598 research outputs found
Fibre DFB lasers in a 4x10 Gbit/s WDM link with a single sinc-sampled fibre grating dispersion compensator
WDM transmission and dispersion compensation at 40 Gbit/s over 200 km standard fibre is demonstrated on a 100 GHz grid using four high power single-polarisation single-sided output DFB fibre laser based transmitters and a single 4 channel WDM chirped fibre Bragg grating dispersion compensator
Optimisation of DSF and SOA based phase conjugators by incorporating noise-suppressing fibre gratings
We compare the performance of dispersion-shifted-fibre (DSF) and semiconductor-optical-amplifier (SOA) based phase conjugators for a 10 Gb/s non-return-to-zero system with respect to conversion efficiency, noise figure and distortion. Fibre gratings are used for signal extraction and amplified spontaneous emission (ASE) suppression, allowing closer wavelength spacing and reducing the conjugation noise figure by up to 12 dB. Despite the higher SOA conversion efficiency, both conjugators give similar noise figures with ASE suppression. However, the DSF based conjugator has the advantage of distortion tolerance at higher input power. Introduction: Optical phase conjugation has attracted much recent research attention due to its potential application for group-velocity-dispersion and self-phase-modulation compensation in mid-point spectral inversion (MPSI) systems, and also for coherent wavelength conversion in optical switching and routing. The two most promising optical phase conjugation techniques are four-wave mixing (FWM) in either dispersion-shifted fibre (DSF), or semiconductor optical amplifiers (SOA). A DSF based conjugator requires phase matching close to its zero dispersion wavelength for efficient four-wave mixing. This restricts its wavelength flexibility compared to an SOA based conjugator which offers a much wider conversion bandwidth. Furthermore, the low FWM conversion efficiency in passive DSF seems to make the SOA a preferred phase conjugating medium. However, in a practical communication system, conjugation optical signal-to-noise ratio (SNR) is more important than conversion efficiency. The noise at the conjugate wavelength is usually dominated by the amplified spontaneous emission (ASE) noise from the pump and signal. The reduction of this noise has been demonstrated in an SOA based conjugator (i) by bandpass filtering of the pump and/or signal waves before mixing, and (ii) by the insertion of a notch filter at the conjugate wavelength before the conjugator. In this letter, SOA and DSF based conjugators are compared by investigating the conversion efficiency, noise and eye opening in a 10 Gb/s non-return-to-zero (NRZ) externally-modulated system, using an identical filtering network. We report for the first time the use of fibre gratings for efficient ASE noise filtering and conjugate signal extraction. The performance enhancement using these noise-suppressing gratings is also investigated
The Solar Flare Iron Abundance
The abundance of iron is measured from emission line complexes at 6.65 keV
(Fe line) and 8 keV (Fe/Ni line) in {\em RHESSI} X-ray spectra during solar
flares. Spectra during long-duration flares with steady declines were selected,
with an isothermal assumption and improved data analysis methods over previous
work. Two spectral fitting models give comparable results, viz. an iron
abundance that is lower than previous coronal values but higher than
photospheric values. In the preferred method, the estimated Fe abundance is
(on a logarithmic scale, with ),
or times the photospheric Fe abundance. Our estimate is based on
a detailed analysis of 1,898 spectra taken during 20 flares. No variation from
flare to flare is indicated. This argues for a fractionation mechanism similar
to quiet-Sun plasma. The new value of has important implications
for radiation loss curves, which are estimated.Comment: Accepted by Astrophysical Journa
Highly Ionized Potassium Lines in Solar X-ray Spectra and the Abundance of Potassium
The abundance of potassium is derived from X-ray lines observed during flares
by the RESIK instrument on the solar mission CORONAS-F between 3.53 A and 3.57
A. The lines include those emitted by He-like K and Li-like K dielectronic
satellites, which have been synthesized using the CHIANTI atomic code and newly
calculated atomic data. There is good agreement of observed and synthesized
spectra, and the theoretical behavior of the spectra with varying temperature
estimated from the ratio of the two GOES channels is correctly predicted. The
observed fluxes of the He-like K resonance line per unit emission measure gives
log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9.
This is higher than photospheric abundance estimates by a factor 5.5, a
slightly greater enhancement than for other elements with first ionization
potential (FIP) less than about 10 eV. There is, then, the possibility that
enrichment of low-FIP elements in coronal plasmas depends weakly on the value
of the FIP which for K is extremely low (4.34 eV). Our work also suggests that
fractionation of elements to form the FIP effect occurs in the low chromosphere
rather than higher up, as in some models.Comment: 14 pages, 3 figure
Ion Charge States in Halo CMEs: What can we Learn about the Explosion?
We describe a new modeling approach to develop a more quantitative
understanding of the charge state distributions of the ions of various elements
detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced
Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution
based on observations of CMEs propagating in the plane of the sky and on
theoretical models, we integrate time dependent equations for the ionization
balance of various elements to compare with ACE data. We find that plasma in
the CME ``core'' typically requires further heating following filament
eruption, with thermal energy input similar to the kinetic energy input. This
extra heating is presumably the result of post eruptive reconnection. Plasma
corresponding to the CME ``cavity'' is usually not further ionized, since
whether heated or not, the low density gives freeze-in close the the Sun. The
current analysis is limited by ambiguities in the underlying model CME
evolution. Such methods are likely to reach their full potential when applied
to data to be acquired by STEREO when at optimum separation. CME evolution
observed with one spacecraft may be used to interpret CME charge states
detected by the other.Comment: 20 pages, accepted by Ap
A Unified Picture of the FIP and Inverse FIP Effects
We discuss models for coronal abundance anomalies observed in the coronae of
the sun and other late-type stars following a scenario first introduced by
Schwadron, Fisk & Zurbuchen of the interaction of waves at loop footpoints with
the partially neutral gas. Instead of considering wave heating of ions in this
location, we explore the effects on the upper chromospheric plasma of the wave
ponderomotive forces. These can arise as upward propagating waves from the
chromosphere transmit or reflect upon reaching the chromosphere-corona
boundary, and are in large part determined by the properties of the coronal
loop above. Our scenario has the advantage that for realistic wave energy
densities, both positive and negative changes in the abundance of ionized
species compared to neutrals can result, allowing both FIP and Inverse FIP
effects to come out of the model. We discuss how variations in model parameters
can account for essentially all of the abundance anomalies observed in solar
spectra. Expected variations with stellar spectral type are also qualitatively
consistent with observations of the FIP effect in stellar coronae.Comment: 25 pages, 4 figures, submitted to Ap
Educating the future workforce: building the evidence about interprofessional learning
This paper addresses the theme of interprofessional education for health and social care professionals as it effects on the development of the work force. The drivers for change in the UK, typified by the Bristol Royal Infirmary and Victoria Climbié inquiries and the response to this in the form of Department of Health policy, are discussed. The need for rapid development of the evidence base around this subject is evident form literature reviews of the impact of interprofessional education. Directions for future research and investment in this area are proposed including the need for a stronger theoretical base and for longitudinal studies over extended periods of time in order to examine short, medium and long term outcomes in relation to health care practice
KONSEP ILUSI ANAMORFOSIS DALAM ARSITEKTUR
Seiring perkembang dan kemajuan teknologi yang ada suatu karya seni yang sesungguhnya mulai tergantikan dengan setiap fasilitas teknologi yang memberikan berbagai hal yang mudah dan instan dalam menciptakan suatu karya yang menarik, di Indonesia sendiri karena perkembangan zaman yang demikian ketergantugan akan teknologi makin tinggi akibatnya kreatifitas mulai memiliki batasan-batasan karena tidak dapat berdiri sendiiri oleh karena ini juga rasa penghargaan akan suatu karya yang di lakukan dengan ketrampilan yang telaten kurang terpakai atau bahkan kurang dihargai. Oleh sebab itu tema arsitektur zaman renaissance Italia yang bergaya kontemporer lewat pembahasan dari âIlusi Anamorfosis dalam Arsitekturâ dipilih sebagai suatu tema yang memberikan edukasi bagi masyarakat luas untuk melihat dan menghargai lebih dalam suatu karya yang memiliki unsur seni yang dapat diterapkan dalam arsitektur dan memberikan motifasi bagi generasi selanjutnya dalam berkarya.Pada tulisan ini, dimuat informasi mengenai kajian teoritik yaitu pengkajian tema ilusi anamorfosis dalam arsitektur dan studi preseden dari penerapan atau aplikasi tema pada objek-objek arsitektural kemudian dilanjutkan dengan strategi implementasi tema degan membandingan antara teori dan studi preseden. hal-hal apa saja yang berkaitan dengan arsitektural untuk mencari tahu implementsi tema pada objek arsitektur.Ilusi anamorfosis lebih cocok diterapkan pada bangunan komersial karena keunikan yang menjual dan menjadi daya tarik, tenik ini juga lazim di gunakan pada interior bangunan, gubahan masa, ruang luar dan selubung / fasade bangunan. Implementasi ilusi tersebut umumnya diimplementasikan pada elemen arsitektural yang dapat dilihat secara langsung, karena tema Ilusi anamorfosis dalam Arsitektur mengandalkan teknik visualisasi untuk dapat dinikmati / dirasakan. Lewat anamorfosis ini arsitektur dan seni menjadi suatu kesatuan yang menghasilkan karya yang tidak umum dijumpai dan menjadi hal yang dapat membangkitkan semangat atau motifasi bagi para seniman maupun masyarakat dalam berkarya baik di dunia seni maupun dalam arsitektural. Kata Kunci : Ilusi, Anamorfosis, Arsitektu
Non-Maxwellian Proton Velocity Distributions in Nonradiative Shocks
The Balmer line profiles of nonradiative supernova remnant shocks provide the
means to measure the post-shock proton velocity distribution. While most
analyses assume a Maxwellian velocity distribution, this is unlikely to be
correct. In particular, neutral atoms that pass through the shock and become
ionized downstream form a nonthermal distribution similar to that of pickup
ions in the solar wind. We predict the H alpha line profiles from the
combination of pickup protons and the ordinary shocked protons, and we consider
the extent to which this distribution could affect the shock parameters derived
from H alpha profiles. The Maxwellian assumption could lead to an underestimate
of shock speed by up to about 15%. The isotropization of the pickup ion
population generates wave energy, and we find that for the most favorable
parameters this energy could significantly heat the thermal particles.
Sufficiently accurate profiles could constrain the strength and direction of
the magnetic field in the shocked plasma, and we discuss the distortions from a
Gaussian profile to be expected in Tycho's supernova remnant.Comment: 13 pages, 6 figure
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