16,819 research outputs found
Optimum matchings in weighted bipartite graphs
Given an integer weighted bipartite graph we consider the problems of finding all the edges that occur in
some minimum weight matching of maximum cardinality and enumerating all the
minimum weight perfect matchings. Moreover, we construct a subgraph of
which depends on an -optimal solution of the dual linear program
associated to the assignment problem on that allows us to reduced
this problems to their unweighed variants on . For instance, when
has a perfect matching and we have an -optimal solution of the dual
linear program associated to the assignment problem on , we solve the
problem of finding all the edges that occur in some minimum weight perfect
matching in linear time on the number of edges. Therefore, starting from
scratch we get an algorithm that solves this problem in time
, where , , and .Comment: 11 page
Excited bands in odd-mass rare-earth nuclei
Normal parity bands are studied in 157Gd, 163Dy and 169Tm using the pseudo
SU(3) shell model. Energies and B(E2) transition strengths of states belonging
to six low-lying rotational bands with the same parity in each nuclei are
presented. The pseudo SU(3) basis includes states with pseudo-spin 0 and 1, and
1/2 and 3/2, for even and odd number of nucleons, respectively. States with
pseudo-spin 1 and 3/2 must be included for a proper description of some excited
bands.Comment: 8 pages, 6 figures, Submitted to Phys. Rev.
Inter-band B(E2) transition strengths in odd-mass heavy deformed nuclei
Inter-band B(E2) transition strengths between different normal parity bands
in 163Dy and 165Er are described using the pseudo-SU(3) model. The Hamiltonian
includes Nilsson single-particle energies, quadrupole-quadrupole and pairing
interactions with fixed, parametrized strengths, and three extra rotor terms
used to fine tune the energy spectra. In addition to inter-band transitions,
the energy spectra and the ground state intra-band B(E2) strengths are
reported. The results show the pseudo-SU(3) shell model to be a powerful
microscopic theory for a description of the normal parity sector in heavy
deformed odd-A nuclei.Comment: 4 figures, 2 table
Cities and regions in Britain through hierarchical percolation
Urban systems present hierarchical structures at many different scales. These are observed as administrative regional delimitations which are the outcome of complex geographical, political and historical processes which leave almost indelible footprints on infrastructure such as the street network. In this work, we uncover a set of hierarchies in Britain at different scales using percolation theory on the street network and on its intersections which are the primary points of interaction and urban agglomeration. At the larger scales, the observed hierarchical structures can be interpreted as regional fractures of Britain, observed in various forms, from natural boundaries, such as National Parks, to regional divisions based on social class and wealth such as the well-known North–South divide. At smaller scales, cities are generated through recursive percolations on each of the emerging regional clusters. We examine the evolution of the morphology of the system as a whole, by measuring the fractal dimension of the clusters at each distance threshold in the percolation. We observe that this reaches a maximum plateau at a specific distance. The clusters defined at this distance threshold are in excellent correspondence with the boundaries of cities recovered from satellite images, and from previous methods using population density
Evaluación briológica de los efectos de la contaminación atmosférica en la Ciudad de México
The Index of Atmospheric Purity (IAP) was used to make a preliminary evaluation of epiphytic moss response to atmospheric pollution in the urban area of Mexico City. Areal analysis indicates that there is a significant negative correlation (p < 0.5) between IAP values and SO2, NO2, NOx, Pb and temperature values of -0.45, -0.90, -0.80, -0.80, -0.90. Significant positive correlation (p < 0.05) between IAP values and O3, rainfall and relative atmospheric humidity with values of 0.70, 0.80, 0.90. Increase in atmospheric pollutants in Mexico City have promoted a gradual decrease in frequency and cover of epiphytic mosses even though some ecological factors may show the oposite effect.Se hace una evaluación preliminar de la respuesta de los musgos epífitos a la contaminación atmosférica usando el Indice de Pureza Atmosférica (IPA) en el área urbana de la Ciudad de México. El análisis por zonas indica que hay una relación inversa y significativa (p < 0.5) entre el IPA y SO2, NO2, NOx, Pb y la temperatura con valores de -0.45, -0.90, -0.80, -0.80, -0.90. También se encontró una relación directa y significativa (p < 0.05) entre el IPA y el O3, la precipitación pluvial y la humedad relativa con valores de 0.70, 0.80, 0.90. Los incrementos en los niveles de algunos contaminantes atmosféricos en la Ciudad de México han promovido la disminución gradual en la frecuencia de aparición y cobertura de musgos epífitos, aunque algunas variables ambientales pueden tener el efecto opuesto
Efecto de un nuevo xanthanólido sesquiterpeno sobre la activación de mastocitos inducida por neurópeptidos pro-inflamatorios
Los mastocitos son células del tejido conectivo que participan en la génesis y
modulación de las respuestas inflamatorias celulares. En trabajos previos hemos
demostrado que xanthatina (xanthanólido sesquiterpeno aislado de Xanthium
cavanillesii Schouw) inhibe la activación de mastocitos inducida por secretagogos
experimentales. Sin embargo, se desconoce su efecto sobre la activación de
mastocitos inducida por estímulos fisiopatológicos. Estos estímulos incluyen, entre
otros, los neuropéptidos pro-inflamatorios sustancia P y neurotensina, responsables
de una de las principales vías de inflamación neurogénica. El objetivo del presente
trabajo fue estudiar el efecto de xanthatina sobre la activación de mastocitos inducida
por sustancia P y neurotensina. Mastocitos peritoneales de rata se incubaron con: 1)
PBS (basal); 2) sustancia P (100 Fm); 3) neurotensina (50 Fm); 4) xanthatina (8-320
Fm)+sustancia P; 5) xanthatina (8-320 Fm)+neurotensina. La viabilidad de los
mastocitos se evaluó con azul tripán. En las soluciones de incubación se cuantificó
serotonina liberada (marcador de activación). En las células se cuantificó serotonina
remanente (no liberada) y se analizó la morfología celular por microscopía óptica y
electrónica de transmisión. Tratamiento estadístico: ANOVA-1 y Tukey-Kramer. La
incubación de mastocitos con xanthatina inhibió (P<0,01), en forma dosisdependiente,
la liberación de serotonina inducida por sustancia P y neurotensina, sin
modificar la viabilidad celular. Los mastocitos tratados con neuropéptidos mostraron
características morfológicas de degranulación, mientras que la morfología de los
mastocitos tratados con xanthatina+neuropéptido fue semejante a los basales. En
conclusión, xanthatina inhibe la activación de mastocitos inducida por sustancia P y
por neurotensina. Este sesquiterpeno podría representar una nueva alternativa en el
tratamiento de las inflamaciones neurogénicas.The present study was designed to examine the effects of a novel natural
xanthanolide with anti-ulcer and anti-inflammatory properties (xanthatin) on mast cell
activation induced by pro-inflammatory peptides, such as substance P and neurotensin.
Peritoneal mast cells from male adult were purified in Percoll, preincubated in the
presence of xanthatin and then challenged with the mast cell activators substance P
(100 Fm) or neurotensin (50 Fm). Concentration-response studies of mast cell
serotonin release evoked by pro-inflammatory neuropeptides, evaluation of mast cell
viability and morphology by light and electron microscopy, and drug stability analysis by
thin layer chromatography (TLC) were performed. Serotonin release studies, carried
out together with morphological studies, showed the effectiveness of xanthatin to
stabilize mast cells. The present study provides the first strong evidence in favour of
the hypothesis that xanthatin inhibits substance P- and neurotensin-induced serotonin
release from peritoneal mast cells, acting thus as a mast cell stabilizer. Our findings
may provide an insight into the design of novel pharmacological agents which may be
used to regulate the mast cell response in neurogenic inflammation.Fil: Vargas, P..
Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos"Fil: Martino, E..
Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Área de Anatomía NormalFil: Fogal, T..
Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos"Fil: Tonn, C..
Universidad Nacional de San Luis. Facultad de Química,
Bioquímica y Farmacia. Departamento de Química.Fil: Penissi, A..
Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos
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