957 research outputs found
Covalent organic frameworks as catalyst support: A case study of thermal, hydrothermal, and mechanical pressure stability of β-ketoenamine-linked TpBD-Me2
Covalent organic frameworks (COFs) are crystalline, ordered networks, that, due to their high surface areas and the opportunity for periodic placement of catalytically active sites, are interesting materials for catalysis. Despite the great interest in the use of COFs for this application, there is currently a lack of fundamental understanding on how catalytically relevant conditions affect the integrity of the materials. To gain insight into the stability of COFs as catalyst supports, we herein subjected a β-ketoenamine-linked COF to thermal treatment at high temperatures, to autogenous pressure in water at different temperatures, and to mechanical pressure during pelletizing, after which the materials were thoroughly characterized to gain insight into the structural changes occurring during these catalytically relevant treatments. The COF was largely stable under all hydrothermal conditions studied, highlighting the applicability of β-ketoenamine-linked COFs under aqueous and vapor conditions. On the other hand, thermal and pressure treatments led to a rapid decline in the surface area already at the lowest temperatures and pressures studied. Theoretical calculations indicated this loss to stem from interlayer rearrangement or buckling of the COF layers induced by the applied conditions. This study demonstrates the suitability of β-ketoenamine-linked COFs for use under hydrothermal conditions, and sheds light on the degradation pathways under thermal and pressure treatments, opening the path to the design of COFs with increased stability under such conditions.Fundação para a Ciência e a Tecnologia | Ref. UTA-EXPL/NPN/0055/2019Fundação para a Ciência e a Tecnologia | Ref. PTDC/QUI-OUT/2095/2021Fundação para a Ciência e a Tecnologia | Ref. PTDC/EQU-EQU/1707/2020Agencia Estatal de Investigación | Ref. RYC2020-030414-IUniversidade de Vigo/CISU
Critical point network for drainage between rough surfaces
In this paper, we present a network method for computing two-phase flows between two rough surfaces with significant contact areas. Low-capillary number drainage is investigated here since one-phase flows have been previously investigated in other contributions. An invasion percolation algorithm is presented for modeling slow displacement of a wetting fluid by a non wetting one between two rough surfaces. Short-correlated Gaussian process is used to model random rough surfaces.The algorithm is based on a network description of the fracture aperture field. The network is constructed from the identification of critical points (saddles and maxima) of the aperture field. The invasion potential is determined from examining drainage process in a flat mini-channel. A direct comparison between numerical prediction and experimental visualizations on an identical geometry has been performed for one realization of an artificial fracture with a moderate fractional contact area of about 0.3. A good agreement is found between predictions and observations
A Review of Sympathetic and Parasympathetic Innervation in the Structural and Functional Maintenance of the Male Gonad
The nervous system controls and coordinates the functions of all body systems, including the male reproductive system. The male gonad, responsible for spermatogenesis and steroidogenesis, receives autonomous sympathetic and parasympathetic innervation, having a great influence on the structural and functional integrity of this organ. The testis receives autonomic innervation primarily at the superior and inferior poles, specifically by the superior and inferior spermatic nerves. This nervous control is wired into all testicular cell populations such as contractile cells (myoid cells), germ cells, and steroidogenic cells. Many studies have also described the influence of autonomic innervation on Sertoli cell control. Thus, any possible interference of physical or chemical agents whose action is directly or indirectly linked to the nervous control of the testicle can result in changes and/or damage to male reproduction, with emphasis on testicular impairment. The present chapter consists of a review of data about the effects of physical or chemical alterations on the autonomous innervation and its repercussions on male gonad. For this, it is necessary to understand the general aspect of the nervous system and the male gonad morphology and innervation, as well as the action of drugs or any methods that promote changes in the communication between these two systems
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
Measurement of charm production at central rapidity in proton-proton collisions at TeV
The -differential production cross sections of the prompt (B
feed-down subtracted) charmed mesons D, D, and D in the rapidity
range , and for transverse momentum GeV/, were
measured in proton-proton collisions at TeV with the ALICE
detector at the Large Hadron Collider. The analysis exploited the hadronic
decays DK, DK, DD, and their charge conjugates, and was performed on a
nb event sample collected in 2011 with a
minimum-bias trigger. The total charm production cross section at TeV and at 7 TeV was evaluated by extrapolating to the full phase space
the -differential production cross sections at TeV
and our previous measurements at TeV. The results were compared
to existing measurements and to perturbative-QCD calculations. The fraction of
cdbar D mesons produced in a vector state was also determined.Comment: 20 pages, 5 captioned figures, 4 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/307
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