1,129 research outputs found
Suppressing Diffusion-Mediated Exciton Annihilation in 2D Semiconductors Using the Dielectric Environment
Atomically thin semiconductors such as monolayer MoS2 and WS2 exhibit
nonlinear exciton-exciton annihilation at notably low excitation densities
(below ~10 excitons/um2 in MoS2). Here, we show that the density threshold at
which annihilation occurs can be tuned by changing the underlying substrate.
When the supporting substrate is changed from SiO2 to Al2O3 or SrTiO3, the rate
constant for second-order exciton-exciton annihilation, k_XX [cm2/s], is
reduced by one or two orders of magnitude, respectively. Using transient
photoluminescence microscopy, we measure the effective room-temperature exciton
diffusion coefficient in chemical-treated MoS2 to be D = 0.06 +/- 0.01 cm2/s,
corresponding to a diffusion length of LD = 350 nm for an exciton lifetime of
{\tau} = 20 ns, which is independent of the substrate. These results, together
with numerical simulations, suggest that the effective exciton-exciton
annihilation radius monotonically decreases with increasing refractive index of
the underlying substrate. Exciton-exciton annihilation limits the overall
efficiency of 2D semiconductor devices operating at high exciton densities; the
ability to tune these interactions via the dielectric environment is an
important step toward more efficient optoelectronic technologies featuring
atomically thin materials
High-Order Numerical Method for 1D Non-local Diffusive Equation
In this paper we present a non-local numerical scheme based on the Local
Discontinuous Galerkin method for a non-local diffusive partial differential
equation with application to traffic flow. In this model, the velocity is
determined by both the average of the traffic density as well as the changes in
the traffic density at a neighborhood of each point. We discuss nonphysical
behaviors that can arise when including diffusion, and our measures to prevent
them in our model. The numerical results suggest that this is an accurate
method for solving this type of equation and that the model can capture desired
traffic flow behavior. We show that computation of the non-local convolution
results in complexity, but the increased computation time
can be mitigated with high-order schemes like the one proposed.Comment: 17 pages and 8 figure
Blue shifting of the A exciton peak in folded monolayer 1H-MoS2
The large family of layered transition-metal dichalcogenides is widely
believed to constitute a second family of two-dimensional (2D) semiconducting
materials that can be used to create novel devices that complement those based
on graphene. In many cases these materials have shown a transition from an
indirect bandgap in the bulk to a direct bandgap in monolayer systems. In this
work we experimentally show that folding a 1H molybdenum disulphide (MoS2)
layer results in a turbostratic stack with enhanced photoluminescence quantum
yield and a significant shift to the blue by 90 meV. This is in contrast to the
expected 2H-MoS2 band structure characteristics, which include an indirect gap
and quenched photoluminescence. We present a theoretical explanation to the
origin of this behavior in terms of exciton screening.Comment: 16 pages, 8 figure
EARTH OBSERVATION AND CLIMATE SERVICES FOR FOOD SECURITY AND AGRICULTURAL DECISION MAKING IN SOUTH AND SOUTHEAST ASIA
Deliberations on new developments in the use of Earth observation for agriculture and food security in South and Southeast Asia gathered 120 participants to discuss i) agricultural and hydrological drought monitoring and early warning systems, ii) crop mapping and yield estimation, and iii) risk financing and agrometeorological advisory services
Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2ᅠfield effect transistors
We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility
Adiponectin: Serum-saliva associations and relations with oral and systemic markers of inflammation
This study addresses gaps in our understanding about the validity and utility of using salivary adiponectin to
index serum adiponectin levels. Matched blood and saliva samples were collected on a single occasion from
healthy adults (n=99; age 18–36 years, 53% male). Serum and saliva was assayed for adiponectin and
inflammatory cytokines (IL-1β, IL-6, IL-8, TNFα), and saliva was also assayed for markers of blood
contamination (transferrin), total protein (salivary flow rate) and matrix metalloproteinase-8 (MMP-8). We
examined the extent to which salivary adiponectin was associated with serum adiponectin, and the influence of
potential confounders on the serum-saliva correlation, including age, sex, body mass index, and markers of
inflammation, oral health, salivary blood contamination, and flow rate. Findings revealed a modest serum-saliva
association for adiponectin, and strong positive associations between salivary adiponectin and salivary levels of
inflammatory cytokines, MMP-8, transferrin, and total protein. By contrast, salivary adiponectin was not related
to serum levels of inflammatory activity. The magnitude of the serum-saliva association was strengthened when
controlling for total protein in saliva, blood leakage into oral fluid, salivary inflammatory cytokines, and MMP-8.
The pattern of findings extends our understanding of salivary adiponectin and its potential use as an index of
circulating adiponectin levels
Glass is a viable substrate for precision force microscopy of membrane proteins
Scientific Reports ; 5:12550 ; DOI: 10.1038/srep12550.Chada, N. et al. Glass is a Viable Substrate for Precision Force Microscopy of Membrane Proteins. Sci. Rep. 5, 12550; doi: 10.1038/srep12550 (2015).8 pages.Received: 01 April 2015 ; Accepted: 02 July 2015 ; Published: 31 July 2015.Though ubiquitous in optical microscopy, glass has long been overlooked as a specimen supporting surface for high resolution atomic force microscopy (AFM) investigations due to its roughness. Using bacteriorhodopsin from Halobacterium salinarum and the translocon SecYEG from Escherichia coli, we demonstrate that faithful images of 2D crystalline and non-crystalline membrane proteins in lipid bilayers can be obtained on microscope cover glass following a straight-forward cleaning procedure. Direct comparison between AFM data obtained on glass and on mica substrates show no major differences in image fidelity. Repeated association of the ATPase SecA with the cytoplasmic protrusion of SecYEG demonstrates that the translocon remains competent for binding after tens of minutes of continuous AFM imaging. This opens the door for precision long-timescale investigations of the active translocase in near-native conditions and, more generally, for integration of high resolution biological AFM with many powerful optical techniques that require non-birefringent substrates.Includes bibliographical references
Glass is a viable substrate for atomic force microscopy of membrane proteins : [abstract]
Abstract only."2314-Pos Board B6.""Page 458a, Tuesday, February 18, 2014."--At top of page.Abstract in program book: Since its invention in the mid-1980s, the atomic force microscope (AFM) has become an invaluable complementary tool for studying membrane proteins in near-native environments. Historically, mica is the most common substrate utilized for biological AFM. Glass being amorphous, transparent, and optically homogeneous has its own set of advantages over mica and has the potential to broaden the use the AFM into fields that require high quality non-birefringent optical access. The use of silanized glass as AFM substrates has been reported as a means to fine tune surface chemistry. However, such coatings usually require hours of additional preparation time and can lead to increased surface roughness. In this work, we present a simple technique for preparing borosilicate glass as a substrate for two membrane systems: non-crystalline translocons (SecYEG) of the general secretary system from E. coli, and bacteriorhodopsin (BR) from H. salinarum. For both these membrane proteins, quantitative comparisons of the measured protein structures on glass versus mica substrates show agreement. An additional advantage of glass is that lipid coverage is rapid (< 10 minutes) and complete (occupying the entire surface). A goal is to study the bacterial export system using recently developed precision measurement techniques such as ultra-stable AFM
- …