731 research outputs found
Atmospheric concentrations of carbon dioxide and its isotopic composition in southern Poland: comparison of high-altitude mountain site and a near-by urban environment
International audienceThe results of regular observations of atmospheric CO2 mixing ratios and its carbon isotope composition (?13C, ?14C), carried out at two continental sites located in central Europe are presented and discussed. The sites (Kasprowy Wierch, 49°14' N, 19°59' E, 1989 m a.s.l.; Krakow, 50°04' N, 19°55' E, 220 m a.s.l.), are located in two contrasting environments: (i) high-altitude mountaneous area, relatively free of anthropogenic influences, and (ii) typical urban environment with numerous local sources of carbon dioxide. Despite of relative proximity of those sites (ca. 100 km), substantial differences in both the recorded CO2 levels and their isotopic composition were detected. The CO2 mixing ratios measured in the urban atmosphere revealed quasi-permanent excess concentration of this gas when compared with near-by background atmosphere. The annual mean CO2 concentration recorded in Krakow in 2004 was almost 10% higher than that recorded at high-altitude mountain site (Kasprowy Wierch). Such effect is occuring probably in all urban centers. Carbon isotopic composition of atmospheric CO2 proved to be efficient tool for identification the surface CO2 fluxes into the atmosphere related to fossil fuel burning and their influence on the recorded levels of this gas in the local atmosphere. The available records of ?14C for Krakow and Kasprowy Wierch suggest gradual reduction of 14C-free CO2 fluxes into the urban atmosphere of Krakow in the past several years
Relaxation effects in twisted bilayer molybdenum disulfide: structure, stability, and electronic properties
Manipulating the interlayer twist angle is a powerful tool to tailor the
properties of layered two-dimensional crystals. The twist angle has a
determinant impact on these systems' atomistic structure and electronic
properties. This includes the corrugation of individual layers, formation of
stacking domains and other structural elements, and electronic structure
changes due to the atomic reconstruction and superlattice effects. However, how
these properties change with the twist angle (ta) is not yet well understood.
Here, we monitor the change of twisted bilayer MoS2 characteristics as function
of ta. We identify distinct structural regimes, with particular structural and
electronic properties. We employ a hierarchical approach ranging from a
reactive force field through the density-functional-based tight-binding
approach and density-functional theory. To obtain a comprehensive overview, we
analyzed a large number of twisted bilayers with twist angles in the range
0.2-59.6deg. Some systems include up to half a million atoms, making structure
optimization and electronic property calculation challenging. For 13<ta<47, the
structure is well-described by a moir\'e regime composed of two rigidly twisted
monolayers. At small ta (ta<3 and 57<ta), a domain-soliton regime evolves,
where the structure contains large triangular stacking domains, separated by a
network of strain solitons and short-ranged high-energy nodes. The corrugation
of the layers and the emerging superlattice of solitons and stacking domains
affects the electronic structure. Emerging predominant characteristic features
are Dirac cones at K and kagome bands. These features flatten for ta
approaching 0 and 60deg. Our results show at which ta range the characteristic
features of the reconstruction emerge and give rise to exciting electronics. We
expect our findings also to be relevant for other twisted bilayer systems
Non equilibrium anisotropic excitons in atomically thin ReS
We present a systematic investigation of the electronic properties of bulk
and few layer ReS van der Waals crystals using low temperature optical
spectroscopy. Weak photoluminescence emission is observed from two
non-degenerate band edge excitonic transitions separated by 20 meV. The
comparable emission intensity of both excitonic transitions is incompatible
with a fully thermalized (Boltzmann) distribution of excitons, indicating the
hot nature of the emission. While DFT calculations predict bilayer ReS to
have a direct fundamental band gap, our optical data suggests that the
fundamental gap is indirect in all cases
Effects of Alcohol and Saccharin Deprivations on Concurrent Ethanol and Saccharin Operant Self-Administration by Alcohol-Preferring (P) Rats
Consumption of sweet solutions has been associated with a reduction in withdrawal symptoms and
alcohol craving in humans. The objective of the present study was to determine the effects of
EtOH and saccharin (SACC) deprivations on operant oral self-administration. P rats were allowed
to lever press concurrently self-administer EtOH (15% v/v) and SACC (0.0125% g/v) for 8 weeks.
Rats were then maintained on daily operant access (non-deprived), deprived of both fluids (2
weeks), deprived of SACC and given 2 ml of EtOH daily, or deprived of EtOH and given 2 ml of
SACC daily. All groups were then given two weeks of daily operant access to EtOH and SACC,
followed by an identical second deprivation period. P rats responded more for EtOH than SACC.
All deprived groups increased responding on the EtOH lever, but not on the SACC lever. Daily
consumption of 2 ml EtOH decreased the duration of the ADE. Home cage access to 2 ml SACC
also decreased the ADE but to a lesser extent than access to EtOH. A second deprivation period
further increased and prolonged the expression of an ADE. These results show EtOH is a more
salient reinforcer than SACC. With concurrent access to EtOH and SACC, P rats do not display a
saccharin deprivation effect. Depriving P rats of both EtOH and SACC had the most pronounced
effect on the magnitude and duration of the ADE, suggesting that there may be some interactions
between EtOH and SACC in their CNS reinforcing effects
The operational window of carbon nanotube electrical wires treated with strong acids and oxidants
Conventional metal wires suffer from a significant degradation or complete failure in their electrical performance, when subjected to harsh oxidizing environments, however wires constructed from Carbon Nanotubes (CNTs) have been found to actually improve in their electrical performance when subjected to these environments. These opposing reactions may provide new and interesting applications for CNT wires. Yet, before attempting to move to any real-world harsh environment applications, for the CNT wires, it is essential that this area of their operation be thoroughly examined. To investigate this, CNT wires were treated with multiple combinations of the strongest acids and halogens. The wires were then subjected to conductivity measurements, current carrying capacity tests, as well as Raman, microscopy and thermogravimetric analysis to enable the identification of both the limits of oxidative conductivity boosting and the onset of physical damage to the wires. These experiments have led to two main conclusions. Firstly, that CNT wires may operate effectively in harsh oxidizing environments where metal wires would easily fail and secondly, that the highest conductivity increase of the CNT wires can be achieved through a process of annealing, acetone and HCl purification followed by either H2O2 and HClO4 or Br2 treatment
Phase-Transition-Induced Carrier Mass Enhancement in 2D Ruddlesden-Popper Perovskites
There is a variety of possible ways to tune the optical properties of 2D
perovskites, though the mutual dependence between different tuning parameters
hinders our fundamental understanding of their properties. In this work we
attempt to address this issue for (CHNH)PbI (with
n=4,6,8,10,12) using optical spectroscopy in high magnetic fields up to 67T.
Our experimental results, supported by DFT calculations, clearly demonstrate
that the exciton reduced mass increases by around 30% in the low temperature
phase. This is reflected by a 2-3 fold decrease of the diamagnetic coefficient.
Our studies show that the effective mass, which is an essential parameter for
optoelectronic device operation, can be tuned by the variation of organic
spacers and/or moderate cooling achievable using Peltier coolers. Moreover, we
show that the complex absorption features visible in absorption/transmission
spectra track each other in magnetic field providing strong evidence for the
phonon related nature of the observed side bands.S.D.S acknowledges the Royal Society and Tata Group (UF150033). The work was supported by a Royal Society International Exchanges Cost Share award (IEC\R2\170108). The authors thank EPSRC for funding through grant EP/M05143/
Non equilibrium anisotropic excitons in atomically thin ReS2
We present a systematic investigation of the electronic properties of bulk and few layer ReS2 van der Waals crystals using low temperature optical spectroscopy. Weak photoluminescence emission is observed from two non-degenerate band edge excitonic transitions separated by similar to 20 meV. The comparable emission intensity of both excitonic transitions is incompatible with a fully thermalized (Boltzmann) distribution of excitons, indicating the hot nature of the emission. While DFT calculations predict bilayer ReS2 to have a direct fundamental band gap, our optical data suggests that the fundamental gap is indirect in all cases
Second trimester inflammatory and metabolic markers in women delivering preterm with and without preeclampsia.
ObjectiveInflammatory and metabolic pathways are implicated in preterm birth and preeclampsia. However, studies rarely compare second trimester inflammatory and metabolic markers between women who deliver preterm with and without preeclampsia.Study designA sample of 129 women (43 with preeclampsia) with preterm delivery was obtained from an existing population-based birth cohort. Banked second trimester serum samples were assayed for 267 inflammatory and metabolic markers. Backwards-stepwise logistic regression models were used to calculate odds ratios.ResultsHigher 5-α-pregnan-3β,20α-diol disulfate, and lower 1-linoleoylglycerophosphoethanolamine and octadecanedioate, predicted increased odds of preeclampsia.ConclusionsAmong women with preterm births, those who developed preeclampsia differed with respect metabolic markers. These findings point to potential etiologic underpinnings for preeclampsia as a precursor to preterm birth
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