Abstract-Correlation Between Saturated Fatty Acid Chain-Length and Intermolecular Forces Determined with Terahertz Spectroscopy

 Shuting Fan,  Michael Ruggiero,  Zhengfang Qian,  Vincent P. Wallace

https://chemrxiv.org/articles/Correlation_Between_Saturated_Fatty_Acid_Chain-Length_and_Intermolecular_Forces_Determined_with_Terahertz_Spectroscopy/7553054

We measured crystalline (C-form) saturated fatty acids with even carbon numbers ranging from 12 to 20 using temperature dependent terahertz time-domain spectroscopy (THz-TDS). Absorption features between 0.5 to 2.75 THz were identified at temperatures from 96 K to 293 K, and a systematic red-shift was observed with the increasing carbon chain length. The origins of these absorption bands were uncovered using state-of-the-art ab initio density functional theory (DFT) calculations. Similar vibrational motions in the absorption bands of the different materials highlight the unique role that THz-TDS has for probing weak non-covalent interactions in these materials. Our results showcase the utility of the terahertz region, which is beyond the scope of related vibrational techniques, providing direct evidence of the effect of chain length on the intermolecular interactions of these molecules.

Abstract-Quantitative characterization of bovine serum albumin thin-films using terahertz spectroscopy and machine learning methods

Yiwen Sun, Pengju Du, Xingxing Lu, Pengfei Xie, Zhengfang Qian, Shuting Fan, and Zexuan Zhu

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-7-2917

The development of new spectral analysis methods in bio thin-film detection has generated intense interest in terahertz (THz) spectroscopy and its application in a wide range of fields. In this paper, it is the first time that machine learning methods are applied to the quantitative characterization of bovine serum albumin (BSA) deposited thin-films detected by terahertz time-domain spectroscopy. The spectra data of BSA thin-films prepared by solutions with concentrations ranging from 0.5 to 35 mg/ml are analyzed using the support vector regression method to learn the underlying model of the frequency against the target concentration. The learned mode successfully predicts the concentrations of the unknown test samples with a coefficient of determination R2 = 0.97932. Furthermore, aiming to identify the relevance of each frequency to the concentration, the maximal information coefficient statistical analysis is used and the three most discriminating frequencies in THz frequency are identified at 1.2, 1.1 and 0.5 THz respectively, which means a good prediction for BSA concentration can be achieved by using the top three relevant frequencies. Moreover, the top discriminating frequencies are in good agreement with the frequencies predicted by a long-wavelength elastic vibration model for BSA protein.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Backward Wave Radiation from the Interaction of High-order Mode and Double Sheet Electron Beams

Guoxiang Shu1, Guo Liu2, Le Chen3, Hasitha Bambarandage4 and Zhengfang Qian5


http://iopscience.iop.org/article/10.1088/1361-6463/aaa20e/pdf



Terahertz (THz) radiation obtained from the interaction between multiple sheet electron beams and a high-order mode (HOM) provides an effective method to extend the operating frequency and power capacity. Two ridges were introduced in the double staggered grating waveguide slow wave structure (SWS) to achieve a suitable band-gap between the HOM and low-order mode (LOM) for the HOM operation of a backward wave oscillator (BWO). The dispersion and transmission simulations of this improved SWS showed that a good frequency selective property was achieved and the LOM competition was effectively suppressed. Particle-in-cell analysis predicted that the HOM BWO could radiate >0.46 W output power in the range of 1.19-1.24 THz. It is indicated that the HOM BWO is a promising compact radiation source for generating high power THz-wave.