618 research outputs found
A profitability comparison between a “one-way” car sharing service and a "modified one-way" car sharing service
The research looks at comparing the different performance offered by two types
of one-way car sharing services. In particular, we compare the “traditional” service in which
users can return vehicles to a pre-determined permitted parking space to the “modified”
service in which the decision of where to return the vehicle to is made at the end of its usage
and vehicles can be returned also outside the permitted parking areas. The comparison is
based on common and given demand/offer assumptions. The mathematical modelling uses
state of the art algorithms that allow us to determine for both types of service the optimal
number of personnel to re-position the vehicles in order to maximise profit. In particular,
the attractiveness of the two services herewith compared, has been analysed both in terms of
overall profitability as well as in terms of maximum number of users. The results show and
quantify how the “modified” service, whilst allowing a greater degree of flexibility to users in
terms of return locations, causes lower economic returns for the service company and lowers
the number of users that can be served. Finally, the model allows us to calculate the required
tariff increase necessary to transform a “traditional” service into a “modified” service assuming
an inelastic demand curve as well as constant profits for the service company
Photon spectra from WIMP annihilation
If the present dark matter in the Universe annihilates into Standard Model
particles, it must contribute to the fluxes of cosmic rays that are detected on
the Earth, and in particular, to the observed gamma ray fluxes. The magnitude
of such contribution depends on the particular dark matter candidate, but
certain features of the produced photon spectra may be analyzed in a rather
model-independent fashion. In this work we provide the complete photon spectra
coming from WIMP annihilation into Standard Model particle-antiparticle pairs
obtained by extensive Monte Carlo simulations. We present results for each
individual annihilation channel and provide analytical fitting formulae for the
different spectra for a wide range of WIMP masses.Comment: 23 pages, 37 figures and 23 table
In-situ multicore fibre-based pH mapping through obstacles in integrated microfluidic devices
Microfluidic systems with integrated sensors are ideal platforms to study and
emulate processes such as complex multiphase flow and reactive transport in
porous media, numerical modeling of bulk systems in medicine, and in
engineering. Existing commercial optical fibre sensing systems used in
integrated microfluidic devices are based on single-core fibres, limiting the
spatial resolution in parameter measurements in such application scenarios.
Here, we propose a multicore fibre-based pH system for in-situ pH mapping with
tens of micrometer spatial resolution in microfluidic devices. The
demonstration uses custom laser-manufactured glass microfluidic devices (called
further micromodels) consisting of two round ports. The micromodels comprise
two lintels for the injection of various pH buffers and an outlet. The two-port
system facilitates the injection of various pH solutions using independent
pressure pumps. The multicore fibre imaging system provides spatial information
about the pH environment from the intensity distribution of fluorescence
emission from the sensor attached to the fibre end facet, making use of the
cores in the fibre as independent measurement channels. As a proof-of-concept,
we performed pH measurements in micromodels through obstacles (glass and rock
beads), showing that the particle features can be clearly distinguishable from
the intensity distribution from the fibre sensor.Comment: 12 pages of main draft with 10 figures, 2 pages of supplementary
information with 3 figures. Total 14 page
Evaluación de efectos difusionales sobre la cinética de hidrólisis de lecitina de soja con fosfolipasa A2
Soluble or immobilized A2 phospholipase liberates one mole of fatty acid of the C-2 position in soybean lecithin phospholipids to product lysolecithins. When using the enzyme in its immobilized form the enzymatic activity decreases due to substrate and product transport phenomenon. By comparison of the kinetic parameters of the hydrolysis reaction catalized by A2 phospholipase immobilized on alumina or on DEAE-Sephadex against those of the soluble enzyme, for soybean lecithin hydrolysis reaction, the diffusive effects were evaluated. The decrease of the reaction rate was quantified in presence of diffusive effects and the effectiveness factors were calculated. The Michaelis-Menten kinetic parameters were determined: KM = 8,2.10-2 mol·l-1 and 5,36.10-2 mol·l-1 and Vmax = 7,7.10-5 mol·l-1 .min-1 and 9,5.10-5 mol·l-1 ·min-1 for the enzyme immobilized on alumina and on DEAE-Sephadex, respectively. The effectiveness factors were 0,277 for alumina and 0,376 for DEAE-Sephadex.La Fosfolipasa A2, soluble o inmovilizada, libera un mol de ácido graso de la posición C-2 de los fosfolípidos de la lecitina de soja para producir lisolecitinas. Cuando se utiliza la enzima en su forma inmovilizada, la actividad enzimática decrece debido al fenómeno de transporte de sustrato y de producto. Se evaluaron los efectos de difusión comparando los parámetros cinéticos de la reacción de hidrólisis de lecitina de soja catalizada por fosfolipasa A2 inmovilizada sobre alúmina o sobre DEAE-Sephadex, frente a los de enzima soluble. La disminución de la velocidad de reacción fue cuantificada en presencia de efectos difusionales y se calcularon los factores de eficiencia. Se determinaron los parámetros de Michaelis-Menten: KM = 8,2.10-2 mol·l-1 and 5,36.10-2 mol·l-1 y Vmax = 7,7.10-5 mol·l-1 .min-1 y 9,5.10-5 mol·l-1 ·min-1 para la enzima inmovilizada sobre alúmina y sobre DEAE-Sephadex, respectivamente. El factor de eficiencia fue 0.277 para alúmina y 0.376 para DEAE-Sephadex
Estudio cinético de la reacción de hidrólisis de lecitina de soja pura en polvo con fosfolipasa A2 inmovilizada
Immobilized A2 phospholipase enzyme promotes the hydrolytic reaction of pure powder soybean lecithin releasing a mole of fatty acid from C-2 position. The main purpose of this paper was to determine the kinetic parameters of this reaction when the enzyme was adsorbed on alumina or DEAE-sephadex. The best conditions for the reaction were: temperature: 45-48ºC, Ca ions concentration: 6mM, pH: 8,65. Tested conditions for substrate concentration were: 6,3; 12,7; 19 and 25 mM working in a batch type reactor and with the immobilized enzyme. The incubating time did not change the enzymatic activity. The hydrolytic activity of alumina or DEAE-sephadex adsorbed A2 phospholipase enzyme was lower than of the soluble enzyme because the intrinsic properties are modified by immobilization. For substrate concentrations ranging between 6 and 19 mM first order kinetic velocity constants were k = 9, 88. 10-2 min-1 and k = 1,766. 10-1 min-1 for alumina and DEAEsephadex respectively. For the same supports but at higher substrate concentration (25mM) the zero order kinetic velocity constants were k= 1,62. 10-3 mol.l-1min-1 (alumina) and k = 3,58. 10-3 mol.l-1 min-1 (DEAE-sephadex).La enzima fosfolipasa A2 inmovilizada promueve la reacción hidrolítica de lecitina de soja pura en polvo liberando un mol de ácido graso de la posición C-2. El principal propósito de este trabajo fue determinar los parámetros cinéticos de la reacción cuando la enzima fue adsorbida sobre alúmina o sobre DEAE-sephadex. Las mejores condiciones para la reacción son: temperatura 45-48ºC: concentración de iones Ca 6 mM y pH 8,65. Las concentraciones de sustrato ensayadas fueron 6,3; 12,7; 19 y 25 mM trabajando en un reactor tipo batch y con la enzima inmovilizada. El tiempo de incubación no modificó la actividad enzimática. La actividad hidrolítica de fosfolipasa A2 adsorbida sobre alúmina o sobre sephadex fue menor que la de la enzima soluble porque las propiedades intrínsecas de la enzima se modificaron con la inmovilización. Para concentraciones de sustrato entre 6 y 19 mM las constantes de velocidad para cinética de 1er orden fueron k = 9,88.10-2 min-1 para enzima inmovilizada sobre alúmina y k = 1,766.10-1 min-1 para enzima inmovilizada sobre DEAE-sephadex. Para los mismos soportes, pero a mayores concentraciones de sustrato (25mM) las constantes de velocidad para cinética de orden cero fueron k = 1,62.10-3 mol.l-1min-1 (alúmina) y k = 3,58. 10-3 mol.l-1 min-1 (DEAE-sephadex)
Cosmic magnetic fields and dark energy in extended electromagnetism
We discuss an extended version of electromagnetism in which the usual gauge
fixing term is promoted into a physical contribution that introduces a new
scalar state in the theory. This new state can be generated from vacuum quantum
fluctuations during an inflationary era and, on super-Hubble scales, gives rise
to an effective cosmological constant. The value of such a cosmological
constant coincides with the one inferred from observations as long as inflation
took place at the electroweak scale. On the other hand, the new state also
generates an effective electric charge density on sub-Hubble scales that
produces both vorticity and magnetic fields with coherent lengths as large as
the present Hubble horizon.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish
Relativity Meeting 2010, Granada, Spain, 6-10 September 201
Production of spin 3/2 particles from vacuum fluctuations
We study the production of spin 3/2 particles in homogeneous scalar and
gravitational backgrounds from the mode-mixing Bogolyubov method. Considering
only helicity states we can reduce the problem to a standard Dirac
fermion calculation and apply the standard techniques in a straightforward way.
As an example we consider a supergravity inflationary model and calculate the
spectrum of gravitinos created during preheating at the end of inflation.Comment: 4 pages, RevTeX, 1 figure. New comments and references added. Final
version to appear in Phys.Rev.Let
Brane oscillations and the cosmic coincidence problem
We show that, under general assumptions, in six-dimensional brane-world
models with compactified large extra dimensions, the energy density of brane
oscillations scales as that of cold dark matter and its present value is
compatible with observations. Such value is obtained from the only dimensional
scale in the theory, namely, the fundamental scale of gravity in six dimensions
TeV, without any fine-tuning or the introduction of additional mass
scales apart from the large size of the extra dimensions. It has been suggested
that the same kind of models could provide also the correct magnitude of the
cosmological constant. This observation can be relevant for the resolution of
the cosmic coincidence problem in the brane-world scenario.Comment: 5 pages, RevTeX. Comments on the renormalization of the branon mass
included. Final version to appear in Phys.Rev.D (R
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