Electrical conduction of silicon oxide containing silicon quantum dots

Current-voltage measurements have been made at room temperature on a Si-rich silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$^\circ$C. The thickness of oxide between Si quantum dots embedded in the film increases with the increase of annealing temperature. This leads to the decrease of current density as the annealing temperature is increased. Assuming the Fowler-Nordheim tunneling mechanism in large electric fields, we obtain an effective barrier height $\phi_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling through an oxide layer between Si quantum dots. The Frenkel-Poole effect can also be used to adequately explain the electrical conduction of the film under the influence of large electric fields. We suggest that at room temperature Si quantum dots can be regarded as traps that capture and emit electrons by means of tunneling.Comment: 14 pages, 5 figures, submitted to J. Phys. Conden. Mat

A multiscale model to predict current absolute risk of femoral fracture in a postmenopausal population

Osteoporotic hip fractures are a major healthcare problem. Fall severity and bone strength are important risk factors of hip fracture. This study aims to obtain a mechanistic explanation for fracture risk in dependence of these risk factors. A novel modelling approach is developed that combines models at different scales to overcome the challenge of a large space–time domain of interest and considers the variability of impact forces between potential falls in a subject. The multiscale model and its component models are verified with respect to numerical approximations made therein, the propagation of measurement uncertainties of model inputs is quantified, and model predictions are validated against experimental and clinical data. The main results are model predicted absolute risk of current fracture (ARF0) that ranged from 1.93 to 81.6% (median 36.1%) for subjects in a retrospective cohort of 98 postmenopausal British women (49 fracture cases and 49 controls); ARF0 was computed up to a precision of 1.92 percentage points (pp) due to numerical approximations made in the model; ARF0 possessed an uncertainty of 4.00 pp due to uncertainties in measuring model inputs; ARF0 classified observed fracture status in the above cohort with AUC = 0.852 (95% CI 0.753–0.918), 77.6% specificity (95% CI 63.4–86.5%) and 81.6% sensitivity (95% CI 68.3–91.1%). These results demonstrate that ARF0 can be computed using the model with sufficient precision to distinguish between subjects and that the novel mechanism of fracture risk determination based on fall dynamics, hip impact and bone strength can be considered validated

Characterization of the highly divergent U2 RNA homolog in the microsporidian Vairimorpha necatrix.

An RNA homologous to U2 RNA and a single copy gene encoding the RNA homolog have been characterized in the microsporidian, Vairimorpha necatrix. The RNA which is 165 nucleotides in length possesses significant similarity to U2 RNA, particularly in the 5' half of the molecule. The U2 homolog contains the highly conserved GUAGUA branch point binding sequence seen in all U2 RNAs except those of the trypanosomes. A U2 RNA sequence element implicated in a U2:U6 RNA intermolecular pairing is also present in the U2 homolog. The V. necatrix U2 RNA homolog differs at positions previously found to be invariant in U2 RNAs and appears to lack an Sm binding site sequence. The RNA can be folded into a secondary structure possessing three of the four principal stem-loops proposed for the consensus U2 RNA structure. A cis-diol containing cap structure is present at the 5' end of the U2 homolog. Unlike the cap structures seen in U-snRNAs and mRNAs it is neither 2,2,7-trimethylguanosine, gamma-monomethyl phosphate, nor 7-methylguanosine

Porfiria cutanea tarda in soggetto emodializzato: problematiche diagnostiche e terapeutiche

Presentiamo il caso di una donna di 73 anni, emodializzata, giunta alla nostra osservazione per bolle ed erosioni aflegmasiche, dolorose, localizzate al dorso delle mani e dei piedi, ipertricosi ed iperpigmentazione del volto. Queste ultime due manifestazioni erano comparse qualche mese prima delle bolle. Il quadro clinico appariva piuttosto suggestivo per una forma di porfiria cutanea, ma, la condizione di anuria della paziente non permetteva un rapido dosaggio delle porfirine urinarie. Le porfirine totali plasmatiche tuttavia risultavano elevate, e le porfirine frazionate a livello sia plasmatico che fecale confermavano il sospetto di porfiria cutanea tarda. L'insorgenza di porfiria cutanea tarda è stata descritta nei pazienti dializzati, anche se la sua genesi non è chiara. Un'ipotesi si basa sulla incapacità delle membrane di dialisi comuni di filtrare le porfirine in eccesso legate a proteine plasmatiche. Un'altra ipotesi chiama in causa un' alterata ridistribuzione del ferro dai depositi nei soggetti dializzati con conseguente incremento della sintesi delle porfirine. Particolarmente complesso è risultato il problema terapeutico, in quanto il classico impiego di salassi era controindicato per la persistente anemia. Un lieve miglioramento è stato ottenuto combinando una parziale salassoterapia con l'incremento della somministrazione di eritropoietina, anche se il quadro clinico globale della paziente appare tuttora sconfortante

Preliminary evaluation of a zinc-copper-citric acid biocomplex for the control of Plenodomus tracheiphilus causal agent of citrus mal secco disease

In this study we evaluated a zinc copper-citric acid biocomplex (Dentamet®) for the effect on citrus mal secco disease caused by Plenodomus tracheiphilus. In vitro tests highlighted an inhibitory activity of the compound on mycelial growth and phialoconidia germination. Independent in vivo trials were performed in a growth chamber inoculating a virulent fungal isolate on sour orange seedlings and young plants of two lines of Femminello lemon, namely ‘Zagara bianca’ and ‘2Kr’, grafted on sour orange and grown in pots. The compound was leaf sprayed three days before the inoculation by wounds with phialoconidia. Overall, disease index and disease progress curve in plants inoculated with P. tracheiphilus were reduced to a different extent by single leaf treatment. Additional post-inoculation treatments did not significantly affect the results. Quantification of DNA of P. tracheiphilus in leaf disks at the inoculation sites leads to conclude that the lessening of disease symptoms is not strictly related to a direct effect of the compound on the pathogen, and a host defence stimulation maybe involved