Simulation and optimization of reflection optical module design for single LED

Illuminance uniformity and illuminating efficiency are always the key problems of light emitting diode (LED) lighting system design. Based on the new design of the reflection optical module, illuminance uniformity and illuminating efficiency are investigated simultaneously in this paper. At the first stage, a reflector with various profile designs is installed to improve the uniformity and efficiency of irradiances collected through the receiver. Using the macro commands, an effective process is presented through the optimal design of the reflector geometries, and the merit function is used as the optical quality objective to find the optimal design value of $K2$ K 2 and $R2$ R 2 parameters of the reflector. At the second stage, based on the optimal design result, the displacement between LED source and reflector is further adjusted automatically by the macro commands too. The results from the ray tracing simulation indicate that the optimal design can be achieved through the compromise of Illuminance uniformity and illuminating efficiency. Finally, we obtain the merit function value of $1.81$ 1.81 with $K2=-1.09, R2=1.11\,\hbox {mm}$ K 2 = - 1.09 , R 2 = 1.11 mm , and the source position $Z1= 1.68\,\hbox {mm}$ Z 1 = 1.68 mm . The results shown in this paper could be beneficial for machine vision systems which are heavily demanded in the light source applications for the uniform and efficient illuminance.     

Carbon Dioxide Measurement Based on Multimode Diode Laser Correlation Spectroscopy Employing Wavelength Modulation Techniques

The use of a tunable multimode diode laser system based on correlation spectroscopy and wavelength modulation spectroscopy to measure the concentration of the carbon dioxide in ambient air through the 2 υ₁ + 2υ₂ + υ₃ absorption lines around 1570 nm is reported. The carbon dioxide concentrations are derived from the relationship between the normalized second-harmonic signal peak heights of the measurement and reference signals. The validation of the system is conducted by a set of experiments with controlled carbon dioxide and nitrogen mixtures. The correlation and standard deviation between the measured and actual carbon dioxide concentrations are 0.9973 and 4.03%, respectively, over the tested range. A detection limit of 340 ppm m was achieved using 30 successive measurements during 30 min. All these results demonstrated potential utility of the system for carbon dioxide sensing.     

Study on LiFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript>/C used as cathode materials for lithium-ion batteries with low Sm component

LiFe_1???x Sm _x PO₄/C cathode materials were synthesized though a facile hydrothermal method. Compared with high-temperature solid-phase sintering, the method can allow for the fabrication of low Sm content (2 %), a scarce and expensive rare earth element, while the presence of an optimized carbon coating with large amount of sp²-type carbon sharply increases the material’s electrochemical performance. The high-rate dischargeability at 5 C, as well as the exchange current density, can be increased by 21 and 86 %, respectively, which were attributed to the fine size and the large cell parameter a/c as much. It should be pointed out that the a/c value will be increased for the LiFePO₄ Sm-doped papered by both of the two methods, while the mechanism is different: The value c is increased for the front and the value a is decreased for the latter, respectively.     

Two-level injection in fiber-delay line based oscillator

Two-level injection-locked opto-electronic oscillator is proposed for low phase noise. Dielectric resonator oscillator (DRO) is used as the first injection source, injection locking a long-fiber loop based opto-electronic oscillator, then its output is injection locking another long-fiber opto-electronic oscillator for getting a lower-phase noise output carrier. After the first injection, the single side band (SSB) phase noise at 10 kHz offset frequency decreases from −123 dBc/Hz to −135 dBc/Hz, then through the second injection the SSB phase noise drops down to −146 dBc/Hz.     

Iterative temporal clustering analysis for the detection of multiple response peaks in fMRI

The temporal clustering analysis (TCA) is a novel and effective technique for obtaining brain activation maps when the timing and location of the activation are completely unknown. Performing the TCA method once can only detect the largest peak of the activation time windows well, if multiple response peaks at the same location of the brain occur. However, this limitation can be removed by using a TCA method in an iterative way in order for the smaller peaks to be detected. Our in vivo fMRI experiments with event-related visual tasks have demonstrated this ability.     

On the Upper Bound of Second Eigenvalues for Uniformly Elliptic Operators of any Orders

Abstract Let Ω R~m(m≥1)be a bounded domain with piecewise smooth boundary Ω.Let t and r bepositive integers with t>r+1. We consider the eigenvalue problems(1.1)and(12),and obtain Theorem 1and Theorem 2, which generalize the results in[1,2.5].     

All fiber supercontinuum light source using photonic crystal fibers pumped by nanosecond fiber laser pulses

A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened through nonlinear effects of PCF.     

Effect of the laser fluence on the surface characterization of β-FeSi2 films prepared by pulsed laser deposition

Single-phase β-FeSi₂ films on silicon (1 0 0) were fabricated by pulse laser deposition. The structure and crystal quality of the samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The field scanning electron microscopy showed that the film thickness increases with the increasing of the laser fluence. Moreover, atomic force microscopy observations revealed the changes of surface properties with different laser fluence. Based upon all experimental results, it is found that 7 J/cm² is the most favorable for the formation of β-FeSi₂ thin films.     

Characteristic of high-organized PS/BPS photonic crystals

B2O3-P2O5-SiO2 (BPS) three-dimensional (3D) high-organized polystyrene (PS) opals and inverse opals with large domain were fabricated and characterized.