3,318 research outputs found
Unified formalism for higher-order non-autonomous dynamical systems
This work is devoted to giving a geometric framework for describing
higher-order non-autonomous mechanical systems. The starting point is to extend
the Lagrangian-Hamiltonian unified formalism of Skinner and Rusk for these
kinds of systems, generalizing previous developments for higher-order
autonomous mechanical systems and first-order non-autonomous mechanical
systems. Then, we use this unified formulation to derive the standard
Lagrangian and Hamiltonian formalisms, including the Legendre-Ostrogradsky map
and the Euler-Lagrange and the Hamilton equations, both for regular and
singular systems. As applications of our model, two examples of regular and
singular physical systems are studied.Comment: 43 pp. We have corrected and clarified the statement of Propositions
2 and 3. A remark is added after Proposition
Nonholonomic constraints in -symplectic Classical Field Theories
A -symplectic framework for classical field theories subject to
nonholonomic constraints is presented. If the constrained problem is regular
one can construct a projection operator such that the solutions of the
constrained problem are obtained by projecting the solutions of the free
problem. Symmetries for the nonholonomic system are introduced and we show that
for every such symmetry, there exist a nonholonomic momentum equation. The
proposed formalism permits to introduce in a simple way many tools of
nonholonomic mechanics to nonholonomic field theories.Comment: 27 page
Aplicación de las tecnologías de la información a la tecnologia ictiológica: el sitio web 'www.ictioterm.es'
Aplicació de les tecnologies de la informació a la terminologia ictiològica: el lloc web www.ictioterm.es. ICTIOTERM és una base de dades que conté informació de tipus
terminològic, lingüístic i biològic sobre més de tres-centes espècies
marines de peixos, mol·luscos, crustacis i altres invertebrats.
En aquest article es descriuen amb detall els continguts del web
www.ictioterm.es, així com la seva estructura d'emmagatzematge
de la informació i les diverses opcions de cerca.Application of Information Technology to Ichthyology Terms: ww.ictioterm.es ICTIOTERM is a database containing terminological, linguistic
and biological information on more than 300 marine
species of fish, molluscs, crustaceans and other invertebrates.
In this paper, we describe the contents of the web site www.ictioterm.es, as well as its information storage structure and
search options.ICTIOTERM es una base de datos que contiene información de
tipo terminológico, lingüístico y biológico sobre más de trescientas
especies marinas de peces, moluscos, crustáceos y otros
invertebrados. En el presente trabajo, se describen de manera
pormenorizada los contenidos del web www.ictioterm.es, así
como su estructura de almacenamiento de la información y sus
diferentes opciones de búsqueda
U and Th speciation in river sediments
A study of the distribution of some natural radionuclides in different chemical fractions of river bottom sediments has been carried out. The study has shown that the majority of the total U in sediments is located in the non-residual fractions, while Th is more likely to be present in the residual ones. This difference between U and Th reflects largely a much higher mobility of U relative to Th in surface and near-surface environments. Coprecipitation with amorphous ferromanganese oxyhydroxides is the main process of U and Th incorporation from the water column into the soil particles. Moreover, the distribution of the radionuclides and the analysis of the Th/U mass ratios in different chemical fractions of sediments has made an unequivocal connection between the enhanced U content in river sediments and the wastes discharged into the rivers by the operation of fertilizer industries
Symmetries in Classical Field Theory
The multisymplectic description of Classical Field Theories is revisited,
including its relation with the presymplectic formalism on the space of Cauchy
data. Both descriptions allow us to give a complete scheme of classification of
infinitesimal symmetries, and to obtain the corresponding conservation laws.Comment: 70S05; 70H33; 55R10; 58A2
Changes in volatile compounds of pork loin (fresh and marinated) with different irradiation and packaging during storage
The analysis of volatile compounds by gas chromatography- mass spectrometry after extraction by purge and trap has been used to investigate the volatile compounds of fresh and marinated pork loin after E-beam treatmet as a function of packaging type (air, vacuum and modified atmosphere), radiation dose (1 and 2 kGy) and storage temperature (4 and 8 °C). Major differences were found between fresh and marinated samples but, in general, only minor differences were found in the volatile compounds of both types of loin due to storage temperature, packaging method and doses of irradiation. It is concluded that the application of E-beam is a very useful way to extend the shelflife of fresh and marinated pork loin with no changes in the odor of the products.<br><br>Se ha utilizado la cromatografía de gases/espectrometría de masas, la extracción mediante purga y trampa para estudiar los compuestos volátiles de lomo de cerdo fresco y adobado, tratados con electrones acelerados (1 y 2 kGy) y almacenado en refrigeración (4 y 8 °C) bajo diferentes atmósferas (aire, vacío y atmósfera modificada). Se observaron diferencias importantes entre las muestras de lomo fresco y adobado pero, en general, solo pequeñas diferencias fueron observadas en algunos compuestos volátiles de ambos tipos de lomo debidas al efecto de la temperatura, tiempo de almacenamiento, tipo de atmósfera o dosis de radiación. Se ha concluido que la aplicación de electrones acelerados es una tecnología muy eficaz para ampliar la vida útil del lomo de cerdo fresco y adobado sin que se detecten cambios en el olor de los productos
CAR T cells for T-cell leukemias: Insights from mathematical models
Immunotherapy has the potential to change the way all cancer types are
treated and cured. Cancer immunotherapies use elements of the patient immune
system to attack tumor cells. One of the most successful types of immunotherapy
is CAR-T cells. This treatment works by extracting patient's T-cells and adding
to them an antigen receptor allowing tumor cells to be recognized and targeted.
These new cells are called CAR-T cells and are re-infused back into the patient
after expansion in-vitro. This approach has been successfully used to treat
B-cell malignancies (B-cell leukemias and lymphomas). However, its application
to the treatment of T-cell leukemias faces several problems. One of these is
fratricide, since the CAR-T cells target both tumor and other CAR-T cells. This
leads to nonlinear dynamical phenomena amenable to mathematical modeling. In
this paper we construct a mathematical model describing the competition of
CAR-T, tumor and normal T-cells and studied some basic properties of the model
and its practical implications. Specifically, we found that the model
reproduced the observed difficulties for in-vitro expansion of the therapeutic
cells found in the laboratory. The mathematical model predicted that CAR-T cell
expansion in the patient would be possible due to the initial presence of a
large number of targets. We also show that, in the context of our mathematical
approach, CAR-T cells could control tumor growth but not eradicate the disease
- …