How local crustal thermal properties influence the amount of denudation derived from low-temperature thermochronometry: Reply

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New insights into electron spin dynamics in the presence of correlated noise

The changes of the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which keeps into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examinating the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitude lower than the Gunn field, the dephasing length shortens with the increasing of the noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track Communications", 11 pages, 9 figure

Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorods

Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured surfaces. Understanding the origin of such improved performances is therefore very important for pushing nanofiber-based analytical technologies to their upper limit. Here we report on polymer nanofiber mats which can be exploited as substrates for enhancing the Raman spectra of adsorbed probe molecules. The increased surface area and the scattering of light in the nanofibrous system are individually analyzed as mechanisms to enhance Raman scattering. The deposition of gold nanorods on the fibers further amplifies Raman signals due to SERS. This study suggests that Raman signals can be finely tuned in intensity and effectively enhanced in nanofiber mats and arrays by properly tailoring the architecture, composition, and light-scattering properties of the complex networks of filaments.Comment: 29 pages, 9 figures, 1 Tabl

From source to sink in central Gondwana: Exhumation of the Precambrian basement rocks of Tanzania and sediment accumulation in the adjacent Congo basin

Apatite fission track (AFT) and (U-Th)/He (AHe) thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated (>1000 m above sea level) but low-relief Tanzanian Craton. Coeval episodes of sedimentation documented within adjacent Paleozoic to Mesozoic basins of southern Tanzania and the Congo basin of the Democratic Republic of Congo indicate that most of the cooling in the basement rocks in Tanzania was linked to erosion. Basement samples were from an exploration borehole located within the craton and up to 2200 m below surface. Surface samples were also analyzed. AFT dates range between 317 ± 33 Ma and 188 ± 44 Ma. Alpha (Ft)-corrected AHe dates are between 433 ± 24 Ma and 154 ± 20 Ma. Modeling of the data reveals two important periods of cooling within the craton: one during the Carboniferous-Triassic (340–220 Ma) and a later, less well constrained episode, during the late Cretaceous. The later exhumation is well detected proximal to the East African Rift (70 Ma). Thermal histories combined with the estimated geothermal gradient of 9°C/km constrained by the AFT and AHe data from the craton and a mean surface temperature of 20°C indicate removal of up to 9 ± 2 km of overburden since the end of Paleozoic. The correlation of erosion of the craton and sedimentation and subsidence within the Congo basin in the Paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far-field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes

How local crustal thermal properties influence the amount of denudation derived from low temperature thermochronometry

ranslating amounts and rates of rock cooling derived from low-temperature thermochronometry into denudation requires assumptions about the local geothermal gradient. The temperature gradient in the crust depends on many factors, including basal heat flow, crustal heat production, and thermal conductivity. Consequently, geothermal gradients may be variable on time scales over which rock cooling is tracked by thermochronometry. Using one-dimensional numerical modeling of heat transfer in rocks of varying thermal characteristics, we show that the geothermal gradient of the eroded layer is the most important factor for accurate estimation of denudation amounts. Using a three-dimensional numerical model (Pecube), we demonstrate the impact of crustal heat production and thermal conductivity on estimates of total denudation derived from apatite fission track data from central west Britain. We show that the regional variation in cooling ages measured in Caledonian granites can be explained by geothermal gradient variation due to the presence of a heat-producing granite batholith and removal of insulating sedimentary rocks, and does not require variable denudation. Neglecting the blanketing effect leads to twofold overestimation of the amount of denudation. The occurrence of heat-producing basement that was once covered by a sedimentary blanket is common, in particular in the core of mountain belts. Accurate determination of the amount and rate of denudation from thermochronometric studies in these situations must take into account the composition of the eroded rocks

Control of photon transport properties in nanocomposite nanowires

Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a wide variety of fields, including optoelectronics, photonics, energy harvesting, nanoelectronics, and microelectromechanical systems. Realizing nanocomposite nanofibers is especially interesting in this respect. In particular, methods suitable for embedding inorganic nanocrystals in electrified jets and then in active fiber systems allow for controlling light-scattering and refractive index properties in the realized fibrous materials. We here report on the design, realization, and morphological and spectroscopic characterization of new species of active, composite nanowires and nanofibers for nanophotonics. We focus on the properties of light-confinement and photon transport along the nanowire longitudinal axis, and on how these depend on nanoparticle incorporation. Optical losses mechanisms and their influence on device design and performances are also presented and discussed.Comment: 7 pages, 3 figures, 29 references. Invited contribution. Copyright (2016) Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibite

Late Cretaceous-Eocene exhumation of the northern Lhasa terrane and topographic implications for the Central Tibet

The central Tibetan Plateau has an average altitude of ∼5000 m; its exhumation and chemical weathering greatly influence the global climate and ocean chemistry. The modern central Tibet is characterized by low-relief, high elevation topography with endorheic drainage. When and how these geomorphic characteristics of central Tibet were initiated remains controversial. Here, we have applied zircon Usingle bondPb dating and low-temperature thermochronology on the Cretaceous plutons from Coqin Basin of central Tibet in order to assess timings of exhumation. The thermal history modeling indicates a period of relatively rapid cooling (2.5–4 °C/Ma) occurred in Late Cretaceous to Middle Eocene times (from ∼80 Ma to ∼40 Ma), with the exhumation rates of 0.2–0.4 mm/yr assuming a geothermal gradient of 25 °C/km. Cooling rates then slowed to ∼0.5 °C/Ma during the Middle Eocene to the present, with a relatively lower exhumation rates of ∼0.02–0.03 mm/yr. Synchronous rapid cooling and exhumation has also been identified in central Tibet; this signal of widespread Late Cretaceous exhumation across the region may be viewed as evidence for the initial surface uplift and erosion of the central Tibetan plateau. Lower exhumation rate since ∼40 Ma, combined with sedimentological data suggests that the low-relief, internally drained topography of central Tibet was initiated around this time

Validation of an elastic registration technique to estimate anatomical lung modification in Non-Small-Cell Lung Cancer Tomotherapy

<p>Abstract</p> <p>Background</p> <p>The study of lung parenchyma anatomical modification is useful to estimate dose discrepancies during the radiation treatment of Non-Small-Cell Lung Cancer (NSCLC) patients. We propose and validate a method, based on free-form deformation and mutual information, to elastically register planning kVCT with daily MVCT images, to estimate lung parenchyma modification during Tomotherapy.</p> <p>Methods</p> <p>We analyzed 15 registrations between the planning kVCT and 3 MVCT images for each of the 5 NSCLC patients. Image registration accuracy was evaluated by visual inspection and, quantitatively, by Correlation Coefficients (CC) and Target Registration Errors (TRE). Finally, a lung volume correspondence analysis was performed to specifically evaluate registration accuracy in lungs.</p> <p>Results</p> <p>Results showed that elastic registration was always satisfactory, both qualitatively and quantitatively: TRE after elastic registration (average value of 3.6 mm) remained comparable and often smaller than voxel resolution. Lung volume variations were well estimated by elastic registration (average volume and centroid errors of 1.78% and 0.87 mm, respectively).</p> <p>Conclusions</p> <p>Our results demonstrate that this method is able to estimate lung deformations in thorax MVCT, with an accuracy within 3.6 mm comparable or smaller than the voxel dimension of the kVCT and MVCT images. It could be used to estimate lung parenchyma dose variations in thoracic Tomotherapy.</p

Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells

Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in this way in terms of homogeneous charge transport behavior and formation of effective interfaces for diffusion and dissociation of photogenerated excitons. The interaction of the organic filaments with light, exhibiting specific light-scattering properties of the nanofibrous mat, might also contribute to spreading incident radiation across the active layers, thus potentially enhancing photovoltaic performance. This method might be applied to other electron donor-electron acceptor material systems for the fabrication of solar cell devices enhanced by nanofibrillar morphologies embedding conjugated polymers and fullerene compounds.Comment: 35 pages, 9 figure