Order Spectra Research Articles

Graphene quantum dots obtained by unfolding fullerene

Graphene quantum dots (GQDs) have recently been proposed as fluorescent sensors for metal ions dissolved in water. The physical origin of this fluorescence is still not completely clear, therefore further studies on GQDs and their properties are required. Graphene-like quantum dots were prepared by oxidation and unfolding of commercial buckminsterfullerene. This process was carried out by a modified Hummers method. After dialysis, the solution was diluted with deionized water to obtain the reference solution for optical measurements. Part of the solution was dried to obtain the unfolded fullerene powder. The metal ions were allowed to interact with GQDs by adding the metal-salt water solution to the stock solution of unfolded fullerene. The properties of GQDs before and after incorporation of metal ions (Hg, Cd, Pb, Cu, Ni and As) were characterized by using X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy, UV–vis and fluorescent spectroscopies. In XPS, a particular attention was given to the analysis of photoemission C 1 s and Auger C KVV spectra in order to determine the carbon electronic configuration and its changes after incorporation of metal ions into GQDs. Obtained quantum dots were composed of graphene with oxidized borders. Optical measurements showed that the interaction with metal ions was changing the fluorescence intensity and optical absorbance, with different characteristics for each distinct ionic species. This behavior could be used for a selective multiple sensor detecting different heavy metals in water solutions.

Simultaneous detection of different probe molecules using silver nanowires as SERS substrates.

Metallic silver nanowires with high yield were synthesized using a modified seed mediated approach at room temperature. Ribbon-like nanostructures were obtained when the concentration of NaOH was lower and further increase of NaOH transformed it into long nanowires. These nanowires possess high aspect ratio, with length and diameter ~6.5 μm and 17 nm respectively. The surface enhanced Raman scattering activity of these nanowires was tested with three different probe molecules viz., crystal violet, malachite green and nile blue chloride using visible (514.4 nm) and near-infrared (784.8 nm) excitation lines. The minimum detection limits for crystal violet and nile blue chloride molecules were found to be down to 10-7 M with good linear responses, as evidenced by values of correlation coefficients, indicating their potential for a variety of applications such as sensing. Principal component analysis was performed with the surface enhanced Raman spectra in order to discriminate the dye molecules and their mixture, simultaneously. The first two principal components, which provided 69.80 and 27.93% of the total data variance, could be conveniently represented as a two dimensional PCA score plot. The score plot showed clear clustering of probe molecules and their mixture. The relative contribution of wavenumbers to each of the two principal components was identified by plotting the PCA loading matrix. These results further promote possibilities of quantification of multiplexed SERS detection and analysis.

Integrating magnetic and stratigraphic data to delineate the subsurface features in and around new Galala City, Northern Galala Plateau, Egypt

ABSTRACTThe Egyptian Government is developing a new city, Galala, above the Northern Galala Plateau, western side of Gulf of Suez between Ain Sukhna and Zafarana. The aim of the study is integrating magnetic and stratigraphic data to delineate the subsurface features beneath the New Galala City, in order to avoid the possible geological hazards. The stratigraphic succession in the study area consists of Precambrian basement complex overlain unconformably by Phanerozoic sequence. The Phanerozoic sequence composed mainly of siliciclastic-dominated rocks superimposed by carbonate-dominated rocks. The carbonate-dominated rocks cover most surface area, whilst the siliciclastic-dominated rocks exposed along eastern and southern foot slope of the Northern Galala Plateau. The observed palaeo-karst surfaces, fissures, caves, sink-holes and fault zones within carbonate rocks may cause some geological hazards in the study area. The total intensity aeromagnetic map was subjected to un-prescribed structural index 3D-Euler Deconvolution (ED), the tilt angle derivative (TDR) and the power spectrum in order to estimate both trends and source depths. The source depths range from 500 m to 4000 m, which result from the Precambrian basement complex. However, the trends of encountered structural elements are mainly NE–SW, NW–SE, NNW–SSE and E–W directions.

Binding effects in sulfur Kα and Kβ X-ray emission spectra

Sulfur samples in different oxidation states (+4, +6, 0 and −2) were irradiated in a commercial microscope, acquiring Kα and Kβ spectra in order to investigate the influence of the chemical bond on the occurrence of different sulfur decays to 1s vacancy states.

Factor of Natural Curative Resources in Context of Legal Regulation of Medical Rehabilitation

Introduction: Human health is understood as a condition at which physical, psychological and social well-being is maintained when implementing a set of relevant measures directed to its support. The process of recovery of the proper state of health is maintained by measures which have a different character of origin and direction and cover a greater sphere of influence in order to obtain the most positive result when rehabilitating. It is an important component for returning the vital activity which existed before its loss. Natural curative resources as components of the environment play an important role during medical rehabilitation that allows receiving a positive effect while using their therapeutic natural properties. Aim: The article is aimed at researching different sources of legal regulation with respect to using natural curative resources during medical rehabilitation. Review and Conclusions: Integrated, reasonable and rational approaches when improving the rehabilitation process should be based on individual peculiarities of the human body, previous diseases and chosen restoration methods. When studying peculiarities which determine uniqueness of a natural object having therapeutic peculiarities, it is necessary to use their whole spectrum in order to achieve a better result in less time. Legal regulation of the defined set of issues allows outlining certain borders which form the proper behavior and understanding of its consequences. However, consolidation of certain aspects of one set of issues in various sources of legal regulation limits possibility of a more comprehensive and systematic approach to this issue.

Development of Validated Q-absorbance Ratio, Derivative Spectrophotometric and Stability indicating RP-HPLC methods for the simultaneous estimation of Losartan Potassium & Hydrochlorothiazide in Pharmaceutical Dosage Form and comparison of the results by ANOVA

Hypertension is estimated to cause 7.5 million deaths, leading to 12.8 % of the total of all deaths worldwide. In the recent years, the combination of Losartan Potassium and Hydrochlorothiazide has attained significant popularity in reducing the risk of heart diseases particularly in the patients with hypertension and ventricular hypertrophy. The literature survey revealed that there were several chromatographic and spectroscopic methods for the simultaneous estimation of the selected drugs but it was noted that there were no reported comparative studies of the developed methods. Hence the authors attempted to develop new validated Q- absorbance ratio, Derivative spectrophotometric and Stability indicating RP-HPLC methods for the simultaneous estimation of Losartan Potassium and Hydrochlorothiazide in pharmaceutical dosage form. The authors also propose to compare the results obtained by ANOVA. The two Spectrophotometric methods were carried out using an Agilent Cary 60 UV-Visible double beam Spectrophotometer. In Q-absorbance ratio method, samples were measured at two wavelengths, 230 nm (isoabsorptive point) and 225.5 nm (?max of Hydrochlorothiazide). In Derivative spectroscopy, analysis was performed by derivatizing the zero order spectrum to the corresponding second order spectrum. Stability indicating RP-HPLC method was performed using Eclipse XDB C18 column where the samples were analyzed using a mixture of Acetonitrile and Water in the ratio of 70:30 % v/v as mobile phase at a flow rate of 1 ml/min. The drugs were monitored at 230 nm. The retention times for Losartan Potassium and Hydrochlorothiazide were found to be 1.010 minutes and 1.387 minutes respectively. The proposed methods were validated as per ICH guidelines. The results obtained from the three developed methods were then compared by ANOVA which indicated that the proposed methods can successfully be used for the analysis of Losartan Potassium and Hydrochlorothiazide in bulk or in combined dosage forms.

UV Spectrophotometric Estimation of Emtricitabine by Zero order and area under Curve methods in Bulk and Pharmaceutical Dosage Form

Simple and precise UV spectrophotometric methods by UV spectroscopy and area under curve [AUC] – in zero order derivative spectrums have been developed and validated for the estimation of emtricitabine in pharmaceutical formulation. The standard and sample solutions of emtricitabine were prepared in distilled water. Emtricitabine was estimated at 280 nm for the UV-spectrophotometric method (A), while in area under curve (AUC) method (B) the zero order spectrum of Emtricitabine was measured in between 272–286 nm. Beer's law was obeyed in both the methods in the concentration range of 2 to 20 μg/ml with coefficient of correlation value 0.9999. These methods were validated for various parameters according to ICH guidelines. The precision expressed as relative standard deviation were 0.2584% and 0.0640% for the above two methods respectively. The proposed methods were successfully applied for the determination of emtricitabine in pharmaceutical formulation. Results of the analysis were validated statistically and were found to be satisfactory. The proposed methods are simple, easy to apply and low-cost.

ISVD-Based In-Band Noise Reduction Approach Combined With Envelope Order Analysis for Rolling Bearing Vibration Monitoring Under Varying Speed Conditions

In practical applications, the signal measured from a complex mechanical system is usually disturbed by various noises due to the compounded effect of interferences of other machine elements and background noises, especially under varying speed conditions. Resonance-based approaches have been proven to be effective methods to address this problem. However, even if the optimal resonance band is accurately determined, the in-band noise with frequency content in the range covered by the band-pass filter is not eliminated. To avoid missed diagnosis and misdiagnosis of faults in bearings, an iterated SVD (ISVD)-based in-band noise reduction method combined with envelope order spectrum analysis is proposed in this paper. First, the optimal frequency band of a vibrational signal is determined with the help of an enhanced wavelet packet transform kurtogram, in which the kurtosis of each node is calculated based on the envelope spectrum of a signal be reconstructed using the wavelet packet coefficients. The node with the maximum kurtosis value is used to reconstruct the signal. Second, the envelope of a reconstructed signal is calculated by Hilbert transform and the ISVD method is applied to it to reduce the in-band noise. To avoid the destruction of useful information caused by excessive iteration, a threshold is set to determine the number of iterations. After iterative processing, a de-noised signal is reconstructed based on the relationship between the singular value and a frequency component. Finally, the reconstructed signal is resampled and transformed into the fault characteristic order domain where the bearing fault type can be identified from the envelope order spectra. The simulations and experiments were used to validate the efficacy of the proposed method. Compared with the spectral subtraction method, the ISVD method can suppress in-band noise efficiently and beneficial to extract the fault characteristic order under variable speed conditions.

Automatic Diagnosis of Rolling Element Bearing Under Different Conditions Based on RVMD and Envelope Order Capture

Fault characteristic frequency is the main basis for rolling element bearing diagnostics but finding a suitable frequency band for demodulation and searching for the fault characteristic frequencies consume a lot of time and manpower in practice. A data-driven method based on recursive variational mode decomposition (RVMD), and an envelope order capture is proposed to realize the automatic fault diagnosis of bearing under different operating conditions. The process starts with a new proposed RVMD of the vibration signal, where the mode with maximum kurtosis of the unbiased autocorrelation of the envelope is selected to get envelope order spectrum. Thereafter, an order capture algorithm is designed to automatically search for the fault characteristic orders in theory, which are used for constructing feature vectors for diagnosis. The proposed method is tested on two test-beds which both contain the same type of bearing (SKF6205) but operate in different conditions, and gets good performance in bearing diagnosis. In addition, the fault diagnosis of test-bed two using training samples that are from test-bed one is investigated. This method reveals well generalization capability in the fault diagnosis of the same type of rolling element bearing under different operating conditions.

UV Spectrophotometric Estimation of Imatinib mesylate by Area under Curve Methods in Bulk and Pharmaceutical Dosage form

Simple and precise UV spectrophotometric method by area under curve [AUC]-have been developed and validated for the estimation of imatinib mesylate in bulk and its tablet formulation. The standard and sample solutions of imatinib mesylate were prepared in distilled water. Imatinib mesylate was estimated area under curve (AUC) method, the zero order spectrum of imatinib mesylate was measured in between 250 nm to 270 nm. Beer's law was obeyed in the concentration range of 1 to 20 μg/ml with coefficient of correlation value 0.9999. These methods were tested and validated for various parameters according to ICH guidelines. The precision expressed as relative standard deviation were of 0.0444% respectively. The proposed method was successfully applied for the determination of imatinib mesylate in pharmaceutical formulation. Results of the analysis were validated statistically and were found to be satisfactory. The proposed method is simple, easy to apply, low-cost and require relatively inexpensive instruments.

Noise reduction for near-infrared spectroscopy data using extreme learning machines

The near infrared (NIR) spectra technique is an effective approach to predict chemical properties and it is typically applied in petrochemical, agricultural, medical, and environmental sectors. NIR spectra are usually of very high dimensions and contain huge amounts of information. Most of the information is irrelevant to the target problem and some is simply noise. Thus, it is not an easy task to discover the relationship between NIR spectra and the predictive variable. However, this kind of regression analysis is one of the main topics of machine learning. Thus machine learning techniques play a key role in NIR based analytical approaches. Pre-processing of NIR spectral data has become an integral part of chemometrics modeling. The objective of the pre-processing is to remove physical phenomena (noise) in the spectra in order to improve the regression or classification model. In this work, we propose to reduce the noise using extreme learning machines which have shown good predictive performances in regression applications as well as in large dataset classification tasks. For this, we use a novel algorithm called C-PL-ELM, which has an architecture in parallel based on a non-linear layer in parallel with another non-linear layer. Using the soft margin loss function concept, we incorporate two Lagrange multipliers with the objective of including the noise of spectral data. Six real-life dataset were analyzed to illustrate the performance of the developed models. The results for regression and classification problems confirm the advantages of using the proposed method in terms of root mean square error and accuracy.

STM/STS and photoemission study of Ag thin films on Ga/Si(111) ([formula omitted])R30°

Silver thin films have been formed by room temperature deposition of Ag on a Ga/Si(111) (3×3)R30° surface. Scanning tunneling microscopy and spectroscopy (STM/STS) have been used to study both the clean Ga/Si(111) (3×3)R30° surface and Ag films with different coverages. For the film formation, Ag first grows into 2D islands on Ga/Si(111) (3×3)R30°. The first layer of the islands forms atomic lines with three-fold symmetry in the 1 × 1 direction of the underlying Si(111) substrate. From a 2 ML coverage, the growth becomes layer-by-layer mode. STS measurements have been performed on Ag films with different coverages in order to investigate their electronic structures. Between 2–4 ML, the STS spectra reveal 2 and 3 peaks below the Fermi level. These peaks move towards the Fermi level with increased film thicknesses and thus share the same behavior as those of quantum well states (QWSs). The energy positions of the peaks have been compared with valence band photoelectron spectra in order to assign them to various parts of the QWSs. In addition, the photoemission results also confirm the existence of QWSs for a 2 ML Ag film on Ga/Si(111) (3×3)R30°.

CZEKAJĄC NA WIELKĄ STRATEGIĘ USA W STOSUNKU DO CHIN. PODSUMOWANIE USTALEŃ I ZALECEŃ KOMISJI PRZEGLĄDU BEZPIECZEŃSTWA RELACJI USA–CHINY W LATACH 2002-2018

The article is a summary of works of almost two decades of the US-China Security Review Commission. As the US Congress notices the challenges posed by China to a wide spectrum of US interests and orders the US President to develop a comprehensive strategy on China, author highlights that such an awareness was already present among US officials much earlier. Article focuses on three key areas, i.e.: geostrategic posture, military posture and technological development, anticipating, that most of the problem defined by the Commission in these areas have not been eliminated and are most likely to be observed by the creator of the upcoming strategy. Author argues that China has a significant advantage over US, resulting from two major factors. First, its the inflow of capital followed by inflow of US technologies to Chinese industries and businesses. Second, it’s the centrally planned and governed Chinese system that allows CCP to steer the economy and society with higher predictability, as opposed to freedom-based economy on the US side, which is independent of the Congressional/Administrational guidance. The article’s overall goal is to allow readers a better insight into the Presidential Strategy on China, which is to be published 180 days from the enactment of the National Defense Authorization Act for FY 2019.

Tying Together Multiscale Calculations for Charge Transport in P3HT: Structural Descriptors, Morphology, and Tie-Chains.

Evaluating new, promising organic molecules to make next-generation organic optoelectronic devices necessitates the evaluation of charge carrier transport performance through the semi-conducting medium. In this work, we utilize quantum chemical calculations (QCC) and kinetic Monte Carlo (KMC) simulations to predict the zero-field hole mobilities of ∼100 morphologies of the benchmark polymer poly(3-hexylthiophene), with varying simulation volume, structural order, and chain-length polydispersity. Morphologies with monodisperse chains were generated previously using an optimized molecular dynamics force-field and represent a spectrum of nanostructured order. We discover that a combined consideration of backbone clustering and system-wide disorder arising from side-chain conformations are correlated with hole mobility. Furthermore, we show that strongly interconnected thiophene backbones are required for efficient charge transport. This definitively shows the role “tie-chains” play in enabling mobile charges in P3HT. By marrying QCC and KMC over multiple length- and time-scales, we demonstrate that it is now possible to routinely probe the relationship between molecular nanostructure and device performance.

Quantum Spin Liquid Intertwining Nematic and Superconducting Order in Fese.

Despite its seemingly simple composition and structure, the pairing mechanism of FeSe remains an open problem due to several striking phenomena. Among them are nematic order without magnetic order, nodeless gap and unusual inelastic neutron spectra with a broad continuum, and gap anisotropy consistent with orbital selection of unknown origin. Here we propose a microscopic description of a nematic quantum spin liquid that reproduces key features of neutron spectra. We then study how the spin fluctuations of the local moments lead to pairing within a spin-fermion model. We find the resulting superconducting order parameter to be nodeless s±d wave within each domain. Further we show that orbital dependent Kondo-like coupling can readily capture observed gap anisotropy. Our prediction calls for inelastic neutron scattering in a detwinned sample.

Feature Extraction and Similarity of Movement Detection during Sleep, Based on Higher Order Spectra and Entropy of the Actigraphy Signal: Results of the Hispanic Community Health Study/Study of Latinos.

The aim of this work was to develop a new unsupervised exploratory method of characterizing feature extraction and detecting similarity of movement during sleep through actigraphy signals. We here propose some algorithms, based on signal bispectrum and bispectral entropy, to determine the unique features of independent actigraphy signals. Experiments were carried out on 20 randomly chosen actigraphy samples of the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) database, with no information other than their aperiodicity. The Pearson correlation coefficient matrix and the histogram correlation matrix were computed to study the similarity of movements during sleep. The results obtained allowed us to explore the connections between certain sleep actigraphy patterns and certain pathologies.

Higher-order moments, cumulants, and spectra of continuous quantum noise measurements

We present general quantum mechanical expressions for higher order moments, cumulants, and spectra of continuously measured quantum systems with applications in spin noise spectroscopy, quantum transport, and measurement theory in general. Starting from the so-called stochastic master equation of continuous measurement theory, we find that the leading orders of the fluctuating detector output $z(t)$ with respect to the measurement strength $\beta$ are a white shot noise background, a constant measurement offset, and the leading order quantum noise of the measured operator $A$. Starting from quantum expressions for the multi-time moments $\langle z(t_n)\cdots z(t_1) \rangle$ we derive three- and four-time cumulants that are valid in all orders of $\beta$ covering the full regime between the weak and strong measurement limit (Zeno-limit). Intriguingly, quantum expressions for the cumulants were found that exhibit the same simple structure as those for the moments after introduction of only a slightly modified system propagator. Very compact expressions for the cumulant-based third and fourth order spectra (bispectrum and trispectrum) follow naturally. We illustrate the usefulness of higher order spectra by treating a real world two-spin system with strong hyperfine interaction.Moreover, spin noise spectroscopy is shown to have the potential for investigating the transition from weak measurements to the famous quantum Zeno regime for realistic probe laser intensities.

Molecular organization and optical switching of liquid-crystalline azobenzenes in monomolecular films

The photoisomerization and thermal relaxation processes of three amphiphilic azobenzene derivatives (LCAn) showing liquid-crystalline properties were studied in solutions and in monomolecular films formed using Langmuir and Langmuir-Blodgett techniques. The well-controlled isomeric state of LCAn in chloroform during the UV irradiation allowed to prepare spreading solutions containing trans isomers, cis isomers or their mixture and to investigate molecular organization in the Langmuir films made of them. Surface pressure-mean molecular area isotherms and compression modulus-surface pressure dependences delivered information on a thermodynamic state, phase transitions and intermolecular interaction in the monolayers. LCAn in the trans state create densely-packed films, in which the photoisomerization do not occur due to the lack of free volume for the change of the molecules conformation and their strong tendency for the H-type aggregation. However, the reversible switching of the LCAn conformation during cyclic photoisomerization and thermal relaxation processes was observed in the LB films initially deposited onto quartz substrates in the cis state, where molecules are loosely-packed and exist in the monomeric form. Kinetics and rate constants of the photoisomerization and thermal relaxation were determined based on the recorded absorption spectra in order to obtain information on their efficiency and on the impact of the replacement of the alkyl chain attached in the LCAn para position with the alkyloxy chain. Our research show that LCAn are promising materials for application in optical memories, logic gates and holographic gratings.

An adaptive energy aware strategy based on game theory to add privacy in the physical layer for cognitive WSNs

The expansion of big data and the evolution of Internet of Things (IoT) technologies will play an important role in the feasibility of Smart City initiatives. In this IoT network infrastructure Cognitive Wireless Sensor Networks (WSNs), as a network of nodes that work in a cooperative way to sense the spectrum and control the environment surrounding them, are one of the main technologies. Security and privacy appear as key aspects for the development of new applications and services. In this work we propose a novel artificial noise generation strategy based on game theory in order to improve the security against privacy attacks in CWSNs. Artificial noise generation consists in introducing interferences in the spectrum in order to mask the real information. The decision whether or not to introduce artificial noise is modeled through a light non-cooperative game designed for low-resources networks that balance security enhancement and energy consumption. We show, using several simulations, that even with a cognitive attacker our strategy has reduced the information obtained by the attacker (Secrecy Outage Probability) to a value under 10%. The overhead (energy consumption and spectrum occupancy) of the strategy has also been deeply analyzed. All possible cases our approach provides better results, in the ratio energy consumption - security, than not using the strategy or using a random noise generation strategy. Also, although the saturation of the radio spectrum is strongly affected, the reliability of the network is maintained in 95% of application packages received. Therefore, we can conclude that an improvement of the privacy in the physical layer is obtained, taking into account energy consumption and maintaining levels of spectrum saturation suitable for the application proposes.

Application of Fractional Differential Calculation in Pretreatment of Saline Soil Hyperspectral Reflectance Data

Pretreatment of spectrum data is a necessary and effective method for improving the accuracy of hyperspectral model building. Traditional differential calculation pretreatment only considers the integer-order differential, such as the 1st order and 2nd order, and overlooks important spectrum information located at fractional order. Since fractional differential (FD) has rarely been applied to spectrum field measurement, there are few reports on the spectrum features of saline soils under different degrees of human interference. We used FD to analyze field spectrum data of saline soil collected from Xinjiang’s Fukang City. Order interval of 0.2 was adopted to divide 0–2 orders into 11-order differentials. MATLAB programming was used to convert the raw spectral reflectance and its four common types of mathematics and to conduct FD calculation. Spectrum data for area A (no human interference area) and area B (human interference area) was separately processed. From the statistical analysis of soil salinization characteristics, the salinization degree and type for area B were more diverse and complicated than area A. MATLAB simulation results showed that FD calculation could depict the minute differences between different FD order spectra under different human interference areas. The overall differential value trend appeared to move towards 0 reflectance value. After differential processing, the trend of bands that passed the 0.05 significance test of correlation coefficient (CC) showed an increase first then decrease later. The maximum CC absolute value for five spectrum transformations all appeared in the fractional order. FD calculation could significantly increase the correlation between spectral reflectance and soil salt content both for full-band and single-band spectra. Results of this study can serve as a reference for the application of FD in field hyperspectral monitoring of soil salinization for different human interference areas.