43,534 research outputs found
On multistability of delayed genetic regulatory networks with multivariable regulation functions
The official published version of the article can be found at the link below.Many genetic regulatory networks (GRNs) have the capacity to reach different stable states. This capacity is defined as multistability which is an important regulation mechanism. Multiple time delays and multivariable regulation functions are usually inevitable in such GRNs. In this paper, multistability of GRNs is analyzed by applying the control theory and mathematical tools. This study is to provide a theoretical tool to facilitate the design of synthetic gene circuit with multistability in the perspective of control theory. By transforming such GRNs into a new and uniform mathematical formulation, we put forward a general sector-like regulation function that is capable of quantifying the regulation effects in a more precise way. By resorting to up-to-date techniques, a novel Lyapunov–Krasovskii functional (LKF) is introduced for achieving delay dependence to ensure less conservatism. New conditions are then proposed to ensure the multistability of a GRN in the form of linear matrix inequalities (LMIs) that are dependent on the delays. Our multistability conditions are applicable to several frequently used regulation functions especially the multivariable ones. Two examples are employed to illustrate the applicability and usefulness of the developed theoretical results.This work was supported in part by the Biotechnology and Biological Sciences Research Council (BBSRC) of the UK under Grants BB/C506264/1 and 100/EGM17735, the Royal Society of the UK, the National Natural Science Foundation of China under Grant 61028008, and the International Science and Technology Cooperation Project of China under Grant 2009DFA32050
Monostability and multistability of genetic regulatory networks with different types of regulation functions
The official published version of the article can be found at the link below.Monostability and multistability are proven to be two important topics in synthesis biology and system biology. In this paper, both monostability and multistability are analyzed in a unified framework by applying control theory and mathematical tools. The genetic regulatory networks (GRNs) with multiple time-varying delays and different types of regulation functions are considered. By putting forward a general sector-like regulation function and utilizing up-to-date techniques, a novel Lyapunov–Krasovskii functional is introduced for achieving delay dependence to ensure less conservatism. A new condition is then proposed for the general stability of a GRN in the form of linear matrix inequalities (LMIs) that are dependent on the upper and lower bounds of the delays. Our general stability conditions are applicable to several frequently used regulation functions. It is shown that the existing results for monostability of GRNs are special cases of our main results. Five examples are employed to illustrate the applicability and usefulness of the developed theoretical results.This work was supported in part by the Biotechnology and Biological Sciences Research Council (BBSRC) of the U.K. under Grant BB/C506264/1, the Royal Society of the U.K., the National Natural Science Foundation of China under Grants 60504008 and 60804028, the Program for New Century Excellent Talents in Universities of China, and the Alexander von Humboldt Foundation of Germany
H∞ and L2–L∞ filtering for two-dimensional linear parameter-varying systems
This is the post print version of the article. The official published version can be obtained from the link below - Copyright 2007 Wiley-BlackwellIn this paper, the H∞ and l2–l∞ filtering problem is investigated for two-dimensional (2-D) discrete-time linear parameter-varying (LPV) systems. Based on the well-known Fornasini–Marchesini local state-space (FMLSS) model, the mathematical model of 2-D systems under consideration is established by incorporating the parameter-varying phenomenon. The purpose of the problem addressed is to design full-order H∞ and l2–l∞ filters such that the filtering error dynamics is asymptotic stable and the prescribed noise attenuation levels in H∞ and l2–l∞ senses can be achieved, respectively. Sufficient conditions are derived for existence of such filters in terms of parameterized linear matrix inequalities (PLMIs), and the corresponding filter synthesis problem is then transformed into a convex optimization problem that can be efficiently solved by using standard software packages. A simulation example is exploited to demonstrate the usefulness and effectiveness of the proposed design method
MmWave Massive MIMO Based Wireless Backhaul for 5G Ultra-Dense Network
Ultra-dense network (UDN) has been considered as a promising candidate for
future 5G network to meet the explosive data demand. To realize UDN, a
reliable, Gigahertz bandwidth, and cost-effective backhaul connecting
ultra-dense small-cell base stations (BSs) and macro-cell BS is prerequisite.
Millimeter-wave (mmWave) can provide the potential Gbps traffic for wireless
backhaul. Moreover, mmWave can be easily integrated with massive MIMO for the
improved link reliability. In this article, we discuss the feasibility of
mmWave massive MIMO based wireless backhaul for 5G UDN, and the benefits and
challenges are also addressed. Especially, we propose a digitally-controlled
phase-shifter network (DPSN) based hybrid precoding/combining scheme for mmWave
massive MIMO, whereby the low-rank property of mmWave massive MIMO channel
matrix is leveraged to reduce the required cost and complexity of transceiver
with a negligible performance loss. One key feature of the proposed scheme is
that the macro-cell BS can simultaneously support multiple small-cell BSs with
multiple streams for each smallcell BS, which is essentially different from
conventional hybrid precoding/combining schemes typically limited to
single-user MIMO with multiple streams or multi-user MIMO with single stream
for each user. Based on the proposed scheme, we further explore the fundamental
issues of developing mmWave massive MIMO for wireless backhaul, and the
associated challenges, insight, and prospect to enable the mmWave massive MIMO
based wireless backhaul for 5G UDN are discussed.Comment: This paper has been accepted by IEEE Wireless Communications
Magazine. This paper is related to 5G, ultra-dense network (UDN), millimeter
waves (mmWave) fronthaul/backhaul, massive MIMO, sparsity/low-rank property
of mmWave massive MIMO channels, sparse channel estimation, compressive
sensing (CS), hybrid digital/analog precoding/combining, and hybrid
beamforming. http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=730653
Klein-Nishina effects on the high-energy afterglow emission of gamma-ray bursts
Extended high-energy(>100MeV) gamma-ray emission that lasts much longer than
the prompt sub-MeV emission has been detected from quite a few gamma-ray bursts
(GRBs) by Fermi Large Area Telescope (LAT) recently. A plausible scenario is
that this emission is the afterglow synchrotron emission produced by electrons
accelerated in the forward shocks. In this scenario, the electrons that produce
synchrotron high-energy emission also undergo inverse-Compton (IC) loss and the
IC scattering with the synchrotron photons should be in the Klein-Nishina
regime. Here we study effects of the Klein-Nishina scattering on the
high-energy synchrotron afterglow emission. We find that, at early times the
Klein-Nishina suppression effect on those electrons that produce the
high-energy emission is usually strong and therefore their inverse-Compton loss
is small with a Compton parameter Y < a few for a wide range of parameter
space. This leads to a relatively bright synchrotron afterglow at high energies
that can be detected by Fermi LAT. As the Klein-Nishina suppression effect
weakens with time, the inverse-Compton loss increases and could dominate over
the synchrotron loss in some parameter space. This will lead to a faster
temporal decay of the high-energy synchrotron emission than what is predicted
by the standard synchrotron model, which may explain the observed rapid decay
of the early high-energy gamma-ray emission in GRB090510 and GRB090902B.Comment: 8 page (emulateapj style), 8 figures, submitted to Ap
In situ imaging of field emission from individual carbon nanotubes and their structural damage
©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/80/856/1DOI:10.1063/1.1446994Field emission of individual carbon nanotubes was observed by in situ
transmission electron microscopy. A fluctuation in emission current was due to a
variation in distance between the nanotube tip and the counter electrode owing
to a "head-shaking" effect of the nanotube during field emission. Strong
field-induced structural damage of a nanotube occurs in two ways: a
piece-by-piece and segment-by-segment pilling process of the graphitic layers,
and a concentrical layer-by-layer stripping process. The former is believed
owing to a strong electrostatic force, and the latter is likely due to heating
produced by emission current that flowed through the most outer graphitic
layers
Statistics of Substructures in Dark Matter Haloes
We study the amount and distribution of dark matter substructures within dark
matter haloes, using a large set of high-resolution simulations ranging from
group size to cluster size haloes, and carried our within a cosmological model
consistent with WMAP 7-year data. In particular, we study how the measured
properties of subhaloes vary as a function of the parent halo mass, the
physical properties of the parent halo, and redshift. The fraction of halo mass
in substructures increases with increasing mass. There is, however, a very
large halo-to-halo scatter that can be explained only in part by a range of
halo physical properties, e.g. concentration. At given halo mass, less
concentrated haloes contain significantly larger fractions of mass in
substructures because of the reduced strength of tidal disruption. Most of the
substructure mass is located at the outskirts of the parent haloes, in
relatively few massive subhaloes. This mass segregation appears to become
stronger at increasing redshift, and should reflect into a more significant
mass segregation of the galaxy population at different cosmic epochs. When
haloes are accreted onto larger structures, their mass is significantly reduced
by tidal stripping. Haloes that are more massive at the time of accretion
(these should host more luminous galaxies) are brought closer to the centre on
shorter time-scales by dynamical friction, and therefore suffer of a more
significant stripping. The halo merger rate depends strongly on the environment
with substructure in more massive haloes suffering more important mergers than
their counterparts residing in less massive systems. This should translate into
a different morphological mix for haloes of different mass.Comment: 13 pages, 11 figures and 1 table. MNRAS 2011 in pres
2-Aminoanilinium 6-carboxypicolinate monohydrate
In the title compound, C6H9N2
+·C7H4NO4
−·H2O, one amino group of diaminobenzene is protonated while one carboxy group of pyridine-2,6-dicarboxylic acid is deprotonated. In the anion, the CO2 and CO2H groups make dihedral angles of 4.0 (5) and 8.7 (4)° with the pyridine ring. In the crystal, extensive N—H⋯O, N—H⋯N and O—H⋯O hydrogen bonds occur between anions, cations and water molecules
Robust fault detection for networked systems with communication delay and data missing
n this paper, the robust fault detection problem is investigated for a class of discrete-time networked systems with unknown input and multiple state delays. A novel measurement model is utilized to represent both the random measurement delays and the stochastic data missing phenomenon, which typically result from the limited capacity of the communication networks. The network status is assumed to vary in a Markovian fashion and its transition probability matrix is uncertain but resides in a known convex set of a polytopic type. The main purpose of this paper is to design a robust fault detection filter such that, for all unknown inputs, possible parameter uncertainties and incomplete measurements, the error between the residual signal and the fault signal is made as small as possible. By casting the addressed robust fault detection problem into an auxiliary robust H∞ filtering problem of a certain Markovian jumping system, a sufficient condition for the existence of the desired robust fault detection filter is established in terms of linear matrix inequalities. A numerical example is provided to illustrate the effectiveness and applicability of the proposed technique
Spatial Interference: From Coherent To Incoherent
It is well known that direct observation of interference and diffraction
pattern in the intensity distribution requires a spatially coherent source.
Optical waves emitted from portions beyond the coherence area possess
statistically independent phases, and will degrade the interference pattern. In
this paper we show an optical interference experiment, which seems contrary to
our common knowledge, that the formation of the interference pattern is related
to a spatially incoherent light source. Our experimental scheme is very similar
to Gabor's original proposal of holography[1], just with an incoherent source
replacing the coherent one. In the statistical ensemble of the incoherent
source, each sample field produces a sample interference pattern between object
wave and reference wave. These patterns completely differ from each other due
to the fluctuation of the source field distribution. Surprisingly, the sum of a
great number of sample patterns exhibits explicitly an interference pattern,
which contains all the information of the object and is equivalent to a
hologram in the coherent light case. In this sense our approach would be
valuable in holography and other interference techniques for the case where
coherent source is unavailable, such as x-ray and electron sources.Comment: 8 pages, 5 figure
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