357 research outputs found
On the quantumness of multiparameter estimation problems for qubit systems
No full textThe estimation of more than one parameter in quantum mechanics is a fundamental problem with relevant practical applications. In fact, the ultimate limits in the achievable estimation precision are ultimately linked with the non-commutativity of different observables, a peculiar property of quantum mechanics. We here consider several estimation problems for qubit systems and evaluate the corresponding quantumness R, a measure that has been recently introduced in order to quantify how incompatible the parameters to be estimated are. In particular, R is an upper bound for the renormalized difference between the (asymptotically achievable) Holevo bound and the SLD Cramér-Rao bound (i.e., the matrix generalization of the single-parameter quantum Cramér-Rao bound). For all the estimation problems considered, we evaluate the quantumness R and, in order to better understand its usefulness in characterizing a multiparameter quantum statistical model, we compare it with the renormalized difference between the Holevo and the SLD-bound. Our results give evidence that R is a useful quantity to characterize multiparameter estimation problems, as for several quantum statistical model, it is equal to the difference between the bounds and, in general, their behavior qualitatively coincide. On the other hand, we also find evidence that, for certain quantum statistical models, the bound is not in tight, and thus R may overestimate the degree of quantum incompatibility between parameters
Volcanic Records at GPS1, GPS2, 31DPT and M2 Stations along the 1998-99 ITASE Traverse (East Antarctica).
No full text3D reconstruction of two-phase random heterogeneous material from 2D sections: An approach via genetic algorithms
No full textThis paper introduces a method to reconstruct the three-dimensional (3D) microstructure of two-phase materials, e.g., porous materials such as highly irradiated nuclear fuel, from two-dimensional (2D) sections via a multi-objective optimization genetic algorithm. The optimization is based on the comparison between the reference and reconstructed 2D sections on specific target properties, i.e., 2D pore number, and mean value and standard deviation of the pore-size distribution. This represents a multi-objective fitness function subject to weaker hypotheses compared to state-of-the-art methods based on n-points correlations, allowing for a broader range of application. The effectiveness of the proposed method is demonstrated on synthetic data and compared with state-of-the-art methods adopting a fitness based on 2D correlations. The method here developed can be used as a cost-effective tool to reconstruct the pore structure in highly irradiated materials using 2D experimental data
Enantioselective organocatalytic reductions
No full textThe enantioselective organocatalytic methodologies described in this chapter are a clear demonstration of the enormous potentiality of metal-free catalytic reductions. Despite the historical need for and continued interest in chiral amines, their synthesis remains challenging. In one case, binaphthol-derived phosphoric acids have been successfully employed in a process that involves the use of a dihydropyridine-based compound as the reducing agent. In another strategy the reducing agent is trichlorosilane; finally in the very last few years a novel approach has been developed to realize metal-free hydrogenation of imines: The Frustrated Lewis Pair (FLP) method involves the use of a combination of a strong Lewis acid with a variety of sterically encumbered Lewis bases to activate hydrogen at ambient conditions. It is recognized that these chemical adducts could find application in catalytic hydrogenation reactions
Extracting Quantitative Information at Quantum Mechanical Level from Noncovalent Interaction Index Analyses
No full textThe noncovalent interaction (NCI) index is nowadays a well-known strategy to detect NCIs in molecular systems. Even though it initially provided only qualitative descriptions, the technique has been recently extended to also extract quantitative information. To accomplish this task, integrals of powers of the electron distribution were considered, with the requirement that the overall electron density can be clearly decomposed as sum of distinct fragment contributions to enable the definition of the (noncovalent) integration region. So far, this was done by only exploiting approximate promolecular electron densities, which are given by the sum of spherically averaged atomic electron distributions and thus represent too crude approximations. Therefore, to obtain more quantum mechanically (QM) rigorous results from NCI index analyses, in this work, we propose to use electron densities obtained through the transfer of extremely localized molecular orbitals (ELMOs) or through the recently developed QM/ELMO embedding technique. Although still approximate, the electron distributions resulting from the abovementioned methods are fully QM and, above all, are again partitionable into subunit contributions, which makes them completely suitable for the NCI integral approach. Therefore, we benchmarked the integrals resulting from NCI index analyses (both those based on the promolecular densities and those based on ELMO electron distributions) against interaction energies computed at a high quantum chemical level (in particular, at the coupled cluster level). The performed test calculations have indicated that the NCI integrals based on ELMO electron densities outperform the promolecular ones. Furthermore, it was observed that the novel quantitative NCI-(QM/)ELMO approach can be also profitably exploited both to characterize and evaluate the strength of specific interactions between ligand subunits and protein residues in protein-ligand complexes and to follow the evolution of NCIs along trajectories of molecular dynamics simulations. Although further methodological improvements are still possible, the new quantitative ELMO-based technique could be already exploited in situations in which fast and reliable assessments of NCIs are crucial, such as in computational high-throughput screenings for drug discovery
Evaluation of growth hormone response to GHRH plus arginine test in children with idiopathic short stature: role of peak time
No full textPURPOSE:
To describe the course of growth hormone response to growth hormone releasing hormone (GHRH) plus arginine provocative test in children with idiopathic short stature (ISS) and to evaluate the role of peak time.
METHODS:
A retrospective study was performed analyzing 344 GHRH plus arginine provocative tests performed in children and adolescents with short stature. Serum GH levels were measured at four-time points (T0', T30', T45' and T60') and GH peak was defined as the maximum value at any time point. Mean (T30'-T60') GH value and area under the curve (AUC) were calculated.
RESULTS:
When analyzing the time of peak at the provocative test, the most frequent peak time was T45' (53.8%) in the ISS group, with no differences in gender, age, and pubertal stage. Analyzing GHD subjects, the most frequent time of peak was T30 (50%). Analyzing the whole population, the GH T0' levels were significantly lower in subjects with the GH peak at T45' than those with the GH peak at T30' (1.7 ± 2.0 vs. 3.2 ± 4.0, p < 0.001). In subjects with GH peak at T45', the value of GH peak, AUC and mean GH were significantly higher than in those with GH peak at T30' and T60'. A direct correlation was found between the value of GH peak and growth velocity SDS (r = 0.127, p = 0.04) and a negative one between GH peak and GH level at T0' (r = - 0.111, p = 0.04), even when adjusted for gender, age, pubertal stage and BMI Z score.
CONCLUSIONS:
The time peak at 45 min seems to be associated with a better response to the test considering GH peak, mean and AUC. Patients with a GH peak at 30 min more probably could have a derangement in GH secretion showing worst growth pattern and/or a GH deficiency and should be carefully observed
Intracoronary bivalirudin: a new way to appease the hostile thrombus?
No full textIntracoronary thrombi are a common finding in the setting of acute coronary syndromes and correlate with intraprocedural complications, adverse prognosis and unpredictable response to standard pharmacological and interventional treatment. Interventional cardiologists have learned to fear the so-called hostile thrombus, with its aggressive and unstable behavior often leading to abrupt and refractory vessel closure. Here we report a case series of intracoronary bivalirudin administration to treat massive intracoronary thrombi, leading to rapid clot disappearance and coronary blood flow restoration. Interventional cardiologists might consider intracoronary bivalirudin administration as a bailout strategy during unusual critical situations. (C) 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins
- …
