209 research outputs found
Charged exctions in two-dimensional transition-metal dichalcogenides - semiclassical calculation of Berry-curvature effects
We theoretically study the role of the Berry curvature on neutral and charged
excitons in two-dimensional transition-metal dichalcogenides. The Berry
curvature arises due to a strong coupling between the conduction and valence
bands in these materials that can to great extent be described within the model
of massive Dirac fermions. The Berry curvature lifts the degeneracy of exciton
states with opposite angular momentum. Using an electronic interaction that
accounts for non-local screening effects, we find a Berry-curvature induced
splitting of meV between the 2 and 2 exciton states in
WS, consistent with experimental findings. Furthermore, we calculate the
trion binding energies in WS and WSe for a large variety of screening
lenghts and different dielectric constants for the environment. Our approach
indicates the prominent role played by the Berry curvature along with non-local
electronic interactions in the understanding of the energy spectra of neutral
and charged excitons in transition-metal dichalcogenides and in the the
interpretation of their optical properties.Comment: 11 pages, 3 figure
Polyamide from lactams by reactive rotational molding via anionic ring-opening polymerization: Optimization of processing parameters
A reactive rotational molding (RRM) process was developed to obtain a PA6 by activated anionic ring-opening polymerization of epsilon-caprolactam (APA6). Sodium caprolactamate (C10) and caprolactam magnesium bromide (C1) were employed as catalysts, and difunctional hexamethylene-1,6-dicarbamoylcaprolactam (C20) was used as an activator. The kinetics of the anionic polymerization of !-caprolactam into polyamide 6 was monitored through dynamic rheology and differential scanning calorimetry measurements. The effect of the processing parameters, such as the polymerization temperature, different catalyst/activator combinations and concentrations, on the kinetics of polymerization is discussed. A temperature of 150°C was demonstrated to be the most appropriate. It was also found that crystallization may occur during PA6 polymerization and that the combination C1/C20 was well suited as it permitted a suitable induction time. Isoviscosity curves were drawn in order to determine the available processing window for RRM. The properties of the obtained APA6 were compared with those of a conventionally rotomolded PA6. Results pointed at lower cycle times and increased tensile properties at weak deformation
Hybridized quadrupole-dipole exciton effects in - Organic Heterostructure
In the present work we discuss resonant hybridization of the quadrupole
Wannier-Mott exciton (WE) in a quantum well with the Frenkel (FE)
dipole exciton in an adjacent layer of organic DCM2:CA:PA. The coupling between
excitons is due to interaction between the gradient of electric field induced
by DCM2 Frenkel exciton and the quadrupole moment of the transition in the
cuprous oxide. The specific choice of the organic allows us to use the
mechanism of 'solid state solvation' to dynamically tune the WE and FE into
resonance during time (comparable with the big life time of
the WE) of the 'slow' phase of the solvation. The quadrupole-dipole hybrid
utilizes the big oscillator strength of the FE along with the big lifetime of
the quadrupole exciton, unlike dipole-dipole hybrid exciton which utilizes big
oscillator strength of the FE and big radius of the dipole allowed WE. Due to
strong spatial dispersion and big mass of the quadrupole WE the hybridization
is not masked by the kinetic energy or the radiative broadening. The lower
branch of the hybrid dispersion exhibits a pronounced minimum and may be used
in applications. Also we investigate and report noticeable change in the
coupling due to a induced 'Stark effect' from the strong local electric field
of the FE. We investigated the fine energy structure of the quantum well
confined ortho and para excitons in cuprous oxide
Indium selenide: An insight into electronic band structure and surface excitations
We have investigated the electronic response of single crystals of indium selenide by means of angle-resolved photoemission spectroscopy, electron energy loss spectroscopy and density functional theory. The loss spectrum of indium selenide shows the direct free exciton at similar to 1.3 eV and several other peaks, which do not exhibit dispersion with the momentum. The joint analysis of the experimental band structure and the density of states indicates that spectral features in the loss function are strictly related to single-particle transitions. These excitations cannot be considered as fully coherent plasmons and they are damped even in the optical limit, i.e. for small momenta. The comparison of the calculated symmetry-projected density of states with electron energy loss spectra enables the assignment of the spectral features to transitions between specific electronic states. Furthermore, the effects of ambient gases on the band structure and on the loss function have been probed
DREAM: III.A helium survey in exoplanets on the edge of the hot Neptune desert with GIANO-B@TNG
The population of close-in exoplanets features a desert of hot Neptunes whose
origin is uncertain. These planets may have lost their atmosphere, eroding into
mini-Neptunes and super-Earths. Direct observations of evaporating atmospheres
are essential to derive mass-loss estimates and constrain this scenario. The
metastable 1083.3nm HeI triplet represents a powerful diagnostic of atmospheric
evaporation since it traces the hot gas in extended exoplanet atmospheres, is
observable from the ground, and is weakly affected by interstellar medium
absorption. We conducted a uniform HeI transmission spectroscopy survey,
focusing on 9 planets located at the edges of the Neptunian desert, aiming to
gain insights into the role of photo-evaporation in its formation. We observed
one transit per planet using the high-resolution, near-infrared spectrograph
GIANO-B on the Telescopio Nazionale Galileo. We focused our analysis on the HeI
triplet by computing high-resolution transmission spectra. We then employed the
p-winds model to interpret the observed transmission spectra. We found no sign
of planetary absorption in the HeI triplet in any of the investigated targets.
We thus provided 3sigma upper-limit estimations on the thermosphere absorption,
temperature, and mass loss, and combined them with past measurements to search
for correlations with parameters thought to be drivers in the formation of the
HeI triplet. Our results strengthen the importance of performing homogeneous
surveys and analyses to bring clarification in the HeI detection and hence in
the Neptunian desert origin. Our findings corroborate the literature
expectations that the HeI absorption signal correlates with the stellar mass
and the received XUV flux. However, these trends seem to disappear in terms of
mass-loss rates; further studies are essential to shed light on this aspect and
to understand better the photo-evaporation process.Comment: 23 pages, 13 figures, accepted for publication in A&A, after language
editin
Vibrational Enhancement of the Effective Donor - Acceptor Coupling
The paper deals with a simple three sites model for charge transfer phenomena
in an one-dimensional donor (D) - bridge (B) - acceptor (A) system coupled with
vibrational dynamics of the B site. It is found that in a certain range of
parameters the vibrational coupling leads to an enhancement of the effective
donor - acceptor electronic coupling as a result of the formation of the
polaron on the B site. This enhancement of the charge transfer efficiency is
maximum at the resonance, where the effective energy of the fluctuating B site
coincides with the donor (acceptor) energy.Comment: 5 pages, 3 figure
Characterizations of pepsin-soluble collagen derived from lizardfish (saurida tumbil bloch, 1795) skin, bone and scales
Reducing food waste is critical for sustainability. In the case of fish processing, more than sixty percent of by-products are generated as waste. Lizardfish (Saurida tumbil Bloch, 1795) is an economically important species for surimi production. To address waste disposal and maximize income, an effective utilization of fish by-products is essential. This study aims to isolate and characterize pepsin-soluble collagens from the skin, bone and scales of lizardfish. Significant differences (p 70%) in acidic conditions (particularly at pH 4.0) and at low sodium chloride concentrations (0–30 g/L). Microstructural analysis depicted that all extracted collagens were multi-layered, irregular, dense, sheet-like films linked by random coiled filaments. Overall, pepsin-soluble collagens from lizardfish skin, bone and scales could serve as potential alternative sources of collagens
Physical and functional properties of fish gelatin-based film incorporated with mangrove extracts
Background. The fishery processing industry produces a remarkable number of by-products daily. Fish skin accounts for one of the significant wastes produced. Fish skin, however, can be subjected to extraction to yield gelatine and used as the primary raw material for edible film production. To increase the functionality of edible films, bioactive compounds can be incorporated into packaging. Mangroves produce potential bioactive compounds that are suitable as additional agents for active packaging. This study aimed to create a fish gelatine-based edible film enriched with mangrove extracts and to observe its mechanical and biological properties. Methods. Two mangrove species (Bruguiera gymnorhiza and Sonneratia alba) with four extract concentrations (control, 0.05%, 0.15%, 0.25%, and 0.35%) were used to enrich edible films. The elongation, water vapour transmission, thickness, tensile strength, moisture content, antioxidant and antibacterial properties of the resulting packaging were analysed. Results. The results showed that the mangrove species and extract concentration significantly affected (p < 0.05) the physical properties of the treated films such as elongation (16.89–19.38%), water vapour transmission (13.31–13.59 g/m2 ), and active packaging-antioxidant activities (12.36%–60.98%). The thickness, tensile strength, and water content were not significantly affected. Potent antioxidant activity and relatively weak antimicrobial activity of this active gelatine packaging were observed
Case studies of geothermal system response to perturbations in groundwater flow and thermal regimes
Global demands for energy efficient heating and cooling systems coupled with rising commitments toward net zero emissions is resulting in wide deployment of shallow geothermal systems, typically installed to a depth of 100 to 200m, and in the continued growth of the global ground source heat pump (GSHP) market. Ground coupled heat pump (GCHP) systems take up to 85% of the global GSHP market. With increasing deployment of GCHP systems in urban areas coping with limited regulations, there is growing potential and risk for these systems to impact the subsurface thermal regime and to interact with each other or with nearby heat‐sensitive subsurface infrastructures. In this paper, we present three numerical modelling case studies, from the UK and Canada, which examine GCHP systems’ response to perturbation of the wider hydrogeological and thermal regimes. The studies demonstrate how GCHP systems can be impacted by external influences and perturbations arising from subsurface activities that change the thermal and hydraulic regimes in the area surrounding these systems. Additional subsurface heat loads near existing schemes are found to have varied impacts on system efficiency with reduction ranging from <1 % to 8 %, while changes in groundwater flow rates (due to a nearby groundwater abstraction) reduced the effective thermal conductivity at the study site by 13%. The findings support the argument in favour of regulation of GCHP systems or, to a minimum, their registration with records of locations and approximate heat pump capacity – even though these systems do not abstract / inject groundwater
- …