68,753 research outputs found
Characterization and Theoretical Study of Mid-infrared Quantum Cascade Lasers
The technology and performance of quantum cascade lasers has rapidly developed since it was firstly unveiled in 1994. This type of laser has a feasible design, micro meter size and potential for emission of long wavelength (mid-infrared to far-infrared); hence, it can be useful for multiple applications. Because of the lack of light source in the mid-infrared range (wavelengths of 3-30 μm), the mid-infrared quantum cascade lasers with high quality radiation are playing important roles in several research fields such as chemical and bio-chemical spectroscopy, free space gas sensing and communication.
This work reports the design, fabrication and characterization of the mid-infrared quantum cascade lasers. The theoretical part of this thesis presents the simulation methods of the mid-infrared quantum cascade lasers. The modeling results include the Schrödinger equation solver, quantum transition simulation, and the optical property calculation, among others. The experimental part reports the whole process of the mid-infrared quantum cascade lasers completed at the University of Waterloo.
In summary, the design, optimization, fabrication and characterization of the mid-infrared quantum cascade lasers is verified and improved
The Lifecycle and Cascade of WeChat Social Messaging Groups
Social instant messaging services are emerging as a transformative form with
which people connect, communicate with friends in their daily life - they
catalyze the formation of social groups, and they bring people stronger sense
of community and connection. However, research community still knows little
about the formation and evolution of groups in the context of social messaging
- their lifecycles, the change in their underlying structures over time, and
the diffusion processes by which they develop new members. In this paper, we
analyze the daily usage logs from WeChat group messaging platform - the largest
standalone messaging communication service in China - with the goal of
understanding the processes by which social messaging groups come together,
grow new members, and evolve over time. Specifically, we discover a strong
dichotomy among groups in terms of their lifecycle, and develop a separability
model by taking into account a broad range of group-level features, showing
that long-term and short-term groups are inherently distinct. We also found
that the lifecycle of messaging groups is largely dependent on their social
roles and functions in users' daily social experiences and specific purposes.
Given the strong separability between the long-term and short-term groups, we
further address the problem concerning the early prediction of successful
communities. In addition to modeling the growth and evolution from group-level
perspective, we investigate the individual-level attributes of group members
and study the diffusion process by which groups gain new members. By
considering members' historical engagement behavior as well as the local social
network structure that they embedded in, we develop a membership cascade model
and demonstrate the effectiveness by achieving AUC of 95.31% in predicting
inviter, and an AUC of 98.66% in predicting invitee.Comment: 10 pages, 8 figures, to appear in proceedings of the 25th
International World Wide Web Conference (WWW 2016
Biophysical modelling of a drosophila photoreceptor
It remains unclear how visual information is co-processed
by different layers of neurons in the retina. In particular, relatively little is known how retina translates vast environmental light changes into
neural responses of limited range. We began examining this question in a bottom-up way in a relatively simple °y eye. To gain understanding of how complex bio-molecular interactions govern the conversion of light input into voltage output (phototransduction), we are building a
biophysical model of the Drosophila R1-R6 photoreceptor. Our model, which relates molecular dynamics of the underlying biochemical reactions to external light input, attempts to capture the molecular dynamics of
phototransduction gain control in a quantitative way
Cascade-Exciton Model Analysis of Proton Spallation from 10 MeV to 5 GeV
We have used an extended version of the Cascade-Exciton Model (CEM) to
analyze more than 600 excitation functions for proton induced reactions on 19
targets ranging from C-12 to Au-197, for incident energies ranging from 10 MeV
to 5 GeV. We have compared the calculations to available data, to calculations
using approximately two dozen other models, and to predictions of several
phenomenological systematics. We present here our conclusions concerning the
relative roles of different reaction mechanisms in the production of specific
final nuclides. We comment on the strengths and weaknesses of the CEM and
suggest possible further improvements to the CEM and to other models.Comment: 9 pages, to be published in Nuclear Instruments and Methods
Noise control and utility: From regulatory network to spatial patterning
Stochasticity (or noise) at cellular and molecular levels has been observed
extensively as a universal feature for living systems. However, how living
systems deal with noise while performing desirable biological functions remains
a major mystery. Regulatory network configurations, such as their topology and
timescale, are shown to be critical in attenuating noise, and noise is also
found to facilitate cell fate decision. Here we review major recent findings on
noise attenuation through regulatory control, the benefit of noise via
noise-induced cellular plasticity during developmental patterning, and
summarize key principles underlying noise control
From Micro to Macro: Uncovering and Predicting Information Cascading Process with Behavioral Dynamics
Cascades are ubiquitous in various network environments. How to predict these
cascades is highly nontrivial in several vital applications, such as viral
marketing, epidemic prevention and traffic management. Most previous works
mainly focus on predicting the final cascade sizes. As cascades are typical
dynamic processes, it is always interesting and important to predict the
cascade size at any time, or predict the time when a cascade will reach a
certain size (e.g. an threshold for outbreak). In this paper, we unify all
these tasks into a fundamental problem: cascading process prediction. That is,
given the early stage of a cascade, how to predict its cumulative cascade size
of any later time? For such a challenging problem, how to understand the micro
mechanism that drives and generates the macro phenomenons (i.e. cascading
proceese) is essential. Here we introduce behavioral dynamics as the micro
mechanism to describe the dynamic process of a node's neighbors get infected by
a cascade after this node get infected (i.e. one-hop subcascades). Through
data-driven analysis, we find out the common principles and patterns lying in
behavioral dynamics and propose a novel Networked Weibull Regression model for
behavioral dynamics modeling. After that we propose a novel method for
predicting cascading processes by effectively aggregating behavioral dynamics,
and propose a scalable solution to approximate the cascading process with a
theoretical guarantee. We extensively evaluate the proposed method on a large
scale social network dataset. The results demonstrate that the proposed method
can significantly outperform other state-of-the-art baselines in multiple tasks
including cascade size prediction, outbreak time prediction and cascading
process prediction.Comment: 10 pages, 11 figure
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