Water-mediated height artifacts in dynamic atomic force microscopy.

Amplitude modulation atomic force microscopy is one of the most broadly used techniques for the nanoscale characterization of a large variety of surfaces because it can routinely provide topography images with nanometer and subnanometer resolution in air, i.e. under ambient conditions, using available commercial instruments. The topographic map results from the convolution of the different interactions (van der Waals, capillary, adhesion, etc.) sensed by the probe and the presence of nanometer-thick water films on both the surface and the tip of the probe, as is usually the case under ambient conditions, can lead to apparent heights markedly different from the real heights due to formation and rupture of water menisci, particularly when the surfaces exhibit regions with different affinity to water (hydrophilic and hydrophobic). In order to systematically explore such a well-known but usually ignored phenomenon, we have performed a combined experimental and theoretical study using (hydrophobic) self-assembled monolayers of stearic acid grown on (hydrophilic) freshly cleaved mica surfaces and a simplified point mass on a spring model to simulate the tip dynamics. We show that, depending on the operation parameters (free oscillation amplitude and setpoint), the apparent heights can vary in magnitude and sign (contrast inversion) and, most important, that the true height cannot be measured in the presence of water layers when surface affinity to water is not homogeneous even if menisci are not formed. We suggest to revise, within the perspective of the present investigation, those published works where the determination of heights is critical.

Dipolar origin of water etching of amino acid surfaces.

The etching induced by water on hydrophobic (001) surfaces of enantiomeric L-, D- and racemic DL-valine crystals has been characterized by means of atomic force microscopy (AFM) at ambient conditions. Well-defined chiral parallelepipedic shallow patterns, one bilayer deep, are observed for the enantiomeric crystals with sides (steps) oriented along low index crystallographic directions. Hence, chirality can be readily identified by visual inspection of an AFM image after etching. The formation of such regular patterns can be rationalized using basic concepts of electrical dipolar interactions. The key factor that determines the relative etching rate for each step and thus defines the shape of the etching patterns is the orientation of the molecular dipoles with respect to the step edge. The simplicity of the approach allows the prediction of the effect of water etching on other amino acid crystals as well as the effect of the interaction of water with amino acid molecules forming part of more complex structures.

Strong water-mediated friction asymmetry and surface dynamics of zwitterionic solids at ambient conditions: L-alanine as a case study.

Water molecules strongly interact with freshly cleaved (011) surfaces of L-alanine single crystals at low relative humidity (below 10%) promoting diffusion of L-alanine molecules. Species mobility is enhanced above ~40% leading to the formation of two-dimensional islands with long-range order through Ostwald ripening. Scanning force microscopy experiments reveal that both, islands and terraces, are identical in nature (composition and crystallographic structure) but a relevant friction asymmetry appearing upon water-surface interaction evidences that orientation dependent properties exist between them at the molecular level. We interpret this observation as due to water incorporation in the topmost surface crystal structure. Eventually, for high humidity values, surface dissolution and roughening occur.

Paediatric nasal irrigation: The "fencing" method.

Nasal irrigation is a grade A recommendation treatment, which is essential in many pathological conditions. Very heterogeneous practices are observed in paediatrics as a result of poor instruction in this technique. We propose to describe the nasal irrigation technique developed by a team of respiratory physiotherapists in Lille for the management of cystic fibrosis and bronchiolitis. This technique is intended for children over the age of 6 months, as it requires an oral breathing reflex and cough reflex that are not systematically acquired before this age. Nasal irrigation is performed on a 30° upward inclined plane on a calm and cooperative child, away from meals. The child is maintained gently, without pressure, in the fencing position with the head turned away from the practitioner. Using a continuous flow spray, the practitioner grasps the top of the upper nostril and irrigates the nostril for an average of 3 s (6mL per nostril). These steps are then repeated until satisfactory patency is achieved in both nostrils. This technique constitutes a practical tool to help healthcare professionals and parents perform nasal irrigation in young children over the age of 6 months.

Two-dimensional wetting: the role of atomic steps on the nucleation of thin water films on BaF2(111) at ambient conditions.

The interaction of water with freshly cleaved BaF(2)(111) surfaces at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes. The images strongly suggest a high surface diffusion of water molecules on the surface indicated by the accumulation of water at step edges forming two-dimensional bilayered structures. Steps running along the 110 crystallographic directions show a high degree of hydrophilicity, as evidenced by small step-film contact angles, while steps running along other directions exhibiting a higher degree of kinks surprisingly behave in a quite opposite way. Our results prove that morphological defects such as steps can be crucial in improving two-dimensional monolayer wetting and stabilization of multilayer grown on surfaces that show good lattice mismatch with hexagonal ice.

Amphiphillic organic crystals.

The amphiphillic character, that is, the capacity to simultaneously attract and repel water, has been traditionally reserved to organic molecules such as phospholipids and surfactants, containing both hydrophilic and hydrophobic groups within the same molecule. However, this general concept can be extended to artificial structures such as micrometer-sized particles, the so-called Janus particles, and patterned surfaces. Here we provide an example of an amphiphillic crystalline solid, l-alanine, by combining atomic force microscopy measurements performed on two different cleavage surfaces showing contrasting behaviors when exposed to water vapor, with computer simulations that allow us to clarify the dipolar origin of this behavior. Although we take l-alanine as an example, our results should apply quite generally to dipolar molecular crystals.

Influence of the macroscopic shape of the tip on the contrast in scanning polarization force microscopy images.

We demonstrate that a quantitative analysis of the contrast obtained in electrostatic force microscopy images that probe the dielectric response of the sample (scanning polarization force microscopy (SPFM)) requires numerical simulations that take into account both the macroscopic shape of the tip and the nanoscopic tip apex. To simulate the SPFM contrast, we have used the generalized image charge method (GICM), which is able to accurately deal with distances between a few nanometers and several microns, thus involving more than three orders of magnitude. Our numerical simulations show that the macroscopic shape of the tip accounts for most of the SPFM contrast. Moreover, we find a quasi-linear relation between the working tip-sample distance and the contrast for tip radii between 50 and 200 nm. Our calculations are compared with experimental measurements of the contrast between a thermally grown silicon oxide sample and a few-layer graphene film transferred onto it.

Thin water films grown at ambient conditions on BaF(2)(111) studied by scanning polarization force microscopy.

The interaction of water with freshly cleaved BaF(2)(111) surfaces has been studied using scanning force microscopy operated in different modes at room temperature and under controlled humidity. The Kelvin probe microscopy (KPM) mode has been used to study the evolution of the surface potential differences (SPDs). In the 20%-50% relative humidity (RH) range, adsorbed water forms two-dimensional solidlike bilayers (islands). The SPD between water islands and the bare substrate surface exhibits a sign crossover from negative ( approximately -30 mV) at low RHs to positive ( approximately +50 mV) at higher RHs, evidencing a cooperative and irreversible flipping of the preferential orientation of water dipoles, from pointing toward the surface evolving into the opposite direction. The KPM results suggest that the classical hexagonal (I(h)) bilayer configuration is not the most favorable structure.

Substrate Dependence of the Freezing Dynamics of Supercooled Water Films: A High-Speed Optical Microscope Study.

The freezing of supercooled water films on different substrates was investigated using a high-speed camera coupled to an optical microscope, obtaining details of the freezing process not described in the literature before. We observed the two well known freezing stages (fast dendritic growth and slow freezing of the water liquid left after the dendritic growth), but we separated the process into different phenomena that were studied separately: two-dimensional dendrite growth on the substrate interface, vertical dendrite growth, formation and evolution of ice domains, trapping of air bubbles and freezing of the water film surface. We found all of these processes to be dependent on both the supercooling temperature and the substrate used. Ice dendrite (or ice front) growth during the first stage was found to be dependent on thermal properties of the substrate but could not be unequivocally related to them. Finally, for low supercooling, a direct relationship was observed between the morphology of the dendrites formed in the first stage, which depends on the substrate, and the roughness and the shape of the surface of the ice, when freezing of the film was completed. This opens the possibility of using surfaces and coatings to control ice morphology beyond anti-icing properties.

A Model for the Characterization of the Polarizability of Thin Films Independently of the Thickness of the Film.

The dielectric properties of thin films can be modified relative to the bulk material because the interaction between film and substrate influences the mobility of the atoms or molecules in the first layers. Here we show that a strong scale effect occurs in nanometer size octadecylammine thin films. This effect is attributed to the different distribution of molecules depending on the size of the film. To accurately describe this effect, we have developed a model which is a reinterpretation of the linearized Thomas-Fermi approximation. Within this model, we have been able to characterize the polarizability of thin films independently of the thickness of the film.

Induced water condensation and bridge formation by electric fields in atomic force microscopy.

We present an analytical model that explains how, in humid environments, the electric field near a sharp tip enhances the formation of water menisci and bridges between the tip and a sample. The predictions of the model are compared with experimental measurements of the critical distance where the field strength causes bridge formation.

High survival rate in infant acute leukemia treated with early high-dose chemotherapy and stem-cell support. Groupo Español de Trasplante de Médula Osea en Niños.

PURPOSE: Infants with acute leukemia have a poor prognosis when treated with conventional chemotherapy. It is still unknown if stem-cell transplantation (SCT) can improve the outcome of these patients. In the present study, we review our experience with SCT in infant acute leukemia to clarify this issue. PATIENTS AND METHODS: We report the results of 26 infants who were submitted to a SCT for acute leukemia. There were 15 cases of acute myeloid leukemia and 10 cases of acute lymphoid leukemia. One patient had a bilineal leukemia. Twenty-two patients were in their first complete response (CR1), three were in their second CR, and one was in relapse. Eight patients were submitted to allogeneic SCT, and 18 underwent autologous SCT. RESULTS: With a median follow-up of 67 months, the 5-year overall survival and disease-free survival (DFS) are 64% (SE = 9%) and 63% (SE = 10%), respectively. Autologous and allogeneic SCT offered similar outcome. There was not any transplant-related mortality, and all deaths were caused by relapse in the first 6 months after SCT. In multivariate analysis, the single factor associated with better DFS was an interval between CR1 and SCT of less than 4 months (P: <.025). CONCLUSION: SCT is a valid option in the treatment of infant acute leukemia, and it may overcome the high risk of relapse with conventional chemotherapy showing very reduced toxicity. This study suggests that SCT should be performed in CR1 in the early phase of the disease.

Breakage and detachment of an Abrams needle in the pleural cavity during performance of a pleural biopsy.

This is the report of a case of breakage and detachment in the pleural cavity of the tip of a nearly new Abrams needle during performance of a pleural biopsy. We have not found any reference in the literature to similar accidents and do not know what later complications may be produced by the metal body in the pleural cavity. In this case, there have been no complications 12 months after the incident.

Bone marrow transplantation in 46 pediatric patients with non-Hodgkin's lymphoma. Spanish Working Party for Bone Marrow Transplantation in Children.

We report a retrospective analysis on 46 pediatric patients (median age 9 years, range 1-17 years) with non-Hodgkin's lymphoma (NHL), transplanted in six Spanish centers. Fourteen patients underwent allogeneic bone marrow transplantation (BMT) and 32 autologous BMT. Most patients were boys (36 of 46). Twenty one cases were of lymphoblastic lymphoma, 19 Burkitt's lymphoma and six diffuse large cell lymphoma. Maximal Murphy's stage any time before BMT was stage III in 17 cases and stage IV in 29 cases. At BMT, 13 cases were in first CR, 21 in second CR, seven in third CR, four with sensitive active disease and one with refractory disease. All patients transplanted in CRl were considered candidates for BMT because of delayed CR (two cases), failure of the first-line therapy (seven cases) or central nervous system (CNS) or BM infiltration at diagnosis (four cases). Conditioning therapy included TBI in 33 patients and 13 cases were conditioned with chemotherapy alone. Toxic mortality was 13% (three of 14 in the allogeneic BMT group and three of 32 in the autologous group). No toxic deaths were registered in 13 patients undergoing BMT in CR1 (three allogeneic BMT and ten autologous BMT). Twelve patients relapsed 1-7 months after BMT. Overall event-free survival (EFS) was 58% (42-73%; confidence interval (CI) 95%), with a median follow-up of 33 months. EFS was similar for allogeneic BMT and autologous patients. Disease status at BMT was the only predictive factor for EFS (P < 0.01). There were no significant differences between patients in CR1 (82.5%) and CR2 (68%).(ABSTRACT TRUNCATED AT 250 WORDS)

[Giant cells arteritis. A disease previously reported as various syndromes (author's transl)]. / Arteritis de células gigantes. Enfermedad históricamente descrita como distintos síndromes.

Thirteen cases of giant cell arteritis admitted to a Department of Internal Medicine between 1962 and 1977 are reviewed. Giant cell arteritis exhibited different clinical forms, including: temporal arteritis, rheumatic polymyalgia, syndrome of the supra-aortic trunks, cranial arteritis in its ophthalmic and neurologic forms, and generalized arteritis. On the basis of the clinical data, overall examinations, laboratory tests, X-rays, angiograms and histopathologic findings the authors conclude that a single disease is involved. The fact that various of the symptoms occur simultaneously in different patients and that all of the clinical forms have a common pathologic basis points toward giant cell arteritis with different clinical manifestations.

[Incidence of nosocomial infections. Comparison of 2 surveillance systems: clinical vs microbiological follow-up]. / Incidencia de la infección nosocomial. Comparación de dos sistemas de vigilancia: seguimiento clínco frente a seguimiento microbiológico.

The effectiveness of a clinical and a microbiological follow-up systems for the detection of hospital-acquired infection (HI), both independently and simultaneously applied, were prospectively evaluated. The observed incidence rate was 11.4%. The clinical follow-up detected 81.3% of HI while microbiological follow-up detected 59.7%. This difference was statistically significant (p less than 0.001). It took 43 and 45 minutes to detect each instance of HI with the clinical and microbiological methods, respectively. Clinical methods are the most adequate to obtain maximal sensitivity in the overall surveillance of hospital-acquired infection, whereas microbiological follow-up may be useful for the detection of some types of HI such as bacteremia or urinary tract infection.