Reliability of short-term follow-up for assessing bioprosthetic heart valve performancE

[No abstract available

Ab initio molecular dynamics study of an aqueous NaCl solution under an electric field

We report on an ab initio molecular dynamics study of an aqueous NaCl solution under the effect of static electric fields. We found that at low-to-moderate field intensity regimes chlorine ions have a greater mobility than sodium ions which, being a sort of “structure makers”, are able to drag their own coordination shells. However, for field strengths exceeding 0.15 V Å−1 the mobility of sodium ions overcomes that of chlorine ions as both types of ions do actually escape from their respective hydration cages. The presence of charged particles lowers the water dissociation threshold (i.e., the minimum field strength which induces a transfer of protons) from 0.35 V Å−1 to 0.25 V Å−1; moreover, a protonic current was also recorded at the estimated dissociation threshold of the solution. The behaviour of the current–voltage diagram of the protonic response to the external electric field is Ohmic as in pure water, with a resulting protonic conductivity of about 2.5 S cm−1. This value is approximately one third of that estimated in pure water (7.8 S cm−1), which shows that the partial breaking of hydrogen bonds induced by the solvated ions hinders the migration of protonic defects. Finally, the conductivity of Na+ and Cl− ions (0.2 S cm−1) is in fair agreement with the available experimental data for a solution molarity of 1.7 M

Si nanocrystal-based LEDs fabricated by ion implantation and plasma-enhanced chemical vapour deposition

Dept. ElectrònicaAn in-depth study of the physical and electrical properties of Si-nanocrystal-based MOSLEDs is presented. The active layers were fabricated with different concentrations of Si by both ion implantation and plasma-enhanced chemical vapour deposition. Devices fabricated by ion implantation exhibit a combination of direct current and field-effect luminescence under a bipolar pulsed excitation. The onset of the emission decreases with the Si excess from 6 to 3 V. The direct current emission is attributed to impact ionization and is associated with the reasonably high current levels observed in current–voltage measurements. This behaviour is in good agreement with transmission electron microscopy images that revealed a continuous and uniform Si nanocrystal distribution. The emission power efficiency is relatively low, ~10−3%, and the emission intensity exhibits fast degradation rates, as revealed from accelerated ageing experiments. Devices fabricated by chemical deposition only exhibit field-effect luminescence, whose onset decreases with the Si excess from 20 to 6 V. The absence of the continuous emission is explained by the observation of a 5 nm region free of nanocrystals, which strongly reduces the direct current through the gate. The main benefit of having this nanocrystal-free region is that tunnelling current flow assisted by nanocrystals is blocked by the SiO2 stack so that power consumption is strongly reduced, which in return increases the device power efficiency up to 0.1%. In addition, the accelerated ageing studies reveal a 50% degradation rate reduction as compared to implanted structures

Neural crest is involved in development of abnormal myocardial function

Around 85% of embryos homozygous for the splotch (Sp(2H)) allele (Sp(2H)/Sp(2H)), a Pax3 mutation, develop persistent truncus arteriosus (PTA), a defect related to the cardiac neural crest. These embryos die by 14.5 days post coitum. In an investigation of the cause of lethality in these embryos, we used digital video imaging microscopy to examine beating embryonic hearts in situ at 13.5 dpc. The hearts of Sp(2H)/Sp(2H) embryos with PTA clearly showed poor function when compared with normal litter mates. Contractile force was examined in detergent-skinned ventricular muscle strips from Sp(2H)/Sp(2H) embryos at ages 12.5 and 13.5 dpc. There was no significant difference in the maximum force or in myosin content between Sp(2H)/Sp(2H) and control groups, indicating no significant dysfunction of the contractile apparatus in hearts from Sp(2H)/Sp(2H) embryos. Ca2+ transients were examined in enzymatically-dissociated ventricular myocytes and were significantly reduced in defective hearts, indicating that reduced cardiac function in Sp(2H)/Sp(2H) embryos with PTA was due to impaired excitation-contraction (EC) coupling. Ca2+ currents were examined using the perforated patch clamp technique. The magnitude of the Ca2+ current was found to be reduced by ≈3.2-fold in Sp(2H)/Sp(2H) hearts with PTA compared to normal. Since the sarcoplasmic reticulum is sparse or absent in the embryonic heart, the impaired EC coupling was due to the reduction in Ca2+ current. These observations suggest that neural crest abnormalities result in a defect in EC coupling, causing depressed myocardial function and death in utero from cardiac failure. Interestingly, Sp(2H)/Sp(2H) hearts without PTA had normal EC coupling. These results indicated that impaired EC coupling was secondary to the Pax3 mutation. The findings in this report indicate an important role for the neural crest in the development of normal myocardial function, and represent the first demonstration of impaired excitation-contraction coupling in a genetically-defined embryonic mammalian model of a cardiac structural defect