Broadband diffuse optical spectroscopy of two-layered scattering media containing oxyhemoglobin,deoxyhemoglobin,water,and lipids

We investigated the relationship between chromophore concentrations in two-layered scattering media and the apparent chromophore concentrations measured with broadband optical spectroscopy in conjunction with commonly used homogeneous medium inverse models.We used diffusion theory to generate optical data from a two-layered distribution of relevant tissue absorbers,namely,oxyhemoglobin,deoxyhemoglobin,water,and lipids,with a top-layer thickness in the range 1–15 mm.The generated data consisted of broadband continuous-wave(CW)diffuse reflectance in the wavelength range 650–1024 nm,and frequency-domain(FD)diffuse reflectance at 690 and 830 nm;two source-detector distances of 25 and 35mm were used to simulate a dual-slope technique.The data were inverted using diffusion theory for a semi-infinite homogeneous medium to generate reduced scattering coeffcients at 690 and 830nm(from FD data)and effective absorption spectra in the range 650–1024nm(from CW data).The absorption spectra were then converted into effective total concentration and oxygen saturation of hemoglobin,as well as water and lipid concentrations.For absolute values,it was found that the effective hemoglobin parameters are typically representative of the bottom layer,whereas water and lipid represent some average of the respective concentrations in the two layers.For concentration changes,lipid showed a significant cross-talk with other absorber concentrations,thus indicating that lipid dynamics obtained in these conditions may not be reliable.These systematic simulations of broadband spectroscopy of two-layered media provide guidance on how to interpret effective optical properties measured with similar instrumental setups under the assumption of medium homogeneity.

Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OCIO and CH20 in Cl-initiated Photooxidation Experiment

Chlorine dioxide （OC10） is an important indicator for Cl-activation. The monitoring of OC10 appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We report the development of a Xe arc lamp based near-ultraviolet （335-375 nm） incoherent broad- band cavity enhanced absorption spectroscopy （IBBCEAS） spectrometer for quantitative assessment of OC10 in an atmospheric simulation chamber. The important intermediate compound CH20, and other key atmospheric trace species （NO2） were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.

Molecular dynamics of amorphous pharmaceutical fenofibrate studied by broadband dielectric spectroscopy

Fenofibrate is mainly used to reduce cholesterol level in patients at risk of cardiovascular disease. Thermal transition study with the help of differential scanning calorimetry （DSC） shows that the aforesaid active pharmaceutical ingredient （API） is a good glass former. Based on our DSC study, the molecular dynamics of this API has been carried out by broadband dielectric spectroscopy （BDS） covering wide temperature and frequency ranges. Dielectric measurements of amorphous fenofibrate were per- formed after its vitrification by fast cooling from a few degrees above the melting point （Tm=354.11 K） to deep glassy state. The sample does not show any crystallization tendency during cooling and reaches the glassy state. The temperature dependence of the structural relaxation has been fitted by single Vogel- Fulcher-Tamman （VFT） equation. From VFT fit, glass transition temperature （Tg） was estimated as 250.56 K and fragility （m） was determined as 94.02. This drug is classified as a fragile glass former. Deviations of experimental data from Kohlrausch-Williams-Watts （KWW） fits on high-frequency flank of α-peak indicate the presence of an excess wing in fenofibrate. Based on Ngai＇s coupling model, we identified the excess wing as true Johari-Goldstein （JG） process. Below the glass transition temperature one can clearly see a secondary relaxation （γ） with an activation energy of 32.67 kJ/mol.

Ordering effects of cholesterol on sphingomyelin monolayers investigated by high-resolution broadband sum-frequency generation vibrational spectroscopy

This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectroscopy （HR-BB-SFG-VS）. The SFG spectra of the three nature sphingomyelin/cholesterol mixture monolayers with two concentrations of the cholesterol at the air/water interface are performed under different polarization combination. A new resolved CH2 symmetric stretching （d＋, ~2834 cm-1） and the CH3 symmetric stretching （r＋, ~2874 cm-1） mode are applied to characterize the conformational order in the sphingomyelin/cholesterol mixture monolayers. It was found that the cholesterol make the sphingosine backbones more conformational order. During this process, the conformational order of the N-linked acyl chain remains unaltered. Moreover, the sphingosine backbones of SMs have much larger contributions to gauche defects of SMs than one in the N-linked acyl chain. These results presented here not only shed lights on understanding of the interactions of sphingomyelin molecules with cholesterol molecules at interface but also demonstrates the ability of HR-BB-SFG to probe such complicated molecular systems.

A portable single-cell analysis system integrating hydrodynamic trapping with broadband impedance spectroscopy

In this paper, we present a portable single-cell analysis system with the hydrodynamic cell trapping and the broadband electrical impedance spectroscopy （EIS）. Using the least flow resistance path principle, the hydrodynamic cell trapping in serpentine arrays can be carried out in a deterministic and automatic manner without the assistance of any external fields. The experimental results show that a cell trap rate of higher than 95% can be easily achieved in our ceil trapping microdevices. Using the maximum length sequences （MLS） technique, our home-made EIS is capable of measuring the impedance spectrum ranging from 1.953 kHz to 1 MHz in approximately 0.5 ms. Finally, on the basis of the developed single-cell analysis system, we precisely monitor the trapping process of human breast tumor cells （MCF-7 cells） according to the changes of electrical impedance. The MCF-7 cells with different trapping conditions or sizes can also be clearly distinguished through the impedance signals. Our portable single-cell analysis system may provide a promising tool to monitor single cells for long periods of time or to discriminate cell types.

Pure Rotational Spectrum of Dibenzofuran in Range of 2-6 GHz

We report the observation and assignment of the rotational spectra of dibenzofuran measured in the range of 2-6 GHz with a newly constructed broadband chirped-pulse Fourier transform microwave(cp-FTMW)spectrometer.An analysis of the microwave spectra led to the assignment of 40 b-type transitions,resulting in the accurate determination of the rotational constants A=2278.19770(38)MHz,B=601.12248(10)MHz,and C=475.753120(98)MHz.

Application of broadband terahertz spectroscopy in semiconductor nonlinear dynamics

Semiconductor nonlinearity in the range of terahertz （THz） frequency has been attracting considerable attention due to the recent development of high-power semiconductor-based nanodevices. However, the underlying physics concerning carrier dynamics in the presence of high-field THz transients is still obscure. This paper introduces an ultrafast, time-resolved THz pump/THz probe approach to study semiconductor properties in a nonlinear regime. The cartier dynamics regarding two mechanisms, intervalley scattering and impact ionization, was observed for doped InAs on a sub-picosecond time scale. In addition, polaron modulation driven by intense THz pulses was experimentally and theoretically investigated. The observed polaron dynamics verifies the interaction between energetic electrons and a phonon field. In contrast to previous work which reported optical phonon responses, acoustic phonon modulations were addressed in this study. A further understanding of the intense field interacting with solid materials will accelerate the development of semiconductor devices. This paper can be divided into 4 sections. Section 1 starts with the design and performance of a table-top THz spectrometer, which has the advantages of ultraroad bandwidth （one order higher bandwidth compared to a conventional ZnTe sensor） and high electric field strength （〉 100kV/cm）. Unlike the conventional THz timedomain spectroscopy, the spectrometer integrated a novel THz air-biased-coherent-detection （THz-ABCD） technique and utilized gases as THz emitters and sensors. In comparison with commonly used electro-optic （EO） crystals or photoconductive （PC） dipole antennas, the gases have the benefits of no phonon absorption as existing in EO crystals and no carrier life time limitation as observed in PC dipole antennas. In Section 2, the newly development THz-ABCD spectrometer with a strong THz field strength capability provides a platform for various research topics especially on the nonlinear carrier dynamics of semiconductors. Two mechanisms, electron intervalley scattering and impact ionization of InAs crystals, were observed under the excitation of intense THz field on a sub-picosecond time scale. These two competing mechanisms were demonstrated by changing the impurity doping type of the semiconductors and varying the strength of the THz field. Another investigation of nonlinear carrier dynamics in Section 3 was the observation of coherent polaron oscillation in n-doped semiconductors excited by intense THz pulses. Through modulations of surface reflection with a THz pump/THz probe technique, this work experimentally verifies the interaction between energetic electrons and a phonon field, which has been theoretically predicted by previous publications, and shows that this interaction applies for the acoustic phonon modes. Usually, two transverse acoustic （2TA） phonon responses are inactive in infrared measurement, while they are detectable in second-order Raman spectroscopy. The study ofpolaron dynamics, with nonlinear THz spectroscopy （in the far- infrared range）, provides a unique method to diagnose the overtones of 2TA phonon responses of semiconductors, and therefore incorporates the abilities of both infrared and Raman spectroscopy. Finally, some conclusions were presented in Section 4. In a word, this work presents a new milestone in wave-matter interaction and seeks to benefit the industrial applications in high power, small scale devices.

Study of broadband THz time-domain spectroscopy at different relative humidity levels

Two detection techniques of broadband terahertz（THz）time-domain spectroscopy-THz air-biased coherent detection（THz-ABCD;from 0.3 to 14 THz）and electro-optical（EO）detection（from 0.3 to 7 THz）-are both performed at several different relative humidity levels.The THz power exponentially decays with the increase in relative humidity.The dynamic range of the main pulse in the time domain linearly decreases as the relative humidity increases from 0%to 40%,and linear fittings show that the slopes are-0.017 and-0.019 for THz-ABCD and EO detection,respectively.Because of the multiple reflections caused by the crystal in the common EO detection,THz-ABCD has better spectral resolution（17 GHz）than that of EO detection（170 GHz）.The spectrum of water vapor absorption measured by THz-ABCD is also compared with that measured by the Fourier transform infrared spectroscopy（FTIR）.