4,923 research outputs found
Three-body bound states with zero-range interaction in the Bethe-Salpeter approach
The Bethe-Salpeter equation for three bosons with zero-range interaction is
solved for the first time. For comparison the light-front equation is also
solved. The input is the two-body scattering length and the outputs are the
three-body binding energies, Bethe-Salpeter amplitudes and light-front wave
functions. Three different regimes are analyzed: ({\it i}) For weak enough
two-body interaction the three-body system is unbound. ({\it ii}) For stronger
two-body interaction a three-body bound state appears. It provides an
interesting example of a deeply bound Borromean system. ({\it iii}) For even
stronger two-body interaction this state becomes unphysical with a negative
mass squared. However, another physical (excited) state appears, found
previously in light-front calculations. The Bethe-Salpeter approach implicitly
incorporates three-body forces of relativistic origin, which are attractive and
increase the binding energy.Comment: 13 pages, 7 figure
Solving the three-body bound-state Bethe-Salpeter equation in Minkowski space
The scalar three-body Bethe-Salpeter equation, with zero-range interaction,
is solved in Minkowski space by direct integration of the four-dimensional
integral equation. The singularities appearing in the propagators are treated
properly by standard analytical and numerical methods, without relying on any
ansatz or assumption. The results for the binding energies and transverse
amplitudes are compared with the results computed in Euclidean space. A fair
agreement between the calculations is found.Comment: 10 pages, 2 figures, version accepted for publication in Phys. Lett.
Bound state structure and electromagnetic form factor beyond the ladder approximation
We investigate the response of the bound state structure of a two-boson
system, within a Yukawa model with a scalar boson exchange, to the inclusion of
the cross-ladder contribution to the ladder kernel of the Bethe-Salpeter
equation. The equation is solved by means of the Nakanishi integral
representation and light-front projection. The valence light-front wave
function and the elastic electromagnetic form factor beyond the impulse
approximation, with the inclusion of the two-body current, generated by the
cross-ladder kernel, are computed. The valence wave function and
electromagnetic form factor, considering both ladder and ladder plus
cross-ladder kernels, are studied in detail. Their asymptotic forms are found
to be quite independent of the inclusion of the cross-ladder kernel, for a
given binding energy. The asymptotic decrease of form factor agrees with the
counting rules. This analysis can be generalized to fermionic systems, with a
wide application in the study of the meson structure.Comment: 19 pages, 6 figures, submitted to Phys. Lett.
Outcomes of Vaginal Birth After Caesarean: Experience of a Portuguese Hospital
info:eu-repo/semantics/publishedVersio
Site-selective protein modification via disulfide rebridging for fast tetrazine/trans-cyclooctene bioconjugation
An inverse electron demand Diels–Alder reaction between tetrazine and trans-cyclooctene (TCO) holds great promise for protein modification and manipulation. Herein, we report the design and synthesis of a tetrazine-based disulfide rebridging reagent, which allows the site-selective installation of a tetrazine group into disulfide-containing peptides and proteins such as the hormone somatostatin (SST) and the antigen binding fragment (Fab) of human immunoglobulin G (IgG). The fast and efficient conjugation of the tetrazine modified proteins with three different TCO-containing substrates to form a set of bioconjugates in a site-selective manner was successfully demonstrated for the first time. Homogeneous, well-defined bioconjugates were obtained underlining the great potential of our method for fast bioconjugation in emerging protein therapeutics. The formed bioconjugates were stable against glutathione and in serum, and they maintained their secondary structure. With this work, we broaden the scope of tetrazine chemistry for site-selective protein modification to prepare well-defined SST and Fab conjugates with preserved structures and good stability under biologically relevant conditions
Lift-up, Kelvin-Helmholtz and Orr mechanisms in turbulent jets
Three amplification mechanisms present in turbulent jets, namely lift-up, Kelvin–Helmholtz and Orr, are characterized via global resolvent analysis and spectral proper orthogonal decomposition (SPOD) over a range of Mach numbers. The lift-up mechanism was recently identified in turbulent jets via local analysis by Nogueira et al. (J. Fluid Mech., vol. 873, 2019, pp. 211–237) at low Strouhal number ( St ) and non-zero azimuthal wavenumbers ( m ). In these limits, a global SPOD analysis of data from high-fidelity simulations reveals streamwise vortices and streaks similar to those found in turbulent wall-bounded flows. These structures are in qualitative agreement with the global resolvent analysis, which shows that they are a response to upstream forcing of streamwise vorticity near the nozzle exit. Analysis of mode shapes, component-wise amplitudes and sensitivity analysis distinguishes the three mechanisms and the regions of frequency–wavenumber space where each dominates, finding lift-up to be dominant as St/m→0 . Finally, SPOD and resolvent analyses of localized regions show that the lift-up mechanism is present throughout the jet, with a dominant azimuthal wavenumber inversely proportional to streamwise distance from the nozzle, with streaks of azimuthal wavenumber exceeding five near the nozzle, and wavenumbers one and two most energetic far downstream of the potential core
Stability of casein micelles cross-linked with genipin: a physicochemical study as a function of pH
Chemical or enzymatic cross-linking of casein micelles (CMs) increases their
stability against dissociating agents. In this paper, a comparative study of
stability between native CMs and CMs cross-linked with genipin (CMs-GP) as a
function of pH is described. Stability to temperature and ethanol were
investigated in the pH range 2.0-7.0. The size and the charge
(-potential) of the particles were determined by dynamic light
scattering. Native CMs precipitated below pH 5.5, CMs-GP precipitated from pH
3.5 to 4.5, whereas no precipitation was observed at pH 2.0-3.0 or pH 4.5-7.0.
The isoelectric point of CMs-GP was determined to be pH 3.7. Highest stability
against heat and ethanol was observed for CMs-GP at pH 2, where visible
coagulation was determined only after 800 s at 140 C or 87.5% (v/v) of
ethanol. These results confirmed the hypothesis that cross-linking by GP
increased the stability of CMs.Comment: 5 pages, 2 figures, International Dairy Journal, 201
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