1,813 research outputs found
Elastic precession of electronic spin states in interacting integer quantum Hall edge channels
We consider the effect of Coulomb interactions in the propagation of
electrons, prepared in arbitrary spin states, on chiral edge channels in the
integer quantum Hall regime. Electrons are injected and detected at the same
energy at different locations of the Hall bar, which is modeled as a chiral
Tomonaga-Luttinger liquid. The current is computed perturbatively in the
tunneling amplitudes, within a non-crossing approximation using exact solutions
of the interacting Green's functions. In the case of different channel
velocities, the spin precession effect is evaluated, and the role of
interaction parameters and wavevectors is discussed.Comment: 5 pages, 3 figure
Edge channel mixing induced by potential steps in an integer quantum Hall system
We investigate the coherent mixing of co-propagating edge channels in a
quantum Hall bar produced by step potentials. In the case of two edge channels
it is found that, although a single step induces only a few percent mixing, a
series of steps could yield 50% mixing. In addition, a strong mixing is found
when the potential height of a single step allows a different number of edge
channels on the two sides of the step. Charge density probability has been also
calculated even for the case where the step is smoothened.Comment: final version: 7 pages, 6 figure
Action minimizing orbits in the n-body problem with simple choreography constraint
In 1999 Chenciner and Montgomery found a remarkably simple choreographic
motion for the planar 3-body problem (see \cite{CM}). In this solution 3 equal
masses travel on a eight shaped planar curve; this orbit is obtained minimizing
the action integral on the set of simple planar choreographies with some
special symmetry constraints. In this work our aim is to study the problem of
masses moving in \RR^d under an attractive force generated by a potential
of the kind , , with the only constraint to be a simple
choreography: if are the orbits then we impose the
existence of x \in H^1_{2 \pi}(\RR,\RR^d) such that q_i(t)=x(t+(i-1) \tau),
i=1,...,n, t \in \RR, where . In this setting, we first
prove that for every d,n \in \NN and , the lagrangian action
attains its absolute minimum on the planar circle. Next we deal with the
problem in a rotating frame and we show a reacher phenomenology: indeed while
for some values of the angular velocity minimizers are still circles, for
others the minima of the action are not anymore rigid motions.Comment: 24 pages; 4 figures; submitted to Nonlinearit
Oral health and depressive symptoms: findings from the English Longitudinal Study of Ageing
Aim We assessed the cross-sectional association between depressive symptoms and oral health using a nationally representative sample of older adults aged 50 years and older living in England.Methods Data came from wave 7 (2014-2015) of the English Longitudinal Study of Ageing. Multiple logistic regression analyses were conducted to assess the association between depressive symptoms, measured through the eight-item Centre for Epidemiologic Studies Depression Scale and three oral health outcomes, namely self-rated oral health, edentulousness and oral impacts.Results The analytical sample comprised 3,617 individuals. The proportion of participants that reported poor self-rated oral health, being edentate and having at least one oral health impact in the last six months was 19.8%, 7.7% and 8.9%, respectively. Around a tenth of the participants reported having depressive symptoms (10%). All unadjusted associations between depressive symptoms and the oral health measures were statistically significant. However, after accounting for potential confounders, only the relationship between depressive symptoms and self-rated oral health remained significant (OR = 1.38; 95% CI 1.01-1.89). Socioeconomic and general health-related variables appeared to influence the associations between depressive symptoms and oral health, particularly edentulousness and oral impacts.Conclusion Depressive symptoms were associated with poor self-rated oral health in older English adults
Adjunctive therapy with vitamin c and thiamine in patients treated with steroids for refractory septic shock: A propensity matched before-after, case-control study
Purpose: Triple therapy with steroids, vitamin C and thiamine has been recently proposed as a safe and beneficial in patients with sepsis. In 2017, we added the use of intravenous vitamin C and thiamine in septic shock patients receiving low dose hydrocortisone because poorly responsive to vasopressors. Aim of this study is to verify whether triple therapy rather than steroids alone can improve outcome in patients with refractory shock. Materials and methods: In this before-after retrospective analysis, we compared septic shock patients admitted to our intensive care unit (ICU) who received triple therapy from June 2017 to November 2019 to septic shock patients who received only hydrocortisone from January 2015 to June 2017. Patients of the two study periods were matched 1:1 using a propensity score model. Results: A final cohort of 56 patients treated with triple therapy were matched to 56 patients treated only with steroids. Triple therapy reduced the length of mechanical ventilation (p = 0,01) and showed a trend in lowering the 30-day and hospital mortality compared to therapy with only hydrocortisone. Conclusions: Although with significant limitations, our experience indicated that triple therapy seems to provide an improvement of clinical outcomes in patients with refractory septic shock
DTI Parameter Optimisation for Acquisition at 1.5T: SNR Analysis and Clinical Application
Background. Magnetic Resonance (MR) diffusion
tensor imaging (DTI) is able to quantify in vivo tissue
microstructure properties and to detect disease related pathology
of the central nervous system. Nevertheless, DTI is limited by low
spatial resolution associated with its low signal-to-noise-ratio
(SNR). Aim. The aim is to select a DTI sequence
for brain clinical studies, optimizing SNR and resolution.
Methods and Results. We applied 6 methods for SNR
computation in 26 DTI sequences with different parameters using 4
healthy volunteers (HV). We choosed two DTI sequences for their
high SNR, they differed by voxel size and b-value. Subsequently,
the two selected sequences were acquired from 30 multiple
sclerosis (MS) patients with different disability and lesion load
and 18 age matched HV. We observed high concordance between mean
diffusivity (MD) and fractional anysotropy (FA), nonetheless the
DTI sequence with smaller voxel size displayed a better
correlation with disease progression, despite a slightly lower
SNR. The reliability of corpus callosum (CC) fiber tracking with
the chosen DTI sequences was also tested.
Conclusions. The sensitivity of DTI-derived
indices to MS-related tissue abnormalities indicates that the
optimized sequence may be a powerful tool in studies aimed at
monitoring the disease course and severity
Symbolic dynamics for the -centre problem at negative energies
We consider the planar -centre problem, with homogeneous potentials of
degree -\a<0, \a \in [1,2). We prove the existence of infinitely many
collisions-free periodic solutions with negative and small energy, for any
distribution of the centres inside a compact set. The proof is based upon
topological, variational and geometric arguments. The existence result allows
to characterize the associated dynamical system with a symbolic dynamics, where
the symbols are the partitions of the centres in two non-empty sets
An innovative method for the extraction and HPLC analysis of bioactive policosanols from non-psychoactive Cannabis sativa L.
Policosanols (PCs) refer to a mixture of long-chain aliphatic alcohols. Sugar cane is the main industrial source of PCs, but others, including beeswax and Cannabis sativa L., are also known. In the raw material PCs are bonded to fatty acids to form long-chain esters, known as waxes. PCs are mainly used as a cholesterol-lowering product, even though their efficacy is controversial. More recently, the pharmacological interest in PCs has increased, as they have been investigated as antioxidant, anti-inflammatory and anti-proliferative agents. Given their promising biological implications, the development of efficient extraction and analytical methodologies for the determination of PCs is extremely important to identify new potential sources of these compounds and to ensure the reproducibility of biological data. Conventional techniques used for the extraction of PCs involve time-consuming approaches leading to low yields, while analytical methods for their quantification are based on gas-chromatographic (GC) techniques, which require an additional derivatization step during the sample preparation to increase their volatility. In the light of all the above, this work was aimed at the development of an innovative method for the extraction of PCs from non-psychoactive C. sativa (hemp) inflorescences, taking advantage of the microwave-assisted technology. In addition, a new analytical method based on high-performance liquid chromatography (HPLC) coupled with an evaporative light scattering detector (ELSD) was developed for the first time for both the qualitative and quantitative analysis of these compounds in the extracts. The method was validated according to ICH guidelines, and it was applied to the analysis of PCs in hemp inflorescences belonging to different varieties. The results were analyzed using Principal Component Analysis (PCA) and hierarchical clustering analysis to rapidly identify samples with the highest content of PCs, which might find an application as alternative sources of these bioactive compounds in both the pharmaceutical and nutraceutical fields
Limits on the low energy antinucleon-nucleus annihilations from the Heisenberg principle
We show that the quantum uncertainty principle puts some limits on the
effectiveness of the antinucleon-nucleus annihilation at very low energies.
This is caused by the fact that the realization a very effective short-distance
reaction process implies information on the relative distance of the reacting
particles. Some quantitative predictions are possible on this ground, including
the approximate A-independence of antinucleon-nucleus annihilation rates.Comment: 10 pages, no figure
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