577 research outputs found
A two-way regularization method for MEG source reconstruction
The MEG inverse problem refers to the reconstruction of the neural activity
of the brain from magnetoencephalography (MEG) measurements. We propose a
two-way regularization (TWR) method to solve the MEG inverse problem under the
assumptions that only a small number of locations in space are responsible for
the measured signals (focality), and each source time course is smooth in time
(smoothness). The focality and smoothness of the reconstructed signals are
ensured respectively by imposing a sparsity-inducing penalty and a roughness
penalty in the data fitting criterion. A two-stage algorithm is developed for
fast computation, where a raw estimate of the source time course is obtained in
the first stage and then refined in the second stage by the two-way
regularization. The proposed method is shown to be effective on both synthetic
and real-world examples.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS531 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Coupled Reversible and Irreversible Bistable Switches Underlying TGF-\beta-induced Epithelial to Mesenchymal Transition
Epithelial to mesenchymal transition (EMT) plays important roles in embryonic
development, tissue regeneration and cancer metastasis. While several feedback
loops have been shown to regulate EMT, it remains elusive how they coordinately
modulate EMT response to TGF-\beta treatment. We construct a mathematical model
for the core regulatory network controlling TGF-\beta-induced EMT. Through
deterministic analyses and stochastic simulations, we show that EMT is a
sequential two-step program that an epithelial cell first transits to partial
EMT then to the mesenchymal state, depending on the strength and duration of
TGF-\beta stimulation. Mechanistically the system is governed by coupled
reversible and irreversible bistable switches. The SNAIL1/miR-34 double
negative feedback loop is responsible for the reversible switch and regulates
the initiation of EMT, while the ZEB/miR-200 feedback loop is accountable for
the irreversible switch and controls the establishment of the mesenchymal
state. Furthermore, an autocrine TGF-\beta/miR-200 feedback loop makes the
second switch irreversible, modulating the maintenance of EMT. Such coupled
bistable switches are robust to parameter variation and molecular noise. We
provide a mechanistic explanation on multiple experimental observations. The
model makes several explicit predictions on hysteretic dynamic behaviors,
system response to pulsed stimulation and various perturbations, which can be
straightforwardly tested.Comment: 32 pages, 8 figures, accepted by Biophysical Journa
Syntheses and applications of soluble polyisobutylene (PIB)-supported transition metal catalysts
Soluble polymer supports facilitate the recovery and recycling of expensive
transition metal complexes. Recently, polyisobutylene (PIB) oligomers have been found
to be suitable polymer supports for the recovery of a variety of transition metal catalysts
using liquid/liquid biphasic separations after a homogeneous reaction. Our work has
shown that PIB-supported Ni(II) and Co(II) β-diketonates prepared from commercially
available vinyl terminated PIB oligomers possess catalytic activity like that of their low
molecular weight analogs in Mukaiyama epoxidation of olefins.
Carboxylic acid terminated PIB derivatives can act as carboxylate ligands for
Rh(II) cyclopropanation catalysts. An achiral PIB-supported Rh(II) carboxylate catalyst
showed good activity in cyclopropanation of styrene in hydrocarbon solvents, and could
be easily recycled nine times by a post reaction extraction. Further application of PIB
supports in asymmetric cyclopropanation reactions were investigated using PIBsupported
arenesulfonyl Rh(II) prolinates derived from L-proline as examples. The PIBsupported
chiral Rh carboxylates demonstrated moderate activity and were recovered and reused for four to five cycles. The prolinate catalyst prepared from PIB-anisole also
showed encouraging enantioselectivity and about 8% ee and 13% ee were observed on
trans- and cis-cyclopropanation product respectively.
Finally, PIB oligomers can be modified in a multi step sequence to prepare PIBsupported
chiral bisoxazolines that can in turn be used to prepare active, recyclable PIBsupported
Cu(I) bisoxazoline complexes for olefin cyclopropanation. These chiral
copper catalysts showed moderate catalytic activity and good stereoselectivity in
cyclopropanation of styrene. A chiral ligand prepared from D-phenylglycinol provided
the most effective stereo control and gave the trans- and cis-cyclopropanation product in
94% ee and 68% ee respectively. All three PIB-supported chiral bisoxazoline-Cu(I)
catalysts could be reused five to six times
A unit cost adjusting heuristic algorithm for the integrated planning and scheduling of a two-stage supply chain
Purpose: The stable relationship of one-supplier-one-customer is replaced by a dynamic
relationship of multi-supplier-multi-customer in current market gradually, and efficient
scheduling techniques are important tools of the dynamic supply chain relationship establishing
process. This paper studies the optimization of the integrated planning and scheduling problem
of a two-stage supply chain with multiple manufacturers and multiple retailers to obtain a
minimum supply chain operating cost, whose manufacturers have different production
capacities, holding and producing cost rates, transportation costs to retailers.
Design/methodology/approach: As a complex task allocation and scheduling problem, this
paper sets up an INLP model for it and designs a Unit Cost Adjusting (UCA) heuristic
algorithm that adjust the suppliers’ supplying quantity according to their unit costs step by step
to solve the model.
Findings: Relying on the contrasting analysis between the UCA and the Lingo solvers for
optimizing many numerical experiments, results show that the INLP model and the UCA
algorithm can obtain its near optimal solution of the two-stage supply chain’s planning and
scheduling problem within very short CPU time.
Research limitations/implications: The proposed UCA heuristic can easily help managers to
optimizing the two-stage supply chain scheduling problems which doesn’t include the delivery time and batch of orders. For two-stage supply chains are the most common form of actual
commercial relationships, so to make some modification and study on the UCA heuristic
should be able to optimize the integrated planning and scheduling problems of a supply chain
with more reality constraints.
Originality/value: This research proposes an innovative UCA heuristic for optimizing the
integrated planning and scheduling problem of two-stage supply chains with the constraints of
suppliers’ production capacity and the orders’ delivering time, and has a great practical
significance to the dynamic relationship establishment of multi-supplier-multi-customer in
current market.Peer Reviewe
A unit cost adjusting heuristic algorithm for the integrated planning and scheduling of a two-stage supply chain
Purpose: The stable relationship of one-supplier-one-customer is replaced by a dynamic
relationship of multi-supplier-multi-customer in current market gradually, and efficient
scheduling techniques are important tools of the dynamic supply chain relationship establishing
process. This paper studies the optimization of the integrated planning and scheduling problem
of a two-stage supply chain with multiple manufacturers and multiple retailers to obtain a
minimum supply chain operating cost, whose manufacturers have different production
capacities, holding and producing cost rates, transportation costs to retailers.
Design/methodology/approach: As a complex task allocation and scheduling problem, this
paper sets up an INLP model for it and designs a Unit Cost Adjusting (UCA) heuristic
algorithm that adjust the suppliers’ supplying quantity according to their unit costs step by step
to solve the model.
Findings: Relying on the contrasting analysis between the UCA and the Lingo solvers for
optimizing many numerical experiments, results show that the INLP model and the UCA
algorithm can obtain its near optimal solution of the two-stage supply chain’s planning and
scheduling problem within very short CPU time.
Research limitations/implications: The proposed UCA heuristic can easily help managers to
optimizing the two-stage supply chain scheduling problems which doesn’t include the delivery time and batch of orders. For two-stage supply chains are the most common form of actual
commercial relationships, so to make some modification and study on the UCA heuristic
should be able to optimize the integrated planning and scheduling problems of a supply chain
with more reality constraints.
Originality/value: This research proposes an innovative UCA heuristic for optimizing the
integrated planning and scheduling problem of two-stage supply chains with the constraints of
suppliers’ production capacity and the orders’ delivering time, and has a great practical
significance to the dynamic relationship establishment of multi-supplier-multi-customer in
current market.Peer Reviewe
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