276 research outputs found
Quantum information analysis of the phase diagram of the half-filled extended Hubbard model
We examine the phase diagram of the half-filled one-dimensional extended
Hubbard model using quantum information entropies within the density-matrix
renormalization group. It is well known that there is a charge-density-wave
phase at large nearest-neighbor and small on-site Coloumb repulsion and a
spin-density-wave at small nearest-neighbor and large on-site Coloumb
repulsion. At intermediate Coulomb interaction strength, we find an additional
narrow region of a bond-order phase between these two phases. The phase
transition line for the transition out of the charge-density-wave phase changes
from first-order at strong coupling to second-order in a parameter regime where
all three phases are present. We present evidence that the additional
phase-transition line between the spin-density-wave and bond-order phases is
infinite order. While these results are in agreement with recent numerical
work, our study provides an independent, unbiased means of determining the
phase boundaries by using quantum information analysis, yields values for the
location of some of the phase boundaries that differ from those previously
found, and provides insight into the limitations of numerical methods in
determining phase boundaries, especially those of infinite-order transitions.Comment: 8 pages, 7 figure
Determination of the Weak Axial Vector Coupling from a Measurement of the Beta-Asymmetry Parameter A in Neutron Beta Decay
We report on a new measurement of the neutron beta-asymmetry parameter
with the instrument \perkeo. Main advancements are the high neutron
polarization of from a novel arrangement of super mirror
polarizers and reduced background from improvements in beam line and shielding.
Leading corrections were thus reduced by a factor of 4, pushing them below the
level of statistical error and resulting in a significant reduction of
systematic uncertainty compared to our previous experiments. From the result
, we derive the ratio of the axial-vector to the vector
coupling constant Comment: 5 pages, 4 figure
Measurement of the Neutrino Asymmetry Parameter B in Neutron Decay
A new measurement of the neutrino asymmetry parameter B in neutron decay, the
angular correlation between neutron spin and anti-neutrino momentum, is
presented. The result, B=0.9802(50), agrees with the Standard Model expectation
and earlier measurements, and permits improved tests on ``new physics'' in
neutron decay.Comment: 4 pages, 2 figures; v2: revised PRL versio
Measurement of the Proton Asymmetry Parameter C in Neutron Beta Decay
The proton asymmetry parameter C in neutron decay describes the correlation
between neutron spin and proton momentum. In this Letter, the first measurement
of this quantity is presented. The result C=-0.2377(26) agrees with the
Standard Model expectation. The coefficient C provides an additional parameter
for new and improved Standard Model tests. From a differential analysis of the
same data (assuming the Standard Model), we obtain lambda=-1.275(16) as ratio
of axial-vector and vector coupling constant.Comment: 4 pages, 2 figure
Characterization of a ballistic supermirror neutron guide
We describe the beam characteristics of the first ballistic supermirror
neutron guide H113 that feeds the neutron user facility for particle physics
PF1B of the Institute Laue-Langevin, Grenoble (ILL). At present, the neutron
capture flux density of H113 at its 20x6cm2 exit window is 1.35x10^10/cm^2/s,
and will soon be raised to above 2x10^10/cm^2/s. Beam divergence is no larger
than beam divergence from a conventional Ni coated guide. A model is developed
that permits rapid calculation of beam profiles and absolute event rates from
such a beam. We propose a procedure that permits inter-comparability of the
main features of beams emitted from ballistic or conventional neutron guides.Comment: 15 pages, 11 figures, to be submitted to Nuclear Instruments and
Methods
Bestimmung der Haftfestigkeit von aufgedampften, metallischen Dickschichten auf Polymersubstrat
Inaktivkomponenten in der Batterieherstellung, wie z. B. Stromsammler, Separator oder die Kontaktierungstaps rücken zunehmend in den Fokus der Forschung. Der Wechsel zu leichteren und günstigeren Materialien ist Gegenstand aktueller Forschungsarbeiten. In diesem Zusammenhang wird auch das Potential von Verbundstromkollektoren näher betrachtet. Dabei handelt es sich um Polymerfolien, die beidseitig mit 0,5 µm bis 1,5 µm dicken Aluminium- oder Kupferschichten metallisiert sind. Als Verbundmaterial müssen dabei im Vergleich zu konventionellen, metallischen Stromkollektoren zusätzliche Materialeigenschaften betrachtet werden. Dazu gehört vor allem die
Haftfestigkeit der metallischen Beschichtungen auf den Folien. Es muss ausgeschlossen werden, dass durch wechselnde mechanische Beanspruchungen oder chemische Wechselwirkungen (z.B. mit dem Elektrolyten) in der Li-Ionen-Batteriezelle
Delaminationen auftreten und sich die Metallisierung ablöst. Dazu ist eine quantitative Methode zur Bestimmung der Haftfestigkeit notwendig. Nur so kann eine Korrelation zwischen der Haftfestigkeit und dem Verhalten in der Zelle hergestellt werden. Bisherige Versuchsmethoden decken den Anwendungsfall von beidseitig metallisierten Polymersubstraten als Stromkollektorfolie jedoch nicht ab. Aus diesem Grund werden in dieser Studie Prüfverfahren zur Bestimmung der Haftfestigkeit, die bereits in Normen spezifiziert werden, zur Bewertung der Haftfestigkeiten der Verbundfolien adaptiert und bewertet. Die betrachteten Verfahren umfassen Schälversuche, Stirnabzugs- und Zugschertests, welche hinsichtlich ihrer Eignung zur Beurteilung der Haftfestigkeit von Verbundstromkollektoren evaluiert werden. Dabei werden Verbundfolien mit unterschiedlicher Schicht- sowie Substratdicke und variierendem Beschichtungsmaterial berücksichtigt, sodass die Sensitivität der Verfahren zur Bestimmung der Haftfestigkeit aufgelöst und darauf aufbauend deren Eignung zur Charakterisierung der Verbundfolien bewertet werden kann
Mixing of mineral dust with urban pollution aerosol over Dakar (Senegal): Impact on dust physico-chemical and radiative properties.
In the framework of the Saharan Mineral Dust Experiment (SAMUM) in 2008, the mixing of the urban pollution
plume of Dakar (Senegal) with mineral dust was studied in detail using the German research aircraft Falcon which was
equipped with a nadir-looking high spectral resolution lidar (HSRL) and extensive aerosol in situ instrumentation. The
mineral dust layer as well as the urban pollution plume were probed remotely by the HSRL and in situ. Back trajectory
analyses were used to attribute aerosol samples to source regions.We found that the emission from the region of Dakar
increased the aerosol optical depth (532 nm) from approximately 0.30 over sea and over land east of Dakar to 0.35 in the city outflow. In the urban area, local black carbon (BC) emissions, or soot respectively, contributed more than 75% to aerosol absorption at 530 nm. In the dust layer, the single-scattering albedo at 530 nm was 0.96 � 0.99, whereas
we found a value of 0.908 �± 0.018 for the aerosol dominated by urban pollution. After 6h of transport over the North
Atlantic, the externally mixed mode of secondary aerosol particles had almost completely vanished, whereas the BC
agglomerates (soot) were still externally mixed with mineral dust particles
A Chern-Simons approach to Galilean quantum gravity in 2+1 dimensions
We define and discuss classical and quantum gravity in 2+1 dimensions in the
Galilean limit. Although there are no Newtonian forces between massive objects
in (2+1)-dimensional gravity, the Galilean limit is not trivial. Depending on
the topology of spacetime there are typically finitely many topological degrees
of freedom as well as topological interactions of Aharonov-Bohm type between
massive objects. In order to capture these topological aspects we consider a
two-fold central extension of the Galilei group whose Lie algebra possesses an
invariant and non-degenerate inner product. Using this inner product we define
Galilean gravity as a Chern-Simons theory of the doubly-extended Galilei group.
The particular extension of the Galilei group we consider is the classical
double of a much studied group, the extended homogeneous Galilei group, which
is also often called Nappi-Witten group. We exhibit the Poisson-Lie structure
of the doubly extended Galilei group, and quantise the Chern-Simons theory
using a Hamiltonian approach. Many aspects of the quantum theory are determined
by the quantum double of the extended homogenous Galilei group, or Galilei
double for short. We study the representation theory of the Galilei double,
explain how associated braid group representations account for the topological
interactions in the theory, and briefly comment on an associated
non-commutative Galilean spacetime.Comment: 38 pages, 1 figure, references update
Selective targeting of activating and inhibitory Smads by distinct WWP2 ubiquitin ligase isoforms differentially modulates TGFβ signalling and EMT
Ubiquitin-dependent mechanisms have emerged as essential regulatory elements controlling cellular levels of Smads and TGFß-dependent biological outputs such as epithelial–mesenchymal transition (EMT). In this study, we identify a HECT E3 ubiquitin ligase known as WWP2 (Full-length WWP2-FL), together with two WWP2 isoforms (N-terminal, WWP2-N; C-terminal WWP2-C), as novel Smad-binding partners. We show that WWP2-FL interacts exclusively with Smad2, Smad3 and Smad7 in the TGFß pathway. Interestingly, the WWP2-N isoform interacts with Smad2 and Smad3, whereas WWP2-C interacts only with Smad7. In addition, WWP2-FL and WWP2-C have a preference for Smad7 based on protein turnover and ubiquitination studies. Unexpectedly, we also find that WWP2-N, which lacks the HECT ubiquitin ligase domain, can also interact with WWP2-FL in a TGFß-regulated manner and activate endogenous WWP2 ubiquitin ligase activity causing degradation of unstimulated Smad2 and Smad3. Consistent with our protein interaction data, overexpression and knockdown approaches reveal that WWP2 isoforms differentially modulate TGFß-dependent transcription and EMT. Finally, we show that selective disruption of WWP2 interactions with inhibitory Smad7 can stabilise Smad7 protein levels and prevent TGFß-induced EMT. Collectively, our data suggest that WWP2-N can stimulate WWP2-FL leading to increased activity against unstimulated Smad2 and Smad3, and that Smad7 is a preferred substrate for WWP2-FL and WWP2-C following prolonged TGFß stimulation. Significantly, this is the first report of an interdependent biological role for distinct HECT E3 ubiquitin ligase isoforms, and highlights an entirely novel regulatory paradigm that selectively limits the level of inhibitory and activating Smads
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