A composite electrodynamic mechanism to reconcile spatiotemporally resolved exciton transport in quantum dot superlattices

Quantum dot (QD) solids are promising optoelectronic materials; further advancing their device functionality depends on understanding their energy transport mechanisms. The commonly invoked near-field F\"orster resonance energy transfer (FRET) theory often underestimates the exciton hopping rate in QD solids, yet no consensus exists on the underlying cause. In response, we use time-resolved ultrafast stimulated emission depletion (TRUSTED) microscopy, an ultrafast transformation of stimulated emission depletion (STED) microscopy to spatiotemporally resolve exciton diffusion in tellurium-doped CdSe-core/CdS-shell QD superlattices. We measure the concomitant time-resolved exciton energy decay due to excitons sampling a heterogeneous energetic landscape within the superlattice. The heterogeneity is quantified by single-particle emission spectroscopy. This powerful multimodal set of observables provides sufficient constraints on a kinetic Monte Carlo simulation of exciton transport to elucidate a composite transport mechanism that includes both near-field FRET and previously-neglected far-field emission/reabsorption contributions. Uncovering this mechanism offers a much-needed unified framework in which to characterize transport in QD solids and additional principles for device design.Comment: 47 pages, including supplemen

Effects of TGF-β1 and IGF-1 on proliferation of human nucleus pulposus cells in medium with different serum concentrations

BACKGROUND: The low proliferative viability of human nucleus pulposus(NP) cells is considered as a cause of intervertebral discs degeneration. Growth factors, such as TGF-β1 and IGF-1, have been implicated in cell proliferation and matrix synthesis. OBJECTIVE: To investigate the dose-response and time-course effect of transforming growth factorβ1(TGF-β1) and insulin-like growth factor-1(IGF-1) on proliferation of NP cells. STUDY DESIGN: 3-(4,5-dimethylthiazolyl)-2,5-diphenyl-tetrazolium bromide (MTT) is reduced by dehydrogenase in mitochondria of live cells. The proliferative viability of cells corresponds to the amount of MTT reduced, which is measured with an enzyme-linked immunosorbent assay plate reader. In this study, we assessed dose- and time-dependent effects of NP cells to TGF-β1 and IGF-1 in medium with different serum concentrations by MTT assay. METHODS: After release of informed consent, tissue samples of NP were obtained from anterior surgical procedures performed on five donors with idiopathic scoliosis. Isolated cells were cultured in F12 medium supplemented with 10% fetal bovine serum(FBS). Cells were seeded in 96-well plates at 1 × 10(3 )cells/well. After synchronization, medium was replaced by F12 containing 1% or 10% FBS with either single or combination of TGF-β1 and IGF-1. Dose-response and time-course effect were examined by MTT assay. RESULTS: In the presence of 1% FBS, the response to IGF-1 was less striking, whereas TGF-β1 had a remarkably stimulating effect on cell proliferation. In 10% FBS, both of the two growth factors had statistical significant mitogenic effects, especially TGF-β1. The dose-dependent effect of TGF and IGF on cell proliferation was found within different concentrations of each growth factor(TGF-β1 1–10 μg/L, IGF-1 10–100 μg/L). The time-course effect showed a significant elevation three days later. CONCLUSION: TGF-β1 and IGF-1 were efficient to stimulate cell proliferation of human NP cells in vitro with a dose- and time-dependent manner. These results support the therapeutic potentials of the two growth factors in the treatment of disc degeneration

Timing and mechanisms of multiple episodes of migmatization in the Korla Complex, northern Tarim Craton, NW China: Constraints from zircon U-Pb-Lu-Hf isotopes and implications for crustal growth

Formation of ubiquitous migmatites in high-grade metamorphic terranes may involve both closed- and open-system processes, e.g., in situ anatexis, infiltration of external melts and fluids. Coupled CL-imaging, in situ U-Th-Pb and Lu-Hf isotopic analyses of zircons from various migmatites and their components, i.e., leucosomes and melanosomes, enabled us to determine the time and mechanism(s) of three episodes of migmatization in the Korla Complex, northern Tarim Craton. The first episode of migmatization took place at ca. 1.85. Ga and probably resulted from in situ partial melting due to a regional high-grade metamorphic event. The second migmatization event was marked by the presence of abundant ca. 830. Ma leucogranitic veins, dykes and small plutons. Zircon Hf isotopic data indicate that these leucogranites were probably derived from anatexis of a relatively juvenile crustal source, rather than their immediate country rocks, implying large-scale melt migration and infiltration. These two episodes of migmatization might have resulted from two regional orogenic events at ca. 1.85. Ga and 830. Ma, respectively. In contrast, the third episode of migmatization at ca. 660. Ma was probably a local remelting event induced by intrusion of small quartz syenite plutons into previously migmatized rocks.In addition, zircon domains with extremely low Th (0.003-10. ppm) and U (3-30. ppm) contents were found in samples related to the ca. 830. Ma migmatization event. These domains generally occur as CL-bright rims that penetrate the primary zoned zircons without changing their morphology, and are ascribed to strong hydrothermal alteration via the interface-coupled dissolution-reprecipitation mechanism. A compilation of published zircon Hf isotopic data reveals three episodes of crustal growth during ca. 3.1-3.4. Ga, 2.5-2.8. Ga and 1.6-1.9. Ga in the northern Tarim Craton. However, these 'peaks' of crustal growth may be biased by selective sampling and magma mixing. Zircon Hf isotopic data from a ca. 2.29. Ga orthogneiss and the least recrystallized detrital cores from the migmatized sedimentary rocks suggest that continental crust older than ca. 3.3. Ga might have existed in the northern Tarim Craton

Detrital zircon U-Pb ages and Hf isotopes of Neoproterozoic strata in the Aksu area, northwestern Tarim Craton: Implications for supercontinent reconstruction and crustal evolution

The northern margin of the Tarim Craton plays a pivotal role in understanding the crustal evolution and supercontinent reconstruction of the Tarim Craton. Here we integrate LA-ICP-MS U-Pb ages and Hf isotopic data for detrital zircons from Neoproterozoic successions in the Aksu area, NW Tarim. A total of 679 concordant U-Pb ages define four age populations of 2600-2200Ma, 2050-1800Ma, 950-700Ma and 680-600Ma, which are consistent with the episodes of magmatism and metamorphism documented in the northern Tarim Craton, suggesting that the detritus were likely sourced from the northern Tarim Craton itself. The oldest age population corresponds to the Neoarchean to early Paleoproterozoic magmatic event related to an important stage in the development of the proto continental crust in the Tarim Craton. The 2050-1800Ma age population represents a magmatic-metamorphic event during a middle Paleoproterozoic orogeny, possibly related to the assembly of Tarim to the Columbia supercontinent. The dominant Neoproterozoic detrital zircons display a major cluster between 950Ma and 700Ma (peak at ca. 850Ma), much younger than the typical Grenvillian ages. This is similar to detrital zircon data sets from Yangzte and northern India, implying that these blocks shared a similar evolution pattern in the Rodinia supercontinent. The early Pan-African (680-600Ma) ages are comparable with those reported from the Arabian-Nubian Shield, but quite different from those from other Gondwana blocks, implying a possible correlation of Tarim with the Eastern Africa Orogen. Abundant zircons yield Archean (3.9-2.5Ga) Hf model ages (TDMC), suggesting the presence of extensive Archean basement as old as Paleoarchean in the Tarim Craton. Some Neoarchean and Neoproterozoic zircons have high positive e{open}Hf(t) values, indicating significant juvenile addition from the depleted mantle at those periods. However, most detrital zircons show negative e{open}Hf(t) values, suggesting that crustal reworking was the dominant process in the generation of the episodes of magmatism in the Tarim Craton. At last, based on the stratigraphic settings and the comparison of detrital zircon data, the Aksu Group and the Qiaoenbrak Formation are most likely units with equivalent depositional age

Parametric finite element study on slotted rectangular and square HSS tension connections

A parametric finite element analysis study was carried out on slotted rectangular and square hollow structural section (HSS) tension connections without welding at the end of the gusset plate for different weld length ratio, slot orientation, weld size and level of HSS corner strength compared to its flat segment. Finite element models for the parametric study were developed and validated against test results of the connection with the tube slotted. The modified weld length ratio was found to be a better parameter than the modified eccentricity ratio in characterizing the net section efficiency of a slotted HSS tension member when the weld length is short. Improvements to provisions in CSA-S16-01 and ANSI/AISC-360-05 for slotted tubular tension connections were proposed based on results of the study

Revisiting the Yejishan Group of the Lüliang Complex, North China: Implications for a Paleoproterozoic active continental marginal basin in the Trans-North China Orogen

Widespread Paleoproterozoic supracrustal rocks in the Trans-North China Orogen (TNCO) contain important information for the tectonic evolution of the North China Craton (NCC). Here, we report new in situ LA-ICP-MS detrital zircon U-Pb ages, Lu-Hf isotopic data, and whole-rock geochemical data for the Yejishan Group in the Lüliang Complex. The group is a well-preserved volcanic-sedimentary assemblage and can be subdivided into the Qingyangshuwan, Bailongshan, and Chengdaogou formations from bottom up. The Bailongshan Formation consists dominantly of meta-basalts interbedded with several layers of clastic rocks, and the other two formations are composed exclusively of sedimentary rocks. In this study, samples of fourteen clastic rocks and thirteen basalts from the Yejishan Group were collected for measurements based on detailed fieldwork. Detrital zircon U-Pb dating of six clastic samples from the three formations display similar age distributions and give youngest ages between ca. 1870 and 1988 Ma. The youngest age peak of 1870 Ma obtained from the Qingyangshuwan Formation is regarded as the maximum depositional age of the Yejishan Group for the first time. The ca. 1779 Ma mafic dyke intruding into the Yejishan Group constrains the depositional age between 1870 and 1779 Ma. Clastic interlayer in the Bailongshan basalts has a youngest age peak of ca. 1988 Ma, suggesting that the basalts should erupt after 1988 Ma. The time constraint of the Bailongshan basalts in this study disapproves the previous view that the Bailongshan Formation should be removed from the Yejishan Group and assigned to the Lüliang Group. According to the geochemical features, the Yejishan clastic rocks had a chemical immature source mixed of felsic and basaltic magmatic rocks with weak weathering, and suggestive of an active tectonic setting. The basalts show variable LREE enrichment, prominent Nb-Ta, Ti, P anomalies, probably derived from a subcontinental lithospheric mantle metasomatized by subduction-related fluids. Taken together the geochemical and chronological data, we propose that the Yejishan Group were formed in an active continental marginal basin at ca. 1870–1780 Ma. The conclusion is consistent with model of the ca. 1850 Ma collision in the TNCO

Demonstration of the detection of buckling effects in steel pipelines and beams by the distributed Brillouin sensor

We conducted the strain measurements to monitor steel pipe buckling for the first time using distributed Brillouin sensor system. Two specimens (steel pipeline and beam) were prepared by locally thinning the inner wall to provoke buckling. Fibre was laid along the external walls of the specimens. Strain gauges were glued in thinned wall area. An axial load was applied to the specimens and increased while compressive strain was measured by both Brillouin sensor and the strain gauges. The Brillouin sensor measurements showed the convolution of the all the strain distribution within the spatial resolution, the fitting Brillouin peak corresponds to the average strain over the spatial resolution, hence its reading can be smaller than the strain gauge reading depending on the location. With the Brillouin sensors, we observed compression in the whole specimens while elongation was detected in the neighbourhood of the thinned wall at onset of the buckling for the first time. The buckling was identified and localized with the Brillouin sensor measurement