Search results for "transition"
showing 10 items of 3988 documents
WS 2 /MoS 2 Heterostructures through Thermal Treatment of MoS 2 Layers Electrostatically Functionalized with W 3 S 4 Molecular Clusters
2020
The preparation of 2D stacked layers combining flakes of different nature gives rise to countless numbers of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides, WS2 /MoS2 , has awakened great interest owing to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here, a suspension of negatively charged MoS2 flakes is mixed with a methanolic solution of a cationi…
Pattern formation and transition to chaos in a chemotaxis model of acute inflammation
2021
We investigate a reaction-diffusion-chemotaxis system that describes the immune response during an inflammatory attack. The model is a modification of the system proposed in Penner, Ermentrout, and Swigon [SIAM J. Appl. Dyn. Syst., 11 (2012), pp. 629-660]. We introduce a logistic term in the immune cell dynamics to reproduce the macrophages' activation, allowing us to describe the disease evolution from the early stages to the acute phase. We focus on the appearance of pattern solutions and their stability. We discover steady-state (Turing) and wave instabilities and classify the bifurcations deriving the corresponding amplitude equations. We study stationary radially symmetric solutions an…
Effects of high-pressure on the structural, vibrational, and electronic properties of monazite-type PbCrO4
2012
We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of PbCrO 4 (the mineral crocoite) at ambient and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. X-ray-diffraction, Raman, and optical absorption experiments have allowed us also to completely characterize two pressure-induced structural phase transitions. The first transition is from a monoclinic structure to another monoclinic structure. It maintains the symmetry of the crystal but has important consequences in the physical properties; among others, a band-gap collapse is induced. The second one invo…
Baseline design of the thermal blocking filters for the X-IFU detector on board ATHENA
2014
ATHENA is an advanced X-ray observatory designed by a large European consortium to address the science theme "Hot and Energetic Universe" recently selected by ESA for L2 – the second Large-class mission within the Cosmic Vision science program (launch scheduled in 2028). One of the key instruments of the mission is the X-ray Integral Field Unit (X-IFU), an array of Transition Edge Sensor (TES) micro-calorimeters with high energy resolution (2.5 eV @ 6 keV) in the energy range 0.2÷12 keV, operating at the focal plane of a large effective area high angular resolution (5" HEW) grazing incidence X-ray telescope. The X-IFU operates at temperatures below 100 mK and thus requires a sophisticated c…
The focal plane assembly for the Athena X-ray Integral Field Unit instrument
2016
This paper summarizes a preliminary design concept for the focal plane assembly of the X-ray Integral Field Unit on the Athena spacecraft, an imaging microcalorimeter that will enable high spectral resolution imaging and point-source spectroscopy. The instrument's sensor array will be a ~ 3840-pixel transition edge sensor (TES) microcalorimeter array, with a frequency domain multiplexed SQUID readout system allowing this large-format sensor array to be operated within the thermal constraints of the instrument's cryogenic system. A second TES detector will be operated in close proximity to the sensor array to detect cosmic rays and secondary particles passing through the sensor array for off…
Synthetic Pathways for New Tubular Transition Metal Hydroxo- and Fluoro-Selenites: Crystal Structures ofM12(X)2(SeO3)8(OH)6(M=Co2+,Ni2+;X= OH−)
1996
The dumortierite-family structuresM12X2(SeO3)8(OH)6(M= Co2+and Ni2+;X= OH−and F−) have been synthesized. The crystal structures of the hydroxo-derivatives have been refined from X?ray powder diffraction data in the space groupP63mc(Z= 1) witha= 12.887(3) A andc= 4.981(4) A (M= Co2+,X= OH−or F−) anda= 12.704(5) A andc= 4.925(6) A (M= Ni2+,X= OH−or F−). Application of the Partial Charge Transference Model allows the understanding of the selenite derivatives crystal chemistry.
DSC, Dilatometric, Dielectric, and1H NMR Studies of Phase Transitions and Molecular Motions in [N(C2H5)4]3M2Cl9 (M = Sb, Bi) Crystals
1995
Results in the dependence of stoichiometry of obtained tetraethylammonium (TEA) chloroantiomonate and chlorobismuthate salts on the molar ratio of reactants used in the synthesis are presented. Seven tetraethylammonium salts are obtained: (TEA) 6 M 8 Cl 30 , TEAMCI 4 , (TEA) 3 M 2 Cl 9 (M = Sb, Bi) and (TEA) 2 SbCl 5 . Preliminary X-ray diffraction studies on (TEA) 3 M 2 Cl 9 (M = Sb, Bi) show that they are isomorphous, crystallizing at room temperature in monoclinic symmetry. The dilatometric, dielectric, and DSC studies show that (TEA) 3 Bi 2 Cl 9 undergoes two phase transitions at T c2 = 144 K and at T c1 = 322 K while (TEA) 3 Sb 2 Cl 9 undergoes three transitions at T c3 = 185, T c2 = 2…
Statics and Dynamics of a Glassy Crystal: A NMR- and Neutron Scattering Investigation of (NaCl) 0.35 (NaCN) 0.65
1987
The statics and the dynamics of the glass transition in (NaCl)0.35(NaCN)0.65 have been investigated by inelastic neutron scattering and are directly compared to NMR results. Insight into the relaxation dynamics is gained via the temperature dependence of the transverse acoustic phonon modes and via the spin relaxation time T1. The statics of the system is reflected by the growth of a central peak and by the distribution of electric-field gradients. Both quantities are directly related to the glass order parameter. The temperature dependence of the order parameter provides experimental evidence that in NaCl:NaCN mixed crystals the glass transition is dominated by random fields rather than by…
Optical Properties of Natural and Synthetic Beryl Crystals
2015
The results of investigation of photoluminescence and UV-Visible absorption spectra of natural beryl crystals from Ural Mountains before and after fast neutron irradiation and synthetic crystal grown in Belarus and Russia are presented. Photoluminescence (PL) spectra of synthetic beryl crystals contain a broad band with maxima 740 nm excited both by UV light (λex = 260 nm, 271 nm) and laser excitation (λex =263 nm). This band is connected with Fe 2+ ions. The temperature lowering down to 8 K leads to appearance of narrow lines in the 680 - 720 nm regions. Emission lines observed in the luminescence spectra are connected with electron transition 2 Eg→ 4 A2g of the Cr 3+ ions: R-lines (682.5 …
On structural phase transitions inn-butylammonium chloroantimonate(III) and chlorobismuthate(III) crystals: x-ray, differential scanning calorimetry,…
1997
Numerous structural phase transitions are detected in new crystals of the n-butylammonium compounds: , and by means of differential scanning calorimetry, dilatometric and dielectric dispersion (1 kHz - 1 MHz) studies. For the transitions the basic thermodynamic data are determined. Interesting dielectric properties are found in a metastable form of the crystals. Debye-like dispersion of the electric permittivity between 30 and 800 MHz is observed around the 310 K phase transition for this crystal. The activation energy of the reorientation of the n-butylammonium cations is found to be 16 kJ . The structure of ( form) has been refined to R = 0.0439 and shows isolated units and two non-equiva…