Natural Gas Analysis Using Polarized Raman Spectroscopy.

Raman spectroscopy is a promising tool for measuring the composition of natural gas. However, to obtain high measurement accuracy, it is necessary to take into account changes in the spectral characteristics of methane, since its spectrum overlaps the characteristic bands of other species. In this study we present a technique for natural gas analysis based on polarized Raman spectroscopy. It is shown that the use of only isotropic components of spectra simplifies the procedure for extracting concentrations and improves the measurement accuracy of components whose spectral bands are significantly overlapped in conventional Raman spectra. The presented technique will be very useful both in the field of analysis of various multicomponent gas mixtures and in the field of measuring the isotopic composition of molecules.

Deposition of Thick SiO2 Coatings to Carbonyl Iron Microparticles for Thermal Stability and Microwave Performance.

Thick dielectric SiO2 shells on the surface of iron particles enhance the thermal and electrodynamic parameters of the iron. A technique to deposit thick, 500-nm, SiO2 shell to the surface of carbonyl iron (CI) particles was developed. The method consists of repeated deposition of SiO2 particles with air drying between iterations. This method allows to obtain thick dielectric shells up to 475 nm on individual CI particles. The paper shows that a thick SiO2 protective layer reduces the permittivity of the 'Fe-SiO2-paraffin' composite in accordance with the Maxwell Garnett medium theory. The protective shell increases the thermal stability of iron, when heated in air, by shifting the transition temperature to the higher oxide. The particle size, the thickness of the SiO2 shells, and the elemental analysis of the samples were studied using a scanning electron microscope. A coaxial waveguide and the Nicholson-Ross technique were used to measure microwave permeability and permittivity of the samples. A vibrating-sample magnetometer (VSM) was used to measure the magnetostatic data. A synchronous thermal analysis was applied to measure the thermal stability of the coated iron particles. The developed samples can be applied for electromagnetic compatibility problems, as well as the active material for various types of sensors.

Broadening of the ν2 Raman Band of CH4 by C3H8 and C4H10.

Raman spectroscopy is a promising method for the analysis of natural gas. It is necessary to account for the broadening effects on spectral lines to improve measurement accuracy. In this study, the broadening coefficients for methane lines in the region of the ν2 band perturbed by propane, n-butane, and isobutane at room temperature were measured. We estimated the measurement errors of the concentration of oxygen and carbon dioxide in the case of neglecting the broadening effects on the methane spectrum by the pressure of C2-C6 alkanes. The obtained data are suited for the correct simulation of the methane spectrum in the hydrocarbon-bearing gases and can be used to improve the accuracy of the analysis of natural gas by Raman spectroscopy.

Equivalent MIMO Channel Matrix Sparsification for Enhancement of Sensor Capabilities.

One of the development directions of new-generation mobile communications is using multiple-input multiple-output (MIMO) channels with a large number of antennas. This requires the development and utilization of new approaches to signal detection in MIMO channels, since the difference in the energy efficiency and the complexity between the optimal maximum likelihood algorithm and simpler linear algorithms become very large. The goal of the presented study is the development of a method for transforming a MIMO channel into a model based on a sparse matrix with a limited number of non-zero elements in a row. It was shown that the MIMO channel can be represented in the form of a Markov process. Hence, it becomes possible to use simple iterative MIMO demodulation algorithms such as message-passing algorithms (MPAs) and Turbo.

Raman Natural Gas Analyzer: Effects of Composition on Measurement Precision.

Raman spectroscopy is a promising method for analyzing natural gas due to its high measurement speed and the potential to monitor all molecular components simultaneously. This paper discusses the features of measurements of samples whose composition varies over a wide range (0.005-100%). Analysis of the concentrations obtained during three weeks of experiments showed that their variation is within the error caused by spectral noise. This result confirms that Raman gas analyzers can operate without frequent calibrations, unlike gas chromatographs. It was found that a variation in the gas composition can change the widths of the spectral lines of methane. As a result, the measurement error of oxygen concentration can reach 200 ppm. It is also shown that neglecting the measurement of pentanes and n-hexane leads to an increase in the calculated concentrations of other alkanes and to errors in the density and heating value of natural gas.

Doping Independent Work Function and Stable Band Gap of Spinel Ferrites with Tunable Plasmonic and Magnetic Properties.

Tuning optical or magnetic properties of nanoparticles, by addition of impurities, for specific applications is usually achieved at the cost of band gap and work function reduction. Additionally, conventional strategies to develop nanoparticles with a large band gap also encounter problems of phase separation and poor crystallinity at high alloying degree. Addressing the aforementioned trade-offs, here we report Ni-Zn nanoferrites with energy band gap (Eg) of ≈3.20 eV and a work function of ≈5.88 eV. While changes in the magnetoplasmonic properties of the Ni-Zn ferrite were successfully achieved with the incorporation of bismuth ions at different concentrations, there was no alteration of the band gap and work function in the developed Ni-Zn ferrite. This suggests that with the addition of minute impurities to ferrites, independent of their changes in the band gap and work function, one can tune their magnetic and optical properties, which is desired in a wide range of applications such as nanobiosensing, nanoparticle based catalysis, and renewable energy generation using nanotechnology.

Deposition of a SiO2 Shell of Variable Thickness and Chemical Composition to Carbonyl Iron: Synthesis and Microwave Measurements.

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment.

Depolarization Ratio of the ν1 Raman Band of Pure CH4 and Perturbed by N2 and CO2.

In this work, the effect of nitrogen and carbon dioxide on the depolarization ratio of the ν1 band of methane in the pressure range of 0.1-5 MPa is studied. A high-sensitivity single-pass Raman spectrometer was used to obtain accurate results. Moreover, we took into account the overlap of the ν1 band by the ν3 and ν2 + ν4 bands using the simulation of their spectra. The depolarization ratio of the ν1 band in pure methane is within 0-0.001, and the effect of nitrogen and carbon dioxide on this parameter is negligible in the indicated pressure range. The obtained results are useful for correct simulation of the Raman spectrum of methane at different pressures, which is necessary to improve the accuracy of gas analysis methods using Raman spectroscopy.

Nonclassical Attack on a Quantum Key Distribution System.

The article is focused on research of an attack on the quantum key distribution system and proposes a countermeasure method. Particularly noteworthy is that this is not a classic attack on a quantum protocol. We describe an attack on the process of calibration. Results of the research show that quantum key distribution systems have vulnerabilities not only in the protocols, but also in other vital system components. The described type of attack does not affect the cryptographic strength of the received keys and does not point to the vulnerability of the quantum key distribution protocol. We also propose a method for autocompensating optical communication system development, which protects synchronization from unauthorized access. The proposed method is based on the use of sync pulses attenuated to a photon level in the process of detecting a time interval with a signal. The paper presents the results of experimental studies that show the discrepancies between the theoretical and real parameters of the system. The obtained data allow the length of the quantum channel to be calculated with high accuracy.

Silver holographic gratings as substrates for surface-enhanced Raman scattering gas analysis.

This work is devoted to the investigation of the enhancement of Raman signals of nonadsorbed gases in the vicinity of corrugated metallic surfaces supporting propagating surface plasmon-polaritons (PSPPs). Simulation of the PSPP excitation efficiency on holographic gratings coated with silver films of various thicknesses at different groove heights was carried out. Verification showed good agreement between theory and experiment. Also, it was found that an increase of the PSPP excitation efficiency may not lead to an increase in the enhancement factor of Raman signals of gases located near the surface-enhanced Raman scattering active surface. For a holographic grating with a period of 667 nm, a groove height of 70 nm, and a silver film thickness of 30 nm coated with a protective ${{\rm Al}_2}{{\rm O}_3}$Al2O3 layer, the enhancement factor of Raman signals of nonadsorbed nitrogen molecules was $\sim{{\rm 4\cdot10}^3}$∼4⋅103.

Photopolarimetrical properties of coronavirus model particles: Spike proteins number influence.

Coronavirus virions have spherical shape surrounded by spike proteins. The coronavirus spike proteins are very effective molecular mechanisms, which provide the coronavirus entrance to the host cell. The number of these spikes is different; it dramatically depends on external conditions and determines the degree of danger of the virus. A larger number of spike proteins makes the virus infectivity stronger. This paper describes a mathematical model of the shape of coronavirus virions. Based on this model, the characteristics of light scattered by the coronavirus virions were calculated. It was found two main features of coronavirus model particles in the spectral region near 200 nm: a minimum of intensity and a sharp leap of the linear polarization degree. The effect of the spike protein number on the intensity and polarization properties of the scattered light was studied. It was determined that when the number of spike proteins decreases, both the intensity minimum and the position of the linear polarization leap shift to shorter wavelengths. This allows us to better evaluate the shape of the coronavirus virion, and, therefore, the infectious danger of the virus. It was shown that the shorter the wavelength of scattered light, the more reliably one can distinguish viruses from non-viruses. The developed model and the light scattering simulations based on it can be applied not only to coronaviruses, but also to other objects of a similar structure, for example, pollen.

Depolarization Ratios of Methane Raman Bands as a Function of Pressure.

In this work, we measured the intensities of Q-branches of the ν1, ν2 and ν3 bands in the polarized and depolarized methane Raman spectra in the pressure range of 1-60 atm. It was established that the pressure dependence of depolarization ratios of the ν2 and ν3 bands are negligible. In turn, the depolarization ratio of the ν1 band increases with increasing pressure and reaches approximately 0.0045 at 60 atm. These data are more precise than previously published ones because ν1 band intensities were determined taking into account the contribution of overlapping lines of ν3 band. The presented data will be useful in calculating the methane polarizabilities at high pressure, as well as in calculating methane Raman spectra for measuring the natural gas composition using Raman spectroscopy.

Enhancement of Raman scattering of a gaseous medium near the surface of a silver holographic grating.

The Letter demonstrates a possibility to enhance the Raman scattering of a gaseous medium due to an enhanced electromagnetic field caused by the excitation of propagating surface plasmon polaritons (PSPPs) on a silver holographic grating. Efficiency of collinear and noncollinear schemes of PSPP excitation on a metal-gaseous medium interface was studied. When using a collinear scheme, we registered an eightfold enhancement of the Raman scattering of atmospheric nitrogen and oxygen, where the average gain near the PSPP-active surface was ∼4×103.

High-fat diet-induced deregulation of hippocampal insulin signaling and mitochondrial homeostasis deficiences contribute to Alzheimer disease pathology in rodents.

Global obesity is a pandemic status, estimated to affect over 2 billion people, that has resulted in an enormous strain on healthcare systems worldwide. The situation is compounded by the fact that apart from the direct costs associated with overweight pathology, obesity presents itself with a number of comorbidities, including an increased risk for the development of neurodegenerative disorders. Alzheimer disease (AD), the main cause of senile dementia, is no exception. Spectacular failure of the pharmaceutical industry to come up with effective AD treatment strategies is forcing the broader scientific community to rethink the underlying molecular mechanisms leading to cognitive decline. To this end, the emphasis is once again placed on the experimental animal models of the disease. In the current study, we have focused on the effects of a high-fat diet (HFD) on hippocampal-dependent memory in C57/Bl6 Wild-type (WT) and APPswe/PS1dE9 (APP/PS1) mice, a well-established mouse model of familial AD. Our results indicate that the continuous HFD administration starting at the time of weaning is sufficient to produce ß-amyloid-independent, hippocampal-dependent memory deficits measured by a 2-object novel-object recognition test (NOR) in mice as early as 6months of age. Furthermore, the resulting metabolic syndrome appears to have direct effects on brain insulin regulation and mitochondrial function. We have observed pathological changes related to both the proximal and distal insulin signaling pathway in the brains of HFD-fed WT and APP/PS1 mice. These changes are accompanied by a significantly reduced OXPHOS metabolism, suggesting that mitochondria play an important role in hippocampus-dependent memory formation and retention in both the HFD-treated and AD-like rodents at a relatively young age.

Multipass optical system for a Raman gas spectrometer.

In the present work, a multipass optical system intended for increasing the sensitivity of a Raman gas spectrometer based on the 90° geometry of scattered light collection is described. The system is characterized by an adjustment stability and an increased number of laser beams that pass through a small scattering volume, thus allowing the intensities of Raman signals from components of the gas medium in this volume to be increased. It is demonstrated that the application of this multipass optical system allows the sensitivity of the Raman gas spectrometer to be increased practically by 20 times (to several ppm for the 30-s registration time).

Collection optics for a Raman spectrometer based on the 90° geometry of scattered light collection.

In the present work, efficiency of classical lens, mirror-lens, and pure mirror variants of the collection optics for a Raman spectrometer based on 90° geometry of scattered light collection is investigated. It is experimentally established that, despite a smaller collection angle, in the case of a relatively narrow input slit of the spectrometer (<100 µm), the lens optics with corrected off-axis and chromatic aberrations allows larger signal intensities to be registered. However, the low f/# mirror collection optics described in the work provide a more stable adjustment and can be used to increase the Raman signal intensities in cases when the image of the scattering volume formed by them is commensurable with the sizes of the input slit of the spectrometer.

Current Research Therapeutic Strategies for Alzheimer's Disease Treatment.

Alzheimer's disease (AD) currently presents one of the biggest healthcare issues in the developed countries. There is no effective treatment capable of slowing down disease progression. In recent years the main focus of research on novel pharmacotherapies was based on the amyloidogenic hypothesis of AD, which posits that the beta amyloid (Aß) peptide is chiefly responsible for cognitive impairment and neuronal death. The goal of such treatments is (a) to reduce Aß production through the inhibition of ß and γ secretase enzymes and (b) to promote dissolution of existing cerebral Aß plaques. However, this approach has proven to be only modestly effective. Recent studies suggest an alternative strategy centred on the inhibition of the downstream Aß signalling, particularly at the synapse. Aß oligomers may cause aberrant N-methyl-D-aspartate receptor (NMDAR) activation postsynaptically by forming complexes with the cell-surface prion protein (PrPC). PrPC is enriched at the neuronal postsynaptic density, where it interacts with Fyn tyrosine kinase. Fyn activation occurs when Aß is bound to PrPC-Fyn complex. Fyn causes tyrosine phosphorylation of the NR2B subunit of metabotropic glutamate receptor 5 (mGluR5). Fyn kinase blockers masitinib and saracatinib have proven to be efficacious in treating AD symptoms in experimental mouse models of the disease.

Early alterations in energy metabolism in the hippocampus of APPswe/PS1dE9 mouse model of Alzheimer's disease.

The present study had focused on the behavioral phenotype and gene expression profile of molecules related to insulin receptor signaling in the hippocampus of 3 and 6 month-old APPswe/PS1dE9 (APP/PS1) transgenic mouse model of Alzheimer's disease (AD). Elevated levels of the insoluble Aß (1-42) were detected in the brain extracts of the transgenic animals as early as 3 months of age, prior to the Aß plaque formation (pre-plaque stage). By the early plaque stage (6 months) both the soluble and insoluble Aß (1-40) and Aß (1-42) peptides were detectable. We studied the expression of genes related to memory function (Arc, Fos), insulin signaling, including insulin receptor (Insr), Irs1 and Irs2, as well as genes involved in insulin growth factor pathways, such as Igf1, Igf2, Igfr and Igfbp2. We also examined the expression and protein levels of key molecules related to energy metabolism (PGC1-α, and AMPK) and mitochondrial functionality (OXPHOS, TFAM, NRF1 and NRF2). 6 month-old APP/PS1 mice demonstrated impaired cognitive ability, were glucose intolerant and showed a significant reduction in hippocampal Insr and Irs2 transcripts. Further observations also suggest alterations in key cellular energy sensors that regulate the activities of a number of metabolic enzymes through phosphorylation, such as a decrease in the Prkaa2 mRNA levels and in the pAMPK (Thr172)/Total APMK ratio. Moreover, mRNA and protein analysis reveals a significant downregulation of genes essential for mitochondrial replication and respiratory function, including PGC-1α in hippocampal extracts of APP/PS1 mice, compared to age-matched wild-type controls at 3 and 6 months of age. Overall, the findings of this study show early alterations in genes involved in insulin and energy metabolism pathways in an APP/PS1 model of AD. These changes affect the activity of key molecules like NRF1 and PGC-1α, which are involved in mitochondrial biogenesis. Our results reinforce the hypothesis that the impairments in both insulin signaling and energy metabolism precede the development of AD amyloidogenesis.

Generalized Efimov Effect in One Dimension.

We study a one-dimensional quantum problem of two particles interacting with a third one via a scale-invariant subcritically attractive inverse square potential, which can be realized, for example, in a mixture of dipoles and charges confined to one dimension. We find that above a critical mass ratio, this version of the Calogero problem exhibits the generalized Efimov effect, the emergence of discrete scale invariance manifested by a geometric series of three-body bound states with an accumulation point at zero energy.