801 research outputs found
Optical detection and modulation at 2µm-2.5µm in silicon
Recently the 2µm wavelength region has emerged as an exciting prospect for the next generation of telecommunications. In this paper we experimentally characterise silicon based plasma dispersion effect optical modulation and defect based photodetection in the 2-2.5µm wavelength range. It is shown that the effectiveness of the plasma dispersion effect is dramatically increased in this wavelength window as compared to the traditional telecommunications wavelengths of 1.3µm and 1.55µm. Experimental results from the defect based photodetectors show that detection is achieved in the 2-2.5µm wavelength range, however the responsivity is reduced as the wavelength is increased away from 1.55µm
Examining Periodic Solar Wind Density Structures Observed in the SECCHI Heliospheric Imagers
We present an analysis of small-scale, periodic, solar-wind density
enhancements (length-scales as small as \approx 1000 Mm) observed in images
from the Heliospheric Imager (HI) aboard STEREO A. We discuss their possible
relationship to periodic fluctuations of the proton density that have been
identified at 1 AU using in-situ plasma measurements. Specifically, Viall,
Kepko, and Spence (2008) examined 11 years of in-situ solar-wind density
measurements at 1 AU and demonstrated that not only turbulent structures, but
also non-turbulent periodic density structures exist in the solar wind with
scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall,
Spence, and Kasper (2009) analyzed the {\alpha} to proton solar-wind abundance
ratio measured during one such event of periodic density structures,
demonstrating that the plasma behavior was highly suggestive that either
temporally or spatially varying coronal source plasma created those density
structures. Large periodic density structures observed at 1 AU, which were
generated in the corona, can be observable in coronal and heliospheric
white-light images if they possess sufficiently high density contrast. Indeed,
we identify such periodic density structures as they enter the HI field of view
and follow them as they advect with the solar wind through the images. The
smaller periodic density structures that we identify in the images are
comparable in size to the larger structures analyzed in-situ at 1 AU, yielding
further evidence that periodic density enhancements are a consequence of
coronal activity as the solar wind is formed.Comment: 15 pages, 12 figures. The final publication is available at
http://www.springerlink.co
Long-range attraction between particles in dusty plasma and partial surface tension of dusty phase boundary
Effective potential of a charged dusty particle moving in homogeneous plasma
has a negative part that provides attraction between similarly charged dusty
particles. A depth of this potential well is great enough to ensure both
stability of crystal structure of dusty plasma and sizable value of surface
tension of a boundary surface of dusty region. The latter depends on the
orientation of the surface relative to the counter-ion flow, namely, it is
maximal and positive for the surface normal to the flow and minimal and
negative for the surface along the flow. For the most cases of dusty plasma in
a gas discharge, a value of the first of them is more than sufficient to ensure
stability of lenticular dusty phase void oriented across the counter-ion flow.Comment: LATEX, REVTEX4, 7 pages, 6 figure
Nowhere to hide: radio-faint AGN in the GOODS-N field: II. Multi-wavelength AGN selection techniques and host galaxy properties
Large scale structure and cosmolog
Baseline neutrophil-lymphocyte ratio holds no prognostic value for esophageal and junctional adenocarcinoma in patients treated with neoadjuvant chemotherapy
BACKGROUND: Several studies have reported that neutrophil-lymphocyte ratio (NLR) can predict survival in esophageal and gastroesophageal junction adenocarcinoma, as it reflects systemic inflammation. Hence, we aimed to determine whether baseline NLR holds prognostic value for esophageal adenocarcinoma patients treated with neoadjuvant chemotherapy (nCT) followed by surgery. METHODS: We studied the data of 139 patients that received nCT before undergoing esophagectomy with curative intent, all identified from a prospectively maintained database (1998-2016). Pretreatment hematology reports were used to calculate the baseline NLR. A receiver operating characteristic curve (ROC-curve) was plotted to determine an optimal cutoff value. NLR quartiles were used to display possible differences between groups in relation to overall survival (OS) and disease-free survival (DFS) using the method of Kaplan-Meier. Cox regression analysis was performed to assess the prognostic value of NLR. RESULTS: The median OS and DFS times were 46 months (interquartile range [IQR]: 19-166) and 30 months (IQR: 13-166], respectively, for the entire cohort. The ROC-curve showed that NLR has no discriminating power for survival status (area under the curve = 0.462) and therefore no optimal cutoff value could be determined. There were no statistically significant differences in median OS times for NLR quartiles: 65 (Q1), 32 (Q2), 45 (Q3), and 46 months (Q4) (P = 0.926). Similarly, DFS showed no difference between quartile groups, with median survival times of 27 (Q1), 19 (Q2), 36 (Q3), and 20 months (Q4) (P = 0.973). Age, pN, pM, and resection margin were independent prognostic factors for both OS and DFS. On the contrary, NLR was not associated with OS or DFS in univariable and multivariable analyses. CONCLUSION: Baseline NLR holds no prognostic value for esophageal and gastroesophageal junction adenocarcinoma patients treated with nCT in this study, in contrast to other recently published papers. This result questions the validity of NLR as a reliable prognostic indicator and its clinical usefulness in these patients
Rotating inclined cylinder and the effect of the tilt angle on vortices
We study numerically some possible vortex configurations in a rotating
cylinder that is tilted with respect to the rotation axis and where different
numbers of vortices can be present at given rotation velocity. In a long
cylinder at small tilt angles the vortices tend to align along the cylinder
axis and not along the rotation axis. We also show that the axial flow along
the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson
instability above some critical tilt angle. When the vortices become unstable
the final state often appears to be a dynamical steady state, which may contain
turbulent regions where new vortices are constantly created. These new vortices
push other vortices in regions with laminar flow towards the top and bottom
ends of the cylinder where they finally annihilate. Experimentally the inclined
cylinder could be a convenient environment to create long lasting turbulence
with a polarization which can be adjusted with the tilt angle.Comment: 10 pages, 10 figure
An ALMA survey of CO in submillimetre galaxies: companions, triggering, and the environment in blended sources
We present ALMA observations of the mid-J 12CO emission from six single-dish selected 870-μm sources in the Extended Chandra Deep Field-South and UKIDSS Ultra-Deep Survey fields. These six single-dish submillimetre sources were selected based on previous ALMA continuum observations, which showed that each comprised a blend of emission from two or more individual submillimetre galaxies (SMGs), separated on 5–10 arcsec scales. The six single-dish submillimetre sources targeted correspond to a total of 14 individual SMGs, of which seven have previously measured robust optical/near-infrared spectroscopic redshifts, which were used to tune our ALMA observations. We detect CO(3–2) or CO(4–3) at z = 2.3–3.7 in 7 of the 14 SMGs, and in addition serendipitously detect line emission from three gas-rich companion galaxies, as well as identify four new 3.3 mm selected continuum sources in the six fields. Joint analysis of our CO spectroscopy and existing data suggests that 64(±18)percent of the SMGs in blended submillimetre sources are unlikely to be physically associated. However, three of the SMG fields (50 per cent) contain new, serendipitously detected CO-emitting (but submillimetre-faint) sources at similar redshifts to the 870 μm selected SMGs we targeted. These data suggest that the SMGs inhabit overdense regions, but that these are not sufficiently overdense on ∼100 kpc scales to influence the source blending given the short lifetimes of SMGs. We find that 21±12percent of SMGs have spatially distinct and kinematically close companion galaxies (∼8–150 kpc and ≲ 300 km s−1), which may have enhanced their star formation via gravitational interactions
An ALMA survey of the S2CLS UDS field: optically invisible submillimetre galaxies
We analyse a robust sample of 30 near-infrared-faint (KAB > 25.3, 5σ) submillimetre galaxies (SMGs) selected from a 0.96 deg2 field to investigate their properties and the cause of their faintness in optical/near-infrared wavebands. Our analysis exploits precise identifications based on Atacama Large Millimeter Array (ALMA) 870-μm continuum imaging, combined with very deep near-infrared imaging from the UKIDSS Ultra Deep Survey. We estimate that SMGs with KAB > 25.3 mag represent 15 ± 2 per cent of the total population brighter than S870 = 3.6 mJy, with a potential surface density of ∼450 deg−2 above S870 ≥ 1 mJy. As such, they pose a source of contamination in surveys for both high-redshift ‘quiescent’ galaxies and very high redshift Lyman-break galaxies. We show that these K-faint SMGs represent the tail of the broader submillimetre population, with comparable dust and stellar masses to KAB ≤ 25.3 mag SMGs, but lying at significantly higher redshifts (z = 3.44 ± 0.06 versus z = 2.36 ± 0.11) and having higher dust attenuation (AV = 5.2 ± 0.3 versus AV = 2.9 ± 0.1). We investigate the origin of the strong dust attenuation and find indications that these K-faint galaxies have smaller dust continuum sizes than the KAB ≤ 25.3 mag galaxies, as measured by ALMA, which suggests their high attenuation is related to their compact sizes. We identify a correlation of dust attenuation with star formation rate surface density (SFR), with the K-faint SMGs representing the higher SFR and highest AV galaxies. The concentrated, intense star formation activity in these systems is likely to be associated with the formation of spheroids in compact galaxies at high redshifts, but as a result of their high obscuration these galaxies are completely missed in ultraviolet, optical, and even near-infrared surveys
The SCUBA-2 Cosmology Legacy Survey: ALMA resolves the bright-end of the submillimeter number counts
We present high-resolution 870 μm Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1 degree2 850 μm maps from the SCUBA-2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median = 8.7 ± 0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4σ significance in our 30 ALMA maps. In of the ALMA maps the single-dish source comprises a blend of ≥2 SMGs, where the secondary SMGs are Ultra-luminous Infrared Galaxies (ULIRGs) with 1012 . The brightest SMG contributes on average of the single-dish flux density, and in the ALMA maps containing ≥2 SMGs the secondary SMG contributes of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S870 > 7.5 mJy, and by 60% at S870 > 12 mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power law with a break at 8.5 ± 0.6 mJy. The break corresponds to a luminosity of ~6 × 1012 or a star formation rate (SFR) of ~103 . For the typical sizes of these SMGs, which are resolved in our ALMA data with = 1.2 ± 0.1 kpc, this yields a limiting SFR density of ~100 yr−1 kpc−2 Finally, the number density of S870 2 mJy SMGs is 80 ± 30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs are likely to be physically associated
Point vortices and polynomials of the Sawada-Kotera and Kaup-Kupershmidt equations
Rational solutions and special polynomials associated with the generalized
K_2 hierarchy are studied. This hierarchy is related to the Sawada-Kotera and
Kaup-Kupershmidt equations and some other integrable partial differential
equations including the Fordy-Gibbons equation. Differential-difference
relations and differential equations satisfied by the polynomials are derived.
The relationship between these special polynomials and stationary
configurations of point vortices with circulations Gamma and -2Gamma is
established. Properties of the polynomials are studied. Differential-difference
relations enabling one to construct these polynomials explicitly are derived.
Algebraic relations satisfied by the roots of the polynomials are found.Comment: 23 pages, 8 figure
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