a
probability distribution for the number of MACHO microlens candidates that are
true microlensing events. This analysis shows that 10-12 of the 13 events that
passed the MACHO selection criteria are likely to be microlensing events, with
the other 1-3 being variable stars. This likelihood analysis is also used to
show that the main conclusions of the MACHO LMC analysis are unchanged by the
variable star contamination. The microlensing optical depth toward the LMC is =
1.0 +/- 0.3 * 10^{-7}. If this is due to microlensing by known stellar
populations, plus an additional population of lens objects in the Galactic
halo, then the new halo population would account for 16% of the mass of a
standard Galactic halo. The MACHO detection exceeds the expected background of
2 events expected from ordinary stars in standard models of the Milky Way and
LMC at the 99.98% confidence level. The background prediction is increased to 3
events if maximal disk models are assumed for both the MilkyWay and LMC, but
this model fails to account for the full signal seen by MACHO at the 99.8%
confidence level.Comment: 20 pages, 2 postscript figues, accepted by Ap
Effect of a polyphenol–vacuum packaging on lipid deterioration during an 18-month frozen storage of Coho Salmon (Oncorhynchus kisutch)
10 páginas, 3 tablas, 2 figuras.-- The final publication is
available at www.springerlink.comA packaging system combining a polyphenolrich
film and vacuum (PPRF–VP) was applied to farmed
coho salmon (Oncorhynchus kisutch) muscle for an 18-
month storage (−18 °C). For it, two different concentrations
of polyphenol compounds (namely, p-coumaric and ferulic
acids) obtained from a barley husk extract were applied
(PPRF–VP conditions) and compared to vacuum packaging
without polyphenol presence (vacuum control; VP condition)
and to packaging in the absence of vacuum and
polyphenols (control; CP condition). The study was
addressed to lipid hydrolysis and oxidation development
and to lipid changes related to nutritional value. Both
PPRF–VP conditions provided an inhibitory effect (p<
0.05) on conjugated diene and fluorescent compound
formation in frozen salmon. Compared to CP condition,
vacuum packaging (PPRF–VP and VP conditions) led to
lower (p<0.05) peroxide and anisidine values and to an
inhibitory effect (p<0.05) on α- and γ-tocopherol losses.
No effect (p>0.05) of polyphenol presence and vacuum
packaging could be inferred on free fatty acid formation
(hydrolysis development) and on polyunsaturated fatty acid
retention (polyene index assessment). A low rancid odour
development was observed in all kinds of fish samples, this
being lower (p<0.05) in fish kept under vacuum (PPRF–VP
and VP) conditions.Peer reviewe
Quality enhancement of chilled fish by including alga Bifurcaria bifurcata extract in the icing medium
9 páginas, 4 tablasBifurcaria bifurcata is a widely extended brown macroalga, whose antimicrobial and antioxidant properties have previously been described. In this study, ethanolic extracts of B. bifurcata were included in the icing medium employed for the chilled storage of megrim (Lepidorhombus whiffiagonis). For it, two different concentrations of this brown macroalga extract (0.67 and 2.50 g lyophilized alga L−1 aqueous solution; B-1 and B-2 batches, respectively) were tested for a 14-day storage. The effect of the alga extract was compared with a counterpart batch stored in traditional ice prepared only from water (B-0 batch). Significant (p < 0.05) inhibitions of microbial activity (aerobes, psychrotrophs, lipolytic bacteria, proteolytic bacteria and Enterobacteriaceae) as well as of pH and trimethylamine formation were observed as a result of the incorporation of the alga extract in the icing medium, being this effect especially relevant in the B-2 batch. Concerning lipid damage development, a significantly (p < 0.05) lower formation of free fatty acids (lipid hydrolysis development) and of fluorescent compounds (tertiary lipid oxidation development) in samples corresponding to both alga-including batches could also be observed; this inhibitory effect was more intense in fish belonging to the B-2 batch. The icing medium proposed in this work constitutes a promising strategy in order to apply algae extracts to enhance fish quality retention during the different steps of storage and commercialization of marine speciesThis work was supported by the Consejo Superior de Investigaciones CientÃficas (CSIC; Spain) through the project PIE 201370E001Peer reviewe
Enzymatic activity during frozen storage of Atlantic horse mackerel (Trachurus trachurus) pre-treated by high-pressure processing
The assessment of enzymatic activity on Atlantic horse mackerel (Trachurus trachurus) during frozen storage
was carried out in samples pre-treated by high-pressure processing (HPP) combinations of 150, 300 and 450 MPa with 0-, 2.5- and 5-min holding time (untreated samples were used as controls). The activities of four enzymes (acid phosphatase, cathepsins B and D, and lipase) in fish muscle were quantified during accelerated storage conditions (up to 3 months at −10 °C). The experimental data were fitted to second-order
polynomial models to determine the effect of pressure level, holding time and frozen storage time on these enzyme activities and to identify conditions of maximum/minimal enzyme inactivation. Acid phosphatase and cathepsin (B and D) activities were significantly (p<0.05) influenced by HPP, showing behaviours during frozen storage different from control samples. Acid phosphatase and cathepsin B activities decreased (p<0.05) with HPP treatments, being this effect more intense for cathepsin B, particularly at 450 MPa. Regarding cathepsin D, the activity increased (p<0.05) at intermediate pressure (300MPa) and decreased (p<0.05) at higher pressure (450 MPa). During frozen storage, cathepsin D enzymatic activity tended to increase over time indicating activity recovery of these enzymes. Although a predictive model for its activity was not acceptable, the increase in lipase activity during storage was the most pronounced trend observed
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