756 research outputs found
From Garrisoned District to Chinese Town: Land and Boundaries at the Kowloon Walled City, 1898-1912
The Kowloon Walled City in Hong Kong became a named entity around 1810 and was demolished in 1994, but its architecture had long been unclassified. Not until the years just prior to its demolition did this dense slum of informal multi-story buildings receive sustained attention from architects and architectural historians. However, the architectural nature of the six-acre area predated its late-20th-century state. After its founding as a Qing military outpost, it underwent various structural additions and renovations, including an imperial Chinese administrative complex known as a yamen (衙門) and an outer wall, after which the Walled City was named. Against the grain of scholarship that has focused on the Walled City’s postwar, informal architecture, this article considers the site’s early years, arguing that the Walled City’s yamen and outer wall played a crucial role in the region’s land management practices. These two architectural structures make legible the Walled City’s evolution from a Qing administrative zone to a crowded slum. The Convention of 1898 ushered in a British-led land surveying effort throughout the New Territories region of Hong Kong, followed by the creation of an intricate bureaucracy for managing land lots. This clash of empires saw the use of two forms of land knowledge, Qing land deeds and British cadastral land surveys. In between these systems existed the Walled City, its inhabitation falling outside the British conception of land division but its historical contours very much shaped by the architectural boundaries that gave it its name
2D non-LTE Modeling for Axi-symmetric Winds. II. A Short Characteristic Solution for Radiative Transfer in Rotating Winds
We present a new radiative transfer code for axi-symmetric stellar
atmospheres and compare test results against 1D and 2D models with and without
velocity fields. The code uses the short characteristic method with
modifications to handle axi-symmetric and non-monotonic 3D wind velocities, and
allows for distributed calculations. The formal solution along a characteristic
is evaluated with a resolution that is proportional to the velocity gradient
along the characteristic. This allows us to accurately map the variation of the
opacities and emissivities as a function of frequency and spatial coordinates,
but avoids unnecessary work in low velocity regions. We represent a
characteristic with an impact-parameter vector p (a vector that is normal to
the plane containing the characteristic and the origin) rather than the
traditional unit vector in the direction of the ray. The code calculates the
incoming intensities for the characteristics by a single latitudinal
interpolation without any further interpolation in the radiation angles. Using
this representation also provides a venue for distributed calculations since
the radiative transfer can be done independently for each p.Comment: 18 pages, 12 figures, accepted for publication in A&
Near-field spectroscopy of Dirac plasmons in Bi2Se3 ribbon arrays
Plasmons supported in the massless electron surface states of topological insulators (TIs), known as Dirac plasmons, have great potential in next generation optoelectronics. However, their inherent confinement to the surface makes the investigation of Dirac plasmons challenging. Near-field techniques provide the ideal platform to directly probe Dirac plasmons due to the sensitivity to evanescent fields at the surface. Here, we demonstrate the use of aperture near-field spectroscopy for the investigation of localized terahertz (THz) Dirac plasmon resonances in Bi2Se3 ribbon arrays with widths ranging from 10 to 40 µm. Unlike scattering THz near-field techniques, the aperture method is most sensitive to plasmons with the relevant lower-momenta corresponding to plasmon wavelengths on the scale of ∼20 µm. The combination of THz time-domain spectroscopy and aperture near-field microscopy enables sampling of localized Dirac plasmons in the near-field zone in the 0.5–2.5 THz range. We map the plasmon dispersion, which reveals a coupled plasmon–phonon polariton interaction. The near-field spectra show a higher contrast of the upper polariton branch in comparison with far-field observations. The information revealed by aperture near-field spectroscopy could deepen our understanding of the behavior of Dirac plasmons, leading to the potential development of real-world TI devices
The Axially Symmetric Ejecta of Supernova 1987A
Extensive early observations proved that the ejecta of supernova 1987A (SN
1987A) are aspherical. Fifteen years after the supernova explosion, the Hubble
Space Telescope has resolved the rapidly expanding ejecta. The late-time images
and spectroscopy provide a geometrical picture that is consistent with early
observations and suggests a highly structured, axially symmetric geometry. We
present here a new synthesis of the old and new data. We show that the Bochum
event, presumably a clump of Ni, and the late-time image, the locus of
excitation by Ti, are most naturally accounted for by sharing a common
position angle of about 14\degree, the same as the mystery spot and early
speckle data on the ejecta, and that they are both oriented along the axis of
the inner circumstellar ring at 45\degree to the plane of the sky. We also
demonstrate that the polarization represents a prolate geometry with the same
position angle and axis as the early speckle data and the late-time image and
hence that the geometry has been fixed in time and throughout the ejecta. The
Bochum event and the Doppler kinematics of the [Ca II]/[O II] emission in
spatially resolved HST spectra of the ejecta can be consistently integrated
into this geometry. The radioactive clump is deduced to fall approximately
along the axis of the inner circumstellar ring and therefore to be redshifted
in the North whereas the [Ca II]/[O II] 7300 \AA emission is redshifted in the
South. We present a jet-induced model for the explosion and argue that such a
model can account for many of the observed asymmetries. In the jet models, the
oxygen and calcium are not expected to be distributed along the jet, but
primarily in an expanding torus that shares the plane and northern blue shift
of the inner circumstellar ring.Comment: To Appear in Ap
Functional Conservation of Asxl2, a Murine Homolog for the Drosophila Enhancer of Trithorax and Polycomb Group Gene Asx
Polycomb-group (PcG) and trithorax-group (trxG) proteins regulate histone methylation to establish repressive and active chromatin configurations at target loci, respectively. These chromatin configurations are passed on from mother to daughter cells, thereby causing heritable changes in gene expression. The activities of PcG and trxG proteins are regulated by a special class of proteins known as Enhancers of trithorax and Polycomb (ETP). The Drosophila gene Additional sex combs (Asx) encodes an ETP protein and mutations in Asx enhance both PcG and trxG mutant phenotypes. The mouse and human genomes each contain three Asx homologues, Asx-like 1, 2, and 3. In order to understand the functions of mammalian Asx-like (Asxl) proteins, we generated an Asxl2 mutant mouse from a gene-trap ES cell line.We show that the Asxl2 gene trap is expressed at high levels in specific tissues including the heart, the axial skeleton, the neocortex, the retina, spermatogonia and developing oocytes. The gene trap mutation is partially embryonic lethal and approximately half of homozygous animals die before birth. Homozygotes that survive embryogenesis are significantly smaller than controls and have a shortened life span. Asxl2(-/-) mice display both posterior transformations and anterior transformation in the axial skeleton, suggesting that the loss of Asxl2 disrupts the activities of both PcG and trxG proteins. The PcG-associated histone modification, trimethylation of histone H3 lysine 27, is reduced in Asxl2(-/-) heart. Necropsy and histological analysis show that mutant mice have enlarged hearts and may have impaired heart function.Our results suggest that murine Asxl2 has conserved ETP function and plays dual roles in the promotion of PcG and trxG activity. We have also revealed an unexpected role for Asxl2 in the heart, suggesting that the PcG/trxG system may be involved in the regulation of cardiac function
Deprojection technique for galaxy cluster considering point spread function
We present a new method for the analysis of Abell 1835 observed by
XMM-Newton. The method is a combination of the Direct Demodulation technique
and deprojection. We eliminate the effects of the point spread function (PSF)
with the Direct Demodulation technique. We then use a traditional depro-jection
technique to study the properties of Abell 1835. Compared to that of
deprojection method only, the central electron density derived from this method
increases by 30%, while the temperature profile is similar.Comment: accepted for publication in Sciences in China -- G, the Black Hole
special issu
The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A
The presence of narrow high-temperature emission lines from nitrogen-rich gas
close to SN 1987A has been the principal observational constraint on the evolu-
tionary status of the supernova's progenitor. A new analysis of the complete
five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A
(1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII]
1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and
systematic errors and reveals significant short-term fluctuations in the light
curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days
and show a progression from high to low ionization potential, implying an ioni-
zation gradient in the emitting region. The line emission turns on suddenly at
83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches
peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and
inclination of 41.0+/-3.9 is derived from these times, assuming a circular
ring. The probable role of resonant scattering in the N V light curve
introduces systematic errors that leads us to exclude this line from the timing
analysis. A new nebular analysis yields improved CNO abundance ratios
N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in
our previous paper. From the late-time behavior of the light curves we find
that the emission origi- nates from progressively lower density gas. We
estimate the emitting mass near maximum (roughly 400 days) to be roughly
4.7E{-2} solar masses, assuming a filling factor of unity and an electron
density of 2.6E4 cm^{-3}. These results are discussed in the context of current
models for the emission and hydrodynamics of the ring.Comment: 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in pres
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Flavin Mononucleotide as a Biomarker of Organ Quality-A Pilot Study.
BACKGROUND: Flavin mononucleotide (FMN), released from damaged mitochondrial complex I during hypothermic liver perfusion, has been shown to be predictive of 90-day graft loss. Normothermic machine perfusion (NMP) and normothermic regional perfusion (NRP) are used for organ reconditioning and quality assessment before transplantation. This pilot study aimed to investigate the changes of FMN levels during normothermic reperfusion of kidneys, livers, and lungs and examine whether FMN could serve as a biomarker to predict posttransplant allograft quality. METHODS: FMN concentrations, in perfusates collected during NMP of kidneys, abdominal NRP, and ex vivo lung perfusion, were measured using fluorescence spectrometry and correlated to the available perfusion parameters and clinical outcomes. RESULTS: Among 7 transplanted kidneys out of the 11 kidneys that underwent NMP, FMN levels at 60 minutes of NMP were significantly higher in the allografts that developed delayed graft function and primary nonfunction (P = 0.02). Fifteen livers from 23 circulatory death donors that underwent NRP were deemed suitable for transplantation. Their FMN levels at 30 minutes of NRP were significantly lower than those not procured for transplantation (P = 0.004). In contrast, little FMN was released during the 8 lung perfusions. CONCLUSIONS: This proof of concept study suggested that FMN in the perfusates of kidney NMP has the potential to predict posttransplant renal function, whereas FMN at 30 minutes of NRP predicts whether a liver would be accepted for transplantation. More work is required to validate the role of FMN as a putative biomarker to facilitate safe and reliable decision-making before embarking on transplantation.NIHR BTR
On model selection forecasting, Dark Energy and modified gravity
The Fisher matrix approach (Fisher 1935) allows one to calculate in advance
how well a given experiment will be able to estimate model parameters, and has
been an invaluable tool in experimental design. In the same spirit, we present
here a method to predict how well a given experiment can distinguish between
different models, regardless of their parameters. From a Bayesian viewpoint,
this involves computation of the Bayesian evidence. In this paper, we
generalise the Fisher matrix approach from the context of parameter fitting to
that of model testing, and show how the expected evidence can be computed under
the same simplifying assumption of a gaussian likelihood as the Fisher matrix
approach for parameter estimation. With this `Laplace approximation' all that
is needed to compute the expected evidence is the Fisher matrix itself. We
illustrate the method with a study of how well upcoming and planned experiments
should perform at distinguishing between Dark Energy models and modified
gravity theories. In particular we consider the combination of 3D weak lensing,
for which planned and proposed wide-field multi-band imaging surveys will
provide suitable data, and probes of the expansion history of the Universe,
such as proposed supernova and baryonic acoustic oscillations surveys. We find
that proposed large-scale weak lensing surveys from space should be able
readily to distinguish General Relativity from modified gravity models.Comment: 6 pages, 2 figure
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