Flat telescope based on an all-dielectric metasurface doublet enabling polarization-controllable enhanced beam steering

A flat telescope (FTS), which incorporates an all-dielectric metasurface doublet (MD) based on hydrogenated amorphous silicon nanoposts, is proposed and demonstrated to achieve flexibly magnified angular beam steering that is sensitive to both light polarization and deflection direction. Specifically, for transverse-electric-polarized incident beams, the MD exhibits deflection magnification factors of +5 and +2, while for transverse magnetic polarization, the beam is steered in reverse to yield magnification factors of −5 and −2 in the horizontal and vertical directions, respectively. The proposed MD comprises cascaded metalenses, which can invoke polarization-selective transmission phases. The MD which emulates a set of convex and concave lenses renders positively increased beam deflection, whereas the case corresponding to a pair of convex lenses facilitates negatively amplified beam deflection. The essential phase profiles required for embodying the MD are efficiently extracted from its geometric lens counterpart. Furthermore, the implemented FTS, operating in the vicinity of a 1550 nm wavelength, can successfully enable enhanced beam steering by facilitating polarization-sensitive bidirectional deflection amplifications. The proposed FTS can be applied in the development of a miniaturized light detection and ranging system, where the beam scanning range can be effectively expanded in two dimensions.

Simplified method of analysis of adjacent precast “deck free” concrete box beams used in accelerated bridge construction

The prefabricated bridge is common method in construction since it provides controlled environmental conditions and long-term durability. These adjacent precast box beams are placed side by side with 15mm gaps, the top flanges connected with longitudinal shear keys poured on-site to assist in truckload distribution. Since the concrete-filled joints provide transverse shear rigidity, the load transferred from one beam to another takes place through transverse shear. A parametric study is conducted to investigate the accuracy of simplified analysis method in CHBDC for shear-connected beams to the adjacent box beams. A 3D finite-element was conducted on a wide range of box beams to obtain their magnification factors for moment and shear when subjected to truck loading. The obtained results were correlated with CHBDC and a more reliable simplified equations for distribution factors was developed. Special attention was given to the limitations of CHBDC simplified method and how it can be revised to include the adjacent box-beam.

Simplified method of analysis of adjacent precast “deck free” concrete box beams used in accelerated bridge construction

The prefabricated bridge is common method in construction since it provides controlled environmental conditions and long-term durability. These adjacent precast box beams are placed side by side with 15mm gaps, the top flanges connected with longitudinal shear keys poured on-site to assist in truckload distribution. Since the concrete-filled joints provide transverse shear rigidity, the load transferred from one beam to another takes place through transverse shear. A parametric study is conducted to investigate the accuracy of simplified analysis method in CHBDC for shear-connected beams to the adjacent box beams. A 3D finite-element was conducted on a wide range of box beams to obtain their magnification factors for moment and shear when subjected to truck loading. The obtained results were correlated with CHBDC and a more reliable simplified equations for distribution factors was developed. Special attention was given to the limitations of CHBDC simplified method and how it can be revised to include the adjacent box-beam.

Levels of selected pesticides and trophic transfer of DDTs through the aquatic food web in the Lake Ziway ecosystem

The levels of 27 selected pesticides and trophic biomagnification of DDT were investigated in biota samples of the Lake Ziway in the Rift valley region, Ethiopia. Pesticide residues were analyzed using gas chromatography coupled with mass spectrometry (GC MS). Carbon source and trophic position were calculated by using 13C and 15N stable isotopes, individually, and trophic magnification factors (TMFs) were inferred. Among pesticides analyzed, only DDT and its metabolites (o,pʹ-DDD, o,pʹ-DDE, p,pʹ-DDD, and p,pʹ-DDE) were quantified in biota samples. The most prominent metabolite was p,pʹ-DDE with mean concentration ranging from the 0.22-7.7ngg− 1 wet weight. Moreover, the ratio of DDT/DDD + DDE in all the biota samples was less than 1 signifying historical DDT application. The trophic magnification factor (TMF) for p,pʹ-DDE, and ΣDDT were 1.18 and 1.19 respectively. Regression of log [ΣDDT] vs TL (trophic level) among all biota species showed a significant correlation, indicating that DDTs are biomagnifying along with the food web of Lake Ziway. The concentrations of DDTs and other organochlorine pesticides found in biota from Lake Ziway were, in general, lower than studies found in previous studies carried out in the same lake.

Numerical simulation of transient processes in propeller shaft straining under ice loads

Object and purpose of research. The object of the research is the shaftline of an icebreaker and ice-going vessels, the purpose is to develop an algorithm for determining the loads for calculating the strength of the shafts of icebreakers and icegoing vessels under ice loads in a nonlinear dynamic setting and determining the dynamic magnification factor. Materials and methods. The study is based on finite element method (FEM). Main results. As a result of numerical analysis, the magnification factors of ice loads acting on the propeller shaft when vessel moves in an ice field up to 4 m thick are investigated. Conclusion. The research results can be used to calculate the fatigue strength of the icebreakers and ice-going vessels shaftlines.