6,215 research outputs found
White Clover Soil Fatigue: An Establishment Problem on Large and Intensive Dairy Farms
In recent years a new constraint, clover soil fatigue, has appeared for the establishment of white clover (Trifolium repens) in Denmark. Increasing dairy farm size has led to more intensive use of clover in crop rotation schemes in the grazing areas located at convenient distances from stables. It has become common practice to establish new clover/grass in the fields just after ploughing clover/grass swards, and soil fatigue is becoming more common. On fatigued land the clover plants emerge, then become stunted and eventually disappear within the same year. The problem tends to cover the full field area. Obviously, this is a major constraint since the importance of N-inputs derived from fixation is growing in Danish dairy farming
Transverse radiation force in a tailored optical fiber
We show, by means of simple model calculations, how a weak laser beam sent
through an optical fiber exerts a transverse radiation force if there is an
azimuthal asymmetry present in the fiber such that one side has a slightly
different refractive index than the other. The refractive index difference
needs only to be very small, of order , in order to produce
an appreciable transverse displacement of order 10 microns. We argue that the
effect has probably already been seen in a recent experiment of She et al.
[Phys. Rev. Lett. 101, 243601 (2008)], and we discuss correspondence between
these observations and the theory presented. The effect could be used to bend
optical fibers in a predictable and controlled manner and we propose that it
could be useful for micron-scale devices.Comment: 4 pages, 3 figures. Accepted for publication as Rapid Communication
in Phys. Rev.
Ly-alpha emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshift
The traditional view that Ly-alpha emission and dust should be mutually
exclusive has been questioned more and more often; most notably, the
observations of Ly-alpha emission from ULIRGs seem to counter this view. In
this paper we seek to address the reverse question. How large a fraction of
Ly-alpha selected galaxies are ULIRGs? Using two samples of 24/25 Ly-alpha
emitting galaxies at z = 0.3/2.3, we perform this test, including results at z
= 3.1, and find that, whereas the ULIRG fraction at z = 3.1 is very small, it
systematically increases towards lower redshifts. There is a hint that this
evolution may be quite sudden and that it happens around a redshift of z ~ 2.5.
After measuring the infrared luminosities of the Ly-alpha emitters, we find
that they are in the normal to ULIRG range in the lower redshift sample, while
the higher redshift galaxies all have luminosities in the ULIRG category. The
Ly-alpha escape fractions for these infrared bright galaxies are in the range
1-100 % in the z = 0.3 galaxies, but are very low in the z = 2.3 galaxies, 0.4
% on average. The unobscured star formation rates are very high, ranging from
500 to more than 5000 M_sun/yr, and the dust attenuation derived are in the
range 0.0 < A_V < 3.5.Comment: 5 pages, 5 figures, 1 table, published in A&A, 508, L2
Effect of feeding fermentable fibrerich feedstuffs on meat quality with emphasis on chemical and sensory boar taint in entire male and female pigs
Skatole, androstenone and other compounds such as indole cause boar taint in entire male pork. However, female pigs also produce skatole and indole. The purpose of this experiment was to minimise boar taint and increase overall impression of sensory quality by feeding entire male and female pigs with fibrerich feedstuffs. The pigs have been fed three organic diets for either 1 or 2 weeks prior to slaughter of which two diets contained different fermentable fibre-rich feedstuffs â 10â13.3% dried chicory roots or
25% blue lupines. These two treatments were compared with pigs fed with an organic control diet for either 1 or 2 weeks prior to slaughter. Lupines significantly reduced skatole in blood and backfat for both genders after 1 week. Moreover, lupines showed negative impact on growth rate and feed conversion whilst chicory showed no significant differences in this respect. However, the indole concentration was significantly lower in chicory than lupine fed pigs. From a sensory perspective, chicory and lupine feeding reduced boar taint since odour and flavour of manure related to skatole and urine associated to androstenone were minimised. The level of boar taint in the entire male pigs was most effectively reduced after 14 days by both fibre-rich feeds while lupine had the largest influence on ââboarâ taint reduction in female pigs
Measuring the effective phonon density of states of a quantum dot
We employ detuning-dependent decay-rate measurements of a quantum dot in a
photonic-crystal cavity to study the influence of phonon dephasing in a
solid-state quantum-electrodynamics experiment. The experimental data agree
with a microscopic non-Markovian model accounting for dephasing from
longitudinal acoustic phonons, and identifies the reason for the hitherto
unexplained difference between non-resonant cavity feeding in different
nanocavities. From the comparison between experiment and theory we extract the
effective phonon density of states experienced by the quantum dot. This
quantity determines all phonon dephasing properties of the system and is found
to be described well by a theory of bulk phonons.Comment: 5 pages, 3 figures, submitte
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.Comment: Accepted for publishing in MNRAS lette
Instrumental Variable Identification of Dynamic Variance Decompositions
Macroeconomists increasingly use external sources of exogenous variation for
causal inference. However, unless such external instruments (proxies) capture
the underlying shock without measurement error, existing methods are silent on
the importance of that shock for macroeconomic fluctuations. We show that, in a
general moving average model with external instruments, variance decompositions
for the instrumented shock are interval-identified, with informative bounds.
Various additional restrictions guarantee point identification of both variance
and historical decompositions. Unlike SVAR analysis, our methods do not require
invertibility. Applied to U.S. data, they give a tight upper bound on the
importance of monetary shocks for inflation dynamics
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