Objective and efficient terahertz signal denoising by transfer function reconstruction

As an essential processing step in many disciplines, signal denoising efficiently improves data quality without extra cost. However, it is relatively under-utilized for terahertz spectroscopy. The major technique reported uses wavelet denoising in the time-domain, which has a fuzzy physical meaning and limited performance in low-frequency and water-vapor regions. Here, we work from a new perspective by reconstructing the transfer function to remove noise-induced oscillations. The method is fully objective without a need for defining a threshold. Both reflection imaging and transmission imaging were conducted. The experimental results show that both low- and high-frequency noise and the water-vapor influence were efficiently removed. The spectrum accuracy was also improved, and the image contrast was significantly enhanced. The signal-to-noise ratio of the leaf image was increased up to 10 dB, with the 6 dB bandwidth being extended by over 0.5 THz

Classification for glucose and lactose Terahertz spectra based on SVM and DNN methods

In recent decades, terahertz (THz) radiation has been widely applied in many chemical and biomedical areas. Due to its ability to resolve the absorption features of many compounds noninvasively, it is a promising technique for chemical recognition of substances such as drugs or explosives. A key challenge for THz technology is to be able to accurately classify spectral measurements acquired in unknown complicated environments, rather than those from ideal laboratory conditions. Support vector machine (SVM) and deep neural networks (DNNs) are powerful and widely adopted approaches for complex classification with a high accuracy. In this article, we explore and apply the SVM and DNN methods for classifying the frequency spectra of glucose and lactose. We measured 372 groups of independent signals under different conditions to provide a sufficient training set. The classification accuracies achieved were 99% for the SVM method and 89.6% for the DNN method. These high classification accuracies demonstrate great potential in chemical recognition

An introduction to terahertz time-domain spectroscopic ellipsometry

Terahertz spectroscopy has mainly been performed based on terahertz time-domain spectroscopy systems in a transmission or a window/prism-supported reflection configuration. These conventional approaches have limitations in characterizing opaque solids, conductive thin-films, multiple-layer structures and anisotropic materials. Ellipsometry is a self-reference characterization technique with a wide adaptibility that can be applied for nearly all sample types. However, terahertz ellipsometry has not yet been widely applied, mainly due to the critical requirement on the optical setting, the large discrepancy to traditional terahertz spectroscopy and conventional optical ellipsometry. In this paper we introduce terahertz time-domain spectroscopic ellipsometry from the basic concept, theory, optical configuration, error calibration to characterization methods. Experimental results on silicon wafers of different resistivities are presented as examples. This paper is serving as a tutorial to provide key technical guidance and skills for accurate terahertz time-domain spectroscopic ellipsometry

Genetic algorithm based optimization for terahertz time-domain adaptive sampling

We propose a genetic algorithm (GA) based method to improve the sampling efficiency in THz time domain spectroscopy (THz-TDS). For a typical time domain THz signal, most information are contained in a short region of the pulse which needs to be densely sampled, while the other regions fluctuating around zero can be represented by fewer points. Based on this clustering feature of the THz signal, we can use much fewer sampling points and optimize the distribution by using a GA to achieve an accurate scanning in less time. Both reflection and transmission measurements were conducted to experimentally verify the performance. The measurement results show that the sampling time can be greatly reduced while maintaining very high accuracy both in the time-domain and frequency-domain compared with a high-resolution step scan. This method significantly improves the measurement efficiency. It can be easily adapted to most THz-TDS systems equipped with a mechanical delay stage for fast detection and THz imaging

Inhibition of Aurora B by CCT137690 sensitizes colorectal cells to radiotherapy

Colorectal cancer is the third most commonly diagnosed cancer worldwide. Although surgery remains the best treatment for this disease, adjuvant chemotherapy and radiotherapy are also very important in clinical practice. However, the notorious refractory lack of responses to radiochemotherapy greatly limits the application of radiochemotherapy in the context of colorectal cancer. There is a growing interest in the role that Aurora B may play in colorectal cancer cell survival as well as other cancer subtypes. In the current study, we sought to ascertain whether blocking of Aurora B signaling machinery by a small molecule inhibitor, CCT137690, could synergize radiation-induced colorectal cancer cell death. Results showed that CCT137690 increases the sensitivity of SW620 cells to radiation. Mechanistic studies revealed that Aurora B-Survivin pathway may be involved in this synergistic effect. Taken together, our results for the first time show that Aurora B inhibition and radiation exert a synergistic effect, resulting in enhanced colorectal cancer cell death. This synergistic effect is clinically relevant as lower doses of radiation could be used for cancer treatment, and could provide significant clinical benefits in terms of colorectal cancer management, while reducing unwanted side-effects

Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides

We propose a multilayer geometry to characterize thin-film samples in reflection terahertz time domain spectroscopy. Theory indicates that this geometry has higher sensitivity compared to ordinary transmission or reflection geometries when characterizing both low- and high-absorption samples. Pure water and water–ethanol mixtures are measured to verify the characterization accuracy of the proposed geometry and its capability to measure trace liquids. Paraffin-embedded oral cancer tissue is imaged to further show how the proposed geometry enhances the sensitivity for solid low-absorptive films

Highly efficient ultra‐broadband terahertz modulation using bidirectional switching of liquid crystals

Accurately manipulating field strength and polarization state are essential in various terahertz applications. Such manipulations are based on the efficient modulation of the amplitude and phase of electromagnetic waves. However, there is a lack of such terahertz modulators with sufficient efficiency and bandwidth. Herein, the Brewster–critical angle is exploited for modulation by using a nematic liquid crystal. Unlike liquid crystal phase shifters that only give a narrowband phase delay via a one‐directional switch, the presented device modulates both the amplitude and phase across an ultra‐broadbandwidth via a bidirectional active switch. An average intensity modulation depth over 99.6% is achieved for 0.2–1.6 THz. Furthermore, highly accurate polarization conversion between linear and circular states is also realized for 0.4–1.8 THz, with the average degree of linear and circular polarizations as high as 0.994 and 0.998, respectively. The superior accuracy, bandwidth, and active control achieved provide great potential for multifunctional terahertz modulation

Self-reported Rates of Abuse, Neglect, and Bullying Experienced by Transgender and Gender-Nonbinary Adolescents in China

open access articleImportance This is the first comprehensive national study reporting the rates of abuse, neglect, and bullying from family and classmates or teachers among Chinese transgender and gender-nonbinary adolescents and identifying risk factors associated with poor mental health in this population. Objective To assess the rates of abuse, neglect, and bullying and their association with poor mental health among Chinese transgender and gender nonbinary adolescents. Design, Setting, and Participants This national survey study used an online self-selecting survey conducted between January 1, 2017, and September 29, 2017, in China. Eligibility criteria included reporting being aged 12 to 18 years and being transgender or gender nonbinary. Data analysis was performed from March 25 to 28, 2019. Main Outcomes and Measures The main outcome was self-reported poor mental health, including depressive symptoms, anxiety symptoms, and suicidal ideation. Depressive symptoms were measured using the Center for Epidemiological Studies Depression 9-item scale. Anxiety symptoms were measured using the 7-item General Anxiety Disorder scale. Suicidal ideation was measured using standardized questions adapted from previous Chinese studies. Abuse, neglect, and bullying were measured using specifically designed questions. Results Of 564 responses collected, 385 respondents (mean [SD] age, 16.7 [1.2] years) met inclusion criteria, including 109 (28.3%) transgender adolescent boys, 167 (43.4%) transgender adolescent girls, and 109 (28.3%) gender-nonbinary adolescents. Among 319 respondents who reported that their parents were aware of their gender identity, 296 (92.8%) reported having experienced parental abuse or neglect. Among the full cohort, 295 respondents (76.6%) reported having experienced abuse or bullying owing to being transgender or gender nonbinary in school from classmates or teachers. There were 173 respondents (44.9%) with Center for Epidemiological Studies Depression 9-item scale scores indicating they were at risk of major depressive disorder, and 148 respondents (38.4%) had 7-item General Anxiety Disorder scale scores indicating they were at risk of an anxiety disorder. In univariate analysis, reporting experiences of bullying from a classmate or teacher was significantly associated with suicidal ideation (odds ratio, 1.68 [95% CI, 1.04-2.70]; P = .03), but the association was no longer statistically significant after controlling for level of educational attainment, aversion to assigned sex, and depressed mood at the onset of puberty (odds ratio, 1.63 [95% CI, 0.97-2.73]; P = .06). Conclusions and Relevance In this survey study, transgender and gender-nonbinary adolescents in China reported high rates of abuse, neglect, and bullying at home and in school and high rates of symptoms associated with poor mental health. This study highlights the importance of reducing home- and school-based abuse, neglect, and bullying of transgender and gender-nonbinary adolescents in China to improve mental health outcomes; however, broader change in the social environment may be required to address the prejudice and stigma aimed at gender minorities