432 research outputs found
Stability of Minkowski spacetime in exterior regions
In 1993, the global stability of Minkowski spacetime has been proven in the
celebrated work of Christodoulou and Klainerman \cite{Ch-Kl} in a maximal
foliation. In 2003, Klainerman and Nic\`olo \cite{Kl-Ni} gave a second proof of
the stability of Minkowski in the case of the exterior of an outgoing null
cone. In this paper, we give a new proof of \cite{Kl-Ni}. Compared to
\cite{Kl-Ni}, we reduce the number of derivatives needed in the proof, simplify
the treatment of the last slice, and provide a unified treatment of the decay
of initial data. Also, concerning the treatment of curvature estimates, we
replace the vectorfield method used in \cite{Kl-Ni} by the --weighted
estimates of Dafermos and Rodnianski \cite{Da-Ro}.Comment: 80 pages, 3 figure
N-recollements and Virtually Gorenstein Algebras
The relation between the -recollements of stable categories of Gorenstein
projective modules and the virtual Gorensteinness of algebras are investigated.
Let , and be finite dimensional algebras. We prove that if the stable
category of Gorenstein projective -modules admits a -recollement relative
to that of and with , then is virtually Gorenstein if and
only if so are and
An index theorem on asymptotically static spacetimes with compact Cauchy surface
We consider the Dirac operator on asymptotically static Lorentzian manifolds
with an odd-dimensional compact Cauchy surface. We prove that if
Atiyah-Patodi-Singer boundary conditions are imposed at infinite times then the
Dirac operator is Fredholm. This generalizes a theorem due to B\"ar-Strohmaier
in the case of finite times, and we also show that the corresponding index
formula extends to the infinite setting. Furthermore, we demonstrate the
existence of a Fredholm inverse which is at the same time a Feynman parametrix
in the sense of Duistermaat-H\"ormander. The proof combines methods from
time-dependent scattering theory with a variant of Egorov's theorem for
pseudo-differential hyperbolic systems.Comment: 40 page
Study on the Transit Network Evaluation Method Based on the Transit Ridership Model
AbstractTraditional four-step travel forecasting models are usually used to predict changes in car travel patterns and to evaluate the road transportation system. The application is unsatisfactory when they are used to evaluate the transit transportation system. Based on the transit origin-destination (OD) adjustment, this paper proposes a framework on future transit network evaluations, where the transit ridership model and OD difference method are simultaneously used. The proposed method formulates the relationship between transit ridership and zonal population, employment, transit service level, and so on. In addition, the difference between transit counts and estimates for base year are considered in the development of the transit OD for future year. It is expected to perform better than conventional models in terms of transit network evolutions. The validation of the proposed method is tested in Fuzhou City Transit Development Project
Inactivation of presenilins causes pre-synaptic impairment prior to post-synaptic dysfunction
Synaptic dysfunction is widely thought to be a pathogenic precursor to neurodegeneration in Alzheimerâs disease (AD), and the extent of synaptic loss provides the best correlate for the severity of dementia in AD patients. Presenilins 1 and 2 are the major causative genes of earlyâonset familial AD. Conditional inactivation of presenilins in the adult cerebral cortex results in synaptic dysfunction and memory impairment, followed by ageâdependent neurodegeneration. To characterize further the consequence of presenilin inactivation in the synapse, we evaluated the temporal development of preâsynaptic and postâsynaptic deficits in the Schaefferâcollateral pathway of presenilin conditional double knockout (PS cDKO) mice prior to onset of neurodegeneration. Following presenilin inactivation at 4âweeks, synaptic facilitation and probability of neurotransmitter release are impaired in PS cDKO mice at 5âweeks of age, whereas postâsynaptic NMDA receptor (NMDAR)âmediated responses are normal at 5âweeks but impaired at 6âweeks of age. Longâterm potentiation induced by theta burst stimulation is also reduced in PS cDKO mice at 6âweeks of age. These results show that loss of presenilins results in preâsynaptic deficits in shortâterm plasticity and probability of neurotransmitter release prior to postâsynaptic NMDAR dysfunction, raising the possibility that presenilins may regulate postâsynaptic NMDAR function in part via a transâsynaptic mechanism.This work was supported by the National Institute of Health NS041783 (to J.S.). We would like to thank Xiaoyan Zou and Huailong Zhao for technical assistance. (NS041783 - National Institute of Health)Published versio
In Situ Engineering and Characterization of Correlated Materials with Integrated OMBEâARPES
Oxide molecular beam epitaxy has emerged as an effective technique to fabricate complex oxide thin films and novel superlattices with atomicâlevel precision. In this chapter, we first briefly introduce the oxide molecular beam epitaxy technique and then show how to use this technique to achieve highâquality thin films with good stoichiometry. Moreover, we exhibit that the combination of oxide molecular beam epitaxy and in situ angleâresolved photoemission spectroscopy is indeed a versatile toolkit to tailor and characterize properties of novel quantum materials
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