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Leafy spurge and purple loosestrife are invasive weeds that displace native vegetation. Herbicides are often applied to these weeds during flowering, making it ideal to identify them early in the season, possibly by the leaves. This paper evaluates the spectral separability of the inflorescences and leaves of these plants from surrounding vegetation. Leafy spurge, purple loosestrife, and surrounding vegetation were collected from sites in southeastern North Dakota and subjected to spectral analysis. Partial least squares discriminant analysis (PLS-DA) was used to separate the spectral signatures of these weeds in the visible and near-infrared wavelengths. Using PLS-DA the weeds were discriminated from their surroundings with R2 values of 0.86 to 0.92. Analysis of the data indicated that the bands contributing the most to each model were in the red and red edge spectral regions. Identifying these weeds by the leaves allows them to be mapped earlier in the season, providing more time to plan herbicide application. The spectral signatures identified in this proof-of-concept study are the first step before using ultra-high resolution aerial imagery to classify and identify leafy spurge and purple loosestrife.
The lithostratigraphic characteristics of the iconic Blue Lias Formation of southern Britain are influenced by sedimentation rates and stratigraphic gaps. Evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content. Standard spectral analysis, including allowing for false discovery rates, demonstrates several scales of regular cyclicity in depth. Bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites. The frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity, obliquity and precession cycles. Using local tuned time scales, 62 ammonite biohorizons have minimum durations of 0.7 to 276 ka, with 94% of them <41 ka. The duration of the Hettangian Stage is ≥2.9 Ma according to data from the West Somerset and Devon/Dorset coasts individually, increasing to ≥3.7 Ma when combined with data from Glamorgan and Warwickshire. A composite time scale, constructed using the tuned time scales plus correlated biohorizon limits treated as time lines, allows for the integration of local stratigraphic gaps. This approach yields an improved duration for the Hettangian Stage of ≥4.1 Ma, a figure that is about twice that suggested in recent time scales.
Using remotely sensed land-cover data in 1994 and 2014, and cross-sectional survey data in 2014, this study examines the association between land use and cover change and agricultural productivity in northern Ghana. We document a significant expansion of crop land and settlements (productive use) at the expense of natural vegetation cover. Land areas converted from natural cover to productive use have higher maize yield (0.17 tons per hectare) and harvest value (1,021 Ghanaian Cedi) compared with those converted from bare soil to productive cover. Moreover, areas that were covered by shrubs or savannah in 1994 were more productive in 2014 relative to bare soils in 1994. Although our data do not allow us to establish causality, the evidence suggests the importance of past land-cover conditions in affecting current agricultural performance, especially in resource-stricken settings where conservation and restoration practices are not as common.
The purpose of this study was to clarify the association between hand, foot, and mouth disease (HFMD) epidemics and meteorological conditions. We used HFMD surveillance data of all 47 prefectures in Japan from January 2000 to December 2015. Spectral analysis was performed using the maximum entropy method (MEM) for temperature-, relative humidity-, and total rainfall-dependent incidence data. Using MEM-estimated periods, long-term oscillatory trends were calculated using the least squares fitting (LSF) method. The temperature and relative humidity thresholds of HFMD data were estimated from the LSF curves. The average temperature data indicated a lower threshold at 12 °C and a higher threshold at 30 °C for risk of HFMD infection. Maximum and minimum temperature data indicated a lower threshold at 6 °C and a higher threshold at 35 °C, suggesting a need for HFMD control measures at temperatures between 6 and 35 °C. Based on our findings, we recommend the use of maximum and minimum temperatures rather than the average temperature, to estimate the temperature threshold of HFMD infections. The results obtained might aid in the prediction of epidemics and preparation for the effect of climatic changes on HFMD epidemiology.
Disease detection and control is thus one of the main objectives of vineyard research in France. Monitoring diseases manually is fastidious and time consuming, so current research aims to develop an automatic detection of vineyard diseases. This project explored the use of a high-resolution multi-spectral camera embedded on a UAV (Unmanned Aerial Vehicle) to identify the infected zones in a field. In-field spectrometry studies were performed to identify the best spectral bands for the sensor design. The best models were found to be the function of the grapevine variety considered and the 520-600-650-690-730-750-800 nm bands were found to be the most efficient for all types of grapevines, with an overall classification accuracy of more than 94%.
Tick-borne encephalitis (TBE) is peculiar due to its unstable dynamics with profound inter-annual fluctuations in case numbers – a phenomenon not well understood to date. Possible reasons – apart from variable human contact with TBE foci – include external factors, e.g. climatic forcing, autonomous oscillations of the disease system itself, or a combined action of both. Spectral analysis of TBE data from six regions of central Europe (CE) revealed that the ostensibly chaotic dynamics can be explained in terms of four superposed (quasi-)periodical oscillations: a quasi-biennial, triennial, pentennial, and a decadal cycle. These oscillations exhibit a high degree of regularity and synchrony across CE. Nevertheless, some amplitude and phase variations are responsible for regional differences in incidence patterns. In addition, periodic changes occur in the degree of synchrony in the regions: marked in-phase periods alternate with rather off-phase periods. Such a feature in the disease dynamics implies that it arises as basically diverging self-oscillations of local disease systems which, at intervals, receive synchronizing impulses, such as periodic variations in food availability for key hosts driven by external factors. This makes the disease dynamics synchronized over a large area during peaks in the synchronization signal, shifting to asynchrony in the time in between.
We investigated the seasonality of age-specific tuberculosis (TB) in Japan. To allow the development of TB control strategies for different age groups we used a time-series analysis, including a spectral analysis and least squares method, to analyse the monthly age-specific numbers of newly registered cases of all forms of active TB in Japan from January 1998 to December 2013. The time-series data are reported in 10-year age groups: 0–9, 10–19, …, 70–79, and ⩾80 years. We defined the contribution ratio of the 1-year cycle, Q1, as the contribution of the amplitude of a 1-year cycle to the whole amplitude of the time-series data. The Q1 values in the age groups corresponding to adolescence and middle life (10–39 years) and old age (⩾70 years) were high. The peaks in the active TB epidemics for the ⩾70 years age group occurred in August and September, 1–2 months behind the peaks for the 10–39 years age group (June and July). An active TB epidemic might be attributable to travel by public transport and irregular employment in the 10–39 years age group and immune system suppression by low winter temperatures in the ⩾70 years age group.
Atomic force microscopy (AFM) and laser scanning microscopy (LSM) measurements on a series of specially designed roughness artifacts were performed and the results characterized by spectral analysis. As demonstrated by comparisons, both AFM and LSM can image the complex structures with high resolution and fidelity. When the surface autocorrelation length increases from 200 to 500 nm, the cumulative power spectral density spectra of the design, AFM and LSM data reach a better agreement with each other. The critical wavelength of AFM characterization is smaller than that of LSM, and the gap between the measured and designed critical wavelengths is reduced with an increase in the surface autocorrelation length. Topography measurements of surfaces with a near zero or negatively skewed height distribution were determined to be accurate. However, obvious discrepancies were found for surfaces with a positive skewness owing to more severe dilations of either the solid tip of the AFM or the laser tip of the LSM. Further surface parameter evaluation and template matching analysis verified that the main distortions in AFM measurements are tip dilations while those in LSM are generally larger and more complex.
This paper falls within the context of diagnosis of rotating machines in speed variable
regime. Based on simulation signals, this work has the purpose to find relevant indicators
for the diagnosis of gear transmissions in a variable regime. Two indicators are proposed;
the first indicator is the RMS value applied to the vibration signal divided by its
corresponding instantaneous frequency. The second is the normalised gear frequency by
averaging speed. The gear frequency and averaging speed are estimated from the
spectrogram. To test the proposed indicators simulate signals have been used. These
signals are the results of a dynamic modelling of the gears transmission and are
calculated by using the Newmark integration diagram. This dynamic modelling takes into
account the eccentricity defect.
We investigated the seasonality of tuberculosis (TB) in Wuhan, China, to evaluate the increased risk of disease transmission during each season and to develop an effective TB control strategy. We applied spectral analysis to the weekly prevalence data of sputum smear positive (SSP) and sputum smear negative (SSN) pulmonary TB reported from 2006 to 2010. Cases of both SSP and SSN feature 1·0- and 0·5-year periodic modes. The least squares method was used to fit curves to the two periodic modes for SSP and SSN data. The curves demonstrated dominant peaks in spring similar to cases reported previously for other locations. Notably for SSP, dominant peaks were also observed in summer. The spring peaks of SSP and SSN were explained in terms of poorly ventilated and humid rooms and vitamin D deficiency. For the summer peaks of SSP, summer influenza epidemics in Wuhan may contribute to the increase in TB prevalence.
This paper is concerned with the existence and stability of travelling front solutions
for more general autocatalytic chemical reaction systems ut = duxx − uf(v), vt = vxx + uf(v)
with d > 0 and d ≠ 1, where
f(v) has super-linear or linear degeneracy at
v = 0. By applying Lyapunov-Schmidt decomposition method in some
appropriate exponentially weighted spaces, we obtain the existence and continuous
dependence of wave fronts with some critical speeds and with exponential spatial decay for
d near 1. By applying special phase plane analysis and approximate
center manifold theorem, the existence of traveling waves with algebraic spatial decay or
with some lower exponential decay is also obtained for d > 0. Further,
by spectral estimates and Evans function method, the wave fronts with exponential spatial
decay are proved to be spectrally or linearly stable in some suitable exponentially
weighted spaces. Finally, by adopting the main idea of proof in  and some similar arguments as in , the waves with critical speeds or with non-critical speeds are proved to be
locally exponentially stable in some exponentially weighted spaces and Lyapunov stable in
Cunif(ℝ) space, if the initial perturbation of the waves is
small in both the weighted and unweighted norms; the perturbation of the waves also stays
small in L1(ℝ) norm and decays algebraically in
Cunif(ℝ) norm, if the initial perturbation is in addition
small in L1 norm.
This paper uses spectral theory to develop the following two testable hypotheses in a unified framework for the predictions of business-cycle and endogenous growth models: (i) financial development affects only business-cycle volatility; and (ii) shocks affect both business-cycle volatility and long-run volatility of GDP growth. In other words, volatility caused by shocks is more persistent than that caused by financial underdevelopment. We decompose the business-cycle and long-run volatility by the spectral method and then test the hypotheses at the cross-country level. Empirical evidence provides support for both hypotheses. Higher private credit, a bank-based measure of financial development, dampens business-cycle volatility but not long-run volatility. Volatility of shocks, as measured by the volatility of changes in the terms of trade, magnifies both business-cycle and long-run volatility. The results are robust to accounting for endogeneity, a market-based measure of financial development, and an alternative method of volatility decomposition.
We compare spectral and wavelet estimators of the response amplitude operator (RAO) of a linear system, with various input signals and added noise scenarios. The comparison is based on a model of a heaving buoy wave energy device (HBWED), which oscillates vertically as a single mode of vibration linear system. HBWEDs and other single degree of freedom wave energy devices such as oscillating wave surge convertors (OWSC) are currently deployed in the ocean, making such devices important systems to both model and analyse in some detail. The results of the comparison relate to any linear system. It was found that the wavelet estimator of the RAO offers no advantage over the spectral estimators if both input and response time series data are noise free and long time series are available. If there is noise on only the response time series, only the wavelet estimator or the spectral estimator that uses the cross-spectrum of the input and response signals in the numerator should be used. For the case of noise on only the input time series, only the spectral estimator that uses the cross-spectrum in the denominator gives a sensible estimate of the RAO. If both the input and response signals are corrupted with noise, a modification to both the input and response spectrum estimates can provide a good estimator of the RAO. A combination of wavelet and spectral methods is introduced as an alternative RAO estimator. The conclusions apply for autoregressive emulators of sea surface elevation, impulse, and pseudorandom binary sequences (PRBS) inputs. However, a wavelet estimator is needed in the special case of a chirp input where the signal has a continuously varying frequency.
The Indian summer Southwest Monsoon plays an important part in influencing, and regulating, the productivity and sedimentation in the northwest Arabian Sea at the present day, by driving coastal upwelling. This leaves permanent sedimentological and geochemical records in the accumulating deep-sea sediments. Cores 722B and 724C were raised from the Owen Ridge and Oman Margin, respectively, during Leg 117 of the Ocean Drilling Program and have been subjected to geochemical analyses and α-spectrometry. A comparative core, CD17–30, situated on the adjacent Indus Fan abyssal plain, has also been studied. The chronostratigraphy of the cores has been established with δ 18O stratigraphy, giving a 350 ka climate record. Changes in the total sediment mass accumulation rates occur on glacial/interglacial time scales, with maximum fluxes occurring during glacial episodes. The high fluxes are predominantly due to wind-transported dust at the ridge and margin sites. Compositional parameters (e.g. the Ti/Al ratio) indicating the proportion of heavy minerals present within the dust, suggests that strong winds associated with the Southwest Monsoon, occur with Milankovitch periodicities, and are dominated by the precession (23 ka) frequency. The wind strength controls the proportion of heavy minerals transported to the Arabian Sea, whilst continental aridity influences the timing of deflation from the Arabian and Somalian peninsulas. Tracers of palaeoproductivity (Ba/Al) indicate strong coherence and phase with the proxy ice volume (foraminiferal δ 18O) signal, suggesting global climate parameters (ice volume, continental aridity) determine coastal productivity by influencing nutrient supply. In relation to productivity, the roles of oceanic circulation/stratification and nutrient supply through continental runoff are discussed. This study shows that the Southwest Monsoon appears to only affect the shorter period (precession cycle, 23 ka band) productivity signal. Evidence from excess 230Th suggests deep oceanic circulation (at about 2000 m depth) was more intense 110 ka BP decreasing toward 40 ka BP. By the use of these various geochemical tracers a new, and comprehensive, view of the interaction of the Monsoon and global climate with marine productivity through the late Pleistocene has been obtained.
The paper deals with a Dirichlet spectral problem for an elliptic operator with
ε-periodic coefficients in a 3D bounded domain of small thickness
δ. We study the asymptotic behavior of the spectrum as
ε and δ tend to zero. This asymptotic behavior depends
crucially on whether ε and δ are of the same order
(δ ≈ ε), or ε is much less than
δ(δ = ετ, τ < 1),
or ε is much greater than
δ(δ = ετ, τ > 1).
We consider all three cases.
A new type of spectrum analyzer using RF interferometry is presented. The stationary wave integrated Fourier transform spectrometer is dedicated to the measurement of transient wideband signals. The spectrometer is mobile and cheap. It consists of spatial samplers placed along a waveguide ended by a short circuit. The standing wave caused by the short circuit is sampled and the spectrum is obtained by an FFT computation. A 0.3–5 GHz analyzer was built as a proof-of-principle demonstration and an application to RF dosimetry is shown.
Dans ce travail, on s’intéresse à l’étude et à la caractérisation expérimentale par la
technique vélocimétrie laser à effet Doppler, du phénomène de détachement tourbillonnaire
lors de l’interaction couche limite cavité. L’étude est effectuée en changeant la longueur
et la hauteur de la cavité, ainsi que la vitesse de l’écoulement, afin de modifier la
nature des structures présentes à l’intérieur de la cavité. La variation du nombre de
Strouhal en fonction du nombre de Reynolds conduit à un regroupement pour chaque mode
d’instabilité, permettant de bien séparer les modes les uns des autres.
We study the dynamic behavior and stability of two connected
Rayleigh beams that are subject to, in addition to two sensors and
two actuators applied at the joint point, one of the actuators also
specially distributed along the beams. We show that with the
distributed control employed, there is a set of generalized
eigenfunctions of the closed-loop system, which forms a Riesz basis
with parenthesis for the state space. Then both the
spectrum-determined growth condition and exponential stability are
concluded for the system. Moreover, we show that the exponential
stability is independent of the location of the joint. The range of
the feedback gains that guarantee the system to be exponentially
stable is identified.
This paper studies asset returns adopting an alternative strategy to assess a model's goodness of fit. Based on spectral analysis, this approach considers a model as an approximation to the process generating the observed data, and characterizes the dimensions for which the model provides a good approximation and those for which it does not. Our aim is to offer new evidence regarding the size and the location of approximation errors of a set of stochastic growth models considered to be decisive steps in the progress of the asset pricing research program. Our specific objective is to reevaluate the results of Jermann's (1998) model extending the calculations to the spectral domain. Spectral results are relatively satisfactory: the benchmark model needs very few contributions of approximation errors to account for the empirical equity premium. Second, the location of the approximation errors, when they are substantial, seems to be essentially concentrated at high frequencies.
Cave temperature monitoring was carried out in the Cueva del Agua de Iznalloz, Granada, Spain, a cave that has great tourist potential and which has been maintained under natural conditions for over 30 years. The cave temperature under natural conditions was used to identify possible anthropogenic influences, in order to distinguish these from the variations directly related to natural changes. In particular, the relative influence of external weather conditions, thermal modification caused by visitors and the subsequent thermal recovery of the cave were identified. In addition, controlled experiments investigated the effect of two large-scale visits (980 and 2088 visitors day−1) to the cave interior, before any tourist activities in the cave were undertaken. Correlation and spectral analyses of time series were used to determine the thermal behaviour of the cave over time. The effect of both mass visits on the air temperature in the interior of the cave was very rapid (2.5 min). The maximum perturbation of air temperature within the cave during the two experiments was after 30 and 70 min. The memory effect for temperature whilst the cave was open to the public was estimated to be 5–6 h, whilst the response to external meteorological changes exceeded one week. A permanent visitor capacity of 53 people ensures that the natural cave temperature can be regained within 4–5 h. The cave can only support small groups of visitors, not the massive visits characteristic of show caves.