Biomedical subjects

Rubén Pérez

Publications and source records attributed to Rubén Pérez.

7 recordsLinked to original sources

PubMed2006

Single atomic contact adhesion and dissipation in dynamic force microscopy.

By combining dynamic force microscopy experiments and first-principles calculations, we have studied the adhesion associated with a single atomic contact between a nanoasperity--the tip apex--and a semiconductor surface--the Ge(111)-c(2 x 8). The nanoasperity's termination has been atomically characterized by extensive comparisons of the measured short-range force at specific sites with the chemical forces calculated using many atomic models that vary in structure, composition, and relative orientation with respect to the surface. This thorough characterization has allowed us to explain the dissipation signal observed in atomic-resolution images and force spectroscopic measurements, as well as to identify a dissipation channel and the associated atomic processes.

Journal Article↗

PubMed2006

Hydrogen dissociation over Au nanowires and the fractional conductance quantum.

The dissociation of H2 molecules over stretched Au nanowires and its effect on the conductance are analyzed using a combination of density functional theory (DFT) total energy calculations and nonequilibrium Keldysh-Green function methods. Our DFT simulations reproduce the characteristic formation of Au monatomic chains with a conductance close to G0=2e2/h. These stretched Au nanowires are shown to be better catalysts for dissociation than Au surfaces. This is confirmed by the nanowire conductance evidence: while insensitive to molecular hydrogen, atomic hydrogen induces the appearance of fractional conductances (G approximately 0.5G0) as observed experimentally.

Journal Article↗

PubMed2005

Gastrointestinal parasitism reduces the plasma availability of doramectin in lambs.

A study was undertaken to investigate the effect of parasitism on plasma availability and pharmacokinetic behaviour of doramectin (DRM) in lambs. Fourteen parasitised grey face Suffolk lambs (26.9 +/- 1.5 kg bodyweight) were selected for the study. Seven pairs of lambs were allocated to two groups to obtain an approximately even weight distribution. Group I (non-parasitised) was pre-treated with three repeated administrations of 5 mg/kg fenbendazole to maintain a parasite free condition. In group II (parasitised), the lambs did not receive any anthelmintic treatment. After the 85-day pre-treatment period, both groups of animals were treated with DRM by subcutaneous (SC) injection in the shoulder area at 200 microg/kg. Throughout the experimental period, both groups were maintained together under similar feeding and management conditions. Blood samples were collected by jugular venepuncture at different set times between 0.5 h and 60 days post-treatment. After plasma extraction and derivatisation, samples were analysed by high performance liquid chromatography (HPLC) with fluorescence detection. A computerised kinetic analysis was performed and the data were compared using the Student's paired t test. The parent molecule was detected in plasma between 30 min and either day 20 (parasitised) or day 35 (non-parasitised) post-DRM treatment. The AUC values of the parasitised group (143.0 +/- 18 ng d/mL) were significantly lower (P<0.05) than those observed in the parasitically naïve animals (229.6 +/- 21.7 ng d/mL). The mean residence time (MRT) in the parasitised group (3.4 +/- 0.3 days) was significantly shorter (P<0.05) than in the healthy group (6.6 +/- 0.6 days). Study results have shown that parasitic disease, through alteration in the body condition, can produce significant changes in the plasma disposition of DRM when administered SC to parasitised lambs.

Animals↗

PubMed2005

Nanomanipulation using only mechanical energy.

We present the first computational study targeting the nanomanipulation capability of dynamic surface force microscopy. Using a very simple but challenging model, an antisite defect on a III-V(110) surface, we show how the defect can be manipulated in both the attractive and the repulsive modes and identify the role of the tip-sample interaction: either lowering the barriers or pushing the system over a high stress state using exclusively the mechanical energy stored in the oscillating cantilever. Our study also sheds light on other key issues, such as chemical resolution, explaining why vacancies are the only defects imaged in topography, and dissipation contrast formation, identifying a physical mechanism to explain the intriguing small shift between topographical and damping images.

Journal Article↗

PubMed2005

Intrinsic character of the (3 x 3) to (square root 3 x square root 3) phase transition in Pb/Si(111).

We have investigated the (3 x 3) to (square root 3 x square root 3) reversible phase transition in Pb/Si(111) by means of variable temperature scanning tunneling microscopy and density functional first-principles calculations. By tracking exactly the same regions of the surface with atomic resolution in a temperature range between 40 and 200 K, we have observed the phase transition in real time. The ability to prepare and track exceptionally large domains without defects has allowed us to detect the intrinsic character of the phase transition at temperatures around 86 K. This intrinsic character is in full agreement with our first-principles calculations. Moreover, our results show that the hypothesis that point defects play a fundamental role as the driving force, reported for similar systems, can be discarded for Pb/Si(111).

Journal Article↗

PubMed2004

Quantification of Enterococcus faecalis and Enterococcus faecium in different foods using rRNA-targeted oligonucleotide probes.

The abundance of Enterococcus faecalis and Enterococcus faecium in different Spanish foods was evaluated by using taxon-specific oligonucleotide probes targeted against extracted rRNA. Two satisfactory methods were developed for RNA extraction. Although the yield and purity of total RNA obtained largely depended on the type of food, method 1 should be recommended. The quantitative results obtained with the oligonucleotide probes DB6 for E. faecium and DB8 for E. faecalis showed that these two species accounted for less than 0.5% of the active microflora in all the food samples tested. These results suggest that enterococci form only a minor portion of the microflora of these products.

Animals↗

PubMed2003

Covalent and reversible short-range electrostatic imaging in noncontact atomic force microscopy.

We present a computational study of atomic-scale image formation in noncontact atomic force microscopy on metallic surfaces. We find two imaging scenarios: (1). atomic resolution arising due to very strong covalent tip-sample interaction exhibiting striking similarity with the imaging mechanism found on semiconductor surfaces, and (2). a completely new mechanism, reversible short-range electrostatic imaging, arising due to subtle charge-transfer interactions. Contrary to the strong covalent-bond imaging, the newly identified mechanism causes only negligible surface perturbation and can account for results recently observed experimentally.

Journal Article↗