368 research outputs found
Non-Gaussianity and purity in finite dimension
No full textWe address truncated states of continuous variable systems and analyze their statistical
properties numerically by generating random states in finite-dimensional Hilbert spaces.
In particular, we focus to the distribution of purity and non-Gaussianity for dimension
up to d = 21. We found that both quantities are distributed around typical values
with variances that decrease for increasing dimension. Approximate formulas for typical
purity and non-Gaussianity as a function of the dimension are derived
Daemonic ergotropy in continuously monitored open quantum batteries
No full textThe amount of work that can be extracted from a quantum system can be increased by exploiting the information obtained from a measurement performed on a correlated ancillary system. The concept of daemonic ergotropy has been introduced to properly describe and quantify this work extraction enhancement in the quantum regime. We here explore the application of this idea in the context of continuously monitored open quantum systems, where information is gained by measuring the environment interacting with the energy-storing quantum device. We first show that the corresponding daemonic ergotropy takes values between the ergotropy and the energy of the corresponding unconditional state. The upper bound is achieved by assuming an initial pure state and a perfectly efficient projective measurement on the environment, independently of the kind of measurement performed. On the other hand, if the measurement is inefficient or the initial state is mixed, the daemonic ergotropy is generally dependent on the measurement strategy. This scenario is investigated via a paradigmatic example of an open quantum battery: a two-level atom driven by a classical field and whose spontaneously emitted photons are continuously monitored via either homodyne, heterodyne, or photodetection
Specificity of firstline tests for the diagnosis of Cushing's syndrome. Assessment in a large series.
No full textContext: The diagnosis of Cushing’s syndrome requires highly sensitive screening tests. Therefore, diagnostic cutoffs have been lowered
to maximize sensitivity and identify all patients. However, few studies have investigated the impact of these refinements on the specificity of first-line tests. Objective: The aim of the study was the assessment of the specificity of three widely used screening tests in a large series of Cushing’s syndrome suspects referred to our endocrine service.
Patients: We retrospectively reviewed the results of urinary free cortisol (UFC), 1-mg dexamethasone suppression test [overnight suppression test (OST)], and serum cortisol at midnight in 3461, 357, and 864 patients, respectively, with clinical features suggestive of Cushing’s syndrome but in whom this diagnosis was subsequently excluded.
Results: UFC and OST at the 5 μg/dl cutoff exhibited the highest specificities [91% (95% confidence intervals [CI] 90.2–92.1%) and 97% (95% CI 96.3–98.5%), respectively]. Conversely, midnight serum cortisol yielded 87% (95% CI 84.3–91.1%) specificity only with the 7.5 μg/dl cutoff, whereas the 1.8 μg/dl threshold resulted in an unacceptably
high proportion of false positives at only 20% specificity (95% CI 16.0–24.4%). Gender and age may lead to misleading results in all three screening tests. Conclusions: Specificity of tests for Cushing’s syndrome varies considerably, with OST and UFC presenting the best performances, and
circadian rhythm appearing heavily impaired by lowering of diagnostic cutoffs. Indeed, the vast majority of individuals in our series presented midnight serum cortisol values greater than 0.8 μg/dl; thus, caution has to be exercised when this criterion is used to exclude Cushing’s syndrome
Vitamin D Status, enterovirus infection, and type 1 diabetes in italian children/adolescents
No full textAt the time of the clinical onset of type 1 diabetes (T1D), we investigated 82 pediatric cases in parallel with 117 non‐diabetic controls matched by age, geographic area, and time of collection. The occurrence of an enteroviral infection was evaluated in peripheral blood using a sensitive method capable of detecting virtually all human enterovirus (EV) types. While non‐diabetic controls were consistently EV‐negative, 65% of T1D cases carried EVs in blood. The vitamin D status was assessed by measuring the concentration of 25‐hydroxyvitamin D [25(OH)D] in serum. Levels of 25(OH)D were interpreted as deficiency (≤50 nmol/L), insufficiency (52.5‐72.5 nmol/L), sufficiency (75‐250 nmol/L).
In T1D cases the median serum concentration of 25(OH)D was 54.4±27.3 nmol/L vs. 74.1±28.5 nmol/L in controls (p=0.0001). Diabetic children/adolescents showed deficient levels of vitamin D 25(OH)D (i.e., 72.5 nmol/L) in 48.8% cases vs. 17.9% in non‐diabetic controls (p=0.0001). Unexpectedly, the median vitamin D concentration was significantly reduced in virus‐positive vs. virus‐negative diabetics (48.2±22.5 vs. 61.8±31.2 nmol/L; p=0.015), with deficient levels in 58.5% vs. 31.0%, respectively.
Thus, at the time of clinical onset, EV‐positive cases had reduced vitamin D levels compared to EV‐negative cases. This could indicate either that the virus‐negative children/adolescents had been hit by a non‐infectious T1D‐triggering event, or that children/adolescents with proper levels of vitamin D had been able to rapidly clear the virus. Thus, it would be important to assess whether adequate vitamin D supplementation before or during the pre‐diabetic phase of T1D may counteract the diabetogenic potential of infectious pathogens
New Catalytic Methods for Carbon Nitrogen Double Bond Transformations
No full textOver the last years, the use of trichlorosilane as a reducing agent has attracted much attention; the employment of a metal-free methodology could address the cost and waste remediation issues associated with main group hydrides, as well as avoid the expense and potentially toxic nature of metal catalysts. To promote the reaction, the trichlorosilane needs to be activated by coordination with a Lewis base: in particular, the use of chiral Lewis bases offers the potential to control the absolute stereochemistry of the process.1
Recently we decided to extend this methodology to the enantioselective reduction of fluorinated ketoimines, due to the great interest that organofluorine chemistry has received in many fields, such as material and pharmaceutical sciences.2 In spite of the great activity that fluorine attracted lately, it continues to challenge the organic chemistry community, since the presence of fluorine functional groups profoundly modifies the physicochemical and biological properties. In particular, the stereocontrol at carbon center featuring a fluorinated motif is an highly challenging task. The use of trichlorosilane combines the advantages of an environmentally friendly technique and the avoidance of the problems linked to the stereoselective insertion of a fluorinated group, while retaining high levels of enantioselectivity.
During our studies we’ve synthesized a set of fluorinated aromatic ketimines, both aromatic and aliphatic. Their trichlorosilane mediated reduction, after a proper tuning of reaction and workup conditions, allowed us to isolate the corresponding amines with high chemical yield and very good enantioselectivity, up to 90% e.e. Some variously substitued aromatic substrates were also examined, showing a good tolerance for electrowithdrawing and electrodonating substituents on the aromatic ring.
References:
1. a) Guizzetti S., Benaglia M. Eur. J. Org. Chem. 2010, 5529–5541, b) Jones S., Warner C. J. A. Org. Biomol. Chem. 2012,
10, 2189–2200
2. Nie J., Guo H., Cahard D, Ma J. Chem. Rev. 2011, 111, 455–52
EXPLORING NOVEL ORGANOCATALYTIC METHODOLOGIES FOR CARBON-NITROGEN DOUBLE BOND REDUCTION
No full textThe development of novel methodologies for the preparation of enantiomerically pure compounds is a topic of great interest for several fields. In particular, it must be mentioned that chiral amines are finding applications in an ever-increasing number of fields, so the possibility of developing an organocatalytic approach has gained much attention.
During my work, the enantioselective organocatalytic reduction of fluorinated ketimines was successfully realized by using trichlorosilane as reducing agent in the presence of catalytic amounts of an inexpensive and readily available picolinamide derived from ephedrine. The methodology allowed to reduce imines derived both from aryl and alkyl trifluoromethyl ketones in very good yields and high enantioselectivities, typically of 90% e.e. and up to 98% e.e.. With a ACE (Asymmetric Catalyst Efficiency) value of about 44, the ephedrine-derived picolinamidic catalyst established itself as one of the most efficient and versatile catalyst for the reduction of a wide range of fluorinated imines, favourably comparing both with chiral phosphoric acids and even with organometallic catalysts. The well documented possibility to easily remove the N-PMP residue or the benzyl group makes the present method a viable and attractive synthesis also for highly enantiomerically enriched fluorinated primary amines.
Moreover, the straight forward synthesis of a novel class of cinchona-based chiral Lewis bases was developed. A series of enantiomerically pure Lewis bases were obtained by performing a Mitsunobu reaction on the commercially available alkaloids followed by simple condensation with picolinic acid. Under the optimized reaction conditions, such compounds were shown to promote the enantioselective reduction of ketimines with trichlorosilane with nearly quantitative chemical yield and high enantioselectivity. Even more interestingly, these high levels of yields and enantioselectivity remained constant when the reaction was carried out with only a 1 mol % catalyst loading. Further modification of these compounds allowed to raise the enantioselectivity of the process, leading to the quantitative formation of the corresponding amine with up to 88% e.e..
These catalyst were successfully employed also in the organocatalytic reduction of alpha-imino and beta-enamino esters with trichlorosilane, obtaining the corresponding products with high chemical yield and good enantiomeric excess. Moreover, the combination of this low cost, easy to make metal-free catalyst and an inexpensive chiral auxiliary allowed to obtain chiral beta-amino esters with nearly total control of the stereoselectivity.
In the field of catalytic methods for carbon nitrogen double bond reduction, I’ve also studied a very novel catalytic approach to realize the activation and utilization of H2: the concept of frustrated Lewis pair (FLP) recently introduced by the Stephan’s research group. Once performed a screening of several additives to find an efficient catalytic pair, the FLP catalyzed diastereoselective hydrogenation of a chiral ketimine was accomplished with 67% yield and 82:18 d.r. without the necessity to perform the reaction in glovebox.
Finally, taking into account the excellent enantioselectivities obtained in the reduction of C-N double-bonds with phosphoric acid catalysis, we decided to explore the performance of these systems employing HSiCl3 as reducing agent. After an optimization of the stoichiometry of the reaction, we were able to achieve up to 29% e.e. using 10 mol % unsubstituted BINOL-derived phosphoric acid, which could be raised up to 60% e.e. using a stoichiometric amount of the acid
X-ray Constrained Spin-Coupled Wavefunction: a New Tool to Extract Chemical Information from X-ray Diffraction Data
No full textThe X-ray constrained wavefunction (XCW) approach is a reliable and widely used method of quantum crystallography that allows the determination of wavefunctions compatible with X-ray diffraction data. So far, all the existing XCW techniques have been developed in the framework of molecular orbital theory and, consequently, provide only pictures of the “experimental” electronic structures that are far from the traditional chemical perception. Here a new strategy is proposed that, by combining the XCW philosophy with the spin-coupled method of valence bond theory, enables direct extraction of traditional chemical information (e.g., weights of resonance structures) from X-ray diffraction measurements. Preliminary results have shown that the new technique is really able to efficiently capture the effects of the crystal environment on the electronic structure, and can be considered as a new useful tool to perform chemically sound analyses of the X-ray diffraction data
Entanglement-assisted, noise-assisted, and monitoring-enhanced quantum bath tagging
No full textWe analyze the capability of discriminating the statistical nature of a thermal bath in the presence of three different types of side resources: prior entanglement between the probing system and an external (dynamically neutral) memory element, the interaction between the probe and an auxiliary bath, and the continuous monitoring of the system mediated by real-time measurements of the auxiliary bath. We discuss in detail how to obtain improved performances in the discrimination by considering different kinds of interactions, i.e., different jump operators, and different monitoring strategies corresponding to continuous homodyne detection and photodetection. We find that the presence of the auxiliary environment can be beneficial, allowing bath discrimination in regimes where in the standard scenario discrimination is not possible. We then show how additionally monitoring this environment, via either continuous homodyne detection or photodetection, is naturally advantageous for quantum bath tagging, in particular in the long-time limit where a large improvement in the discrimination performance is indeed observed. Our approach can in principle be implemented in a circuit QED setup and paves the way to further developments of quantum probing via continuous monitoring
Continuous-variable phase estimation with unitary and random linear disturbance
No full textWe address the problem of continuous-variable quantum phase estimation in the presence of linear disturbance at the Hamiltonian level by means of Gaussian probe states. In particular we discuss both unitary and random disturbance by considering the parameter which characterizes the unwanted linear term present in the Hamiltonian as fixed (unitary disturbance) or random with a given probability distribution (random disturbance). We derive the optimal input Gaussian states at fixed energy, maximizing the quantum Fisher information over the squeezing angle and the squeezing energy fraction, and we discuss the scaling of the quantum Fisher information in terms of the output number of photons, nout. We observe that, in the case of unitary disturbance, the optimal state is a squeezed vacuum state and the quadratic scaling is conserved. As regards the random disturbance, we observe that the optimal squeezing fraction may not be equal to one and, for any nonzero value of the noise parameter, the quantum Fisher information scales linearly with the average number of photons. Finally, we discuss the performance of homodyne measurement by comparing the achievable precision with the ultimate limit imposed by the quantum Cramér-Rao bound
3D 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
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