Asymmetries in symmetric quantum walks on two-dimensional networks

We study numerically the behavior of continuous-time quantum walks over networks which are topologically equivalent to square lattices. On short time scales, when placing the initial excitation at a corner of the network, we observe a fast, directed transport through the network to the opposite corner. This transport is not ballistic in nature, but rather produced by quantum mechanical interference. In the long time limit, certain walks show an asymmetric limiting probability distribution; this feature depends on the starting site and, remarkably, on the precise size of the network. The limiting probability distributions show patterns which are correlated with the initial condition. This might have consequences for the application of continuous time quantum walk algorithms.Comment: 9 pages, 12 figures, revtex

Quantum transport on two-dimensional regular graphs

We study the quantum-mechanical transport on two-dimensional graphs by means of continuous-time quantum walks and analyse the effect of different boundary conditions (BCs). For periodic BCs in both directions, i.e., for tori, the problem can be treated in a large measure analytically. Some of these results carry over to graphs which obey open boundary conditions (OBCs), such as cylinders or rectangles. Under OBCs the long time transition probabilities (LPs) also display asymmetries for certain graphs, as a function of their particular sizes. Interestingly, these effects do not show up in the marginal distributions, obtained by summing the LPs along one direction.Comment: 22 pages, 11 figure, acceted for publication in J.Phys.

Thermal Conductivity Enhancement of Al2O3 Nanofluid in Ethylene Glycol and Water Mixture

AbstractThe ability of nanofluids that exhibits enhanced thermal performance is acknowledged by researchers through studies since decades ago. However, the observation of thermal properties for nanofluids in water and ethylene glycol based is not fully explored yet. Hence, this paper presents the thermal conductivity of water and ethylene glycol (EG) based Al2O3 nanofluid. The 13 nm sized Al2O3 nanoparticles were dispersed into three different volume ratio of water: EG such as 40:60, 50:50 and 60:40 using a two-step method. The measurement of thermal conductivity was performed using KD2 Pro Thermal Properties Analyzer at working temperatures of 30 to 70 ̊C for volume concentration of 0.5 to 2.0%. The results indicate that the thermal conductivity increases with the increase of nanofluid concentration and temperature. While the percentage of ethylene glycol increase, the range of thermal conductivity decreases due to ethylene glycol properties. The measurement data of the nanofluids give maximum enhancement of thermal conductivity at condition 2.0% volume concentration, temperature of 70 ̊C and for all base fluid

COMBINED USE OF SPACE-BORNE OBSERVATIONS OF NO2 AND REGIONAL CTM MODEL FOR AIR QUALITY MONITORING IN NORTHERN ITALY

The use of space-borne measurements of trace gas constituents for air quality monitoring is considerably increased during the past decade. This is due mainly to the new generation sensors able to observe large areas with good temporal resolution and due to new assimilation techniques that allow a synergetic use of information from satellite and from Chemical Transport Models (CTM). In fact the in situ sampling method used by the local environmental agencies for air quality monitoring is becoming too expensive to be further continued without a sensible reduction in the number of observing stations. In this paper we present the work that has been performed so far within the QUITSAT project funded by the Italian Space Agency. SCIAMACHY (Uv-Vis spectrometer on board ESA-ENVISAT platform from 2002) observations of earth radiance are used to retrieve NO2 tropospheric column by DOAS spectrometric technique and radiative transfer modelling for AMF computation. Such kind of product has been widely used to estimate emissions, to monitor pollution hot spot as well as cross country and intercontinental transport. Within this work we have merged the column measurements of nitrogen dioxide with the simulations of the Transport Chemical Aerosol Model (TCAM) to improve the model output at the ground level. The method used is a weighted rescaling of the model column in the troposphere according to the SCIAMACHY observations where the weights are the measurement errors and the model column variances within the satellite ground-pixel, respectively. The employed data are related to the Northern Italy area. The obtained ground concentrations of NO2 have been compared with in-situ observations performed by the regional environmental agencies. Results show good agreement mainly where well horizontal mixing is present. The ground concentration from SCIAMACHY-TCAM gives an average NO2 amount within the satellite ground-pixel of 30x60 km2 that is important information for air quality assessment on a regional and/or national scale not easy to obtain only with ground-based observations. Our conclusions thus stress also the actual potential role of satellite observations combined with regional CTM models in the context of air quality monitoring, mainly in rural area, where the ground-based observations are missing

The COVID-19 Student Stress Questionnaire: Validation in Spanish university students from health sciences

This study aimed to validate the Spanish version of the COVID-19 Student Stress Questionnaire (CSSQ), a 7-item tool assessing COVID-19-related stressors among university students, namely, Relationships and Academic Life, Isolation, and Fear of Contagion. Participants were 331 Spanish university students. Factor analyses sustained the three factor solution of the original tool. Data also revealed satisfactory convergent and discriminant validity, suitable internal consistency, and significant associations with psychological symptoms, as measured by the Symptom Checklist-90-Revised. The Spanish version of the CSSQ represents a valid tool to be used in clinical settings to timely identify students at high psychological risk and to develop evidence-based interventions during/after the pandemic

Migraine mediates the influence of C677T MTHFR genotypes on ischemic stroke risk with a stroke-subtype effect.

BACKGROUND AND PURPOSE: The objective was to investigate the role of C677T MTHFR polymorphism in migraine pathogenesis and in the migraine-ischemic stroke pathway. METHODS: A first genotype-migraine association study was conducted on 100 patients with migraine with aura (MA), 106 with migraine without aura (MO), and 105 subjects without migraine, which provided evidence in favor of association of the TT677 MTHFR genotype with increased risk of MA compared with both control subjects (OR, 2.48; 95% CI, 1.11 to 5.58) and patients with MO (OR, 2.21; 95% CI, 1.01 to 4.82). Based on these findings, mediational models of the genotype-migraine-stroke pathway were fitted on a group of 106 patients with spontaneous cervical artery dissection, 227 young patients whose ischemic stroke was unrelated to a spontaneous cervical artery dissection (noncervical artery dissection), and 187 control subjects, and a genotype-migraine partial mediation model was selected. RESULTS: Both migraine and the TT genotype were more strongly associated to the subgroup of patients with spontaneous cervical artery dissection (OR, 4.06; 95% CI, 1.63 to 10.02 for MA; OR, 5.45; 95% CI, 3.03 to 9.79 for MO; OR, 2.87; 95% CI, 1.45 to 5.68 for TT genotype) than to the subgroup of patients with noncervical artery dissection ischemic stroke (OR, 2.22; 95% CI, 1.00 to 4.96 for MA; OR, 1.81; 95% CI, 1.02 to 3.22 for TT genotype) as compared with controls. CONCLUSIONS: Migraine may act as mediator in the methylenetetrahydrofolate reductase-ischemic stroke pathway with a more prominent effect in the subgroup of patients with spontaneous artery dissection