9,550 research outputs found
Design of a New CIM-DCSK-Based Ambient Backscatter Communication System
To improve the data rate in differential chaos shift keying (DCSK) based
ambient backscatter communication (AmBC) system, we propose a new AmBC system
based on code index modulation (CIM), referred to as CIM-DCSK-AmBC system. In
the proposed system, the CIM-DCSK signal transmitted in the direct link is used
as the radio frequency source of the backscatter link. The signal format in the
backscatter link is designed to increase the data rate as well as eliminate the
interference of the direct link signal. As such, the direct link signal and the
backscatter link signal can be received and demodulated simultaneously.
Moreover, we derive and validate the theoretical bit error rate (BER)
expressions of the CIM-DCSK-AmBC system over multipath Rayleigh fading
channels. Regarding the short reference DCSK-based AmBC (SR-DCSK-AmBC) system
as a benchmark system, numerical results reveal that the CIM-DCSK-AmBC system
can achieve better BER performance in the direct link and higher throughput in
the backscatter link than the benchmark system
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SAM-dependent enzyme-catalysed pericyclic reactions in natural product biosynthesis.
Pericyclic reactions-which proceed in a concerted fashion through a cyclic transition state-are among the most powerful synthetic transformations used to make multiple regioselective and stereoselective carbon-carbon bonds. They have been widely applied to the synthesis of biologically active complex natural products containing contiguous stereogenic carbon centres. Despite the prominence of pericyclic reactions in total synthesis, only three naturally existing enzymatic examples (the intramolecular Diels-Alder reaction, and the Cope and the Claisen rearrangements) have been characterized. Here we report a versatile S-adenosyl-l-methionine (SAM)-dependent enzyme, LepI, that can catalyse stereoselective dehydration followed by three pericyclic transformations: intramolecular Diels-Alder and hetero-Diels-Alder reactions via a single ambimodal transition state, and a retro-Claisen rearrangement. Together, these transformations lead to the formation of the dihydropyran core of the fungal natural product, leporin. Combined in vitro enzymatic characterization and computational studies provide insight into how LepI regulates these bifurcating biosynthetic reaction pathways by using SAM as the cofactor. These pathways converge to the desired biosynthetic end product via the (SAM-dependent) retro-Claisen rearrangement catalysed by LepI. We expect that more pericyclic biosynthetic enzymatic transformations remain to be discovered in naturally occurring enzyme 'toolboxes'. The new role of the versatile cofactor SAM is likely to be found in other examples of enzyme catalysis
Text-driven Editing of 3D Scenes without Retraining
Numerous diffusion models have recently been applied to image synthesis and
editing. However, editing 3D scenes is still in its early stages. It poses
various challenges, such as the requirement to design specific methods for
different editing types, retraining new models for various 3D scenes, and the
absence of convenient human interaction during editing. To tackle these issues,
we introduce a text-driven editing method, termed DN2N, which allows for the
direct acquisition of a NeRF model with universal editing capabilities,
eliminating the requirement for retraining. Our method employs off-the-shelf
text-based editing models of 2D images to modify the 3D scene images, followed
by a filtering process to discard poorly edited images that disrupt 3D
consistency. We then consider the remaining inconsistency as a problem of
removing noise perturbation, which can be solved by generating training data
with similar perturbation characteristics for training. We further propose
cross-view regularization terms to help the generalized NeRF model mitigate
these perturbations. Our text-driven method allows users to edit a 3D scene
with their desired description, which is more friendly, intuitive, and
practical than prior works. Empirical results show that our method achieves
multiple editing types, including but not limited to appearance editing,
weather transition, material changing, and style transfer. Most importantly,
our method generalizes well with editing abilities shared among a set of model
parameters without requiring a customized editing model for some specific
scenes, thus inferring novel views with editing effects directly from user
input. The project website is available at http://sk-fun.fun/DN2NComment: Project Website: http://sk-fun.fun/DN2
1-(3-Pyridyl)pyrrolidine-2,5-dione
In the title molecule, C9H8N2O2, the dihedral angle between the pyridine and the pyrrolidine rings is 64.58 (12)°. In the crystal structure, weak C—H⋯π-electron ring interactions stabilize the packing
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