Design of a high-precision time-to-digital converter in an Elitestek Ti60 field-programmable-gate-array.

The time-to-digital converter (TDC) implemented in a field-programmable-gate-array has garnered widespread attention due to its flexibility and high-performance capabilities. However, issues such as non-uniformity, the bubble in the tapped delay line, and the presence of certain ultra-wide delay units can significantly compromise the precision and nonlinearity of the TDC. In this paper, we propose a high-precision TDC in an Elitestek Ti60 FPGA, effectively eliminating the adverse effects of non-uniformity, the bubble, and certain ultra-wide delay units. The TDC is constructed with a 318-stage delay chain and operates at a low system clock frequency of 150 MHz. The least significant bit (LSB) of the TDC is 21.92 ps. The differential nonlinearity (DNL) is between (-0.976, 1.615) LSB and the integral nonlinearity (INL) is between (-1.446, 2.678) LSB. The TDC achieves a root-mean-square error of 14.783 ps when utilized for measuring various time intervals.

Time-bin phase-encoding quantum key distribution using Sagnac-based optics and compatible electronics.

In this work, we present a new time-bin phase-encoding quantum key distribution (QKD), where the transmitter utilizes an inherently stable Sagnac-type interferometer, and has comparable electrical requirements to existing polarization or phase encoding schemes. This approach does not require intensity calibration and is insensitive to environmental disturbances, making it both flexible and high-performing. We conducted experiments with a compact QKD system to demonstrate the stability and secure key rate performance of the presented scheme. The results show a typical secure key rate of 6.2 kbps@20 dB and 0.4 kbps@30 dB with channel loss emulated by variable optical attenuators. A continuous test of 120-km fiber spool shows a stable quantum bit error rate of the time-bin basis within 0.4%∼0.6% over a consecutive 9-day period without any adjustment. This intrinsically stable and compatible scheme of time-bin phase encoding is extensively applicable in various QKD experiments, including BB84 and measurement-device-independent QKD.

High-Speed Variable Polynomial Toeplitz Hash Algorithm Based on FPGA.

In the Quantum Key Distribution (QKD) network, authentication protocols play a critical role in safeguarding data interactions among users. To keep pace with the rapid advancement of QKD technology, authentication protocols must be capable of processing data at faster speeds. The Secure Hash Algorithm (SHA), which functions as a cryptographic hash function, is a key technology in digital authentication. Irreducible polynomials can serve as characteristic functions of the Linear Feedback Shift Register (LFSR) to rapidly generate pseudo-random sequences, which in turn form the foundation of the hash algorithm. Currently, the most prevalent approach to hardware implementation involves performing block computations and pipeline data processing of the Toeplitz matrix in the Field-Programmable Gate Array (FPGA) to reach a maximum computing rate of 1 Gbps. However, this approach employs a fixed irreducible polynomial as the characteristic polynomial of the LFSR, which results in computational inefficiency as the highest bit of the polynomial restricts the width of parallel processing. Moreover, an attacker could deduce the irreducible polynomials utilized by an algorithm based on the output results, creating a serious concealed security risk. This paper proposes a method to use FPGA to implement variational irreducible polynomials based on a hashing algorithm. Our method achieves an operational rate of 6.8 Gbps by computing equivalent polynomials and updating the Toeplitz matrix with pipeline operations in real-time, which accelerates the authentication protocol while also significantly enhancing its security. Moreover, the optimization of this algorithm can be extended to quantum randomness extraction, leading to a considerable increase in the generation rate of random numbers.

Degradation and transformation of 17α-trenbolone in aerobic water-sediment systems.

Synovex® ONE is an extended-release implant containing the active ingredients estradiol benzoate and trenbolone acetate for use in beef steers and heifers. Trenbolone acetate is rapidly hydrolyzed in cattle to form 17ß-trenbolone and its isomer, 17α-trenbolone, which are further transformed to a secondary metabolite, trendione. As part of the environmental assessment for the use of Synovex ONE, data were generated to characterize the fate of 17α-trenbolone, which is the principal metabolite found in cattle excreta, in the environment. A study was conducted to determine the degradation and transformation of [14 C]-17α-trenbolone in 2 representative water-sediment systems under aerobic conditions. The same transformation products, 17ß-trenbolone and trendione, were formed, principally in the sediment phase, in both systems. From the production of these transformation products, the 50% disappearance time (DT50) values of 17ß-trenbolone and trendione were determined, along with the DT50 values of the parent compound and the total drug (17α-trenbolone + 17ß-trenbolone + trendione). The DT50 values for the total system (aqueous and sediment phase) and for the total residues (17α-trenbolone + 17ß-trenbolone + trendione) in the 2 systems were 34.7 d and 53.3 d, respectively. Environ Toxicol Chem 2017;36:630-635. © 2016 SETAC.

Degradation and transformation of 17α-estradiol in water-sediment systems under controlled aerobic and anaerobic conditions.

One of the principal metabolites in cattle excreta following the administration of Synovex® ONE, which contains estradiol benzoate and trenbolone acetate, is 17α-estradiol. As part of the environmental assessment of the use of Synovex ONE, data were generated to characterize the fate of 17α-estradiol in the environment. Studies were conducted to determine the degradation and transformation of 17α-[14 C]-estradiol in 2 representative water-sediment systems each under aerobic and anaerobic conditions. The same transformation products-estriol, 17ß-estradiol, and estrone-were formed, principally in the sediment phase, under both conditions in both systems. From the production of these transformation products, the 50% disappearance time (DT50) values of estrone and 17ß-estradiol were determined, along with the DT50 values of 17α-estradiol and the total drug (17α-estradiol + 17ß-estradiol + estrone). The results indicate that 17 α-[14 C]-estradiol was more persistent under anaerobic conditions than under aerobic conditions and that 17 α-[14 C]-estradiol was less persistent than its transformation products. The DT50 values for the total system (aqueous and sediment phases) and for the total residues (17α-estradiol, 17ß-estradiol, and estrone) were selected for use in modeling the environmental fate of estradiol benzoate. For aerobic degradation in the water-sediment system, the DT50 was 31.1 d, and it was 107.8 d for the anaerobic system. Environ Toxicol Chem 2017;36:621-629. © 2016 SETAC.

Sorption and desorption of 17α-trenbolone and trendione on five soils.

The metabolites 17α-trenbolone and 17α-estradiol are principal metabolites in cattle excreta following the administration of Synovex® ONE, which contains trenbolone acetate and estradiol benzoate. As part of the environmental assessment of the use of Synovex ONE, data were generated to characterize the fate of 17α-trenbolone, and its metabolite trendione in the environment. Predictions of the fate and environmental concentrations of these hormones after land application require accurate estimates of the sorption of these compounds in soils. The sorption and desorption of 17α-trenbolone and trendione were measured at 5 nominal concentrations in 5 soils from different geologic settings using a batch equilibrium technique following guideline 106 of the Organisation for Economic Co-operation and Development. Both the sorption and desorption of 17α-trenbolone and trendione to soils were adequately described by the Freundlich sorption model and by linear partition coefficients. The mean sorption coefficients were 9.04 mL/g and 32.2 mL/g for 17α-trenbolone and trendione, respectively. The corresponding mean Freundlich sorption exponents were 0.88 and 0.98, respectively. Sorption of 17α-trenbolone and trendione was correlated principally with soil organic carbon. Average sorption coefficients normalized to soil organic carbon content (KOC ) were 460 mL/g and 1804 mL/g for 17α-trenbolone and trendione, respectively. The mean desorption coefficients were 22.1 mL/g and 43.8 mL/g for 17α-trenbolone and trendione, respectively. Calculated hysteresis coefficients based on the difference in the area between sorption and desorption isotherms indicated that sorption equilibrium was not fully reversible and hysteresis of desorption isotherms occurred for both 17α-trenbolone and trendione. Environ Toxicol Chem 2017;36:613-620. © 2016 SETAC.

Quantitative analysis of over 20 years of golf course monitoring studies.

The purpose of the present study was to comprehensively evaluate available golf course water quality data and assess the extent of impacts, as determined by comparisons with toxicologic and ecologic reference points. Most water quality monitoring studies for pesticides have focused on agriculture and often the legacy chemicals. There has been increased focus on turf pesticides since the early 1990s, due to the intense public scrutiny proposed golf courses receive during the local permitting process, as well as pesticide registration evaluations by the U.S. Environmental Protection Agency under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). Results from permit-driven studies are frequently not published and knowledge about them is usually not widespread. Forty-four studies involving 80 courses from a 20-year period passed our quality control and other review criteria. A total of 38,827 data entries (where one analysis for one substance in one sample equals a data entry) from pesticide, pesticide metabolite, total phosphorus, and nitrate analyses of surface water and groundwater were evaluated. Analytes included 161 turf-related pesticides and pesticide metabolites. Widespread and/or repeated water quality impacts by golf courses had not occurred at the sites studied, although concerns are raised herein about phosphorus. Individual pesticide database entries that exceed toxicity reference points for groundwater and surface water are 0.15 and 0.56%, respectively. These percentages would be higher if they could be expressed in terms of samples collected rather than chemicals analyzed. The maximum contaminant level ([MCL]; 10 mg/L) for nitrate-nitrogen was exceeded in 16/1,683 (0.95%) of the groundwater samples. There were 1,236 exceedances of the total phosphorus ecoregional criteria in five ecoregions for 1,429 (86.5%) data entries. (This comparison is conservative because many of the results in the database are derived from storm flow events.) Thus, phosphorus appears to present the greatest water quality problem in these studies. Pesticides detected in wells had longer soil metabolism half-lives (49 d) compared with those not detected (22 d), although the means were not significantly different.

A simulation study of the DQE of a linear plastic scintillating fiber array for hard gamma-rays.

The detector quantum efficiency (DQE) of a linear plastic scintillating fiber (PSF) array coupled with a charge-coupled device (CCD) for hard gamma-ray imaging is studied using a Monte Carlo simulation. The focus is on the energy from a few MeV to about 12 MeV. The excellent characteristic of PSF offers a method to balance the detection efficiency and spatial resolution. Our simulation results indicate that the modulation transfer function (MTF) for different energies become almost the same below the certain frequency and the DQE should be better at lower frequency for imaging lower incident energy. These characteristics suggest that the PSF may be useful for detecting high energy gamma-rays.

MeV X-ray imaging using plastic scintillating fiber area detectors: a simulation study.

Due to their low cost, flexibility, and convenience for long distance data transfer, plastic scintillating fibers (PSFs) have been increasingly used in building detectors or sensors for detecting various radiations and imaging. In this work, the possibility of using PSF coupled with charge-coupled devices (CCD) to build area detectors for X-ray imaging is studied using a Monte Carlo simulation. The focus is on X-ray imaging with energy from a few 100 keV to about 20 MeV. It is found that the efficiency of PSF in detecting X-ray in this energy range is low. The performance can be improved by coating a PSF with X-ray absorption layers and the MTF of the system is presented. It seems possible to build such area detectors with PSFs for imaging hard X-rays under certain environment.

Field dissipation of acetochlor in two New Zealand soils at two application rates.

The persistence of pesticides in soils has both economic and environmental significance and is often used as a key parameter in pesticide risk assessment. Persistence of acetochlor [2'-ethyl-6'-methyl-N-(ethoxymethyl)-2-chloroacetylanilide] in two New Zealand field soils was measured over two years and the data were used to identify models that adequately describe acetochlor persistence in the field. Acetochlor was sprayed onto six fallow plots (3 x 9 m each) at each site at the recommended rate (2.5 kg a.i. ha(-1)) and at twice that rate. Acetochlor concentrations were measured in soil cores. Simple first-order kinetics (Model 1) adequately described acetochlor persistence in Hamilton clay loam soil (Humic Hapludull, Illuvial Spadic) at the high application rate, but overestimated it at the low application rate. A quadratic model (Model 2), a first-order double-exponential model (Model 3), a first-order biphasic model (Model 4), or a two-compartment model (Model 5) better described acetochlor persistence at the low application rate. The time for 50% (DT50) and 90% (DT90) of initial acetochlor loss was approximately 9 and 56 d, and 18 and 63 d at low and high application rates, respectively. The more complex Models 2 through 5 also better described the biphasic dissipation of acetochlor in Horotiu sandy loam soil (Typic Orthic Allophanic) than Model 1, with Model 1 significantly underestimating acetochlor concentrations on the day of application at both application rates. The DT50 and DT90 values were 5 and 29 d and 7 and 31 d at low and high application rates, respectively. Overall, application rate significantly affected the DT50 and DT90 values in the Hamilton soil, but not in the Horotiu soil. Faster acetochlor loss in the Horotiu soil possibly resulted from the higher soil organic carbon content that retained more acetochlor near the soil surface where higher temperature and photolysis accelerated the loss.

Application of the Root Zone Water Quality Model (RZWQM) to pesticide fate and transport: an overview.

Pesticide transport models are tools used to develop improved pesticide management strategies, study pesticide processes under different conditions (management, soils, climates, etc) and illuminate aspects of a system in need of more field or laboratory study. This paper briefly overviews RZWQM history and distinguishing features, overviews key RZWQM components and reviews RZWQM validation studies. RZWQM is a physically based agricultural systems model that includes sub-models to simulate: infiltration, runoff, water distribution and chemical movement in the soil; macropore flow and chemical movement through macropores; evapotranspiration (ET); heat transport; plant growth; organic matter/nitrogen cycling; pesticide processes; chemical transfer to runoff; and the effect of agricultural management practices on these processes. Research to date shows that if key input parameters are calibrated, RZWQM can adequately simulate the processes involved with pesticide transport (ET, soil-water content, percolation and runoff, plant growth and pesticide fate). A review of the validation studies revealed that (1) accurate parameterization of restricting soil layers (low permeability horizons) may improve simulated soil-water content; (2) simulating pesticide sorption kinetics may improve simulated soil pesticide concentration with time (persistence) and depth and (3) calibrating the pesticide half-life is generally necessary for accurate pesticide persistence simulations. This overview/review provides insight into the processes involved with the RZWQM pesticide component and helps identify model weaknesses, model strengths and successful modeling strategies.

Documenting the pesticide processes module of the ARS RZWQM agroecosystem model.

We describe the theory and current development state of the pesticide process module of the USDA-Agricultural Research Service Root Zone Water Quality Model, or RZWQM. Several processes which are significant in determining the fate of a pesticide application are included together in this module for the first time, including application technique, root uptake, ionic dissociation, soil depth dependence of persistence, volatilization, wicking upward in soil and aging of residues. The pesticide module requires a large number of parameters to run (as does the RZWQM model as a whole) and it is becoming clear that RZWQM will find most interest and use as part of a 'scenario' in which all data requirements are supplied and the predictions of the system compared with a real (usually partial) data set. Such a scenario may then be modified to examine the response of the system to changes in inputs. It also has significant potential as a technology transfer or teaching tool, providing detailed understanding of a specific agronomic system and its potential impacts on the environment.

The pesticide module of the Root Zone Water Quality Model (RZWQM): testing and sensitivity analysis of selected algorithms for pesticide fate and surface runoff.

The Root Zone Water Quality Model (RZWQM) is a one-dimensional, numerical model for simulating water movement and chemical transport under a variety of management and weather scenarios at the field scale. The pesticide module of RZWQM includes detailed algorithms that describe the complex interactions between pesticides and the environment. We have simulated a range of situations with RZWQM, including foliar interception and washoff of a multiply applied insecticide (chlorpyrifos) to growing corn, and herbicides (alachlor, atrazine, flumetsulam) with pH-dependent soil sorption, to examine whether the model appears to generate reasonable results. The model was also tested using chlorpyrifos and flumetsulam for the sensitivity of its predictions of chemical fate and water and pesticide runoff to various input parameters. The model appears to generate reasonable representations of the fate and partitioning of surface- and foliar-applied chemicals, and the sorption of weakly acidic or basic pesticides, processes that are becoming increasingly important for describing adequately the environmental behavior of newer pesticides. However, the kinetic sorption algorithms for charged pesticides appear to be faulty. Of the 29 parameters and variables analyzed, chlorpyrifos half-life, the Freundlich adsorption exponent, the fraction of kinetic sorption sites, air temperature, soil bulk density, soil-water content at 33 kPa suction head and rainfall were most sensitive for predictions of chlorpyrifos residues in soil. The latter three inputs and the saturated hydraulic conductivity of the soil and surface crusts were most sensitive for predictions of surface water runoff and water-phase loss of chlorpyrifos. In addition, predictions of flumetsulam (a weak acid) runoff and dynamics in soil were sensitive to the Freundlich equilibrium adsorption constant, soil pH and its dissociation coefficient.

Modeling hydrology, metribuzin degradation and metribuzin transport in macroporous tilled and no-till silt loam soil using RZWQM.

Due to the complex nature of pesticide transport, process-based models can be difficult to use. For example, pesticide transport can be effected by macropore flow, and can be further complicated by sorption, desorption and degradation occurring at different rates in different soil compartments. We have used the Root Zone Water Quality Model (RZWQM) to investigate these phenomena with field data that included two management conditions (till and no-till) and metribuzin concentrations in percolate, runoff and soil. Metribuzin degradation and transport were simulated using three pesticide sorption models available in RZWQM: (a) instantaneous equilibrium-only (EO); (b) equilibrium-kinetic (EK, includes sites with slow desorption and no degradation); (c) equilibrium-bound (EB, includes irreversibly bound sites with relatively slow degradation). Site-specific RZWQM input included water retention curves from four soil depths, saturated hydraulic conductivity from four soil depths and the metribuzin partition coefficient. The calibrated parameters were macropore radius, surface crust saturated hydraulic conductivity, kinetic parameters, irreversible binding parameters and metribuzin half-life. The results indicate that (1) simulated metribuzin persistence was more accurate using the EK (root mean square error, RMSE = 0.03 kg ha(-1)) and EB (RMSE = 0.03 kg ha(-1)) sorption models compared to the EO (RMSE = 0.08 kg ha(-1)) model because of slowing metribuzin degradation rate with time and (2) simulating macropore flow resulted in prediction of metribuzin transport in percolate over the simulation period within a factor of two of that observed using all three pesticide sorption models. Moreover, little difference in simulated daily transport was observed between the three pesticide sorption models, except that the EB model substantially under-predicted metribuzin transport in runoff and percolate >30 days after application when transported concentrations were relatively low. This suggests that when macropore flow and hydrology are accurately simulated, metribuzin transport in the field may be adequately simulated using a relatively simple, equilibrium-only pesticide model.

Test of the Root Zone Water Quality Model (RZWQM) for predicting runoff of atrazine, alachlor and fenamiphos species from conventional-tillage corn mesoplots.

The Root Zone Water Quality Model (RZWQM) is a comprehensive, integrated physical, biological and chemical process model that simulates plant growth and movement of water, nutrients and pesticides in a representative area of an agricultural system. We tested the ability of RZWQM to predict surface runoff losses of atrazine, alachlor, fenamiphos and two fenamiphos oxidative degradates against results from a 2-year mesoplot rainfall simulation experiment. Model inputs included site-specific soil properties and weather, but default values were used for most other parameters, including pesticide properties. No attempts were made to calibrate the model except for soil crust/seal hydraulic conductivity and an adjustment of pesticide persistence in near-surface soil. Approximately 2.5 (+/- 0.9), 3.0 (+/- 0.8) and 0.3 (+/- 0.2)% of the applied alachlor, atrazine and fenamiphos were lost in surface water runoff, respectively. Runoff losses in the 'critical' events--those occurring 24 h after pesticide application--were respectively 91 (+/- 5), 86 (+/- 6) and 96 (+/- 3)% of total runoff losses for these pesticides. RZWQM adequately predicted runoff water volumes, giving a predicted/observed ratio of 1.2 (+/- 0.5) for all events. Predicted pesticide concentrations and loads from the 'critical' events were generally within a factor of 2, but atrazine losses from these events were underestimated, which was probably a formulation effect, and fenamiphos losses were overestimated due to rapid oxidation. The ratios of predicted to measured pesticide concentrations in all runoff events varied between 0.2 and 147, with an average of 7. Large over-predictions of pesticide runoff occurred in runoff events later in the season when both loads and concentrations were small. The normalized root mean square error for pesticide runoff concentration predictions varied between 42 and 122%, with an average of 84%. Pesticide runoff loads were predicted with a similar accuracy. These results indicate that the soil-water mixing model used in RZWQM is a robust predictor of pesticide entrainment and runoff.

Herbicide leaching as affected by macropore flow and within-storm rainfall intensity variation: a RZWQM simulation.

Within-event variability in rainfall intensity may affect pesticide leaching rates in soil, but most laboratory studies of pesticide leaching use a rainfall simulator operating at constant rainfall intensity, or cover the soil with ponded water. This is especially true in experiments where macropores are present--macroporous soils present experimental complexities enough without the added complexity of variable rainfall intensity. One way to get around this difficulty is to use a suitable pesticide transport model, calibrate it to describe accurately a fixed-intensity experiment, and then explore the affects of within-event rainfall intensity variation on pesticide leaching through macropores. We used the Root Zone Water Quality Model (RZWQM) to investigate the effect of variable rainfall intensity on alachlor and atrazine transport through macropores. Data were used from an experiment in which atrazine and alachlor were surface-applied to 30 x 30 x 30 cm undisturbed blocks of two macroporous silt loam soils from glacial till regions. One hour later the blocks were subjected to 30-mm simulated rain with constant intensity for 0.5 h. Percolate was collected and analyzed from 64 square cells at the base of the blocks. RZWQM was calibrated to describe accurately the atrazine and alachlor leaching data, and then a median Mid-west variable-intensity storm, in which the initial intensity was high, was simulated. The variable-intensity storm more than quadrupled alachlor losses and almost doubled atrazine losses in one soil over the constant-intensity storm of the same total depth. Also rainfall intensity may affect percolate-producing macroporosity and consequently pesticide transport through macropores. For example, under variable rainfall intensity RZWQM predicted the alachlor concentration to be 2.7 microg ml(-1) with an effective macroporosity of 2.2 E(-4) cm(3) cm(-3) and 1.4 microg ml(-1) with an effective macroporosity of 4.6 E(-4) cm(3) cm(-3). Percolate-producing macroporosity and herbicide leaching under different rainfall intensity patterns, however, are not well understood. Clearly, further investigation of rainfall intensity variation on pesticide leaching through macropores is needed.