7,612 research outputs found
Migration, Social Security, and Economic Growth
This paper studies the effect of population aging on economic performance in an overlapping-generations model with international migration. Fertility is endogenized so that immigrants and natives can have different fertility rates. Fertility is an important determinant to the tax burden of social security since it affects the quantity and quality of future tax payers. We find that introducing immigrants into the economy can reduce the tax burden of social security. If life expectancy (or the replacement ratio) is high enough, the growth rate of GDP per worker for an economy with international migration will be higher than for a closed economy. Regarding migration policies, our numerical results indicate that economic growth rate of GDP per worker will first decrease then increase as the flow of immigrants increases. Increasing the quality of immigrants will enhance economic growth.Economic growth; Fertility; Migration; Social security.
Cellular membrane trafficking of mesoporous silica nanoparticles
This dissertation mainly focuses on the investigation of the cellular membrane trafficking of mesoporous silica nanoparticles. We are interested in the study of endocytosis and exocytosis behaviors of mesoporous silica nanoparticles with desired surface functionality. The relationship between mesoporous silica nanoparticles and membrane trafficking of cells, either cancerous cells or normal cells was examined. Since mesoporous silica nanoparticles were applied in many drug delivery cases, the endocytotic efficiency of mesoporous silica nanoparticles needs to be investigated in more details in order to design the cellular drug delivery system in the controlled way.
It is well known that cells can engulf some molecules outside of the cells through a receptor-ligand associated endocytosis. We are interested to determine if those biomolecules binding to cell surface receptors can be utilized on mesoporous silica nanoparticle materials to improve the uptake efficiency or govern the mechanism of endocytosis of mesoporous silica nanoparticles. Arginine-glycine-aspartate (RGD) is a small peptide recognized by cell integrin receptors and it was reported that avidin internalization was highly promoted by tumor lectin. Both RGD and avidin were linked to the surface of mesoporous silica nanoparticle materials to investigate the effect of receptor-associated biomolecule on cellular endocytosis efficiency. The effect of ligand types, ligand conformation and ligand density were discussed in Chapter 2 and 3.
Furthermore, the exocytosis of mesoporous silica nanoparticles is very attractive for biological applications. The cellular protein sequestration study of mesoporous silica nanoparticles was examined for further information of the intracellular pathway of endocytosed mesoporous silica nanoparticle materials. The surface functionality of mesoporous silica nanoparticle materials demonstrated selectivity among the materials and cancer and normal cell lines. We aimed to determine the specific organelle that mesoporous silica nanoparticles could approach via the identification of harvested proteins from exocytosis process.
Based on the study of endo- and exocytosis behavior of mesoporous silica nanoparticle materials, we can design smarter drug delivery vehicles for cancer therapy that can be effectively controlled. The destination, uptake efficiency and the cellular distribution of mesoporous silica nanoparticle materials can be programmable. As a result, release mechanism and release rate of drug delivery systems can be a well-controlled process. The deep investigation of an endo- and exocytosis study of mesoporous silica nanoparticle materials promotes the development of drug delivery applications
Evanescent Electron Wave Spin
Our study shows that an evanescent electron wave exists outside both finite
and infinite quantum wells, by solving exact solutions of the Dirac equation in
a cylindrical quantum well and maintaining wavefunction continuity at the
boundary. Furthermore, we demonstrate that the evanescent wave spins
concurrently with the wave inside the quantum well, by deriving analytical
expressions of the current density in the whole region. Our findings suggest
that it is possible to probe or eavesdrop on quantum spin information through
the evanescent wave spin without destroying the entire spin state. The wave
spin picture interprets spin as a global and deterministic property of the
electron wave that includes both the evanescent and confined wavefunctions.
This suggests that a quantum process or device based on the manipulation and
probing of the electron wave spin is deterministic in nature rather than
probabilistic.Comment: 6 pages, 5 figure
Role of in the reaction near threshold
The role of the resonance in the reaction near threshold is studied within an effective Lagrangian
approach. We perform a calculation for the total and differential cross section
of the reaction by including the contributions
from the intermediate state decaying into
dominated by and mesons exchanges, the nucleon pole and
resonance decaying into dominated by exchanges of
and mesons. Besides, the non-resonance process and contact terms
to keep the total scattering amplitude gauge invariant are also considered.
With our model parameters, the total cross section of this reaction is of the
order of nanobarn at photon beam energy GeV. It is
expected that our model predictions could be tested by future experiments.Comment: Published versio
Parametric Instability in Long Optical Cavities and Suppression by Dynamic Transverse Mode Frequency Modulation
Three mode parametric instability has been predicted in Advanced
gravitational wave detectors. Here we present the first observation of this
phenomenon in a large scale suspended optical cavity designed to be comparable
to those of advanced gravitational wave detectors. Our results show that
previous modelling assumptions that transverse optical modes are stable in
frequency except for frequency drifts on a thermal deformation time scale is
unlikely to be valid for suspended mass optical cavities. We demonstrate that
mirror figure errors cause a dependence of transverse mode offset frequency on
spot position. Combined with low frequency residual motion of suspended
mirrors, this leads to transverse mode frequency modulation which suppresses
the effective parametric gain. We show that this gain suppression mechanism can
be enhanced by laser spot dithering or fast thermal modulation. Using Advanced
LIGO test mass data and thermal modelling we show that gain suppression factors
of 10-20 could be achieved for individual modes, sufficient to greatly
ameliorate the parametric instability problem
Mining of novel thermo-stable cellulolytic genes from a thermophilic cellulose-degrading consortium by metagenomics
published_or_final_versio
Possible approach to improve sensitivity of a Michelson interferometer
We propose a possible approach to achieve an 1/N sensitivity of Michelson
interferometer by using a properly designed random phase modulation. Different
from other approaches, the sensitivity improvement does not depend on
increasing optical powers or utilizing the quantum properties of light.
Moreover the requirements for optical losses and the quantum efficiencies of
photodetection systems might be lower than the quantum approaches and the
sensitivity improvement is frequency independent in all detection band.Comment: 8 pages, 3 figures, new versio
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