Molecular-dynamics study of collision, implantation, and fragmentation of Ag7 on Pd(100)

By using embedded-atom-method interatomic potentials and molecular-dynamics simulations, we study the collision of a single Ag/sub 7/ cluster on the Pd(100) substrate, at impact energies in the direction perpendicular to the (100) surface E/sub 1/=20 eV (2.86 eV/atom) and E/sub 2/=95 eV (13.6 eV/atom). Our results indicate that implantation occurs at both impact energies, but it is more important at E/sub 2/. As opposed to what is shown experimentally, little fragmentation takes place for E/sub 1/, while the calculated cluster fragmentation is in good agreement with the experimental data for E/sub 2/

Thalamocortical bistable switch as a theoretical model of fibromyalgia pathogenesis inferred from a literature survey

Fibromyalgia (FM) is an unsolved central pain processing disturbance. We aim to provide a unifying model for FM pathogenesis based on a loop network involving thalamocortical regions, i.e., the ventroposterior lateral thalamus (VPL), the somatosensory cortex (SC), and the thalamic reticular nucleus (TRN). The dynamics of the loop have been described by three differential equations having neuron mean firing rates as variables and containing Hill functions to model mutual interactions among the loop elements. A computational analysis conducted with MATLAB has shown a transition from monostability to bistability of the loop behavior for a weakening of GABAergic transmission between TRN and VPL. This involves the appearance of a high-firing-rate steady state, which becomes dominant and is assumed to represent pathogenic pain processing giving rise to chronic pain. Our model is consistent with a bulk of literature evidence, such as neuroimaging and pharmacological data collected on FM patients, and with correlations between FM and immunoendocrine conditions, such as stress, perimenopause, chronic inflammation, obesity, and chronic dizziness. The model suggests that critical targets for FM treatment are to be found among immunoendocrine pathways leading to GABA/glutamate imbalance having an impact on the thalamocortical system

Human kallikrein gene 5 (KLK5) expression is an indicator of poor prognosis in ovarian cancer

Kallikrein gene 5 (KLK5, also known as KLK-L2), located on chromosome 19q13.4, is one of the newly identified members of the kallikrein gene family, which is a subgroup of the serine protease enzyme family. In normal human tissues, KLK5 is highly expressed in skin, mammary gland and testis. Preliminary RT-PCR analysis has indicated that KLK5 is expressed in a subset of ovarian tumours. We have thus hypothesized that KLK5 may be a new prognostic indicator in ovarian cancer. We have examined the mRNA expression of KLK5 in 142 malignant ovarian tissues. Tumours were pulverized, total RNA was extracted, and cDNA was prepared by reverse transcription. KLK5 was amplified by PCR using gene specific primers, and the identity of the PCR product was verified by sequencing. Ovarian tissues were then classified as KLK5 positive or negative, based on ethidium bromide staining of the PCR product on agarose gels. KLK5 was found to be highly expressed in 58/142 (41%) of ovarian cancer samples while its level of expression was very low in normal ovarian tissues. We found a strong positive relation between KLK5 expression and tumour grade (P = 0.006) and disease stage (P = 0.027). Univariate survival analysis revealed that patients with ovarian tumours positive for KLK5 expression had an increased risk for relapse and death (P = 0.018 and 0.022, respectively). In multivariate analysis, KLK5 expression showed independent prognostic value only in the subset of tumours with lower grade disease (grades I and II). We conclude that KLK5 expression is associated with more aggressive forms of epithelial ovarian carcinoma and has indepdent prognostic value in low grade tumours. © 2001 Cancer Research Campaign http://www.bjcancer.co

Heart and Lungs in COPD. Close friends in real life - separate in daily medical practice?

Chronic obstructive pulmonary disease (COPD) is associated with a 2-3 times higher rate of cardiovascular disorders (CVD) which is independent of other risk factors. A low FEV1 is a specific predictor of mortality as a result of cardiac causes, even stronger than increased cholesterol: for each 10% reduction of FEV1, cardiovascular mortality increases by 28%. The main causes of death among COPD patients are of cardiovascular origin. COPD and CVD have two major risk factors in common - advanced age and tobacco smoking. The search for a pathogenetic link between the two conditions focuses mainly on systemic extension of pulmonary inflammation. Despite such a frequent association, pulmonologists and cardiologists in both the clinical and the research settings often underestimate the importance of a correct diagnosis and severity stratification of the two combined conditions. Spirometry, in particular, is largely underprescribed. Missed diagnosis and severity stratification, incomplete knowledge of adverse drug events and lack of resources lead to undertreatment of patients combining COPD and CVD, and in particular, the underuse of beta-blockers, inhaled bronchodilators and rehabilitation. Clinical studies focusing on this group of patients should be promoted in the future to test therapies and manage options. Furthermore, efforts must be made to improve the present standards of care, which falls short of recommended levels, starting from the often-neglected use of spirometry to confirm a diagnosis of COPD

Supercell technique for total-energy calculations of finite charged and polar systems

We study the behavior of total-energy supercell calculations for dipolar molecules and charged clusters. Using a cutoff Coulomb interaction within the framework of a plane-wave basis set formalism, with all other aspects of the method (pseudopotentials, basis set, exchange-correlation functional) unchanged, we are able to assess directly the interaction effects present in the supercell technique. We find that the supercell method gives structures and energies in almost total agreement with the results of calculations for finite systems, even for molecules with large dipole moments. We also show that the performance of finite-grid calculations can be improved by allowing a degree of aliasing in the Hartree energy, and by using a reciprocal space definition of the cutoff Coulomb interaction

Morphology and evolution of size-selected metallic clusters deposited on a metal surface: Ag19+ / Pd(100)

We study size-selected deposition of Ag/sub 19//sup +/ clusters on Pd(100) at total kinetic energies of 20 and 95 eV using thermal energy atom scattering and molecular-dynamics simulations. Contrary to the case of Ag/sub 7/ where fragmentation is crucial to explain the data, the deposition leads at low temperature to noncompact structures localized around the impact point. We propose a model in which morphology changes take place between 200 and 300 K resulting in well-separated compact structures

Physical Origin of the Boson Peak Deduced from a Two-Order-Parameter Model of Liquid

We propose that the boson peak originates from the (quasi-) localized vibrational modes associated with long-lived locally favored structures, which are intrinsic to a liquid state and are randomly distributed in a sea of normal-liquid structures. This tells us that the number density of locally favored structures is an important physical factor determining the intensity of the boson peak. In our two-order-parameter model of the liquid-glass transition, the locally favored structures act as impurities disturbing crystallization and thus lead to vitrification. This naturally explains the dependence of the intensity of the boson peak on temperature, pressure, and fragility, and also the close correlation between the boson peak and the first sharp diffraction peak (or prepeak).Comment: 5 pages, 1 figure, An error in the reference (Ref. 7) was correcte

Density functional study of Aun_n (n=2-20) clusters: lowest-energy structures and electronic properties

We have investigated the lowest-energy structures and electronic properties of the Au$_n$(n=2-20) clusters based on density functional theory (DFT) with local density approximation. The small Au$_n$ clusters adopt planar structures up to n=6. Tabular cage structures are preferred in the range of n=10-14 and a structural transition from tabular cage-like structure to compact near-spherical structure is found around n=15. The most stable configurations obtained for Au$_{13}$ and Au$_{19}$ clusters are amorphous instead of icosahedral or fcc-like, while the electronic density of states sensitively depend on the cluster geometry. Dramatic odd-even alternative behaviors are obtained in the relative stability, HOMO-LUMO gaps and ionization potentials of gold clusters. The size evolution of electronic properties is discussed and the theoretical ionization potentials of Au$_n$ clusters compare well with experiments.Comment: 6 pages, 7 figure

Aplicación del modelo hidrológico - Swat - en una microcuenca agrícola de la pampa ondulada

Behrends Kraemer, Filipe. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.Chagas, Celio Ignacio. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.Vázquez Amábile, Gabriel G. Universidad de La Plata. Facultad de Ciencias Agrarias y Forestales. La Plata. Buenos Aires, Argentina.Palacín, Esteban Anselmo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.Santanatoglia, Oscar José. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.Castiglioni, Mario Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.Massobrio, Marcelo Juan. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Manejo y Conservación de Suelos. Buenos Aires, Argentina.75-82El modelado hidrológico es a menudo el primer paso en el desarrollo de sistemas de decisión espacial para identificar áreas vulnerables a la contaminación por nutrientes, pesticidas así como también contaminantes biológicos. En este sentido el SWAT (Soil and Water Assesment Tool) fue desarrollado para predecir impactos de las prácticas de manejo de las tierras en las aguas, sedimentos y agroquímicos en cuencas hidrográficas con diferentes suelos, usos y prácticas en largos períodos de tiempo. Aunque el mismo está siendo aplicado en todo el mundo, todavía no esta difundido su uso en la Argentina, no encontrándose al momento reportes al respecto. Este modelo se utilizó en una microcuenca agrícola de la Pampa Ondulada (Argentina) y fue calibrado y validado utilizando los valores de escurrimientos medidos in situ. Se encontraron buenas eficiencias a escala diaria (R2: 0.55; R2ENS: 0.52) y pobres a escala mensual (R2: 0.34; R2ENS: 0.04). En la calibración, los escurrimientos fueron sobreestimados en un 31.8 por ciento y 32,6 por ciento para la escala mensual y diaria respectivamente, mientras que en la validación se sobreestimó un 42,5 por ciento para los valores mensuales y un 41,2 por ciento para los diarios. La aplicación del SWAT en esta microcuenca agrícola resultó auspiciosa y conduce a la inclusión de dicho modelo en futuros trabajos