Development of underwater housings for the deep sea made of ultra-high performance concrete (UHPC) and long-term testing at the Arctic Sea
The aim of this research is the design and analysis of underwater housings made of ultra-high performance concrete (UHPC) within the Helmholtz Alliance “ROBEX” (robotic exploration of extreme environments) [1]. Due to the extremely corrosive maritime environment, mainly expensive materials such as titanium, ceramics, special stainless steel and aluminum are used so far for the construction of temporary and permanent research stations to guarantee long-term deployment. In this project the suitability of high-strength concrete with compressive strength up to 210 MPa for underwater pressure housings and constructions is examined to provide a low cost and durable alternative especially for large housings in future.
Influence of Compressive Strength and Wall Thickness on Behavior of Concrete Cylindrical Hulls Under Hydrostatic Loading
Abstract : Sixteen unreinforced, cylindrical concrete hull models of 16-inch outside diameter were subjected to external hydrostatic loading to determine the effect of concrete strength and wall thickness on implosion and strain behavior. The test results showed that an increase in concrete strength of 70% produced an average increase in implosion pressure of 87%, while increases in hull wall thickness by factors of 2 and 6 produced increases in implosion pressure by factors of approximately 2 and 11, respectively. Changes in concrete strength had little effect on strain behavior; however, strain magnitudes generally increased with increasing wall thickness when comparisons were made at a constant percentage of P(im). Design recommendations are presented to aid in the design of cylindrical concrete hulls for underwater use.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.