28,901 research outputs found
Model-Robust Designs for Quantile Regression
We give methods for the construction of designs for linear models, when the
purpose of the investigation is the estimation of the conditional quantile
function and the estimation method is quantile regression. The designs are
robust against misspecified response functions, and against unanticipated
heteroscedasticity. The methods are illustrated by example, and in a case study
in which they are applied to growth charts
The globalization of Chinese energy companies
This repository item contains a report from the Boston University Global Economic Governance Initiative. The Global Economic Governance Initiative (GEGI) is a research program of the Center for Finance, Law & Policy, the Frederick S. Pardee Center for the Study of the Longer-Range Future, and the Frederick S. Pardee School of Global Studies. It was founded in 2008 to advance policy-relevant knowledge about governance for financial stability, human development, and the environment
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Directed Placement for mVLSI Devices
Continuous-flow microfluidic devices based on integrated channel networks are becoming increasingly prevalent in research in the biological sciences. At present, these devices are physically laid out by hand by domain experts who understand both the underlying technology and the biological functions that will execute on fabricated devices. The lack of a design science that is specific to microfluidic technology creates a substantial barrier to entry. To address this concern, this article introduces Directed Placement, a physical design algorithm that leverages the natural "directedness" in most modern microfluidic designs: fluid enters at designated inputs, flows through a linear or tree-based network of channels and fluidic components, and exits the device at dedicated outputs. Directed placement creates physical layouts that share many principle similarities to those created by domain experts. Directed placement allows components to be placed closer to their neighbors compared to existing layout algorithms based on planar graph embedding or simulated annealing, leading to an average reduction in laid-out fluid channel length of 91% while improving area utilization by 8% on average. Directed placement is compatible with both passive and active microfluidic devices and is compatible with a variety of mainstream manufacturing technologies
Semimetallic molecular hydrogen at pressure above 350 GPa
According to the theoretical predictions, insulating molecular hydrogen
dissociates and transforms to an atomic metal at pressures P~370-500 GPa. In
another scenario, the metallization first occurs in the 250-500 GPa pressure
range in molecular hydrogen through overlapping of electronic bands. The
calculations are not accurate enough to predict which option is realized. Here
we show that at a pressure of ~360 GPa and temperatures <200 K the hydrogen
starts to conduct, and that temperature dependence of the electrical
conductivity is typical of a semimetal. The conductivity, measured up to 440
GPa, increases strongly with pressure. Raman spectra, measured up to 480 GPa,
indicate that hydrogen remains a molecular solid at pressures up to 440 GPa,
while at higher pressures the Raman signal vanishes, likely indicating further
transformation to a good molecular metal or to an atomic state
The Enhancement of Interfacial Exciton Dissociation by Energetic Disorder is a Nonequilibrium Effect
The dissociation of excited electron-hole pairs is a microscopic process that
is fundamental to the performance of photovoltaic systems. For this process to
be successful, the oppositely charged electron and hole must overcome an
electrostatic binding energy before they undergo ground state recombination.
Here we use a simple model of charge dynamics to investigate the role of
molecular disorder in this process. This model reveals that moderate spatial
variations in electronic energy levels, such as those that arise in disordered
molecular systems, can actually increase charge dissociation yields. We
demonstrate that this is a nonequilibrium effect that is mediated by the
dissipation driven formation of partially dissociated intermediate states that
are long-lived because they cannot easily recombine. We present a kinetic model
that incorporates these states and show that it is capable of reproducing
similar behavior when it is parameterized with nonequilibrium rates.Comment: 25 pages, 7 figure
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Mitigating ground effect on mini quadcopters with model reference adaptive control
Mitigating ground effect becomes a big challenge for autonomous aerial vehicles when they are flying in close proximity to the ground. This paper aims to develop a precise model of ground effect on mini quadcopters, provide an advanced control algorithm to counter the model uncertainty and, as a result, improves the command tracking performance when the vehicle is in the ground effect region. The mathematical model of ground effect has been established through a series of experiments and validated by a flight test. The experiments show that the total thrust generated by rotors increases linearly as the vehicle gets closer to the ground, which is different from the commonly-used ground effect model for a single rotor vehicle. In addition, the model switches from a piecewise linear to a quadratic function when the rotor to rotor distance is increased. A control architecture that utilizes the model reference adaptive controller (MRAC) has also been designed, where MRAC is added to the altitude loop. The performance of the proposed control algorithm has been evaluated through a set of flight tests on a mini quadcopter platform and compared with a traditional proportional–integral–derivative (PID) controller. The results demonstrate that MRAC dramatically improves the tracking performance of altitude command and can reduce the rise time by 80 % under the ground effect
Validation of multiprocessor systems
Experiments that can be used to validate fault free performance of multiprocessor systems in aerospace systems integrating flight controls and avionics are discussed. Engineering prototypes for two fault tolerant multiprocessors are tested
Light pseudoscalar eta and H->eta eta decay in the simplest little Higgs mode
The SU(3) simplest little Higgs model in its original framework without the
so-called mu term inevitably involves a massless pseudoscalar boson eta, which
is problematic for b-physics and cosmological axion limit. With the mu term
introduced by hand, the eta boson acquires mass m_eta ~ mu, which can be
lighter than half the Higgs boson mass in a large portion of the parameter
space. In addition, the introduced mu term generates sizable coupling of
H-eta-eta. The Higgs boson can dominantly decay into a pair of eta's especially
when mH below the WW threshold. Another new decay channel of H->Z+eta can be
dominant or compatible with H -> WW for mH above the Z+eta threshold. We show
that the LEP bound on the Higgs boson mass is loosened to some extent due to
this new H->eta eta decay channel as well as the reduced coupling of H-Z-Z. The
Higgs boson mass bound falls to about 110 GeV for f=3-4 TeV. Since the eta
boson decays mainly into a bb pair, H-> eta eta -> 4b and H-> Z eta -> Z bb
open up other interesting search channels in the pursuit of the Higgs boson in
the future experiments. We discuss on these issues.Comment: major modification considering the simplest little Higgs model with
the mu ter
Let Your CyberAlter Ego Share Information and Manage Spam
Almost all of us have multiple cyberspace identities, and these {\em
cyber}alter egos are networked together to form a vast cyberspace social
network. This network is distinct from the world-wide-web (WWW), which is being
queried and mined to the tune of billions of dollars everyday, and until
recently, has gone largely unexplored. Empirically, the cyberspace social
networks have been found to possess many of the same complex features that
characterize its real counterparts, including scale-free degree distributions,
low diameter, and extensive connectivity. We show that these topological
features make the latent networks particularly suitable for explorations and
management via local-only messaging protocols. {\em Cyber}alter egos can
communicate via their direct links (i.e., using only their own address books)
and set up a highly decentralized and scalable message passing network that can
allow large-scale sharing of information and data. As one particular example of
such collaborative systems, we provide a design of a spam filtering system, and
our large-scale simulations show that the system achieves a spam detection rate
close to 100%, while the false positive rate is kept around zero. This system
has several advantages over other recent proposals (i) It uses an already
existing network, created by the same social dynamics that govern our daily
lives, and no dedicated peer-to-peer (P2P) systems or centralized server-based
systems need be constructed; (ii) It utilizes a percolation search algorithm
that makes the query-generated traffic scalable; (iii) The network has a built
in trust system (just as in social networks) that can be used to thwart
malicious attacks; iv) It can be implemented right now as a plugin to popular
email programs, such as MS Outlook, Eudora, and Sendmail.Comment: 13 pages, 10 figure
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