arXiv subjects

Liu

Publications and source records attributed to Liu.

65 records · Page 4Linked to original sources

arXiv2010

Interference and nuclear medium effects on the eta-mesic nuclear spectrum

The missing-mass spectrum obtained in a recoil-free transfer reaction p($^{27}$Al,$^{3}$He)$π^{-}$p'X is analyzed. We find that the observed peak structure arises from the coherent contributions from two reaction processes in the energy region corresponding to a bound eta ($η$) meson. In one of the processes the intermediate $η$ is captured by the nucleus to form the $η$-mesic nucleus $^{25}$Mg$_η$. In the other process, the $η$ does not form $η$-nucleus bound state. The interference between these two processes has caused the peak of the spectrum to appear at an $η$ binding energy stronger than the actual one. Our analysis also indicates that the data are consistent with an attractive N*(1535)-nucleus interaction at energies below the $η$N threshold.

nucl-th↗

arXiv2010

MIMO B-MAC Interference Network Optimization under Rate Constraints by Polite Water-filling and Duality

We take two new approaches to design efficient algorithms for transmitter optimization under rate constraints, to guarantee the Quality of Service in general MIMO interference networks, which is a combination of multiple interfering broadcast channels (BC) and multiaccess channels (MAC) and is named B-MAC Networks. Two related optimization problems, maximizing the minimum of weighted rates under a sum-power constraint and minimizing the sum-power under rate constraints, are considered. The first approach takes advantage of existing efficient algorithms for SINR problems by building a bridge between rate and SINR through the design of optimal mappings between them. The approach can be applied to other optimization problems as well. The second approach employs polite water-filling, which is the optimal network version of water-filling that we recently found. It replaces most generic optimization algorithms currently used for networks and reduces the complexity while demonstrating superior performance even in non-convex cases. Both centralized and distributed algorithms are designed and the performance is analyzed in addition to numeric examples.

cs.IT↗

arXiv2010

Technical Report: MIMO B-MAC Interference Network Optimization under Rate Constraints by Polite Water-filling and Duality

We take two new approaches to design efficient algorithms for transmitter optimization under rate constraints to guarantee the Quality of Service in general MIMO interference networks, named B-MAC Networks, which is a combination of multiple interfering broadcast channels (BC) and multiaccess channels (MAC). Two related optimization problems, maximizing the minimum of weighted rates under a sum-power constraint and minimizing the sum-power under rate constraints, are considered. The first approach takes advantage of existing efficient algorithms for SINR problems by building a bridge between rate and SINR through the design of optimal mappings between them so that the problems can be converted to SINR constraint problems. The approach can be applied to other optimization problems as well. The second approach employs polite water-filling, which is the optimal network version of water-filling that we recently found. It replaces almost all generic optimization algorithms currently used for networks and reduces the complexity while demonstrating superior performance even in non-convex cases. Both centralized and distributed algorithms are designed and the performance is analyzed in addition to numeric examples.

cs.IT↗

arXiv2009

Pauli blocking and final-state interaction in electron-nucleus quasielastic scattering

The nucleon final-state interaction in inclusive electron-nucleus quasielastic scattering is studied. Based on the unitarity equation satisfied by the scattering-wave operators, a doorway model is developed to take into account the final-state interaction including the Pauli blocking of nucleon knockout. The model uses only experimental form factors as the input and can be readily applied to light- and medium-mass nuclei. Pauli blocking effects in these latter nuclei are illustrated with the case of the Coulomb interaction. Significant effects are noted for beam energies below ~ 350 MeV and for low momentum transfers.

nucl-th↗

arXiv2008

Maximum Likelihood Fitting of Tidal Streams With Application to the Sagittarius Dwarf Tidal Tails

We present a maximum likelihood method for determining the spatial properties of tidal debris and of the Galactic spheroid. With this method we characterize Sagittarius debris using stars with the colors of blue F turnoff stars in SDSS stripe 82. The debris is located at (alpha, delta, R) = (31.37 deg +/- 0.26 deg, 0.0 deg, 29.22 +/- 0.20 kpc), with a (spatial) direction given by the unit vector < -0.991 +/- 0.007 kpc, 0.042 +/- 0.033 kpc, 0.127 +/- 0.046 kpc >, in Galactocentric Cartesian coordinates, and with FWHM = 6.74 +/- 0.06 kpc. This 2.5 degee-wide stripe contains 0.9% as many F turnoff stars as the current Sagittarius dwarf galaxy. Over small spatial extent, the debris is modeled as a cylinder with a density that falls off as a Gaussian with distance from the axis, while the smooth component of the spheroid is modeled with a Hernquist profile. We assume that the absolute magnitude of F turnoff stars is distributed as a Gaussian, which is an improvement over previous methods which fixed the absolute magnitude at Mg0 = 4.2. The effectiveness and correctness of the algorithm is demonstrated on a simulated set of F turnoff stars created to mimic SDSS stripe 82 data, which shows that we have a much greater accuracy than previous studies. Our algorithm can be applied to divide the stellar data into two catalogs: one which fits the stream density profile and one with the characteristics of the spheroid. This allows us to effectively separate tidal debris from the spheroid population, both facilitating the study of the tidal stream dynamics and providing a test of whether a smooth spheroidal population exists.

astro-ph↗

arXiv2008

How Many Users should be Turned On in a Multi-Antenna Broadcast Channel?

This paper considers broadcast channels with L antennas at the base station and m single-antenna users, where L and m are typically of the same order. We assume that only partial channel state information is available at the base station through a finite rate feedback. Our key observation is that the optimal number of on-users (users turned on), say s, is a function of signal-to-noise ratio (SNR) and feedback rate. In support of this, an asymptotic analysis is employed where L, m and the feedback rate approach infinity linearly. We derive the asymptotic optimal feedback strategy as well as a realistic criterion to decide which users should be turned on. The corresponding asymptotic throughput per antenna, which we define as the spatial efficiency, turns out to be a function of the number of on-users s, and therefore s must be chosen appropriately. Based on the asymptotics, a scheme is developed for systems with finite many antennas and users. Compared with other studies in which s is presumed constant, our scheme achieves a significant gain. Furthermore, our analysis and scheme are valid for heterogeneous systems where different users may have different path loss coefficients and feedback rates.

cs.IT↗

arXiv2007

How Many Users should be Turned On in a Multi-Antenna Broadcast Channel?

This paper considers broadcast channels with L antennas at the base station and m single-antenna users, where each user has perfect channel knowledge and the base station obtains channel information through a finite rate feedback. The key observation of this paper is that the optimal number of on-users (users turned on), say s, is a function of signal-to-noise ratio (SNR) and other system parameters. Towards this observation, we use asymptotic analysis to guide the design of feedback and transmission strategies. As L, m and the feedback rates approach infinity linearly, we derive the asymptotic optimal feedback strategy and a realistic criterion to decide which users should be turned on. Define the corresponding asymptotic throughput per antenna as the spatial efficiency. It is a function of the number of on-users s, and therefore, s should be appropriately chosen. Based on the above asymptotic results, we also develop a scheme for a system with finite many antennas and users. Compared with other works where s is presumed constant, our scheme achieves a significant gain by choosing the appropriate s. Furthermore, our analysis and scheme is valid for heterogeneous systems where different users may have different path loss coefficients and feedback rates.

cs.IT↗

arXiv1998

On decoherence in quantum algorithm via dynamic models for quantum measurement

The possible effect of environment on the efficiency of a quantum algorithm is considered explicitely. It is illustrated through the example of Shor's prime factorization algorithm that this effect may be disastrous. The influence of environment on quantum computation is probed on the basis of its analogy to the problem of wave function collapse in quantum measurement.Techniques from the Hepp-Colemen approach and its generalization are used to deal with decoherence problems in quantum computation including dynamic mechanism of decoherence, quantum error avoiding tricks and calculation of decoherence time.

quant-ph↗

arXiv1997

An Overview of $D^0\bar{D}^0$ Mixing Search Techniques

The search for $D^0\bar{D}^0$ mixing may carry a large discovery potential for new physics since the $D^0\bar{D}^0$ mixing rate is expected to be small in the Standard Model. This paper gives a brief review of the experimental techniques which can be used to search for $D^0\bar{D}^0$ mixing in the future. Some ideas, applicable to future mixing searches at hadron machines (such as Tevatron and LHC), and fixed target experiments (such as HEAR-B) are introduced.

hep-ph↗

arXiv1995

An Overview of $D^0\bar{D}^0$ Mixing Search Techniques: Current Status and Future Prospects

The search for $D^0\bar{D}^0$ mixing may carry a large discovery potential for new physics. This paper discusses the techniques, current experimental status, and future prospects for the mixing search. Some new ideas, applicable to future mixing searches, are introduced. In this paper, the importance of separately measuring the decay rate difference and the mass difference of the two CP eigenstates (in order to observe New Physics) has been emphasized, since the theoretical calculations for long distance effects are still plagued by large uncertainties.

hep-ph↗

arXiv1994

The $D^0\bar{D}^0$ Mixing Search --- Current Status and Future Prospects

The search for $D^0\bar{D}^0$ mixing carries a large discovery potential for new physics since the $D^0\bar{D}^0$ mixing rate is expected to be very small in the Standard Model. The past decade has seen significant experimental progress in sensitivity, from 20\% down to 0.37\%. This paper discusses the techniques, current experimental status, and future prospects for the mixing search. Some new ideas, applicable to future mixing searches, are introduced. One of the new ideas is to use Singly Cabibbo Suppressed Decays (SCSD), such as $D^0 \to K+K-, π^+π^-$, to study mixing. A postscript version will be available through World-Wide-Web in http://w4.lns.cornell.edu/public/TALK/1994 soon.

hep-ph↗