Spin/momentum properties of the paraxial optical beams

Spin angular momentum, an elementary dynamical property of classical electromagnetic fields, plays an important role in spin-orbit and light-matter interactions, especially in near-field optics. The research on optical spins has led to the discovery of phenomena such as optical spin-momentum locking and photonic topological quasiparticles, as well as applications in high-precision detection and nanometrology. Here, we investigate spin-momentum relations in paraxial optical systems and show that the optical spin angular momentum contains transverse and longitudinal spin components simultaneously. The transverse spin originates from inhomogeneities of field and governed by the vorticity of the kinetic momentum density, whereas the longitudinal spin parallel to the local canonical momentum is proportional to the polarization ellipticity of light. Moreover, the skyrmionlike spin textures arise from the optical transverse spin can be observed in paraxial beams, and their topologies are maintained free from the influence of the Gouy phase during propagation. Interestingly, the optical singularities, including both phase and polarization singularities, can also affect the spin-momentum properties significantly. Our findings describe the intrinsic spin-momentum properties in paraxial optical systems and apply in the analysis of the properties of spin-momentum in optical focusing, imaging, and scattering systems.Comment: 20 pages; 6 figures, 151 reference

Root-knot nematode (Meloidogyne incognita) infection alters vegetative growth and nitrogen uptake and distribution in grapevine

Root-knot nematodes (RKN, Meloidogyne spp.) manipulate host cell developmental processes to build specialized feeding structure from which the larvae enlist nutrients. Nitrogen (N) is one of the most important components of plant metabolites, and isotopic tracers make it possible for us to study the transportation of the nitrogen metabolites in the whole plant. In order to figure out vegetative and physiological responses caused by RKN infection in vine, pot experiment was performed in this paper. The results showed that RKN infection weakened vine vigor with decreased biomass and increased root-shoot ratio. Whereas, before bursting the galls exhibited a higher metabolic activity, in comparison with control root, the root dehydrogenase activities improved 85 % and 71 % in the galls and adjacent roots respectively. In addition, RKN infection didn’t significantly alter nitrogen content and distribution in various tissues, which might be due to feeding pressure or duration. 15N Root labeling results indicated that RKN infection enhanced Nitrogen derived from fertilizer (Ndff) and nitrogen utilization efficiency of the annual root. It suggested that RKN temporarily turned grape root into nitrogen sinks to meet their demand. Finally, the infected plant retained relatively few storage nutrients in the root and shoot after defoliation

PrivGraph: Differentially Private Graph Data Publication by Exploiting Community Information

Graph data is used in a wide range of applications, while analyzing graph data without protection is prone to privacy breach risks. To mitigate the privacy risks, we resort to the standard technique of differential privacy to publish a synthetic graph. However, existing differentially private graph synthesis approaches either introduce excessive noise by directly perturbing the adjacency matrix, or suffer significant information loss during the graph encoding process. In this paper, we propose an effective graph synthesis algorithm PrivGraph by exploiting the community information. Concretely, PrivGraph differentially privately partitions the private graph into communities, extracts intra-community and inter-community information, and reconstructs the graph from the extracted graph information. We validate the effectiveness of PrivGraph on six real-world graph datasets and seven commonly used graph metrics.Comment: To Appear in the 32nd USENIX Security Symposiu

The hidden spin-momentum locking and topological defects in unpolarized light fields

Electromagnetic waves characterized by intensity, phase, and polarization degrees of freedom are widely applied in data storage, encryption, and communications. However, these properties can be substantially affected by phase disorders and disturbances, whereas high-dimensional degrees of freedom including momentum and angular momentum of electromagnetic waves can offer new insights into their features and phenomena, for example topological characteristics and structures that are robust to these disturbances. Here, we discover and demonstrate theoretically and experimentally spin-momentum locking and topological defects in unpolarized light. The coherent spin is locked to the kinetic momentum except for a small coupling spin term, due to the simultaneous presence of transverse magnetic and electric components in unpolarized light. To cancel the coupling term, we employ a metal film acting as a polarizer to form some skyrmion-like spin textures at the metal/air interface. Using an in-house scanning optical microscopic system to image the out-of-plane spin density of the focused unpolarized vortex light, we obtained experimental results that coincide well with our theoretical predictions. The theory and technique promote the applications of topological defects in optical data storage, encryption, and decryption, and communications.Comment: 9 pages, 3 figures, 47 reference