22,691 research outputs found
Accurate measurement of Cn2 profile with Shack-Hartmann data
The precise reconstruction of the turbulent volume is a key point in the
development of new-generation Adaptive Optics systems. We propose a new Cn2
profilometry method named CO-SLIDAR (COupled Slope and scIntillation Detection
And Ranging), that uses correlations of slopes and scintillation indexes
recorded on a Shack-Hartmann from two separated stars. CO-SLIDAR leads to an
accurate Cn2 retrieval for both low and high altitude layers. Here, we present
an end-to-end simulation of the Cn2 profile measurement. Two Shack-Hartmann
geometries are considered. The detection noises are taken into account and a
method to subtract the bias is proposed. Results are compared to Cn2 profiles
obtained from correlations of slopes only or correlations of scintillation
indexes only.Comment: 10 pages, 8 figures, SPIE Conference "Astronomical Telescopes and
Instrumentation" 2012, Amsterdam, paper 8447-19
Structure and electronic properties of new model dinitride systems: A density-functional study of CN2, SiN2, and GeN2
The dinitrides CN2, SiN2, and GeN2 in assumed pyrite-type structures are
studied by means of density functional theory using both ultrasoft
pseudopotentials and the augmented spherical wave (ASW) method. The former two
materials constitute the large-x limit of the broader class of CNx and SiNx
compounds, which are well known for their interesting mechanical and electronic
properties. For CN2 a large bulk modulus B_0 of 405 GPa was determined . While
SiN2 is found to be a wide band gap compound, the calculated gaps of CN2 and
GeN2 are considerably smaller. The trends in structural and electronic
properties as e.g. bond lengths, band gaps and covalency are well understood in
terms of the interplay of different types of bonding.Comment: 9 pages, 5 figure
Analyzing the Effects of Meteorology on Radar Measured Index of Refraction Structure Parameter
Forecasting optical turbulence is essential for the Air Force\u27s Airborne Laser program to optimize placement of aircraft. To find bow meteorology affects Cn2, the intensity of turbulence in the index of refraction, case studies of synoptically interesting times are first chosen. Correlation coefficients are then computed between radar measured Cn2 and meteorological quantities. The potential for mechanically turbulent activity is looked at. In the analysis of this work, six meteorological features were found likely to affect Cn2. Two features associated with affecting potential refractivity, and thus Cn2, are jets and inversions. North of jet core level in the northern hemisphere, higher values of Cn2 can be found north of the core, with lower values to the south. With temperature inversions, typically higher values of can be found just above inversions with comparatively lower Cn2 values underneath. The remaining four features affecting Cn2 are not directly related to potential refractivity alone. The first is bands of high Cn2 occurring within regions of strong vertical wind shear. The second feature is high Cn2 occasionally seen underneath inversions during the approach of jets that are associated with gravity wave activity. The other two meteorological features are tropopause boundaries and trough passage
Preceding rule induction with instance reduction methods
A new prepruning technique for rule induction is presented which applies instance reduction before rule induction. An empirical evaluation records the predictive accuracy and size of rule-sets generated from 24 datasets from the UCI Machine Learning Repository. Three instance reduction algorithms (Edited Nearest Neighbour, AllKnn and DROP5) are compared. Each one is used to reduce the size of the training set, prior to inducing a set of rules using Clark and Boswell's modification of CN2. A hybrid instance reduction algorithm (comprised of AllKnn and DROP5) is also tested. For most of the datasets, pruning the training set using ENN, AllKnn or the hybrid significantly reduces the number of rules generated by CN2, without adversely affecting the predictive performance. The hybrid achieves the highest average predictive accuracy
Optical turbulence vertical distribution with standard and high resolution at Mt. Graham
A characterization of the optical turbulence vertical distribution (Cn2
profiles) and all the main integrated astroclimatic parameters derived from the
Cn2 and the wind speed profiles above the site of the Large Binocular Telescope
(Mt. Graham, Arizona, US) is presented. The statistic includes measurements
related to 43 nights done with a Generalized Scidar (GS) used in standard
configuration with a vertical resolution Delta(H)~1 km on the whole 20 km and
with the new technique (HVR-GS) in the first kilometer. The latter achieves a
resolution Delta(H)~20-30 m in this region of the atmosphere. Measurements done
in different periods of the year permit us to provide a seasonal variation
analysis of the Cn2. A discretized distribution of Cn2 useful for the Ground
Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis
for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case
is done including the calculation of the 'gray zones' for J, H and K bands. Mt.
Graham confirms to be an excellent site with median values of the seeing
without dome contribution epsilon = 0.72", the isoplanatic angle theta0 = 2.5"
and the wavefront coherence time tau0= 4.8 msec. We find that the optical
turbulence vertical distribution decreases in a much sharper way than what has
been believed so far in proximity of the ground above astronomical sites. We
find that 50% of the whole turbulence develops in the first 80+/-15 m from the
ground. We finally prove that the error in the normalization of the
scintillation that has been recently put in evidence in the principle of the GS
technique, affects these measurements with an absolutely negligible quantity
(0.04").Comment: 11 figures. MNRAS, accepte
Up-regulation of CNDP2 facilitates the proliferation of colon cancer
BACKGROUND: Cytosolic nonspecific dipetidase (CN2) belongs to the family of M20 metallopeptidases. It was stated in previous articles that higher expression levels of CN2 were observed in renal cell carcinoma and breast cancer. Our study explored the correlation between CN2 and colon carcinogenesis. METHODS: We analysed the relationship between 183 patients clinicopathological characteristics and its CN2 expression. To detect the levels of CN2 in colon cancer cell lines and colon cancer tissues by western blot. To verify cell proliferation in colon cancer cells with knockdown of CNDP2 and explore the causes of these phenomena. RESULTS: The expression levels of CN2 in clinical colon tumors and colon cancer cell lines were significantly higher than that in normal colon mucosa and colon cell lines. The difference in CN2 levels was associated with tumor location (right- and left-sided colon cancer), but there was no significant association with age, gender, tumor size, tumor grade, tumor stage or serum carcinoembryonic antigen (CEA). Knockdown of CNDP2 inhibited cell proliferation, blocked cell cycle progression and retarded carcinogenesis in an animal model. The signaling pathway through which knockdown of CNDP2 inhibited cell proliferation and tumorigenesis involved in EGFR, cyclin B1 and cyclin E. CONCLUSIONS: Knockdown of CNDP2 can inhibit the proliferation of colon cancer in vitro and retarded carcinogenesis in vivo
Methods for Determining The Refractive Index Structure Parameter in the Marine Atmospheric Boundary Layer
An experimental study of the marine atmospheric boundary layer effects on the index of refraction was conducted off the coast of Portsmouth, NH between Battery Farnsworth and Wood Island. This study aimed to compare measured changes in the refractive index structure parameter (Cn2) to estimates using time series data of single point atmospheric variables, including temperature, pressure, and wind velocity. A scintillometer transmitter and receiver located at Battery Farnsworth and Wood Island, respectively, provided direct measurements of Cn2. Data from a weather tower containing a sonic anemometer was used to estimate Cn2.
Three methods of analysis to estimate Cn2 from the time-series data from single point atmospheric variables were employed. The three methods were a two-point structure function method (most common method in practice owing to its simplicity), a spectral analysis method assuming Kolmogorov turbulence with r2/3 (k -5/3) scaling, and a spectral analysis not assumingKolmogorov scaling. Here r (or wavenumber k) refers to the turbulent length scales.
The measurements of Cn2 acquired in the present study are consistent with Cn2 measurements from other studies in the literature. The data for all three methods to estimate Cn2 closely followed Cn2 measured from the scintillometer, with the spectral analysis methods showing the best agreement. The study lends credence to the use of structure functions obtained from time-series data from single point measurements of atmospheric variables to accurately estimate Cn2 within the marine atmospheric boundary layer
Mt. Graham: Optical turbulence vertical distribution at standard and high vertical resolution
A characterization of the optical turbulence vertical distribution and all
the main integrated astroclimatic parameters derived from the CN2 and the wind
speed profiles above Mt. Graham is presented. The statistic includes
measurements related to 43 nights done with a Generalized Scidar (GS) used in
standard configuration with a vertical resolution of ~1 km on the whole 20-22
km and with the new technique (HVR-GS) in the first kilometer. The latter
achieves a resolution of ~ 20-30 m in this region of the atmosphere.
Measurements done in different periods of the year permit us to provide a
seasonal variation analysis of the CN2. A discretized distribution of the
typical CN2 profiles useful for the Ground Layer Adaptive Optics (GLAO)
simulations is provided and a specific analysis for the LBT Laser Guide Star
system ARGOS case is done including the calculation of the 'gray zones' for J,
H and K bands. Mt. Graham confirms to be an excellent site with median values
of the seeing without dome contribution equal to 0.72", the isoplanatic angle
equal to 2.5" and the wavefront coherence time equal to 4.8 msec. We provide a
cumulative distribution of the percentage of turbulence developed below H*
where H* is included in the (0,1 km) range. We find that 50% of the whole
turbulence develops in the first 80 m from the ground. The turbulence
decreasing rate is very similar to what has been observed above Mauna Kea.Comment: 12 pages, 6 figures, Proc. SPIE Conference "Ground-based and Airborne
Telescopes III", 27 June 2010, San Diego, California, US
Very low bias stress in n-type organic single crystal transistors
Bias stress effects in n-channel organic field-effect transistors (OFETs) are
investigated using PDIF-CN2 single-crystal devices with Cytop gate dielectric,
both under vacuum and in ambient. We find that the amount of bias stress is
very small as compared to all (p-channel) OFETs reported in the literature.
Stressing the PDIF-CN2 devices by applying 80 V to the gate for up to a week
results in a decrease of the source drain current of only ~1% under vacuum and
~10% in air. This remarkable stability of the devices leads to characteristic
time constants, extracted by fitting the data with a stretched exponential -
that are \tau ~ 2\cdot10^9 s in air and \tau ~ 5\cdot10^9 s in vacuum -
approximately two orders of magnitude larger than the best values reported
previously for p-channel OFETs.Comment: Submitted to Applied Physics Letters; 14 pages, 3 figure
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