21,653 research outputs found
A metal–organic framework/α-alumina composite with a novel geometry for enhanced adsorptive separation
The development of a metal–organic framework/α-alumina composite leads to a novel concept: efficient adsorption occurs within a plurality of radial micro-channels with no loss of the active adsorbents during the process. This composite can effectively remediate arsenic contaminated water producing potable water recovery, whereas the conventional fixed bed requires eight times the amount of active adsorbents to achieve a similar performance
Optical Resonances in Reflectivity near Crystal Modes with Spatial Dispersion
We study the effect of spatial dispersion of crystal modes on optical
properties such as the reflectivity . As an example for isotropic media, we
investigate the simplest model for phonons in ionic crystals and compare with
previous results for highly anisotropic plasmons, which are now understood from
a more general point of view. As a consequence of the wave vector dependence of
the dielectric function small changes in the lineshape are predicted. Beyond
that, if the frequency of minimal is near a pole of the dispersionless
dielectric function, the relative amplitude of dips in with normal and
anomalous dispersion differ significantly, if dissipation and disorder are low.Comment: 4 pages, 7 eps figures, minor change
Effect of nonlinear filters on detrended fluctuation analysis
We investigate how various linear and nonlinear transformations affect the
scaling properties of a signal, using the detrended fluctuation analysis (DFA).
Specifically, we study the effect of three types of transforms: linear,
nonlinear polynomial and logarithmic filters. We compare the scaling properties
of signals before and after the transform. We find that linear filters do not
change the correlation properties, while the effect of nonlinear polynomial and
logarithmic filters strongly depends on (a) the strength of correlations in the
original signal, (b) the power of the polynomial filter and (c) the offset in
the logarithmic filter. We further investigate the correlation properties of
three analytic functions: exponential, logarithmic, and power-law. While these
three functions have in general different correlation properties, we find that
there is a broad range of variable values, common for all three functions,
where they exhibit identical scaling behavior. We further note that the scaling
behavior of a class of other functions can be reduced to these three typical
cases. We systematically test the performance of the DFA method in accurately
estimating long-range power-law correlations in the output signals for
different parameter values in the three types of filters, and the three
analytic functions we consider.Comment: 12 pages, 7 figure
A Machine-Synesthetic Approach To DDoS Network Attack Detection
In the authors' opinion, anomaly detection systems, or ADS, seem to be the
most perspective direction in the subject of attack detection, because these
systems can detect, among others, the unknown (zero-day) attacks. To detect
anomalies, the authors propose to use machine synesthesia. In this case,
machine synesthesia is understood as an interface that allows using image
classification algorithms in the problem of detecting network anomalies, making
it possible to use non-specialized image detection methods that have recently
been widely and actively developed. The proposed approach is that the network
traffic data is "projected" into the image. It can be seen from the
experimental results that the proposed method for detecting anomalies shows
high results in the detection of attacks. On a large sample, the value of the
complex efficiency indicator reaches 97%.Comment: 12 pages, 2 figures, 5 tables. Accepted to the Intelligent Systems
Conference (IntelliSys) 201
Effect of nonstationarities on detrended fluctuation analysis
Detrended fluctuation analysis (DFA) is a scaling analysis method used to
quantify long-range power-law correlations in signals. Many physical and
biological signals are ``noisy'', heterogeneous and exhibit different types of
nonstationarities, which can affect the correlation properties of these
signals. We systematically study the effects of three types of
nonstationarities often encountered in real data. Specifically, we consider
nonstationary sequences formed in three ways: (i) stitching together segments
of data obtained from discontinuous experimental recordings, or removing some
noisy and unreliable parts from continuous recordings and stitching together
the remaining parts -- a ``cutting'' procedure commonly used in preparing data
prior to signal analysis; (ii) adding to a signal with known correlations a
tunable concentration of random outliers or spikes with different amplitude,
and (iii) generating a signal comprised of segments with different properties
-- e.g. different standard deviations or different correlation exponents. We
compare the difference between the scaling results obtained for stationary
correlated signals and correlated signals with these three types of
nonstationarities.Comment: 17 pages, 10 figures, corrected some typos, added one referenc
Characterization of Sleep Stages by Correlations of Heartbeat Increments
We study correlation properties of the magnitude and the sign of the
increments in the time intervals between successive heartbeats during light
sleep, deep sleep, and REM sleep using the detrended fluctuation analysis
method. We find short-range anticorrelations in the sign time series, which are
strong during deep sleep, weaker during light sleep and even weaker during REM
sleep. In contrast, we find long-range positive correlations in the magnitude
time series, which are strong during REM sleep and weaker during light sleep.
We observe uncorrelated behavior for the magnitude during deep sleep. Since the
magnitude series relates to the nonlinear properties of the original time
series, while the signs series relates to the linear properties, our findings
suggest that the nonlinear properties of the heartbeat dynamics are more
pronounced during REM sleep. Thus, the sign and the magnitude series provide
information which is useful in distinguishing between the sleep stages.Comment: 7 pages, 4 figures, revte
A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing
It is proposed that all flavor mixing is caused by the mixing of the three
quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of
SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are
generated by a single matrix. The entire 3-by-3 complex mass matrix of the
neutrinos M_{nu} is then found to have a simple expression in terms of two
complex parameters and an overall scale. Thus, all the presently unknown
neutrino parameters are predicted. The best fits are for theta_{atm} less than
or approximately 40 degrees. The leptonic Dirac CP phase is found to be
somewhat greater than pi radians.Comment: 10 pages, 4 figures, one table. Typos correcte
Evidence for Magnetic Pseudoscaling in Overdoped La(2-x)Sr(x)CuO(4)
We report the results of electronic Raman scattering experiments on an
overdoped La(1.78)Sr(0.22)CuO(4) single crystal as a function of temperature.
The scattering rate Gamma(w->0,T) has been determined from the normal state
B(1g) spectra in the range 50 K < T < 300 K. Gamma(T) decreases linearly from
300 K to about 175 K and then undergoes a reduction with respect to the
expected mean-field behavior. This trend suggests a crossover to pseudoscaling
regime at about T(cr)=160 K. The results are in good agreement with the
prediction of the nearly antiferromagnetic Fermi liquid model. There is no
evidence of a pseudogap in the spectra obtained from this overdoped sample.Comment: RevTex, 4 pages with 3 PS figures included, replaced with minor
changes in the text and reference
Muon-spin-relaxation study of the magnetic penetration depth in MgB2
The magnetic vortex lattice (VL) of polycrystalline MgB2 has been
investigated by transverse-field muon-spin-relaxation (TF-MuSR). The evolution
of TF-MuSR depolarization rate, sigma, that is proportional to the second
moment of the field distribution of the VL has been studied as a function of
temperature and applied magnetic field. The low temperature value s exhibits a
pronounced peak near Hext = 75 mT. This behavior is characteristic of strong
pinning induced distortions of the VL which put into question the
interpretation of the low-field TF-MuSR data in terms of the magnetic
penetration depth lambda(T). An approximately constant value of sigma, such as
expected for an ideal VL in the London-limit, is observed at higher fields of
Hext > 0.4 T. The TF-MuSR data at Hext = 0.6 T are analyzed in terms of a
two-gap model. We obtain values for the gap size of D1 = 6.0 meV (2D1/kBTc =
3.6), D2 = 2.6 meV (2D2/kBTc = 1.6), a comparable spectral weight of the two
bands and a zero temperature value for the magnetic penetration depth of lambda
= 100 nm. In addition, we performed MuSR-measurements in zero external field
(ZF-MuSR). We obtain evidence that the muon site (at low temperature) is
located on a ring surrounding the center of the boron hexagon. Muon diffusion
sets in already at rather low temperature of T > 10 K. The nuclear magnetic
moments can account for the observed relaxation rate and no evidence for
electronic magnetic moments has been obtained.Comment: 15 pages, 4 figure
Producing high fidelity single photons with optimal brightness via waveguided parametric down-conversion
Parametric down-conversion (PDC) offers the possibility to control the
fabrication of non-Gaussian states such as Fock states. However, in
conventional PDC sources energy and momentum conservation introduce strict
frequency and photon number correlations, which impact the fidelity of the
prepared state. In our work we optimize the preparation of single-photon Fock
states from the emission of waveguided PDC via spectral filtering. We study the
effect of correlations via photon number resolving detection and quantum
interference. Our measurements show how the reduction of mixedness due to
filtering can be evaluated. Interfering the prepared photon with a coherent
state we establish an experimentally measured fidelity of the produced target
state of 78%.Comment: 15 pages, 10 Figures, published versio
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