68 research outputs found
How greater mouse-eared bats deal with ambiguous echoic scenes
Echolocating bats have to assign the received echoes to the correct call that generated them. Failing to do so will result in the perception of virtual targets that are positioned where there is no actual target. The assignment of echoes to the emitted calls can be ambiguous especially if the pulse intervals between calls are short and kept constant. Here, we present first evidence that greater mouse-eared bats deal with ambiguity by changing the pulse interval more often, in particular by reducing the number of calls in the terminal group before landing. This strategy separates virtual targets from real ones according to their change in position. Real targets will always remain in a constant position, and virtual targets will jitter back and forth according to the change in the time interval
Blue Whales Respond to Anthropogenic Noise
Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood
Analysis of Finite Microstrip Structures Using an Efficient Implementation of the Integral Equation Technique
An efficient numerical implementation of the Integral Equation technique (IE) has
been developed for the analysis of the electrical characteristics of finite microstrip structures.
The technique formulates a volume version of the IE for the finite dielectric objects, and a
standard surface IE technique for the metallic areas. The system of integral equations formu-
lated are solved with special numerical techniques described in this paper. The input impedances
of several microstrip antennas have been computed, showing good agreement with respect mea-
surements. The technique has shown to be accurate even for complex geometries containing
several stacked dielectric layers. The radiation patterns of the structures have also been com-
puted, and measured results from real manufactured hardware confirm that backside radiation
and secondary lobes are accurately predicted by the theoretical model. The paper also discuss
a suitable excitation model for finite size ground planes, and investigates the possibilities for
an independent meshing of the metallic areas and the dielectric objects inside a given geom-
etry. The practical value of the approach derived is that microstrip circuits can be designed
minimizing the volume and size of the dielectric substrates.This work has been supported bythe Spanish National Project ESP2001-4546-PE, and RegionalSeneca Project PB/4/FS/02
Estudio del esfuerzo de rodadura en tractores articulados (4WD) y de tracción delantera asistida (FWA)
p.221-229En el autotransporte del tractor se producen tros tipos de pérdidas de transmisión, pérdidas por rodadura y pérdida por patinaje. Las pérdidas por transmisión conciernen al diseño de la misma, las pérdidas por patinaje y rodadura son las que más preocupan al productor (FWA y 4WD) comunes a nuestro mercado agrícola, sobre estas condiciones de suelo diferentes, suelo arado, cama de siembra y siembra directa. Los parámetros evaluados fueron: esfuerzos de rodadura fueron contrastados con las fórmulas de predicción de Wismer y Luth y de MCallister. Las conclusiones obtenidas fueron 1) La potencia pérdida en rodadura se incrementó en suelos de baja capacidad portante; 2) Para predecir esfuerzo de rodadura en tractores (FWA y 4WD) cuando transitan sobre suelos arados se puede utilizar la ecuación de predicción de Wismer y Luth; 3) El porcentaje de potencia del motor pérdida por rodadura fue mayor para el tractor FWA cuando transitó sobre suelos de baja capacidad portante, 4) La menor relación potencia pérdida en rodadura 7 potencia motor fue mejor para el 4 WD en suelo cama de siembra y suelo arado, no así en siembra directa y 5) Se encontró, sobre los suelos blandos, una relación directa entre profundidad de huella y el peso del tractor que lo transitó
Search of dark-matter axions in the microwave frequency range with full-wave modal techniques
Axions, originally proposed to solve the strong Charge-Parity problem of
Quantum Chromo-Dynamics theory, emerge now as leading candidates of dark
matter. In fact, the search of dark-matter axions in the microwave frequency
range has been developed by different research groups during the last twenty
years. In this demanding scenario, several microwave passive components
(haloscopes) have been designed and fabricated for such axions detection based
on the use of cavities and multi-cavities. From an electromagnetic point of view,
comercial software (ANSFT HFSS, CST MICROWAVE STUDIO, etc ) has been
employed for the design of different kind of haloscopes. In this work we propose
to use the BI-RME 3D method (Boundary Integral – Resonant Mode Expansion)
as an alternative to analyze the axion-photon coupling existing within an
haloscope. This full-wave modal technique has provided interesting wide-band
results for the design of new haloscopes
On the development of new tuning and inter-coupling techniques using ferroelectric materials in the detection of dark matter axions
Tuning is an essential requirement for the search of dark matter axions employing haloscopes
since its mass is not known yet to the scientific community. At the present day, most haloscope tuning systems
are based on mechanical devices which can lead to failures due to the complexity of the environment in which
they are used. However, the electronic tuning making use of ferroelectric materials can provide a path that
is less vulnerable to mechanical failures and thus complements and expands current tuning systems. In this
work, we present and design a novel technique for using the ferroelectric Potassium Tantalate (KTaO3 or
KTO) material as a tuning element in haloscopes based on coupled microwave cavities. In this line, the
structures used in the Relic Axion Detector Exploratory Setup (RADES) group are based on several cavities
that are connected by metallic irises, which act as interresonator coupling elements. In this article, we also
show how to use these KTaO3 films as interresonator couplings between cavities, instead of inductive or
capacitive metallic windows used in the past. These two techniques represent a crucial upgrade over the
current systems employed in the dark matter axions community, achieving a tuning range of 2.23% which
represents a major improvement as compared to previousworks (<0.1%) for the same class of tuning systems.
The theoretical and simulated results shown in this work demonstrate the interest of the novel techniques
proposed for the incorporation of this kind of ferroelectric media in multicavity resonant haloscopes in the
search for dark matter axions.This work was supported in part by the ‘‘MCIN/AEI/10.13039/501100011033/’’ and ‘‘European Regional Development Fund (ERDF)
A way of making Europe’’ under Grant PID2019-108122GB-C33, in part by the ‘‘MCIN/AEI/10.13039/501100011033/’’ and ‘‘European
Social Fund (ESF) Investing in your future’’ under Grant FPI BES-2017-079787, and in part by the European Research Council (ERC) under Grant ERC-2018-StG-802836 (AxScale)
Analysis and implementation of different topologies of transversal filters in planar technology
This paper uses a simple configuration to implement microwave transversal filters
based on microstrip technology. The structure is of second order and implements two
transmission zeros and two reflection zeros in the frequency response of the filter. The
basic configuration consists of input and output ports coupled in a shunt configuration to
two printed resonators of different lengths. A modification of the original structure is
introduced to allow an additional direct coupling between the source and the load.
Depending on the value and the sign of the coupling terms, different frequency responses
can be obtained. In this way, small modifications in the basic structure allow to obtain
band-pass or band-stop responses. Following this circuit topology, the paper discusses the
possibilities to have transmission zeros in the real or in the complex plane and their effects
on the frequency response and on the group delay of the filter. Also, two practical
implementations in microstrip technology are proposed, and a third filter implementing
group delay equalization is demonstrated. Measured results confirm theoretical predictions
and validate the structures for practical applications.Ministerio de Educación y Ciencia, Ref. TEC2007-67630-C03-02.
Fundación Séneca, Ref. 08833/PI/0
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