1,533 research outputs found
Neutron Star Merger Remnants: Braking Indices, Gravitational Waves, and the Equation Of State
The binary neutron star merger GW170817/GRB170817A confirmed that at least
some neutron star mergers are the progenitors of short gamma-ray bursts. Many
short gamma-ray bursts have long-term x-ray afterglows that have been
interpreted in terms of post-merger millisecond magnetars---rapidly rotating,
highly magnetised, massive neutron stars. We review our current understanding
of millisecond magnetars born in short gamma-ray bursts, focusing particularly
three main topics. First, whether millisecond magnetars really do provide the
most plausible explain for the x-ray plateau. Second, determining and observing
the gravitational-wave emission from these remnants. Third, determining the
equation of state of nuclear matter from current and future x-ray and
gravitational-wave measurements.Comment: Conference Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of
Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy (January
3 - 7, 2019, Xiamen, China
Envy Freedom and Prior-free Mechanism Design
We consider the provision of an abstract service to single-dimensional
agents. Our model includes position auctions, single-minded combinatorial
auctions, and constrained matching markets. When the agents' values are drawn
from a distribution, the Bayesian optimal mechanism is given by Myerson (1981)
as a virtual-surplus optimizer. We develop a framework for prior-free mechanism
design and analysis. A good mechanism in our framework approximates the optimal
mechanism for the distribution if there is a distribution; moreover, when there
is no distribution this mechanism still performs well.
We define and characterize optimal envy-free outcomes in symmetric
single-dimensional environments. Our characterization mirrors Myerson's theory.
Furthermore, unlike in mechanism design where there is no point-wise optimal
mechanism, there is always a point-wise optimal envy-free outcome.
Envy-free outcomes and incentive-compatible mechanisms are similar in
structure and performance. We therefore use the optimal envy-free revenue as a
benchmark for measuring the performance of a prior-free mechanism. A good
mechanism is one that approximates the envy free benchmark on any profile of
agent values. We show that good mechanisms exist, and in particular, a natural
generalization of the random sampling auction of Goldberg et al. (2001) is a
constant approximation
Recommended from our members
Surgical technique for arthroscopic onlay suprapectoral biceps tenodesis with an all-suture anchor.
The long head of the biceps is a frequent pain generator in the shoulder. Tendinopathy of the long head of the biceps may be treated with biceps tenodesis. There has been great debate about the optimal technique for biceps tenodesis, without a clear distinction between different techniques. Biceps tenodesis fixation may include interference fixation, suspensory fixation, all-suture anchors, and soft tissue fixation. In this technical note, we describe an all-arthroscopic onlay suprapectoral biceps tenodesis with an all-suture anchor
Credible, Truthful, and Two-Round (Optimal) Auctions via Cryptographic Commitments
We consider the sale of a single item to multiple buyers by a
revenue-maximizing seller. Recent work of Akbarpour and Li formalizes
\emph{credibility} as an auction desideratum, and prove that the only optimal,
credible, strategyproof auction is the ascending price auction with reserves
(Akbarpour and Li, 2019).
In contrast, when buyers' valuations are MHR, we show that the mild
additional assumption of a cryptographically secure commitment scheme suffices
for a simple \emph{two-round} auction which is optimal, strategyproof, and
credible (even when the number of bidders is only known by the auctioneer).
We extend our analysis to the case when buyer valuations are
-strongly regular for any , up to arbitrary
in credibility. Interestingly, we also prove that this construction cannot be
extended to regular distributions, nor can the be removed with
multiple bidders
Lienard-Wiechert Potentials due to a 'classically' spinning point-charge in Non-Relativistic arbitrary motion
Lienard-Wiechert potentials have been derived for a non-relativistically
moving and 'classically' spinning point-charge; assuming it to be a rigid,
moving and spinning charged-sphere, and subsequently reducing its dimensions to
"point-particle" limit. The paper demonstrates that when the effect of
"rotational-acceleration" were considered, together with causality, expressions
for the LW potentials accompany additional correction terms that contain
spin-angular-momentum (or simply the "classical spin") of the point-charge.Comment: 17 pages, 3 figure
Development of Sound Presentation System (SPS) for Characterization of Sound Induced Displacements in Tympanic Membranes
The conventional methods for diagnosing pathological conditions of the tympanic membrane (TM) and other abnormalities require measuring its motion to an acoustic excitation for its use in a clinical environment. To obtain comprehensive quantitative diagnostic information from the motion of the entire surface of the TM, it is necessary to devise an integrated system capable of accurately recording the motion and induce an acoustic stimulus. To accomplish this goal, a sound presentation system (SPS) capable of impinging acoustic stimulus in the frequency range of 20Hz to 8 kHz at known amplitudes is synthesized in this thesis. This system is then integrated with optoelectronic digital holographic system (OEDHO) which utilizes laser interferometry to record and reconstruct phase shifted images with the help of a digital camera. The OEDHO is capable of accurately recording nanometer scale motion of the TM. The preliminary design of the SPS depends on the physical dimensions of the human ear, such as the diameter of the TM (6-9mm), depth of the ear canal (about 30mm), and also dimensions of the OEDHO system such as: diameter of tip of the otoscope head for optical access (8mm), and possible locations for integration with the OEDHO. The characteristics of the system are based on the intensity of the acoustic stimulus necessary to vibrate the TM (90-110dB SPL), and method of impinging the stimulus. To accomplish this goal, the nature of sound wave propagation through a circular pipe with known dimensions is analyzed analytically, experimentally, and by using finite element analysis (FEA). The pipe is further investigated for optimum parameters using FEA by introducing changes in the diameter (3.8mm, 6mm, 10mm), length of the pipe (30mm, 60mm, 90mm), radius of the curvature (50mm, 75mm, 100mm), and strength of the sound power source (0.2W, 0.4W, 0.6W). The comparative results provide guidelines for the design of the first version of the SPS (SPS_V1). The SPS_V1 consists of a symmetric design to impinge the acoustic stimulus towards the TM and a microphone to measure the sound pressure at the TM. The system is capable of housing a range of speakers from 2mm to 15mm in diameter. The SPS_V1 can directly interface with the standard medical speculums used for human ear testing. Also, the system is capable of interfacing with all available versions of the OEDHO. The SPS_V1 is currently being evaluated in a medical-research environment to address basic otological questions regarding TM function. The performance characterization of the system inside an artificial ear canal with two different speaker configurations is herein shown, and the potential improvements and utilization are discusse
A Comparison of Microstructure and Uniaxial Compressive Response of Ice-Templated Porous Alumina Scaffolds Fabricated from Two Different Particle Sizes
Development of bio-inspired highly porous (\u3e50 vol.%) cellular ceramics is crucial to meet the demand of high-performance lightweight and damage-tolerant materials for a number of cutting-edge applications including impact energy absorption, biomedical implants, and energy storage. A key design feature that is observed in many natural materials (e.g., nacre, bamboo, wood, etc.) is the presence of hierarchical microstructure that results in an excellent synergy of various material properties, which are otherwise considered as mutually exclusive in current paradigm of materials design. To this end, development of multilayered, interconnected and anisotropic cellular ceramics could benefit the aforementioned applications. However, mimicking natural design principles to develop robust cellular materials is of paramount challenge because most of the available processing techniques are limited to the fabrication of simple materials microstructures. In contrast, freeze casting is one emerging technique that has shown great promise to develop nature-inspired hierarchical cellular ceramics. While a large number of recent studies focused on the development of process-structure correlations of freeze-cast ceramics, understanding of the structure-property relationships has been extremely limited. Therefore, this thesis develops a custom-made unidirectional freeze casting device to investigate the effects of the variation of the particle size (0.3 μm vs. 0.9 μm) on the microstructure and uniaxial compressive response of ice-templated sintered alumina scaffolds as a function of solids loading and freezing front velocity (FFV). For comparable solids loading and FFV, particle size effects on the microstructure of the scaffolds are observed to be significant. Moreover, transition of the pore morphology with the increasing solids loading and FFV is observed to be more drastic for the scaffolds processed from the 0.9 μm particles compared to the 0.3 μm particles. Similarly, particle size variations also significantly influenced the relative density and porosity of the scaffolds. However, in spite of the observed differences of the microstructure, relative density and porosity, uniaxial compressive stress-strain measurements revealed marginal particle size effects on the compressive strength. The apparent marginal particle size effects on the compressive strength are rationalized based on the relative variation of the relative density, pore aspect ratio, and interlamellae bridge density in between the sintered alumina scaffolds processed from 0.3 μm and 0.9 μm particle sizes. This study also suggests that particle size variation within a range of submicrometer to few micrometers (typical particle size range used in ceramic processing) can be uniquely employed to systematically modify the microstructure of the ice-templated sintered ceramic scaffolds, without significantly altering their uniaxial compressive response; which can be useful to optimize the structure-property relationships of the ice-templated scaffolds for the structural, biomedical and functional applications
- …