Continuous Absorption Spectrum Research Articles

Callistemon citrinus: A plant‐mediated synthesis of sustainable Rhodium nanoparticles and their antimicrobial activity

AbstractThis work investigates the potential of using Callistemon citrinu flower extract, commonly known as bottlebrush, in the environmentally friendly synthesis of Rhodium nanoparticles (Rh NPs). Callistemon citrinu flower extract contains a high concentration of flavonoids and other phytochemicals. Hence, the extract was used to provide the essential components for an environmentally, sustainable synthesis method of Rh NPs. Different characterization analyses were used to evaluate the different properties of the synthesized particles. UV spectroscopy analysis demonstrated a continuous UV absorption spectrum attributed to the formation of Rh NPs. The XRD data and SAED analysis showed an amorphous nature of the synthesized Rh NPs. The HRTEM imaging provided morphological information about the Rh NPs tested sample, where the efficiency of Callistemon citrinu flower extract as a capping agent was reported. Furthermore, Raman spectra displayed the characteristic vibrational bands of the synthesized Rh NPs. The antimicrobial activity of the synthesized samples was tested against several dental pathogens, that play a role in dental caries, Staphylococcus aureus (SA), Bacillus subtilis (BS), Candida albicans (CA), Escherichia coli (Eco), and Staphylococcus epidermidis (S. Epi). In comparison with the control, Chlorhexidine (CHX), Rh NPs showed a greater impact on C. albicans (20 ≤ Zone of inhibition (ZOI) (mm) ≤ 26). The statistical analysis demonstrated that Rh NPs had a greater mean ZOI than the Callistemon citrinu flower extract. These results reveal the considerable potential and biological capacity Rh NPs have as an antifungal agent for dental applications.

Design of a broadband metasurface sound absorber based on Hilbert fractal

In this paper, a new fractal-based broadband metasurface absorber is developed, which is based on the excellent space-filling ability of the Hilbert fractal. Each unit cell in absorber consists of a micro perforated panel (MPP) and a coplanar coiled cavity. In order to gain a deep insight into the sound absorption mechanism and perform a rapid design, a theoretical model for analyzing the sound absorption characteristics of the unit cell is established, in which the Fok function is used to account for the coupling effect between holes. Afterward, the absorption mechanism as well as the effects of parameter variations on absorption characteristics are investigated. To increase the space utilization, each unit cell is arranged in space according to the Hilbert fractal curve. Consequently, a metasurface absorber with 6 detuned unit cells is constructed. The multiple resonant cavities with dissimilar lengths can provide peak absorptions at multiple frequencies, thereby broadening the attenuation frequency range. Finally, the absorption performance of the designed absorber is obtained by theoretical calculations, finite element (FEM) simulations and experimental measurements, respectively. The experimental results show that a continuous absorption spectrum is achieved in the range of 855–1359 Hz with absorption coefficient above 0.8 under a deeply sub-wavelength thickness (22.2 mm). This study provides an effective way for the design of a space-limited broadband absorber. With the advantages of ultrathin thickness, broadband, and compactness, the developed fractal-based metasurface absorber has great potential in the field of noise reduction.

Methane as a reddish coating agent

Experiments in quartz ampoules that simulate the saltation of quartz grains in a methane atmosphere show that the solid phase acquires a reddish color, reminiscent of the color observed on Triton, Pluto, and Charon. Reflection spectroscopy of the coated grains show a wide, continuous absorption spectrum peaking at near-UV wavelengths, in line with the reddish color. X-ray photoelectron spectroscopy indicates the grains are coated with a substance containing CC and CO bonds, and estimates the average thickness of the surface layer to 2.3 Å. Solid state Raman measurements of the coating shows a transition at 1540 cm−1. A model is proposed to describe these measurements. The model is a polydiene, anchored to the quartz surface. Electron structure calculations show that a polydiene with around 8 CH units reproduces the measurements. AFM-IR experiments support this result. Our findings suggest a pathway for synthesis of complex molecules with CC bonds on planets and moons with a solid surface and a methane-containing atmosphere.

Computational optimal transport for molecular spectra: The semi-discrete case.

Comparing a discrete molecular spectrum to a continuous molecular spectrum in a quantitative manner is a challenging problem, for example, when attempting to fit a theoretical stick spectrum to a continuous spectrum. In this paper, the use of computational optimal transport is investigated for such a problem. In the optimal transport literature, the comparison of a discrete and a continuous spectrum is referred to as semi-discrete optimal transport and is a situation where a metric such as least-squares may be difficult to define except under special conditions. The merits of an optimal transport approach for this problem are investigated using the transport distance defined for the semi-discrete case. A tutorial on semi-discrete optimal transport for molecular spectra is included in this paper, and several well-chosen synthetic spectra are investigated to demonstrate the utility of computational optimal transport for the semi-discrete case. Among several types of investigations, we include calculations showing how the frequency resolution of the continuous spectrum affects the transport distance between a discrete and a continuous spectrum. We also use the transport distance to measure the distance between a continuous experimental electronic absorption spectrum of SO2 and a theoretical stick spectrum for the same system. The comparison of the theoretical and experimental SO2 spectra also allows us to suggest a theoretical value for the band origin that is closer to the observed band origin than previous theoretical values.

Development of a Panel Membrane Resonant Absorber

The bass ratio describes the relationship between the reverberation energy in the low frequency region and that of the middle frequency. An appropriate bass ratio can create a warm sound; however, too much bass can influence speech clarity (C50) and work efficiency and can even cause listeners to feel tired or exhausted. Using perforated plate resonance theory and membrane resonance theory, this research developed the panel membrane resonant absorber (PMRA), which not only provides an outstanding continuous absorption spectrum in the broadband range of 100–800 Hz but also presents an aesthetic appearance at a low cost. We divided this study into two parts: (1) PMRA development and experiment and (2) field application and measurement to confirm the sound absorption performance of the PMRA. In part 1, PMRA was developed by combining different materials and thicknesses of the air cavity. In the field study of part 2, the PMRA with the appropriate sound-absorbing curve was installed in a small auditorium, where we conducted field measurements for reverberation time (RT) and speech clarity (C50). According to the experimental results, the PMRA had great absorption performance at a low frequency. In the field validation, the PMRA was found to effectively decrease the low-frequency RT while also maintaining the RT of middle-high frequency. The C50 of the auditorium was also improved.

Quantum electromechanics with levitated nanoparticles

Preparing and observing quantum states of nanoscale particles is a challenging task with great relevance for quantum technologies and tests of fundamental physics. In contrast to atomic systems with discrete transitions, nanoparticles exhibit a practically continuous absorption spectrum and thus their quantum dynamics cannot be easily manipulated. Here, we demonstrate that charged nanoscale dielectrics can be artificially endowed with a discrete level structure by coherently interfacing their rotational and translational motion with a superconducting qubit. We propose a pulsed scheme for the generation and read-out of motional quantum superpositions and entanglement between several levitated nanoparticles, providing an all-electric platform for networked hybrid quantum devices.

Nonlocal effects in singular plasmonic metasurfaces

A local model of the dielectric response of a metal predicts that singular surfaces, such as sharp-edged structures, have a continuous absorption spectrum and extreme concentration of energy at the singularity. Here we show that nonlocality drastically alters this picture: the spectrum is now discrete and energy concentration, though still substantial, is greatly reduced.

A thin low-frequency broadband metasurface with multi-order sound absorption

We present a theoretical and experimental realization of a thin multi-unit metasurface with multi-order sound absorption that exhibits a continuous near-perfect absorption spectrum in the broadband range of 450 Hz–1360 Hz. The metasurface unit is a perforated composite Helmholtz-resonator (PCHR) that is constructed by inserting one or more separating plates with a small hole into the interior of a Helmholtz resonator (HR). The multi-order sound absorption mechanism can be achieved so that with the original absorption peak and the structural size unchanged, multiple near-perfect peaks are obtained in higher frequencies by a PCHR unit. This extraordinary multi-peak performance is the result of the upgraded multi-degree-of-freedom system with the separating plates, which is explained well by the equivalent acoustic circuit. The specific absorption properties of the PCHR unit are investigated thoroughly with a theoretical approach similar to the plane wave expansion method, and verified via the finite element simulations. On this basis, by precisely balancing the parameters of each unit, the absorption bandwidth of the subwavelength 8-unit metasurface is dramatically broadened about 65% by the proposed mechanism. This work would offer a new guidance for the achievement of the wider absorption band and has great potential in engineering applications.

The Research of a New Iteration of the Circular Algorithm

Abstract It is a problem of spectra analysis of flue gas that how to separate and calculate the concentration of different kinds of gas from continuous mixed gas absorption spectrum signal. So based on experimental data, a new iteration of the circular algorithm is put forward on the basis of Lambert-Beer’s law. The algorithm uses different UV-light wavelengths at 190nm-290nm for different characteristics of UV light with different absorption peaks. The iteration is repeated until the concentration difference between adjacent two gases is less than a certain value. It is considered that the elemental gas The exact concentration, and through the programming to achieve the results. it has strong anti-jamming capability and is suitable for practical application of engineering.

The Portable Gas Analyzer Based on the Spectrum

Abstract It is a problem of spectra analysis of flue gas that how to separate and calculate the concentration of different kinds of gas from continuous mixed gas absorption spectrum signal. So based on experimental data, a new iteration of the circular algorithm is put forward on the basis of Lambert-Beer’s law. This algorithm, using the superposition of the absorbance, makes data nonlinear fitting. It takes the advantages of the wavelength optimum and the circular iteration to distinguishing the gas mixture of different composition. Experimental results show that: this method can at once calculate a variety of harmful gas concentration and accuracy up to ± 3%. it has strong anti-jamming capability and is suitable for practical application of engineering.

Disorder-induced absorption of far-infrared waves by acoustic modes in nematic liquid crystals

A mechanism of light absorption at THz frequencies in nematic liquid crystals based on intermolecular dynamics is proposed. In this mechanism, the energy conservation is supplied by acoustic phonons, whereas momentum conservation is provided by static spatial fluctuations of the director field. The mechanism predicts a continuous absorption spectrum in a broad frequency range.

Quick measurement of continuous absorption spectrum in ion beam pulse radiolysis: Application of optical multi-channel detector into transient species observation

Abstract A quick measurement system of a continuous absorption spectrum covering a wide range from 200 to 950 nm was constructed by employing an optical multi-channel detector. Ion beam pulse radiolysis with 12.5 MeV/u He, 18.3 MeV/u C and 17.5 MeV/u Ne ions were performed with the measurement system. Transient absorption spectrum of ( S C N ) 2 • − was clearly observed in KSCN aqueous solutions within a few minutes in spite of their very small absorbance, demonstrating high sensitivity of 0.001–0.003 in absorbance in the range from 260 to 660 nm as well as short measurement time of a few minutes. Two different absorption peaks attributed to Br 2 • − and Br 3 − were observed simultaneously in NaBr aqueous solutions, showing powerfulness of the measurement system in overviewing chemical kinetics under ion beam irradiation especially in not well investigated chemical systems.

Nanofocusing performance of the crescent-shaped cylinder for various surrounding media

In this work, adjustable broadband light harvesting and field enhancement on the surface of a crescent-shaped cylinder were achieved by considering the surrounding medium in conformal transformation theory. The continuous absorption spectrum shows that the broadband effect is quite robust to the surrounding media. By considering the material properties, we provide a comprehensive discussion of how the material properties of the nanosystem affect the field enhancement and nanofocusing. Furthermore, an optical gain medium is employed to compensate for the absorption losses in the materials. A considerable field enhancement and super-nanofocusing are thus expected. The presented results provide important guidance for optimizing such a nanosystem in experimental studies.

Flue Gas Analysis Based on Recursive Iteration Algorithm

The key point of flue gas spectra analysis is how to separate and calculate the concentration of different kinds of gas, which is from continuous mixed gas absorption spectrum signal. In this paper, a new iteration of the recursive algorithm is put forward on the basis of Lambert-Beer's law. This algorithm, using the superposition of the absorbance, achieves data nonlinear fitting. It takes the advantages of the wavelength optimum and the circular iteration to distinguish the gas mixture of different composition. Experimental results show that this method can calculate a variety of harmful gas concentration immediately, and the accuracy is up to ± 2%. In addition, this algorithm could be used to measure the concentration of many kinds of gases at one time, and it obtains strong anti-jamming capability which is suitable for practical application of engineering.

Biosynthesis of Palladium Nanoparticles Using Delonix regia Leaf Extract and Its Catalytic Activity for Nitro-aromatics Hydrogenation

This work presents the biosynthesis of palladium nanoparticles (Pd-NPs) using Delonix regia (D. regia) leaf extract, and their catalytic activity was evaluated for 2-nitrophenol (2-NP) and 2-nitroaniline (2-NA) hydrogenation reactions. The appearance of a broad continuous absorption spectrum in the visible–ultraviolet region in UV–visible spectra confirmed the synthesis of Pd-NPs. The crystalline structure of Pd-NPs (with size range of 2–4 nm) was confirmed by X-ray diffraction and transmission electron microscopy analysis, respectively. The appearance of an optical absorption peak at 2.80 keV in energy dispersive spectra further confirmed the presence of Pd-NPs. Fourier transform infrared analysis suggested the role of water-soluble polyols present in the D. regia leaf extract in mediating the synthesis of Pd-NPs. Moreover, the catalytic activity of Pd-NPs for hydrogenation reactions was studied by UV–visible spectroscopy. Pd-NPs showed catalytic activity through electron relay effect. The hydrogenation ...

Multispectral imaging via luminescent down-shifting with colloidal quantum dots

The high infrared quantum yield, continuous absorption spectrum, and band edge tunability of colloidal quantum dots (QD) has opened up new opportunities to use luminescent down shifting for multispectral imaging in the infrared. We demonstrate a QD sensitized short wavelength infrared (SWIR) camera which is capable of UV-SWIR multispectral imaging. The application of multispectral cameras for UV tagging applications is demonstrated and the extension of this technology to the mid infrared spectral region is discussed.

Transient absorption and laser gain in e-beam-excited Ar/Kr/NF3(F2 + N2) gas mixtures

AbstractNewly developed erosion-plasma-source probe technique has been applied for virtually single shot recording of absorption/fluorescence spectra in the 190–510 nm spectral range of e-beam-excited Ar/Kr/NF3(F2 + N2) mixtures. The e-beam excitation rate of about 1 MW/cm3 is typical of large-volume rare-gas halide lasers. It is experimentally observed that, in Kr/F2 and Ar/F2 mixtures, fluorescence and absorption spectra of Rg2F species are shifted with respect to each other in the opposite direction. Continuous absorption spectrum of Ar2F excimer is reported, as far as we know, for the first time in the refereed literature. Strong overlapping between the fluorescence and absorption spectra of Ar2F is responsible for absence of lasing on Ar2F molecule. Absorption spectrum of Kr2F excimer is recorded in pure form using the mixture (Ne/Kr/F2) with no alternative broadband absorber. Minor additive of nitrogen to Ar/Kr/F2 mixture or use of NF3 instead of F2 has been found to result in broadband optical amplification centered at λ ~ 460 nm. The maximum optical gain is estimated as about 0.1 ± 0.05 m−1.

Broadened Far-Infrared Absorption Spectra for Hydrated and Dehydrated Myoglobin

The far-infrared absorption spectra of myoglobin powder at hydration levels between 3.6 and 42 wt % were measured with terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy. Absorption is dominated by the water content, but even the driest specimens have a nearly continuous spectrum without identifiable sharp features. Inhomogeneous broadening plus the intrinsically high spectral density of vibrational modes in the region below 2.0 THz apparently combine to obscure the lowest frequency vibrational modes expected for protein molecules of this size. A continuous absorption spectrum for hydrated protein powders suggests that the absorption mechanisms are similar to those in liquid water, and hinders the spectroscopic identification of biomolecules in this frequency range.

Resonant and near-resonant inelastic X-ray scattering spectroscopy and lifetime-broadening-removed XANES of CuO

Being a second order optical phenomenon, resonant inelastic X-ray scattering (RIXS) spectroscopy can be used to disentangle bound-state excitations from continuous absorption spectrum more effectively than ordinary first order absorption spectroscopy. When the excitation energy is lower than the K absorption threshold by about 10 eV or more, RIXS spectra observed approach a mirror image of 1s-core-hole lifetime-broadening-removed (LBR) XANES spectra, although the scattering intensity is prohibitively weak because of the unsatisfactory resonant condition employed. Approaching closer to the resonance, RIXS intensity increases by several orders of magnitude and concurrently observed is a surprisingly complicated set of spectra which heavily depends on the excitation energies. From each RIXS spectrum obtained under close to the resonant conditions, 1s-core-hole LBR-XANES or 1s- and 2p-core-hole LBR-XANES can be deduced by analytical method or numerical calculations. The RIXS-XANES method has been applied to CuO to reveal an existence of hidden electronic states near the absorption threshold.

High resolution ion imaging study of BrCl photolysis in the wavelength range 330–570 nm

The photodissociation of jet-cooled BrCl molecules has been investigated at many different excitation wavelengths in the range 330–570 nm by velocity map imaging of the ground state Br and ground and spin–orbit excited Cl atom products. Image analysis confirms literature values for the energies of the ground, Br(2P3/2)+Cl(2P3/2), and first excited [Br(2P3/2)+Cl(2P1/2)] dissociation asymptotes, and provides measures of the electronic branching into these two active product channels, and the recoil anisotropy of each set of products, as a function of parent vibrational level (v″⩽2) and excitation wavelength. The availability of such experimental data allows mapping of the partial cross-sections for parallel (i.e., ΔΩ=0) and perpendicular (i.e., ΔΩ=±1) absorption as a function of excitation energy, and thus deconvolution of the room temperature parent absorption spectrum into contributions associated with excitation to the A 3Π(1), B 3Π(0+), and C 1Π(1) excited states of BrCl. This analysis of the continuous absorption spectrum of BrCl, when considered in conjuction with existing spectroscopic data for the ground electronic state and for the bound levels supported by the B state potential, allows determination of key regions of the potential energy curves for, and transition moments to, each of these three excited states. Further wave packet calculations, which reproduce the experimentally measured wavelength dependent product channel branching ratios and product recoil anisotropies very well, serve to validate the excited state potential energy functions so derived and allow estimation of the strength (∼80 cm−1) of the coupling between the bound (B) and dissociative (Y) diabatic states of 0+ symmetry.