85 research outputs found
Newly-Discovered Globular Clusters in NGC 147 and NGC 185 from PAndAS
Using data from the Pan-Andromeda Archaeological Survey (PAndAS), we have
discovered four new globular clusters (GCs) associated with the M31 dwarf
elliptical (dE) satellites NGC 147 and NGC 185. Three of these are associated
with NGC 147 and one with NGC 185. All lie beyond the main optical boundaries
of the galaxies and are the most remote clusters yet known in these systems.
Radial velocities derived from low resolution spectra are used to argue that
the GCs are bound to the dwarfs and are not part of the M31 halo population.
Combining PAndAS with UKIRT/WFCAM data, we present the first homogeneous
optical and near-IR photometry for the entire GC systems of these dEs.
Colour-colour plots and published colour-metallicity relations are employed to
constrain GC ages and metallicities. It is demonstrated that the clusters are
in general metal poor ([Fe/H] < -1.25 dex), while the ages are more difficult
to constrain. The mean (V-I) colours of the two GC systems are very similar
to those of the GC systems of dEs in the Virgo and Fornax clusters, as well as
the extended halo GC population in M31. The new clusters bring the GC specific
frequency (S_N) to ~9 in NGC 147 and ~5 in NGC 185, consistent with values
found for dEs of similar luminosity residing in a range of environments.Comment: 14 pages, 6 figures, 6 tables, accepted for publication in MNRA
Self-organization of (001) cubic crystal surfaces
Self-organization on crystal surface is studied as a two dimensional spinodal
decomposition in presence of a surface stress. The elastic Green function is
calculated for a cubic crystal surface taking into account the crystal
anisotropy. Numerical calculations show that the phase separation is driven by
the interplay between domain boundary energy and long range elastic
interactions. At late stage of the phase separation process, a steady state
appears with different nanometric patterns according to the surface coverage
and the crystal elastic constants
Fabrication and characterisation of nanocrystalline graphite MEMS resonators using a geometric design to control buckling
The simulation, fabrication and characterisation of nanographite MEMS resonators is reported in this paper. The deposition of nanographite is achieved using plasma-enhanced chemical vapour deposition directly onto numerous substrates such as commercial silicon wafers. As a result, many of the reliability issues of devices based on transferred graphene are avoided. The fabrication of the resonators is presented along with a simple undercutting method to overcome buckling, by changing the effective stress of the structure from 436 MPa compressive, to 13 MPa tensile. The characterisation of the resonators using electrostatic actuation and laser Doppler vibrometry is reported, demonstrating resonator frequencies from 5–640 kHz and quality factor above 1819 in vacuum obtained
High-isolation antenna array using SIW and realized with a graphene layer for sub-terahertz wireless applications
This paper presents the results of a study on developing an effective technique to increase the performance characteristics of antenna arrays for sub-THz integrated circuit applications. This is essential to compensate the limited power available from sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain performance however in the case of small-sized array structures the radiation properties can be adversely affected by mutual coupling that exists between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling effects. Prototype of 2x3 antenna arrays were designed and constructed on a polyimide dielectric substrate with thickness of 125 mu m for operation across 0.19-0.20 THz. The dimensions of the array were 20x13.5x0.125 mm(3). Metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding the patch antennas in the array with sub-wavelength slots. Compared to the reference array the metamaterial inspired structure exhibits improvement in isolation, radiation gain and efficiency on average by 28 dB, 6.3 dBi, and 34%, respectively. These results show the viability of proposed approach in developing antenna arrays for application in sub-THz integrated circuits
Fabrication and characterisation of resistive nanocrystalline graphite
This work demonstrates the feasibility of fabricating resistive nanocrystalline graphite (NCG) on a Si substrate. The NCG film thickness of 9 nm was deposited using metal-free plasma enhanced chemical vapour deposition (PECVD) on a 6-inch p-type silicon wafer. The surface and electrical properties of the resistors produced were investigated. The average grain size of the NCG thin film is 35 nm with 0.8 nm of surface roughness. The electrical characterization of the NCG strips show metal-like behaviour in which the resistance is proportional to the strip lengths. The sheet resistance is found to be 39 kohm/sq which is two orders of magnitude larger than graphene deposited using Chemical Vapour Deposition. This indicates the carrier transport across grain boundaries has a large influence on the overall resistance of the device. However, the nano-sized grains on the NCG material could be used to enhance the sensitivity of the material towards the environment
Newly discovered globular clusters in NGC 147 and NGC 185 from PAndAS
Using data from the Pan-Andromeda Archaeological Survey (PAndAS), we have discovered four new globular clusters (GCs) associated with the M31 dwarf elliptical (dE) satellites NGC 147 and NGC 185. Three of these are associated with NGC 147 and one with NG
Movement patterns of forest elephants (Loxodonta cyclotis Matschie, 1900) in the Odzala-Kokoua National Park, Republic of Congo
[Otros] Les éléphants de forêt d'Afrique (Loxodonta cyclotis Matschie, 1900) sont des ingénieurs en écologie qui jouent un rôle fondamental dans la dynamique de la végétation. L'espèce constitue une préoccupation immédiate pour la conservation,
mais elle est relativement peu étudiée. Pour combler cette lacune de connaissances,
nous avons étudié les facteurs de déplacements quotidiens (déplacements linéaires)
des éléphants de forêt ¿ caractérisés par un ensemble de variables géographiques,
météorologiques et anthropiques ¿ dans le Parc National d'Odzala¿Kokoua, en
République du Congo. Concrètement, nous avons utilisé la forêt d'arbres décisionnels pour modéliser et démêler les principaux facteurs environnementaux régissant
les déplacements de six éléphants de forêt, équipés de colliers GPS et suivis pendant
16 mois. Les résultats ont montré que les femelles se déplaçaient plus loin que les
mâles, tandis que la présence de routes ou d¿établissements humains perturbait le comportement des éléphants, ce qui accélérait les déplacements. Les éléphants de
forêt se déplaçaient plus rapidement dans les cours d¿eau et dans les forêts dont le
sous¿bois était dominé par les forêts de Marantaceae et les bais, mais se déplaçait plus
lentement dans les savanes. Enfin, les zones inondables ¿ characterisées par l¿altitude
et les précipitations accumulées ¿ et les températures plus élevées empêchaient des
déplacements plus longs. Nous espérons que ces résultats amélioreront les connaissances sur les mouvements des espèces à travers différents habitats, ce qui serait
bénéfique pour la gestion de leur conservation.[EN] African forest elephants (Loxodonta cyclotis Matschie, 1900) are ecological engineers
that play a fundamental role in vegetation dynamics. The species is of immediate conservation concern, yet it is relatively understudied. To narrow this knowledge gap,
we studied the drivers of daily movement patterns (linear displacements) of forest
elephants¿characterised by a set of geographical, meteorological and anthropogenic
variables¿in the Odzala¿Kokoua National Park, Republic of Congo. Explicitly, we used
conditional random forest to model and disentangle the main environmental factors
governing the displacements of six forest elephants,fitted with GPS collars and tracked
over 16 months. Results indicated that females moved further distances than males,
while the presence of roads or human settlements disrupted elephant behaviour resulting in faster displacements. Forest elephants moved faster along watercourses
and through forest with understory dominated by Marantaceae forests and bais, but
moved slower in savannahs. Finally, flood¿prone areas¿described by elevation and
accumulated precipitation¿and higher temperatures prevented longer displacements.
We expect these results to improve the knowledge on the species movements through
different habitats, which would benefit its conservation management.The fieldwork was financed by African Parks. We are grateful
to the Congolese wildlife authorities (Ministère de l'Économie
Forestière et de l'Environnement) for the permission to carry
out this study, and we are deeply indebted to the director of the
OKNP and to the conservation, wildlife monitoring and research
manager, Erik Marav, respectively, for their continued support
during our study. We are particularly grateful to Dr. Mike Kock,
veterinarian, for collaring the elephants and to the field tracking
team. We are also grateful to Séan Cahill for the useful comments
and English correction that helped improve this manuscript. The
authors of the present study certify that they have no affiliations
with or involvement in any organisation or entity with any financial or nonfinancial interest in the subject matter or materials discussed in this manuscript.Molina-Vacas, G.; Muñoz-Mas, R.; Martinez-Capel, F.; Rodriguez-Teijeiro, JD.; Le Fohlic, G. (2019). Movement patterns of forest elephants (Loxodonta cyclotis Matschie, 1900) in the Odzala-Kokoua National Park, Republic of Congo. African Journal of Ecology. 58:23-33. https://doi.org/10.1111/aje.12695S233358Arlot, S., & Celisse, A. (2010). A survey of cross-validation procedures for model selection. Statistics Surveys, 4(0), 40-79. doi:10.1214/09-ss054Bermejo, M. (1999). Status and conservation of primates in Odzala National Park, Republic of the Congo. Oryx, 33(4), 323-331. doi:10.1046/j.1365-3008.1999.00081.xBirkett, P. J., Vanak, A. T., Muggeo, V. M. R., Ferreira, S. M., & Slotow, R. (2012). Animal Perception of Seasonal Thresholds: Changes in Elephant Movement in Relation to Rainfall Patterns. 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Animal cultures matter for conservation
This is the author accepted manuscript. The final version is available from AAAS via the DOI in this record.No abstrac
High-Isolation Antenna Array Using SIW and Realized with a Graphene Layer for Sub-Terahertz Wireless Applications
This paper presents the results of a study on developing an effective technique to increase the performance characteristics of array antennas for sub-THz integrated circuit applications. This is an essential to compensate the limited power of sub-THz sources. Although conventional array structures can provide a solution to enhance the radiation-gain however in the case of small-sized array structures the radiation properties can be adversely affect due to mutual coupling between the radiating elements. It is demonstrated here the effectiveness of using SIW technology to suppress surface wave propagations and near field mutual coupling. Prototype 2×3 antenna array with dimensions 20×13.5×0.125 mm 3 were designed and constructed on a dielectric substrate with thickness of 125 m for operation across 0.19-0.20 THz. The metallization of the antenna was coated with 500 nm layer of Graphene. With the proposed technique the isolation between the radiating elements was improved on average by 22.5 dB compared to a reference array antenna with no SIW isolation. The performance of the array was enhanced by transforming the patch to exhibit metamaterial characteristics. This was achieved by embedding an array of periodic slots of sub-wavelength in the patch. Compared to the reference array the metamaterial inspired structure exhibits an isolation, radiation gain and efficiency improvement on average by 28.5dB, 6.7dBi, and 36%, respectively. These results show the viability of proposed approach in developing array antennas for application in sub-THz integrated circuits. Keywords: Sub-terahertz (THz) frequency, substrate integrated waveguide (SIW), metamaterial (MTM), high isolation, high gain, graphene-layer, antennas arrays
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