152 research outputs found
Global Distribution of Water Vapor and Cloud Cover--Sites for High Performance THz Applications
Absorption of terahertz radiation by atmospheric water vapor is a serious
impediment for radio astronomy and for long-distance communications.
Transmission in the THz regime is dependent almost exclusively on atmospheric
precipitable water vapor (PWV). Though much of the Earth has PWV that is too
high for good transmission above 200 GHz, there are a number of dry sites with
very low attenuation. We performed a global analysis of PWV with
high-resolution measurements from the Moderate Resolution Imaging Spectrometer
(MODIS) on two NASA Earth Observing System (EOS) satellites over the year of
2011. We determined PWV and cloud cover distributions and then developed a
model to find transmission and atmospheric radiance as well as necessary
integration times in the various windows. We produced global maps over the
common THz windows for astronomical and satellite communications scenarios.
Notably, we show that up through 1 THz, systems could be built in excellent
sites of Chile, Greenland and the Tibetan Plateau, while Antarctic performance
is good to 1.6 THz. For a ground-to-space communication link up through 847
GHz, we found several sites in the Continental United States where mean
atmospheric attenuation is less than 40 dB; not an insurmountable challenge for
a link.Comment: 15 pages, 23 figure
Subdomain Model for Predicting Armature Reaction Field of Dual-Stator Consequent-Pole PM Machines Accounting for Tooth-Tips
International audienceThis paper presents an exact analytical subdomain model of dual-stator consequent-pole permanent-magnet (DSCPPM) machines accounting for tooth-tips, which can accurately predict the armature reaction field distribution in DSCPPM machines. In the proposed subdomain model, the field domain is composed of four types of sub-regions, viz. magnets, outer/inner air gaps, slots and slot openings. The analytical expressions of vector potential in each sub-region are determined by boundary and interface conditions. In comparison to the analytically predicted results, the corresponding flux density field distributions computed by finite element (FE) method are analyzed, which confirms the excellent accuracy of the developed subdomain model
Universal Adversarial Perturbations for CNN Classifiers in EEG-Based BCIs
Multiple convolutional neural network (CNN) classifiers have been proposed
for electroencephalogram (EEG) based brain-computer interfaces (BCIs). However,
CNN models have been found vulnerable to universal adversarial perturbations
(UAPs), which are small and example-independent, yet powerful enough to degrade
the performance of a CNN model, when added to a benign example. This paper
proposes a novel total loss minimization (TLM) approach to generate UAPs for
EEG-based BCIs. Experimental results demonstrated the effectiveness of TLM on
three popular CNN classifiers for both target and non-target attacks. We also
verified the transferability of UAPs in EEG-based BCI systems. To our
knowledge, this is the first study on UAPs of CNN classifiers in EEG-based
BCIs. UAPs are easy to construct, and can attack BCIs in real-time, exposing a
potentially critical security concern of BCIs
Chandra Observations of the Cl1604 Supercluster at z=0.9: Evidence for an Overdensity of Active Galactic Nuclei
We present the results of Chandra observations of the Cl1604 supercluster at
z~0.9. The system is the largest structure mapped at redshifts approaching
unity, containing at least eight spectroscopically confirmed galaxy clusters
and groups. Using two 50-ksec ACIS-I pointings we examine both the X-ray point
source population and the diffuse emission from individual clusters in the
system. We find a 2.5\sigma excess of point sources detected in the hard band
(2-10 keV) relative to the number of sources found in blank fields observed by
Chandra. No such excess is observed in the soft band (0.5-2 keV). The hard-band
source density is 1.47 times greater than that of a blank field, in agreement
with the previously reported correlation between overdensity amplitude and
cluster redshift. Using a maximum likelihood technique we have matched 112 of
the 161 detected X-ray point sources to optical counterparts and found 15
sources that are associated with the supercluster. All 15 sources have
rest-frame luminosities consistent with emission from active galactic nuclei
(AGN). We find that the supercluster AGN largely avoid the densest regions of
the system and are instead distributed on the outskirts of massive clusters or
within poorer clusters and groups. We have also detected diffuse emission from
two of the eight clusters and groups in the system, clusters Cl1604+4304 and
Cl1604+4314. The systems have bolometric luminosities of 1.43x10^44 and
8.20x10^43 h70^-2 erg s^-1 and gas temperatures of 3.50 (+1.82-1.08) and 1.64
(+0.65-0.45) keV, respectively. Using updated velocity dispersions, we compare
the properties of these systems to the cluster scaling relations followed by
other X-ray and optically selected galaxy clusters at high redshift.Comment: 24 pages, 14 figures, submitted to Ap
Electrochemical detection of low-copy number salivary RNA based on specific signal amplification with a hairpin probe
We developed a technique for electrochemical detection of salivary mRNA employing a hairpin probe (HP). Steric hindrance (SH) suppresses unspecific signal and generates a signal-on amplification process for target detection. The stem-loop configuration brings the reporter end of the probe into close proximity with the surface and makes it unavailable for binding with the mediator. Target binding opens the hairpin structure of the probe, and the mediator can then bind to the accessible reporter. Horseradish peroxidase is utilized to generate electrochemical signal. This signal-on process is characterized by a low basal signal, a strong positive readout and a large dynamic range. The SH is controlled via hairpin design and electrical field. By applying electric field control to HPs, the limit of detection of RNA is about 0.4 fM, which is 10 000-fold more sensitive than conventional linear probes. Endogenous Interleukin-8 mRNA is detected with the HP, and good correlation with the quantitative PCR technique is obtained. The resultant process allows a simple setup and by reducing the number of steps it is suited for the point-of-care detection of specific nucleic acid sequences from complex body fluids such as saliva
Extended Radio AGN at z ∼ 1 in the ORELSE Survey: The Confining Effect of Dense Environments
Recent hydrodynamic simulations and observations of radio jets have shown that the surrounding environment has a large effect on their resulting morphology. To investigate this, we use a sample of 50 Extended Radio Active Galactic Nuclei (ERAGN) detected in the Observations of Redshift Evolution in Large-Scale Environments survey. These sources are all successfully cross-identified to galaxies within a redshift range of 0.55 ≤ z ≤ 1.35, either through spectroscopic redshifts or accurate photometric redshifts. We find that ERAGN are more compact in high-density environments than those in low-density environments at a significance level of 4.5σ. Among a series of internal properties under our scrutiny, only the radio power demonstrates a positive correlation with their spatial extent. After removing the possible radio power effect, the difference of size in low- and high-density environments persists. In the global environment analyses, the majority (86%) of high-density ERAGN reside in the cluster/group environment. In addition, ERAGN in the cluster/group central regions are preferentially compact with a small scatter in size, compared to those in the cluster/group intermediate regions and fields. In conclusion, our data appear to support the interpretation that the dense intracluster gas in the central regions of galaxy clusters plays a major role in confining the spatial extent of radio jets
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