Smaller Absorption Research Articles

Simultaneous determination of the scattering and absorption coefficients of turbid media based on Mueller matrix

The simultaneous determination of scattering and absorption coefficients of turbid media is studied by a three-dimensional polarization-sensitive Monte Carlo (PSMC) model. The results show that the scattering and absorption coefficient have strong correlations with the main diagonal elements of the Mueller matrix, rather than the off-diagonal elements of Mueller matrix. For turbid medium with smaller absorption ( μ a ≤ 1 cm−1), the relationship between the scattering and absorption coefficients, and the main diagonal elements is linear or quasilinear. The maximum errors of the estimated scattering coefficient and absorption coefficient using linear fitted method are 5.0% and 1.0%, respectively. For turbid medium with bigger absorption ( μ a > 1 cm−1), the relationship between the scattering and absorption coefficients, and the main diagonal elements is nonlinear, which can be specified by the lookup table method. The maximum errors of the determination scattering coefficient and absorption coefficient are 8.7% and 2.7%, respectively.

Numerical Simulation of Enhancement of Superficial Tumor Laser Hyperthermia with Silicon Nanoparticles

Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in water and ethanol as agents for laser tumor hyperthermia, we numerically simulated effects of heating a millimeter-size nodal basal-cell carcinoma with embedded nanoparticles by continuous-wave laser radiation at 633 nm. Based on scanning electron microscopy data for the synthesized SiNPs size distributions, we used Mie theory to calculate their optical properties and carried out Monte Carlo simulations of light absorption inside the tumor, with and without the embedded nanoparticles, followed by an evaluation of local temperature increase based on the bioheat transfer equation. Given the same mass concentration, SiNPs obtained by the laser ablation of silicon nanowires in ethanol (eSiNPs) are characterized by smaller absorption and scattering coefficients compared to those synthesized in water (wSiNPs). In contrast, wSiNPs embedded in the tumor provide a lower overall temperature increase than eSiNPs due to the effect of shielding the laser irradiation by the highly absorbing wSiNPs-containing region at the top of the tumor. Effective tumor hyperthermia (temperature increase above 42 °C) can be performed with eSiNPs at nanoparticle mass concentrations of 3 mg/mL and higher, provided that the neighboring healthy tissues remain underheated at the applied irradiation power. The use of a laser beam with the diameter fitting the size of the tumor allows to obtain a higher temperature contrast between the tumor and surrounding normal tissues compared to the case when the beam diameter exceeds the tumor size at the comparable power.

Optical and electrical optimization of all-perovskite pin type junction tandem solar cells

A definitive breakthrough of perovskite solar cells towards large scale industrialization is believed to be the demonstration of higher efficiencies than conventional silicon technology, suggesting the exploration of perovskite tandem cell configurations. Since high efficiency tandem solar cells require careful optimization of photoactive as well as contact and additional functional layers, we propose an optical-electrical model to obtain the optimum layer thicknesses and the attainable electrical output parameters of two-terminal perovskite-perovskite tandem solar cells. The optical model takes into account the coherent propagation of light through the layer stack comprising two perovskite semiconductors and the corresponding contact layers, while the electrical model assumes two series-connected analytical current/voltage equations for pin solar cells. This model allows to assess the impact of the main physical parameters on each perovskite layer without requiring the high specificity needed in more rigorous numerical simulations. Efficiencies above 34% are predicted considering available perovskites with non-optimum bandgap and contact materials already proven in efficient laboratory solar cells. The requisite to attain such efficiencies is that recombination at the interfaces between the perovskite and contact materials is kept low in both bottom and top cells. Furthermore, within the assumption of non-optimum bandgaps of currently available perovskites, the simulation results suggest that efficiencies around 37% are possible when adopting contact materials with smaller absorption, more adequate refraction indices, and lower resistivity.

Terahertz absorption spectra of several polymer nanocomposites indicating polymer-filler interactions

Optical absorption spectra in a frequency range from 0.5 to 5.0 THz were measured in several epoxy resin nanocomposites with and without co-addition of micro-sized fillers, aiming at obtaining important information on intermolecular interactions between filler and polymer. As a result, significantly large absorption appears when both micro-sized MgO and nano-sized SiO2 fillers were added in epoxy resin. Similar but smaller absorption is also found in an epoxy resin composite with nano-sized TiO2 fillers.

Kvašenje i namakanje bolničkog zaštitnog tekstila

Moisture management, as one of the key performance criteria in terms of fabric comfort, specifically on cotton fabrics intended for use in a hospital environment, was investigated in this paper. For this purpose, commercial cotton fabrics for surgical gowns and hospital linen were used, as well as standard cotton fabrics treated with various cationic antimicrobial protection agents. The antimicrobial properties were achieved by cationization with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride, or reactive polyammonium compounds Rewin OS; and by treatment with quaternary ammonium compounds (QACs), N-cetylpyridinium chloride (N-CPC) and cetylpyridinium bromide (CPB), which act as surfactants and antiseptics. Standard cotton fabric has excellent hydrophilicity, fast absorption and spreading, large spreading area and good one-way transport. It is characterized as Moisture management fabric. Hospital white linen fabric has a water repellent finish; however, it is breathable and can be characterized as a Water penetration fabric. Hospital green fabric for gowns and instrument covers, due to dyestuff blocking the active groups have smaller absorption, and is characterized as Fast absorbing and quick drying fabric. Cotton fabrics have negative zeta potential. Cationization change surface charge, as well as antimicrobial activity. In MMT both cationized cotton fabrics are characterized as Fast absorbing and quick drying fabric, as they have fast wetting, absorption and spreading, a large spreading area, but poor one-way transport. For the QAC treated fabrics this effect is more enhanced. However, these fabrics have excellent antimicrobial activity even after desorption. Based on the results of wetting and wicking, zeta potential and antimicrobial activity, CPB treatment is proposed for the processing of cotton fabrics.

Errata: Optical properties of mice skull bone in the 455- to 705-nm range.

Rodent brain is studied to understand the basics of brain function. The activity of cell populations and networks is commonly recorded in vivo with wide-field optical imaging techniques such as intrinsic optical imaging, fluorescence imaging, or laser speckle imaging. These techniques were recently adapted to unrestrained mice carrying transcranial windows. Furthermore, optogenetics studies would benefit from optical stimulation through the skull without implanting an optical fiber, especially for longitudinal studies. In this context, the knowledge of bone optical properties is requested to improve the quantitation of the depth and volume of imaged or stimulated tissues. Here, we provide experimental measurements of absorption and reduced scattering coefficients of freshly excised mice skull for wavelengths between 455 and 705 nm. Absorption coefficients from 6 to 8 months mice skull samples range between 1.67 ± 0.28 ?? mm ? 1 at 455 nm and 0.47 ± 0.07 ?? mm ? 1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79 ± 0.26 ?? mm ? 1 at 455 nm up to 2.29 ± 0.12 ?? mm ? 1 at 705 nm. In comparison, measurements carried out on 4 to 5 weeks mice showed similar spectral profiles but smaller absorption and reduced scattering coefficients by a factor of about 2 and 1.5, respectively.

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom–field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.

Optical properties of mice skull bone in the 455- to 705-nm range.

Rodent brain is studied to understand the basics of brain function. The activity of cell populations and networks is commonly recorded in vivo with wide-field optical imaging techniques such as intrinsic optical imaging, fluorescence imaging, or laser speckle imaging. These techniques were recently adapted to unrestrained mice carrying transcranial windows. Furthermore, optogenetics studies would benefit from optical stimulation through the skull without implanting an optical fiber, especially for longitudinal studies. In this context, the knowledge of bone optical properties is requested to improve the quantitation of the depth and volume of imaged or stimulated tissues. Here, we provide experimental measurements of absorption and reduced scattering coefficients of freshly excised mice skull for wavelengths between 455 and 705 nm. Absorption coefficients from 6 to 8 months mice skull samples range between 1.67 ± 0.28 ?? mm ? 1 at 455 nm and 0.47 ± 0.07 ?? mm ? 1 at 705 nm, whereas reduced scattering coefficients were in the range of 2.79 ± 0.26 ?? mm ? 1 at 455 nm up to 2.29 ± 0.12 ?? mm ? 1 at 705 nm. In comparison, measurements carried out on 4 to 5 weeks mice showed similar spectral profiles but smaller absorption and reduced scattering coefficients by a factor of about 2 and 1.5, respectively.

Investigation of absorption characteristics for thermal-load fluctuation using HTTR

ABSTRACTA commercial very high-temperature gas-cooled reactor (VHTR) hydrogen cogeneration system named gas turbine high temperature reactor 300-cogeneration (GTHTR300C) is designed and developed in Japan Atomic Energy Agency (JAEA). Moreover, it has been planned that hydrogen production system and gas turbine system is connect to high-temperature engineering test reactor (HTTR). The reactor system is required to continue a stable and safety operation as well as a stable power supply in the case that thermal-load is fluctuated by the occurrence of abnormal event in the heat utilization system like as the hydrogen production facility. Then, it is necessary to confirm that the thermal-load fluctuation could be absorbed by the reactor system so as to continue the stable and safety operation. The thermal-load fluctuation absorption tests using the HTTR were planned to clarify the absorption characteristics of the HTGR system. However, it is difficult to clarify the phenomenon due to many kinds of fluctuation in nuclear thermal power in the reactor core. Moreover, the actual data regarding how the delay of the temperature response is effective for the reactor system had been gained quantitatively.The thermal-load fluctuation absorption tests without nuclear heating were planned and conducted in JAEA to clarify the absorption characteristic of thermal-load fluctuation mainly by the reactor and by the intermediate heat exchanger (IHX). The absorption characteristics of thermal-load fluctuation can be revealed with sufficient temperature fluctuation. So the tests were conducted with the primary coolant temperature 120 °C which is the start-up temperature of the HTTR. As a result it was revealed that the reactor has the larger absorption capacity of thermal-load fluctuation than the expected one and that the IHX can be contributed to the absorption of the thermal-load fluctuation generated in the heat utilization system in the reactor system. It was confirmed from their results that the reactor and the IHX has effective absorption capacity of the thermal-load fluctuation generated in the heat utilization system. Moreover, the calculation with the safety evaluation code based on RELAP5/MOD3 was performed. It was confirmed that the calculated temperature for the reactor is almost same to the measured one with the new analysis model. On the other hand, it was confirmed that the calculated temperature for the IHX decreased faster than the measured one due to smaller absorption capacity in the calculation model than that in actual one. It can be considered that the calculation for the IHX produces the conservative result. It was summarized that the safety evaluation code can represent the thermal-load fluctuation absorption behavior conservatively.

Spatial variations of seismic attenuation and heterogeneity in the Pyrenees: Coda Q and peak delay time analysis

Abstract Lateral variations of seismic attenuation in the Pyrenees are explored from the analysis of local earthquake records. Scattering loss and intrinsic absorption both control the propagation of short period S waves through the crust. The role of intrinsic and scattering attenuation is analyzed in two steps. Firstly, the coda quality factor Q c , which quantifies the energy decay of coda waves, is estimated at large lapse time in five frequency bands and interpreted as intrinsic absorption. Next, we systematically measure the peak delay time defined as the time lag from the direct S-wave onset to the maximum amplitude arrival. This parameter quantifies the strength of multiple forward scattering due to random inhomogeneities along the seismic ray path. Comparison of coda- Q and peak delay time measurements allows a qualitative interpretation of the origin of seismic attenuation (scattering/absorption) in the Pyrenean crust. At low frequency, coda- Q variations mainly depend on the tectonic units of the Pyrenees, with stronger absorption in sedimentary basins and smaller absorption in Paleozoic basements. At high frequency, coda- Q is low at the location of Neogene structures in the Eastern Pyrenees. A more enigmatic low- Q c anomaly is also observed at the location of the Maladeta Massif in the Central Pyrenees. In all frequency bands, peak delay time measurements systematically show stronger scattering in the Western Pyrenees. In the Labourd–Mauleon area, absorption and scattering are both important at low frequency. The Western Pyrenees also correspond to a high-velocity/density anomaly revealed from tomography and gravity data analysis. This suggests that the high level of inhomogeneities and absorption may be related to intrusion of mantle and/or lower-crustal materials. In the Eastern Pyrenees, absorption appears dominant over scattering at high frequency. We hypothesize that the strong absorption observed in this area may be related to volcanic structures.

Soot Optical Properties in the Terahertz Spectra Domain

For understanding and accurately modeling combustion, the important questions are what species are present in the flame, and the spatial distribution and temperature of these species. Traditional optical methods used only the electromagnetic waves in the wavelength region from the ultraviolet region up to the infrared. Terahertz time-domain spectroscopy technique can be used for the combustion research as a novel tool. However, for some sooty combustion environments, the strong absorption, spectral interference from soot scattering, and fluorescence from large molecules must be considered. The optical properties of soot in the terahertz domain are the main basic data for terahertz application. In this paper, the terahertz time-domain spectroscopy technique was used to study the optical properties of flame soot within 0.2–1.6 THz. The complex refractive indices of the soot were deduced by the fixed-point iteration method. In order to validate the results, the complex refractive indices of the soot from the four different fuel flames were deduced. It was found that the complex refractive indices in the terahertz domain of the soot from the different fuel flames are very close to each other. The comparisons of complex refractive indices between the visible–IR domain and the terahertz domain indicate that the value of absorption index in terahertz domain is smaller than in IR domain, which implies that the terahertz wave will penetrate the sooty flame with smaller absorption than the IR rays. The results can provide the basic optical data of flame soot for the application of terahertz time-domain spectroscopy technique in the optical combustion diagnostics and extend the optical combustion diagnostics application area.

Effect of Feeding Condition on the Gastrointestinal Absorption of D-Xylose in Rats

The potential effect of feeding condition-associated alteration of gastrointestinal physiology on passive absorption was examined in rats, using D-xylose, a five-carbon monosaccharide, as a model solute. The fraction of D-xylose dose absorbed after oral administration was decreased to 0.856 in rats without fasting, compared with 0.961 in fasted rats. This was attributable to a smaller intestinal absorption rate constant (ka) in the former, because the intestinal transit was suggested to be unchanged. The reduction in ka was most likely attributable to an increase in the luminal volume as a physiological parameter. In the intestinal loop in-situ, D-xylose absorption was independent of concentration, consistent with the passive transport mechanism, and also unaffected by feeding condition. These results suggest that a decrease in absorption can occur in fed rats, compared with fasted rats, without involvement of carrier-mediated transport which is competitively inhibited by nutritional substrates.

Terahertz properties of liquid crystals with negative dielectric anisotropy

We present what is believed to be the first terahertz time-domain study of a set of liquid crystals (LCs) with negative dielectric anisotropy. From the measured data, refractive indices, and absorption coefficients for ordinary and extraordinary polarization are extracted. We find that the investigated materials exhibit a much smaller absorption than LCs with positive dielectric anisotropy. Thus, these materials are more useful for switchable terahertz devices. Moreover, the LC 1808 shows what is to our knowledge the largest terahertz birefringence reported so far.

Influence of material properties on extraordinary optical transmission through hole arrays

We present a theoretical study, based on the finite difference time domain method, of the optical response of circular hole arrays drilled in several metal films (Ag, Au, Cu, Al, Ni, Cr, and W). Two series of structures are studied. In the first one, transmittance peaks are analyzed as all geometrical parameters defining the system are scaled, except for the metal thickness which is kept constant, showing good agreement with existing experimental data. In the second series, the metal thickness is also scaled. This allows a clear distinction in the behavior of different metals: Ag, Au, and Cu show even larger transmittance peaks than hole arrays in a perfect conductor with the same nominal parameters. This is due to both a larger effective hole area and smaller absorption. In the case of Ni and Cr, the transmittance is much smaller due to absorption. Band structure calculations confirm that surface electromagnetic modes sustained by the perforated metal film are responsible for the extraordinary optical transmission phenomenon.

Detailed Theoretical Investigation on Enhanced Nondegenerate Four-Wave Mixing in Passive Mode-Locked Semiconductor Lasers

The passive mode-locked semiconductor laser (PMLL) can realize terahertz (THz) four-wave mixing (FWM) with high conversion efficiency and no need for pump input. Theoretical investigation on its FWM characteristics has been carried out by using the traveling wave and carrier rate equations combined with nonlinear dynamics of carrier density pulsation (CDP), carrier heating (CH), and spectral-hole burning (SHB). The stable mode-locked conjugate pulse with short-duration high-repetition frequency can be obtained by the PMLL. The pedestal-free conjugate pulse has narrower width and larger amplitude jitter compared with the pump wave. Smaller absorption recovery time is helpful to extend the stable conjugate output regime. There exists a down-limit for absorption recovery time to avoid self-pulsation (SP) instability. The larger injection current is required for smaller absorption recovery time to reach the given conversion efficiency. The larger conversion efficiency and narrower conjugate pulse can be obtained by proper design of distributed Bragg reflector (DBR) coupling strength. The DBR bandwidth must be designed to be within signal-pump detuning to avoid resonance-induced conjugate pulse distortion. The FWM in PMLL has considerable potential such as demultiplexing in optical time-division multiplexing systems.

X-Ray Emission-Line Profiles of Three Early-Type Stars Observed with Chandra

Abstract We analyzed the X-ray emission-line profiles of three early-type stars ($\zeta$ Pup, $\delta$ Ori, and $\tau$ Sco) obtained with Chandra. A phenomenological model, where X-ray sources are distributing in wind above some lower limit radius, can fit the line profiles of $\zeta$ Pup and $\delta$ Ori; however, the fitting requires a much smaller absorption than expected from the mass-loss rate. This suggests that, if this phenomenological model represents the real X-ray emission region, there is substantial ionization or clumping of the stellar wind. The parameters derived from the line profile of $\tau$ Sco indicate that the X-ray-emitting plasma is concentrated on the stellar surface, suggesting the existence of a confined plasma on the stellar surface.

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO3 in the THz range

The absorption coefficient and the index of refraction of undoped and Mg-doped stoichiometric and congruent LiNbO3 crystals were determined for polarization parallel to the z axis in the far-infrared (FIR) 30−180-cm−1 frequency range for different Mg-doping levels and temperatures down to 10 K. For stoichiometric LiNbO3, smaller absorption and index of refraction were found, than for congruent samples. At a Mg content near the photorefractive threshold, the FIR absorption coefficient has the lowest value in the stoichiometric crystals, which are most suitable for efficient pulse generation in the terahertz range.

The phase transition temperatures of a liquid crystal determined from FT-IR spectra explored by principal component analysis

The FT-IR spectra of a thin layer of pure 4-chloro-2′-hydroxy-4′-pentyloxyazobenzene (CHPAB) were studied as a function of temperature. A detailed analysis of the intensity variations was performed by a method based on principal component analysis (PCA). It was shown that the phase transition temperatures obtained by means of PCA and those determined by differential scanning calorimetry (DSC), the most widely used technique in the field, were nearly identical. The PCA results revealed that the transition from solid to a liquid crystalline (LC) phase (smectic A) is more drastic phase transition in terms of infrared absorption changes. The nematic to isotropic phase transition is much less infrared sensitive. Very much smaller absorption changes are associated with the transition between the smectic and nematic mesophases. The pattern of the intensity changes strictly is correlated with the orientation of the CHPAB molecules towards the surface windows due to the surface-induced homeotropic alignment of LC molecules. The important role of hydrogen bonding interaction on the observed transition is disclosed.

Doppler shift of femtosecond laser pulses from solid density plasmas

Doppler-shift of short UV pulses (248 nm, 700 fs) reflected from aluminum, polystyrene and gold targets were measured at focused intensities up to 5×1015 W/cm2. In spite of the fact that the Doppler-shifts are expected to be dependent on the atomic weight of the target material, experimentally similar shifts are found for all targets. A possible explanation is provided by the well known dependence of the Doppler shift on the plasma temperature, if different absorption coefficients are assumed for the different targets. This coefficient shows good agreement with that one deduced from a theory based on collisional absorption in the case of aluminum, but in the case of the other targets, however, the experimentally observed Doppler-shift suggests smaller absorption for lighter and larger absorption for heavier target materials.

Estimation of Direct Radiative Forcing of Asian Dust Aerosols with Sun/Sky Radiometer and Lidar Measurements at Gosan, Korea

In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model simulation at Gosan, Jeju using the data from a sun/sky radiometer, a Micro-Pulse Lidar (MPL), and column radiometer measurements of solar downwelling irradiance in April, 2001. We suggest a method of determining aerosol parameters for the radiative transfer model from the Aerosol Robotic Network (AERONET) data set. Since the AERONET measurements provide the refractive indices at only four wavelengths, and the aerosol parameters can be calculated at these wavelengths with a Mie code, we use a linear regression method for extending these measurements to the full wavelength spectrum of the radiative transfer model. The aerosol forcing by the Asian dust aerosols is estimated and compared to the aerosol forcing of non-dust aerosols. On the Asian dust event day, April 13, the daily average ADRF was estimated as -58.1 W/m² at the surface and -25.7 W/m² at the top of the atmosphere (TOA). On April 15, a nondust day slightly influenced by anthropogenic aerosols, the ADRF was -29.0 W/m² at the surface and -11.6 W/m² at the TOA. Although the Asian dust aerosols show larger forcing, its forcing efficiency (forcing per unit optical thickness) is smaller than that of non-dust aerosols; ²41.0 W/m²/τ670 at the TOA and -94.9 W/m²/τ670 at the surface on the dust day for dust aerosols, as opposed to -50.0 W/m²/τ670 at the TOA and -129.3 W/m²/τ670 at the surface on the non-dust day for non-dust aerosols. We believe that this is due to the larger single scattering albedo of dust aerosols, which causes smaller absorption, and the larger asymmetry factor which causes more forward scattering or less reflection, compared to anthropogenic aerosols. The model results were validated with the surface irradiance measurement data and the comparison showed a good agreement. The radiative transfer calculation underestimates the solar irradiance of 2∼3% on average. The aerosol profiles measured by lidar are used to estimate the influence of the vertical distribution of Asian dust aerosols on the ADRF. Using the vertical aerosol profiles, we found an instantaneous short wave radiative heating larger than 2 K/day. We believe the enhanced heating rate by the aerosol layers contributes to the increase in static stability within the dust layer. This fact is verified by the temperature profile measured by the sonde, and may explain the longevity and consequently long-range transport of Asian dust.