261 research outputs found
SPHERES, J\"ulich's High-Flux Neutron Backscattering Spectrometer at FRM II
SPHERES (SPectrometer with High Energy RESolution) is a third-generation
neutron backscattering spectrometer, located at the 20 MW German neutron source
FRM II and operated by the Juelich Centre for Neutron Science. It offers an
energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31
micro-eV, and a signal-to-noise ratio of up to 1750:1.Comment: 12 pages, 7 figures, 2 tables. Supplemental material consists of 3
pages, 2 figures, 2 table
Role of physically effective fiber and estimation of dietary fiber adequacy in high-producing dairy cattle
Highly fermentable diets require the inclusion of adequate amounts of fiber to
reduce the risk of subacute rumen acidosis (SARA). To assess the adequacy of
dietary fiber in dairy cattle, the concept of physically effective neutral
detergent fiber (peNDF) has received increasing attention because it
amalgamates information on both chemical fiber content and particle size (PS)
of the feedstuffs. The nutritional effects of dietary PS and peNDF are complex
and involve feed intake behavior (absolute intake and sorting behavior),
ruminal mat formation, rumination and salivation, and ruminal motility. Other
effects include fermentation characteristics, digesta passage, and nutrient
intake and absorption. Moreover, peNDF requirements depend on the
fermentability of the starch source (i.e., starch type and endosperm
structure). To date, the incomplete understanding of these complex
interactions has prevented the establishment of peNDF as a routine method to
determine dietary fiber adequacy so far. Therefore, this review is intended to
analyze the quantitative effects of and interactions among forage PS, peNDF,
and diet fermentability with regard to rumen metabolism and prevention of
SARA, and aims to give an overview of the latest achievements in the
estimation of dietary fiber adequacy in high-producing dairy cattle. Recently
developed models that synthesize the effects of both peNDF and fermentable
starch on rumen metabolism appear to provide an appropriate basis for
estimation of dietary fiber adequacy in high-producing dairy cows. Data
suggest that a period lasting more than 5 to 6h/d during which ruminal pH is
<5.8 should be avoided to minimize health disturbances due to SARA. The
knowledge generated from these modeling approaches recommends that average
amounts of 31.2% peNDF inclusive particles >1.18mm (i.e., peNDF(>1.18)) or
18.5% peNDF inclusive particles >8mm (i.e., peNDF(>8)) in the diet (DM basis)
are required. However, inclusion of a concentration of peNDF(>8) in the diet
beyond 14.9% of diet DM may lower DM intake level. As such, more research is
warranted to develop efficient feeding strategies that encourage inclusion of
energy-dense diets without the need to increase their content in peNDF above
the threshold that leads to lower DM intake. The latter would require
strategies that modulate the fermentability characteristics of the diet and
promote absorption and metabolic capacity of ruminal epithelia of dairy cows
Spectator detection for the measurement of proton neutron interactions at ANKE
A telescope of three silicon detectors has been installed close to the
internal target position of the ANKE spectrometer, which is situated inside the
ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and
identification of slow protons and deuterons emerging from a deuterium
cluster-jet target thus becomes feasible. A good measurement of the energy and
angle of such a spectator proton (p_sp) allows one to identify a reaction as
having taken place on the neutron in the target and then to determine the
kinematical variables of the ion-neutron system on an event-by-event basis over
a range of c.m. energies.
The system has been successfully tested under laboratory conditions. By
measuring the spectator proton in the p d to p_sp d pi^0 reaction in
coincidence with a fast deuteron in the ANKE Forward Detector, values of the p
n to d pi^0 total cross-section have been deduced. Further applications of the
telescope include the determination of the luminosity and beam polarisation
which are required for several experiments.Comment: 16 pages, 9 figure
Cross section and analyzing power of pol{p}p -> pn pi+ near threshold
The cross section and analyzing power of the pol{p}p -> pn pi+ reaction near
threshold are estimated in terms of data obtained from the pol{p}p -> d pi+ and
pp -> pp pi0 reactions. A simple final state interaction theory is developed
which depends weakly upon the form of the pion-production operator and includes
some Coulomb corrections. Within the uncertainties of the model and the input
data, the approach reproduces well the measured energy dependence of the total
cross section and the proton analyzing power at a fixed pion c.m. angle of
90deg, from threshold to T_p = 330 MeV. The variation of the differential cross
section with pion angle is also very encouraging.Comment: 20 pages, Latex including 4 eps figure
On the close to threshold meson production in neutron-neutron collisions
A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.
Kaon Pair Production in Proton--Proton Collisions
The differential and total cross sections for kaon pair production in the
pp->ppK+K- reaction have been measured at three beam energies of 2.65, 2.70,
and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Juelich
accelerator. These near-threshold data are separated into pairs arising from
the decay of the phi-meson and the remainder. For the non-phi selection, the
ratio of the differential cross sections in terms of the K-p and K+p invariant
masses is strongly peaked towards low masses. This effect can be described
quantitatively by using a simple ansatz for the K-p final state interaction,
where it is seen that the data are sensitive to the magnitude of an effective
K-p scattering length. When allowance is made for a small number of phi events
where the K- rescatters from the proton, the phi region is equally well
described at all three energies. A very similar phenomenon is discovered in the
ratio of the cross sections as functions of the K-pp and K+pp invariant masses
and the identical final state interaction model is also very successful here.
The world data on the energy dependence of the non-phi total cross section is
also reproduced, except possibly for the results closest to threshold.Comment: 12 two-column pages, 12 figures, 1 tabl
Charge dependence of
We calculate the isospin symmetry violating effects to the reactions
and arising from the different
hadron masses and from the Coulomb interaction between the positive pion and
the deuteron. These effects are large enough in the cross section and analyzing
power that they should be taken into account in comparisons of accurate
experiments in different charge channels.Comment: 10 pages plus 2 figures, submitted to Phys. Lett.
Detailed comparison of the pp -> \pi^+pn and pp -> \pi^+d reactions at 951 MeV
The positively charged pions produced in proton-proton collisions at a beam
momentum of 1640 MeV/c were measured in the forward direction with a high
resolution magnetic spectrograph. The missing mass distribution shows the bound
state (deuteron) clearly separated from the continuum. Despite the very
good resolution, there is no evidence for any significant production of the
system in the spin-singlet state. However, the cross section ratio is about twice as large as
that predicted from -wave final-state-interaction theory and it is suggested
that this is due to -state effects in the system.Comment: 8 pages, 3 figure
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