Quantum thermal transport in nanostructures Wang, J.-S.; Wang, J.; Lü, J. T.
The European physical journal. B, Condensed matter physics,
04/2008, Volume:
62, Issue:
4
Journal Article
Peer reviewed
Open access
.
In this colloquia review we discuss methods for thermal transport calculations for nanojunctions connected to two semi-infinite leads served as heat-baths. Our emphases are on fundamental quantum ...theory and atomistic models. We begin with an introduction of the Landauer formula for ballistic thermal transport and give its derivation from scattering wave point of view. Several methods (scattering boundary condition, mode-matching, Piccard and Caroli formulas) of calculating the phonon transmission coefficients are given. The nonequilibrium Green's function (NEGF) method is reviewed and the Caroli formula is derived. We also give iterative methods and an algorithm based on a generalized eigenvalue problem for the calculation of surface Green's functions, which are starting point for an NEGF calculation. A systematic exposition for the NEGF method is presented, starting from the fundamental definitions of the Green's functions, and ending with equations of motion for the contour ordered Green's functions and Feynman diagrammatic expansion. In the later part, we discuss the treatments of nonlinear effects in heat conduction, including a phenomenological expression for the transmission, NEGF for phonon-phonon interactions, molecular dynamics (generalized Langevin) with quantum heat-baths, and electron-phonon interactions. Some new results are also shown. We briefly review the experimental status of the thermal transport measurements in nanostructures.
Prospective randomized.
Intraoperative methylprednisolone is a common adjunct following microscopic laminectomy/microdiscectomy. The goal of epidural instillation is a rapid symptomatic reduction in ...irritation of neural elements. There is inconsistent data supporting its use intraoperatively. To understand whether this maneuver results in any clinical effect, we performed a multiyear prospective study.
Previous work has demonstrated equivocal effects on pain with a suggestion of an increased risk of complication. These studies tend to suffer from small sample sizes and short follow-ups.
Study obtained IRB approval. During the study period from 2013 to 2019, nearly equivalent numbers of patients who had received steroids during MIS decompressions were followed. Primary outcomes included pain (visual analog scale) and disability Oswestry Disability Index (ODI) at 2 weeks and 4 months. Secondary outcomes included complications, readmissions, and reoperation rates during the study period.
Four hundred eighty-six patients were followed for a mean follow-up of 5.17 years. The index case was more likely to be a revision surgery in the steroid group. Across all patients, there was no difference in pain at 2 weeks or 4 months. Disability was reduced at 2 weeks in the steroid group (ODI: 16.71 vs . 21.02, P = 0.04) but not at 4 months. By subgroup analysis, this is largely explained by ODI reduction in patients with high preoperative ODI (13.00 vs . 43.43, P = 0.03). Patients in the steroid cohort were more likely to undergo subsequent spinal surgery during the study period.
Methylprednisolone instillation is associated with a large, transient reduction in ODI for patients with high preoperative ODI; there is no measurable effect on pain. There is equivocal effect on risk of subsequent reoperation. This issue was clarified in peer review but changes did not make it to the abstract. Therefore, the technique is likely best reserved for patients with significant preoperative disability.
To identify regulators of intracellular signaling, we targeted 541 kinases and kinase-related molecules with small interfering RNAs (siRNAs), and determined their effects on signaling with a ...functional proteomics reverse-phase protein array (RPPA) platform assessing 42 phospho and total proteins. The kinome-wide screen demonstrated a strong inverse correlation between phosphorylation of AKT and mitogen-activated protein kinase (MAPK) with 115 genes that, when targeted by siRNAs, demonstrated opposite effects on MAPK and AKT phosphorylation. Network-based analysis identified the MAPK subnetwork of genes along with p70S6K and FRAP1 as the most prominent targets that increased phosphorylation of AKT, a key regulator of cell survival. The regulatory loops induced by the MAPK pathway are dependent on tuberous sclerosis complex 2 but demonstrate a lesser dependence on p70S6K than the previously identified FRAP1 feedback loop. The siRNA screen also revealed novel bi-directionality in the AKT and GSK3 (Glycogen synthase kinase 3) interaction, whereby genetic ablation of GSK3 significantly blocks AKT phosphorylation, an unexpected observation as GSK3 has only been predicted to be downstream of AKT. This method uncovered novel modulators of AKT phosphorylation and facilitated the mapping of regulatory loops.
•A novel effective enhancement method of aluminum foam was reported by tube filling.•Tube enhanced foam has doubled specific compressive strength and energy absorption.•Instability limitation of the ...steel tube caused the dramatically increase.
Aluminum foam was limited when applied as load carrying structures for its lower strength. Therefore, an effective enhancement method of aluminum foam was reported in the present study by filling of 304 stainless steel tube into a pre-perforated hole and fixed by epoxy glue. The experimental results indicate that the novel tube enhanced foam (with equivalent density of foam) can doubled the specific compressive strength and energy absorption of that of aluminum foam, and even larger than that of the sum of tube and foam which were tested separately. The coupling strengthening mechanisms are suggested to be the instability limitation of steel tube due to the lateral supports (external and internal) supplied by aluminum foam.
7075 aluminum alloy weldments were processed by an intensive process known as laser shock peening (LSP), meanwhile its stress corrosion behaviors were observed by scanning electron microscopy (SEM) ...and slow strain rate tensile (SSRT) tests. Results showed that the effect of LSP on corrosion behavior of the joint was fairly useful and obvious. With LSP, the elongation, time of fracture and static toughness after the SSRT test were improved by 11.13%, 20% and 100%, respectively. At the same time, the location of the fracture also changed. LSP led to a transition of the fracture type from transgranular to intergranular The reasons for these enhancements of the joint on corrosion behavior were caused by microstructure, residual stress, micro-hardness, and fracture appearance.
The strain rate sensitivity (m) and activation volume (v⁎) of three nanocrystalline (NC) body-centered cubic (bcc) metals, i.e., W, Mo and Ta, with various grain sizes were evaluated by ...nanoindentation testing. Opposite to the conventional trend that NC bcc metals exhibit reduced m as the grain size was decreased, elevated m was observed as the grain size was reduced from ~90nm to ~30nm for all the samples concerned. It was proposed that the unusual variation trends of m for NC bcc metals were dominated by GB-related mechanisms when the grain size drops below a critical value.
The superior capability of bearing thermal and mechanical loads to other types of open cellular materials has led to advances in developing new periodic cellular materials. We introduce a lightweight ...X-type lattice fabricated via the metal sheet folding and present its thermo-fluidic characteristics in single-phase forced convection. For fixed porosity, thermal conductivity and Reynolds number, the X-type lattice provides overall heat removal capacity up to two times higher than reference periodic cellular materials. The unique morphology of the X-type lattice results in a large scale spiral primary flow, which interacts with several secondary flows. These fluid flow behaviors and the induced complex flow mixing substantially enhance heat transfer on both the substrate and ligaments. However, the X-type lattice causes roughly three times higher pressure drop than reference periodic cellular materials for a given Reynolds number. Overall, superior heat transfer is achieved by the X-type lattice for a fixed pumping power.
This paper explores the critical and post-bulging bifurcation of a cylindrical dielectric elastomer (DE) tube undergoing finite deformation under electro-mechanical coupling loading. Explicit ...expressions for the critical conditions of electro-mechanical bifurcation are derived by using a simplified mathematical method. The post-bifurcation path is comprehensively investigated by specifying the material model as ideal dielectric elastomer. In the post-bifurcation analysis, we analytically establish conditions for the phase coexistence of steady propagation and analyze the physical implications. We demonstrate a global instability under force or voltage control and a localized instability under volume or charge control. Cylindrical tube experiments have been carried out under electro-mechanical coupling loading to verify the theoretical predictions. Good agreements on the critical conditions as well as the post-bifurcation path are obtained. This work characterizes the bifurcation mechanism of rubber-like materials under complex coupling loading.
The fluid-flow and heat-transfer features of cellular metal lattice structures made from copper by transient liquid phase (TLP) bonding and brazing of plane weave copper meshes (screens) were ...experimentally characterized under steady-state forced air convection. Due to the inherent structural anisotropy of this metal textile derived structure, the characterizations were performed for several configurations to identify the preferable orientation for maximizing thermal performance as a heat dissipation medium. Results show that the friction factor of bonded wire screens is not simply a function of porosity as stochastic materials such as open-celled metal foams and packed beds, but also a function of orientation (open area ratio). The overall heat transfer depends on porosity and surface area density, but only weakly on orientation. Comparisons with stochastic metal foams and other heat dissipation media such as packed beds, louvered fins and microtruss lattice cellular materials suggest that wire-screen meshes compete favorably with the best available heat dissipation media. The overall thermal efficiency index of the copper textiles-based media is approximately three times larger than that of stochastic copper foams, principally because of the lower pressure drop encountered during coolant propagation through the periodic wire-screen structure.
Wildfires have a significant adverse impact on air quality in the United States (US). To understand the potential health impacts of wildfire smoke, many epidemiology studies rely on concentrations of ...fine particulate matter (PM) as a smoke tracer. However, there are many gas-phase hazardous air pollutants (HAPs) identified by the Environmental Protection Agency (EPA) that are also present in wildfire smoke plumes. Using observations from the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN), a 2018 aircraft-based field campaign that measured HAPs and PM in western US wildfire smoke plumes, we identify the relationships between HAPs and associated health risks, PM, and smoke age. We find the ratios between acute, chronic noncancer, and chronic cancer HAPs health risk and PM in smoke decrease as a function of smoke age by up to 72% from fresh (<1 day of aging) to old (>3 days of aging) smoke. We show that acrolein, formaldehyde, benzene, and hydrogen cyanide are the dominant contributors to gas-phase HAPs risk in smoke plumes. Finally, we use ratios of HAPs to PM along with annual average smoke-specific PM to estimate current and potential future smoke HAPs risks.
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