428 research outputs found
Online Adaboost-based parameterized methods for dynamic distributed network intrusion detection
Current network intrusion detection systems lack
adaptability to the frequently changing network environments.
Furthermore, intrusion detection in the new distributed archi-
tectures is now a major requirement. In this paper, we propose
two online Adaboost-based intrusion detection algorithms. In the
first algorithm, a traditional online Adaboost process is used
where decision stumps are used as weak classifiers. In the second
algorithm, an improved online Adaboost process is proposed,
and online Gaussian mixture models (GMMs) are used as weak
classifiers. We further propose a distributed intrusion detection
framework, in which a local parameterized detection model is
constructed in each node using the online Adaboost algorithm. A
global detection model is constructed in each node by combining
the local parametric models using a small number of samples in
the node. This combination is achieved using an algorithm based
on particle swarm optimization (PSO) and support vector ma-
chines. The global model in each node is used to detect intrusions.
Experimental results show that the improved online Adaboost
process with GMMs obtains a higher detection rate and a lower
false alarm rate than the traditional online Adaboost process that
uses decision stumps. Both the algorithms outperform existing
intrusion detection algorithms. It is also shown that our PSO,
and SVM-based algorithm effectively combines the local detection
models into the global model in each node; the global model in
a node can handle the intrusion types that are found in other
nodes, without sharing the samples of these intrusion types
SU(2)-in-SU(1,1) Nested Interferometer for Highly Sensitive, Loss-Tolerant Quantum Metrology
We present experimental and theoretical results on a new interferometer
topology that nests a SU(2) interferometer, e.g., a Mach-Zehnder or Michelson
interferometer, inside a SU(1,1) interferometer, i.e., a Mach-Zehnder
interferometer with parametric amplifiers in place of beam splitters. This
SU(2)-in-SU(1,1) nested interferometer (SISNI) simultaneously achieves high
signal-to-noise ratio (SNR), sensitivity beyond the standard quantum limit
(SQL) and tolerance to photon losses external to the interferometer, e.g., in
detectors. We implement a SISNI using parametric amplification by four-wave
mixing (FWM) in Rb vapor and a laser-fed Mach-Zehnder SU(2) interferometer. We
observe path-length sensitivity with SNR 2.2 dB beyond the SQL at power levels
(and thus SNR) 2 orders of magnitude beyond those of previous loss-tolerant
interferometers. We find experimentally the optimal FWM gains and find
agreement with a minimal quantum noise model for the FWM process. The results
suggest ways to boost the in-practice sensitivity of high-power
interferometers, e.g., gravitational wave interferometers, and may enable
high-sensitivity, quantum-enhanced interferometry at wavelengths for which
efficient detectors are not available.Comment: 6 pages + 4 of supplemental material, 5 figure
Absolute sensitivity of phase measurement in an SU(1,1) type interferometer
Absolute sensitivity is measured for the phase measurement in an SU(1,1) type interferometer, and the results are compared to that of a Mach–Zehnder interferometer operated under the condition of the same intra-interferometer intensity. The interferometer is phase locked to a point with the largest quantum noise cancellation, and a simulated phase modulation is added in one arm of the SU(1,1) interferometer. Both the signal and noise level are estimated at the same frequency range, and we obtained 3 dB improvement in sensitivity for the SU(1,1) interferometer over the Mach–Zehnder interferometer. Our results demonstrate a direct phase estimation and may pave the way for practical applications of a nonlinear interferometer
Nano-optomechanical nonlinear dielectric metamaterials
By harnessing the resonant nature of localized electromagnetic modes in a nanostructured silicon membrane, an all-dielectric metamaterial can act as nonlinear medium at optical telecommunications wavelengths. We show that such metamaterials provide extremely large optomechanical nonlinearities, operating at intensities of only a few μW per unit cell and modulation frequencies as high as 152 MHz, thereby offering a path to fast, compact and energy
efficient all-optical metadevices
Structural and optical properties of GaSbBi/GaSb quantum wells [Invited]
GaSbBi/GaSb quantum wells (QWs) with Bi content up to 10.1% were grown using molecular beam epitaxy. High crystalline quality and clear interfaces were confirmed by high resolution transmission electron microscopy. The Bi distribution was investigated using energy dispersive X-ray spectroscopy. Room temperature photoluminescence (PL) reveals that the peak energy redshifts at a rate of 32 meV/Bi%, consistent with the theoretical predication using the 8-band kp model. From the temperature dependent PL, it was found that the temperature-insensitivity of the transition from the GaSbBi QW improved with increasing Bi content
Topological insulator BSTS as a broadband switchable metamaterial
The development of metamaterials into a viable platform for nanophotonic applications, data processing circuits, sensors, etc. requires identification of new plasmonic materials to overcome the limitations of noble metals, in particular their high losses. Here we describe a class of topological insulator materials which support broadband plasmonic response and possess extremely appealing photonic properties ranging from mid-IR to UV. Bi1.5Sb0.5Te1.8Se1.2 (BSTS) is a bulk insulator with robust conducting surface states protected by time-reversal symmetry, due to the strong spin-orbit coupling. BSTS single crystals were synthesized by melting high-purity Bi, Sb, Te and Se powders at 950°C in an evacuated quartz tube. The temperature was then gradually decreased to room temperature over a span of three weeks. The resulting crystals were then cleaved along the (100) family of planes to a thickness of ~0.5 mm. BSTS dielectric constants were derived by ellipsometric measurements and appear to be in excellent agreement with first principle DFT calculations. Unlike common direct or indirect bandgap semiconductors, the anomalous dispersion region falls in the visible part of the spectrum, leading to negative values of the permittivity. This behavior of the optical response is attributed to a combination of bulk interband transitions and surface contribution of the topologically protected states. To prove metallic behavior of BSTS, we fabricated metamaterials and gratings on crystal flakes and registered strong plasmonic response from UV to NIR. The coexistence of plasmonic response of the topological surface with dielectric properties of the semiconducting bulk enables ultrafast (t>100 fs) and broadband (to mid-IR) photo-modulation of the optical response. These findings show the potential of topological insulators as a platform for high-frequency switchable plasmonic metamaterials
Patient-derived small intestinal myofibroblasts direct perfused, physiologically responsive capillary development in a microfluidic gut-on-a-chip model
MADNESS: A Multiresolution, Adaptive Numerical Environment for Scientific Simulation
MADNESS (multiresolution adaptive numerical environment for scientific
simulation) is a high-level software environment for solving integral and
differential equations in many dimensions that uses adaptive and fast harmonic
analysis methods with guaranteed precision based on multiresolution analysis
and separated representations. Underpinning the numerical capabilities is a
powerful petascale parallel programming environment that aims to increase both
programmer productivity and code scalability. This paper describes the features
and capabilities of MADNESS and briefly discusses some current applications in
chemistry and several areas of physics
Health care systems in Sweden and China: Legal and formal organisational aspects
<p>Abstract</p> <p>Background</p> <p>Sharing knowledge and experience internationally can provide valuable information, and comparative research can make an important contribution to knowledge about health care and cost-effective use of resources. Descriptions of the organisation of health care in different countries can be found, but no studies have specifically compared the legal and formal organisational systems in Sweden and China.</p> <p>Aim</p> <p>To describe and compare health care in Sweden and China with regard to legislation, organisation, and finance.</p> <p>Methods</p> <p>Literature reviews were carried out in Sweden and China to identify literature published from 1985 to 2008 using the same keywords. References in recent studies were scrutinized, national legislation and regulations and government reports were searched, and textbooks were searched manually.</p> <p>Results</p> <p>The health care systems in Sweden and China show dissimilarities in legislation, organisation, and finance. In Sweden there is one national law concerning health care while in China the law includes the "Hygienic Common Law" and the "Fundamental Health Law" which is under development. There is a tendency towards market-orientated solutions in both countries. Sweden has a well-developed primary health care system while the primary health care system in China is still under development and relies predominantly on hospital-based care concentrated in cities.</p> <p>Conclusion</p> <p>Despite dissimilarities in health care systems, Sweden and China have similar basic assumptions, i.e. to combine managerial-organisational efficiency with the humanitarian-egalitarian goals of health care, and both strive to provide better care for all.</p
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