6,826 research outputs found
On hitting time, mixing time and geometric interpretations of Metropolis-Hastings reversiblizations
Given a target distribution and a proposal chain with generator on
a finite state space, in this paper we study two types of Metropolis-Hastings
(MH) generator and in a continuous-time setting.
While is the classical MH generator, we define a new generator that
captures the opposite movement of and provide a comprehensive suite of
comparison results ranging from hitting time and mixing time to asymptotic
variance, large deviations and capacity, which demonstrate that enjoys
superior mixing properties than . To see that and are natural
transformations, we offer an interesting geometric interpretation of ,
and their convex combinations as minimizers between and the
set of -reversible generators, extending the results by Billera and
Diaconis (2001). We provide two examples as illustrations. In the first one we
give explicit spectral analysis of and for Metropolised independent
sampling, while in the second example we prove a Laplace transform order of the
fastest strong stationary time between birth-death and .Comment: 17 pages. To appear in J. Theoret. Proba
Direct Measure of Giant Magnetocaloric Entropy Contributions in Ni-Mn-In
Off-stoichiometric alloys based on Ni 2 MnIn have drawn attention due to the
coupled first order magnetic and structural transformations, and the large
magnetocaloric entropy associated with the transformations. Here we describe
calorimetric and magnetic studies of four compositions. The results provide a
direct measure of entropy changes contributions including at the first-order
phase transitions, and thereby a determination of the maximum field-induced
entropy change corresponding to the giant magnetocaloric effect. We find a
large excess entropy change, attributed to magneto-elastic coupling, but only
in compositions with no ferromagnetic order in the high-temperature austenite
phase. Furthermore, a molecular field model corresponding to antiferromagnetism
of the low-temperature phases is in good agreement, and nearly independent of
composition, despite significant differences in overall magnetic response of
these materials
Calorimetric and magnetic study for NiMnIn and relative cooling power in paramagnetic inverse magnetocaloric systems
The non-stoichiometric Heusler alloy NiMnIn undergoes a
martensitic phase transformation in the vicinity of 345 K, with the high
temperature austenite phase exhibiting paramagnetic rather than ferromagnetic
behavior, as shown in similar alloys with lower-temperature transformations.
Suitably prepared samples are shown to exhibit a sharp transformation, a
relatively small thermal hysteresis, and a large field-induced entropy change.
We analyzed the magnetocaloric behavior both through magnetization and direct
field-dependent calorimetry measurements. For measurements passing through the
first-order transformation, an improved method for heat-pulse relaxation
calorimetry was designed. The results provide a firm basis for the analytic
evaluation of field-induced entropy changes in related materials. An analysis
of the relative cooling power (RCP), based on the integrated field-induced
entropy change and magnetizing behavior of the Mn spin system with
ferromagnetic correlations, shows that a significant RCP may be obtained in
these materials by tuning the magnetic and structural transformation
temperatures through minor compositional changes or local order changes
Conditioning of BPM pickup signals for operations of the Duke storage ring with a wide range of single-bunch current
The Duke storage ring is a dedicated driver for the storage ring based
oscillator free-electron lasers (FELs), and the High Intensity Gamma-ray Source
(HIGS). It is operated with a beam current ranging from about 1 mA to 100 mA
per bunch for various operations and accelerator physics studies. High
performance operations of the FEL and gamma-ray source require a stable
electron beam orbit, which has been realized by the global orbit feedback
system. As a critical part of the orbit feedback system, the electron beam
position monitors (BPMs) are required to be able to precisely measure the
electron beam orbit in a wide range of the single-bunch current. However, the
high peak voltage of the BPM pickups associated with high single-bunch current
degrades the performance of the BPM electronics, and can potentially damage the
BPM electronics. A signal conditioning method using low pass filters is
developed to reduce the peak voltage to protect the BPM electronics, and to
make the BPMs capable of working with a wide range of single-bunch current.
Simulations and electron beam based tests are performed. The results show that
the Duke storage ring BPM system is capable of providing precise orbit
measurements to ensure highly stable FEL and HIGS operations
Weak antilocalization and electron-electron interaction in coupled multiple-channel transport in a BiSe thin film
Electron transport properties of a topological insulator BiSe thin
film are studied in Hall-bar geometry. The film with a thickness of 10 nm is
grown by van der Waals epitaxy on fluorophlogopite mica and Hall-bar devices
are fabricated from the as-grown film directly on the mica substrate. Weak
antilocalization and electron-electron interaction effects are observed and
analyzed at low temperatures. The phase-coherence length extracted from the
measured weak antilocalization characteristics shows a strong power-law
increase with decreasing temperature and the transport in the film is shown to
occur via coupled multiple (topological surface and bulk states) channels. The
conductivity of the film shows a logarithmically decrease with decreasing
temperature and thus the electron-electron interaction plays a dominant role in
quantum corrections to the conductivity of the film at low temperatures.Comment: 12 pages, 5 figure
Wireless sensor networks for heritage object deformation detection and tracking algorithm
Deformation is the direct cause of heritage object collapse. It is significant to monitor and signal the early warnings of the deformation of heritage objects. However, traditional heritage object monitoring methods only roughly monitor a simple-shaped heritage object as a whole, but cannot monitor complicated heritage objects, which may have a large number of surfaces inside and outside. Wireless sensor networks, comprising many small-sized, low-cost, low-power intelligent sensor nodes, are more useful to detect the deformation of every small part of the heritage objects. Wireless sensor networks need an effective mechanism to reduce both the communication costs and energy consumption in order to monitor the heritage objects in real time. In this paper, we provide an effective heritage object deformation detection and tracking method using wireless sensor networks (EffeHDDT). In EffeHDDT, we discover a connected core set of sensor nodes to reduce the communication cost for transmitting and collecting the data of the sensor networks. Particularly, we propose a heritage object boundary detecting and tracking mechanism. Both theoretical analysis and experimental results demonstrate that our EffeHDDT method outperforms the existing methods in terms of network traffic and the precision of the deformation detection
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