Extracting fluorescence signal due to direct excitation of the energy acceptor from quantum dot-based FRET

Journal of Nanoparticle Research - An “in situ” strategy for extracting the fluorescence signal of dye acceptors due to direct excitation from Qdot-based FRET systems has been reported....     

Hemodynamic scaling of fMRI-BOLD signal: validation of low-frequency spectral amplitude as a scalability factor

Functional magnetic resonance imaging blood-oxygenation-level-dependent (fMRI-BOLD) signal representing neural activity may be optimized by discriminating MR signal components related to neural activity and those related to intrinsic properties of the cortical vasculature. The objective of this study was to reduce the hemodynamic change independent of neural activity to obtain a scaled fMRI-BOLD response using two factors, namely, low-frequency spectral amplitude (LFSA) and breath-hold amplitude (BHA). Ten subjects (age range, 22–38 years) were scanned during four task conditions: (a) rest while breathing room air, (b) bilateral finger tapping while breathing room air, (c) rest during a partial inspirational breath-hold, and (d) rest during moderate hypercapnia (breathing 5% CO₂, 20% O₂ and 75% N₂). In all subjects who breathed 5% CO₂, regions with significant BOLD response during breath-hold correlated significantly with the percent signal increase during 5% CO₂ inhalation. Finger-tapping-induced responses in the motor cortex were diminished to a similar extent after scaling using either LFSA or BHA. Inter- and intrasubject variation in the amplitude of the BOLD signal response reduced after hemodynamic scaling using LFSA or BHA. The results validated the hemodynamic amplitude scaling using LFSA with the earlier established BHA. LFSA free from motor-task contamination can be used to calibrate the fMRI-BOLD response in lieu of BHA or hypercapnia to minimize intra- and intersubject variation arising from vascular anatomy and vasodilative capacity.     

The design of a peptide linker group to enhance the SERS signal intensity of an atto680 dye‐nanoparticle system

The Surface enhanced resonance Raman spectroscopy (SERRS) spectra of three modified atto680 dyes were recorded using Au nanoparticles and an excitation laser operating at 670 nm. The dyes were modified with linker groups based on the small peptides, Cys, Cys–Gly and Cys–Gly–Gly. The Cys thiol group acted as the coupling point to the Au surface and the Gly  NH₂ group used to attach the dye. The maximum signal was recorded for the Cys–Gly linker. This gave a signal intensity for the 577 cm⁻¹ Raman peak of the atto680 dye that was more than 27 times greater than the unmodified dye. The Au nanoparticles used had a diameter of 49.8 ± 1.2 nm and were synthesised by the citrate reduction method. The Raman dye‐AuNP probes were also used in an immunoassay to detect mouse IgG in the femto mole range. Copyright © 2010 John Wiley & Sons, Ltd.     

Sources of functional magnetic resonance imaging signal fluctuations in the human brain at rest: a 7 T study

Signal fluctuations in functional magnetic resonance imaging (fMRI) can result from a number of sources that may have a neuronal, physiologic or instrumental origin. To determine the relative contribution of these sources, we recorded physiological (respiration and cardiac) signals simultaneously with fMRI in human volunteers at rest with their eyes closed. State-of-the-art technology was used including high magnetic field (7 T), a multichannel detector array and high-resolution (3 mm³) echo-planar imaging. We investigated the relative contribution of thermal noise and other sources of variance to the observed fMRI signal fluctuations both in the visual cortex and in the whole brain gray matter. The following sources of variance were evaluated separately: low-frequency drifts due to scanner instability, effects correlated with respiratory and cardiac cycles, effects due to variability in the respiratory flow rate and cardiac rate, and other sources, tentatively attributed to spontaneous neuronal activity. We found that low-frequency drifts are the most significant source of fMRI signal fluctuations (3.0% signal change in the visual cortex, TE=32 ms), followed by spontaneous neuronal activity (2.9%), thermal noise (2.1%), effects due to variability in physiological rates (respiration 0.9%, heartbeat 0.9%), and correlated with physiological cycles (0.6%). We suggest the selection and use of four lagged physiological noise regressors as an effective model to explain the variance related to fluctuations in the rates of respiration volume change and cardiac pulsation. Our results also indicate that, compared to the whole brain gray matter, the visual cortex has higher sensitivity to changes in both the rate of respiration and the spontaneous resting-state activity. Under the conditions of this study, spontaneous neuronal activity is one of the major contributors to the measured fMRI signal fluctuations, increasing almost twofold relative to earlier experiments under similar conditions at 3 T.     

A model for the dependence of the dielectric loss factor of a ferroelectric on the microwave signal amplitude

The nonlinear phenomena occurring in ferroelectrics were studied using a model for the dependence of the ferroelectric polarization on the amplitude of the applied field. The inclusion of the static internal defect field made it possible to determine the dependence of the complex permittivity of a ferroelectric on the dc electric field strength. The dependences of the complex permittivity and the dielectric loss factor on the amplitude of microwave oscillations were obtained using the Poynting theorem for harmonic microwave oscillations.     

Neuroprotection from NMDA excitotoxic lesion by Cu/Zn superoxide dismutase gene delivery to the postnatal rat brain by a modular protein vector

Background  

Superoxide mediated oxidative stress is a key neuropathologic mechanism in acute central nervous system injuries. We have analyzed the neuroprotective efficacy of the transient overexpression of antioxidant enzyme Cu/Zn Superoxide dismutase (SOD) after excitotoxic injury to the immature rat brain by using a recently constructed modular protein vector for non-viral gene delivery termed NLSCt. For this purpose, animals were injected with the NLSCt vector carrying the Cu/Zn SOD or the control GFP transgenes 2 hours after intracortical N-methyl-D-aspartate (NMDA) administration, and daily functional evaluation was performed. Moreover, 3 days after, lesion volume, neuronal degeneration and nitrotyrosine immunoreactivity were evaluated.     

Covalent attachment of a peptide to the surface of gallium nitride

The properties of GaN have made it not only an ideal material for high power and high frequency electronic devices, but also a semiconductor suitable for application in biosensing devices. The utilization of GaN in electronic biosensors has increased the importance of characterizing robust and easily implemented organic functionalization methods for GaN surfaces. This work demonstrates and characterizes a route to functionalize the GaN (0001) surface with two organic molecules, hexylamine and a peptide, through olefin cross-metathesis with Grubbs first generation catalyst. The GaN (0001) surface was chlorinated, functionalized with a terminal alkene group using a Grignard reaction, and then terminated with a carboxyl group using an olefin cross-metathesis reaction. With a condensation reaction, the final step in the reaction scheme bound hexylamine or a peptide to the carboxyl terminated GaN surface. Qualitative and quantitative X-ray photoelectron spectroscopy (XPS) data verified the success of each step in the reaction scheme. Surface element composition, adlayer coverages, and adlayer thicknesses were calculated based on the XPS data. At least a monolayer of surface molecules covered the GaN surface.     

The signal from a galactic supernova: measuring the tau-neutrino mass

We have developed a comprehensive Monte Carlo analysis in order to simulate the neutrino signal from a galactic supernova in a large water Cerenkov detector. This allows us to demonstrate that, by exploiting the various features of the signal in a way which is largely independent of the supernova model, assuming only that the late-time behaviour of the signal is flavor independent, a sensitivity to a tau-neutrino mass down to the cosmologically interesting range of ≈ 25 eV for a medium luminosity burst is possible. This is the case even though the tau signal involves ≈ 50 out of ≈ 10 000 total events in a detector of the size of that proposed for “Super Kamiokande”. In addition, our results allow us to elucidate several aspects of a supernova neutrino signal in water detectors which had not been previously explored, including new results on the observability of the neutrinization burst.     

Apertureless near field optical microscopy: a contribution to the understanding of the signal detected in the presence of a background field

Apertureless scanning near field optical microscopy techniques have become a common way of studying surface samples. By using a nano-probe that scatters the electromagnetic non-propagative waves emerging from a given sample, this microscopy provides optical images with a resolution beyond the diffraction limit. Despite a great diversity of works covering a wide variety of physical domains, the formation of the images obtained is not yet fully understood. The purpose of this letter is to assess the influence of the tip position and imposed oscillation of the tip in apertureless SNOM when a background field is added to the scattered near field. We propose a simple analytical model which enables us to account for the experimental results and explains how, depending on the experimental conditions, the near field signal can totally disappear or, on the contrary, be greatly enhanced.     

On the accuracy of a method to make film-grain noise independent of the signal

A formalism equivalent to the one previously introduced by the authors is used to determine the accuracy of a method to transform film-grain noise into signal-independent additive noise. Experimental results for film-grain noise that does not follow the classical square-root law are presented.     

Higher order QCD corrections to the photoproduction of a direct photon at HERA

The contribution of resolved photons to the photoproduction cross section of direct photons is reexamined. Higher order,O(α ² α _s), QCD corrections to this contribution are calculated and turn out to be important at HERA energies. The observation of direct photons in the medium-p _⊥ range (p _⊥～5 GeV/c) should provide the opportunity to measure the gluon content of the photon.     

Photonic approach to the measurement of time-difference-of-arrival and angle-of-arrival of a microwave signal

We propose and experimentally demonstrate a photonic approach to the measurement of the time-difference-of-arrival (TDOA) and the angle-of-arrival (AOA) of a microwave signal. In the proposed system, the TDOA and the AOA are equivalently converted into a phase shift between two replicas of a microwave signal received at two cascaded modulators. The light wave from a CW laser is externally modulated by the microwave signal at the first modulator, which is biased to suppress the optical carrier, leading to the generation of two first-order sidebands, which are further modulated by the phase-delayed microwave signal at the second modulator. Two optical components at the carrier wavelength are generated. The total power at the carrier wavelength is a function of the phase shift due to the coherent interference between the two components. Thus, by measuring the optical power, the phase shift is estimated. The AOA is calculated from the measured phase shifts. In our experiment, the phase shift of a microwave signal at 18 GHz from -160° to 40° is measured with measurement errors of less than ±2.5°.     

Application of weigert effect to the pseudocoloration of a black and white signal

We propose here a method to transform the grey levels of a black and white transparency into different colours. The transparency to be processed, illuminated by a beam of linearly polarized white light, is twice recorded on a photograph silver-chloride emulsion. The direction of the light vector is rotated through π/2 between the exposures. The resulting plate is characterized by a spatially varying anisotropy. The main point is that the wavelength λ_B and λ_D, respectively corresponding to the cancellation of birefringence and dichroism, are function of the irradiance of the signal and of the successive exposure times. The plate is then illuminated in white light and observed between two polarizers P and A. It reconstructs an achromatic image of T when the respective axes of P and A are mutually perpendicular. A rotation of A from its setting crossed with P generate a colour distribution on the plate.     

On the ability of resonant diffraction gratings to differentiate a pulsed optical signal

The passage of an optical pulse through a resonant grating is considered. The conditions under which the resonant grating differentiates the envelope of the incident pulse are determined. It is shown that the necessary condition for computing the k-order derivative is the presence of k resonances in the transmission spectrum of the grating in the vicinity of the central frequency of the incident pulse. A method is described for constructing the stacked structure for computing the kth derivative on the basis of repetition of the structure for computing the first derivative. The results of numerical simulation of diffraction of the pulse from the analyzed structure for computing the first, second, and third derivative are presented.     

Signal-to-noise ratio of a dynamical saturating system: Switching from stochastic resonator to signal processor

We consider an isolated dynamical saturating system for processing a noisy sinusoidal signal, and evaluate its performance with the measure of the signal-to-noise ratio. The considered system is linear for small inputs, but exhibits saturation in its response for large inputs. This nonlinearity displays the nonlinear phenomenon of stochastic resonance for a large biased sinusoid in appropriate system parameter regions. Without the stochastic resonance phenomenon, this dynamical saturating system can achieve a signal-to-noise ratio gain exceeding unity for a noisy unbiased sinusoid. These numerical results manifest the nonlinearities and the signal-processing ability of this system acting as a stochastic resonator or a signal processor.     

Applications of the direct Trefftz boundary element method to the free-vibration problem of a membrane

In this paper, the direct Trefftz method is applied to solve the free-vibration problem of a membrane. In the direct Trefftz method, there exists no spurious eigenvalue. However, an ill-posed nature of numerical instability encountered in the direct Trefftz method requires some treatments. The Tikhonov's regularization method and generalized singular-value decomposition method are used to deal with such an ill-posed problem. Numerical results show the validity of the current approach.     

Approximate direct reduction method: infinite series reductions to the perturbed mKdV equation

The approximate direct reduction method is applied to the perturbed mKdV equation with weak fourth order dispersion and weak dissipation. The similarity reduction solutions of different orders conform to formal coherence, accounting for infinite series reduction solutions to the original equation and general formulas of similarity reduction equations. Painlevé II type equations, hyperbolic secant and Jacobi elliptic function solutions are obtained for zero-order similarity reduction equations. Higher order similarity reduction equations are linear variable coefficient ordinary differential equations.     

Near infrared spectroscopy to study the brain: an overview

This paper gives an overview of principles, technologies, and applications using near infrared spectrometry and imaging (NIRS and NIRI) to study brain function. The physical background is reviewed and technologies and their properties are discussed. Advantages and limitations of NIRI are described. The basic functional signals obtained by NIRI, the neuronal and the hemodynamic signal are described and in particular publications about the former are reviewed. Applications in adults and neonates are reviewed, too.