19,126 research outputs found
Enhancement of by disorder in underdoped iron pnictides
We analyze how disorder affects the transition temperature of the
superconducting state in the iron pnictides. The conventional wisdom is
that should rapidly decrease with increasing inter-band non-magnetic
impurity scattering, but we show that this behavior holds only in the overdoped
region of the phase diagram. In the underdoped regime, where superconductivity
emerges from a pre-existing magnetic state, disorder gives rise to two
competing effects: breaking of the Cooper pairs, which tends to reduce ,
and suppression of the itinerant magnetic order, which tends to bring
up. We show that for a wide range of parameters the second effect wins, leading
to an increase of with disorder in the coexistence state. Our results
explain several recent experimental findings and provide another evidence for
-pairing in the iron pnictides.Comment: 5 pages, 3 figures; revised version accepted in PRB-R
Superlens made of a metamaterial with extreme effective parameters
We propose a superlens formed by an ultra-dense array of crossed metallic
wires. It is demonstrated that due to the anomalous interaction between crossed
wires, the structured substrate is characterized by an anomalously high index
of refraction and supports strongly confined guided modes with very short
propagation wavelengths. It is theoretically proven that a planar slab of such
structured material makes a superlens that may compensate for the attenuation
introduced by free-space propagation and restore the subwavelength details of
the source. The bandwidth of the proposed device can be quite significant since
the response of the structured substrate is non-resonant. The theoretical
results are fully supported by numerical simulations.Comment: Accepted for publication in Phys. Rev. B (in press
Assessing consistency of fish survey data : uncertainties in the estimation of mackerel icefish (Champsocephalus gunnari) abundance at South Georgia
Acknowledgments The authors wish to thank the crews, fishermen and scientists who conducted the various surveys from which data were obtained, and Mark Belchier and Simeon Hill for their contributions. This work was supported by the Government of South Georgia and South Sandwich Islands. Additional logistical support provided by The South Atlantic Environmental Research Institute with thanks to Paul Brickle. Thanks to Stephen Smith of Fisheries and Oceans Canada (DFO) for help in constructing bootstrap confidence limits. Paul Fernandes receives funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland), and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. We also wish to thank two anonymous referees for their helpful suggestions on earlier versions of this manuscript.Peer reviewedPostprin
A comprehensive classification of galaxies in the SDSS: How to tell true from fake AGN?
We use the W_Ha versus [NII]/Ha (WHAN) diagram to provide a comprehensive
emission-line classification of SDSS galaxies. This classification is able to
cope with the large population of weak line galaxies that do not appear in
traditional diagrams due to a lack of some of the diagnostic lines. A further
advantage of the WHAN diagram is to allow the differentiation between two very
distinct classes that overlap in the LINER region of traditional diagnostic
diagrams. These are galaxies hosting a weakly active nucleus (wAGN) and
"retired galaxies" (RGs), i.e. galaxies that have stopped forming stars and are
ionized by their hot evolved low-mass stars. A useful criterion to distinguish
true from fake AGN (i.e. the RGs) is the ratio (\xi) of the
extinction-corrected L_Ha with respect to the Ha luminosity expected from
photoionization by stellar populations older than 100 Myr. This ratio follows a
markedly bimodal distribution, with a \xi >> 1 population composed by systems
undergoing star-formation and/or nuclear activity, and a peak at \xi ~ 1
corresponding to the prediction of the RG model. We base our classification
scheme on the equivalent width of Ha, an excellent observational proxy for \xi.
Based on the bimodal distribution of W_Ha, we set the division between wAGN and
RGs at W_Ha = 3 A. Five classes of galaxies are identified within the WHAN
diagram: (a) Pure star forming galaxies: log [NII]/Ha 3 A.
(b) Strong AGN (i.e., Seyferts): log [NII]/Ha > -0.4 and W_Ha > 6 A. (c) Weak
AGN: log [NII]/Ha > -0.4 and W_Ha between 3 and 6 A. (d) RGs: W_Ha < 3 A. (e)
Passive galaxies (actually, line-less galaxies): W_Ha and W_[NII] < 0.5 A. A
comparative analysis of star formation histories and of other properties in
these different classes of galaxies corroborates our proposed differentiation
between RGs and weak AGN in the LINER-like family. (Abridged)Comment: Accepted for publication in MNRA
A retrospective case-series to assess the effectiveness of selective laser trabeculoplasty in the management of open angle glaucoma in black patients
A research report submitted to the Faculty of Health Sciences , University of
the Witwatersrand, Johannesburg in partial fulfillment of the requirements for
the degree of Master of Medicine in OphthalmologyAims
This study aims to evaluate the efficacy of SLT as a treatment option in black patients
with open angle glaucoma and to distinguish which patients are most likely to
respond to SLT.
Methods
The study is a retrospective case-series of black patients collected at St. Johnâs Eye
Hospital in Johannesburg. Data from 46 eyes were collected from the files of
patients who had had SLT at least six months previously. The data collected included
demographic factors, ocular characteristics and intraocular pressure (IOP) before and
at each visit after selective laser trabeculoplasty (SLT). The data were analysed
statistically firstly by comparing the pre-SLT IOP with the average post-SLT IOP, and
secondly by Kaplan-Meir analysis of the duration of IOP control post-SLT.
Results
The mean age of participants was 58,3 years. The mean follow up time was 8
months (range1 week to 33 months). The mean pre-SLT IOP was 20,7mmHg and the
mean postâSLT IOP was 17,8mmHg. The change in IOP was statistically significant
(p<0,001). The mean reduction in IOP was a 12% reduction from baseline. The mean
duration of IOP control by Kaplan-Meier analysis was 13 months. The only
demographic or ocular factor associated with a greater reduction in IOP was
trabecular meshwork pigmentation. Patients with higher pigmentation had a median
IOP reduction of 23,0% and those with low pigmentation a median reduction of
3,5%.
Conclusion
SLT resulted in a statistically significant but modest reduction in IOP in black
glaucoma patients. The average reduction in IOP was 12% from baseline. High
trabecular meshwork pigmentation was associated with a statistically significantly
greater reduction in IOP.MT201
BĂŒchwald-Hartwig reaction applied to synthesis of new luminescent liquid crystal triarylamines derived from isoxazoles
© 2015 Taylor & Francis Group, LLC. The present work describes the synthesis and characterization of novel series of triarylamines isoxazoles (TAA) addressed to the organic photovoltaic materials. Diarylisoxazoles were synthesized by sequential [3+2] 1,3-dipolar cycloaddition reaction between arylnitrile oxides and selected arylalkenes followed by MnO2-oxidation. Isoxazoles were coupled to diarylamines by BĂŒchwald-Hartwig reaction to afford desired compounds 6a-k. Some TAA display liquid-crystalline behaviour and UV-Vis absorption and fluorescence emission were analysed for all samples of TAA 6a-k
Modeling the input history of programs for improved instruction-memory performance
When a program is loaded into memory for execution, the relative position of
its basic blocks is crucial, since loading basic blocks that are unlikely to be
executed first places them high in the instruction-memory hierarchy only to be
dislodged as the execution goes on. In this paper we study the use of Bayesian
networks as models of the input history of a program. The main point is the
creation of a probabilistic model that persists as the program is run on
different inputs and at each new input refines its own parameters in order to
reflect the program's input history more accurately. As the model is thus
tuned, it causes basic blocks to be reordered so that, upon arrival of the next
input for execution, loading the basic blocks into memory automatically takes
into account the input history of the program. We report on extensive
experiments, whose results demonstrate the efficacy of the overall approach in
progressively lowering the execution times of a program on identical inputs
placed randomly in a sequence of varied inputs. We provide results on selected
SPEC CINT2000 programs and also evaluate our approach as compared to the gcc
level-3 optimization and to Pettis-Hansen reordering
Optical and Near Infrared Study of the Cepheus E outflow, a very low excitation object
We present images and spectra of the Cepheus E (Cep E) region at both optical
and infrared wavelengths. Only the brightest region of the southern lobe of the
Cep E outflow reveals optical emission, suggesting that the extinction close to
the outflow source plays an important r\^ole in the observed difference between
the optical and IR morphologies. Cep E is a unique object since it provides a
link between the spectroscopic properties of the optical Herbig-Haro (HH)
objects and those of deeply embedded outflows.Comment: Accepted Astron. J., 8 files: paper, tables plus 6 figure
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