25 research outputs found
The revival-collapse phenomenon in the quadrature field components of the two-mode multiphoton Jaynes-Cummings model
In this paper we consider a system consisting of a two-level atom in an
excited state interacting with two modes of a radiation field prepared
initially in -photon coherent states. This system is described by two-mode
multiphoton (, i.e., ) Jaynes-Cummings model (JCM). For this system
we investigate the occurrence of the revival-collapse phenomenon (RCP) in the
evolution of the single-mode, two-mode, sum and difference quadrature
squeezing. We show that there is a class of states for which all these types of
squeezing exhibit RCP similar to that involved in the corresponding atomic
inversion. Also we show numerically that the single-mode squeezing of the first
mode for provides RCP similar to that of the atomic inversion
of the case , however, sum and difference squeezing give
partial information on that case. Moreover, we show that single-mode, two-mode
and sum squeezing for the case provide information on the
atomic inversion of the single-mode two-photon JCM. We derive the rescaled
squeezing factors giving accurate information on the atomic inversion for all
cases. The consequences of these results are that the homodyne and heterodyne
detectors can be used to detect the RCP for the two-mode JCM.Comment: 18 pages, 6 figure
PIP2-Binding Site in Kir Channels: Definition by Multiscale Biomolecular Simulationsâ€
Phosphatidylinositol bisphosphate (PIP(2)) is an activator of mammalian inwardly rectifying potassium (Kir) channels. Multiscale simulations, via a sequential combination of coarse-grained and atomistic molecular dynamics, enabled exploration of the interactions of PIP(2) molecules within the inner leaflet of a lipid bilayer membrane with possible binding sites on Kir channels. Three Kir channel structures were investigated: X-ray structures of KirBac1.1 and of a Kir3.1-KirBac1.3 chimera and a homology model of Kir6.2. Coarse-grained simulations of the Kir channels in PIP(2)-containing lipid bilayers identified the PIP(2)-binding site on each channel. These models of the PIP(2)-channel complexes were refined by conversion to an atomistic representation followed by molecular dynamics simulation in a lipid bilayer. All three channels were revealed to contain a conserved binding site at the N-terminal end of the slide (M0) helix, at the interface between adjacent subunits of the channel. This binding site agrees with mutagenesis data and is in the proximity of the site occupied by a detergent molecule in the Kir chimera channel crystal. Polar contacts in the coarse-grained simulations corresponded to long-lived electrostatic and H-bonding interactions between the channel and PIP(2) in the atomistic simulations, enabling identification of key side chains
TRAF4 is a novel phosphoinositide-binding protein modulating tight junctions and favoring cell migration
Tumor necrosis factor (TNF) receptor-associated factor 4 (TRAF4) is frequently overexpressed in carcinomas, suggesting a specific role in cancer. Although TRAF4 protein is predominantly found at tight junctions (TJs) in normal mammary epithelial cells (MECs), it accumulates in the cytoplasm of malignant MECs. How TRAF4 is recruited and functions at TJs is unclear. Here we show that TRAF4 possesses a novel phosphoinositide (PIP)-binding domain crucial for its recruitment to TJs. Of interest, this property is shared by the other members of the TRAF protein family. Indeed, the TRAF domain of all TRAF proteins (TRAF1 to TRAF6) is a bona fide PIP-binding domain. Molecular and structural analyses revealed that the TRAF domain of TRAF4 exists as a trimer that binds up to three lipids using basic residues exposed at its surface. Cellular studies indicated that TRAF4 acts as a negative regulator of TJ and increases cell migration. These functions are dependent from its ability to interact with PIPs. Our results suggest that TRAF4 overexpression might contribute to breast cancer progression by destabilizing TJs and favoring cell migration
Determining Aerodynamic Characteristics of an Unmanned Aerial Vehicle using a 3D Scanning Technique
High-Frequency Sensor Data Acquisition System (SDAC) for Flight Control and Aerodynamic Data Collection
Helix 8 of the angiotensin- II type 1A receptor interacts with phosphatidylinositol phosphates and modulates membrane insertion
On-ScalpMEG
The development of new magnetic sensor technologies with relaxed thermal insulation requirements as compared to conventional magnetoencephalography (MEG) sensors has led to the birth of the field of on-scalp MEG, where sensor systems are flexibly placed directly on the scalp surface. Such improved proximity between the sensors and the brain has been theoretically demonstrated to boost signal levels and neuroimaging spatial resolution. Since the first on-scalp MEG measurements in 2012, a number of studies have experimentally verified these advantages with the two leading sensor technologies, namely, high criticaltemperature SQUIDs (high-Tc SQUIDs) and optically pumped magnetometers (OPMs). Current challenges being addressed that are specific to on-scalp MEG include relatively high sensor noise levels (specifically for high-Tc SQUIDs), limited bandwidth (specifically for OPMs), co-registration of a flexible sensor array, increased sensor crosstalk due to the denser spatial sampling required for improved spatial resolution, and engineering of a full-head system. The prospect for discovery of a neuroimaging challenge that on-scalp MEG uniquely solves is likely to push development further and possibly initiate utilization to a similar-or larger-scale as conventional MEG has reached today
Molecular Dynamics Simulations of KirBac1.1 Mutants Reveal Global Gating Changes of Kir Channels
Prokaryotic inwardly
rectifying (KirBac) potassium channels are
homologous to mammalian Kir channels. Their activity is controlled
by dynamical conformational changes that regulate ion flow through
a central pore. Understanding the dynamical rearrangements of Kir
channels during gating requires high-resolution structure information
from channels crystallized in different conformations and insight
into the transition steps, which are difficult to access experimentally.
In this study, we use MD simulations on wild type KirBac1.1 and an
activatory mutant to investigate activation gating of KirBac channels.
Full atomistic MD simulations revealed that introducing glutamate
in position 143 causes significant widening at the helix bundle crossing
gate, enabling water flux into the cavity. Further, global rearrangements
including a twisting motion as well as local rearrangements at the
subunit interface in the cytoplasmic domain were observed. These structural
rearrangements are similar to recently reported KirBac3.1 crystal
structures in closed and open conformation, suggesting that our simulations
capture major conformational changes during KirBac1.1 opening. In
addition, an important role of protein–lipid interactions during
gating was observed. Slide-helix and C-linker interactions with lipids
were strengthened during activation gating