4,363 research outputs found
On the unitarity of higher-dervative and nonlocal theories
We consider two simple models of higher-derivative and nonlocal quantu
systems.It is shown that, contrary to some claims found in literature, they can
be made unitary.Comment: 8 pages, no figure
Multipotent adult hippocampal progenitor cells maintained as neurospheres favor differentiation toward glial lineages
Adult hippocampal progenitor cells (AHPCs) are generally maintained as a dispersed monolayer population of multipotent neural progenitors. To better understand cell-cell interactions among neural progenitors and their influences on cellular characteristics, we generated free-floating cellular aggregates, or neurospheres, from the adherent monolayer population of AHPCs. Results from in vitro analyses demonstrated that both populations of AHPCs were highly proliferative under maintenance conditions, but AHPCs formed in neurospheres favored differentiation along a glial lineage and displayed greater migrational activity, than the traditionally cultured AHPCs. To study the plasticity of AHPCs from both populations in vivo, we transplanted GFP-expressing AHPCs via intraocular injection into the developing rat eyes. Both AHPC populations were capable of surviving and integrating into the developing host central nervous system, but considerably more GFP-positive cells were observed in the retinas transplanted with neurosphere AHPCs, compared to adherent AHPCs. These results suggest that the culture configuration during maintenance for neural progenitor cells (NPCs) influences cell fate and motility in vitro as well as in vivo. Our findings have implication for understanding different cellular characteristics of NPCs according to distinct intercellular architectures and for developing cell-based therapeutic strategies using lineage-committed NPCs
Unimodular Loop Quantum Cosmology
Unimodular gravity is based on a modification of the usual Einstein-Hilbert
action that allows one to recover general relativity with a dynamical
cosmological constant. It also has the interesting property of providing, as
the momentum conjugate to the cosmological constant, an emergent clock
variable. In this paper we investigate the cosmological reduction of unimodular
gravity, and its quantization within the framework of flat homogeneous and
isotropic loop quantum cosmology. It is shown that the unimodular clock can be
used to construct the physical state space, and that the fundamental features
of the previous models featuring scalar field clocks are reproduced. In
particular, the classical singularity is replaced by a quantum bounce, which
takes place in the same condition as obtained previously. We also find that
requirement of semi-classicality demands the expectation value of the
cosmological constant to be small (in Planck units). The relation to spin foam
models is also studied, and we show that the use of the unimodular time
variable leads to a unique vertex expansion.Comment: 26 pages. Revised version taking into account referee's comment
Dynamics of on-orbit construction process
The topics covered are presented in viewgraph form and include the following: problem definition and motivation; survey of current technology; focus problems; approach; progress/discussion; and future direction and anticipated results
Backpropagation neural network as earthquake early warning tool using a new modified elementary Levenberg–Marquardt Algorithm to minimise backpropagation errors
A new modified elementary Levenberg–Marquardt Algorithm (M-LMA) was used to minimise
backpropagation errors in training a backpropagation neural network (BPNN) to
predict the records related to the Chi-Chi earthquake from four seismic
stations: Station-TAP003, Station-TAP005, Station-TCU084, and Station-TCU078
belonging to the Free Field Strong Earthquake Observation Network, with the
learning rates of 0.3, 0.05, 0.2, and 0.28, respectively. For these four
recording stations, the M-LMA has been shown to produce smaller predicted
errors compared to the Levenberg–Marquardt Algorithm (LMA). A sudden predicted
error could be an indicator for Early Earthquake Warning (EEW), which
indicated the initiation of strong motion due to large earthquakes. A
trade-Off decision-making process with BPNN (TDPB), using two alarms,
adjusted the threshold of the magnitude of predicted error without a mistaken
alarm. With this approach, it is unnecessary to consider the problems of
characterising the wave phases and pre-processing, and does not require
complex hardware; an existing seismic monitoring network-covered research
area was already sufficient for these purposes.</p
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