408 research outputs found
Dimensional Analysis and the Time Required to Urinate
According to the recently discovered 'Law of Urination', mammals, ranging in
size from mice to elephants, take, on the average, 21s to urinate. We attempt
to gain insights into the physical processes responsible for this uniformity
using simple dimensional analysis. We assume that the biological apparatus for
urination in mammals simply scales with linear size, and consider the scenarios
where the driving force is gravity or elasticity, and where the response is
dominated by inertia or viscosity. We ask how the time required for urination
depends on the length scale, and find that for the time to be independent of
body size, the dominant driving force must be elasticity, and the dominant
response viscosity. Our note demonstrates that dimensional analysis can indeed
readily give insights into complex physical and biological processes
Kondo regime of the impurity spectral function and the current noise spectrum in the double impurity Anderson model
The dissipaton equations of motion (DEOM) method is one of the most popular
methods for simulating quantum impurity systems. In this article, we use DOEM
theory to deal with the Kondo problem of the double quantum dots (DQDs)
impurity system. We focus on the impurity spectral function and the total noise
spectral function, this two function will be used to describe the Kondo effect
of this system. The influence of the interaction, the hooping and the
difference of the chemical potential between the two dots on the Kondo effect
of the system is studied. We find that the interaction between the two dots can
influence the Kondo effect of the system a lot
The quantum solvation, adiabatic versus nonadiabatic, and Markovian versus non-Markovian nature of electron transfer rate processes
In this work, we revisit the electron transfer rate theory, with particular
interests in the distinct quantum solvation effect, and the characterizations
of adiabatic/nonadiabatic and Markovian/non-Markovian rate processes. We first
present a full account for the quantum solvation effect on the electron
transfer in Debye solvents, addressed previously in J. Theore. & Comput. Chem.
{\bf 5}, 685 (2006). Distinct reaction mechanisms, including the quantum
solvation-induced transitions from barrier-crossing to tunneling, and from
barrierless to quantum barrier-crossing rate processes, are shown in the fast
modulation or low viscosity regime. This regime is also found in favor of
nonadiabatic rate processes. We further propose to use Kubo's motional
narrowing line shape function to describe the Markovian character of the
reaction. It is found that a non-Markovian rate process is most likely to occur
in a symmetric system in the fast modulation regime, where the electron
transfer is dominant by tunneling due to the Fermi resonance.Comment: 13 pages, 10 figures, submitted to J. Phys. Chem.
GIS and urban data science
With the emergence of new forms of geospatial/urban big data and advanced spatial analytics and machine learning methods, new patterns and phenomena can be explored and discovered in our cities and societies. In this special issue, we presented an overview of nine studies to understand how to use urban data science and GIS in healthcare services, hospitality and safety, transportation and mobility, economy, urban planning, higher education, and natural disasters, spreading across developed countries in North America and Europe, as well as Global South areas in Asia and the Middle East. The embrace of diverse geo-computational methods in this special issue brings forward an outlook to future GIS and Urban Data Science towards more advanced computational capability, global vision and urban-focused research
Commande non-linéaire et analyse de stabilité de réseaux multi-terminaux haute tension à courant continu
This dissertation was devoted to the study of multi-terminal high voltage direct current (MTDC) networks. The main contributions were in the field of nonlinear automatic control, applied to power systems, power electronics and renewable energy sources. The research work was started with the intention of filling some gaps between the theory and the practice, in particular: 1) to investigate various control approaches for the purpose of improving the performance of MTDC systems; 2) to establish connections between existing empirical control design and theoretical analysis; 3) to improve the understanding of the multi-time-scale behavior of MTDC systems characterized by the presence of slow and fast transients in response to external disturbances. As a consequence, this thesis work can be put into three areas, namely nonlinear control design of MTDC systems, analysis of MTDC system's dynamic behaviors and application of MTDC systems for frequency control of AC systems.Cette thèse a été consacrée à l'étude des réseaux multi-terminaux haute tension à courant continu (MTDC). Les principales contributions étaient dans le domaine du contrôle automatique non linéaire, appliquées aux systèmes électriques, électronique de puissance et les sources d'énergie renouvelables. Le travail de recherche a été lancé avec l'intention de combler certaines lacunes entre la théorie et la pratique, en particulier: 1) d'enquêter sur diverses approches de contrôle pour le but d'améliorer la performance des systèmes MTDC; 2) d'établir des connexions entre la conception du contrôle empiriques existantes et analyse théorique; 3) d'améliorer la compréhension du comportement multi-échelle de temps des systèmes MTDC caractérisés par la présence de transitoires lents et rapides en réponse aux perturbations externes. En conséquence, ce travail de thèse peut être mis en trois domaines, à savoir la conception non linéaire de commande de systèmes MTDC, analyse des comportements dynamiques de système MTDC et l'application de systèmes MTDC pour le contrôle de fréquence des systèmes de climatisation
Investigating the mechanism by which thalamocortical projections reach the cerebral cortex
This thesis provides insights into the mechanism by which thalamocortical axons
(TCAs) approach the cortex from their origin in the thalamus. Previous studies
suggested that the reciprocal projections from the prethalamus and the ventral
telencephalon guide TCAs to descend through the prethalamus and cross the
diencephalic-telencephalic boundary (DTB), after which TCAs navigate through
permissive corridor cells in the ventral telencephalon and cross the pallial-subpallial
boundary (PSPB) before reaching their final targets in the cortex. The ‘Handshake
Hypothesis’ proposed that pioneer axons from cortical preplate neurons guide TCAs
into corresponding cortical areas. However, there is a lack of convincing evidence on
whether TCAs need any guidance to cross the PSPB.
In the current study, Adenomatous polyposis (Apc) gene is conditionally deleted
from the cortex, by using Emx1Cre-APCloxP recombination technology. Apc is widely
expressed in the nervous system including the cortical plate of the cortex and
regulates axonal growth and neuronal differentiation. Deleting Apc may block neurite
extension and/or affect the formation of attractive or repulsive cues in the cortex. By
using DiI tracing as well as L1 immunohistochemistry techniques, I showed that in
the Apc mutants cortical axons are absent and that TCAs initially navigate into the
ventral telencephalon normally but fail to complete their journey into the cortex.
They stop as they approach the PSPB, although the PSPB doesn’t seem to be directly
affected by the mutation of Apc in the cortex. Additionally, Ig-Nrg1 (Neuregulin-1),
the secreted protein that was suggested to play long-range roles in attracting TCAs
towards the cortex, is present in the Apc mutant. This implies that Ig-Nrg1 is not
sufficient for guiding TCAs into the cortex, and that additional guidance factors are
needed. Moreover, my in vitro explant culture experiments show that the mutant
cortex neither repel nor inhibit thalamic axonal outgrowth, indicating that the failure
of TCAs in reaching the cortex is not due to the change of repulsive cues secreted by
the mutant cortex. It rather indicates that the guidance factors for TCAs are likely to
function through cell-cell contact mediated mechanisms. The Apc mutant cortex
lacks these guidance factors, which might be the cortical axons. In conclusion, my data reveal a choice point for TCAs at the PSPB. Guidance factors
from the cortex are needed for TCAs to cross the PSPB, which are absent in the Apc
mutant. TCAs may need the direct contact with cortical axons and use them as an
axonal scaffold to navigate into the cerebral cortex
Experimental Realization and Theoretical Studies of Novel All-optical Devices Based on Nano-scale Waveguides
Ph.DDOCTOR OF PHILOSOPH
Robust output regulation of linear system subject to modeled and unmodeled uncertainty
In this paper, a novel robust output regulation control framework is proposed
for the system subject to noise, modeled disturbance and unmodeled disturbance
to seek tracking performance and robustness simultaneously. The output
regulation scheme is utilized in the framework to track the reference in the
presence of modeled disturbance, and the effect of unmodeled disturbance is
reduced by an compensator. The Kalman filter can be also
introduced in the stabilization loop to deal with the white noise. Furthermore,
the tracking error in the presence/absence of noise and disturbance is
estimated. The effectiveness and performance of our proposed control framework
is verified in the numerical example by applying in the Furuta Inverted
Pendulum system
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