12,777 research outputs found
Higher-Order Differential Operators on a Lie Group and Quantization
This talk is devoted mainly to the concept of higher-order polarization on a
group, which is introduced in the framework of a Group Approach to
Quantization, as a powerful tool to guarantee the irreducibility of
quantizations and/or representations of Lie groups in those anomalous cases
where the Kostant-Kirilov co-adjoint method or the Borel-Weyl-Bott
representation algorithm do not succeed.Comment: 9 pages, latex, no figures, uses IJMPB.sty (included). New version
partially rewritten (title changed!), presented to the II Int. Workshop on
Class. and Quant. Integrable Systems, Dubna (Rusia) 1996, and published in
Int. J. Mod. Phys.
Shiga Toxin Detection Methods : A Short Review
The Shiga toxins comprise a family of related protein toxins secreted by
certain types of bacteria. Shigella dysenteriae, some strain of Escherichia
coli and other bacterias can express toxins which caused serious complication
during the infection. Shiga toxin and the closely related Shiga-like toxins
represent a group of very similar cytotoxins that may play an important role in
diarrheal disease and hemolytic-uremic syndrome. The outbreaks caused by this
toxin raised serious public health crisis and caused economic losses. These
toxins have the same biologic activities and according to recent studies also
share the same binding receptor, globotriosyl ceramide (Gb3). Rapid detection
of food contamination is therefore relevant for the containment of food-borne
pathogens. The conventional methods to detect pathogens, such as
microbiological and biochemical identification are time-consuming and
laborious. The immunological or nucleic acid-based techniques require extensive
sample preparation and are not amenable to miniaturization for on-site
detection. In the present are necessary of techniques of rapid identification,
simple and sensitive which can be employed in the countryside with
minimally-sophisticated instrumentation. Biosensors have shown tremendous
promise to overcome these limitations and are being aggressively studied to
provide rapid, reliable and sensitive detection platforms for such
applications.Comment: 16 pages, 2 figure
Thermal stability of the cu-ceo2 interface on silica and alumina, and its relation with activity in the oxidation reaction of co and the decomposition of n2o
Indexación: Scopus; Scielo.The effect of the support on the formation of the Cu-CeO2 interface and its thermal stability after calcination at 500, 700 and 900 °C is studied. The supports used are SiO2, because of its inert character, and Al2O3, because it can interact with the Cu and Ce species on the surface. The catalysts were characterized by BET, XRD, UV-vis DRS, and TPR with H2. The catalytic activity in the CO oxidation reactions with O2 at low temperature and the decomposition of N2O were selected to visualize the effect of temperature on the concentration of Cu-CeO2 interfacial sites. The results show that at a calcination temperature of 500 °C the formation of the Cu-CeO2 interface is favored over the SiO2 support. However, the stability of the Cu-CeO2 interface on SiO2 is much lower than on Al2O3, causing a substantial decrease of the interfacial sites calcining at 700 °C, and segregation of the Cu and Ce species on the surface of the silica, with complete loss of the catalytic activity in both reactions when calcining at 900 °C. In contrast, on alumina the Cu-CeO2 interface is more stable and presents a significant catalytic activity in both reactions, even when calcining at 900 °C. The characterization results show that the sintering process of Cu species and CeO2 particles is less on the alumina support due to the greater interaction of the Cu and Ce with this support. © 2018 Sociedad Chilena de Quimica.all rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0717-97072018000304102&lng=en&nrm=iso&tlng=e
Nematic phase in the J-J square lattice Ising model in an external field
The J-J Ising model in the square lattice in the presence of an
external field is studied by two approaches: the Cluster Variation Method (CVM)
and Monte Carlo simulations. The use of the CVM in the square approximation
leads to the presence of a new equilibrium phase, not previously reported for
this model: an Ising-nematic phase, which shows orientational order but not
positional order, between the known stripes and disordered phases. Suitable
order parameters are defined and the phase diagram of the model is obtained.
Monte Carlo simulations are in qualitative agreement with the CVM results,
giving support to the presence of the new Ising-nematic phase. Phase diagrams
in the temperature-external field plane are obtained for selected values of the
parameter which measures the relative strength of the
competing interactions. From the CVM in the square approximation we obtain a
line of second order transitions between the disordered and nematic phases,
while the nematic-stripes phase transitions are found to be of first order. The
Monte Carlo results suggest a line of second order nematic-disordered phase
transitions in agreement with the CVM results. Regarding the stripes-nematic
transitions, the present Monte Carlo results are not precise enough to reach
definite conclusions about the nature of the transitions.Comment: 13 pages, 10 figure
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