2,649 research outputs found
Methods for Site-Selective Chemical Pretein Immobilization
Els bioxips de proteïnes (micro arrays) requereixen, per a una implementació eficient, d'un desenvolupament de les tècniques
d'immobilització de proteïnes.Es comenten diverses aproximacions químiques per tal dassolir la immobilització de proteïnes duna manera específica
amb enllaços covalents. El desenvolupament en aquesta àrea condueix a millores tecnològiques per al desenvolupament
de bioxips de proteïnes
Identification of a novel vitispirane precursor in Riesling wine
Glycoconjugated forms of diastereoisomeric 1-(3-hydroxybutyl)-6,6-dimethyl-2-methylene-3-cyclohexen-1-ols have been identified as new natural vitispirane precursors in Riesling wine. Model degradation studies carried out with synthetic references of the precursors showed the easy formation of isomeric vitispiranes at pH conditions of wine. Based on these results a hypothetic pathway for vitispiranes in Riesling wine is proposed.Identifizierung eines neuen Vitispiranvorläufers in RieslingweinZwei Diastereomere von 1-(3-Hydroxybutyl)-6,6-dimethyl-2-methylen-3-cyclohexen-1-ol wurden erstmals als Aglykone in Glykosidextrakten von Rieslingwein identifiziert. Modellreaktionen bei pH 3,2 lieferten die isomeren Vitispirane als Hauptabbauprodukte. Aufgrund dieser Ergebnisse wird ein erweitertes Modell zur Vitispiranbildung in Rieslingwein vorgestellt
Q-dependence of the inelastic neutron scattering cross section for molecular spin clusters with high molecular symmetry
For powder samples of polynuclear metal complexes the dependence of the
inelastic neutron scattering intensity on the momentum transfer Q is known to
be described by a combination of so called interference terms. They reflect the
interplay between the geometrical structure of the compound and the spatial
properties of the wave functions involved in the transition. In this work, it
is shown that the Q-dependence is strongly interrelated with the molecular
symmetry of molecular nanomagnets, and, if the molecular symmetry is high
enough, is actually completely determined by it. A general formalism connecting
spatial symmetry and interference terms is developed. The arguments are
detailed for cyclic spin clusters, as experimentally realized by e.g. the
octanuclear molecular wheel Cr8, and the star like tetranuclear cluster Fe4.Comment: 8 pages, 1 figures, REVTEX
A new look at Spitzer primary transit observations of the exoplanet HD189733b
Blind source separation techniques are used to reanalyse two exoplanetary
transit lightcurves of the exoplanet HD189733b recorded with the IR camera IRAC
on board the Spitzer Space Telescope at 3.6m during the "cold" era. These
observations, together with observations at other IR wavelengths, are crucial
to characterise the atmosphere of the planet HD189733b. Previous analyses of
the same datasets reported discrepant results, hence the necessity of the
reanalyses. The method we used here is based on the Independent Component
Analysis (ICA) statistical technique, which ensures a high degree of
objectivity. The use of ICA to detrend single photometric observations in a
self-consistent way is novel in the literature. The advantage of our reanalyses
over previous work is that we do not have to make any assumptions on the
structure of the unknown instrumental systematics. Such "admission of
ignorance" may result in larger error bars than reported in the literature, up
to a factor . This is a worthwhile trade-off for much higher objectivity,
necessary for trustworthy claims. Our main results are (1) improved and robust
values of orbital and stellar parameters, (2) new measurements of the transit
depths at 3.6m, (3) consistency between the parameters estimated from the
two observations, (4) repeatability of the measurement within the photometric
level of in the IR, (5) no evidence of stellar
variability at the same photometric level within 1 year.Comment: 43 pages, 18 figure
Blind extraction of an exoplanetary spectrum through Independent Component Analysis
Blind-source separation techniques are used to extract the transmission
spectrum of the hot-Jupiter HD189733b recorded by the Hubble/NICMOS instrument.
Such a 'blind' analysis of the data is based on the concept of independent
component analysis. The de-trending of Hubble/NICMOS data using the sole
assumption that nongaussian systematic noise is statistically independent from
the desired light-curve signals is presented. By not assuming any prior, nor
auxiliary information but the data themselves, it is shown that spectroscopic
errors only about 10 - 30% larger than parametric methods can be obtained for
11 spectral bins with bin sizes of ~0.09 microns. This represents a reasonable
trade-off between a higher degree of objectivity for the non-parametric methods
and smaller standard errors for the parametric de-trending. Results are
discussed in the light of previous analyses published in the literature. The
fact that three very different analysis techniques yield comparable spectra is
a strong indication of the stability of these results.Comment: ApJ accepte
The quasi-free-standing nature of graphene on H-saturated SiC(0001)
We report on an investigation of quasi-free-standing graphene on 6H-SiC(0001)
which was prepared by intercalation of hydrogen under the buffer layer. Using
infrared absorption spectroscopy we prove that the SiC(0001) surface is
saturated with hydrogen. Raman spectra demonstrate the conversion of the buffer
layer into graphene which exhibits a slight tensile strain and short range
defects. The layers are hole doped (p = 5.0-6.5 x 10^12 cm^(-2)) with a carrier
mobility of 3,100 cm^2/Vs at room temperature. Compared to graphene on the
buffer layer a strongly reduced temperature dependence of the mobility is
observed for graphene on H-terminated SiC(0001)which justifies the term
"quasi-free-standing".Comment: 3 pages, 3 figures, accepted for publication in Applied Physics
Letter
Deformation Quantization of a Certain Type of Open Systems
We give an approach to open quantum systems based on formal deformation
quantization. It is shown that classical open systems of a certain type can be
systematically quantized into quantum open systems preserving the complete
positivity of the open time evolution. The usual example of linearly coupled
harmonic oscillators is discussed.Comment: Major update. Improved main statements. 21 page
Magnetic relaxation studies on a single-molecule magnet by time-resolved inelastic neutron scattering
Time-resolved inelastic neutron scattering measurements on an array of
single-crystals of the single-molecule magnet Mn12ac are presented. The data
facilitate a spectroscopic investigation of the slow relaxation of the
magnetization in this compound in the time domain.Comment: 3 pages, 4 figures, REVTEX4, to appear in Appl. Phys. Lett., for an
animation see also
http://www.dcb.unibe.ch/groups/guedel/members/ow2/trins.ht
Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice
Quantum spin liquids are materials that feature quantum entangled spin
correlations and avoid magnetic long-range order at T = 0 K. Particularly
interesting are two-dimensional honeycomb spin lattices where a plethora of
exotic quantum spin liquids have been predicted. Here, we experimentally study
an effective S=1/2 Heisenberg honeycomb lattice with competing nearest and
next-nearest neighbor interactions. We demonstrate that YbBr avoids order
down to at least T=100 mK and features a dynamic spin-spin correlation function
with broad continuum scattering typical of quantum spin liquids near a quantum
critical point. The continuum in the spin spectrum is consistent with plaquette
type fluctuations predicted by theory. Our study is the experimental
demonstration that strong quantum fluctuations can exist on the honeycomb
lattice even in the absence of Kitaev-type interactions, and opens a new
perspective on quantum spin liquids.Comment: 32 pages, 7 Figure
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