3,562 research outputs found
Observation of intervalley biexcitonic optical Stark effect in monolayer WS2
Coherent optical dressing of quantum materials offers technological
advantages to control their electronic properties, such as the electronic
valley degree of freedom in monolayer transition metal dichalcogenides (TMDs).
Here, we observe a new type of optical Stark effect in monolayer WS2, one that
is mediated by intervalley biexcitons under the blue-detuned driving with
circularly polarized light. We found that such helical optical driving not only
induces an exciton energy downshift at the excitation valley, but also causes
an anomalous energy upshift at the opposite valley, which is normally forbidden
by the exciton selection rules but now made accessible through the intervalley
biexcitons. These findings reveal the critical, but hitherto neglected, role of
biexcitons to couple the two seemingly independent valleys, and to enhance the
optical control in valleytronics
Discrete Element Modeling of Powder Dispensing and Laser Heating in Direct Laser Metal Sintering Process
poster abstractABSTRACT
The growth of reliable methods to improve part created from additive manufacturing technologies greatly depend on the quantitative understanding of the mechanical properties and the microstructural behavior of the powder particles during the 3D printing procedure. To obtain a greater understanding of this process, a particle- based discrete element modeling (DEM) has incredible potential benefits in the field of manufacturing for reducing cost and control specific structures and materials of the parts created from this process.
In this research, we developed a numerical tool and use it to study the powder characterization of the powder deposition process in the Direct Metal Laser Sintering (DLMS) machine. Our simulations include the modelling of particle insertion, particle spreading, and temperature distribution due to laser beam sintering process.
The DEM simulation results show that the particle distribution of the powder bed after powder dispersing process. Temperature distribution after laser heating is also given
Valley-selective optical Stark effect in monolayer WS2
Breaking space-time symmetries in two-dimensional crystals (2D) can
dramatically influence their macroscopic electronic properties. Monolayer
transition-metal dichalcogenides (TMDs) are prime examples where the
intrinsically broken crystal inversion symmetry permits the generation of
valley-selective electron populations, even though the two valleys are
energetically degenerate, locked by time-reversal symmetry. Lifting the valley
degeneracy in these materials is of great interest because it would allow for
valley-specific band engineering and offer additional control in valleytronic
applications. While applying a magnetic field should in principle accomplish
this task, experiments to date have observed no valley-selective energy level
shifts in fields accessible in the laboratory. Here we show the first direct
evidence of lifted valley degeneracy in the monolayer TMD WS2. By applying
intense circularly polarized light, which breaks time-reversal symmetry, we
demonstrate that the exciton level in each valley can be selectively tuned by
as much as 18 meV via the optical Stark effect. These results offer a novel way
to control valley degree of freedom, and may provide a means to realize new
valley-selective Floquet topological phases in 2D TMDs
A Hierarchical Framework Using Approximated Local Outlier Factor for Efficient Anomaly Detection
AbstractAnomaly detection aims to identify rare events that deviate remarkably from existing data. To satisfy real-world appli- cations, various anomaly detection technologies have been proposed. Due to the resource constraints, such as limited energy, computation ability and memory storage, most of them cannot be directly used in wireless sensor networks (WSNs). In this work, we proposed a hierarchical anomaly detection framework to overcome the challenges of anomaly detection in WSNs. We aim to detect anomalies by the accurate model and the approximated model learned at the re- mote server and sink nodes, respectively. Besides the framework, we also proposed an approximated local outlier factor algorithm, which can be learned at the sink nodes. The proposed algorithm is more efficient in computation and storage by comparing with the standard one. Experimental results verify the feasibility of our proposed method in terms of both accuracy and efficiency
Aluminum alters NMDA receptor 1A and 2A/B expression on neonatal hippocampal neurons in rats
<p>Abstract</p> <p>Background</p> <p>High aluminum (Al) content in certain infant formula raises the concern of possible Al toxicity on brain development of neonates during their vulnerable period of growing. Results of in vivo study showed that Al content of brain tissues reached to 74 μM when oral intake up to 1110 μM, 10 times of that in the hi-Al infant formula.</p> <p>Methods</p> <p>Utilizing a cultured neuron cells in vitro model, we have assessed Al influence on neuronal specific gene expression alteration by immunoblot and immunohistochemistry and neural proliferation rate changes by MTT assay.</p> <p>Results</p> <p>Microscopic images showed that the neurite outgrowth of hippocampal neurons increased along with the Al dosages (37, 74 μM Al (AlCl<sub>3</sub>)). MTT results also indicated that Al increased neural cell viability. On the other hand, the immunocytochemistry staining suggested that the protein expressions of NMDAR 1A and NMDAR 2A/B decreased with the Al dosages (p < 0.05).</p> <p>Conclusion</p> <p>Treated hippocampal neurons with 37 and 74 μM of Al for 14 days increased neural cell viability, but hampered NMDAR 1A and NMDAR 2A/B expressions. It was suggested that Al exposure might alter the development of hippocampal neurons in neonatal rats.</p
Metal-free sp(3) C-H functionalization: a novel approach for the syntheses of selenide ethers and thioesters from methyl arenes
A DTBP-promoted metal-free and solvent-free formation of C-Se and C-S bonds through sp(3) C-H functionalization of methyl arenes with diselenides and disulfides is described
Electronic transport and device prospects of monolayer molybdenum disulphide grown by chemical vapour deposition
Layered transition metal dichalcogenides display a wide range of attractive
physical and chemical properties and are potentially important for various
device applications. Here we report the electronic transport and device
properties of monolayer molybdenum disulphide (MoS2) grown by chemical vapour
deposition (CVD). We show that these devices have the potential to suppress
short channel effects and have high critical breakdown electric field. However,
our study reveals that the electronic properties of these devices are at
present, severely limited by the presence of a significant amount of band tail
trapping states. Through capacitance and ac conductance measurements, we
systematically quantify the density-of-states and response time of these
states. Due to the large amount of trapped charges, the measured effective
mobility also leads to a large underestimation of the true band mobility and
the potential of the material. Continual engineering efforts on improving the
sample quality are needed for its potential applications.Comment: 23 pages, 5 figure
Kinetics of cytokine expression in cirrhotic rats
AbstractBackgroundCytokines are involved in liver injury and cirrhosis and systemic and hepatic cytokine levels may help predict cirrhosis evolution. However, the relevant survey has not been performed.MethodsMale Sprague-Dawley rats (240–270g) received either common bile duct ligation (BDL, animal model of cholestatic liver injury) or sham operation (control). Five rats were sacrificed and liver and serum were collected from each in weeks 1, 2, 4, 6, 8 and 10 after surgery. Hepatic expression of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) were analyzed by immunohistochemial staining. The corresponding serum levels were measured by ELISA.ResultsCompared to the corresponding sham groups, hepatic expression of these cytokines in BDL rats was significantly and progressively enhanced during cirrhosis development. However, serum IFN-γ levels of BDL rats did not change significantly. Serum TNF-α of BDL rats increased gradually and reached a peak in week 6. Serum TGF-β level was elevated up to week 8, whereas IL-10 level decreased progressively until week 6.ConclusionCirrhosis development in BDL rats is associated with progressively enhanced expression of hepatic pro-inflammatory and anti-inflammatory cytokines, which is not in accord with the corresponding serum concentration. The circulating cytokine concentration may not totally reflect the hepatic expression level throughout the development of cirrhosis
- …