138 research outputs found
Computational design of chemical nanosensors: Transition metal doped single-walled carbon nanotubes
We present a general approach to the computational design of nanostructured
chemical sensors. The scheme is based on identification and calculation of
microscopic descriptors (design parameters) which are used as input to a
thermodynamic model to obtain the relevant macroscopic properties. In
particular, we consider the functionalization of a (6,6) metallic armchair
single-walled carbon nanotube (SWNT) by nine different 3d transition metal (TM)
atoms occupying three types of vacancies. For six gas molecules (N_{2}, O_{2},
H_{2}O, CO, NH_{3}, H_{2}S) we calculate the binding energy and change in
conductance due to adsorption on each of the 27 TM sites. For a given type of
TM functionalization, this allows us to obtain the equilibrium coverage and
change in conductance as a function of the partial pressure of the "target"
molecule in a background of atmospheric air. Specifically, we show how Ni and
Cu doped metallic (6,6) SWNTs may work as effective multifunctional sensors for
both CO and NH_{3}. In this way, the scheme presented allows one to obtain
macroscopic device characteristics and performance data for nanoscale (in this
case SWNT) based devices.Comment: Chapter 7 in "Chemical Sensors: Simulation and Modeling", Ghenadii
Korotcenkov (ed.), 47 pages, 22 figures, 10 table
Electronic Structure of Low-Dimensional Carbon Î -Systems
X-ray absorption spectroscopy (XAS) is combined with density functional theory (DFT) to determine the orbitals of one- and two-dimensional carbon Ï-systems (lycopene, beta-carotene, retinal, retinol, retinoic acid, coronene, triphenylene). Considerable fine structure is observed for the transition from the C 1s level to the lowest unoccupied molecular orbital (LUMO) and explained by DFT. The wave functions of the one-dimensional chain molecules display the node structure of a vibrating string. The XAS transition energy is decomposed into contributions from the C 1s core level, the Ï* final state, and the electronâhole interaction. For the latter, we develop a simple model that accurately represents a full Î-self-consistent field (ÎSCF) calculation. The distortion of the LUMO because of its interaction with the C 1s hole is investigated. These results illustrate the electronic states of prototypical Ï-bonded carbon structures with low-dimensional character, such as those used in molecular complexes for solar cells, confined graphene structures, and molecular wires
A new mixed-integer programming model for irregular strip packing based on vertical slices with a reproducible survey
The irregular strip-packing problem, also known as nesting or marker making, is defined as the automatic computation of a non-overlapping placement of a set of non-convex polygons onto a rectangular strip of fixed width and unbounded length, such that the strip length is minimized. Nesting methods based on heuristics are a mature technology, and currently, the only practical solution to this problem. However, recent performance gains of the Mixed-Integer Programming (MIP) solvers, together with the known limitations of the heuristics methods, have encouraged the exploration of exact optimization models for nesting during the last decade. Despite the research effort, the current family of exact MIP models for nesting cannot efficiently solve both large problem instances and instances containing polygons with complex geometries. In order to improve the efficiency of the current MIP models, this work introduces a new family of continuous MIP models based on a novel formulation of the NoFit-Polygon Covering Model (NFP-CM), called NFP-CM based on Vertical Slices (NFP-CM-VS). Our new family of MIP models is based on a new convex decomposition of the feasible space of relative placements between pieces into vertical slices, together with a new family of valid inequalities, symmetry breakings, and variable eliminations derived from the former convex decomposition. Our experiments show that our new NFP-CM-VS models outperform the current state-of-the-art MIP models. Finally, we provide a detailed reproducibility protocol and dataset based on our Java software library as supplementary material to allow the exact replication of our models, experiments, and results
Stability and Polaronic Motion of Self-Trapped Holes in Silver Halides:Insight through DFT plus U Calculations
Physical and chemical nature of the scaling relations between adsorption energies of atoms on metal surfaces
Immunohistochemical analysis of Ă3 integrin (CD61): expression in pig tissues and human tumors
CD61 is a membrane glycoprotein that
associates with CD41 (aIIb) to form the heterodimeric
complex gpIIb/IIIa (CD41/CD61), predominantly
expressed in platelets and megakariocytes. CD61 or Ă3
integrin also associates with av (CD51) to form the
vitronectin receptor, which is expressed in many tissues.
We have used a monoclonal antibody against the porcine
gpIIIa or CD61 (JM2E5) to study the distribution of this
molecule in different normal pig tissues. As in humans,
CD61 was broadly expressed in all tissues examined. In
the kidney, strong expression of CD61 was observed in
epithelial cells from renal tubules. In the testis, CD61
expression was detected in the Leydig cells. However, in
liver, CD61 was weak or not detected.
Many integrins are particularly involved in
tumogenicity and in tumor progression mediating cellcell
interaction. Immunofluorescence experiments using
cultured human tumor HeLa cells showed nuclear and
cytoplasmic staining of mAb JM2E5. Immunohistochemical
analysis of human tumor sections from several
organs showed a heterogeneus distribution in metastatic
cases from colon and breast carcinoma. However, no
staining was found in metastasis from melanom
Insulators containing CuCl<sub>4</sub>X<sub>2</sub><sup>2-</sup> (X=H<sub>2</sub>O, NH<sub>3</sub>) units: Origin of the orthorhombic distortion observed only for CuCl<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub><sup>2-</sup>
Origin of Small Barriers in JahnâTeller Systems:Quantifying the Role of 3dâ4s Hybridization in the Model System NaCl:Ni<sup>+</sup>
Despite its relevance, the microscopic origin of the energy barrier, B, between the compressed and elongated geometries of JahnâTeller (JT) systems is not well understood yet because of a lack of quantitative data about its various contributions. Seeking to clear up this matter, we have carried out both periodic and cluster ab initio calculations on the model system NaCl:Ni+. This system is particularly puzzling because, according to experimental data, its barrier is much smaller than that for other d9 and d7 ions in similar lattices. All calculations performed on the model system lead, in fact, to values |B| †160 cmâ1, which are certainly smaller than B = 500 cmâ1 derived for NaCl:M2+ (M = Ag, Rh) or B = 1024 cmâ1 obtained for KCl:Ag2+. As a salient feature, analysis of calculations carried out as a function of the QΞ (3z2 â r2) coordinate unveils the microscopic origin of the barrier. It is quantitatively proven that the elongated geometry observed for NaCl:Ni+ is due to the 3dâ4s vibronic admixture, which is slightly larger than the anharmonicity in the eg JT mode that favors a compressed geometry. The existence of these two competing mechanisms explains the low value of B for the model system, contrary to cases where the complex formed by d9 or d7 ions is elastically decoupled from the host lattice. Although the magnitude of B for NaCl:Ni+ is particularly small, the tunneling splitting, 3Î, is estimated to be below 9 cmâ1, thus explaining why the coherence is easily destroyed by random strains and thus a static JT effect is observed experimentally. As a main conclusion, the barrier in JT systems cannot be understood neglecting the tiny changes of the electronic density involved in small distortions. The present calculations reasonably explain the experimental g tensor of NaCl:Ni+, pointing out that the dâd transitions in NiCl65â are much smaller than those for CuCl64â and the optical electronegativity of Ni+ is only around 1.</p
UV-B radiation reduces in vitro germination of Metarhizium anisopliae s.l. but does not affect virulence in fungustreated Aedes aegypti adults and development on dead mosquitoes
Fil: Falvo, Marianel LucĂa. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios ParasitolĂłgicos y de Vectores; ArgentinaFil: Pereira-Junior, Ronaldo Alves. Universidade Federal de Goias. Instituto de Patologia Tropical e Saude Publica (IPTSP); BrasilFil: Rodrigues, J.. Universidade Federal de Goias. Instituto de Patologia Tropical e Saude Publica (IPTSP); BrasilFil: LĂłpez Lastra, Claudia Cristina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios ParasitolĂłgicos y de Vectores; ArgentinaFil: GarcĂa, Juan JosĂ©. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios ParasitolĂłgicos y de Vectores; ArgentinaFil: Fernandes, Everton K.K.. Fil
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