Noise Values Research Articles

Combination T2 multiple echo data imaging and fast spin echo fat saturation technique to improve image quality on ankle magnetic resonance imaging

Objective: To determine the effect of the T2 Fast Spin Echo Fat Saturation (T2 FSE FAT SAT) sequence and T2 Multiple Echo Data Imaging Combination (T2 MEDIC) sequence on ankle images MRI. Methodology: The sequence variations were T2 FSE FAT SAT and T2 MEDIC. The effect of the sequence on the quality of the MRI ankle image was analyzed on the image of one patient and the sound intensity value through a sound level meter. Result: Data analysis was carried out quantitatively with the Region of Interest (ROI) method directly on the computer image of the MRI, then SNR (Signal to Noise Ratio) and CNR (Contras to Noise Ratio) analysis were carried out, and PSNR and MSE analysis was carried out through digital image processing to determine the value magnitudes. The highest SNR and CNR were found in the T2 MEDIC sequence. The lowest acoustic noise value is in the T2 MEDIC sequence. The differences in the physical mechanism of image formation are T2 FSE FAT SAT refocusing 180º RF and T2 MEDIC refocusing gradient fields. Conclusion: Because the SNR and CNR on T2 MEDIC are higher and the value of the sound intensity level is low, it can be said that the sequence provides optimal results and low acoustic noise.

Residential Sorting and Environmental Externalities: the Case of Non-linearities and Stigma in Aviation Noise Values

Residential Sorting and Environmental Externalities: the Case of Non-linearities and Stigma in Aviation Noise Values

Evaluation of Campus Soundscape Construction

With the vigorous construction of beautiful China and the rise of soundscape research, the application of soundscape in campus environment becomes gradually widespread. The article takes the small garden of the No. 1 teaching building in the North Campus of Henan Polytechnic University as an example, and conducts a study on the soundscape of colleges and universities based on objective sound pressure level measurement and subjective questionnaire research. The objective measurement results show that the average noise value of the garden during daytime is 63dB (A), which is higher than the national standard of 55dB (A). The results of the questionnaire survey indicated that people's overall satisfaction with the soundscape at this location was not highly rated and some degree of soundscape improvement was needed. Accordingly, the article investigates the relationship between sound comfort and sound pressure level, and adopts optimization measures in three aspects: vegetation planning strategy, characteristic soundscape shaping, and environmental material improvement, in order to provide reference for the study of university soundscape.

Application of three-dimensional (3D) magnetic resonance (MR) Multi-Echo iN Steady-state Acquisition sequences in preoperative evaluation of lumbar disc herniation: a prospective study.

Conventional spinal magnetic resonance imaging (MRI) cannot provide accurate diagnosis and surgical planning; thin-layer scanning can enhance the diagnostic efficacy. This study aimed to investigate the value of 3-dimensional (3D) magnetic resonance (MR) in preoperative evaluation of lumbar disc herniation, with a focus on the application of Multi-Echo iN Steady-state Acquisition (MENSA) sequence. A total of 51 patients who underwent lumbar disc herniation surgery in West China Hospital of Sichuan University from June 2021 to December 2021 were prospectively enrolled. A cross-sectional study was conducted on those patients. The Cube group was scanned using 3D-FSE-Cube sequence, the Cube stir group was scanned using 3D-FSE-Cube Short Tau Inversion Recovery (STIR) sequence, and the MENSA group was scanned using MENSA sequence. Signal and noise values of nerve, herniated disc, ligamentum flavum (LF), and soft tissue were measured on the 3 groups. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Objective scores were calculated by analysis of variance (ANOVA). Image quality was scored by a 5-point method. Friedman test was used to compare subjective scores, and Kappa test was used to evaluate the consistency of 2 readers' scores. The nerve root SNRs in the MENSA and Cube stir groups were higher than that in the Cube group (P<0.01), but there was no substantial statistical difference between the 2 groups. The herniated disc and LF SNRs of the MENSA group were greater than those of the Cube stir and Cube groups (P<0.01). Soft tissue SNR was greater in the MENSA group compared with the Cube stir group (P<0.01), which was greater than the SNR in the Cube group (P<0.01). The nerve root CNR of the Cube group (102.88±73.19) was greater than that of the MENSA group (55.98±25.26, P<0.01), which was higher than the CNR in the Cube Stir group (29.42±16.22, P<0.01). The herniated disc CNR was higher in the MENSA and Cube groups than that in the Cube Stir group. The CNR of LF was greater in the MENSA group (37.71±16.87) compared to the Cube group (29.76±25.73, P=0.03), which was greater than that in the Cube stir group (10.50±7.75, P<0.01). Among the subjective ratings of 2 reviewers, MENSA sequence scored highest in the qualitative measures of image quality. In the consistency test, the Kappa values of 2 readers for 3 groups of images were all greater than 0.73, indicating good consistency. The differences of subjective scores among all groups were statistically significant (P<0.05). Overall, it was indicated that the consistency test results of the 2 readers were statistically significant and consistent. The MENSA group had the highest accuracy in diagnosing nerve compression. In addition, MENSA sequence ranked highest among the 3 sequences with 94.1% diagnostic accuracy. The preoperative 3D MRI MENSA sequence can clearly depict the nerve roots and offer desirable contrast between the nerve roots, LF, bone, and intervertebral discs (IVDs). Patients with lumbar degeneration can effectively benefit from MENSA sequence since it provides useful imaging information to help understand disc herniation and compression of adjacent tissues when developing preoperative surgical strategies.

A Study on Radiation Dose and Image Quality using High-Pitch Mode when Examining the Lumbar Region with Dual-Energy Computed Tomography

The purpose of this study was to investigate whether the high pitch protocol method of dual-energy computed tomography can be successfully applied to a lumbar vertebrae CT scan and reduce the effect of exposure dose; the main indicators were the image quality and reduced scan time. This study was conducted using MDCT 256 row dual source, Somatom Definition Flash (Siemens medical system: Germany), on 69 patients who had lumbar vertebrae CT scans from March 1, 2021, to June 30, 2021. First, to determine the applicability of the high pitch protocol method, the phantom images quality was compared with that of the existing lumbar vertebrae CT scan method and the examination method using the high pitch protocol method with the AAPM phantom, respectively. In the phantom image, CT noise, uniformity, and spatial resolution were not significantly different between the existing lumbar vertebrae CT scan method and the examination method using the high pitch protocol. In addition, in images examined from clinical patients, single-sample t-test results of the comparison of the mean value of CT noise, uniformity, and spatial resolution did not show statistically significant differences, 0.081, 0.078, and 0.387, respectively. The results of the qualitative evaluation showed that all were also higher than 3 points, which is fair, and the radiation dose was reduced by 9.76% in the high pitch protocol. When examining the lumbar region with dual-energy computed tomography, the examination method using high-pitch mode reduced the radiation dose and shortened the examination time, with the same image quality as that of the existing lumbar vertebrae CT scan.

Improved DIQKD protocols with finite-size analysis

The security of finite-length keys is essential for the implementation of device-independent quantum key distribution (DIQKD). Presently, there are several finite-size DIQKD security proofs, but they are mostly focused on standard DIQKD protocols and do not directly apply to the recent improved DIQKD protocols based on noisy preprocessing, random key measurements, and modified CHSH inequalities. Here, we provide a general finite-size security proof that can simultaneously encompass these approaches, using tighter finite-size bounds than previous analyses. In doing so, we develop a method to compute tight lower bounds on the asymptotic keyrate for any such DIQKD protocol with binary inputs and outputs. With this, we show that positive asymptotic keyrates are achievable up to depolarizing noise values of 9.33&amp;#x0025;, exceeding all previously known noise thresholds. We also develop a modification to random-key-measurement protocols, using a pre-shared seed followed by a "seed recovery" step, which yields substantially higher net key generation rates by essentially removing the sifting factor. Some of our results may also improve the keyrates of device-independent randomness expansion.

Advanced fault location scheme for superconducting cables based on deep learning algorithms

This paper addresses the challenge of fault localization in power grids which incorporate Superconducting Cables (SCs) and presence of inverter-connected generation, by proposing a novel data-driven fault location scheme. The developed fault location algorithm utilizes the transformation of time domain fault current and voltage signatures, to time–frequency domain and exploits the advantages of a Convolutional Neural Network (CNN) to estimate the fault position along SCs. The proposed algorithm has been tested using a verified model of SC, and the results revealed that it can provide precise fault localization for a wide range of fault scenarios, including different fault types, fault resistance values and fault inception angles. Furthermore, the proposed scheme robustness has been verified against different influencing factors accounting for very small increments of fault location, additive noise and different value of sampling frequency. For validation purposes, the effectiveness of the CNN-based algorithm has been compared with other data-driven algorithms and the relevant advantages have been highlighted.

Pengaruh Tingkat Kebisingan Mesin Kapal terhadap Fungsi Pendengaran dan Stress Kerja pada Teknisi Mesin Kapal

This study aimed to determine the effect of ship engine noise level on hearing function and work stress on ship engine technicians. The data collection process was carried out within 30 days, from 15 February 2021 to 15 March 2021. This study took a collation at the Merak port of Banten. The method used is a survey using research subjects, ship engine technicians, and the object of research is noise. This study uses primary data in engine maintenance design and the intensity of noise distribution on the ship's engine. The research sample was 2 units of machines with engine criteria aged 1 year and 6 years. The equipment used in this study is a sound level meter, an object to measure the noise that has been calibrated. This research uses the descriptive analysis method. The results showed that the noise value at full rpm was 70.3-104 dB (A) and 59.2-77.5 dB (A) when in a stationary state. Referring to the data, the age of the machine does not affect the noise level. As a preventive measure against something that can become an obstacle regarding noise on board, it is necessary to use ear protection devices such as ear protection devices called earplugs. Noise can be minimized by regularly lubricating the engine and installing silencers to prevent sound from spreading to other rooms so that it can reduce the risk due to noise that causes stress, headaches, high blood pressure and other diseases

Determination and Evaluation of Noise Pollution in Layer Hen House: A Bursa Case Study

Both animals and employees need to improve the indoor conditions in livestock barns and keep them at an optimum level. With the development of automation systems for increased productivity and mechanisation, more systematic production occurs within the poultry houses and the need for a workforce is reduced. However, the increase in industrialisation and herd size can cause noise pollution problems in the poultry house. In this study, noise levels were measured and statistically evaluated in a laying hen farm operating in a battery-type cage in the Bursa region. It is aimed to be assessed according to environmental pollution and animal welfare. It was measured in the corridors between the rows of cages and on the cage floors with the studied facility's noise meter (EXTECH SDL600). The obtained noise data were determined by the SPSS statistical program, the variance analysis of the differences between the corridors and the relationship between the layer hen house environmental factors (temperature, humidity and wind speed) and the regression analysis. According to the results measured throughout the year in the investigated enterprise, the maximum noise intensity was measured as 80.6 dB, and the minimum noise intensity was measured as 76.3 dB. The differences between the noise values measured in the aisles and floors of the cage rows are statistically significant.

Airborne Single-Pass Multi-Baseline InSAR Layover Separation Method Based on Multi-Look Compressive Sensing

Due to the small number of baselines (2–3), the traditional L1 norm compressive sensing method for layover solution in InSAR has poor separation ability and height estimation stability and a long operation time. This paper, based on the idea of multi-look, adopts a multi-look compressive sensing method and a multi-look compressive sensing method based on separable approximate sparse reconstruction. The layover separation method based on multi-look compressive sensing adopts the surrounding pixels around the current point as independent observations together with this point to increase the observation vector in compressive sensing, and uses the singular value decomposition method to obtain the noise value, which is used to improve the dimensions of measured data in compressive sensing, reduces the noise level, and improves the stability of noise estimation. Meanwhile, the results of the multi-look L1 norm solution method are closer to those of the L0 norm solution, and the sparse reconstruction ability of compressive sensing is improved. Thus, the separation ability of the scatterers in the layover areas and the stability of height estimation are stronger. In addition, the multi-look compressive sensing method based on separable approximate sparse reconstruction constructs differential operation and soft functions, transforms the L1–L2 norm optimization into an iterative soft threshold shrinkage processing mode, and improves the processing speed by means of the threshold iteration method, which can effectively reduce the operation time while maintaining the resolution ability of scatterers in layover areas and the height direction estimation accuracy and provides the possibility for large-scale data processing. These two methods are effectively verified by means of simulation and measured data. The simulation experiments of the two methods are based on the airborne MEMPHIS system with four antennas, and the height values of the layover scatterers solved by the two methods are more reliable, stable, and closer to the real value than those solved by the traditional compressive sensing method. The operation time of the separable approximate sparse reconstruction method is comparable to the processing time of the traditional compressive sensing method and nearly one-quarter that of the multi-look compressive sensing method. The real data experiments of the two methods are based on the airborne Millimeter-wave InSAR system with three antennas. The two methods both have certain height resolutions in the height direction estimation of layover areas and fine elevation continuity, while traditional compressive sensing method cannot satisfy the condition of sparsity and has poor scatterer separation and elevation continuity. Nevertheless, the multi-look compressive sensing method is a little more stable than the separable approximate sparse reconstruction method, and the operation time of the separable approximate sparse reconstruction method is comparable to the traditional compressive sensing method and nearly one-fifth that of the multi-look compressive sensing method.

ANALYSIS OF THE EFFECT OF THE X-RAY TUBE CURRENT ON UNIFORMITY IMAGE NOISE VALUES

This research aimed to evaluate the effects of the X-ray current tube on the uniformity value of CT image noise. This research used the CT images of Siemens head water phantom. The phantom was scanned with a Siemens Somatom Scope CT scanner for various current tubes (i.e., 180 mAs, 200 mAs, 220 mAs, 240 mAs, and 260 mAs) on tube voltage 110 kV, slice thickness 3 mm, and FOV 240 mm. The uniformity values in CT image noise were analyzed using the standard deviation value (SD). The SD was measured by the ROI process in 5 different locations, in the center and at 3 o'clock, 6 o'clock, 9 o'clock, and 12 o'clock on the images CT. Based on the result of a simple linear regression test using IBM SPSS ver 25, it was found that the current tube significantly affected the uniformity value of image noise (r2=0,9768, p&lt;0,05). This result showed that increasing the current tube can reduce image noise uniformity. The highest image noise uniformity value was at a current at 180 mAs with 0,217 HU, and the lowest was at 260 mAs with 0,031 HU. This result also shows that all the values are less than 2 HU and still within the acceptable limit by the BAPETEN standard regulation.

Simulation on venting process and valve opening control method for gas trunk pipelines

Determining the venting time of a gas trunk pipeline segment provides an important basis for formulating an emergency plan in the advent of unexpected accidents. As the natural gas venting process corresponds to the transient flow, it is necessary to establish a transient hydraulic-thermal simulation model in order to determine the venting time. In this paper, based on two kinds of venting scenarios in which there is only one venting point in the venting system of a gas trunk pipeline segment—namely, where the venting point is either at one of the two ends or at the junction of two gas trunk pipeline segments—transient hydraulic-thermal simulation models are established. The models consist of gas flow governing equations, the gas state equation, gas physical property equations, initial conditions, and appropriate boundary conditions. The implicit central difference method is used to discretize the gas flow partial differential equations, and the trust-region-dogleg algorithm is used to solve the equations corresponding to each time step, in order to dynamically simulate the whole venting process. The judgment condition for the end of the venting process is that the average pressure of gas trunk pipeline segment is less than 0.11 MPa (actual pressure). Comparing the simulation results of the proposed model with those of the OLGA software and real operational data, we find that the venting time error is less than 10%. On this basis, a venting valve opening control principle is proposed, which prevents the venting noise from exceeded the specified noise value (85 dB) in the venting design of domestic gas pipeline projects. The established calculation model for venting time (dynamic simulation model) for a gas trunk pipeline segment and the proposed opening control principle of venting valve provide reference for the optimal operation of gas pipeline venting systems.

Prediction and environmental appraisal of traffic noise intensity by auto-regressive integrated moving average technique

Auto-regressive integrated moving average (ARIMA) assessment of traffic noise was conducted on different routes in Port Harcourt, Nigerian metropolis. This was achieved by measuring the traffic noise on the various routes of asphalt flexible and concrete rigid pavement structures with a meter for sound measurement with regards to the volume of traffic, vehicle movement rate, and location away from the midpoint of the highway. The average peak noise of traffic was obtained at selected distances of 5m, 10m, and 15m from the middle of the highway, for locations 1, 2, 3 and their mean average case 4 (Trunk A flexible pavement), for location 5 (Trunk C flexible pavement), and for location 6 (Trunk C rigid pavement). The results of the investigation show that the values of traffic noise at locations 1 to 3 and their mean average case 4 had the same range of high noise intensity as Trunk A flexible pavement and classified as heavy-traveled roads; while conversely, location 5 (Trunk C) had the same range of lower noise intensity, which was classified as light-traveled road. For Trunk C, the noise generated in a flexible pavement was less than that from a rigid pavement. Generally, the R2 values of the ARIMA models showed very good performance along selected travel routes. For case-specific distances, the ARIMA models performed very efficiently and had very high R2 values.

Study of Noise Reduction and Sound Absorption Performance of Drainage Asphalt Pavement Based on Indoor Tire Accelerated Falling Method

In order to study the noise reduction and sound absorption performance of drainage asphalt pavement and porous asphalt concrete (PAC) and the difference of noise reduction and sound absorption effects of conventional AC pavement, single-layer and double-layer PAC pavements are compared and analyzed by improving the indoor noise test of tire accelerated falling method, and then the sound absorption coefficient of single-layer and double-layer PAC pavement is further tested using the standing wave tube method. Based on the standing wave interference principle of sound, the sound absorption characteristics of drainage asphalt pavement are described, the influence of void ratio on the sound absorption coefficient of PAC pavement is analyzed, and the data model between the void parameters and sound absorption coefficient is established. The results show that: (1) using the improved indoor tire accelerated falling method and using the sound level meter to measure the A-weighted sound pressure level and 1/3 octave frequency spectrum of noise under three distance conditions, the noise value of drainage asphalt pavement is 2 to 5 dB(A) lower than that of traditional AC pavement, and the noise reduction ability decreases with the increase of distance from the sound source and increases with the increase of void ratio. The sound absorption coefficient curve of drainage asphalt pavement is measured using the standing wave tube double transfer function method. The average sound absorption coefficient of PAC specimens decreases with the decrease of the void fraction. (2) The sound absorption coefficient curve of single-layer PAC pavement presents a “single peak type”. The sound absorption peak frequencies of a single layer 4 cm-thick PAC pavement and 10 cm-thick PAC pavement are around 1100 Hz and 800 Hz respectively. The corresponding frequencies of the sound absorption peaks of the two specimens are within the common frequency range of traffic noise, which is helpful to alleviate traffic noise. (3) Through CT scanning and three-dimensional reconstruction software, the void parameters of the PAC specimen are obtained, and the sound absorption coefficient prediction model is established. The sound absorption coefficient calculated by the model has a high correlation with the measured value of standing wave tube method, which verifies the accuracy of the sound absorption coefficient model in predicting the sound absorption characteristics of drainage asphalt pavement.

Characterization of rotational symmetry and noise in multifocal contact lens power maps

AbstractPurpose: Spherical multifocal contact lenses are typically designed with a rotationally symmetrical power profile. Imperfections in the raw material, manufacturing and measurement process can break this symmetry, altering the intended lens design. The purpose of this work is to develop a method to separate the intended symmetric design profile from the asymmetries and to give the spatial distribution of the measurement noise uncertainty in diopters.Methods: NIMO TR1504 (Lambda‐X) version V.2.13.2 has been used to measure the local power map of various multifocal contact lenses. From the map, a set of radial power profiles is obtained for different angles (0°, 180°), (0°, 360°). A symmetrical lens should show a constant radial profile for different angles, while asymmetries manifest as differences in the set of radial power profiles. They are analysed using a Principal Components Method (PCA) implemented in MATLAB.Results: The method displays a map of the symmetric radial profile of the lens, another map of the deviations with spatial structure indicating the angles where the deviations are stronger (rotational asymmetries), and noise with three separated components (spatially random variations). Asymmetries of the order of 0.17D (with maximums of 0.4D), and random noise values of 0.12D were found in some lenses.Conclusions: The characterization of multifocal contact lens prescription is important in visual optics. The prescription perceived by the patient depends on the distribution of the radial power profile on the pupil. That is the reason why asymmetries and imperfections estimation is important. The method developed in this work allows to calculate a diopter equivalent number for them.

Characterization and Performance of the 4k×4k CCD Camera Mounted on 104-cm Sampurnanand Telescope

In this paper, we present the instrumental characterization and performance of the 4[Formula: see text]k CCD detector mounted on a 104-cm Sampurnanand telescope located at ARIES, Manora Peak Nainital, India. A detailed description of the filter wheel and its motion is presented. We measured the gain and read-out noise along with the linearity of the detector. Gain estimates are 5–10% higher than manufacturer values. The estimated read-out noise values do not fall within the manufacturer’s range. It is expected that experimentally derived values will be more precise than designed values. It is suggested that the current derived values will be used rather than the designed values. The response to the incident light on the detector is linear to 99% level. To study the performance of a 4[Formula: see text]k CCD camera, we observe an open cluster Czernik 43. The fundamental parameters, i.e. log(age), distance and reddening [Formula: see text] are estimated as 7.9, 2.5[Formula: see text]kpc and 0.65[Formula: see text]mag, respectively. The estimated parameters of the cluster are comparable to the values derived in the literature within the error. Our detailed analysis illustrates that the detector is precise enough to carry out routine astronomical observations.

Noisy voter model: Explicit expressions for finite system size.

Urn models are classic stochastic models that have been used to describe a diverse kind of complex systems. Voter and Ehrenfest's models are very well-known urn models. An opinion model that combines these two models is presented in this work and it is used to study a noisy voter model. In particular, at each temporal step, an Ehrenfest's model step is done with probability α or a voter step is done with probability 1-α. The parameter α plays the role of noise. By performing a spectral analysis, it is possible to obtain explicit expressions for the order parameter, susceptibility, and Binder's fourth-order cumulant. Recursive expressions in terms of the dual Hahn polynomials are given for first passage and return distributions to consensus and the equal coexistence of opinions. In the cases where they follow power-law distributions, their exponents are computed. This model has a pseudocritical noise value that depends on the system size; a discussion about thermodynamic limits is given.

Analysis of Precise Orbit Determination of BDS-3 MEO and IGSO Satellites Based on Several Dual-Frequency Measurement Combinations

The Chinese BeiDou-3 navigation satellite system (BDS-3) is capable of transmitting both old B1I, B3I signals and new B1C, B2a, B2b signals. Current BDS-3 precise orbits are generally calculated using a B1I/B3I combination considering overlap with the BeiDou-2 navigation satellite system (BDS-2). In this contribution, the observation quality of BDS-3 medium earth orbit (MEO) satellites and inclined geosynchronous orbit (IGSO) satellites are analyzed based on three aspects, i.e., carrier to noise ratio (C/N0), pseudo-range noise and pseudo-range multipath (MP). The C/N0 of the MEO satellite is 2~3 dB higher than that of the IGSO satellite at the same elevation angle. Meanwhile, the order of the Root Mean Square (RMS) values of both pseudo-range noise and MP is B1I &lt; B1C &lt; B3I &lt; B2a ≈ B2b. Three kinds of combinations, i.e., B1CB2a, B1CB2b and B1IB3I, are selected for the BDS-3 precise orbit determination (POD) experiment. Orbits are assessed by the orbit-only signal-in-space range error (SISRE) computed between pairs of the three kinds of combinations in this contribution, CODE and GFZ final orbits. Orbit-only SISRE assessment shows that B1CB2a/CODE, B1CB2b/CODE, B1CB2a/GFZ and B1CB2b/GFZ are at the same level with CODE/GFZ, and the orbit-only SISRE is at the level of 5 cm for MEOs and 9 cm for IGSOs, respectively. Meanwhile, B1IB3I/CODE and B1IB3I/GFZ are about 1–2 cm worse. Inter-solution comparison between B1CB2a, B1CB2b and B1IB3I also indicate that B1CB2a and B1CB2b have good consistency, while B1IB3I shows poor performance. Satellite laser ranging (SLR) residuals indicate that the mean RMS is 3–4 cm for the four BDS-3 MEOs for CODE final orbit, GFZ final orbit, B1CB2a and B1CB2b combinations, while the mean RMS value for B1IB3I combination is a few millimeters worse, at approximately 4–5 cm.

A 1-μm-Band Injection-Locked Semiconductor Laser with a High Side-Mode Suppression Ratio and Narrow Linewidth.

We demonstrate a narrow-linewidth, high side-mode suppression ratio (SMSR) semiconductor laser based on the external optical feedback injection locking technology of a femtosecond-apodized (Fs-apodized) fiber Bragg grating (FBG). A single frequency output is achieved by coupling and integrating a wide-gain quantum dot (QD) gain chip with a Fs-apodized FBG in a 1-μm band. We propose this low-cost and high-integration scheme for the preparation of a series of single-frequency seed sources in this wavelength range by characterizing the performance of 1030 nm and 1080 nm lasers. The lasers have a maximum SMSR of 66.3 dB and maximum output power of 134.6 mW. Additionally, the lasers have minimum Lorentzian linewidths that are measured to be 260.5 kHz; however, a minimum integral linewidth less than 180.4 kHz is observed by testing and analyzing the power spectra of the frequency noise values of the lasers.

Variability of Annual and Monthly Streamflow Droughts over the Southeastern United States

Understanding the patterns of streamflow drought frequency and intensity is critical in defining potential environmental and societal impacts on processes associated with surface water resources; however, analysis of these processes is often limited to the availability of data. The objective of this study is to quantify the annual and monthly variability of low flow river conditions over the Southeastern United States (US) using National Water Model (NWM) retrospective simulations (v2.1), which provide streamflow estimates at a high spatial density. The data were used to calculate sums of outflow deficit volumes at annual and monthly scales, from which the autocorrelation functions (ACF), partial autocorrelation functions (PACF) and the Hurst exponent (H) were calculated to quantify low flow patterns. The ACF/PACF approach is used for examining the seasonal and multiannual variation of extreme events, while the Hurst exponent in turn allows for classification of “process memory”, distinguishing multi-seasonal processes from white noise processes. The results showed diverse spatial and temporal patterns of low flow occurrence across the Southeast US study area, with some locations indicating a strong seasonal dependence. These locations are characterized by a longer temporal cycle, whereby low flows were arranged in series of several to dozens of years, after which they did not occur for a period of similar length. In these rivers, H was in the range 0.8 (+/−0.15), which implies a stronger relation with groundwater during dry periods. In other river segments within the study region the probability of low flows appeared random, determined by H oscillating around the values for white noise (0.5 +/−0.15). The initial assessment of spatial clusters of the low flow parameters suggests no strict relationships, although a link to geologic characteristics and aquifer depth was noticed. At monthly scales, low flow occurrence followed precipitation patterns, with streamflow droughts first occurring in the Carolinas and along the Gulf Coast around May and then progressing upstream, reaching maxima around October for central parts of Mississippi, Alabama and Georgia. The relations for both annual and monthly scales are better represented with PACF, for which statistically significant lags were found in around 75% of stream nodes, while ACF explains on average only 20% of cases, indicating that streamflow droughts in the region occur in regular patterns (e.g., seasonal). This repeatability is of greater importance to defining patterns of extreme hydrologic events than the occurrence of high magnitude random events. The results of the research provide useful information about the spatial and temporal patterns of low flow occurrence across the Southeast US, and verify that the NWM retrospective data are able to differentiate the time processes for the occurrence of low flows.