1,261 research outputs found
On rigid supersymmetry and notions of holomorphy in five dimensions
We study the equations governing rigid N=1 supersymmetry in five dimensions.
If the supersymmetry spinor satisfies a reality condition, these are foliations
admitting families of almost complex structures on the leaves. In other words,
all these manifolds have families of almost Cauchy-Riemann (CR) structures.
After deriving integrability conditions under which circumstances the almost CR
structure defines a CR manifold or a transversally holomorphic foliation (THF),
we discuss implications on localization. We also discuss potential global
obstructions to the existence of solutions.Comment: 14 pages; typos corrected; references adde
The Charge Collection Properties of CVD Diamond
The charge collection properties of CVD diamond have been investigated with
ionising radiation. In this study two CVD diamond samples, prepared with
electrical contacts have been used as solid state ionisation chambers. The
diamonds have been studied with beta particles and 10 keV photons, providing a
homogeneous ionisation density and with protons and alpha particles which are
absorbed in a thin surface layer. For the latter case a strong decrease of the
signal as function of time is observed, which is attributed to polarisation
effects inside the diamond. Spatially resolved measurements with protons show a
large variation of the charge collection efficiency, whereas for photons and
minimum ionising particles the response is much more uniform and in the order
of 18%. These results indicate that the applicability of CVD diamond as a
position sensitive particle detector depends on the ionisation type and appears
to be promising for homogeneous ionisation densities as provided by
relativistic charged particles.Comment: 26 pages (Latex), submitted to NIM
Anomalous Spontaneous Reversal in Magnetic Heterostructures
We observe a thermally induced spontaneous magnetization reversal of
epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied
magnetic field. Unlike any other magnetic system, the magnetization
spontaneously reverses, aligning anti-parallel to an applied field with
decreasing temperature. We show that this unusual phenomenon is caused by the
interfacial antiferromagnetic coupling overcoming the Zeeman energy of the
ferromagnet. A significant temperature hysteresis exists, whose height and
width can be tuned by the field applied during thermal cycling. The hysteresis
originates from the intrinsic magnetic anisotropy in the system. The
observation of this phenomenon leads to open questions in the general
understanding of magnetic heterostructures. Moreover, this shows that in
general heterogeneous nanostructured materials may exhibit unexpected phenomena
absent in the bulk.Comment: 14 pages, 4 figure
Efficient Singlet Fission and Triplet-Pair Emission in a Family of Zethrene Diradicaloids.
Singlet fission offers the potential to overcome thermodynamic limits in solar cells by converting the energy of a single absorbed photon into two distinct triplet excitons. However, progress is limited by the small family of suitable materials, and new chromophore design principles are needed. Here, we experimentally vindicate the design concept of diradical stabilization in a tunable family of functionalized zethrenes. All molecules in the series exhibit rapid formation of a bound, spin-entangled triplet-pair state TT. It can be dissociated by thermally activated triplet hopping and exhibits surprisingly strong emission for an optically "dark" state, further enhanced with increasing diradical character. We find that the TT excited-state absorption spectral shape correlates with the binding energy between constituent triplets, providing a new tool to understand this unusual state. Our results reveal a versatile new family of tunable materials with excellent optical and photochemical properties for exploitation in singlet fission devices
Chronic–Progressive Dopaminergic Deficiency Does Not Induce Midbrain Neurogenesis
Background: Consecutive adult neurogenesis is a well-known phenomenon in the ventricular–subventricular zone of the lateral wall of the lateral ventricles (V–SVZ) and has been controversially discussed in so-called “non-neurogenic” brain areas such as the periventricular regions (PVRs) of the aqueduct and the fourth ventricle. Dopamine is a known modulator of adult neural stem cell (aNSC) proliferation and dopaminergic neurogenesis in the olfactory bulb, though a possible interplay between local dopaminergic neurodegeneration and induction of aNSC proliferation in mid/hindbrain PVRs is currently enigmatic. Objective/Hypothesis: To analyze the influence of chronic–progressive dopaminergic neurodegeneration on both consecutive adult neurogenesis in the PVRs of the V–SVZ and mid/hindbrain aNSCs in two mechanistically different transgenic animal models of Parkinson´s disease (PD). Methods: We used Thy1-m[A30P]h α synuclein mice and Leu9′Ser hypersensitive α4* nAChR mice to assess the influence of midbrain dopaminergic neuronal loss on neurogenic activity in the PVRs of the V–SVZ, the aqueduct and the fourth ventricle. Results: In both animal models, overall proliferative activity in the V–SVZ was not altered, though the proportion of B2/activated B1 cells on all proliferating cells was reduced in the V–SVZ in Leu9′Ser hypersensitive α4* nAChR mice. Putative aNSCs in the mid/hindbrain PVRs are known to be quiescent in vivo in healthy controls, and dopaminergic deficiency did not induce proliferative activity in these regions in both disease models. Conclusions: Our data do not support an activation of endogenous aNSCs in mid/hindbrain PVRs after local dopaminergic neurodegeneration. Spontaneous endogenous regeneration of dopaminergic cell loss through resident aNSCs is therefore unlikely
Identification and functional characterization of DR6, a novel death domain‐containing TNF receptor
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116991/1/feb2s0014579398007911.pd
Relationformer: A Unified Framework for Image-to-Graph Generation
A comprehensive representation of an image requires understanding objects and their mutual relationship, especially in image-to-graph generation, e.g., road network extraction, blood-vessel network extraction, or scene graph generation. Traditionally, image-to-graph generation is addressed with a two-stage approach consisting of object detection followed by a separate relation prediction, which prevents simultaneous object-relation interaction. This work proposes a unified one-stage transformer-based framework, namely Relationformer, that jointly predicts objects and their relations. We leverage direct set-based object prediction and incorporate the interaction among the objects to learn an object-relation representation jointly. In addition to existing [obj]-tokens, we propose a novel learnable token, namely [rln]-token. Together with [obj]-tokens, [rln]-token exploits local and global semantic reasoning in an image through a series of mutual associations. In combination with the pair-wise [obj]-token, the [rln]-token contributes to a computationally efficient relation prediction. We achieve state-of-the-art performance on multiple, diverse and multi-domain datasets that demonstrate our approach's effectiveness and generalizability
Brillouin light storage for 100 pulse widths
Signal processing based on stimulated Brillouin scattering (SBS) is limited
by the narrow linewidth of the optoacoustic response, which confines many
Brillouin applications to continuous wave signals or optical pulses longer than
several nanoseconds. In this work, we experimentally demonstrate Brillouin
interactions at the 150 ps time scale and a delay for a record 15 ns which
corresponds to a delay of 100 pulse widths. This breakthrough experimental
result was enabled by the high local gain of the chalcogenide waveguides as the
optoacoustic interaction length reduces with pulse width. We successfully
transfer 150ps-long pulses to traveling acoustic waves within a Brillouin-based
memory setup. The information encoded in the optical pulses is stored for 15 ns
in the acoustic field. We show the retrieval of eight amplitude levels,
multiple consecutive pulses and low distortion in pulse shape. The extension of
Brillouin-based storage to the ultra-short pulse regime is an important step
for the realisation of practical Brillouin-based delay lines and other optical
processing applications.Comment: 6 pages, 6 figure
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