589 research outputs found
Design and implementation of an electro-optical backplane with pluggable in-plane connectors
The design, implementation and characterisation of an electro-optical
backplane and an active pluggable in-plane optical connector technology
is presented. The connection architecture adopted allows line cards to
be mated to and unmated from a passive electro-optical backplane with
embedded polymeric waveguides. The active connectors incorporate a
photonics interface operating at 850 nm and a mechanism to passively
align the interface to the optical waveguides embedded in the backplane.
A demonstration platform has been constructed to assess the viability of
embedded electro-optical backplane technology in dense data storage
systems. The demonstration platform includes four switch cards, which
connect both optically and electronically to the electro-optical backplane
in a chassis. These switch cards are controlled by a single board
computer across a Compact PCI bus on the backplane. The electrooptical
backplane is comprised of copper layers for power and low speed
bus communication and one polymeric optical layer, wherein waveguides
have been patterned by a direct laser writing scheme. The optical
waveguide design includes densely arrayed multimode waveguides with
a centre to centre pitch of 250Îźm between adjacent channels, multiple
cascaded waveguide bends, non-orthogonal crossovers and in-plane
connector interfaces. In addition, a novel passive alignment method
has been employed to simplify high precision assembly of the optical
receptacles on the backplane. The in-plane connector interface is based
on a two lens free space coupling solution, which reduces susceptibility
to contamination. Successful transfer of 10.3 Gb/s data along multiple
waveguides in the electro-optical backplane has been demonstrated and
characterised
Fragments of ML Decidable by Nested Data Class Memory Automata
The call-by-value language RML may be viewed as a canonical restriction of
Standard ML to ground-type references, augmented by a "bad variable" construct
in the sense of Reynolds. We consider the fragment of (finitary) RML terms of
order at most 1 with free variables of order at most 2, and identify two
subfragments of this for which we show observational equivalence to be
decidable. The first subfragment consists of those terms in which the
P-pointers in the game semantic representation are determined by the underlying
sequence of moves. The second subfragment consists of terms in which the
O-pointers of moves corresponding to free variables in the game semantic
representation are determined by the underlying moves. These results are shown
using a reduction to a form of automata over data words in which the data
values have a tree-structure, reflecting the tree-structure of the threads in
the game semantic plays. In addition we show that observational equivalence is
undecidable at every third- or higher-order type, every second-order type which
takes at least two first-order arguments, and every second-order type (of arity
greater than one) that has a first-order argument which is not the final
argument
Pulsed Magnetic Field Measurements of the Composite Fermion Effective Mass
Magnetotransport measurements of Composite Fermions (CF) are reported in 50 T
pulsed magnetic fields. The CF effective mass is found to increase
approximately linearly with the effective field , in agreement with our
earlier work at lower fields. For a of 14 T it reaches , over 20
times the band edge electron mass. Data from all fractions are unified by the
single parameter for all the samples studied over a wide range of
electron densities. The energy gap is found to increase like at
high fields.Comment: Has final table, will LaTeX without error
Flower and fruit development of Parkia pendula (Fabaceae, Mimosoideae)
Parkia pendula occurs in Brazil in Amazonia and in the northeastern Atlantic Forest. In the latter, its buds, nectar, and seedpod gum are discussed to be keystone resources for the mammalian fauna. To enhance the knowledge about these important nourishment sources, the aim of this study was to detect and describe distinct phases in the flower and pod development. The study was conducted in a 306 ha forest fragment in Igarassu, Pernambuco, northeastern Brazil. Six morphometrical variables were measured weekly at five inflorescences of two individuals from September 2003 to January 2004. Eleven distinct developmental phases were identified in the 21 weeks lasting development from the very first inflorescences to mature pods and are described in detail. These phases are good predictors for the flowering and fruiting phenology of P. pendula, since they are easily distinguishable from the forest floor. Furthermore, highly synchronized abortions of inflorescences, buds, and pods were observed which support the previously assumed predator satiation defense strategy in Parkia.Parkia pendula ocorre no Brasil, tanto na AmazĂ´nia como na Mata Atlântica nordestina. Seus botĂľes, nĂŠctar e goma da vagem sĂŁo recursos chave para a mastofauna da Mata Atlântica nordestina. Para aumentar o conhecimento sobre estes importantes recursos alimentares, este estudo teve como objetivo detectar e descrever as diferentes fases de desenvolvimento de flores e frutos. Este trabalho foi realizado em um fragmento de Mata Atlântica de 306 ha em Igarassu, Pernambuco, Nordeste do Brasil. Entre setembro de 2003 e janeiro de 2004, seis variĂĄveis morfomĂŠtricas foram medidas semanalmente em cinco inflorescĂŞncias de dois indivĂduos. Onze fases distintas de desenvolvimento puderam ser identificadas e descritas em detalhe nas 21 semanas desde o desenvolvimento das primeiras inflorescĂŞncias atĂŠ as vagens maduras. Essas fases sĂŁo boas preditoras da fenologia de floração e frutificação de P. pendula porque sĂŁo distinguĂveis facilmente do solo da floresta. AlĂŠm disto, a observação de abortos sincronizados de inflorescĂŞncias, botĂľes e vagens corrobora a estratĂŠgia de defesa previamente sugerida para Parkia, de saciedade de predadores
Online teacher development: collaborating in a virtual learning environment
Over recent years educational institutions have been making increasing use of virtual environments to set up collaborative activities for learners. While it is recognized that teachers play an important role in facilitating learner collaboration online they may not have the necessary skills to do so successfully. Thus, a small scale professional development programme was set up and piloted by two distance universities. The aims were to develop teachersâ experience of online group work; to trial a set of pilot activities which would raise awareness of factors contributing to successful collaborative online activity; and to identify professional development needs in this area. This article reports on the hands-on experience of a group of 20 teachers, examines some of the competences that are needed to successfully collaborate in virtual environments, and presents the skills that teachers need to foster online collaborative learning in the virtual classroom. Quantitative and qualitative data were collected, examining the levels of participation among participants, the collaborative activity of two groups, and teacher perception of the collaboration which took place. The skills identified include planning and managing the collaboration, designing appropriate activities, giving clear instructions and getting students to negotiate ground rules for participation, moderating at the right level, and choosing the right environment and the appropriate tool(s). While this study was carried out with language teachers, many of the findings are applicable to other subject areas where growing emphasis is placed on the development of collaborative skills
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
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