255 research outputs found
Excitation of wakefields in carbon nanotubes: a hydrodynamic model approach
The interactions of charged particles with carbon nanotubes may excite
electromagnetic modes in the electron gas produced in the cylindrical graphene
shell constituting the nanotube wall. This wake effect has recently been
proposed as a potential novel method of short-wavelength high-gradient particle
acceleration. In this work, the excitation of these wakefields is studied by
means of the linearized hydrodynamic model. In this model, the electronic
excitations on the nanotube surface are described treating the electron gas as
a 2D plasma with additional contributions to the fluid momentum equation from
specific solid-state properties of the gas. General expressions are derived for
the excited longitudinal and transverse wakefields. Numerical results are
obtained for a charged particle moving within a carbon nanotube, paraxially to
its axis, showing how the wakefield is affected by parameters such as the
particle velocity and its radial position, the nanotube radius, and a friction
factor, which can be used as a phenomenological parameter to describe effects
from the ionic lattice. Assuming a particle driver propagating on axis at a
given velocity, optimal parameters were obtained to maximize the longitudinal
wakefield amplitude
Novel reaction force for ultra-relativistic dynamics of a classical point charge
The problem of the electromagnetic radiation of an accelerated charged
particle is one of the most controversial issues in Physics since the beginning
of the last century, representing one of the most popular unsolved problems of
the Modern Physics. Different equations of motion have been proposed throughout
history for a point charge including the electromagnetic radiation emitted, but
all these expressions show some limitations. An equation based on the principle
of conservation of energy is proposed in this work for the ultra-relativistic
motion. Different examples are analyzed showing that the energy lost by the
charge agrees with the Li\'enard formula. This proposed equation has been
compared with the Landau-Lifshitz equation obtaining a good agreement in the
range of application of the Landau-Lifshitz formula.Comment: 9 pages, 10 figure
Numerical study of dark current dynamics in a high-gradient backward travelling wave accelerating cavity using the electromagnetic simulation software CST studio.
High-Gradient accelerating cavities are one of the main research lines in the development of
compact linear colliders. However, the operation of such cavities is currently limited by nonlinear
effects that are intensified at high electric fields, such as dark currents and radiation
emission or RF breakdowns.
A new normal-conducting High-Gradient S-band Backward Travelling Wave accelerating
cavity for medical application (v=0.38c) designed and constructed at Conseil Européen pour la
Recherche Nucléaire (CERN) is being tested at Instituto de Física Corpuscular (IFIC) High Power
RF Laboratory. The objective consists of studying its viability in the development of compact
linear accelerators for hadrontherapy treatments in hospitals.
Due to the high surface electric field in the cavity, electrons are emitted following Fowler-
Nordheim equation, also known as dark currents. The emission and dynamic of these
electrons are of fundamental importance on different phenomena such as RF Breakdowns or
radiation dose emission.
In this work, 3D electromagnetic numerical simulations have been performed using the
computer simulation technology software CST Studio Suite. Then, the resulting EM field maps
are used to study the emission and electron dynamics inside the cavity. The simulation results
are compared with experimental data and first conclusions discussed
Relativistic particle motion of a charge including the radiation reaction
The problem of the electromagnetic radiation of an accelerated charged particle is one of the
most controversial issues in Physics since the beginning of the last century representing one of
the most popular unsolved problems of the Modern Physics. Different equations of motion for
a point charge including the electromagnetic radiation emitted have been proposed throughout
history, but all these expressions show some limitations. An equation based on the principle of
conservation of energy is proposed for the ultra-relativistic motion. Different examples are
analyzed showing that the energy lost by the charge agrees with the relativistic generalization
of the Larmor formula. This proposed equation has been compared with the Landau-Lifshitz
equation obtaining a good agreement in the range of application of the Landau-Lifshitz formula.
Finally, it is discussed a possible variation of the typical relativistic particle integrators (e.g. Boris,
Vay or Higuera-Cary methods) in order to include the radiation reaction
Study of the RF pulse heating phenomenon in high gradient accelerating devices by means of analytical approximations
The main objective of this work is to present a
simple method, based on analytical expressions, for obtaining
a quick approximation of the temperature rise due to the Joule
effect inside the metallic walls of an RF accelerating device. This
proposal relies on solving the 1D heat-transfer equation for a
thick wall, where the heat sources inside the wall are the ohmic
losses produced by the RF electromagnetic fields penetrating
the metal with finite electrical conductivity. Furthermore, it is
discussed how the theoretical expressions of this method can be
applied to obtain an approximation to the temperature increase
in realistic 3D RF accelerating structures, taking as an example
the cavity of an RF electron gun. These theoretical results have
been benchmarked with numerical simulations carried out with
commercial finite-element method codes, finding good agreement
among them
Two-dimensional simulation of the electron transport in a photomultiplier tube
Photomultiplier tubes are widely used in experimental physics because they convert small light
signals into a measurable electric current. Although their working principle is well known, it is
very difficult to find simulations of the electron transport in these devices. For this reason, the
electron transport in the Hamamatsu R13408-100 photomultiplier tube has been simulated in
2D. The software SUPERFISH is used for calculating the electrostatic fields and the Boris method
for the effective electron dynamics. The secondary electron emission in the dynodes is
implemented using an effective electron model and the modified Vaughan’s model. Some
figures of merit for photomultiplier tubes (e.g. the gain, the electron transit time or the transit
time spread) in function of the supply voltage and an external magnetic field have been studied
obtaining a good qualitative accordance with the Hamamatsu datasheet. In further studies, we
are going to compare our simulations with experimental measurements
Breast cancer cutaneous metastases are associated to uMUC1 and sialyl Lewis x and to highly malignant primary tumors
Breast cancer spreading to different organs have been related to different molecules and mechanisms, but cutaneous metastasis remains unexplored. Increasing evidence showed that MUC1 and some of its carbohydrate associated antigens may be implicated in breast cancer metastasis. In this study we analyzed these tumor markers in order to identify breast cancer cutaneous metastatic profiles. A cohort of 26 primary tumors from breast cancer patients with cutaneous metastases were included; also, cutaneous and lymphatic node metastatic samples and primary tumors from breast cancer patients without metastases were analysed.
Immunohistochemical (IHC) studies demonstrated that both underglycosylated MUC1 (uMUC1) and sialyl Lewis x (sLex) to be positively associated with cutaneous metastatic primary tumors (p < 0.05). Notably, a high percentage of tumors with cutaneous metastases were characterized as triple negative and Her2+ tumors (37.5 % and 29 %, respectively). Some discordant results were found between primary tumors and their matched cutaneous metastases. To determine if MUC1 variants may be carriers of carbohydrate antigens, subcellular fractions from a cutaneous metastatic lesion were obtained, immunoprecipitated and analyzed by Western blot.
We found that the isolated uMUC1 with a molecular weight of>200 kDa was also the site for binding of antisLex MAb; in coincidence, a high correlation of positive IHC expression of both markers was observed. Our findings confirm that breast cancer cutaneous metastases were associated to highly malignant primary tumors and sustain the hypothesis that u-MUC1 and sLe x may drive breast cancer cutaneous metastases.Centro de Investigaciones Inmunológicas Básicas y Aplicada
Use of a personalised depression intervention in primary care to prevent anxiety: a secondary study of a cluster randomised trial
Background: In the predictD-intervention, GPs used a personalised biopsychosocial programme to prevent depression. This reduced the incidence of major depression by 21.0%, although the results were not statistically significant.
Aim: To determine whether the predictD-intervention is effective at preventing anxiety in primary care patients without depression or anxiety.
Design and setting: Secondary study of a cluster randomised trial with practices randomly assigned to either the predictD-intervention or usual care. This study was conducted in seven Spanish cities from October 2010 to July 2012.
Method: In each city, 10 practices and two GPs per practice, as well as four to six patients every recruiting day, were randomly selected until there were 26–27 eligible patients for each GP. The endpoint was cumulative incidence of anxiety as measured by the PRIME-MD screening tool over 18 months.
Results: A total of 3326 patients without depression and 140 GPs from 70 practices consented and were eligible to participate; 328 of these patients were removed because they had an anxiety syndrome at baseline. Of the 2998 valid patients, 2597 (86.6%) were evaluated at the end of the study. At 18 months, 10.4% (95% CI = 8.7% to 12.1%) of the patients in the predictD-intervention group developed anxiety compared with 13.1% (95% CI = 11.4% to 14.8%) in the usual-care group (absolute difference = −2.7% [95% CI = −5.1% to −0.3%]; P = 0.029).
Conclusion: A personalised intervention delivered by GPs for the prevention of depression provided a modest but statistically significant reduction in the incidence of anxiety
Metástasis cutáneas de cáncer de mama
El objetivo de este estudio es identificar perfiles correspondientes a la metástasis cutánea en el cáncer de mama mediante el análisis de marcadores tumorales tales como MUC1 y antígenos carbohidratos asociados.Facultad de Ciencias Médica
Análisis de la relevancia y factibilidad de indicadores de calidad en las unidades de nutrición
Introducción: La evaluación de la calidad en las actividades
sanitarias exige la elección de unos indicadores
acordes con los resultados que queremos medir. De todos
los posibles, debemos priorizar aquellos que nos permitan
obtener la información más relevante sin sobrecargar el
trabajo habitual de nuestras Unidades.
Objetivo: Conocer la opinión de los socios de SENPE
respecto a la relevancia y la viabilidad del uso de una
selección de indicadores de calidad para su aplicación en
nutrición clínica.
Métodos: Encuesta remitida mediante correo electrónico
a los socios de SENPE solicitando a los mismos su
opinión sobre 12 indicadores de calidad, valorándose
cada uno en cuanto a su relevancia y factibilidad de la
aplicación en su medio.
Resultados: Contestaron 40 encuestados de 40 centros
diferentes de 12 comunidades autónomas. En general, los
indicadores fueron considerados más relevantes que factibles.
Los indicadores mejor puntuados fueron: “identificación
en las bolsas de nutrición artificial”, “posición
semi-incorporada del paciente con nutrición enteral por
sonda nasogástrica” y “protocolos clínicos básicos”. Considerando
los indicadores por grupos (de estructura, proceso
o resultado) los mejor valorados fueron: “identificación
del paciente en las bolsas de nutrición artificial”
(estructura), “posición semi-incorporada” y “protocolos
clínicos básicos” (proceso), y “cumplimiento del objetivo
calórico” (resultado).
Conclusión: Los resultados de la encuesta permiten
seleccionar indicadores prioritarios para su aplicación en
las Unidades de NutriciónIntroduction: The quality assessment in health activities
requires the choice of indicators in line with the
results we want to measure. Of all possible, we should prioritize
those that allow us to obtain the most relevant
information without overloading the regular work of our
units.
Objective: To determine the opinion of the members of
SENPE regarding the relevance and feasibility of using a
selection of quality indicators designed for use in clinical
nutrition.
Methods: E-mail survey sent to members of SENPE
asking them their views on 12 quality indicators, evaluating
each in terms of their relevance and feasibility of
implementation in their environment.
Results: 40 respondents answered from 40 centers in 12
different regions. In general, the indicators were considered
more relevant than feasible. The indicators best
rated were: “identification in artificial nutrition bags,
“semi-recumbent position in patient with nasogastric
tube feeding” and “basic clinical protocols”. Considering
the type of indicator: “patient identification in the bags of
artificial nutrition (structure),” a semi-incorporated
“and” basic clinical protocols (process), and “fulfillment
of the caloric goal” (result).
Conclusion: The results of the survey can make a selection
of indicators that could be considered for first-line
introduction in a Nutrition Uni
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