2,280 research outputs found
System for monitoring physical characteristics of fluids
An apparatus and method are described for measuring physical characteristics of fluid, by placing a drop of the fluid in a batch of a second fluid and passing acoustic waves through the bath. The applied frequency of the acoustic waves is varied, to determine the precise value of a frequency at which the drop undergoes resonant oscillations. The resonant frequency indicates the interfacial tension of the drop in the bath, and the interfacial tension can indicate physical properties of the fluid in the drop
Joint Pilot Design and Uplink Power Allocation in Multi-Cell Massive MIMO Systems
This paper considers pilot design to mitigate pilot contamination and provide
good service for everyone in multi-cell Massive multiple input multiple output
(MIMO) systems. Instead of modeling the pilot design as a combinatorial
assignment problem, as in prior works, we express the pilot signals using a
pilot basis and treat the associated power coefficients as continuous
optimization variables. We compute a lower bound on the uplink capacity for
Rayleigh fading channels with maximum ratio detection that applies with
arbitrary pilot signals. We further formulate the max-min fairness problem
under power budget constraints, with the pilot signals and data powers as
optimization variables. Because this optimization problem is non-deterministic
polynomial-time hard due to signomial constraints, we then propose an algorithm
to obtain a local optimum with polynomial complexity. Our framework serves as a
benchmark for pilot design in scenarios with either ideal or non-ideal
hardware. Numerical results manifest that the proposed optimization algorithms
are close to the optimal solution obtained by exhaustive search for different
pilot assignments and the new pilot structure and optimization bring large
gains over the state-of-the-art suboptimal pilot design.Comment: 16 pages, 8 figures. Accepted to publish at IEEE Transactions on
Wireless Communication
Joint Power Allocation and User Association Optimization for Massive MIMO Systems
This paper investigates the joint power allocation and user association
problem in multi-cell Massive MIMO (multiple-input multiple-output) downlink
(DL) systems. The target is to minimize the total transmit power consumption
when each user is served by an optimized subset of the base stations (BSs),
using non-coherent joint transmission. We first derive a lower bound on the
ergodic spectral efficiency (SE), which is applicable for any channel
distribution and precoding scheme. Closed-form expressions are obtained for
Rayleigh fading channels with either maximum ratio transmission (MRT) or zero
forcing (ZF) precoding. From these bounds, we further formulate the DL power
minimization problems with fixed SE constraints for the users. These problems
are proved to be solvable as linear programs, giving the optimal power
allocation and BS-user association with low complexity. Furthermore, we
formulate a max-min fairness problem which maximizes the worst SE among the
users, and we show that it can be solved as a quasi-linear program. Simulations
manifest that the proposed methods provide good SE for the users using less
transmit power than in small-scale systems and the optimal user association can
effectively balance the load between BSs when needed. Even though our framework
allows the joint transmission from multiple BSs, there is an overwhelming
probability that only one BS is associated with each user at the optimal
solution.Comment: 16 pages, 12 figures, Accepted by IEEE Trans. Wireless Commu
MMT observations of new extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey
We present 6.5-meter MMT spectrophotometry of 20 H II regions in 13 extremely
metal-poor emission-line galaxies selected from the Data Release 5 of the Sloan
Digital Sky Survey to have [O III] 4959/Hbeta < 1 and [N II] 6583/Hbeta < 0.05.
The electron temperature-sensitive emission line [O III] 4363 is detected in 13
H II regions allowing a direct abundance determination. The oxygen abundance in
the remaining H II regions is derived using a semi-empirical method. The oxygen
abundance of the galaxies in our sample ranges from 12+logO/H ~ 7.1 to ~ 7.8,
with 10 H II regions having an oxygen abundance lower than 7.5. The lowest
oxygen abundances, 12+logO/H = 7.14+/-0.03 and 7.13+/-0.07, are found in two H
II regions of the blue compact dwarf galaxy SDSSJ0956+2849=DDO 68, making it
the second most-metal deficient emission-line galaxy known, after SBS
0335-052W.Comment: 28 pages, 3 figures. Accepted for publication in the Astrophysical
Journa
Dependent randomized rounding for clustering and partition systems with knapsack constraints
Clustering problems are fundamental to unsupervised learning. There is an
increased emphasis on fairness in machine learning and AI; one representative
notion of fairness is that no single demographic group should be
over-represented among the cluster-centers. This, and much more general
clustering problems, can be formulated with "knapsack" and "partition"
constraints. We develop new randomized algorithms targeting such problems, and
study two in particular: multi-knapsack median and multi-knapsack center. Our
rounding algorithms give new approximation and pseudo-approximation algorithms
for these problems. One key technical tool, which may be of independent
interest, is a new tail bound analogous to Feige (2006) for sums of random
variables with unbounded variances. Such bounds are very useful in inferring
properties of large networks using few samples
Divorce Reform—One State’s Solution
Although New York has long been a leader in reform legislation, it has also had one of the most ineffective divorce laws in the nation. Therefore, it was not unrealistic to hope that when New York recently revised its divorce laws the new product would serve as a model for future reforms in other jurisdictions. While the new law as finally enacted is defective in several respects, its provisions reflect an attempt to accommodate the basic reform trends in current divorce law. This comment investigates briefly the evolution of governmental controls of divorce, the American tradition prior to the New York reform, and the implications of the procedures finally adopted by that state
SBS 0335-052W: The Lowest-Metallicity Star-Forming Galaxy Known
We present 4-meter Kitt Peak telescope and 6.5-meter MMT spectrophotometry of
the extremely low-metallicity galaxy SBS 0335-052W, the western companion of
the blue compact dwarf galaxy SBS 0335-052E. These observations have been
combined with published 10-meter Keck data to derive for the brightest region
of SBS 0335-052W an oxygen abundance 12+logO/H=7.12+/-0.03. This makes SBS
0335-052W the lowest metallicity star-forming galaxy known in the local
universe. Using a Monte Carlo technique, we fit the spectral energy
distribution of SBS 0335-052W to derive the age of the oldest stars
contributing to its optical light. We find that star formation in SBS 0335-052W
began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Eco-innovation and Corporate Cost of Debt: A Cross-Country Evidence
This study offers cross-country (G7) evidence that eco-innovation (or green innovation, measured by its Refinitive score and a comprehensive index) is negatively and significantly associated with the corporate cost of debt. The results are intensified for firms with more prolonged eco-innovation engagement, as reflected by the eco-innovation years. The study also uncovers that a greater eco-innovation degree facilitates firms to reduce their carbon risk, affecting creditors\u27 lending decisions by lowering debt costs. Furthermore, the lower borrowing cost underneath higher eco-innovation are more likely to be acquired in financially undistressed and constrained businesses. Our extended analysis further shows that climate governance quality reduces the beneficial impact of eco-innovation on the firm\u27s cost of debt. The research offers timely policy implications on eco-innovation, which constitutes an essential consideration in creditors\u27 lending decisions, aligning with the neo-institutional theory in response to increasing global environmentrelated pressures
The dynamics of free liquid drops
The behavior of rotating and oscillating free liquid drops was studied by many investigators theoretically for many years. More recent numerical treatments have yielded predictions which are yet to be verified experimentally. The purpose is to report the results of laboratory work as well as that of the experiments carried out in space during the flight of Spacelab 3, and to compare it with the existing theoretical studies. Ground-based experiments were attempted as a first approximation to the ideal boundary conditions used by the theoretical treatments by neutralizing the overwhelming effects of the Earth's gravitational field with an outside supporting liquid and with the use of levitation technology. The viscous and inertial loading of such a suspending fluid was found to profoundly effect the results, but the information thus gathered has emphasized the uniqueness of the experimental data obtained in the low-gravity environment of space
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