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621.
Pinyot A Nikolovski Z Bosch J Such-Sanmartín G Kageyama S Segura J Gutiérrez-Gallego R 《Analytical and bioanalytical chemistry》2012,402(3):1101-1108
Growth hormone secretagogues (GHS) constitute a new GH deficiency treatment increasing exponentially in number and improved
potency and bioavailability over the last decade. The growth hormone releasing activity makes these compounds attractive for
the artificial improvement of the human sports skills, now that recombinant human growth hormone (rhGH) administration is
effectively detected. The GHS family is extremely diverse both in number and chemical heterogeneity and keeps growing continuously.
In this paper, a general screening test is proposed. To develop a universal method, the single common property of growth hormone
secretagogues has been targeted: their capacity to bind to the GHS receptor 1a (GHS-R1a). Pretreated urine samples have been
tested in a competition assay where eventually the GHS presence detached a radiolabelled ligand from the receptor in a dose-dependent
manner. Blank urine samples were processed to determine potential age, gender and exercise effects, and to define a threshold
beyond which a specimen is considered positive. Samples from a growth hormone releasing peptide 2 (GHRP-2) excretion study
corroborated the screening assay applicability with a detection window of approximately 4.5 h, and results were confirmed
by comparison with a dedicated LC–MS quantification of the intact compound. 相似文献
622.
The Darboux theory of integrability for planar polynomial differential equations is a classical field, with connections to Lie symmetries, differential algebra and other areas of mathematics. In the present paper we introduce the concepts, problems and inverse problems, and we outline some recent results on inverse problems. We also prove a new result, viz. a general finiteness theorem for the case of prescribed integrating factors. A?number of relevant examples and applications is included. 相似文献
623.
624.
The concept of conditional stability constant is extended to the competitive binding of small molecules to heterogeneous surfaces or macromolecules via the introduction of the conditional affinity spectrum (CAS). The CAS describes the distribution of effective binding energies experienced by one complexing agent at a fixed concentration of the rest. We show that, when the multicomponent system can be described in terms of an underlying affinity spectrum [integral equation (IE) approach], the system can always be characterized by means of a CAS. The thermodynamic properties of the CAS and its dependence on the concentration of the rest of components are discussed. In the context of metal/proton competition, analytical expressions for the mean (conditional average affinity) and the variance (conditional heterogeneity) of the CAS as functions of pH are reported and their physical interpretation discussed. Furthermore, we show that the dependence of the CAS variance on pH allows for the analytical determination of the correlation coefficient between the binding energies of the metal and the proton. Nonideal competitive adsorption isotherm and Frumkin isotherms are used to illustrate the results of this work. Finally, the possibility of using CAS when the IE approach does not apply (for instance, when multidentate binding is present) is explored. 相似文献
625.
Eva Rentschler Marco Affronte Carlo Massobrio Pierre Rabu Jaume Veciana 《Solid State Sciences》2009,11(5):970-971
A critical outlook of the field of molecular magnetic materials is presented. This article is inspired by an international symposium devoted to the “Design, Characterization and Modelling of Molecule-Based Magnetic Materials (DCM4-II)” that took place at Strasbourg (France), from May 28th to June 1st, within the E-MRS 2007 Spring Meeting (Symposium R) organized by the European Materials Research Society in collaboration with the European Science Foundation. A series of papers linked to this symposium are published in this issue and in the previous issue (Volume 11, Issue 4) of Solid State Sciences. 相似文献
626.
One of the main open problems in secret sharing is the characterization of the access structures of ideal secret sharing schemes.
Brickell and Davenport proved that every one of these ideal access structures is related in a certain way to a unique matroid.
Specifically, they are matroid ports. In addition to the search of general results, this difficult open problem has been studied
in previous works for several families of access structures. In this paper we do the same for access structures with rank
3, that is, structures whose minimal qualified subsets have at most three participants. We completely characterize and classify
the rank-3 access structures that are matroid ports. We prove that all access structures with rank three that are ports of
matroids greater than 3 are ideal. After the results in this paper, the only open problem in the characterization of the ideal
access structures with rank three is to characterize the rank-3 matroids that can be represented by an ideal secret sharing
scheme.
A previous version of this paper appeared in Fifth Conference on Security and Cryptography for Networks, SCN 2006, Lecture Notes in Computer Science
4116 (2006) 201–215. 相似文献
627.
We study the bifurcation of limit cycles from the periodic orbits of a linear differential system in R4 in resonance 1:n perturbed inside a class of piecewise linear differential systems, which appear in a natural way in control theory. Our main result shows that at most 1 limit cycle can bifurcate using expansion of the displacement function up to first order with respect to a small parameter. This upper bound is reached. For proving this result we use the averaging theory in a form where the differentiability of the system is not needed. 相似文献
628.
Let X be a homogeneous polynomial vector field of degree 2 on $
\mathbb{S}^2
$
\mathbb{S}^2
. We show that if X has at least a non-hyperbolic singularity, then it has no limit cycles. We give necessary and sufficient conditions for determining
if a singularity of X on $
\mathbb{S}^2
$
\mathbb{S}^2
is a center and we characterize the global phase portrait of X modulo limit cycles. We also study the Hopf bifurcation of X and we reduce the 16
th
Hilbert’s problem restricted to this class of polynomial vector fields to the study of two particular families. Moreover,
we present two criteria for studying the nonexistence of periodic orbits for homogeneous polynomial vector fields on $
\mathbb{S}^2
$
\mathbb{S}^2
of degree n. 相似文献
629.
Jaume Llibre 《Journal of Differential Equations》2009,246(6):2192-189
In this paper we classify the centers, the cyclicity of its Hopf bifurcation and their isochronicity for the polynomial differential systems in R2 of arbitrary degree d?3 odd that in complex notation z=x+iy can be written as
630.
We deal with nonlinear T-periodic differential systems depending on a small parameter. The unperturbed system has an invariant manifold of periodic solutions. We provide the expressions of the bifurcation functions up to second order in the small parameter in order that their simple zeros are initial values of the periodic solutions that persist after the perturbation. In the end two applications are done. The key tool for proving the main result is the Lyapunov-Schmidt reduction method applied to the T-Poincaré-Andronov mapping. 相似文献