Valley Positions Research Articles

BP-Diff: a conditional diffusion model for cuffless continuous BP waveform estimation using U-Net.

Continuous monitoring of blood pressure (BP) is crucial for daily healthcare. Although invasive methods provide accurate continuous BP measurements, they are not suitable for routine use. Photoplethysmography (PPG), a non-invasive technique that detects changes in blood volume within the microcirculation using light, shows promise for BP measurement. The primary goal of this study is to develop a novel cuffless method based on PPG for accurately estimating continuous BP.
Approach. We introduce BP-Diff, an end-to-end method for cuffless continuous BP waveform estimation utilizing a conditional diffusion probability model combined with a U-Net architecture. This approach takes advantage of the stochastic properties of diffusion models and the strong feature representation capabilities of U-Net. It integrates the continuous BP waveform as the initial status and uses the PPG signal and its derivatives as conditions to guide the training and sampling process.
Main results. BP-Diff was evaluated using both uncalibrated and calibrated schemes. The results indicate that, when uncalibrated, BP-Diff can accurately track BP dynamics, including peak and valley positions, as well as timing. After calibration, BP-Diff achieved highly accurate BP estimations. The mean absolute error (MAE) of the estimated BP waveforms, along with the systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) from the calibrated BP-Diff model, were 2.99 mmHg, 2.6 mmHg, 1.4 mmHg, and 1.44 mmHg, respectively. Consistency tests, including Bland-Altman analysis and Pearson correlation, confirmed its high reliability compared to reference BP. BP-Diff meets the American Association for Medical Instrumentation (AAMI) standards and has achieved a Grade A from the British Hypertension Society (BHS).
Significance. This study utilizes PPG signals to develop a novel cuffless continuous BP measurement method, demonstrating superiority over existing approaches. The method is suitable for integration into wearable devices, providing a practical solution for continuous BP monitoring in everyday healthcare.

Applying the first principle to study the structure, electrical and magnetic properties of ASiNRs-doped Neodymium

In this project, we investigated and investigated the optimal sites in the chemisorption of Neodymium (Nd) on armchair silicene nanoribbons (ASiNRs) to learn about the geometrical and electronic properties of the structures by applying these properties with first principle math. The survey has three steps. The first was to change the top, valley, bridge, and hollow positions to find optimazed positionThe results show that the Bridge position has the lowest absorbed energy value of -2.6eV, has the most stable structure, with the strongest magnetic moment of 4.68 μB, and a buckl degree of 0.69 Å; The Si-Si-Si bond angle at this time is 115053’ almost like the pristine case. The second was to change the Si-Si bondlength of ASiNRs the same purpose. Finally, we survey the distance from Nd atom to pristine adsorbent surface was decreased. The calculation results show that the valley position is the most ideal location, corresponding to the bond length of 2.26 Å and the optimal height of 2.11 Å resulting in a single material adsorption system for the new materials, different from other positions with bandgap changed. This result shows that the absorption method between metals and pristine semiconductor ASiNRs has opened up a very good direction, contributing to enriching the source of materials applied to the field of manufacturing electronic, optoelectronic, and spintronic components in the future.

Potential of pine forest in controlling soil erosion in Himalayan region - Investigation using fallout radionuclide (137Cs) measurements

The Himalayas possess a distinctive topography owe to the dynamic interplay of tectonic activity, geological erosion and sedimentation, glacial processes, and climatic influences over the millions of years. The rugged, steep terrain and poor land management make it more prone to water erosion, negatively impacts the soil, affecting the goods and services supported by the soil ecosystems. Traditional methods used in soil erosion assessment face limitations when dealing with topographically complex hillslopes. The use of Fallout Radionuclide (FRN) -137Cs provides a feasible alternative for measurement of soil erosion in the region with such topography. However, there is lack of 137Cs-based soil erosion studies in the north-west Himalayas. Pine (Pinus roxburghii) is the predominant forest type in the Himalayas, offering numerous benefits to both natural ecosystems and human beings. In this study, we selected a typical steep hillslope covered with pine forest in the Himalayas for soil erosion assessment. The study measured 137Cs reference inventory of 1409 Bq m−2 in the landscape. Importantly, the concentration of 137Cs along the hillslope positions showed a significant variation attributed to topographic variability. Topographic factors, such as the slope shape and gradient, were identified as the major governing parameters of soil erosion in the hilly and mountainous region. The net soil erosion rate over hillslope positions revealed highest at upper hillslope followed by ridge, middle and valley hillslope positions. The net soil erosion rate under the pine forest ranged from 8.0 to 14.6 t ha−1 yr−1, with an average rate of 9.9 t ha−1 yr−1. Erosion rate over the hillslope positions were found in accordance to the soil loss tolerance limit (SLTL) except for the upper hillslope, indicating it as critical slope position requires to adopt suitable conservation measures. The study signifies the role of the forest in mitigating soil erosion and, in turn, conserving soil resources. The findings provide crucial insights and guidance to land managers and decision-makers, emphasizing the necessity of conserving and restoring forests in the Himalayas.

On the electronic and spin-valley coupling of vanadium doped MoS2(1− x )Se2x monolayers

Monolayers of MoS2 with tunable bandgap and valley positions are highly demanding for their applications in opto-spintronics. Herein, selenium (Se) and vanadium (V) co-doped MoS2 monolayers (vanadium doped MoS2(1−x)Se2x (V-MoSSe)) are developed and showed their variations in the electronic and optical properties with dopant content. Vanadium gets substitutionally (in place of Mo) doped within the MoS2 lattice while selenium doped in place of sulfur, as shown by a detailed microstructure and spectroscopy analyses. The bandgap tunability with selenium doping can be achieved while valley shift is occurred due to the doping of vanadium. Chemical vapor deposition assisted grown MoS2 (also selenium doped MoS2 as shown here) is known for its n-type transport behavior while vanadium doping is found to be changing its nature to p-doping. Chirality dependent photoexcitation studies indicate a room temperature valley splitting in V-MoSSe (∼8 meV), where such a valley splitting is verified using density functional theory based calculations.

Prescribed fire and thinning influence snag density and size in the southern Appalachian Mountains

Snags, or standing dead trees, are an important structural component of forest ecosystems. Many animals, including endangered species, depend on snags for foraging, protection, or raising young. Climate change, habitat loss, and modification of natural disturbance regimes contribute to changes in the availability and characteristics of snags in forests. Therefore, understanding what natural and artificial processes promote snags with the characteristics necessary for wildlife is a significant conservation concern. We examined how low-severity prescribed fire affected the density and characteristics of snags at 80 sites in the Talladega National Forest, Alabama. We sampled sites within 4 prescribed fire intervals, including 1–3 (previously thinned 4–23 years ago), > 3–8, > 8–12, and > 12 years. At each site, we measured snags across transects on 3 different slope positions, including the ridge, mid-slope, and valley, to account for slope-influenced fire behavior and stressors. The average diameter of snags increased in stands with the shortest prescribed fire interval, but snag height, decay class, and percentage of bark remaining were similar across all fire intervals. Snag density was lowest in the shortest fire interval due to fewer small- and medium-sized hardwood snags. A higher density of large snags was found in the shortest fire interval compared to the longest fire interval. Ridges had a greater density of snags compared to mid-slope and valley positions due to more small- and medium-sized pine snags. Although thinning followed by frequent, low-severity prescribed fire reduces snag density, the increase in density of large-diameter snags provides high-quality habitat for snag-dependent birds and bats. More intense fire and other stressors on ridges likely promote higher densities of snags. Our research indicates forest managers can use prescribed fire and thinning to accomplish multiple management goals while continuing to produce valuable snags for wildlife.

The impact of valley profile on the mobility and Kerr rotation of transition metal dichalcogenides

The transport and optical properties of semiconducting transition metal dichalcogenides around room temperature are dictated by electron–phonon scattering mechanisms within a complex, spin-textured and multi-valley electronic landscape. The relative positions of the valleys are critical, yet they are sensitive to external parameters and very difficult to determine directly. We propose a first-principles model as a function of valley positions to calculate carrier mobility and Kerr rotation angles, and apply it to MoS2, WS2, MoSe2, and WSe2. The model brings valuable insights, as well as quantitative predictions of macroscopic properties for a wide range of carrier density. The doping-dependent mobility displays a characteristic peak, the height depending on the position of the valleys. In parallel, the Kerr rotation signal is enhanced when same spin-valleys are aligned, and quenched when opposite spin-valleys are populated. We provide guidelines to optimize and correlate these quantities with respect to experimental parameters, as well as the theoretical support for in situ characterization of the valley positions.

Study of SO2 measurement based on a dual optical path Fabry-Perot correlation spectroscopy.

This paper investigates a method for measuring SO2 concentration using Fabry-Perot interferometer correlation spectroscopy. In this method, the experimental system is designed as a separated beam, with the beam entering the F-P cavity at two incidence angles simultaneously to match the peak and valley positions of the SO2 absorption cross-section. The system achieves a 2σ detection limit of 28.2 ppm·m(15 cm) at a sampling frequency of 10 Hz. An outfield comparison experiment with the differential optical absorption spectroscopy method shows good agreement for the simultaneous measurement of SO2 concentration from sulfur combustion, with a correlation coefficient of R2 = 0.93. This study introduces a non-dispersive, highly accurate, and fast gas detection technique.

Stable isotope profiles of soil organic carbon in forested and grassland landscapes in the Lake Alaotra basin (Madagascar): insights in past vegetation changes

Abstract. The extent to which the central highlands of Madagascar were once covered by forests is still a matter of debate: while reconstructing past environments is inherently difficult, the debate is further hampered by the fact that the evidence documenting land cover changes and their effects on carbon and sediment dynamics in Madagascar has hitherto mainly been derived from lake coring studies. Such studies provide an integrated view over relatively large areas but do not provide information on how land-use change affects hillslopes in terms of carbon and sediment dynamics. Such information would not only be complementary to lake inventories but may also help to correctly interpret lake sediment data. Carbon stable isotope ratios (δ13C) are particularly useful tracers to study the past dynamics of soil carbon over time spans ranging from years to millennia and thus to understand the consequences of land-use change over such time spans. We analysed soil profiles down to a depth of 2 m from pristine forests and grasslands in the Lake Alaotra region in central Madagascar. Along grassland hillslopes, soil organic carbon (SOC) content was low, from 0.4 % to 1.7 % in the top layer, and decreased rapidly to ca. 0.2 % below 100 cm depth. The current vegetation predominantly consists of C4 grasses (δ13C ∼ −13 ‰), yet topsoil δ13C-OC ranges between −23.0 ‰ and −15.8 ‰, and most profiles show a decrease in δ13C-OC with depth. This contrasts with our observations in the C3-dominated forest profiles, which show a typical profile whereby δ13C values increase slightly with depth. Moreover, the SOC stock of grasslands was ∼ 55.6 % lower than along the forested hillslopes for the upper 0–30 cm layer. δ13C values in grassland and forest profiles converge to similar values (within 2.0 ± 1.8 ‰) at depths below ∼ 80 cm, suggesting that the grasslands in the Lake Alaotra region have indeed developed on soils formerly covered by a tree vegetation dominated by C3 plants. We also observed that the percent of modern carbon (pMC) of the bulk OC in the top, middle and lower middle positions of grasslands was less than 85 % near the surface. This could reflect a combination of (i) the long residence time of forest OC in the soil, (ii) the slow replacement rate of grassland-derived OC (iii) and the substantial erosion of the top positions towards the valley position of grasslands. At the valley positions under grassland, the upper 80 cm contains higher amounts of recent grass-derived OC in comparison to the hillslope positions. This is likely to be related to the higher productivity of the grassland valleys (due to higher moisture and nutrient availability), and the deposition of OC that was eroded further upslope may also have contributed. The method we applied, which is based on the large difference in δ13C values between the two major photosynthetic pathways (C3 and C4) in (sub-)tropical terrestrial environments, provides a relatively straightforward approach to quantitatively determine changing vegetation cover, and we advocate for its broader application across Madagascar to better understand the island's vegetation history.

Second-order elastic topological insulator with valley-selective corner states

Second-order elastic topological insulators (SETIs) with topologically protected corner states offer new routes for the realization of the robust manipulation of elastic waves in lower dimensions, providing the unprecedented ways for integrated ultrasound sensors and energy harvesting devices. However, traditional SETIs lack the flexibility of turning on and off the corner states on demand. Herein, we proposed a type of SETIs possessing the valley-selective topological corner states, endowing the capability of activating corner states by engineering the valley positions. An extra type of corner states with anti-symmetric displacement profile is also observed in the proposed SETIs, which is attributed to the enhanced long-range effect. The discrete mechanical model is firstly investigated and then expanded into the PC plate, in which the theory of Wannier center can well elucidate the corner states with valley-selectivity. The experimental results validate the existing corner states with valley-selectivity and anti-symmetric displacement profile. The proposed discrete model acts as a versatile platform presenting the relevant topological effects. The achieved valley-selectivity and multi-polarization features hosted in the designed SETI may contribute to their practicality and reconfigurability in elastic energy trapping, detecting, and harvesting device.

Time-Lag Effect of Vegetation Response to Volumetric Soil Water Content: A Case Study of Guangdong Province, Southern China

The content of soil water affects the physiological activities of vegetation, and the type of vegetation also affects the soil water balance. It is of great significance to study the response of vegetation to soil moisture change, which is helpful for understanding the vulnerability of vegetation for regional and environmental protections. The response of vegetation to soil moisture in Guangdong Province from mid-October 2015 to the end of March 2017 was studied by using cloudy region drought index (CRDI) as the drought index and volumetric soil water content (VSWC) as the soil moisture index to measure the level of water stress on vegetation. Taking the peak and valley positions of CRDI and VSWC as characteristic points, the lag time of vegetation to volumetric soil water content was obtained by judging the difference between the peak and valley positions of the two indexes. The results indicate that the response of vegetation to volumetric soil water content in Guangdong lagged 3.33 periods (9–35 days) on average. When VSWC is sufficient, there is no obvious difference in time-lag between different types of vegetation. However, when VSWC is relatively insufficient, grass shows the fastest response to the change of volumetric soil water content. Both longitude and soil moisture affect the lag time of vegetation. Under the same conditions, the higher the soil humidity is, the longer the lag time is, and the longer the delay time is with the greater longitude. CRDI can reflect the time-lag effect between vegetation and VSWC in Guangdong, indicating it is a sensitive and applicable index for characterizing the time-lag phenomena of vegetation to soil moisture.

Hyperspectral characterization and chlorophyll content inversion of reclaimed vegetation in rare earth mines.

The special physical and chemical properties of the reclaimed land caused by the disturbance of rare earth mining and the environmental stress caused by the mining of rare earth lead to the inhibition of the physiological functions of the reclaimed vegetation and the severe challenge of vegetation ecological restoration. This study focuses on the Lingbei rare earth mining area in Dingnan County, Jiangxi Province, and investigates the original spectrum, derivative spectrum, and the continuum-removed spectrum of reclaimed vegetation. The spectral characteristics and trends and the typical reclaimed vegetation are analyzed, the correlation between the chlorophyll content and the spectral indices of the reclaimed vegetation is determined, and the sensitive spectral parameters are extracted. Partial least squares algorithm, a back propagation neural network algorithm, and a sparse autoencoder network are used to estimate the chlorophyll content, and the model's accuracies are compared. The vegetation spectrum of the reclaimed vegetation is characterized by high reflectance in the visible region, a redshift of the green peak and red valley positions, and a blueshift of the red edge positions, a relatively low spectral variation in. The variability of the sensitive spectral parameters of different vegetation type is extracted. The sparse autoencoder network is the optimal estimation model (the R2 value of the three vegetations are 0.9117, 0.7418, and 0.9815, respectively). The results provide a scientific basis for monitoring and managing the growth of different types of reclaimed vegetation in rare earth mining areas under environmental stress and can guide the ecological restoration of reclaimed mining areas.

Effects of strain and electric field on electronic and optical properties of monolayer [formula omitted]-GeX (X [formula omitted] S, Se and Te)

We investigate the mechanical, electronic, and optical properties of monolayer GeX (X= S, Se, and Te) with γ structure based on density-functional theory calculations. We find that the mechanical anisotropy of γ-GeS is higher than those of γ-GeSe and γ-GeTe, because of its strongest ionic bond. In the unstrained case, γ-GeX is an indirect-gap semiconductor with the Mexican-hat (MH) dispersion in the valence band. By applying tensile and biaxial strains, both energy band gap and valley positions are controlled. On the other hand, by applying an external electric field, the energy band gap is decreased to zero because of the downward interlayer band. We also find that the in-plane optical absorptions of monolayer γ-GeX in the visible-light region are comparable to that of the monolayer transition metal dichalcogenides such as MoS2. Due to the unique structure in the z direction, the monolayer γ-GeX also shows a high value of the out-of-plane optical absorptions. The strain engineering significantly modifies the optical absorption in the visible light, while the effect of the external electric field on the optical properties is weak. Our results will be helpful to design the electro-optical devices based on monolayer materials with MH band.

Spurious jumps in wavelength tracking of fiber-optic Fabry–Perot interferometric sensors

Wavelength tracking is a commonly used method for demodulating fiber-optic Fabry–Perot interferometric sensors due to its high resolution and straightforward implementation. We report the observation of random spurious jumps in a commonly used wavelength-tracking method based on curve fitting. These jumps were unrelated to the phase ambiguity of the spectral fringes and led to measurement errors. We analyzed the origin of the spurious jumps through Monte Carlo simulations where the fringe valley positions were obtained using polynomial curve fittings. The simulation results show that the spurious jumps arose mainly from the systematic errors of the curve-fitting function for modeling the sensor spectrum and manifested themselves by the changes in the pixel set for curve fitting. The centroid method also suffered from the spurious jumps. We proposed a modified correlation demodulation method free of the spurious jumps. In this method, the information of the measurand was obtained through the correlation between the measured sensor spectral frames and a sufficiently large number of calibrated frames of the sensor over the measurement range. The simulation and experimental results show that the modified correlation method was free of the spurious jumps encountered in the regular wavelength tracking. The resolution of the method was also studied and compared with the curve-fitting method.

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.

Natural Regeneration After Volcanic Eruptions: Resilience of the Non-legume Nitrogen-Fixing Tree Parasponia rigida

Volcanic eruptions disturb vegetation at a time it is needed for preventing mudflows. A resilient indigenous non-legume nitrogen-fixing tree that is adapted to the ash and spreads rapidly protects areas downstream in a volcanic landscape in Indonesia. Within the volcanic ring of fire both the long-term benefits (including densely populated, fertile agricultural soils) and short-term ecological disturbance of volcanic ash deposition are clear. Mount Kelud in East Java has erupted on a 15–37-years cycle for the past centuries, most recently in 2014, causing damage to settlements, agricultural land, agroforestry, and watershed protection forests, as the ash deposits caused tree mortality, restricted infiltration, and led to ash flows. Rapid “restoration” or recovery of tree-based vegetation with planted Legume trees (such as Calliandra spp.) has been attempted but is not very effective. However, the non-legume nitrogen-fixing Parasponia rigida, symbiotic with rhizobium bacteria, contrasted to its non-symbiotic sibling (Trema orientalis) has been studied in laboratory conditions, but not in its native environment. We mapped and sampled P. rigida in various locations (upper, middle, and lower elevation positions in ridge-slope-valley toposequences) on the Kelud complex starting 1 year after the latest eruption, estimated biomass development, and quantified P. rigida root nodules in relation to N availability in the ash/soil mixtures in these locations. P. rigida was found as a pioneer tree at elevations between 600 and 1,700 m a.s.l. (above sea level) along ridges, in slope, and valley positions. At lower elevations T. orientalis dominated. Within 3 years of the eruption, stem diameters were 3–10 cm. Up to 93% of P. rigida root nodules were found to be effective, based on the hemoglobin color on cross-sections. Rhizobium bacteria were found in root nodule tissue at densities of two to a hundred times higher than in rhizosphere soil. Between a total soil N content from 0.01 to 0.04% the density of effective nodules decreased from 1,200 to 200 m−2. P. rigida stands in the area, especially at ridges close to the crater deserve to be managed proactively as future seed sources, given the high frequency of eruption episodes, while recovery after eruptions on similar volcanoes can likely be facilitated by tactical assisted seed dispersal if effective seed collection and storage methods can be established.

Non-uniform thermal-hydraulic behavior in a 61-rod bundle of supercritical water-cooled reactor

Numerical investigations of supercritical water flowing through a 61-rod bundle based on the fuel assembly of the supercritical water-cooled reactor (SCWR) are performed by using the Reynolds stress model with enhanced wall treatment. Effect of hexagonal outer casing on thermal-hydraulic characteristics under design conditions is investigated. Mass redistribution mainly caused by flow area differences and varied properties of supercritical water is observed and the mass flux difference between the interior sub-channel and side sub-channel is about 523.6 kg·m−2·s−1 at the outlet. It is observed that a strong circumferential wall temperature non-uniformity of the outer rods caused by mass redistribution is over 200 K within 0.5 m near the outlet, which should be carefully and thoroughly considered in the design of SCWR fuel assemblies. The peak and valley positions of wall temperature result from periodical sub-channel structure are offset in the direction of the corner sub-channel and the offset angle increases with the decreasing distance to the corner sub-channel.

Topographic controls on the variability of soil respiration in a humid subtropical forest

Knowledge of the spatial and temporal variabilities of soil respiration is important in estimating the soil carbon budget and in understanding how soils may respond to global changes. In areas with complex terrain, the topography can modify the hydrological conditions and other biophysical variables, which complicates the spatial and temporal heterogeneity of soil respiration. Herein, we investigated soil respiration along topographic transects with ridge, middle slope, lower slope and valley positions in a humid subtropical mountain forest in China to assess the driving factors of the variations in soil respiration. Our results showed that there were substantial temporal and spatial variations in soil respiration. The temporal variation of soil respiration could be well explained by the dynamics of soil temperature and moisture. Soil respiration rates also showed clear topographic pattern and decreased significantly from the ridge to valley soils, with the mean rates equaled 3.43 ± 0.13, 2.64 ± 0.30, 2.13 ± 0.26 and 1.88 ± 0.24 μmol m−2 s−1 at the ridge, middle slope, lower slope, and valley, respectively. Correlation analyses revealed that the spatial variation of soil respiration could be explained by multiple variables (e.g., soil temperature, basal area of the trees, thickness of the forest floor, root biomass and stock of soil dissolved carbon, soil C/N and soil bulk density). Results from partial least squares path modeling suggested that the topography modified the fine root distribution and the lateral losses of light and dissolved organic materials that created areas of high carbon sources for soil respiration at the ridge. The topographically regulated processes further resulted in a high soil C/N at the ridge that favored SOC decomposition. The higher respiration rate for the ridge soil and its higher sensitivity to soil temperature and moisture changes suggested that the ridge position was a potential hot spot for future environmental changes. Future studies and management practices regarding the soil carbon efflux in forest ecosystems with topographical variations should take into account the topographic effects.

Estimating the Spatial Distribution of Soil Properties Using Environmental Variables at a Catchment Scale in the Loess Hilly Area, China.

A comprehensive understanding of the spatial distribution and dynamic changes of soil properties are the basis for sustainable land management. Topography and land use types are key factors affecting soil property variability. This study analyzed the effects of land use types and landscape locations on soil properties, based on data from 111 points of surface soil (0–20 cm) in the Zhujiagou catchment on the Loess Plateau of Northwest China. Soil properties include clay, silt, bulk density (BD), soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP). Land use types include slope farmland (SFL), terrace farmland (TFL), check-dam farmland (CDL), woodland (WL), shrub land (SL) and grassland (GL). Landscape locations include crest (CT), upper slope (US), middle slope (MS), lower slope (LS) and flat valley (FV). Topographical attributes were divided into primary and secondary (or compound) attributes. Correlation analyses were carried out between soil properties and terrain attribute, and multiple-linear regression models were established to estimate soil properties using land use types and topographic attributes as independents. Results indicated that significant differences in soil properties existed between six land use types, except for bulk density. Higher values of clay, silt, SOM and TN occurred in soils from check-dam farmland, but lower values in soils from shrub land. Significant differences among landscape positions were observed for clay, BD, SOM and TN. Clay, SOM and TN contents on flat valley (FV) positions were higher than those of other positions. Different correlations were found between soil properties and terrain attributes. The regression models explained 13% to 63% of the variability of the measured soil properties, and the model for Clay had the highest R2 value, followed by TN, silt, BD, SOM and TP. Validation results of the regression models showed that the model was precise for soil bulk density, but the variation was large and a high smoothing effect existed for predicted values of other soil properties. For TP, the predicted result was poor. Further observations suggested that land use was the dominant factor affecting soil chemical properties. But for soil physical properties, especially for BD, topography was the dominant factor.

Hot Spots and Hot Moments of Soil Moisture Explain Fluctuations in Iron and Carbon Cycling in a Humid Tropical Forest Soil

Soils from humid forests undergo spatial and temporal variations in moisture and oxygen (O2) in response to rainfall, and induce changes in iron (Fe) and carbon (C) biogeochemistry. We hypothesized that high rainfall periods stimulate Fe and C cycling, with the greatest effects in areas of high soil moisture. To test this, we measured Fe and C cycling across three catenas at valley, slope, and ridge positions every two days for a two-month period in a rainforest in Puerto Rico. Over 12 days without rain, soil moisture, FeII, rapidly reducible Fe oxides (FeIIIRR), and dissolved organic C (DOC) declined, but Eh and O2 increased; conversely, during a 10-day period of intense rain (290 mm), we observed the opposite trends. Mixed-effects models suggest precipitation predicted soil moisture, soil redox potential (Eh), and O2, which in turn influenced Fe reduction/oxidation, C dissolution, and mineralization processes. The approximate turnover time for HCl-extractable FeII was four days for both production and consumption, and may be driven by fluctuations in FeIIIRR, which ranged from 42% to 100% of citrate–ascorbate-extractable FeIII (short-range order (SRO)-FeIII) at a given site. Our results demonstrated that periods of high precipitation (hot moments) influenced Fe and C-cycling within day-to-week timescales, and were more pronounced in humid valleys (hot spots).

A novel algorithm for laser self-mixing sensors used with the Kalman filter to measure displacement

This paper proposes a simple and effective method for estimating the feedback level factor C in a self-mixing interferometric sensor. It is used with a Kalman filter to retrieve the displacement. Without the complicated and onerous calculation process of the general C estimation method, a final equation is obtained. Thus, the estimation of C only involves a few simple calculations. It successfully retrieves the sinusoidal and aleatory displacement by means of simulated self-mixing signals in both weak and moderate feedback regimes. To deal with the errors resulting from noise and estimate bias of C and to further improve the retrieval precision, a Kalman filter is employed following the general phase unwrapping method. The simulation and experiment results show that the retrieved displacement using the C obtained with the proposed method is comparable to the joint estimation of C and α. Besides, the Kalman filter can significantly decrease measurement errors, especially the error caused by incorrectly locating the peak and valley positions of the signal.