4,745 research outputs found
Two-component model for the chemical evolution of the Galactic disk
In the present paper, we introduce a two-component model of the Galactic disk
to investigate its chemical evolution. The formation of the thick and thin
disks occur in two main accretion episodes with both infall rates to be
Gaussian. Both the pre-thin and post-thin scenarios for the formation of the
Galactic disk are considered. The best-fitting is obtained through
-test between the models and the new observed metallicity distribution
function of G dwarfs in the solar neighbourhood (Hou et al 1998). Our results
show that post-thin disk scenario for the formation of the Galactic disk should
be preferred. Still, other comparison between model predictions and
observations are given.Comment: 23 pages, 7 figure
Molecular biomechanics of collagen molecules
Collagenous tissues, made of collagen molecules, such as tendon and bone, are intriguing materials that have the ability to respond to mechanical forces by altering their structures from the molecular level up, and convert them into biochemical signals that control many biological and pathological processes such as wound healing and tissue remodeling. It is clear that collagen synthesis and degradation are influenced by mechanical loading, and collagenous tissues have a remarkable built-in ability to alter the equilibrium between material formation and breakdown. However, how the mechanical force alters structures of collagen molecules and how the structural changes affect collagen degradation at molecular level is not well understood. The purpose of this article is to review the biomechanics of collagen, using a bottom-up approach that begins with the mechanics of collagen molecules. The current understanding of collagen degradation mechanisms is presented, followed by a discussion of recent studies on how mechanical force mediates collagen breakdown. Understanding the biomechanics of collagen molecules will provide the basis for understanding the mechanobiology of collagenous tissues. Addressing challenges in this field provides an opportunity for developing treatments, designing synthetic collagen materials for a variety of biomedical applications, and creating a new class of ‘smart’ structural materials that autonomously grow when needed, and break down when no longer required, with applications in nanotechnology, devices and civil engineering.National Science Foundation (U.S.)United States. Office of Naval Research. Presidential Early Career Award for Scientists and EngineersNational Institutes of Health (U.S.) (U01EB014976
Exact Potts Model Partition Functions for Strips of the Honeycomb Lattice
We present exact calculations of the Potts model partition function
for arbitrary and temperature-like variable on -vertex
strip graphs of the honeycomb lattice for a variety of transverse widths
equal to vertices and for arbitrarily great length, with free
longitudinal boundary conditions and free and periodic transverse boundary
conditions. These partition functions have the form
, where
denotes the number of repeated subgraphs in the longitudinal direction. We give
general formulas for for arbitrary . We also present plots of
zeros of the partition function in the plane for various values of and
in the plane for various values of . Explicit results for partition
functions are given in the text for (free) and (cylindrical),
and plots of partition function zeros are given for up to 5 (free) and
(cylindrical). Plots of the internal energy and specific heat per site
for infinite-length strips are also presented.Comment: 39 pages, 34 eps figures, 3 sty file
Some Exact Results on the Potts Model Partition Function in a Magnetic Field
We consider the Potts model in a magnetic field on an arbitrary graph .
Using a formula of F. Y. Wu for the partition function of this model as a
sum over spanning subgraphs of , we prove some properties of concerning
factorization, monotonicity, and zeros. A generalization of the Tutte
polynomial is presented that corresponds to this partition function. In this
context we formulate and discuss two weighted graph-coloring problems. We also
give a general structural result for for cyclic strip graphs.Comment: 5 pages, late
A Projection-Based K-space Transformer Network for Undersampled Radial MRI Reconstruction with Limited Training Subjects
The recent development of deep learning combined with compressed sensing
enables fast reconstruction of undersampled MR images and has achieved
state-of-the-art performance for Cartesian k-space trajectories. However,
non-Cartesian trajectories such as the radial trajectory need to be transformed
onto a Cartesian grid in each iteration of the network training, slowing down
the training process and posing inconvenience and delay during training.
Multiple iterations of nonuniform Fourier transform in the networks offset the
deep learning advantage of fast inference. Current approaches typically either
work on image-to-image networks or grid the non-Cartesian trajectories before
the network training to avoid the repeated gridding process. However, the
image-to-image networks cannot ensure the k-space data consistency in the
reconstructed images and the pre-processing of non-Cartesian k-space leads to
gridding errors which cannot be compensated by the network training. Inspired
by the Transformer network to handle long-range dependencies in sequence
transduction tasks, we propose to rearrange the radial spokes to sequential
data based on the chronological order of acquisition and use the Transformer to
predict unacquired radial spokes from acquired ones. We propose novel data
augmentation methods to generate a large amount of training data from a limited
number of subjects. The network can be generated to different anatomical
structures. Experimental results show superior performance of the proposed
framework compared to state-of-the-art deep neural networks.Comment: Accepted at MICCAI 202
Gender difference in suicide in Taiwan over a century:a time trend analysis in 1905-1940 and 1959-2012
Structure of the Partition Function and Transfer Matrices for the Potts Model in a Magnetic Field on Lattice Strips
We determine the general structure of the partition function of the -state
Potts model in an external magnetic field, for arbitrary ,
temperature variable , and magnetic field variable , on cyclic, M\"obius,
and free strip graphs of the square (sq), triangular (tri), and honeycomb
(hc) lattices with width and arbitrarily great length . For the
cyclic case we prove that the partition function has the form ,
where denotes the lattice type, are specified
polynomials of degree in , is the corresponding
transfer matrix, and () for ,
respectively. An analogous formula is given for M\"obius strips, while only
appears for free strips. We exhibit a method for
calculating for arbitrary and give illustrative
examples. Explicit results for arbitrary are presented for
with and . We find very simple formulas
for the determinant . We also give results for
self-dual cyclic strips of the square lattice.Comment: Reference added to a relevant paper by F. Y. W
Co-evolution of two GTPases enables efficient protein targeting in an RNA-less chloroplast Signal Recognition Particle pathway
The signal recognition particle (SRP) is an essential ribonucleoprotein particle that mediates the co-translational targeting of newly synthesized proteins to cellular membranes. The SRP RNA is a universally conserved component of SRP that mediates key interactions between two GTPases in SRP and its receptor, thus enabling rapid delivery of cargo to the target membrane. Notably, this essential RNA is bypassed in the chloroplast (cp) SRP of green plants. Previously, we showed that the cpSRP and cpSRP receptor GTPases (cpSRP54 and cpFtsY, respectively) interact efficiently by themselves without the SRP RNA. Here, we explore the molecular mechanism by which this is accomplished. Fluorescence analyses showed that, in the absence of SRP RNA, the M-domain of cpSRP54 both accelerates and stabilizes complex assembly between cpSRP54 and cpFtsY. Cross-linking coupled with mass spectrometry and mutational analyses identified a new interaction between complementarily charged residues on the cpFtsY G-domain and the vicinity of the cpSRP54 M-domain. These residues are specifically conserved in plastids, and their evolution coincides with the loss of SRP RNA in green plants. These results provide an example of how proteins replace the functions of RNA during evolution
Metrology Camera System of Prime Focus Spectrograph for Subaru Telescope
The Prime Focus Spectrograph (PFS) is a new optical/near-infrared multi-fiber
spectrograph designed for the prime focus of the 8.2m Subaru telescope. PFS
will cover a 1.3 degree diameter field with 2394 fibers to complement the
imaging capabilities of Hyper SuprimeCam. To retain high throughput, the final
positioning accuracy between the fibers and observing targets of PFS is
required to be less than 10um. The metrology camera system (MCS) serves as the
optical encoder of the fiber motors for the configuring of fibers. MCS provides
the fiber positions within a 5um error over the 45 cm focal plane. The
information from MCS will be fed into the fiber positioner control system for
the closed loop control. MCS will be located at the Cassegrain focus of Subaru
telescope in order to to cover the whole focal plane with one 50M pixel Canon
CMOS camera. It is a 380mm Schmidt type telescope which generates a uniform
spot size with a 10 micron FWHM across the field for reasonable sampling of
PSF. Carbon fiber tubes are used to provide a stable structure over the
operating conditions without focus adjustments. The CMOS sensor can be read in
0.8s to reduce the overhead for the fiber configuration. The positions of all
fibers can be obtained within 0.5s after the readout of the frame. This enables
the overall fiber configuration to be less than 2 minutes. MCS will be
installed inside a standard Subaru Cassgrain Box. All components that generate
heat are located inside a glycol cooled cabinet to reduce the possible image
motion due to heat. The optics and camera for MCS have been delivered and
tested. The mechanical parts and supporting structure are ready as of spring
2016. The integration of MCS will start in the summer of 2016.Comment: 11 pages, 15 figures. SPIE proceeding. arXiv admin note: text overlap
with arXiv:1408.287
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