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

Real-time terahertz imaging with a single-pixel detector

Terahertz (THz) radiation is poised to have an essential role in many imaging applications, from industrial inspections to medical diagnosis. However, commercialization is prevented by impractical and expensive THz instrumentation. Single-pixel cameras have emerged as alternatives to multi-pixel cameras due to reduced costs and superior durability. Here, by optimizing the modulation geometry and post-processing algorithms, we demonstrate the acquisition of a THz-video (32 × 32 pixels at 6 frames-per-second), shown in real-time, using a single-pixel fiber-coupled photoconductive THz detector. A laser diode with a digital micromirror device shining visible light onto silicon acts as the spatial THz modulator. We mathematically account for the temporal response of the system, reduce noise with a lock-in free carrier-wave modulation and realize quick, noise-robust image undersampling. Since our modifications do not impose intricate manufacturing, require long post-processing, nor sacrifice the time-resolving capabilities of THz-spectrometers, their greatest asset, this work has the potential to serve as a foundation for all future single-pixel THz imaging systems

The Mandate of Shepherding: A Socio-Rhetorical Analysis of Shepherding Metaphor Scriptures and Phenomenological Study of a New Shepherding Pastoral Leadership Model

Pastors are increasingly taking on a CEO style of leadership to lead their churches (Goodmanson, 2005; Maddox, 2012; Whitaker, 2013). Pastors have made this shift at the expense of a shepherd mindset, seemingly creating a dichotomy between styles (Tara, 2020; Whitaker, 2013). Consequently, scholars have identified an increasing trend in pastoral burnout (Fee, 2018; Hessel, 2015; Samushonga, 2021). The current study evaluated the pastoral role and its responsibility from a place of Scripture, while also considering popular current leadership trends. The findings revealed a clear shepherd metaphor arc throughout Scripture, beginning in Psalm 23 and ending in 1 Peter 5. The pinnacle of these passages is the Good Shepherd passage of John 10, where Jesus provided a contrast in leadership styles (Carson, 2015; Keener, 1993; Laniak, 2006; Whitacre, 1999). By using John 10 as a focus of the socio-rhetorical method made popular by Robbins (1996a, 1996b) and Henson et al. (2020), 10 critical characteristics of shepherding useful to the church today were identified: spiritual feeding, protection, care, inspection, familiarity, selflessness, willingness, modeling, stewardship, and leadership. Moreover, nine senior pastors were interviewed as part of a phenomenological study to compare their experiences with these 10 themes. The findings of this study provided a clear shepherding model, its foundation within Scripture, its ramifications and implementation within real-world experiences, and provided a firm argument that leadership should be secondary to the role of shepherding for the pastor. A thorough discussion of this new shepherd construct is provided as well as practical implications

Terahertz reflectometry of burn wounds in a rat model

We present sub-millimeter wave reflectometry of an experimental rat skin burn model obtained by the Terahertz Time-Domain Spectroscopy (THz-TDS) technique. Full thickness burns, as confirmed by histology, were created on rats (n = 4) euthanized immediately prior to the experiments. Statistical analysis shows that the burned tissue exhibits higher reflectivity compared to normal skin over a frequency range between 0.5 and 0.7 THz (p < 0.05), likely due to post-burn formation of interstitial edema. Furthermore, we demonstrate that a double Debye dielectric relaxation model can be used to explain the terahertz response of both normal and less severely burned rat skin. Finally, our data suggest that the degree of conformation between the experimental burn measurements and the model for normal skin can potentially be used to infer the extent of burn severity

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

Super sub-nyquist single-pixel imaging by total variation ascending ordering of the Hadamard absis

Single pixel imaging (SPI) captures images without array detectors or raster scanning. When combined with compressive sensing techniques it enables novel solutions for high-speed optical imaging and spectroscopy. However, when it comes to the real-time capture and analysis of a fast event, the challenge is the inherent trade-off between frame rate and image resolution. Due to the lack of sufficient sparsity and the intrinsic iterative process, conventional compressed sensing techniques have limited improvement in capturing natural scenes and displaying the images in real time. In this work, we demonstrate a novel alternative compressive imaging approach employing an efficient and easy-implementation sampling scheme based on reordering the deterministic Hadamard basis through their total variation. By this means, the number of measurements and acquisition are reduced significantly without needing complex minimization algorithms. We can recover a 128 × 128 image with a sampling ratio of 5% at the signal peak signal-to-noise ratio (PSNR) of 23.8 dB, achieving super sub-Nyquist sampling SPI. Compared to other widely used sampling e.g. standard Hadamard protocols and Gaussian matrix methods, this approach results in a significant improvement both in the compression ratio and image reconstruction quality, enabling SPI for high frame rate imaging or video applications

How to study basement membrane stiffness as a biophysical trigger in prostate cancer and other age-related pathologies or metabolic diseases

Here we describe a protocol that can be used to study the biophysical microenvironment related to increased thickness and stiffness of the basement membrane (BM) during age-related pathologies and metabolic disorders (e.g. cancer, diabetes, microvascular disease, retinopathy, nephropathy and neuropathy). The premise of the model is non-enzymatic crosslinking of reconstituted BM (rBM) matrix by treatment with glycolaldehyde (GLA) to promote advanced glycation endproduct (AGE) generation via the Maillard reaction. Examples of laboratory techniques that can be used to confirm AGE generation, non-enzymatic crosslinking and increased stiffness in GLA treated rBM are outlined. These include preparation of native rBM (treated with phosphate-buffered saline, PBS) and stiff rBM (treated with GLA) for determination of: its AGE content by photometric analysis and immunofluorescent microscopy, its non-enzymatic crosslinking by ((sodium dodecyl sulfate polyacrylamide gel electrophoresis)) (SDS PAGE) as well as confocal microscopy, and its increased stiffness using rheometry. The procedure described here can be used to increase the rigidity (elastic moduli, E) of rBM up to 3.2-fold, consistent with measurements made in healthy versus diseased human prostate tissue. To recreate the biophysical microenvironment associated with the aging and diseased prostate gland three prostate cell types were introduced on to native rBM and stiff rBM: RWPE-1, prostate epithelial cells (PECs) derived from a normal prostate gland; BPH-1, PECs derived from a prostate gland affected by benign prostatic hyperplasia (BPH); and PC3, metastatic cells derived from a secondary bone tumor originating from prostate cancer. Multiple parameters can be measured, including the size, shape and invasive characteristics of the 3D glandular acini formed by RWPE-1 and BPH-1 on native versus stiff rBM, and average cell length, migratory velocity and persistence of cell movement of 3D spheroids formed by PC3 cells under the same conditions. Cell signaling pathways and the subcellular localization of proteins can also be assessed

In-line evanescent-field-coupled THz bandpass mux/demux fabricated by additive layer manufacturing technology

In this research, we present the design, fabrication, and experimental validation of 3D printed bandpass filters and mux/demux elements for terahertz frequencies. The filters consist of a set of in-line polystyrene (PS) rectangular waveguides, separated by 100 µm, 200 µm, and 400 µm air gaps. The principle of operation for the proposed filters resides in coupled-mode theory. Q-factors of up to 3.4 are observed, and additionally, the experimental evidence demonstrates that the Q-factor of the filters can be improved by adding fiber elements to the design. Finally, using two independent THz broadband channels, we demonstrate the first mux/demux device based on 3D printed in-line filters for the THz range. This approach represents a fast, robust, and low-cost solution for the next generation of THz devices for communications

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

Development of a novel invertebrate indexing tool for the determination of salinity in aquatic inland drainage channels

Salinisation of freshwater habitats is an issue with global implications that can have serious detrimental effects on the environment resulting in an overall loss in biodiversity. Whilst increases in salinity can occur naturally, such anthropogenic actions as the disposal of industrial and urban effluents and the disturbance of natural hydrological cycles can also result in the salinisation of freshwater habitats. The Water Framework Directive (WFD) requires Member States to restore all freshwater habitats to “good ecological status” and to prevent any further deterioration. Macro-invertebrates are widely used as indicators of river condition for a wide range of reasons and have been designated a key biological element in the assessment of aquatic habitats by the WFD. A review of the available literature, however, found no macro-invertebrate-based biotic indices have been developed for the detection and determination of salinity increases in freshwater habitats that are suitable for application in the United Kingdom for the purposes of the WFD. To this end, a biotic index based on the aquatic macro-invertebrate community response to changes in salinity, termed the Salinity Association Group (SAG) index, was developed. The potential of the SAG index for assessing water quality in terms of salinity in freshwater systems was investigated using data collected from survey sites in Lincolnshire and Norfolk, England, and the results compared to several published salinity indices. Whilst the SAG index was found to show both geographic and seasonal dependence, as is common among many biotic indices, the proposed metric exhibited a stronger relationship to salinity than macro-invertebrate indices employed in Europe for the purposes of the WFD show to their specific pressure. Furthermore, the SAG index was found to be highly selective to only salinity concentration, was significantly related to salinity when used with less detailed information and significantly discriminated between the salinity classes defined by the WFD. It is also highlighted that application of the SAG index with such predictive models as the River InVertebrate Prediction And Classification System (RIVPACS) can resolve the exhibited geographical and seasonal dependence. In a comparison of the SAG index with the published indices, it was found that the SAG index was the superior metric in terms of recognising abundance as required by the WFD, reliably indicating changes in salinity, compatibility with sampling protocols employed by England’s regulatory authority and producing a linear output. Consequently, it was concluded that the SAG index surpasses other published metrics for the detection and determination of salinity increases in freshwater habitats and is a viable biomonitoring tool suitable for use in England for informing aquatic habitat management decisions, research application and the purposes of the WFD. It is proposed, however, that more rigorous sampling protocols for both macro-invertebrate and environmental data may result in more accurate metric scores and reveal further issues or benefits associated with the SAG index and could also be used to further refine the metric. It is also suggested that adaptation and examination of the SAG index at a larger geographical scale would further demonstrate the validity of the proposed metric and illustrate the potential of the SAG index for worldwide application. Furthermore, intercalibration of the SAG index to harmonise WFD reference conditions and class boundaries across Europe would allow the application of the SAG index throughout Europe for the purpose of the WFD