2,682 research outputs found
Mechanism of unidirectional movement of kinesin motors
Kinesin motors have been studied extensively both experimentally and
theoretically. However, the microscopic mechanism of the processive movement of
kinesin is still an open question. In this paper, we propose a hand-over-hand
model for the processivity of kinesin, which is based on chemical, mechanical,
and electrical couplings. In the model the processive movement does not need to
rely on the two heads' coordination in their ATP hydrolysis and mechanical
cycles. Rather, the ATP hydrolyses at the two heads are independent. The much
higher ATPase rate at the trailing head than the leading head makes the motor
walk processively in a natural way, with one ATP being hydrolyzed per step. The
model is consistent with the structural study of kinesin and the measured
pathway of the kinesin ATPase. Using the model the estimated driving force of ~
5.8 pN is in agreements with the experimental results (5~7.5 pN). The
prediction of the moving time in one step (~10 microseconds) is also consistent
with the measured values of 0~50 microseconds. The previous observation of
substeps within the 8-nm step is explained. The shapes of velocity-load (both
positive and negative) curves show resemblance to previous experimental
results.Comment: 22 pages, 6 figure
Model for processive movement of myosin V and myosin VI
Myosin V and myosin VI are two classes of two-headed molecular motors of the
myosin superfamily that move processively along helical actin filaments in
opposite directions. Here we present a hand-over-hand model for their
processive movements. In the model, the moving direction of a dimeric molecular
motor is automatically determined by the relative orientation between its two
heads at free state and its head's binding orientation on track filament. This
determines that myosin V moves toward the barbed end and myosin VI moves toward
the pointed end of actin. During the moving period in one step, one head
remains bound to actin for myosin V whereas two heads are detached for myosin
VI: The moving manner is determined by the length of neck domain. This
naturally explains the similar dynamic behaviors but opposite moving directions
of myosin VI and mutant myosin V (the neck of which is truncated to only
one-sixth of the native length). Because of different moving manners, myosin VI
and mutant myosin V exhibit significantly broader step-size distribution than
native myosin V. However, all three motors give the same mean step size of 36
nm (the pseudo-repeat of actin helix). Using the model we study the dynamics of
myosin V quantitatively, with theoretical results in agreement with previous
experimental ones.Comment: 18 pages, 7 figure
Performance Analysis of Joint Base-Station Multiantenna Multibeam and Channel Assignment Scheme for Hierarchical Cellular System
Different from the traditional configuration of hierarchical cellular, we introduce the joint base-station multi-antenna multi-beam and channel assignment scheme for hierarchical cellular in this paper. The proposed scheme is based on multi-beam base-station antenna splitting in the elevation-radiating plane, and a dynamic channel allocation scheme by combining the adaptive antenna technologies. Simulation results show that the proposed configuration of the hierarchical cellular can enhance the spectral efficiency remarkably
Mid-infrared variability of changing-look AGN
It is known that some active galactic nuclei (AGNs) transited from type 1 to
type 2 or vice versa. There are two explanations for the so-called changing
look AGNs: one is the dramatic change of the obscuration along the
line-of-sight, the other is the variation of accretion rate. In this paper, we
report the detection of large amplitude variations in the mid-infrared
luminosity during the transitions in 10 changing look AGNs using WISE and newly
released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the
variability in the optical band with a time lag expected for dust reprocessing.
The large variability amplitude is inconsistent with the scenario of varying
obscuration, rather supports the scheme of dramatic change in the accretion
rate.Comment: Published by ApjL, 7 pages, 3 figures, 2 table
Discovery of a Mid-infrared Echo from the TDE candidate in the nucleus of ULIRG F01004-2237
We present the mid-infrared (MIR) light curves (LCs) of a tidal disruption
event (TDE) candidate in the center of a nearby ultraluminous infrared galaxy
(ULIRG) F01004-2237 using archival {\it WISE} and {\it NEOWISE} data from 2010
to 2016. At the peak of the optical flare, F01004-2237 was IR quiescent. About
three years later, its MIR fluxes have shown a steady increase, rising by 1.34
and 1.04 mag in and m up to the end of 2016. The host-subtracted
MIR peak luminosity is \,erg\,s. We interpret the MIR
LCs as an infrared echo, i.e. dust reprocessed emission of the optical flare.
Fitting the MIR LCs using our dust model, we infer a dust torus of the size of
a few parsecs at some inclined angle. The derived dust temperatures range from
\,K, and the warm dust mass is . Such a large mass
implies that the dust cannot be newly formed. We also derive the UV luminosity
of \,erg\,s. The inferred total IR energy is
\,erg, suggesting a large dust covering factor. Finally, our
dust model suggests that the long tail of the optical flare could be due to
dust scattering
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