The energy of light generally moves forward along the light propagation direction. However, in recent years, a counter-intuitive effect has been discovered that energy backflow can occur in certain special light fields. Presently, controlling the energy backflow of light for application requirements is becoming a significant challenge. Here we propose a method to generate and control a three-dimensional helical energy backflow (HEB) optical field. By designing an exponential helical conical phase mask, the energy backflow region in a common tightly focused field can be stretched into a three-dimensional helical shape with an ultra-long longitudinal length. The length of the HEB region can be flexibly extended up to 47.6λ by varying the exponential phase index and the initial topological charge. Furthermore, we demonstrate that nanoparticles within the HEB field are subjected to optical pulling forces, thereby drawing the nanoparticles back to the light source. This work presents a new, to the best of our knowledge, approach for the three-dimensional manipulation of the energy backflow field with potential applications in nanoparticle manipulation and detection.
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http://dx.doi.org/10.1364/OL.540915 | DOI Listing |
Polymers (Basel)
January 2025
Department of Mechanical Engineering, University of Massachusetts Lowell, Lowell, MA 01854, USA.
This study presents the design, modeling, and validation of a mixing screw for energy-efficient single-screw extrusion. The screw features a short length-to-diameter (L/D) ratio of 8:1 and incorporates double flights with variable pitch and counter-rotating mixing slots. These features promote enhanced plastication by breaking up the solid bed and improving thermal homogeneity through backflow mechanisms relieving a 3.
View Article and Find Full Text PDFPolymers (Basel)
January 2025
Guangdong Engineering Technology Research Center of Small Household Appliances Innovation Design and Manufacturing, School of Mechanical Engineering, Guangdong Ocean University, Zhanjiang 524088, China.
During the production of medical thin-walled tubes, a thin coating layer is required. This requirement reduces the cross-sectional clearance area of the straight section flow channel formed by the mandrel and the die, leading to excessive pressure of the polymer melt at the shaping section, elevated die pressure, and backflow of the material melt, all of which directly impact the quality of the coating layer. To address these issues, this study conducted a non-isothermal numerical simulation of coating models both with and without a shaping section.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
December 2024
Department of Biochemistry and Biophysics, Stockholm University, Stockholm 10691, Sweden.
Photosystem II (PSII) catalyzes light-driven water oxidation that releases dioxygen into our atmosphere and provides the electrons needed for the synthesis of biomass. The catalysis occurs in the oxygen-evolving oxo-manganese-calcium (MnOCa) cluster that drives the oxidation and deprotonation of substrate water molecules leading to the O formation. However, despite recent advances, the mechanism of these reactions remains unclear and much debated.
View Article and Find Full Text PDFJ Hazard Mater
December 2024
Institute of Nuclear Energy Safety Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui 230031, China. Electronic address:
Vegetation barriers are an important environmental characteristic of spent fuel road transportation accidents. Spent fuel vessels may be affected by force majeure factors during transportation, which leads to damage to spent fuel assemblies and containers and can cause radionuclides to gradually release from assemblies to vessels to the external environment. In this work, considering the growth periods of coniferous vegetation barriers and vessel type, a radionuclide dispersion model based on computational fluid dynamics (CFD) was established by adding a decay term and a pressure loss term.
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