471 research outputs found
Nonlinear eigenvalue problem for optimal resonances in optical cavities
The paper is devoted to optimization of resonances in a 1-D open optical
cavity. The cavity's structure is represented by its dielectric permittivity
function e(s). It is assumed that e(s) takes values in the range 1 <= e_1 <=
e(s) <= e_2. The problem is to design, for a given (real) frequency, a cavity
having a resonance with the minimal possible decay rate. Restricting ourselves
to resonances of a given frequency, we define cavities and resonant modes with
locally extremal decay rate, and then study their properties. We show that such
locally extremal cavities are 1-D photonic crystals consisting of alternating
layers of two materials with extreme allowed dielectric permittivities e_1 and
e_2. To find thicknesses of these layers, a nonlinear eigenvalue problem for
locally extremal resonant modes is derived. It occurs that coordinates of
interface planes between the layers can be expressed via arg-function of
corresponding modes. As a result, the question of minimization of the decay
rate is reduced to a four-dimensional problem of finding the zeroes of a
function of two variables.Comment: 16 page
PADC Detected External Neutron Field by Nuclear Tracks at RFX-mod
Measured neutron signals relevant for plasma diagnostics on Reversed Field pinch eXperiment, RFX-mod, are obtained by nuclear track methodology with PADC-NtD’s. this technique provides the external neutron field values around the RFX-mod installation during pulsed operation. Charged particles from (n, p) and (n, α) reactions are related to formed latent tracks. these are etched in a thermoregulated water bath with a 6.25M, KOh solution at 60oC. Observed tracks were analyzed to determine track density from which neutron fluence spatial values should be derived. Results indicate that the neutron density in the surrounding environment change at most 40%. the epithermal component is 60% higher than that corresponding to the thermal region. the estimated neutron fluence for the whole experiment is 7.5×1010 neutrons cm2/s
A long-period massive planet around HD106515A
We have performed RV monitoring of the components of the binary system HD
106515 over about 11 years using the high resolution spectrograph SARG at TNG.
The primary shows long-period radial velocity variations that indicate the
presence of a low mass companion whose projected mass is in the planetary
regime (m sin i = 9.33 Mjup). The 9.8 years orbit results quite eccentric
(e=0.57), as typical for massive giant planets. Our results confirm the
preliminary announcement of the planet included in Mayor et al. (2011). The
secondary instead does not show significant RV variations. The two components
do not differ significantly in chemical composition, as found for other pairs
for which one component hosts giant planets. Adaptive optics images obtained
with AdOpt@TNG do not reveal additional stellar companions. From the analysis
of the relative astrometry of the components of the wide pair we put an upper
limit on the mass of the newly detected companion of about 0.25 Msun. State of
art or near future instrumentation can provide true mass determination, thanks
to the availability of the wide companion HD106515B as reference. Therefore,
HD106515Ab will allow deeper insight in the transition region between planets
and brown dwarfs.Comment: A&A, accepted, 8 pages, 10 figure
LIFE BEEF CARBON: a common framework for quantifying grass and corn based beef farms’ carbon footprints
peer-reviewedEurope’s roadmap to a low-carbon economy aims to cut greenhouse gas (GHG) emissions 80% below 1990 levels by 2050. Beef
production is an important source of GHG emissions and is expected to increase as the world population grows. LIFE BEEF CARBON
is a voluntary European initiative that aims to reduce GHG emissions per unit of beef (carbon footprint) by 15% over a 10-year
period on 2172 farms in four large beef-producing countries. Changes in farms beef carbon footprint are normally estimated via
simulation modelling, but the methods current models apply differ. Thus, our initial goal was to develop a common modelling
framework to estimate beef farms carbon footprint. The framework was developed for a diverse set of Western Europe farms
located in Ireland, Spain, Italy and France. Whole farm and life cycle assessment (LCA) models were selected to quantify emissions
for the different production contexts and harmonized. Carbon Audit was chosen for Ireland, Bovid-CO2 for Spain and CAP’2ER for
France and Italy. All models were tested using 20 case study farms, that is, 5 per country and quantified GHG emissions associated
with on-farm live weight gain. The comparison showed the ranking of beef systems gross carbon footprint was consistent across the
three models. Suckler to weaning or store systems generally had the highest carbon footprint followed by suckler to beef systems
and fattening beef systems. When applied to the same farm, Carbon Audit’s footprint estimates were slightly lower than CAP’2ER,
but marginally higher than Bovid-CO2. These differences occurred because the models were adapted to a specific region’s production
circumstances, which meant their emission factors for key sources; that is, methane from enteric fermentation and GHG emissions
from concentrates were less accurate when used outside their target region. Thus, for the common modelling framework, regionspecific
LCA models were chosen to estimate beef carbon footprints instead of a single generic model. Additionally, the Carbon
Audit and Bovid-CO2 models were updated to include carbon removal by soil and other environmental metrics included in CAP’2ER,
for example, acidification. This allows all models to assess the effect carbon mitigation strategies have on other potential pollutants.
Several options were identified to reduce beef farms carbon footprint, for example, improving genetic merit. These options were
assessed for beef systems, and a mitigation plan was created by each nation. The cumulative mitigation effect of the LIFE BEEF
CARBON plan was estimated to exceed the projects reduction target (−15%)
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