78 research outputs found
Simulation of dimensionality effects in thermal transport
The discovery of nanostructures and the development of growth and fabrication
techniques of one- and two-dimensional materials provide the possibility to
probe experimentally heat transport in low-dimensional systems. Nevertheless
measuring the thermal conductivity of these systems is extremely challenging
and subject to large uncertainties, thus hindering the chance for a direct
comparison between experiments and statistical physics models. Atomistic
simulations of realistic nanostructures provide the ideal bridge between
abstract models and experiments. After briefly introducing the state of the art
of heat transport measurement in nanostructures, and numerical techniques to
simulate realistic systems at atomistic level, we review the contribution of
lattice dynamics and molecular dynamics simulation to understanding nanoscale
thermal transport in systems with reduced dimensionality. We focus on the
effect of dimensionality in determining the phononic properties of carbon and
semiconducting nanostructures, specifically considering the cases of carbon
nanotubes, graphene and of silicon nanowires and ultra-thin membranes,
underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
The MoS2 Nanotubes with Defect-Controlled Electric Properties
We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large-scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behavior of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration
High-performance shape-engineerable thermoelectric painting
Output power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, here, we present the shape-engineerable thermoelectric painting, geometrically compatible to surfaces of any shape. We prepared Bi2Te3-based inorganic paints using the molecular Sb2Te3 chalcogenidometalate as a sintering aid for thermoelectric particles, with ZT values of 0.67 for n-type and 1.21 for p-type painted materials that compete the bulk values. Devices directly brush-painted onto curved surfaces produced the high output power of 4.0 mW cm(-2). This approach paves the way to designing materials and devices that can be easily transferred to other applications.ope
Ultralow Thermal Conductivity of Isotope-Doped Silicon Nanowires
The thermal conductivity of silicon nanowires (SiNWs) is investigated by
molecular dynamics (MD) simulation. It is found that the thermal conductivity
of SiNWs can be reduced exponentially by isotopic defects at room temperature.
The thermal conductivity reaches the minimum, which is about 27% of that of
pure 28Si NW, when doped with fifty percent isotope atoms. The thermal
conductivity of isotopic-superlattice structured SiNWs depends clearly on the
period of superlattice. At a critical period of 1.09 nm, the thermal
conductivity is only 25% of the value of pure Si NW. An anomalous enhancement
of thermal conductivity is observed when the superlattice period is smaller
than this critical length. The ultra-low thermal conductivity of superlattice
structured SiNWs is explained with phonon spectrum theory.Comment: Nano Lett., ASAP Article 10.1021/nl0725998 S1530-6984(07)02599-4 Web
Release Date: December 21, 200
Phase I study of the IXO regimen, irinotecan (I), capecitabine (X), oxaliplatin (O), as first-line therapy for metastatic colorectal cancer: Final survival results
Thermal conductivity mapping of pyrolytic carbon and silicon carbide coatings on simulated fuel particles by time-domain thermoreflectance
242 Phase I study of irinotecan (I), raltitrexed (R), and 5-fluorouracil (5FU) in the treatment of metastatic colorectal cancer (MCRC) refractory to thymidylate synthase inhibitors (TSI)
Criteria for Cross-Plane Dominated Thermal Transport in Multilayer Thin Film Systems During Modulated Laser Heating
Absolute measurements of neutron yields from DD and DT implosions at the OMEGA laser facility using CR-39 track detectors
The response of CR-39 track detectors to neutrons has been characterized and used to measure neutron yields from implosions of DD- and DT-filled targets at the OMEGA laser facility and the scaling of neutron fluence with R (the target-to-detector distance) has been used to characterize the fluence of backscattered neutrons in the target chamber. A Monte-Carlo code was developed to predict the CR-39 efficiency for detecting DD neutrons, and it agrees well with the measurements. Neutron detection efficiencies of (1.1+/-0.2)x10(-4) and (6.0+/-0.7)x10(-5) for the DD and DT cases, respectively, were determined for standard CR-39 etch conditions. In OMEGA experiments with both DD and DT targets, the neutron fluence was observed to decrease as R-2 up to about 45 cm; at larger distances, a significant backscattered neutron component was seen. The measured backscattered component appears to be spatially uniform, and agrees with predictions of a neutron-transport code. As an additional application of the calibration results, it is shown that the neutron-induced signal in CR-39 used in charged-particle spectrometers on OMEGA can be used to determine DD and DT yields ranging from about 10(10) up to 10(14). With further improvements in the processing and analysis of CR-39, this upper limit can be increased by at least two orders of magnitude
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