Search for light dark matter from atmosphere in PandaX-4T

We report a search for light dark matter produced through the cascading decay of $\eta$ mesons, which are created as a result of inelastic collisions between cosmic rays and Earth's atmosphere. We introduce a new and general framework, publicly accessible, designed to address boosted dark matter specifically, with which a full and dedicated simulation including both elastic and quasi-elastic processes of Earth attenuation effect on the dark matter particles arriving at the detector is performed. In the PandaX-4T commissioning data of 0.63 tonne$\cdot$year exposure, no significant excess over background is observed. The first constraints on the interaction between light dark matter generated in the atmosphere and nucleus through a light scalar mediator are obtained. The lowest excluded cross-section is set at $5.9 \times 10^{-37}{\rm cm^2}$ for dark matter mass of $0.1$ MeV$/c^2$ and mediator mass of 300 MeV$/c^2$. The lowest upper limit of $\eta$ to dark matter decay branching ratio is $1.6 \times 10^{-7}$

A Search for Light Fermionic Dark Matter Absorption on Electrons in PandaX-4T

We report a search on a sub-MeV fermionic dark matter absorbed by electrons with an outgoing active neutrino using the 0.63 tonne-year exposure collected by PandaX-4T liquid xenon experiment. No significant signals are observed over the expected background. The data are interpreted into limits to the effective couplings between such dark matter and electrons. For axial-vector or vector interactions, our sensitivity is competitive in comparison to existing astrophysical bounds on the decay of such dark matter into photon final states. In particular, we present the first direct detection limits for an axial-vector (vector) interaction which are the strongest in the mass range from 25 to 45 (35 to 50) keV/c$^2$

Preparation and characterization of polypyrrole films for three-dimensional micro supercapacitor

Institute for Microsystems Technology at Vestfold University College; Pen-Tung Sah MEMS research center in Xiamen University; State Key laboratory for Physical chemistry of solid surfaces in Xiamen Unive rsityAs electro-active electrodes for supercapacitors, micro polypyrrole (PPy) films doping with ClO(4)(-) (PPY(ClO4)) and Cl(-) (PPy(Cl)) are prepared on Ni layers modified three-dimensional (3D) structures in Si substrates. The key process to fabricate the 3D structures is high-aspect-ratio deep reactive ion etching, which result in significant increase of available surface area. Homogeneous conformal Ni layers and PPy films are deposited on the 3D structures by electroless plating and electropolymerization, respectively. The supercapacitor properties of PPy films are investigated by using cyclic voltammetry (CV). electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge with three-electrode system in NaCl solution. It is shown that doping with ClO(4)(-) results in ideal supercapacitor behaviors with rectangle-like CV shapes at scan rates from 5 to 200 mV s(-1), linear galvanostatic charge/discharge curves at current loads from 0.5 to 2 mA and stable cyclic property. However, doping with Cl(-) gives rise to non-ideal properties of supercapacitor. SEM of the PPY(ClO4) shows that the surface of the PPY(ClO4) electrode is smooth and the thickness of the PPY(ClO4) film is about 2.5 mu m. The geometric capacitance of PPY(ClO4) is calculated as 0.030 F cm(-2) from CV at scan rate of 100 mV s(-1), 0.023 F cm(-2) from EIS and 0.027 F cm(-2) from galvanostatic discharge at 1 mAcm(-2) current density. (C) 2009 Elsevier B.V. All rights reserved

Porous Thin-Wall Hollow Co3O4 Spheres for Supercapacitors with High Rate Capability

In this study, a zeolitic imidazolate framework-67 (ZIF-67) was prepared as a precursor using a facile hydrothermal method. After a calcination reaction in the air, the as-prepared precursor was converted to porous thin-wall hollow Co3O4 with its original frame structure almost preserved. The physical and chemical characterizations of the nanomaterial were analyzed systemically. The electrochemical tests indicate that the obtained Co3O4 possesses large specific capacitances of 988 and 925 F/g at 1 and 20 A/g accompanying an outstanding rate capability (a 93.6% capacitance retention) and retains 96.6% of the specific capacitance, even after 6000 continuous charge/discharge cycles. These excellent properties mark the Co3O4 a promising electrode material for high performance supercapacitors

Application of Artificial Neural Network Based on Traditional Detection and GC-MS in Prediction of Free Radicals in Thermal Oxidation of Vegetable Oil

In this study, electron paramagnetic resonance (EPR) and gas chromatography-mass spectrometry (GC-MS) techniques were applied to reveal the variation of lipid free radicals and oxidized volatile products of four oils in the thermal process. The EPR results showed the signal intensities of linseed oil (LO) were the highest, followed by sunflower oil (SO), rapeseed oil (RO), and palm oil (PO). Moreover, the signal intensities of the four oils increased with heating time. GC-MS results showed that (E)-2-decenal, (E,E)-2,4-decadienal, and 2-undecenal were the main volatile compounds of oxidized oil. Besides, the oxidized PO and LO contained the highest and lowest contents of volatiles, respectively. According to the oil characteristics, an artificial neural network (ANN) intelligent evaluation model of free radicals was established. The coefficients of determination (R2) of ANN models were more than 0.97, and the difference between the true and predicted values was small, which indicated that oil profiles combined with chemometrics can accurately predict the free radical of thermal oxidized oil

Fabrication and tests of a novel three dimensional micro supercapacitor

Conference Name:34th International Conference on Micro- and Nano-Engineering. Conference Address: Athens, GREECE. Time:SEP 15-18, 2008.A three dimensional (3D) micro supercapacitor was designed with an interdigital structure which increases surface area by about 20 times compared with planar structure for the same footprint. The supercapacitor consisting of current collectors, electrodes and solid state electrolyte, was micromachined using UV lithography, RF magnetron sputtering, electroplating, electrochemical polymerization and spin coating methods. Electrochemical tests showed that the single electrode can be used for supercapacitor in application of broad frequency range up to 300 Hz and the specific capacitance of the 3D supercapacitor was about 0.03 F cm(-2) while the specific was about 2 mW cm(-2) at relative large discharge rate. (C) 2008 Elsevier B.V. All rights reserved

Symmetric redox supercapacitor based on micro-fabrication with three-dimensional polypyrrole electrodes

To achieve higher energy density and power density, we have designed and fabricated a symmetric redox supercapacitor based on microelectromechanical system (MEMS) technologies. The supercapacitor consists of a three-dimensional (3D) microstructure on silicon substrate micromachined by high-aspect-ratio deep reactive ion etching (DRIE) method, two sputtered Ti current collectors and two electrochemical polymerized polypyrrole (PPy) films as electrodes. Electrochemical tests, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatical charge/discharge methods have been carried out on the single PPy electrodes and the symmetric supercapacitor in different electrolytes. The specific capacitance (capacitance per unit footprint area) and specific power (power per unit footprint area) of the PPy electrodes and symmetric supercapacitor can be calculated from the electrochemical test data. It is found that NaCl solution is a good electrolyte for the polymerized PPy electrodes. In NaCl electrolyte, single PPy electrodes exhibit 0.128 F cm(-2) specific capacitance and 1.28 mW cm(-2) specific power at 20 mV s(-1) scan rate. The symmetric supercapacitor presents 0.056 F cm(-2) specific capacitance and 0.56 mW cm(-2) specific power at 20 mV s(-1) scan rate. (C) 2010 Elsevier B.V. All rights reserved

Characterizing and smoothing of striated sidewall morphology on UV-exposed thick SU-8 structures for micromachining millimeter wave circuits

Sidewall roughness is a critical parameter when a thick SU-8 process is employed for fabricating millimeter wave circuits, as it determines the conduction loss of the circuit. A striated sidewall morphology was detected in our UV-exposed thick SU-8 structure, and this rough morphology was clearly illustrated and quantitatively characterized by a confocal laser scanning microscope (CLSM) for the first time. The rms line roughness of the striated sidewall is up to similar to 1 mu m, several-fold higher than the skin depth of copper at 220 GHz. We also tried to discuss the possible causes of sidewall striations. A proper counter measure, i.e. higher temperature and longer baking time of post-exposure bake, was effectively employed to flatten the sidewall striations. It was found that the rms line roughness on the sidewall detected by the CLSM is reduced to similar to 72 nm, for the sample post-exposure-baked at 107 degrees C

Laser Spatial Coherence Suppression With Refractive Optical Elements Toward the Improvement of Speckle Reduction by Light Pipes

We study laser speckle reduction by light pipes, and we propose a new method to improve its efficiency. Proof-of-concept refractive optical elements (ROEs) with a staircase-like structure are introduced before a holographic diffuser to split a laser beam into laser sub-beams. Optical paths of the laser sub-beams after transmitting through the ROEs are different, and these partially correlated (or uncorrelated) laser sub-beams are added in intensity basis because of the folded mirror reflections by the light pipe. Thus, laser spatial coherence is suppressed, which helps to reduce speckle. We demonstrate this method in a simplified laser projection system, where subjective speckle contrast is reduced from 0.33 to 0.24 before and after introducing a two-dimensional ROE, respectively. Comparing with other improved speckle reduction methods by light pipes, the proposed method is motionless and simpler