Design of a See-through Off-Axis Head-Mounted-Display Optical System with an Ellipsoidal Surface

Junhua Wang,Qing Zhou,Jie Chen,Lexin Hou,Min Xu 한국광학회 2018 Current Optics and Photonics Vol.2 No.3

A new method to design a see-through off-axis head-mounted-display (OA-HMD) optical system with an ellipsoidal surface is proposed, in which a tilted ellipsoidal surface is used as the combiner, which yields the benefits of easier fabrication and testing compared to a freeform surface. Moreover, we realize a coaxial structure in the relay lens group, which is simple and has looser tolerance requirements, thus making assembly easier. The OA-HMD optical system we realize has a simple structure and consists of a combiner and 7 pieces of coaxial relay lenses. It has a 48° × 36° field of view (FOV) and 12-mm exit pupil diameter.

Background-noise Reduction for Fourier Ptychographic Microscopy Based on an Improved Thresholding Method

Lexin Hou,Hexin Wang,Junhua Wang,Min Xu 한국광학회 2018 Current Optics and Photonics Vol.2 No.2

Fourier ptychographic microscopy (FPM) is a recently proposed computational imaging method that achieves both high resolution (HR) and wide field of view. In the FPM framework, a series of low-resolution (LR) images at different illumination angles is used for high-resolution image reconstruction. On the basis of previous research, image noise can significantly degrade the FPM reconstruction result. Since the captured LR images contain a lot of dark-field images with low signal-to-noise ratio, it is very important to apply a noise-reduction process to the FPM raw dataset. However, the thresholding method commonly used for the FPM data preprocessing cannot separate signals from background noise effectively. In this work, we propose an improved thresholding method that provides a reliable background-noise threshold for noise reduction. Experimental results show that the proposed method is more efficient and robust than the conventional thresholding method.

The synthesis and characterization of polymer-coated FeAu multifunctional nanoparticles

Liu, HongLing,Hou, Peng,Zhang, WengXing,Kim, Young Keun,Wu, JunHua IOP Pub 2010 Nanotechnology Vol.21 No.33

<P>We report the one-pot nanoemulsion synthesis of FeAu magnetic-optical multifunctional nanoparticles coated by the biocompatible triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO). The FTIR study confirms the PEO-PPO-PEO molecules on the surface of the resulting nanoparticles. The structural characterization identifies the crystallographic parameter 4.072 Å of the cubic phase and the morphology analysis gives the nanoparticle shape, size and size distribution, showing the high crystallinity of the FeAu nanoparticles and an average particle size of ∼ 6.5 nm. In addition there is direct confirmation of the alloying by elemental point probing of an individual nanoparticle. Following the visual demonstration of a rapid, efficient and reversible dispersion–collection process of the nanoparticles in solution, the magnetic measurement manifests a soft ferromagnetic behavior of the nanoparticles with a small coercivity of ∼ 60 Oe at room temperature. The corresponding magnetic hysteresis curves were effectively assessed by modified bi-phase Langevin equations, which were satisfactorily explained in terms of a bimodal particle size distribution. The UV–vis studies display the broadband absorption of the PEO-PPO-PEO-coated nanoparticles with the maximum surface plasmon resonance around 585 nm. The characterization and analysis, therefore, shows the unification of iron and gold into one alloy nanostructure entity covered by the biocompatible triblock copolymer thin film, preserving the optical and magnetic properties of the individual constituents. This gives the prospect of enhanced performance in applications. </P>

The Effect of Oxygen Vacancies and Strain on the Curie Temperature of La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO₃ Films

Rongrong Ma,Junhua Hou,Hu Yang 한국자기학회 2018 Journal of Magnetics Vol.23 No.3

The effects of oxygen vacancies and strain on the magnetism and Curie temperature of La0.7Sr0.3MnO₃ (LSMO) thin films deposited by PLD are investigated by changing oxygen partial pressure and increasing the interface mismatch between LSMO and SrTiO₃. The presence of oxygen vacancies reduces the double exchange effect between Mn<SUP>3+</SUP> and Mn<SUP>4+</SUP> ions, and the high-quality crystals effectively increase the Curie temperature of LSMO. Moreover, SrTiO₃ simultaneously exerts strain on the upper and lower interfaces of the LSMO film to promote orbital reconstruction of the eg electrons in the Mn<SUP>3+</SUP> ions. These electrons preferentially occupy the eg(x<SUP>2</SUP>-y<SUP>2</SUP>) orbit and lead to an enhancement in the in-plane ferromagnetic exchange effect, thereby increasing the Curie temperature. These results suggest that the magnetic properties of these materials can be controlled through artificial structure design and provide guidance for their application in high Curie temperature spintronic devices.

Repair of flange damage steel-concrete composite girders using CFRP sheets

Lianguang Wang,Wenyu Hou,Huafeng Han,Junhua Huo 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.3

Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy-bonded carbon fiber-reinforced polymer (CFRP) sheets to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of seven composite girders made of I20A steel sections and 80mm-thick by 900mm-wide concrete slabs were prepared and tested. CFRP sheets and prestressed CFRP sheets were used to repair the specimens. The specimens lost the cross-sectional area of their tension flanges with 30%, 50% and 100%. The results showed that CFRP sheets had no significant effect on the yield loads of strengthened composite girders, but had significant effect on the ultimate loads. The yield loads, elastic stiffness, and ultimate bearing capacities of strengthened composite girders had been changed as a result of prestressed CFRP sheets, the utilization ratio of CFRP sheets could be effectively improved by applying prestress to CFRP sheets. Both the yield loads and ultimate bearing capacities had been changed as a result of steel beam’s flange damage level and CFRP sheets could cover the girders’ shortage of bearing capacity with 30% and 50% flange damage, respectively.

Non-aqueous synthesis of water-dispersible Fe₃O₄–Ca₃(PO₄)₂ core–shell nanoparticles

Liu, HongLing,Wu, JunHua,Min, Ji Hyun,Hou, Peng,Song, Ah-Young,Kim, Young Keun IOP Pub 2011 Nanotechnology Vol.22 No.5

<P>The Fe<SUB>3</SUB>O<SUB>4</SUB>–Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> core–shell nanoparticles were prepared by one-pot non-aqueous nanoemulsion with the assistance of a biocompatible triblock copolymer, poly(ethylene glycol)-<I>block</I>-poly(propylene glycol)-<I>block</I>-poly(ethylene glycol) (PEO–PPO–PEO), integrating the magnetic properties of Fe<SUB>3</SUB>O<SUB>4</SUB> and the bioactive functions of Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> into single entities. The Fe<SUB>3</SUB>O<SUB>4</SUB> nanoparticles were pre-formed first by thermal reduction of Fe(acac)<SUB>3</SUB> and then the Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> layer was coated by simultaneous deposition of Ca<SUP>2 + </SUP> and PO<SUB>4</SUB><SUP>3 − </SUP>. The characterization shows that the combination of the two materials into a core–shell nanostructure retains the magnetic properties and the Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> shell forms an hcp phase (<I>a</I> = 7.490 Å, <I>c</I> = 9.534 Å) on the Fe<SUB>3</SUB>O<SUB>4</SUB> surface. The magnetic hysteresis curves of the nanoparticles were further elucidated by the Langevin equation, giving an estimation of the effective magnetic dimension of the nanoparticles and reflecting the enhanced susceptibility response as a result of the surface covering. Fourier transform infrared (FTIR) analysis provides the characteristic vibrations of Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> and the presence of the polymer surfactant on the nanoparticle surface. Moreover, the nanoparticles could be directly transferred to water and the aqueous dispersion–collection process of the nanoparticles was demonstrated for application readiness of such core–shell nanostructures in an aqueous medium. Thus, the construction of Fe<SUB>3</SUB>O<SUB>4</SUB> and Ca<SUB>3</SUB>(PO<SUB>4</SUB>)<SUB>2</SUB> in the core–shell nanostructure has conspicuously led to enhanced performance and multi-functionalities, offering various possible applications of the nanoparticles.</P>