5,485 research outputs found
Magnetic Moment Formation in Quantum Point Contacts
We study the formation of local magnetic moments in quantum point contacts.
Using a Hubbard-like model to describe point contacts formed in a two
dimensional system, we calculate the magnetic moment using the unrestricted
Hartree approximation. We analyze different type of potentials to define the
point contact, for a simple square potential we calculate a phase diagram in
the parameter space (Coulomb repulsion - gate voltage). We also present an
analytical calculation of the susceptibility to give explicit conditions for
the occurrence of a local moment, we present a simple scaling argument to
analyze how the stability of the magnetic moment depends on the point contact
dimensions.Comment: 7 pages, 2 figure
Origin of the wide-angle hot H2 in DG Tauri: New insight from SINFONI spectro-imaging
We wish to test the origins proposed for the extended hot H2 at 2000K around
the atomic jet from the T Tauri star DGTau, in order to constrain the
wide-angle wind structure and the possible presence of an MHD disk wind. We
present flux calibrated IFS observations in H2 1-0 S(1) obtained with
SINFONI/VLT. Thanks to spatial deconvolution by the PSF and to accurate
correction for uneven slit illumination, we performed a thorough analysis and
modeled the morphology, kinematics, and surface brightness. We also compared
our results with studies in [FeII], [OI], and FUV-pumped H2. The
limb-brightened H2 emission in the blue lobe is strikingly similar to
FUV-pumped H2 imaged 6yr later, confirming that they trace the same hot gas and
setting an upper limit of 12km/s on any expansion proper motion. The wide-angle
H2 rims are at lower blueshifts than probed by narrow long-slit spectra. We
confirm that they extend to larger angle and to lower speed the onion-like
velocity structure observed in optical atomic lines. The latter is shown to be
steady over more/equal than 4yr but undetected in [FeII] by SINFONI, probably
due to strong iron depletion. The H2 rim thickness less/equal than 14AU rules
out excitation by C-shocks, and J-shock speeds are constrained to 10km/s. We
find that explaining the H2 wide-angle emission with a shocked layer requires
either a recent outburst (15yr) into a pre-existing ambient outflow or an
excessive wind mass flux. A slow photoevaporative wind from the dense
irradiated disk surface and an MHD disk wind heated by ambipolar diffusion seem
to be more promising and need to be modeled in more detail
Sensory quality of organic milk based on grazing and high ratio of legumes in the feeding ration
Organic milk forms an important segment of the fresh milk production in Denmark. However, studies are needed to substantiate the high quality and future development of new variations of organic milk for different consumers. Differences in the composition of organically and conventionally produced milk (free fatty acids and a higher content of antioxidants in organic milk) are suggested to be a result of differences in feeding regimes (maize components in conventional production vs. grass and legumes in organic production). Also, milk from dairy cows fed grass silage has a different flavour compared to milk from dairy cows fed maize silage. This study evaluated the sensory properties of organic milk from dairy cows from different feeding trials.
The effect of four different legumes and herbs, lucerne (Medicargo sativa), red clover (Trifolium pratense), white clover (Trifolium repens) and chicory (Cichorium intybus), was studied following a schedule including 4*12 Holstein Frisian cows. Descriptive sensory analysis was performed on the fresh pasteurized unhomogenized full-fat milk (6 replicates in 2 sessions) with a trained panel of 10 assessors.
The preliminary results from the descriptive analysis of summer feeding (grazing) and winter feeding (silage) show that feeding with legumes and grass affects the sensory quality of full-fat unhomogenized organic milk. The most distinct milk was obtained from feeding ration high in chicory. This milk was characterized by a bitter and metallic taste and an astringent aftertaste both from the summer grazing and winter silage feeding trials. Red clover was characterized by a boiled milk flavour (summer), lucerne by a fatty aftertaste (winter) and white clover by a sweet and creamy flavour (winter).
The results of the first season, which will also include relations between the sensory quality and the milk composition, serve as important inputs for the extensive studies to be conducted during the next three seasons. These studies include farm studies and consumer studies (product information, preference and purchase motives)
Quantum Interaction : the Construction of Quantum Field defined as a Bilinear Form
We construct the solution of the quantum wave equation
as a bilinear form which can
be expanded over Wick polynomials of the free -field, and where
is defined as the normal ordered product with
respect to the free -field. The constructed solution is correctly defined
as a bilinear form on , where is a
dense linear subspace in the Fock space of the free -field. On
the diagonal Wick symbol of this bilinear form
satisfies the nonlinear classical wave equation.Comment: 32 pages, LaTe
[OI]63micron jets in class 0 sources detected by Herschel
We present Herschel PACS mapping observations of the [OI]63 micron line
towards protostellar outflows in the L1448, NGC1333-IRAS4, HH46, BHR71 and
VLA1623 star forming regions. We detect emission spatially resolved along the
outflow direction, which can be associated with a low excitation atomic jet. In
the L1448-C, HH46 IRS and BHR71 IRS1 outflows this emission is kinematically
resolved into blue- and red-shifted jet lobes, having radial velocities up to
200 km/s. In the L1448-C atomic jet the velocity increases with the distance
from the protostar, similarly to what observed in the SiO jet associated with
this source. This suggests that [OI] and molecular gas are kinematically
connected and that this latter could represent the colder cocoon of a jet at
higher excitation. Mass flux rates (\.M(OI)) have been measured from
the [OI]63micron luminosity adopting two independent methods. We find values in
the range 1-4 10 Mo/yr for all sources but HH46, for which an order of
magnitude higher value is estimated. \.M(OI) are compared with mass
accretion rates (\.M) onto the protostar and with \.M derived
from ground-based CO observations. \.M(OI)/\.M ratios are in
the range 0.05-0.5, similar to the values for more evolved sources.
\.M(OI) in HH46 IRS and IRAS4A are comparable to \.M(CO), while
those of the remaining sources are significantly lower than the corresponding
\.M(CO). We speculate that for these three sources most of the mass
flux is carried out by a molecular jet, while the warm atomic gas does not
significantly contribute to the dynamics of the system.Comment: 37 pages and 12 figures, accepted for publication on Astrophysical
Journa
Chemistry of a newly detected circumbinary disk in Ophiuchus
(Abridged) Astronomers recently started discovering exoplanets around binary
systems. Therefore, understanding the formation and evolution of circumbinary
disks is crucial for a complete scenario of planet formation. The aim of this
paper is to present the detection of a circumbinary disk around Oph-IRS67 and
analyse its structure. We present high-angular-resolution (0.4", 60 AU)
observations of C17O, H13CO+ , C34S, SO2, C2H and c-C3H2 molecular transitions
with ALMA at 0.8 mm. The spectrally and spatially resolved maps reveal the
kinematics of the circumbinary disk as well as its chemistry. Molecular
abundances are estimated using RADEX. The continuum emission reveals the
presence of a circumbinary disk around the two sources. This disk has a
diameter of ~620 AU and is well traced by C17O and H13CO+ emission. C2H and
c-C3H2 trace a higher-density region which is spatially offset from the sources
(~430 AU). Finally, SO2 shows compact emission around one of the sources,
Oph-IRS67 B. The molecular transitions which trace the circumbinary disk are
consistent with a Keplerian profile on disk scales (< 200 AU) and an infalling
profile for envelope scales (> 200 AU). The Keplerian fit leads to a mass of
2.2 Msun. Inferred CO abundances w.r.t. H2 are comparable to the canonical ISM
value of 2.7e-4. This study proves the first detection of the circumbinary disk
associated with Oph-IRS67. The disk is chemically differentiated from the
nearby high-density region. The lack of methanol emission suggests the extended
disk dominates the mass budget in the inner- most regions of the protostellar
envelope, generating a flat density profile where less material is exposed to
high temperatures. Thus, complex organic molecules would be associated with
lower column densities. Finally, Oph-IRS67 is a promising candidate for the
detection of both circumstellar disks with higher-angular-resolution
observations.Comment: 19 pages, 14 figures, 6 table
Magneto-electrical subbands of freely suspended quantum point contacts
We present a versatile design of freely suspended quantum point contacts with
particular large one-dimensional subband quantization energies of up to 10meV.
The nanoscale bridges embedding a two-dimensional electron system are
fabricated from AlGaAs/GaAs heterostructures by electron-beam lithography and
etching techniques. Narrow constrictions define quantum point contacts that are
capacitively controlled via local in-plane side gates. Employing transport
spectroscopy, we investigate the transition from electrostatic subbands to
Landau-quantization in a perpendicular magnetic field. The large subband
quantization energies allow us to utilize a wide magnetic field range and
thereby observe a large exchange splitted spin-gap of the two lowest
Landau-levels
Water distribution in shocked regions of the NGC1333-IRAS4A protostellar outflow
We present the study of the H2O spatial distribution at two bright shocked
regions along IRAS4A, one of the strongest H2O emitters among the Class 0
outflows. We obtained Herschel-PACS maps of the IRAS4A outflow and HIFI
observations of two shocked positions. The largest HIFI beam of 38 arcsec at
557 GHz was mapped in several key water lines with different upper energy
levels, to reveal possible spatial variations of the line profiles. We detect
four H2O lines and CO (16-15) at the two selected positions. In addition,
transitions from related outflow and envelope tracers are detected. Different
gas components associated with the shock are identified in the H2O emission. In
particular, at the head of the red lobe of the outflow, two distinct gas
components with different excitation conditions are distinguished in the HIFI
emission maps: a compact component, detected in the ground-state water lines,
and a more extended one. Assuming that these two components correspond to two
different temperature components observed in previous H2O and CO studies, the
excitation analysis of the H2O emission suggests that the compact (about 3
arcsec) component is associated with a hot (T~1000 K) gas with densities
~(1-4)x10^5 cm^{-3}, whereas the extended one (10-17 arcsec) traces a warm
(T~300-500 K) and dense gas (~(3-5)x10^7 cm^{-3}). Finally, using the CO
(16-15) emission observed at R2, we estimate the H2O/H2 abundance of the warm
and hot components to be (7-10)x10^{-7} and (3-7)x10^{-5}. Our data allowed us,
for the first time, to resolve spatially the two temperature components
previously observed with HIFI and PACS. We propose that the compact hot
component may be associated with the jet that impacts the surrounding material,
whereas the warm, dense, and extended component originates from the compression
of the ambient gas by the propagating flow.Comment: 13 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysic
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