669 research outputs found
Coulomb Excitation of 68,70Cu: First Use of Postaccelerated Isomeric Beams
We report on the first low-energy Coulomb excitation measurements with radioactive Iπ=6- beams of odd-odd nuclei 68,70Cu. The beams were produced at ISOLDE, CERN and were post-accelerated by REX-ISOLDE to 2.83 MeV/nucleon. γ rays were detected with the MINIBALL spectrometer. The 6- beam was used to study the multiplet of states (3-, 4-, 5-, 6-) arising from the π2p3/2ν1g9/2 configuration. The 4- state of the multiplet was populated via Coulomb excitation and the B(E2;6-→4-) value was determined in both nuclei. The results obtained illustrate the fragile stability of the Z=28 shell and N=40 subshell closures. A comparison with large-scale shell-model calculations using the 56Ni core shows the importance of the proton excitations across the Z=28 shell gap to the understanding of the nuclear structure in the neutron-rich nuclei with N≈40
Pricing and revenue management: The value of coordination
Cataloged from PDF version of article.The integration of systems for pricing and revenue management must trade off potential revenue gains against significant practical and technical challenges. This dilemma motivates us to investigate the value of coordinating decisions on prices and capacity allocation in a stylized setting. We propose two pairs of sequential policies for making static decisions-on pricing and revenue management-that differ in their degree of integration (hierarchical versus coordinated) and their pricing inputs (deterministic versus stochastic). For a large class of stochastic, price-dependent demand models, we prove that these four heuristics admit tractable solutions satisfying intuitive sensitivity properties. We further evaluate numerically the performance of these policies relative to a fully coordinated model, which is generally intractable. We find it interesting that near-optimal performance is usually achieved by a simple hierarchical policy that sets prices first, based on a nonnested stochastic model, and then uses these prices to optimize nested capacity allocation. This tractable policy largely outperforms its counterpart based on a deterministic pricing model. Jointly optimizing price and allocation decisions for the high-end segment improves performance, but the largest revenue benefits stem from adjusting prices to account for demand risk
A 10B-based neutron detector with stacked Multiwire Proportional Counters and macrostructured cathodes
We present the results of the measurements of the detection efficiency for a
4.7 \r{A} neutron beam incident upon a detector incorporating a stack of up to
five MultiWire Proportional Counters (MWPC) with Boron-coated cathodes. The
cathodes were made of Aluminum and had a surface exhibiting millimeter-deep
V-shaped grooves of 45{\deg}, upon which the thin Boron film was deposited by
DC magnetron sputtering. The incident neutrons interacting with the converter
layer deposited on the sidewalls of the grooves have a higher capture
probability, owing to the larger effective absorption film thickness. This
leads to a higher overall detection efficiency for the grooved cathode when
compared to a cathode with a flat surface. Both the experimental results and
the predictions of the GEANT4 model suggests that a 5-counter detector stack
with coated grooved cathodes has the same efficiency as a 7-counter stack with
flat cathodes. The reduction in the number of counters in the stack without
altering the detection efficiency will prove highly beneficial for large-area
position-sensitive detectors for neutron scattering applications, for which the
cost-effective manufacturing of the detector and associated readout electronics
is an important objective. The proposed detector concept could be a
technological option for one of the new chopper spectrometers and other
instruments planned to be built at the future European Spallation Source in
Sweden. These results with macrostructured cathodes generally apply not just to
MWPCs but to other gaseous detectors as well.Comment: 14 pages, 9 figure
Les papallones com a bioindicadores dels hàbitats a Catalunya: l'exemple dels prats de dall i le pastures del Parc Natural dels Aiguamolls de l'Empordà
El Parque Natural de los Aiguamolls de lEmpordà
(PNAE) es uno de los espacios protegidos más conocidos
y emblemáticos de Cataluña. Uno de sus
hábitats más localizados y amenazados son las denominadas
closes, prados de siega destinados a la producción
de forraje, rodeados de canales de desagüe e
inundados durante parte del invierno. Recientemente,
se ha demostrado que la comunidad vegetal más
típicamente asociada con estos prados es la más rica
del Parque y la que alberga las especies más raras.
En este trabajo se utilizan datos de mariposas diurnas
(ropalóceros), obtenidos después de aplicar durante
17 años la metodología del Butterfly Monitoring
Scheme, para evaluar el interés de conservación
de los principales ambientes del PNAE. Las closes
constituyen también para los ropalóceros el
hábitat más valuoso. La coincidencia en los resultados
obtenidos en dos grupos taxonómicos amplios
y que ocupan niveles tróficos distintos, sumada a la
alarmante regresión que han experimentado las
closes en los últimos 50 años y a su singularidad en
el área mediterránea, permiten considerarlas objetivamente
como uno de los hábitats más amenazados
del PNAE y del conjunto de Cataluña. En una segunda
parte del trabajo, se analizan las respuestas
de las mariposas frente al abandono de las closes y
a su recuperación a partir de antiguos cultivos intensivos.
Los cambios que experimentan las comunidades
de mariposas pueden pasar del todo desapercibidos
si los análisis se focalizan en indicadores
generales (p. ej., riqueza específica y abundancia).
Contrariamente, se demuestra que la respuesta de
algunas especies potencialmente bioindicadoras
puede ser muy acusada, si bien es necesario conocer
su ecología para poder interpretarla correctamente.
En concreto, se concluye que Plebejus argus representa
la mejor especie bioindicadora de las peculiares
condiciones ambientales propias de las
closes: las poblaciones responden con descensos
rapidísimos cuando estas condiciones se deterioran,
y también con aumentos progresivos cuando
el hábitat mejora. Además, se trata de una especie
muy sedentaria que se estructura en forma de
metapoblaciones, por lo cual el monitoreo de una
población local refleja también las condiciones
del paisaje de su entorno.Aiguamolls de lEmpordà Natural Park is one of
the most important protected wetland areas on the
Mediterranean coast. In this article, butterfly
assemblages were used to characterize and evaluate
the conservation value of the main habitat types in
this protected area. Butterfly data were obtained
from a number of transects walked as part of the
Catalan Butterfly Monitoring Scheme, which uses a
standardized methodology for monitoring butterflies.
Hay meadows flooded in winter (the so-called
closes) appeared always as the highest ranked
habitat in terms of conservation evaluation: they
have more butterflies and a slight tendency to
harbour more and generally rarer species. This
conclusion coincides with that of previous
investigations indicating that the most diverse and
rare plant communities in the whole Natural Park
are present in the closes, and highlights the
importance of traditionally managed hay meadows
for wildlife. However, these hay meadows are in
alarming decline and have become one of the most
threatened habitats in this area and the whole
Mediterranean region. In a second part of the
article, we analysed the responses of butterfly
communities once the closes are abandonned or
when they are recovered from former arable
fields. Changes may be completely overlooked if
the analyses are focussed on general patterns for
the whole community (e.g. species richness and
abundance). On the other hand, several individual
species showed strong population trends and some
of them may be considered as true bioindicators of
the narrow environmental conditions associated
with this kind of habitat. In particular, we suggest
that Plebejus argus represents an excellent
bioindicator of these traditionally managed hay
meadows: its populations always showed dramatic
decreases once the closes were abadonned,
overgrazed or invaded by exotic weeds, and
progressive increases once the quality of the
meadows improved. Moreover, this highly
sedentary species exists as metapopulations and,
therefore, the wealth of local populations also
reflects that of the surrounding landscape.El Parc Natural dels Aiguamolls de l'Empordà
(PNAE) és un dels espais protegits més coneguts i
emblemàtics a Catalunya. Un dels seus hàbitats
més localitzats i amenaçats són les anomenades
closes, prats destinats a la producció de farratge,
envoltats per canals de desguàs i bosc de ribera,
inundats durant part de l'hivern i dallats periòdicament.
Recentment s'ha demostrat que la comunitat
vegetal més típica de les closes és la més rica
del Parc i la que alberga les espècies més rares. En
aquest treball s'utilitzen dades de papallones
diürnes (ropalòcers), obtingudes després d'aplicar
durant 17 anys la metodologia del Butterfly Monitoring
Scheme, per avaluar l'interès de conservació
dels principals ambients del PNAE. Les closes
constitueixen l'hàbitat més valuós també per als
ropalòcers. La coincidència dels resultats per a
dos grups taxonòmics amplis que ocupen nivells
tròfics diferents, sumada a l'alarmant regressió
que han experimentat les closes en els darrers 50 anys i a la seva singularitat dins de l'àrea mediterrània,
permeten considerar-les objectivament
com un dels hàbitats més amenaçats del PNAE i
de tot Catalunya. En una segona part del treball,
s'analitzen les respostes de les papallones enfront
de l'abandonament de les closes i de la seva
recuperació a partir d'antics conreus intensius. Els
canvis que experimenten les comunitats de
ropalòcers poden passar del tot desapercebuts si
les anàlisis es focalitzen en indicadors generals (p.
ex., riquesa específica i abundància). Contràriament,
es demostra que la resposta d'algunes espècies
potencialment bioindicadores pot ser molt
més acusada, encara que cal conèixer la seva ecologia
per poder-la interpretar correctament. En
concret, es conclou que Plebejus argus representa
la millor espècie bioindicadora d'unes condicions
ambientals pròpies de les closes empordaneses
tradicionals: les poblacions responen amb descensos
rapidíssims quan les condicions òptimes es deterioren,
i també amb augments progressius quan
l'hàbitat millora. A més, es tracta d'una espècie
molt sedentària que s'estructura en forma de
metapoblacions, per la qual cosa el monitoratge
d'una població reflecteix també les condicions del
paisatge del seu entorn
Phenological sensitivity and seasonal variability explain climate-driven trends in Mediterranean butterflies
Although climate-driven phenological shifts have been documented for many taxa across the globe, we still lack knowledge of the consequences they have on populations. Here, we used a comprehensive database comprising 553 populations of 51 species of north-western Mediterranean butterflies to investigate the relationship between phenology and population trends in a 26-year period. Phenological trends and sensitivity to climate, along with various species traits, were used to predict abundance trends. Key ecological traits accounted for a general decline of more than half of the species, most of which, surprisingly, did not change their phenology under a climate warming scenario. However, this was related to the regional cooling in a short temporal window that includes late winter and early spring, during which most species concentrate their development. Finally, we demonstrate that phenological sensitivity-but not phenological trends-predicted population trends, and argue that species that best adjust their phenology to inter-annual climate variability are more likely to maintain a synchronization with trophic resources, thereby mitigating possible negative effects of climate change. Our results reflect the importance of assessing not only species' trends over time but also species' abilities to respond to a changing climate based on their sensitivity to temperature
The Catalan butterfly monitoring scheme has the capacity to detect effects of modifying agricultural practices
Impacts of agricultural management practices on the receiving environment are seldom suitably assessed because environmental monitoring is costly. In this regard, data generated by already existing environmental survey networks (ESNs) may have sufficient capacity to detect effects. Here, we study the capacity of the Catalan butterfly monitoring scheme (CBMS) to detect differences in butterfly abundance due to changes in agricultural practices. As a model, we compared butterfly abundance across two landscape types according to agricultural intensification. A 2 km diameter buffer area was centered on the CBMS transect, the control group were transects located in areas where intensive agriculture represented <20% of the area; a treated group was simulated by selecting transects located in areas where intensive agriculture occupied an area over 40%. The Welch t‐test (α = 0.05 and 80% power) was used to compare butterfly abundance per section across landscape types. The capacity of the t‐test to detect changes in mean butterfly abundance, of 12 butterfly indicators relevant to farmland, was calculated annually and for 5‐, 10‐, and 15‐yr periods. Detection capacity of the t‐test depended mainly on butterfly data sample size and variability; difference in butterfly abundance was less important. The t‐test would be capable of detecting acceptably small population changes across years and sites. For instance, considering a 15‐yr period, it would be possible to detect a change in abundance below 10% of the multispecies indicators (all butterfly species, open habitat species, mobile species, and grassland indicators) and two single species (Lasiommata megera and Lycaena phlaeas). When comparisons were carried out within each year, the t‐test would only be capable of detecting a change below 30% for all butterfly species, mobile species, and L. megera. However, detection capacity rapidly improved with the addition of further years, and with 5 yr of monitoring, all indicators but Thymelicus acteon had a detection capacity below 30%. We therefore conclude that, from a statistical point of view, the CBMS data “as is” are sensitive enough for monitoring effects of changes in agricultural practices. It could be used, for instance, for the general surveillance of genetically modified crops.This work was partially supported by the Spanish Government‐funded project AGL2011‐23996 and a FI‐DGR scholarship to M. Lee from the Catalan Government
On assessment of processing variables on vertical centrifugal casting technique
The aim of the present study is to investigate the influence of the vertical centrifugal casting
technique over mechanical and metallurgical properties of a hypereutectic Al–18Si alloy. Due to
the inherent vibration of the centrifugal casting technique, and in order to study and understand
the individual effects of the equipment vibration and the centrifugal force itself (pressure or fluid
dynamics), as well as the combined effect of both, three different tests were performed: gravity
casting, gravity casting with vibration and centrifugal casting. It was concluded that the
metallurgical and mechanical properties of castings obtained by the centrifugal casting process
depend on the combined effect of the centrifugal pressure and/or fluid dynamics and on the
inherent vibration of the technique itself. Correlations between the different casting techniques
and obtained mechanical and metallurgical properties are presentedFCT - Fundação para a Ciência e Tecnologi
Aplicació de models font-receptor per a determinar àrees font de components biològics (pol·len i papallones)
Els models font-receptor permeten establir relacions entre un punt receptor (punt de mostreig) i les àrees font probables (regions emissores) mitjançant l'associació de valors de concentració en el punt receptor amb les corresponents retrotrajectòries atmosfèriques, i, juntament amb altres tècniques, permeten interpretar fenòmens de transport a escala sinòptica. No obstant això, fins a l'actualitat, pocs treballs han aplicat aquests tipus de models per descriure les àrees font d'organismes biològics. A Catalunya es disposa de registres molt complets de pol·len (dades de la Xarxa Aerobiològica de Catalunya) i de papallones (dades del Catalan Butterfly Monitoring Scheme), un material biològic també susceptible de ser transportat a llargues distàncies i del que pot interessar conèixer les seves àrees d'origen. En aquest treball presentem els resultats de l'ús del model de Seibert et al. aplicat a l'estudi de les regions font de: (1) determinats pol·lens de caràcter al·lergogen, observats a Catalunya i Canàries, i (2) la papallona migratòria Vanessa cardui, observada a Catalunya. Amb els resultats obtinguts podem corroborar la idoneítat d'aquests models per a explicar la procedència de diferents espècies, tant químiques com biològiques, ampliant així les possibilitats d'aplicació del model original al camp molt més extens de l'aerobiologia
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