Boxcar Averager Research Articles

Evaluating Noise Reduction Methods for Raman Spectroscopy in Transmission and Reflection Configurations

This work involved comparing Raman signals obtained from two different Raman spectroscopy configurations, using two distinct noise reduction methods. The excitation light source was a laser diode with a wavelength of 532 nm. A long-pass filter and focusing lens were utilized to block the excited light from the source and concentrate the Raman signals due to their weaker nature compared to the excited light signals. Light of 532 nm wavelength was blocked during green laser diode illumination using a long-pass filter. Two configurations were studied: transmission Raman spectroscopy (TRS) and reflection Raman spectroscopy (RRS). Raman signals from both configurations were compared, and the boxcar averaging and Vancouver Raman algorithm (VRA) noise reduction methods were investigated and compared. The results showed that Raman signals from the transmission configuration were higher than those from the reflection configuration, and noise signals were effectively reduced using both the boxcar averaging and VRA methods.

Boxcar Averaging Scanning Nonlinear Dielectric Microscopy.

Scanning nonlinear dielectric microscopy (SNDM) is a near-field microwave-based scanning probe microscopy method with a wide variety of applications, especially in the fields of dielectrics and semiconductors. This microscopy method has often been combined with contact-mode atomic force microscopy (AFM) for simultaneous topography imaging and contact force regulation. The combination SNDM with intermittent contact AFM is also beneficial for imaging a sample prone to damage and using a sharp microscopy tip for improving spatial resolution. However, SNDM with intermittent contact AFM can suffer from a lower signal-to-noise (S/N) ratio than that with contact-mode AFM because of the shorter contact time for a given measurement time. In order to improve the S/N ratio, we apply boxcar averaging based signal acquisition suitable for SNDM with intermittent contact AFM. We develop a theory for the S/N ratio of SNDM and experimentally demonstrate the enhancement of the S/N ratio in SNDM combined with peak-force tapping (a trademark of Bruker) AFM. In addition, we apply the proposed method to the carrier concentration distribution imaging of atomically thin van der Waals semiconductors. The proposed method clearly visualizes an anomalous electron doping effect on few-layer Nb-doped MoS2. The proposed method is also applicable to other scanning near-field microwave microscopes combined with peak-force tapping AFM such as scanning microwave impedance microscopy. Our results indicate the possibility of simultaneous nanoscale topographic, electrical, and mechanical imaging even on delicate samples.

Artificial intelligence analysis of FTIR and CD spectroscopic data for predicting and quantifying the length and content of protein secondary structures

Besides NMR and X-ray crystallography, FTIR and CD spectroscopy are widely considered to be useful for determining protein secondary structure. These techniques can be used to obtain data in few minutes, using small quantities of proteins, which make them amenable for proteomics research. Here we explore the possibility of using artificial intelligence techniques to simultaneously analyse both FTIR and CD spectroscopic data for an identical set of proteins. Neural network analysis was carried out on normalised regions of FTIR (1700-1600 cm−1) and CD (180-259 nm) spectral data both with and without boxcar averaging in order to quantify the average length and percentages of secondary structures. A hybrid genetic algorithm/neural network approach, that automatically selects structure-sensitive wavelength/frequency, was used for the quantification of the protein secondary structure. Using this algorithm we also successfully identified the region of the CD spectrum that contains the most structure-sensitive information. This was located between 214-251 nm, suggesting that this region alone may be sufficient to rapidly determine the secondary structure content from CD spectral data. Overall, CD spectroscopic analysis produced better results compared to FTIR spectroscopy when selected wavelengths were used, although FTIR was better when the entire region between 1700-1600 cm−1 (FTIR), and 180-259 nm (CD), was subjected to neural network analysis. Application of Adaptive Neuro-Fuzzy Inference System (ANFIS) with fuzzy subtractive clustering for the analysis of the spectral data led to a slightly better prediction of the average helix/sheet length for FTIR spectroscopy compared to CD. Our findings reveal the potential of using artificial intelligence techniques for not only extracting structural information but also for better understanding of the relationship between complex spectral data and biologically important information.

Improving Prediction of Peroxide Value of Edible Oils Using Regularized Regression Models.

We present four unique prediction techniques, combined with multiple data pre-processing methods, utilizing a wide range of both oil types and oil peroxide values (PV) as well as incorporating natural aging for peroxide creation. Samples were PV assayed using a standard starch titration method, AOCS Method Cd 8-53, and used as a verified reference method for PV determination. Near-infrared (NIR) spectra were collected from each sample in two unique optical pathlengths (OPLs), 2 and 24 mm, then fused into a third distinct set. All three sets were used in partial least squares (PLS) regression, ridge regression, LASSO regression, and elastic net regression model calculation. While no individual regression model was established as the best, global models for each regression type and pre-processing method show good agreement between all regression types when performed in their optimal scenarios. Furthermore, small spectral window size boxcar averaging shows prediction accuracy improvements for edible oil PVs. Best-performing models for each regression type are: PLS regression, 25 point boxcar window fused OPL spectral information RMSEP = 2.50; ridge regression, 5 point boxcar window, 24 mm OPL, RMSEP = 2.20; LASSO raw spectral information, 24 mm OPL, RMSEP = 1.80; and elastic net, 10 point boxcar window, 24 mm OPL, RMSEP = 1.91. The results show promising advancements in the development of a full global model for PV determination of edible oils.

Geomagnetically Induced Currents and Harmonic Distortion: High Time Resolution Case Studies

AbstractHigh time resolution (1–5 s) magnetometer, geomagnetically induced current (GIC), and mains harmonic distortion data from the Halfway Bush substation in Dunedin, New Zealand, are analyzed. A recently developed technique using very low frequency (VLF) radio wave data provides high‐resolution measurements of mains harmonic distortion levels. Three case studies are investigated, each involving high rates of change of local geomagnetic field, but with different timescales of magnetospheric driver mechanisms, and different substation transformer configurations. Two cases of enhanced GIC during substorm events are analyzed, and one case of a storm sudden commencement. Time delays between magnetic field fluctuations and induced transformer currents are found to be ~100 s for substorm events, but only ~20 s for the storm sudden commencement containing higher‐frequency variations. Boxcar averaging of the magnetic field fluctuations using running windows of ±2 min leads to spectral power profiles similar to those of GIC profiles, with reduced power at frequencies >0.003 Hz (periods <5 min). Substantially lower mains harmonic distortion levels were observed after the removal of the single phase bank transformer, HWB T4, from the high‐voltage configuration at Halfway Bush. No systematic time delay was found between GIC variations and mains harmonic distortion levels. The power spectra of magnetic field fluctuations and GIC variations during the sudden storm commencement with no harmonic distortion showed low levels of low‐frequency power (<0.003 Hz, periods >5 min). This low‐frequency component of the magnetic field power spectrum appears necessary for mains harmonic distortion to occur.

Boxcar detection for high-frequency modulation in stimulated Raman scattering microscopy

Stimulated Raman scattering (SRS) microscopy is an important non-linear optical technique for the investigation of unlabeled samples. The SRS signal manifests itself as a small intensity exchange between the laser pulses involved in coherent excitation of Raman modes. Usually, high-frequency modulation is applied in one pulse train, and the signal is then detected on the other pulse train via lock-in amplification. While allowing shot-noise limited detection sensitivity, lock-in detection, which corresponds to filtering the signal in the frequency domain, is not the most efficient way of using the excitation light. In this manuscript, we show that boxcar averaging, which is equivalent to temporal filtering, is better suited for the detection of low-duty-cycle signals as encountered in SRS microscopy. We demonstrate that by employing suitable gating windows, the signal-to-noise ratios achievable with lock-in detection can be realized in shorter time with boxcar averaging. Therefore, high-quality images are recorded at a faster rate and lower irradiance which is an important factor, e.g., for minimizing degradation of biological samples.

On Aethalometer measurement uncertainties and an instrument correction factor for the Arctic

Abstract. Several types of filter-based instruments are used to estimate aerosol light absorption coefficients. Two significant results are presented based on Aethalometer measurements at six Arctic stations from 2012 to 2014. First, an alternative method of post-processing the Aethalometer data is presented, which reduces measurement noise and lowers the detection limit of the instrument more effectively than boxcar averaging. The biggest benefit of this approach can be achieved if instrument drift is minimised. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise of the instrument is kept constant. This approach results in a time series with a variable collection time (Δt) but with a constant relative uncertainty with regard to electronic noise in the instrument. An additional advantage of this method is that the detection limit of the instrument will be lowered at small aerosol concentrations at the expense of temporal resolution, whereas there is little to no loss in temporal resolution at high aerosol concentrations ( > 2.1–6.7 Mm−1 as measured by the Aethalometers). At high aerosol concentrations, minimising the detection limit of the instrument is less critical. Additionally, utilising co-located filter-based absorption photometers, a correction factor is presented for the Arctic that can be used in Aethalometer corrections available in literature. The correction factor of 3.45 was calculated for low-elevation Arctic stations. This correction factor harmonises Aethalometer attenuation coefficients with light absorption coefficients as measured by the co-located light absorption photometers. Using one correction factor for Arctic Aethalometers has the advantage that measurements between stations become more inter-comparable.

Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell.

Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1 f and 2 f, respectively) agree with the Beer-Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz-1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2 f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.

Focus on spectroscopy and photonics

Focus on spectroscopy and photonics

Comparison of potential field solutions for Carrington Rotation 2144

AbstractWe examined differences among the coronal magnetic field structures derived with the potential field source surface (PFSS) model for Carrington Rotation 2144, from 21 November to 19 December 2013. We used the synoptic maps of solar photospheric magnetic field from four observatories, the Huairou Solar Observing Station (HSOS), Global Oscillation Network Group (GONG), Helioseismic Magnetic Imager (HMI), and Wilcox Solar Observatory (WSO). We tested two smoothing methods, Gaussian and boxcar averaging, and correction of unbalanced net magnetic flux. The solutions of three‐dimensional coronal magnetic field are significantly different each other. An open‐field region derived with HSOS data agrees best with the corresponding coronal hole observed by Solar Dynamics Observatories/Atmospheric Imaging Assembly, while HMI data yielded best agreements with the near‐Earth OMNI database. The GONG data overall gave agreements as good as the HMI. The PFSS calculations using WSO data were least sensitive to the choices we examined in this work. Differences in PFSS solutions using different choices and parameters in smoothing imply that the photospheric magnetic field distributions with size of several degrees at midlatitude and low‐latitude regions can be decisive, at least, in the examined period. To better determine the global solar corona, therefore, further evaluation of influences from compact bipolar magnetic field is needed.

Causality of manufacturing processes with significant time delays

In this paper, the effects of flow rate, fiber consistency, and pressure fluctuation on basis weight variations were studied based on a set of paper mill operation data that include thick stock flow rate, consistency at eight different stock preparation stages, inlet and outlet pressure of the pressure pulsation attenuator, scanner position, β gauge, and scanner basis weight measurements. In order to focus on the important spectra and correlations within the low frequency range, a boxcar averaging procedure to eliminate high frequency extraneous information was employed. Moreover, two complete sets of data have been obtained for consistent and problematic operational conditions; namely, with and without a stuff box flow control system. The transfer function between the input and output spectra of certain components or processes within approach flow systems is also studied. Particular emphasis is placed on the synchronization procedure necessary for the study of low frequency range signals, as well as the correlation between two signals. All analysis results presented here are derived with an in-house developed program targeted for systems with significant time delays.

Improved Method for the Quantification of Motility in Glia and Other Morphologically Complex Cells

Cells such as astrocytes and radial glia with many densely ramified, fine processes pose particular challenges for the quantification of structural motility. Here we report the development of a method to calculate a motility index for individual cells with complex, dynamic morphologies. This motility index relies on boxcar averaging of the difference images generated by subtraction of images collected at consecutive time points. An image preprocessing step involving 2D projection, edge detection, and dilation of the raw images is first applied in order to binarize the images. The boxcar averaging of difference images diminishes the impact of artifactual pixel fluctuations while accentuating the group-wise changes in pixel values which are more likely to represent real biological movement. Importantly, this provides a value that correlates with mean process elongation and retraction rates without requiring detailed reconstructions of very complex cells. We also demonstrate that additional increases in the sensitivity of the method can be obtained by denoising images using the temporal frequency power spectra, based on the fact that rapid intensity fluctuations over time are mainly due to imaging artifact. The MATLAB programs implementing these motility analysis methods, complete with user-friendly graphical interfaces, have been made publicly available for download.

Estimation of Antarctic ozone loss from ground-based total column measurements

Abstract. The passive tracer method is used to estimate ozone loss from ground-based measurements in the Antarctic. A sensitivity study shows that the ozone depletion can be estimated within an accuracy of ~4%. The method is then applied to the ground-based observations from Arrival Heights, Belgrano, Concordia, Dumont d'Urville, Faraday, Halley, Marambio, Neumayer, Rothera, South Pole, Syowa, and Zhongshan for the diagnosis of ozone loss in the Antarctic. On average, the ten-day boxcar average of the vortex mean ozone column loss deduced from the ground-based stations was about 55±5% in 2005–2009. The ozone loss computed from the ground-based measurements is in very good agreement with those derived from satellite measurements (OMI and SCIAMACHY) and model simulations (REPROBUS and SLIMCAT), where the differences are within ±3–5%. The historical ground-based total ozone observations in October show that the depletion started in the late 1970s, reached a maximum in the early 1990s and stabilised afterwards due to saturation. There is no indication of ozone recovery yet. At southern mid-latitudes, a reduction of 20–50% is observed for a few days in October–November at the newly installed Rio Gallegos station. Similar depletion of ozone is also observed episodically during the vortex overpasses at Kerguelen in October–November and at Macquarie Island in July–August of the recent winters. This illustrates the significance of measurements at the edges of Antarctica.

Linearity of Pulse Excited Coil-Less Fluxgate

In this paper, we study the open-loop linearity of pulse excited coil-less fluxgate. Narrow current pulses can be used instead of classical sinewave for the excitation of the coil-less fluxgate. This method has shown several advantages, mainly regarding reduction of power consumption, normally in order of tens of microwatts. The disadvantage is that traditional phase-sensitive detection cannot be used as it results in a very small sensitivity. Using pulse excitation, the output signal is obtained by integrating a part of the positive pulse and a part of the negative pulse, and then summing up the resulting voltages. This process was realized using two boxcar averagers SR 4153. The achieved open-loop linearity error is much higher than for sinewave excitation and it is not sufficient for precise applications. We show that the linearity strongly depends on the symmetry of the two integrating windows. In order to obtain precise timing, we realized an excitation board using PIC microcontrollers, which provides both the pulsing signals for excitation current and the gating signals for integration. Using this board and optimum position of the integrating window, we obtained a 0.6% maximum nonlinearity in plusmn100-muT range, which is sufficient for portable compass.

Quantitative analysis of impurities in aluminum alloys by laser-induced breakdown spectroscopy without internal calibration

To develop a fast and sensitive alloy elemental analysis method, a laser-induced breakdown spectroscopy(LIBS) system was established and used to carry out quantitative analysis of impurities in aluminum alloys in air at atmospheric pressure. A digital storage oscilloscope was used as signal recording instrument, instead of traditional gate integrator or Boxcar averager, to reduce the cost of the whole system. Linear calibration curves in the concentration range of 4×10 −5–10 −2 are built for Mg, Cr, Mn, Cu and Zn using absolute line intensity without internal calibrations. Limits of detection for these five elements in aluminum alloy are determined to be (2–90)×10 −6. It is demonstrated that LIBS can provide quantitative trace elemental analysis in alloys even without internal calibration. This approach is easy to use in metallurgy industries and relative research fields.

Ion acoustic wave studies near the presheath/sheath boundary in a weakly collisional argon/xenon plasma

Ion acoustic wave (IAW) phase velocities are measured near the sheath/presheath boundary in a weakly collisional argon/xenon plasma. Wave profiles versus position are measured using a boxcar averager with a gate width of 30 ns and CW excitation at 50 or 75 kHz. Variable gate delays allow measurement of details of the wave close to the boundary. It is shown that the phase velocity at the presheath/sheath boundary is approximately twice the phase velocity in the bulk plasma for both argon and argon/xenon plasmas, in agreement with a recent calculation (Lee D et al 2007 Phys. Rev. Lett. 99 155004). This result indicates each ion's drift velocity at the boundary is equal to the IAW phase velocity in the bulk plasma.

Noise Characteristics of an Instrumental Particle Absorbance Technique

Noise characteristics and noise reduction techniques for the particle soot absorption spectrometer (PSAP) are discussed. It is shown through elementary propagation of errors analysis and verified through simulations and by experiments that the PSAP signal noise varies as the −3/2 power of the integration time and not the assumed −1/2. It is also shown that neither simple boxcar averaging of independent absorptivity values nor the commonly used moving boxcar average allow realization of the maximum signal to noise ratio. Instead it is argued that maximal noise reduction is realized by post-processing of the raw reference and sample channel intensities. Finally the implications of these findings are demonstrated with representative field data.

Monitoring surface charge migration in the spectral dynamics of singleCdSe∕CdSnanodot/nanorod heterostructures

Spherical CdSe nanocrystals capped by a CdS rod-like shell exhibit interesting spectral dynamics on the single particle level. Spectral boxcar averaging reveals a high degree of correlation between the emission energy, spectral linewidth, phonon coupling strength, and emission intensity of the single nanocrystal. The results can be described in terms of a spatially varying surface charge density in the vicinity of the exciton localized in the CdSe core, leading to a quantum confined Stark effect which modifies the transition energy and the radiative rate. Whereas internal charging of the particle results in a change in the nonradiative rate, surface charges primarily influence the radiative rate. Additionally, we observe characteristic spectral dynamics in frequency space, the magnitude of which depends slightly on temperature and strongly on excitation density. By distinguishing between continuous spectral jitter and discrete spectral jumping associated with a reversible particle ionization event, we can attribute the spectral dynamics to either a slowly varying surface charge density or a rapidly occurring polarization change due to a reversible expulsion of a charge carrier from the semiconductor nanostructure. Whereas the former exhibits universal Gaussian statistics, the latter is best characterized by a Lorentzian noise spectrum. The Gaussian spectral noise increases with spectral redshift of the emission and with increasing proximity of the surface charge to the localized exciton. The observation of a high degree of correlation between peak position and linewidth right up to room temperature suggests applications of the nanocrystals as extremely sensitive single charge detectors in both solid state devices and in biomolecular labeling, where highly local measurements of the dielectric environment are required. Nanoscale control of the physical shape of nanocrystals provides a versatile test bed for studying electronic noise, making the approach relevant to a wide range of conducting and emissive solid state systems.

Determinação de proteína em café cru por espectroscopia NIR e regressão PLS

A combinação da espectroscopia no infravermelho próximo (NIR) e calibração multivariada (método dos mínimos quadrados parciais - PLS) para a determinação do teor de proteína total em amostras de café cru, foi investigada. Os teores de proteína total foram inicialmente determinados usando-se como método de referência o de Kjeldhal, e, posteriormente foram construídos modelos de regressão a partir dos espectros na região do infravermelho próximo das amostras de café cru. Foram coletados 159 espectros das amostras de café cru utilizando um acessório de reflectância difusa, na faixa espectral de 4500 a 10000cm-1. Os espectros originais no NIR sofreram diferentes transformações e pré-tratamento matemático, como a transformação Kubelka-Munk; correção multiplicativa de sinal (MSC); alisamento (SPLINE); derivada primeira; média móvel e o pré-tratamento dos dados escalados pela variância. O método analítico proposto possibilitou a determinação direta, sem destruição da amostra, com obtenção de resultados rápidos e sem o consumo de reagentes químicos de forma a preservar o meio ambiente. O método proposto forneceu resultados com boa capacidade de previsão do teor de proteína total, sendo que os erros médios foram inferiores a 6,7%.

Experiments with the nonlinear and chaotic behaviour of the multiplicative algebraic reconstruction technique (MART) algorithm for computed tomography

Among the iterative reconstruction algorithms for tomography, the multiplicative algebraic reconstruction technique (MART) has two advantages that make it stand out from other algorithms: it confines the image (and therefore the projection data) to the convex hull of the patient, and it maximizes entropy. In this paper, we have undertaken a series of experiments to determine the importance of MART nonlinearity to image quality. Variants of MART were implemented aiming to exploit and exaggerate the nonlinear properties of the algorithm. We introduce the Power MART, Boxcar Averaging MART and Bouncing MART algorithms. Power MART is linked to the relaxation concept. Its behaviour is similar to that of the chaos of a logistic equation. There appears to be an antagonism between increasing nonlinearity and noise in the projection data. The experiments confirm our general observation that regularization as a means of solving simultaneous linear equations that are underdetermined is suboptimal: it does not necessarily select the correct image from the hyperplane of solutions, and so does not maximize the image quality:x-ray dose ratio. Our investigations prove that there is scope to optimize CT algorithms and thereby achieve greater dose reduction.