Search

International audience; Mixing tree species is a forest management strategy put forward to increase and stabilize primary productivity. Yet, little is known about soil organic carbon (SOC) storage in mixed species forests, particularly under water shortage. In this study, we used a tree diversity experiment in southwestern France to assess the interactive effects of water availability (via irrigation) and mixing tree species (monocultures of pine (Pinus pinaster) and birch (Betula pendula) versus mixed plots of pine-birch and pine-birch-oak (Quercus robur)) on SOC stocks in the forest floor and across five mineral soil layers (0-5, 5-15, 15-30, 30-60 and 60-90 cm deep). We found that SOC stocks were negatively affected by irrigation in the forest floor due to an increase in decomposition rates. However, SOC stocks were positively influenced by both the mixing of tree species and irrigation in the mineral soil, particularly at the 15-30-cm soil depth. This is because root niche partitioning in mixed plots and an increase in tree biomass in irrigated plots may have resulted in greater organic matter inputs through rhizodeposition and the incorporation of microbially-derived compounds. These preliminary results indicate that SOC dynamics and its response to biotic and abiotic factors are strongly dependent on soil depth. Our data further highlight that the positive effect of mixing trees on SOC stocks was higher in irrigated plots, thereby contradicting the idea that tree mixture effects are expected to be greater when environmental conditions are harsher. We conclude that mixing tree species can increase SOC stocks in the short term in temperate forests, even if the exact mechanisms remain to be identified.

Peaks are observed in a depth dependent power spectrum of P-wave velocity fluctuations determined from an inversion of P wave coherences observed by the USArray. These peaks correlate with the dept...

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry-over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry-over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth-dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.

Articular cartilage has well known depth-dependent structure and has recently been shown to have similarly non-uniform depth-dependent mechanical properties. Here, we study anatomic variation of the depth-dependent shear modulus and energy dissipation rate in neonatal bovine knees. The regions we specifically focus on are the patellofemoral groove, trochlea, femoral condyle, and tibial plateau. In every sample, we find a highly compliant region within the first 500 µm of tissue measured from the articular surface, where the local shear modulus is reduced by up to two orders of magnitude. Comparing measurements taken from different anatomic sites, we find statistically significant differences localized within the first 50 µm. Histological images reveal these anatomic variations are associated with differences in collagen density and fiber organization. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 686–691, 2013

Summary: Continuous depth sensing indentation microhardness measurementswere performed to investigate the effect of filler content and dimensionality onthemechanicalbehaviourofdifferentpolymernanocomposites.In1Dfillerreinforcednanocomposites(suchasPP/MWCNTsystem),boththehardnessandtheindentationmoduluswerefoundtoappreciablyincreaseuptoafillerweightfractionof1.6wt.-%.Further addition of the filler changed the properties only insignificantly. In thenanocomposites with 2D filler (such as in PA6/LS) both the hardness and theindentation modulus increase notably with the addition of the filler and showedintense plasticity. In the investigated systems and composition range, the 3D filler(suchasPP/OS2)showednoreinforcingeffectatall.Inwasconcludedthatthe1Dand2D nanofillers play much more effective reinforcing role to improve the mechanicalproperties than the 3D fillers. Keywords: deformation behavior; indentation modulus; Martens hardness;nanocomposites; recording microhardness Introduction The mechanical properties of polymercomposites have been the subject of con-siderable research nowadays

Characterization of streambed hydraulic conductivity from the channel surface to a great depth below the channel surface can provide needed information for the determination of stream-aquifer hydrologic connectedness, and it is also important to river restoration. However, knowledge on the streambed hydraulic conductivity for sediments 1 m below the channel surface is scarce. This study describes a method that was used to determine the distribution patterns of streambed hydraulic conductivity for sediments from channel surface to a depth of 15 m below. The method includes Geoprobe's direct-push techniques and Permeameter tests. Direct-push techniques were used to generate the electrical conductivity (EC) logs and to collect sequences of continuous sediment cores from river channels, as well as from the alluvial aquifer connected to the river. Permeameter tests on these sediment cores give the profiles of vertical hydraulic conductivity (K(v)) of the channel sediments and the aquifer materials. This method was applied to produce K(v) profiles for a streambed and an alluvial aquifer in the Platte River Valley of Nebraska, USA. Comparison and statistical analysis of the K(v) profiles from the river channel and from the proximate alluvial aquifer indicates a special pattern of K(v) in the channel sediments. This depth-dependent pattern of K(v) distribution for the channel sediments is considered to be produced by hyporheic processes. This K(v)-distribution pattern implied that the effect of hyporheic processes on streambed hydraulic conductivity can reach the sediments about 9 m below the channel surface. Copyright (C) 2010 John Wiley & Sons, Ltd.

In recent studies other investigatiors have presented traces of "light scattering" versus depth into the cornea. The present investigation demonstrates that these traces do not measure the actual light scatter intensity and that a proper interpretation of such traces shows that most of the scattering is from within the stroma.

An inversion technique using the Marquardt optimization is developed to interpret the gravity anomalies due to anticlinal and synclinal structures with density contrast varying continuously with depth. The algorithm simultaneously estimates the parameters of the respective models, in addition to the regional gravity background that is invariably associated with the residual gravity anomaly. Forward modelling is realized through analytically derived gravity expressions for the respective models in the space domain. The efficacy of the inversion is demonstrated with the gravity anomaly due to a theoretical model, in each case with and without the regional background. In addition, the applicability is illustrated using the gravity anomalies of the Pays De Bray anticline, situated north-west of Paris, France. The interpreted depth of the Pays De Bray anticline using the present inversion compares well with the drilling depth.

Inspired by the depth-dependent inhomogeneity of articular cartilage, it was hypothesized that a novel layered agarose technique, using a 2% (wt/vol) top and a 3% (wt/vol) bottom layer, would create an inhomogenous tissue construct with distinct material properties in conjoined regions. The biochemical and mechanical development of these constructs was observed alongside uniform 2% and 3% constructs. Initially, uniform 3% agarose disks had the highest bulk Young’s modulus (EY � 28 kPa) of all groups. After 28 days of culture in 20% FBS-containing media, however, uniform 2% chondrocyte-seeded constructs achieved the highest Young’s modulus compared to bilayered and 3% agarose disks. Though all three groups contained similar GAG content (� 1.5% ww), uniform 2% agarose disks on day 28 possessed the highest collagen content (� 1% ww). Unlike in either homogeneous construct type, microscopic analysis of axial strain fields in bilayered constructs in response to applied static compression revealed two mechanically disparate regions on day 0: a softer 2% layer and a stiffer 3% layer. With time in culture, this inhomogeneity became less distinct, as indicated by increased continuity in both the local displacement field and local EY, and depended on the level of FBS supplementation of the feed media, with lower FBS concentrations (10%) more closely maintaining the original distinction of material properties. These results shed positive light on a layered agarose technique for the production of inhomogeneous bilayered chondrocyte-seeded agarose constructs with applications for investigations of chondrocyte mechanotransduction and for possible use in the tissue engineering of inhomogeneous articular cartilage constructs. � 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.

Purpose To measure the proton magnetization transfer ratio (MTR) maps in control and collagen-depleted bovine patellar cartilage specimens as a function of cartilage depth during mechanical compression. Materials and Methods One-dimensional proton projection MR images employing a spin-echo imaging sequence were obtained on a custom-built NMR spectrometer interfaced to an Oxford magnet operating at 2T. The mechanical compressions were performed with a custom-built MR-compatible pressure cell and evaluated dynamically via one-dimensional projection. High-spatial-resolution two-dimensional MT images were obtained using a fast spin-echo (FSE) sequence on a 4T whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA) to quantify the MTR maps of normal and collagen-depleted bovine patellae. Results All of the cartilage plugs from the bovine patellae showed that the MTR value increases continuously as a function of cartilage depth. Although the overall MTR trend as a function of depth is the same in both control and collagen-depleted cartilage, the magnitude of the MTR value differs between the two. The MTR value is decreased with collagen depletion and increased with mechanical compression. The increase in MTR value during compression may be due to a decrease in free water content and volume, resulting in an increase in collagen concentration. Conclusion We demonstrated that the MTR in bovine patellar cartilage is depth-dependent and is relatively higher in the radial zone compared to the superficial zone. The high MTR in the radial zone not only depends on collagen content, it may also reflect a number of other parameters, such as the arrangement of macromolecules, high solid content, bound water fraction attached to macromolecules, radial orientation, etc. J. Magn. Reson. Imaging 2005;22:318–323. © 2005 Wiley-Liss, Inc.

Flow of non-aqueous phase liquids (NAPL) in the unsaturated zone is thought to be driven by gravity with a dominant vertical flow direction, and lateral spreading to be limited to the gradient of the relative permeabilities. The effect of soil profile build-up, preferential flow, aging, and groundwater level fluctuations is mostly neglected. The objective of our study was to check the effects of such processes on the fate of NAPL in the unsaturated soil zone. At a hazardous waste site, we conducted a field survey of the unsaturated soil zone and monitored the groundwater for a two year period. We conducted spatially resolved and depth dependent soil sampling and analysis and the evaluation of former ram and core drilling protocols. The samples were analyzed for the 16 EPA PAH and alkanes with GC-MS and GC-FID. 13C-NMR spectroscopy was used to assess structural changes of the NAPL phase. Flow of bulk NAPL along macropores and along preferential permeability structures, like sedimentation discontinuities, are the dominant transport pathways which cause large lateral spreading beyond those expected by the relative permeability gradient. Accumulation of NAPL was found at locations with abrupt textural changes and within the zone of capillary rise. Aging of NAPL results in the depletion in soluble and volatile compounds but also in oxidation and polymerization. It increases the chemical diversity and decreases the mobility of the NAPL. Thus, NAPL flow ceases much earlier than expected from the capillary forces. As chemical transformation is restricted to the NAPL water/air interface, a skin-like thin film is formed which encapsulates and preserves the bulk NAPL from further hardening, limiting contaminant mass transfer from the NAPL to the aqueous phase. Praferenzieller Fluss und Alterung nichtwassriger flussiger Phasen (NAPL) in der ungesattigten Bodenzone eines Altlastenstandortes: Bedeutung fur den Stofftransport Bei der Abschatzung der Tiefenverlagerung von nichtwassrigen Phasen (NAPL) in der ungesattigten Bodenzone ging man bisher davon aus, dass der Fluss im Boden eine dominante vertikale Flieskomponente besitzt. Die Bedeutung bevorzugter Flieswege, des Bodenprofils und der Alterung fur die Ausbreitung der NAPL wurde bisher nicht untersucht. Ziel unserer Arbeiten war es daher, die Gultigkeit der Vorstellungen zum Transport von NAPL in der ungesattigten Bodenzone zu uberprufen. Hierzu wurde die ungesattigte Bodenzone an einem ehemaligen Teerwerkstandort untersucht und ein zweijahriges Grundwassermonitoring durchgefuhrt. Es wurde eine tiefendifferenzierte und raumlich aufgeloste Probenahme mit Rammkernsondierungen und Linern durchgefuhrt, sowie Bohrprotokolle vorhandener Gutachten ausgewertet. In den Proben wurden Alkane mittels GC-FID und PAK mittels GC-MS bestimmt. NAPL wurden 13C-NMR-spektroskopisch untersucht. Der Fluss von NAPL entlang praferenzieller Fliespfade ist der dominante Prozess der Tiefenverlagerung. Dabei kommt es zu einer starken lateralen Ausbreitung von NAPL weit uber den Bereich hinaus, der aufgrund der heterogenen Verteilung der relativen Permeabilitaten erwartet werden wurde. Innerhalb des Bodenprofils reichern sich NAPL oberhalb der Grenzflachen mit abruptem Texturwechsel und innerhalb der kapillaren Aufstiegszone an. Alterung der NAPL fuhrt zu einer Zunahme der chemischen Diversitat und zu einer Abnahme der Mobilitat. Die Tiefenverlagerung von NAPL kommt viel fruher zum Erliegen als durch Viskositat und Kapillarkrafte zu erwarten ware. Die strukturchemischen Veranderungen beschranken sich jedoch auf die Grenzflache NAPL/Wasser bzw. NAPL/Bodenluft: Es bildet sich eine dunne, verhartete Grenzschicht aus, die die NAPL umhullt, die weitere Alterung verlangsamt und den Stoffaustausch zwischen NAPL und Bodenwasser bzw. der Bodenluft verringert.

A positron beam is applied to investigate 1-Butyl-3-methyl-imidazolium-hexafluorphosphat (BMIm-PF6) by Doppler broadening (DB) measurements. A liquid is principally free of lateral inhomogeneities while its depth dependent structure is influenced by the surface. This structure is studied in-situ and non-destructively by the use of a monoenergetic positron beam.In a second measurement, the ionic liquid performs different phase changes during heating and cooling. Temperature dependent DB measurements of the 511 keV photopeak show very clear influence of phase transitions (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ground water production wells commonly are designed to maximize well yield and, therefore, may be screened over several water-bearing zones. These water-bearing zones usually are identified, and their hydrogeologic characteristics and water quality are inferred, on the basis of indirect data such as geologic and geophysical logs. Production well designs based on these data may result in wells that are drilled deeper than necessary and are screened through zones having low permeability or poor-quality ground water. In this study, we examined the application of flowmeter logging and depth-dependent water quality samples for the improved design of production wells in a complex hydrogeologic setting. As a demonstration of these techniques, a flowmeter log and depth-dependent water quality data were collected from a long-screened production well within a multilayered coastal aquifer system in the Santa Clara-Calleguas Basin, Ventura County, California. Results showed that the well yields most of its water from four zones that constitute 58% of the screened interval. The importance of these zones to well yield was not readily discernible from indirect geologic or geophysical data. The flowmeter logs and downhole water quality data also show that small quantities of poor-quality water could degrade the overall quality of water from the well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. The application of flowmeter and depth-dependent water quality data to well design can reduce installation costs and improve the quantity and quality of water produced from wells in complex multiple-aquifer systems.

Purpose: Total body irradiation (TBI) with moving couch technique has been used in our clinic for years. Moving couch TMR for a field size has been acquired by multiplying TMR for a stationary beam and the ‘m factor’ defined as the ratio between moving phantom dose to stationary beam dose for same setup. The ‘m factor’ has been known to be field size dependent and not depth dependent. In order to replace lung and kidney blocks and achieve better dose uniformity using dynamic MLC, comprehensive understanding on the TMR for variable field sizes for an MLC leaf sequence is required. Method and Materials: A thorough measurement on the moving TMR has been performed. TMR's for field sizes of 5cm×40cm, 10cm×40cm, 15cm×40cm, 20cm×40cm and 30cm×40cm were measured both for the stationary and for the moving phantoms. Field sizes are defined at SAD 100cm and TMR's were measured at SCD 170cm for depths dmax to 34cm in 50cm×50cm×50cm water phantom with 6MV photon (21EX, Varian, Palo Alto, CA). Results: TMR's in moving phantom for different field sizes showed not more than 1% difference, while those of stationary phantom showed up to 34.8% difference for different sizes. The m factor which has been known to be a constant for a given field size rapidly increases after 15cm depth. Analysis of the data allowed us to understand the phenomena of measuring a point dose in a moving phantom. The key to the understanding was that both the phantom scatter and primary dose seen at the measurement position does not vary with field size when normalized to the reference condition. Conclusion: TMR's are independent to field size when couch is moving. This suggests that TMR variation does not need to be considered when designing the dose compensator with dynamic MLC for moving couch TBI.

Analytical solutions exist for the potential of a Point Source in media with depth dependent conductivity of the form σ(z) =σ0(1 +αz)n. Of particular importance is the case of the linear gradient (n= 1). More general distributions of conductivity with depth can be approximated by equivalent sequences of homogeneous layers. Comparison between such approximations and the analytical solution for media with linear gradient of conductivity indicates that already a coarse step function yields a reasonably good approximation. Zusammenfassung Analytische Losungen fur das von einer punktformigen Quelle erzeugte Potential existieren in Medien mit einer Leitfahigkeitsverteilung σ(z) =σ0(1 +αz)n. Besonders wichtig ist der Fall der linearen Leitfahigkeitsanderung (n= 1). Allgemeinere Verteilungen der Leitfahigkeit lassen sich durch aquivalente Folgen homogener Schichten annahern. Der Vergleich zwischen der analytischen Berechnung der Potentialverteilung in einem Medium mit linearem Leitfahigkeitsgradienten und der numerischen Approximation zeigt, das bereits eine relativ grobe Unterteilung eine den praktischen Anforderungen genugende Genauigkeit ergibt.

Instead of using the usual Schrodinger equation, perturbation theory is directly applied to the system of Howie and Whelan. According to the nature of the perturbing dynamical matrix generally three different types of perturbation are distinguished. The perturbing matrix may be a) constant and Hermitian b) constant but not Hermitian c) not constant but depth dependent. The first case has been discussed previously, now case b) is considered. In full matrix notation both generate and degenerate perturbation theory is presented. Special attention is given to the usual treatment of absorption effects. General recurrence relations are presented for the calculation of the corrections on eigenvalues and eigenvectors. The influence of these corrections on the amplitudes and the intensities of the constituent beams is discussed. Anstatt der normalen Schrodingergleichung wird die Storungstheorie direkt auf das System von Howie und Whelan angewendet. In Ubereinstimmung mit der Natur der dynamischen Stormatrix werden im allgemeinen drei verschiedene Arten der Storung unterschieden. Die Stormatrix kann a) konstant und hermitesch, b) konstant, jedoch nicht-hermitesch und c) nicht konstant, sondern tiefenabhangig sein. Nach der fruheren Diskussion des ersten Falles wird nun der Fall b) betrachtet. In vollstandiger Matrixschreibweise werden sowohl entartete als auch nichtentartete Storungstheorie angegeben. Spezielle Beachtung findet die normale Behandlung der Absorptionseffekte. Allgemeine Rekursionsbeziehungen werden fur die Berechnung der Korrekturen zu den Eigenwerten und Eigenvektoren angegeben. Der Einflus dieser Korrekturen auf die Amplituden nnd Intensitaten der Teilstrahlen wird diskutiert.