Morphology and spectral properties of thin films of benzoxazole derivatives of biphenyl

We have studied the spectral properties and morphology of thin films (TVD films) formed by thermal vacuum deposition of 4,4′-bis[(E)-1-(1,3-benzoxazol-2-yl)-2-ethenyl]-1,1′-biphenyl and its substituted derivatives. We have shown that introducing bulky 2,2′-oxyhexyl substituents into the biphenyl units leads to a shift of the fluorescence maximum for the TVD films toward shorter wavelengths, a decrease in their photostability, and aggregation of the films during storage. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 300–303, May–June, 2007.     

Optimization of spectral sensitivities of mosaic five-band camera for estimating chromophore densities from skin images including shading and surface reflections

Optical Review - In this paper, the spectral sensitivities of a mosaic five-band camera were optimized using a numerical skin phantom to perform the separation of chromophore densities, shading and...     

Activities and sensitivities in boolean network models

We study how the notions of importance of variables in Boolean functions as well as the sensitivities of the functions to changes in these variables impact the dynamical behavior of Boolean networks. The activity of a variable captures its influence on the output of the function and is a measure of that variable's importance. The average sensitivity of a Boolean function captures the smoothness of the function and is related to its internal homogeneity. In a random Boolean network, we show that the expected average sensitivity determines the well-known critical transition curve. We also discuss canalizing functions and the fact that the canalizing variables enjoy higher importance, as measured by their activities, than the noncanalizing variables. Finally, we demonstrate the important role of the average sensitivity in determining the dynamical behavior of a Boolean network.     

A reaction-diffusion-problem in the biophysics of photoreceptors

Photoreceptor cells convert light signals into electric signals by transiently opening ionic channels in their cell membrane after photons have been absorbed by rhodopsin molecules in the cell membrane. The spatial information transfer from the positions of the photo-excited rhodopsins to the ionic channels is very likely to be realized by a transmitter molecule released in consequence of photo-excitation, then diffusing to the ionic channels and eventually causing their opening. This kinetic scheme is formulated in terms of a non-linear reaction-diffusion problem on the cell membrane. We propose an, approximation method for calculating the electric signal current response caused by the absorption of one single photon, the so-called quantum bump which can experimentally be observed in many photoreceptors. We also propose a way for interpreting the experimentally observed fluctuations in the quantum bumps in terms of the underlying reaction-diffusion model.Dedicated to Professor Harry Thomas on the occasion of his 60th birthdayThis work was supported by the Deutsche Forschungsgemeinschaft (SFB 160)     

Far-field spectral behaviour and spectral switching of super-Gaussian pulses

We have presented the far-field spectral behaviour of a super-Gaussian pulse diffracted through a rectangular aperture. It has been found that the on-axis modified power spectrum is always blue shifted, whose value increases with the increase in the value of the super-Gaussian parameter (m). For off-axis case, at some critical angle of diffraction, the diffraction induced far-field power spectrum is split into two lines of equal height. The far-field power spectrum is blue shifted when the diffraction angle is greater than the critical angle, whereas it is red shifted when the diffraction angle is less than the critical angle, i.e., spectral switching occurs. The critical angle for switching significantly increases with the increase in the super-Gaussian parameter (m). An important finding is that the switching frequency, the blue and red shift frequencies can be tuned by varying m.     

FPGA implementation of real-time SENSE reconstruction using pre-scan and Emaps sensitivities

Sensitivity Encoding (SENSE) is a widely used technique in Parallel Magnetic Resonance Imaging (MRI) to reduce scan time. Reconfigurable hardware based architecture for SENSE can potentially provide image reconstruction with much less computation time. Application specific hardware platform for SENSE may dramatically increase the power efficiency of the system and can decrease the execution time to obtain MR images. A new implementation of SENSE on Field Programmable Gate Array (FPGA) is presented in this study, which provides real-time SENSE reconstruction right on the receiver coil data acquisition system with no need to transfer the raw data to the MRI server, thereby minimizing the transmission noise and memory usage. The proposed SENSE architecture can reconstruct MR images using receiver coil sensitivity maps obtained using pre-scan and eigenvector (E-maps) methods. The results show that the proposed system consumes remarkably less computation time for SENSE reconstruction, i.e., 0.164 ms @ 200 MHz, while maintaining the quality of the reconstructed images with good mean SNR (29 + dB), less RMSE (< 5 × 10^− 2) and comparable artefact power (< 9 × 10^− 4) to conventional SENSE reconstruction. A comparison of the center line profiles of the reconstructed and reference images also indicates a good quality of the reconstructed images. Furthermore, the results indicate that the proposed architectural design can prove to be a significant tool for SENSE reconstruction in modern MRI scanners and its low power consumption feature can be remarkable for portable MRI scanners.     

夜晚天空光谱辐射测量研究及光谱去噪分析

光电成像器件在实现夜间光辐射探测时,由于其探测环境的光谱特性与标准光源完全不同,势必在成像特性分析上,由于光谱匹配带来较大误差。采用便携式CCD光纤光谱仪对晴朗月空、晴朗星空进行夜晚天光的光谱辐射特性测量,并进行光谱分析从而为正确评价光电成像器件的成像特性提供参考。     

Accuracy of spectrum estimate in fluorescence spectral microscopy with spectral filters

We establish the accuracy of the spectrum that is estimated with an inexpensive fluorescence spectral microscope utilizing a small set of spectral filters [Soriano et al, Opt. Exp. 10, 1458–1464 (2002)]. The spectrum at an arbitrary image location of the fluorescent sample is estimated as a linear superposition of basis spectra that are derived by singular value decomposition (SVD) or principal component analysis (PCA) from a spectral library of fluorescence spectra. Estimation performance is analyzed as a function of library statistics, filter selection and sequencing, minimum negativity constraint and signal to noise ratio (SNR) of fluorescence image. We consider image SNR degradations that arise from weakening of image intensity, additive Gaussian noise, intensity-dependent Poisson noise and quantization errors. The recovery of specific spectral features like spectral resolution, general similarity and peak alignments, is assessed using Linfoot’s criteria of fidelity, structural content, and correlation. We found that estimation with SVD basis spectra is more robust against image noise than that with PCA basis spectra. However for high SNR images, accurate estimation is achieved more quickly with PCA basis spectra and with better response to the application of minimum negativity constraint.     

Temperature and strain sensitivities of surface and hybrid acoustic wave Brillouin scattering in optical microfibers

Temperature and strain sensitivities of surface acoustic wave (SAW) and hybrid acoustic wave (HAW) Brillouin scattering (BS) in 1 μm-1.3 μm diameter optical microfibers are simulated. In contrast to stimulated Brillouin scattering (SBS) from bulk acoustic wave in standard optical fiber, SAW and HAW BS, due to SAWs and HAWs induced by the coupling of longitudinal and shear waves and propagating along the surface and core of microfiber respectively, facilitate innovative detection in optical microfibers sensing. The highest temperature and strain sensitivities of the hybrid acoustic modes (HAMs) are 1.082 MHz/℃ and 0.0289 MHz/με, respectively, which is suitable for microfiber sensing application of high temperature and strain resolutions. Meanwhile, the temperature and strain sensitivities of the SAMs are less affected by fiber diameter changes, ranging from 0.05 MHz/℃/μ to 0.25 MHz/℃/μ and 1×10^-4 MHz/με/μ to 5×10^-4 MHz/με/μ, respectively. It can be found that that SAW BS for temperature and strain sensing would put less stress on manufacturing constraints for optical microfibers. Besides, the simultaneous sensing of temperature and strain can be realized by SAW and HAW BS, with temperature and strain errors as low as 0.30 ℃-0.34 ℃ and 14.47 με-16.25 με.     

Dynamic and spectral mixing in nanosystems

In the framework of a simple spin-boson Hamiltonian we study an interplay between dynamic and spectral roots to stochastic-like behavior. The Hamiltonian describes an initial vibrational state coupled to discrete dense spectrum reservoir. The reservoir states are formed by three sequences with rationally independent periodicities 1; 1 ± δ typical for vibrational states in many nanosize systems (e.g., large molecules containing CH₂ fragment chains, or carbon nanotubes). We show that quantum evolution of the system is determined by a dimensionless parameter δΓ, where Γ is characteristic number of the reservoir states relevant for the initial vibrational level dynamics. When δΓ > 1 spectral chaos destroys recurrence cycles and the system state evolution is stochastic-like. In the opposite limit δΓ < 1 dynamics is regular up to the critical recurrence cycle k _c and for larger k > k _c dynamic mixing leads to quasi-stochastic time evolution. Our semi-quantitative analytic results are confirmed by numerical solution of the equation of motion. We anticipate that both kinds of stochastic-like behavior (namely, due to spectral mixing and recurrence cycle dynamic mixing) can be observed by femtosecond spectroscopy methods in nanosystems in the spectral window 10¹¹–10¹³ s⁻¹     

光场的非傍轴性对光谱移动和光谱开关的影响

利用瑞利衍射积分公式，推导出多色高斯光束被硬边光阑衍射后光谱的解析公式，傍轴近似的光谱公式可作为特例得到.着重研究了束腰宽度与中心波长之比w₀/λ₀和截断参数δ对光谱移动和光谱开关的影响.结果表明，只有当w₀/λ₀和δ满足一定条件时，傍轴近似结果才与非傍轴结果一致.光场的非傍轴性会引起光谱移动不同和产生光谱开关的临界位置变化. 关键词： 非傍轴光场 高斯光束 光谱移动 光谱开关     

Target spectral, dynamic spectral, and duration cues in infant perception of German vowels

Previous studies of vowel perception have shown that adult speakers of American English and of North German identify native vowels by exploiting at least three types of acoustic information contained in consonant-vowel-consonant (CVC) syllables: target spectral information reflecting the articulatory target of the vowel, dynamic spectral information reflecting CV- and -VC coarticulation, and duration information. The present study examined the contribution of each of these three types of information to vowel perception in prelingual infants and adults using a discrimination task. Experiment 1 examined German adults' discrimination of four German vowel contrasts (see text), originally produced in /dVt/ syllables, in eight experimental conditions in which the type of vowel information was manipulated. Experiment 2 examined German-learning infants' discrimination of the same vowel contrasts using a comparable procedure. The results show that German adults and German-learning infants appear able to use either dynamic spectral information or target spectral information to discriminate contrasting vowels. With respect to duration information, the removal of this cue selectively affected the discriminability of two of the vowel contrasts for adults. However, for infants, removal of contrastive duration information had a larger effect on the discrimination of all contrasts tested.     

Comparing the interparticle coupling effect on sensitivities of silver and gold nanoparticles

The wavelength shift of surface plasmon resonance peak resulting from the electromagnetic coupling noble metal nanoparticle increases with the increase in the dielectric constant of the medium and the decrease in the interparticle separation distance. In this work, the discrete dipole approximation method was used to calculate the extinction efficiency spectra of the silver–silver and gold–gold nanoparticle pairs. This work shows that the silver coupled-particle system has higher plasmon resonance sensitivity as compared to the gold coupled-particle system. However, the silver coupled-particle system has lower and a faster near-exponential decay of sensitivity enhancement factor than the gold coupled-particle system. Thus, the silver coupled-particle may be more suited for sensing applications as compared to the gold coupled-particle, but the interparticle coupling effect displays more pronounced effect on the gold coupled-particle system as compared to the silver coupled-particle system.     

Comparisons among sensitivities of different tumor cells to focused ultrasound in vitro

This study is to test the sensitivities of different tumor cells to ultrasound irradiation at the frequency of 2.2 MHz for 60 s duration, and investigate the potential mechanism underlying different sensitivities. Three murine tumor models with distinct aggressiveness (S180, H-22 and EAC) were exposed to ultrasound to evaluate their sonodynamic efficiencies, and several biological parameters such as cell membrane permeability, lipid peroxidation (LPO), ultra-structure observation, intracellular reactive oxygen species (ROS) and mitochondria membrane potential (MMP) were analyzed after exposures. The results showed that cellular responses of different cells were distinct, of interest to note, the aggressive S180 cells were much more sensitive than others, whereas EAC cells were relatively more resistant to ultrasound irradiation. The direct comparisons among different types of cells indicate that the sono-sensitization seems to depend on the physiological and chemical properties of tumor cells. Perhaps sections of cell membrane became destabilized following the initial radical attack and LPO reaction, which caused S180 cells more susceptible to mechanical stresses during sonolysis. This study provides important implications for cancer therapy.     

Comparison of the sensitivities for atom interferometers in two different operation methods

We investigated the sensitivities of atom interferometers in the usual fringe-scanning method(FSM) versus the fringelocking method(FLM). The theoretical analysis shows that for typical noises in atom interferometers, the FSM will degrade the sensitivity while the FLM does not. The sensitivity-improvement factor of the FLM over the FSM depends on the type of noises, which is validated by numerical simulations. The detailed quantitative analysis on this fundamental issue is presented, and our analysis is readily extendable to other kinds of noises as well as other fringe shapes in addition to a cosine one.     

Emergence of spectral line jumps and spectral diffusion in the two-photon correlator of a single impurity center

A dynamic theory of two-photon correlators for a single impurity center developed recently by the author [I. S. Osad’ko, Zh. éksp. Teor. Fiz. 113, 1606 (1998) [JETP 86, 875 (1998)] has been generalized to the case in which the center interacts with nonequilibrium two-level systems (TLSs) in polymers and glasses. Quantum tunneling transitions in TLS manifest themselves as random jumps of a spectral line of an impurity center. These jumps can be either spontaneous or light-induced. Interaction between the impurity center and many nonequilibrium TLSs, which exist in polymers, results in a time dependence of the optical dephasing rate 1/T ₂ of an impurity molecule, i.e., in spectral diffusion. This paper describes how the jumps of the spectral line manifest themselves in the two-photon correlator, which can be measured in experiments. Zh. éksp. Teor. Fiz. 116, 962–985 (September 1999)