Reflection Mode Research Articles

Multifunctional microcapsules based on ZnO and n-octadecane: From thermal energy storage to photocatalytic activity

Energy management is one of the most important issues to be addressed in the near future in many fields, one of which is buildings. In this sense, new phase change materials (PCM) are being widely studied for storing energy. Encapsulating PCM is a good way to incorporate these materials into different applications in which energy storage is useful. In this study, microcapsules based on ZnO containing n-octadecane as a phase change material were synthesized and characterized with regard to their structural, morphological and optical properties according to several synthesis parameters, such as the proportion of precursors, stirring rate and ageing time. The microcapsules were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–Vis spectroscopy in diffuse reflectance mode. The presence of n-octadecane inside the capsules was confirmed. Their thermal behaviour was analysed by means of differential scanning calorimetry. Heating/cooling cycles were performed, after which the microcapsules presented good stability. Furthermore, the encapsulation efficiency was estimated from melting and crystallization enthalpy values, reaching a value of 23.1%. Moreover, the isobaric specific heat of the microcapsules is higher than that of ZnO, which means that substituting ZnO with microcapsules in buildings leads to an important increase in the amount of sensible heat stored. Finally, the photocatalytic activity of the microcapsules was analysed by studying the photodegradation of Crystal Violet dye. The degradation rate increased when the microcapsules were present, so the photocatalytic activity of the microcapsules was confirmed under UV and visible irradiation, which is of interest because they can be used to remove organic pollutants from buildings.

Rugged bialkali photocathodes encapsulated with graphene and thin metal film

Protection of free-electron sources has been technically challenging due to lack of materials that transmit electrons while preventing corrosive gas molecules. Two-dimensional materials uniquely possess both of required properties. Here, we report three orders of magnitude increase in active pressure and factor of two enhancement in the lifetime of high quantum efficiency (QE) bialkali photocathodes (cesium potassium antimonide (CsK2Sb)) by encapsulating them in graphene and thin nickel (Ni) film. The photoelectrons were extracted through the graphene protection layer in a reflection mode, and we achieved QE of ~ 0.17% at ~ 3.4 eV, 1/e lifetime of 188 h with average current of 8.6 nA under continuous illumination, and no decrease of QE at the pressure of as high as ~ 1 × 10–3 Pa. In comparison, the QE decreased drastically at 10–6 Pa for bare, non-protected CsK2Sb photocathodes and their 1/e lifetime under continuous illumination was ~ 48 h. We attributed the improvements to the gas impermeability and photoelectron transparency of graphene.

Plasmonic biosensing with tilted fiber Bragg gratings interrogated using a 512-pixel spectrometer.

Plasmonic tilted fiber Bragg gratings (TFBGs) are very efficient for fast, accurate, and minimally invasive biosensing. Their transmitted amplitude spectrum is a dense comb of narrowband cladding mode resonances (full width at half maximum < 1 nm) that is usually demodulated using highly resolved (wavelength resolution < 10 pm) devices. This work demonstrates the possibility of using a coarsely resolved spectrometer (166 pm) to read out the amplitude spectrum of a gold-coated TFBG. A refined analysis of the spectral content has allowed us to develop signal processing that provides a refractometric sensitivity of 2656 nm/RIU. This is a fivefold improvement compared to previously reported read-out techniques. Biosensing has then been successfully implemented with gold-coated TFBGs implemented in reflection mode for the detection of insulin, with specific antibodies grafted on the gold surface. Our experimental work is a first step toward the industrialization of the FBG technology, as it opens the door to fast parallel biosensing, profiting from the multiple sensing channels (up to 64) of the interrogator and its high processing speed (repetition rate up to 3 kHz).

In Vivo Longitudinal Monitoring of Disease Progression in Inflammatory Arthritis Animal Models Using Raman Spectroscopy.

Current techniques for monitoring disease progression and testing drug efficacy in animal models of inflammatory arthritis are either destructive, time-consuming, subjective, or require ionizing radiation. To accommodate this, we have developed a non-invasive and label-free optical system based on Raman spectroscopy for monitoring tissue alterations in rodent models of arthritis at the biomolecular level. To test different sampling geometries, the system was designed to collect both transmission and reflection mode spectra. Mice with collagen antibody-induced arthritis and controls were subject to in vivo Raman spectroscopy at the tibiotarsal joint every 3 days for 14 days. Raman-derived measures of bone content correlated well with micro-computed tomography bone mineral densities. This allowed for time-resolved quantitation of bone densities, which indicated gradual bone erosion in mice with arthritis. Inflammatory pannus formation, bone erosion, and bone marrow inflammation were confirmed by histological analysis. In addition, using library-based spectral decomposition, we quantified the progression of bone and soft tissue components. In general, the tissue components followed significantly different tendencies in mice developing arthritis compared to the control group in line with the histological analysis. In total, this demonstrates Raman spectroscopy as a versatile technique for monitoring alterations to both mineralized and soft tissues simultaneously in rodent models of musculoskeletal disorders. Furthermore, the technique presented herein allows for objective repeated within-animal measurements potentially refining and reducing the use of animals in research while improving the development of novel antiarthritic therapeutics.

Single-shot wide-field imaging in reflection by using a single multimode fiber

A single multimode fiber (MMF) provides almost an ideal optical channel to constitute a hair-thin endoscope for minimally invasive biomedical imaging at depths in tissue, especially if the imaging operation can be performed with one single shot in reflection mode, which, however, remains challenging to date. In this work, we present single-shot wide-field reflectance imaging by using a single MMF as the illumination unit and imaging probe simultaneously. To achieve single-shot image capture, a reflection matrix of the fiber was built by a learning-assisted approach for the universal inverse conversion from the output amplitudes to the input amplitudes. The performance was tested by imaging more than 30 000 natural scenes projected by a digital micromirror device, and an averaged Pearson correlation coefficient over 0.84 with respect to the ground truth was achieved in the experiment. Furthermore, the ability to image dynamic scenes at a high frame rate of up to 180 frames per second was demonstrated together with real-time observation of a freely moving microneedle located at the distal end of the MMF. The proposed reflection-mode single-fiber imaging scheme paves the way for practical video-rate microendoscopy at depths in tissue in a minimally invasive manner.

The Invariance of Inelastic Overlap Function

In this study, we consider the symmetry property of the inelastic overlap function and its relation to the reflective scattering mode appearance. This symmetry property disfavors an exclusion of one of the scattering modes—the reflective mode—when approaching the asymptotic limit. Predominance of the particular mode correlates with the energy and impact parameters ranges.

Identifying reflective modes in pre-service teachers’ written reflections on the implementation of project-based learning during the school practicum

This study deals with written reflections from final-year undergraduate pre-service teachers on the implementation of project-based learning (PjBL) during the school practicum. The research focuses on highlighting undergraduate pre-service teachers’ meaning through reflexive thematic analysis as well as highlighting modes of expressing positions—according to a specific model categorizing these modes—on the implementation of child-centered instructional approaches such as Pj-BL. The research methodology included written reflections by 40 undergraduate student teachers in a 4-year university BA of preparing primary school teachers by applying the convenient sampling strategy. The participants were attending their final school teaching practice component of their studies. The study identifies prospective teachers’ positive points, concerns, and challenges when applying Pj-BL. The findings also indicate that prospective teachers need to further develop their reflective thinking skills to provide explanations and solutions and identify areas of personal improvement when they produce written reflective reports.

Focused vortex and imaging full-space metasurface

Due to their abilities to adjust the electromagnetic wavefront in both transmission and reflection modes without changing the structure, the full space metasurfaces has attracted extensive attention. However, it is still a challenge to achieve full-space multi-functionalities within a simple metasurface structure. Herein, we proposed a full space metasurface by utilizing a two kinds of medium substrate layers all-dielectric-atom for the right circularly polarized (RCP) and linear polarization (LP) incidences at two distinct operation frequencies. The all-dielectric-atom consists of subwavelength-thickness polyimide and vanadium dioxide (VO2) substrate layer and mushroom-shaped silicon pillar with a period of 100μm. Based on the emerging all-dielectric-atom, the designed multifunctional full space metasurface generates deflection focusing, deflection vortex, focusing vortex, and imaging in both transmission and reflection modes, respectively. Our designed structure not only improves the control space for terahertz wave, but also realizes the linear polarization wave imaging function, which has great potential in terahertz communication and security inspection imaging.

Variable bandwidth, high efficiency microwave resonator for control of spin-qubits in nitrogen-vacancy centers.

Nitrogen-Vacancy (NV) centers in diamond are attractive tools for sensing and quantum information. Realization of this potential requires effective tools for controlling the spin degree of freedom by microwave (mw) magnetic fields. In this work, we present a planar microwave resonator optimized for microwave-optical double resonance experiments on single NV centers in diamond. It consists of a piece of wide microstrip line, which is symmetrically connected to two 50Ω microstrip feed lines. In the center of the resonator, an Ω-shaped loop focuses the current and the mw magnetic field. It generates a relatively homogeneous magnetic field over a volume of 0.07 × 0.1mm3. It can be operated at 2.9GHz in both transmission and reflection modes with bandwidths of 1000 and 400MHz, respectively. The high power-to-magnetic field conversion efficiency allows us to produce π-pulses with a duration of 50ns with only about 200 and 50 mW microwave power in transmission and reflection, respectively. The transmission mode also offers capability for efficient radio frequency excitation. The resonance frequency can be tuned between 1.3 and 6GHz by adjusting the length of the resonator. This will be useful for experiments on NV-centers at higher external magnetic fields and on different types of optically active spin centers.

Time-resolved in-cell IR spectroscopy on the bacterial chloride pump NMHR

In-cell spectroscopic techniques have become a powerful tool to overcome the drawbacks of studying proteins isolated from their native environment. This advancement is of major importance especially for membrane proteins since the recreation of a stabilizing environment using lipids or nanodiscs is challenging and varies substantially from in-vivo conditions, influencing the protein mechanism. A method well-suited for the investigation of the light-induced structural changes of photoreceptors is presented by infrared difference spectroscopy, allowing to detect changes in the cofactor, side chains and secondary structure. In pioneering studies, Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflection (ATR) mode was successfully established to study light-induced changes in soluble blue-light sensors in living E. coli cells.

Artificial Intelligence-based Prediction of In Vitro Dissolution Profile of Immediate Release Tablets with Near-infrared and Raman Spectroscopy

The objective of the present work was to develop an artificial neural network (ANN) model to accurately predict the dissolution profile of immediate release tablets based on non-destructive spectral data. Six different tablet formulations with varying API (caffeine) and disintegrant (potato starch) concentrations were prepared. The near-infrared (NIR) and Raman spectra of each tablet were collected in both reflection and transmission modes, then principal component analysis (PCA) was conducted. The training of the ANN was performed at each hidden neuron number from 1 to 10 in order to determine the optimal number of neurons in the hidden layer. The best results were obtained when a small number of neurons (1–3) was used. In the case of all four spectroscopic methods, the average similarity values (f2) of the optimized ANN models were above 59 for the validation tablets, indicating that the predicted dissolution profiles were similar to the measured dissolution curves. The optimized model based on reflection Raman spectra exhibited the best predictive ability. The results demonstrated the potential of ANN models in the implementation of the real-time release testing of tablet dissolution.

Synthesis and Characterization of Sol–Gel Screen Printed Zn:CdO (ZCO) Film for Optoelectronic Technologies

In present report on Zn doped (5%) CdO thick film is synthesized on to the glass substrate (pre-cleaned) via sol–gel screen printing process. The synthesized sintered Zn:CdO film are then characterized via XRD, SEM, EDX, UV–vis spectroscopy, PL spectroscopy, and dark conductivity measurement examinations. The XRD examination of sintered film informs the polycrystalline nature and authenticates that Zn:CdO film holds the cubic crystalline structure. SEM examination dispenses the information on morphology of Zn:CdO film. The EDX examination supports the existence of Cd, O, and Zn in the sintered film. The UV–vis spectroscopy via reflectance mode substantiates the direct transition of band gap with a value of 2.60 eV. PL spectra of the sintered film manifest a strong near band edge emission located around 500 nm. The Arrhenius plot (log σDC vs 1000/T) attests the semiconducting nature for the sintered film.

A New Green Coating for the Protection of Frescoes: From the Synthesis to the Performances Evaluation

This work presents the formulation and characterization of a new product for the protection of outdoor frescoes from aggressive environmental agents. The formulation is designed as an innovative green coating, prepared through a zero-waste one-pot-synthetic method to form silver nanoparticles (AgNPs) directly in a chitosan-based medium. The AgNPs are seeded and grown in a mixed hydrogel of chitosan, azelaic, and lactic acid, by the reduction of silver nitrate, and using calcium hydroxide as precipitating agent. The rheological properties of this coating base are optimized by the addition of a solvent mixture of glycerol and ethanol with a 1:1 volume ratio. The new formulation and two commercial products (Paraloid® B72 and Proconsol®) are then applied by brush to ad hoc mock-ups to be evaluated for chemical stability, color and gloss variations, morphological variation, hydrophobicity, and water vapor permeability via Fourier-transform infrared spectroscopy (FT-IR) in attenuated total reflection (ATR) mode, spectrophotometer analysis, stereomicroscope observations, UNI EN 15802, and UNI EN 15803, respectively. The results show that the application of the hybrid chitosan-AgNPs coating is promising for the protection of outdoor frescoes and that it can underpin the development of new products that address the lack of conservation strategies specifically designed for wall painting.

On the Importance of Investigating Data Structure in Miniaturized NIR Spectroscopy Measurements of Food: The Case Study of Sugar.

Alongside the increasing proofs of efficacy of miniaturized NIR instruments in food-related scenarios, it is progressively growing the number of end-users, even incentivized by the low-cost of the sensors. While attention is paid to the analytical protocol-from sampling to data collection, up to the data processing, the importance of error investigation in raw data is generally underestimated. Understanding the sources and the structure of uncertainty related to the raw data improves the quality of measurements and suggests the correct planning of the experiments, as well as helps in chemometric model development. The goal of chemometric modeling is to separate information from noise; therefore, a description of the nature of measurement error structure is necessary. Among the different approaches, we present the study of the Error Covariance Matrices (ECMs) and their decomposition in a bilinear structure as a powerful method to study the main sources of variability when using miniaturized NIR sensors in the actual way of use. Granulated and lump sugar samples were chosen as the case study and analyzed with two miniaturized spectrometers working in the NIR regions around 1350-2550 nm and 900-1750 nm, respectively, in dispersive reflectance mode. Results show that having some insights on multivariate measurement errors associated with spectra could be interesting in paving the way for several applications.

Optical Anomalies due to Volume Collective Modes of Plasmonic Metamaterials

AbstractThe emergence of optical anomalies in 3D plasmonic metamaterials upon excitation of volume collective modes is studied. These modes engage a collective response of all the meta‐atoms across the volume of the structure and arise due to coupling of localized plasmonic modes with Bloch modes of the 3D lattice. Two types of volume collective modes are introduced; a reflective mode resilient to the plasmonic absorption, exhibiting reflection that approaches unity with extremely low loss, through a distinct high‐Q spectral locking of the response of all the constituent plasmonic resonators in the volume; in addition, a transmissive mode that supports the emergence of lattice matched scattered waves within the volume, leading to full transmission through a spectral transparency window. These attractive optical properties of the volume collective modes may lead to a breakthrough in the design of low‐loss and efficient 3D plasmonic metamaterials for novel linear and nonlinear photonic applications.

Integrating reflection into a mobile-assisted reading program for learning English as a second language in China

The application of mobile technology in language education is gaining increasing momentum for its potential benefits, and scholars cast attention to issues such as learner motivation, learning effects and learner behaviors in the mobile learning process. Reflection is an essential part in learning as it can record learner behaviors, cultivate self-awareness of knowledge construction, facilitate cognitive growth, and promote academic achievement. Despite of the wide approval of reflection, not much study has been done concerning the application of reflection in mobile language learning process. Therefore, this study aims to investigate students’ perception of a mobile-assisted reading program facilitated with reflective activities as well as their preferences for reflection modes adopted. The participants were 60 students from two classes in a Chinese college. Students read passages on mobile applications and completed a reflection in one mode every two weeks. Four modes (paper journal reflection, e-journal reflection, audio reflection, and collaborative reflection) were adopted in the study. The study lasted approximately nine weeks. At the end of the program, all students were required to complete an anonymous questionnaire concerning their learning perception. In addition, ten students were selected randomly to attend a semi-structured interview. A pretest and a posttest were conducted to observe students’ language gains. A combination of quantitative and qualitative analysis was conducted with the data obtained. Results showed students generally approved of the effect of this mobile-assisted reading and their reading proficiency improved significantly after the program. In addition, most students favored reflective practices as a good way to stimulate interest, deepen understanding and promote reflective and summarizing abilities, but they didn’t consider it a good method to monitor the learning process in the mobile-assisted reading program. As for the preference for reflection mode, most students favored traditional paper reflection and audio reflection, while collaborative reflection and e-journal reflection received the least support. The findings provided implications for educators and app designers. For educators, based on the understanding of students’ age, learning experience, and possible preferences, they may create a good reflective environment with technical and instructional support, and then provide two or three popular modes for students to reflect on whatever they read. For app developers, some preferable reflection modes facilitated with stimulative measures may be offered to cater to more learners to conduct reflective activities.

Burned and buried: A vibrational spectroscopy analysis of burial-related diagenetic changes of heat-altered human bones.

The analysis of burned human remains can be very challenging due to heat-induced alterations. Occasionally, human bones present these coupled with diagenetic changes, offering even more of a challenge, since there is a lack of studies regarding interactions between both taphonomic phenomena. With this study, we aimed to assess and document the effects of inhumation on the chemical composition of both unburned and burned human skeletal remains. We buried, for 5 years, four groups of human bone samples comprising unburned bones and bones experimentally burned at 500, 900, and 1050 °C. Periodic exhumations were carried out to collect bone samples to be analyzed through Fourier transform infrared spectroscopy in attenuated total reflectance mode, in order to calculate four chemical indexes: (1) crystallinity index (CI); (2) type B carbonates to phosphate index (BPI); (3) total carbonates (A + B) to carbonate B ratio (C/C); and (4) OH to phosphate ratio (OH/P). After inhumation, CI and C/C of unburned bones and bones burned at 500 °C, and BPI of bones burned at 1050 °C did not vary significantly. However, the remaining indexes showed both relevant increments and reductions throughout observations, depending on burning temperature and index. Our results suggest that diagenesis can have an effect in bone's molecular composition. However, these effects do not seem to significantly affect the conclusions that can be taken from the analysis of infrared bone spectra, at least in the case of inhumations with a duration of 5 years or less.

Polarization tunable transmitted full-color display enabling switchable bright and dark states.

Although structural colors based on nanostructures have attracted many researchers' attentions due to their superior durability and high resolution, most previous reports focused on the static and dynamic structural colors in reflection mode and few researchers focus on the static and dynamic transmission colors for high-saturation RGB models. Here, the hybrid Al-Si3N4 nanogratings with the top SiO2 capping layer and the bottom MgF2 layer that can switch full-hue and high-saturation transmitted structural colors on and off completely by changing the polarization state are theoretically demonstrated. Meanwhile, the hybrid Al-Si3N4 nanogratings with the top capping layer and the bottom layer also achieve the transmittance spectra with the full width at half maximum of ∼58 nm and the transmittance efficiency of over 70% in the on state. The added top capping layer and bottom layer can suppress the sideband of transmittance spectra in the on state and maintain the near-zero transmittance in the off state, thus improving the switching performance between bright and dark states. The realizable high-saturation colors in the on state can take up 125% sRGB space and 80% Adobe sRGB space. More interestingly, with the incident angle varying from 0° to 50°, full-hue color can be also realized in the on state and nearly black color can be also maintained in the off state. The strategy will provide potential applications in advanced color encryption and multichannel imaging.

Stratigraphy of Fresco Paintings: A New Approach with Photoacoustic and SORS Imaging.

Photoacoustic (PA) imaging is a novel, powerful diagnostic technique utilized in different research fields. In particular, during recent years it has found several applications in Cultural Heritage (CH) diagnostics. PA imaging can be realized in transmittance or epi-illumination (reflectance) modes, obtaining variable levels of contrast and spatial resolution. In this work, we confirmed the applicability of the PA technique as a powerful tool for the imaging of one of the most challenging artwork objects, namely fresco wall paints, to obtain precise stratigraphic profiles in different layered fresco samples. In this regard, we studied some multi-layered fragments of the vault of San Giuseppe Church in Cagliari (1870 AD) and some mock-ups realized specifically to test the potentiality of this technique. Due to complex structures of the frescoes, we used the Spatially Off-set Raman Spectroscopy (SORS) technique to provide complementary information. The experimental results were in agreement for both techniques, even for the three-layered complex structure, and were confirmed with Scanning Electron Microscopy (SEM) analysis of cross-sections. The combined use of these two techniques proved useful to investigate detailed hidden information on the fresco samples.

In Situ Investigation of Upper Airway Occlusion in Sleep Disordered Breathing Using Ultrasonic Transducer Arrays

This work presents a novel application of ultrasound for the real-time, non-invasive investigation of occlusion of the upper airway during events of obstructive sleep apnea/hypopnea syndrome. It is hypothesized that ultrasonic pulses applied to the neck during apneic events produce spectral and temporal features that can detect apnea occurrence. Theoretical models of ultrasound propagation and an in vitro test were conducted to test this hypothesis in both transmission and reflection modes. Complete specifications and technical details of the system design and fabrication, which is mounted on each subject's neck, are presented, including the methodology. Nine patients (seven male and two female, mean age of 42 years, with a range of 25 to 56 years, and body mass index 37.6 ± 6.6 kg/m2) were recruited for a full night study, which included simultaneous nocturnal polysomnography for the validation of the results. Nine temporal features and four spectral features were extracted from the envelope of the received pulse waveform. These were used to compute 26 metrics to quantify the changes in the ultrasonic waveforms between normal breathing and apneic events. The statistical analysis of the collected ultrasonic data showed that at least two or more of the proposed features could detect apneic events in all subjects. The findings establish the feasibility of the proposed method as a cost-effective and non-invasive OSAHS screening tool.