Agent Identification Using a Sparse Bayesian Model

The -carotene is a short chain polyene molecule containing nine -electron conjugated double-bonds. Because of its special molecular structure, -carotene has been used widely in many fields, including functional materials, optoelectronic devices and biological applications of light collection, light protection, anti-cancer, etc. Recently, new applications of -carotene in generation and detection of terahertz (THz) wave have also attracted great attention. In this work, all-trans -carotene films are prepared by spray coating, and the THz spectra in a wavenumber range of 30-400 cm-1 (a frequency range of 0.9-12 THz) of the as-prepared products are experimentally measured at room temperature by Fourier transform infrared spectroscopy. For comparison, the THz spectra in 0.5-3.0 THz are also characterized at the same temperature by THz time-domain spectroscopy. Based on these measurements, the fingerprint peaks of all-trans -carotene in the THz region are experimentally identified to be located at 54 cm-1 (1.62 THz), 57 cm-1 (1.71 THz), 64 cm-1 (1.91 THz), 77 cm-1 (2.32 THz), 90 cm-1 (2.69 THz), 98 cm-1 (2.95 THz), 115 cm-1 (3.45 THz), 124 cm-1 (3.72 THz), 134 cm-1 (4.02 THz), 170 cm-1 (5.11 THz), 247 cm-1 (7.42 THz), and 279 cm-1 (8.38 THz), respectively. It is worth noting that the recent results about the THz spectra of palm leaves are thus verified. Particularly, the B3 LYP method of density functional theory is further utilized in this work to theoretically simulate the THz spectra of all-trans -carotene molecule. It is revealed that the theoretical simulation results accord well with those experimentally measured data. In addition, we also find that the absorption peaks are caused by the torsion, deformation and rocking vibration of the molecules. Accordingly, the vibrational modes of the measured THz characteristic peaks at 148 cm-1 (4.44 THz), 132 cm-1 (3.96 THz), 115 cm-1 (3.45 THz), 76 cm-1 (2.28 THz) and 52 cm-1 (1.56 THz) are theoretically assigned, which provides a reference to explain the formation mechanism of the THz spectra. The valuable results presented in this work will be helpful for promoting the studies of the THz spectral features and response mechanisms of the organics.

Independent component analysis (ICA) has shown much success in blind source separation and channel equalization. Its applications to remotely sensed images are investigated in recent years. Linear spectral mixture analysis (LSMA) has been widely used for subpixel detection and mixed pixel classification in remote sensing image processing and already studied in Chapters 3, 8–10, . It models the spectral signature of an image pixel vector as a linear mixture of spectral signatures of targets present in the image data and the target abundance fractions are assumed to be unknown, but nonrandom constants. This chapter combines these two approaches to one, called ICA-based linear spectral random mixture analysis (LSRMA), which describes an image pixel vector as a random process resulting from a random composition of multiple spectral signatures of distinct targets in the image data. It differs from LSMA in that the abundance fractions of the target signatures in LSRMA are considered to be unknown random independent signal sources. Two major advantages can be benefited from LSRMA. First, LSRMA does not require any prior knowledge of the targets used in the linear mixture model. Second and most importantly, LSRMA models each of target signatures as an independent random signal source so that the spectral variability of target signatures can be captured more effectively in a stochastic manner. The only required knowledge for LSRMA is the number of signal sources, p assumed to be present in the image data. This number is estimated by Neyman-Pearson detection theory-based eigen-thresholding methods to be investigated in Chapter 17.

Fentanyl is one of the most potent synthetic opioid pain relievers. However, the abuse of opioids may lead to death. Rapid identification methods of both known and emerging opioid substances in fentanyl family would help to prevent this abuse. Terahertz (THz) spectra provide the identification information without damaging the sample. In this study, we predict THz spectra of fentanyl and 20 of its analogs in solid state by density-functional theory method PBEh-3c to investigate the frequencies of rotational-vibrational normal modes in THz region (0.1~100 cm−1). Substitution of single bond or aromatic group of fentanyl leads to significant change of crystal packing and is reflected in its THz spectrum. We discuss structure-property relationships of these synthetic opioids such as ohmefentanyl and sufentanil that are more potent than fentanyl. Since new drugs come up in black market frequently, we applied machine learning methods to predict THz spectrum of yet unknown synthetic opioids. Other “white powders” such as sucrose and lactose will be tested to validate our prediction.

In recent years, the field of Terahertz (THz) science and technology has entered a completely new phase of unprecedented expansion that is generating ever-growing levels of broadbased international attention. Indeed, the plethora of activities that have arisen recently in both the technology and scientific arenas associated with the THz frequency domain i.e., between 1 millimeter (300 GHz) and 100 micrometers (3 THz), suggest that the field might be attempting to undergo a dramatic transition that could lead to long-awaited payoffs in a number of application areas. The inherent advantages and potential payoffs of the THz regime for military & security as well as industry relevant applications have long stood as an important driver of interest in this science and technology area. This extremely expansive and spectrally unique portion of the EM spectrum had initial application in space-based communications, upper atmospheric sensing and potentially for short-range terrestrial communications and non-intrusive package screening. However, the very rapid growth in more recent years is arguably most closely linked to the potential payoffs of THz sensing and imaging for an array of military, security and industrial applications. These applications include the spectroscopic-based detection identification and characterization of chemical and biological agents and materials, remote and standoff early-warning for chemicalbiological warfare threats, and imaging of concealed weapons and explosives, just to name a few. In addition, THz-regime finds its application possibilities in industry and private-sector areas as food-industry process control, pharmaceutical industry, biological science, medical diagnostics and security screening. Systems for rapidly emerging applications at THz frequencies thus require reliable highpower sources. In the last few years, the development of suitable sources for this frequency regime is being extensively explored worldwide. There are broadly two technology roadmaps for THz semiconductor devices. Approaching from the lower frequency range in the THz regime, electronic devices such as, Gunn diode, Resonant Tunneling diode (RTD) and nanometer Field Effect Transistors (FET) based on plasma wave have been widely investigated for THz frequency generation. From higher portion of the THz frequency spectrum, the photonics-based device Quantum Cascade Laser (QCL) extends the emission 7

Terahertz (THz) emission from spintronic THz emitters (STEs) has been extensively studied, both for its potential application in THz technologies and as a tool for probing spin dynamics, conductivity, and crystal anisotropy via time-domain THz spectroscopy. However, substrate birefringence can modify the emitted THz polarization, distorting the measured spectra and leading to potential misinterpretation of the results. While some aspects of substrate birefringence on THz emission have been studied in the time domain, its effects on THz spectra have not been discussed in detail. In the THz emission spectrum from STEs, we observe distinct spectral signatures that depend on sample orientation. To understand these signatures, we use STEs grown on c-cut sapphire and systematically vary the orientation of a (100) rutile TiO2 window in both pump-through and THz-through geometries to identify the birefringence-induced effects. These findings demonstrate that substrate birefringence plays a critical role in the emitted THz spectrum and must be carefully considered in the analysis of time-domain THz spectroscopy data. We also show that artifacts from smaller birefringence can have a more misleading effect on the THz spectra.

The terahertz (THz) spectrum of phencyclidine hydrochloride from 7.0 to 100.0 cm(-1) has been measured at cryogenic (78.4 K) temperature. The complete structural analysis and vibrational assignment of the compound have been performed employing solid-state density functional theory utilizing eight generalized gradient approximation density functionals and both solid-state and isolated-molecule methods. The structural results and the simulated spectra display the substantial improvement obtained by using solid-state simulations to accurately assign and interpret solid-state THz spectra. A complete assignment of the spectral features in the measured THz spectrum has been completed at a VWN-BP/DNP level of theory, with the VWN-BP density functional providing the best-fit solid-state simulation of the experimentally observed spectrum. The cryogenic THz spectrum contains eight spectral features that, at the VWN-BP/DNP level, consist of 15 infrared-active vibrational modes. Of the calculated modes, external crystal vibrations are predicted to account for 42% of the total spectral intensity.

Incoherent terahertz (THz) sources can be compact, stable, reliable and cheaper alternative to coherent emitters for compact THz systems. Low power of incoherent THz emitters can be compensated by benefit from extremely high sensitivity of THz micro-detectors. Incoherent THz torch device based on Ga(As,Bi)/AlGaAs parabolic quantum well (PQW) is modeled, fabricated and experimentally investigated paying special attention to the THz spectral range and optical properties. The structures for optical characterization were grown using MBE technique on GaAs substrates. The experimental study was carried out to measure the absorption by intersubband transition of electrons in PQW using vacuum Fourier transform spectroscopy, conventional farinfrared Fourier transform spectroscopy and THz time-domain spectroscopy. Transmittance spectra dependence on temperature and photo-excitation of undoped structures for THz torch device is studied exploring impact of the PQW on THz spectra.

We have developed a tabletop intense broadband terahertz (THz) source in the medium frequency range (≤ 20 THz) based on the interaction of a high-intensity femtosecond laser with solid targets at relativistic laser intensities. When an unpolished copper target is irradiated with a high-intensity femtosecond laser, a maximum of ~2.2 μJ of THz pulse energy is collected and detected with a calibrated pyroelectric detector. The THz spectrum was measured by using a series of bandpass filters, showing a bandwidth of ~7.8 THz full-width at half-maximum (FWHM) with a peak at ~6 THz. With tight focusing to reach high field strengths, we have demonstrated THz nonlinearity exemplified by THz absorption bleaching in a heavily n-doped InGaAs thin film, which enabled us to estimate the peak electric field of the THz pulses. We simulated the experimentally observed bleaching by employing a THz pulse having a bandwidth similar to that measured in our experiments and a temporal profile recoded in single-shot electro-optic detection. Through the simulations, we estimate a peak electric field associated with the THz pulses to be 2.5 MV/cm.

Metal-organic frameworks (MOFs) are porous crystalline materials. Their large pores make them particularly interesting for membranes, gas separation, and gas storage. Furthermore, MOFs are ultralight, making them suitable for a large realm of exciting applications ranging from wearable devices to space technology. Optimizing MOFs for these applications demands a detailed understanding of their low energy dynamics and photophysics, which can be provided by terahertz (THz) spectroscopy. MOFs exhibit structural modes, or phonons, with energies in the meV range, which corresponds to the THz spectral range (0.1–10 THz, 0.4–40 meV). Understanding these modes is crucial in determining how a MOF interacts with guest molecules in the process of gas capture and storage. In this perspective, we discuss how gas-MOF interactions alter the MOFs’ spectral fingerprints. We demonstrate that THz spectroscopy can be used for gas adsorption monitoring and explain how density functional theory, together with THz spectra, can illuminate the dynamic structure of MOFs, providing unique insight into their functionality. THz is also a contact free probe for conductivity and allows us to measure short range conductivity within an individual MOF crystal. We will discuss the advantages of THz as a conductivity probe for MOFs as compared to more established direct current techniques. We will then expand our view to incorporate ultrafast photoconductivity in MOFs measured via optical pump-THz probe spectroscopy, in comparison to more established ultrafast spectroscopic tools such as optical transient absorption and photoluminescence. We will supplement this section with a discussion of THz studies on perovskites, which unveiled electron–phonon interactions not yet explored in MOFs.

Oral squamous cell carcinoma (OSCC) has asymptomatic characteristics that make it challenging to identify in the early stages and lead to metastatic effects. Terahertz (THz) spectroscopy and imaging are recognized as novel techniques for early cancer detection due to their nonionizing nature, the significant THz wave absorption by water’s hydrogen bonds, and the higher hydration of tumors. Despite this potential, there is a lack of research on the THz characterization of oral cancer with various essential biological conditions. THz characterization based on frozen, freshly excised tissue restricts parametric studies on important components and diverse biological situations. Therefore, we cultivated the 3-D, organotypic model of the OSCC, to investigate the THz spectroscopy of the tumor at various phases and the effects of the anticancer drug AG1478 on its THz spectra. Moreover, we have compared the characterization of OSCC with two levels of aggressiveness and we contrasted how well the medication worked on these two types of cell lines. The measurements were performed at the frequency range of 0.4–1.6 THz, and with increasing malignancy of the samples, we observed higher refractive index, absorption coefficient, and complex permittivity than normal tissue. The results demonstrate that although AG1478 shifts the THz spectra in the direction of the normal tissue, it has no effect on aggressive OSCC (AOSCC) under the same circumstances. These findings may contribute to techniques that diagnose and detect tumors at the early stage.

Linear spectral mixture analysis (LSMA) is a widely used technique in remote sensing to estimate abundance fractions of materials present in an image pixel. In order for an LSMA-based estimator to produce accurate amounts of material abundance, it generally requires two constraints imposed on the linear mixture model used in LSMA, which are the abundance sum-to-one constraint and the abundance nonnegativity constraint. The first constraint requires the sum of the abundance fractions of materials present in an image pixel to be one and the second imposes a constraint that these abundance fractions be nonnegative. While the first constraint is easy to deal with, the second constraint is difficult to implement since it results in a set of inequalities and can only be solved by numerical methods. Consequently, most LSMA-based methods are unconstrained and produce solutions that do not necessarily reflect the true abundance fractions of materials. In this case, they can only be used for the purposes of material detection, discrimination, and classification, but not for material quantification. The authors present a fully constrained least squares (FCLS) linear spectral mixture analysis method for material quantification. Since no closed form can be derived for this method, an efficient algorithm is developed to yield optimal solutions. In order to further apply the designed algorithm to unknown image scenes, an unsupervised least squares error (LSE)-based method is also proposed to extend the FCLS method in an unsupervised manner.

Ultra-broadband shielding of cellulose nanofiber commingled biocarbon functional constructs: A paradigm shift towards sustainable terahertz absorbers

One has proved that the collective structural vibrational modes of proteins are in the terahertz (THz) frequency range. These frequencies relate to the polypeptide backbone and are thought to be essential for conformational dynamics necessary for protein function. Hemagglutinin (HA) is the main surface glycoprotein of the influenza A virus. The H9N2 subtype influenza A virus is recognized as the most possible pandemic strain as it crosses the species barrier, infects swine and humans. In this paper we use principal component analysis (PCA) to study the 7 different concentrations dependent terahertz spectra of hemagglutinin proteins, and detect the binding interaction of HA with the broadly neutralizing monoclonal antibody F10 in liquid phase. Spectrum pretreatment and band selection play a vital role in the THz spectroscopic analysis due to the fact that the original spectrum contains a large amount of interference information. In order to compress variables and extract useful information, we use a variety of pretreatment methods, such as second derivative, multiplicative scatter correction (MSC), least square polynomial fitting derivation, standard normalization, smoothing, moving window median filtering before PCA analysis. We even consider MSC + smoothing + SG second derivative + median filtering as the optimized pretreatment method finally. THz spectrum parameters including refractive index, absorption coefficient, reduced absorption cross-section and dielectric loss angle tangent are calculated in a frequency range of 0.1-1.4 THz for comparison. The results indicate that the reduced absorption cross-section presents the highest correlation response to the concentration variation of HA protein, and the dielectric loss angle tangent appears to be more appropriate for qualitative analysis of HA-antibody binding interaction. PCA method provides a feasible and effective way to find the sensitive parameters for further analyzing the function of protein and the antigen-antibody interaction using terahertz spectrum, whereas an appropriate pretreatment method is required.

The growing demand for advanced wireless communication, high‐resolution imaging, and innovative medical applications in the Terahertz (THz) frequency range has driven remarkable developments in meta‐surface‐based antennas. This comprehensive review delves into the cutting‐edge advancements, novel designs, and practical applications of meta‐surfaces in the THz spectrum. The review begins by exploring the materials employed in meta‐surfaces and their crucial role in achieving efficient THz operation. It delves into the realm of polarization diversity, revealing innovative approaches to harnessing the potential of meta‐surfaces for polarization control and conversion. A key area of focus is beam‐steering technology, with a thorough investigation into beam‐steering techniques that have significant implications for enhancing wireless communication, high‐resolution imaging, and the internet of things. The paper highlights the potential of these techniques in addressing real‐world challenges and advancing THz technology. Furthermore, this review provides an in‐depth examination of the innovative antenna designs tailored for THz applications, shedding light on their characteristics and benefits. It also explores the exciting possibilities of THz technology within the medical field, including precise bio sensing and cancer cell detection.

Terahertz (THz) emission from a single-color ultraviolet (UV) (248 nm) filament in air is studied experimentally and compared to that of an infrared (IR) (744 nm) filament for similar pulse durations, focusing conditions, and excess of pulse power over the critical power for self-focusing. An angular distribution of the THz emission for both UV and IR filaments is conical with the close cone angle. In contrast, the THz radiation energy and spectrum differ significantly. The energy of THz emission from the UV filament is 1–2 orders of magnitude lower than the THz yield from the IR filament. The THz spectrum of the UV filament is shifted to the low-frequency range and is narrower compared to the spectrum of THz emission from the IR filament. We explain qualitatively the difference in THz yields and spectra by lower intensity and plasma density in the UV filament.