8,244 research outputs found
Exciton states in monolayer MoSe2 and MoTe2 probed by upconversion spectroscopy
Transitions metal dichalcogenides (TMDs) are direct semiconductors in the
atomic monolayer (ML) limit with fascinating optical and spin-valley
properties. The strong optical absorption of up to 20 % for a single ML is
governed by excitons, electron-hole pairs bound by Coulomb attraction. Excited
exciton states in MoSe and MoTe monolayers have so far been elusive due
to their low oscillator strength and strong inhomogeneous broadening. Here we
show that encapsulation in hexagonal boron nitride results in emission line
width of the A:1 exciton below 1.5 meV and 3 meV in our MoSe and
MoTe monolayer samples, respectively. This allows us to investigate the
excited exciton states by photoluminescence upconversion spectroscopy for both
monolayer materials. The excitation laser is tuned into resonance with the
A:1 transition and we observe emission of excited exciton states up to 200
meV above the laser energy. We demonstrate bias control of the efficiency of
this non-linear optical process. At the origin of upconversion our model
calculations suggest an exciton-exciton (Auger) scattering mechanism specific
to TMD MLs involving an excited conduction band thus generating high energy
excitons with small wave-vectors. The optical transitions are further
investigated by white light reflectivity, photoluminescence excitation and
resonant Raman scattering confirming their origin as excited excitonic states
in monolayer thin semiconductors.Comment: 14 pages, 7 figures, main text and appendi
Dynamical non-axisymmetric instabilities in rotating relativistic stars
We present new results on dynamical instabilities in rapidly rotating
neutron-stars. In particular, using numerical simulations in full General
Relativity, we analyse the effects that the stellar compactness has on the
threshold for the onset of the dynamical bar-mode instability, as well as on
the appearance of other dynamical instabilities. By using an extrapolation
technique developed and tested in our previous study [1], we explicitly
determine the threshold for a wide range of compactnesses using four sequences
of models of constant baryonic mass comprising a total of 59 stellar models.
Our calculation of the threshold is in good agreement with the Newtonian
prediction and improves the previous post-Newtonian estimates. In addition, we
find that for stars with sufficiently large mass and compactness, the m=3
deformation is the fastest growing one. For all of the models considered, the
non-axisymmetric instability is suppressed on a dynamical timescale with an m=1
deformation dominating the final stages of the instability. These results,
together with those presented in [1], suggest that an m=1 deformation
represents a general and late-time feature of non-axisymmetric dynamical
instabilities both in full General Relativity and in Newtonian gravity.Comment: To appear on CQG, NFNR special issue. 16 pages, 5 color figures,
movies from http://www.fis.unipr.it/numrel/BarMode/ResearchBarMode.htm
Ceramic Substrates for High-temperature Electronic Integration
One of the most attractive ways to increase power handling capacity in power modules is to increase the operating temperature using wide-band-gap semiconductors. Ceramics are ideal candidates for use as substrates in high-power high-temperature electronic devices. The present article aims to determine the most suitable ceramic material for this application
Milk exosomes are bioavailable and distinct microRNA cargos have unique tissue distribution patterns
Exosomes participate in cell-to-cell communication, facilitated by the transfer of RNAs, proteins and lipids from donor to recipient cells. Exosomes and their RNA cargos do not exclusively originate from endogenous synthesis but may also be obtained from dietary sources such as the inter-species transfer of exosomes and RNAs in bovine milk to humans. Here, we assessed the bioavailability and distribution of exosomes and their microRNA cargos from bovine, porcine and murine milk within and across species boundaries. Milk exosomes labeled with fluorophores or fluorescent fusion proteins accumulated in liver, spleen and brain following suckling, oral gavage and intravenous administration in mice and pigs. When synthetic, fluorophore-labeled microRNAs were transfected into bovine milk exosomes and administered to mice, distinct species of microRNAs demonstrated unique distribution profiles and accumulated in intestinal mucosa, spleen, liver, heart or brain. Administration of bovine milk exosomes failed to rescue Drosha homozygous knockout mice, presumably due to low bioavailability or lack of essential microRNAs
Milk exosomes are bioavailable and distinct microRNA cargos have unique tissue distribution patterns
Exosomes participate in cell-to-cell communication, facilitated by the transfer of RNAs, proteins and lipids from donor to recipient cells. Exosomes and their RNA cargos do not exclusively originate from endogenous synthesis but may also be obtained from dietary sources such as the inter-species transfer of exosomes and RNAs in bovine milk to humans. Here, we assessed the bioavailability and distribution of exosomes and their microRNA cargos from bovine, porcine and murine milk within and across species boundaries. Milk exosomes labeled with fluorophores or fluorescent fusion proteins accumulated in liver, spleen and brain following suckling, oral gavage and intravenous administration in mice and pigs. When synthetic, fluorophore-labeled microRNAs were transfected into bovine milk exosomes and administered to mice, distinct species of microRNAs demonstrated unique distribution profiles and accumulated in intestinal mucosa, spleen, liver, heart or brain. Administration of bovine milk exosomes failed to rescue Drosha homozygous knockout mice, presumably due to low bioavailability or lack of essential microRNAs
Identification of hydrodynamic changes in rivers by means of freshwater mussels' behavioural response: An experimental investigation
The present work concerns the interaction between hydraulic processes and biological
communities in rivers. In particular, the aim of this study is to investigate the
interactions between flow dynamics and the freshwater mussels (FMs) to verify if the
mussels' behavioural response to the hydrodynamic stress could be used to monitor
natural extreme events in rivers. Although the influence of mussels on the kinematic
characteristics of flow at the waterâsediment interface was investigated by a certain
number of studies, their behavioural response to flow, both in static and dynamic
conditions, remains understudied. Laboratory experiments were performed in an artificial
flume exposing Unio elongatulus to different values of flow discharge, both in
steady and in unsteady conditions either with or without sediment transport. Mussels'
behavioural responses were detected by using Hall sensor technology to measure
gaping frequency, amplitude and duration, both in static conditions and under
the effect of hydrodynamic stresses. Five categories of behavioural response were
identified: Normal Activity (NA), Resting (Re), Transition (Tr), Adaptation (Ad) and
Avoidance (Av). During NA (standard feeding and moving), FMs presented valve gaping,
while during Re valves were kept constantly opened for water filtration. After a
variation of flow discharge (ÎQ), FMs promptly reacted showing a transition from
their normal behaviour, with constant gaping frequency (below 0.01 Hz), to higher
valve gaping frequencies. The mean valves' gaping frequency increased as a function
of ÎQ, and the highest values were reached in the presence of sediment transport.
The mean valve opening amplitude was less sensitive to ÎQ. Its range of variation
was very narrow with the highest values corresponding to the protrusion/retraction
of the animals' foot to move or anchor to the substrate. The percentage of mussels
responding to the discharge variation (Transition behaviour) increases with ÎQ confirming
that mussels' behavioural response represents a promising tool for monitoring
the occurrence of hydrodynamic stressors in fluvial systems
Random template placement and prior information
In signal detection problems, one is usually faced with the task of searching
a parameter space for peaks in the likelihood function which indicate the
presence of a signal. Random searches have proven to be very efficient as well
as easy to implement, compared e.g. to searches along regular grids in
parameter space. Knowledge of the parameterised shape of the signal searched
for adds structure to the parameter space, i.e., there are usually regions
requiring to be densely searched while in other regions a coarser search is
sufficient. On the other hand, prior information identifies the regions in
which a search will actually be promising or may likely be in vain. Defining
specific figures of merit allows one to combine both template metric and prior
distribution and devise optimal sampling schemes over the parameter space. We
show an example related to the gravitational wave signal from a binary inspiral
event. Here the template metric and prior information are particularly
contradictory, since signals from low-mass systems tolerate the least mismatch
in parameter space while high-mass systems are far more likely, as they imply a
greater signal-to-noise ratio (SNR) and hence are detectable to greater
distances. The derived sampling strategy is implemented in a Markov chain Monte
Carlo (MCMC) algorithm where it improves convergence.Comment: Proceedings of the 8th Edoardo Amaldi Conference on Gravitational
Waves. 7 pages, 4 figure
Contralateral effects of unilateral strength and skill training: Modified Delphi consensus to establish key aspects of cross-education
© 2020, The Author(s). Background: Cross-education refers to increased motor output (i.e., force generation, skill) of the opposite, untrained limb following a period of unilateral exercise training. Despite extensive research, several aspects of the transfer phenomenon remain controversial. Methods: A modified two-round Delphi online survey was conducted among international experts to reach consensus on terminology, methodology, mechanisms of action, and translational potential of cross-education, and to provide a framework for future research. Results: Through purposive sampling of the literature, we identified 56 noted experts in the field, of whom 32 completed the survey, and reached consensus (75% threshold) on 17 out of 27 items. Conclusion: Our consensus-based recommendations for future studies are that (1) the term âcross-educationâ should be adopted to refer to the transfer phenomenon, also specifying if transfer of strength or skill is meant; (2) functional magnetic resonance imaging, short-interval intracortical inhibition and interhemispheric inhibition appear to be promising tools to study the mechanisms of transfer; (3) strategies which maximize cross-education, such as high-intensity training, eccentric contractions, and mirror illusion, seem worth being included in the intervention plan; (4) study protocols should be designed to include at least 13â18 sessions or 4â6 weeks to produce functionally meaningful transfer of strength, and (5) cross-education could be considered as an adjuvant treatment particularly for unilateral orthopedic conditions and sports injuries. Additionally, a clear gap in views emerged between the research field and the purely clinical field. The present consensus statement clarifies relevant aspects of cross-education including neurophysiological, neuroanatomical, and methodological characteristics of the transfer phenomenon, and provides guidance on how to improve the quality and usability of future cross-education studies
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