Bose glass behavior in (Yb1−x_{1-x}Lux_x)4_4As3_3 representing the randomly diluted quantum spin-1/2 chains

The site-diluted compound (Yb$_{1-x}$Lu$_x$)$_4$As$_3$ is a scarce realization of the linear Heisenberg antiferromagnet partitioned into finite-size segments and is an ideal model compound for studying field-dependent effects of quenched disorder in the one-dimensional antiferromagnets. It differentiates from the systems studied so far in two aspects - the type of randomness and the nature of the energy gap in the pure sample. We have measured the specific heat of single-crystal (Yb$_{1-x}$Lu$_x$)$_4$As$_3$ in magnetic fields up to 19.5 T. The contribution $C_{\perp}$ arising from the magnetic subsystem in an applied magnetic field perpendicular to the chains is determined. Compared to pure Yb$_4$As$_3$, for which $C_{\perp}$ indicates a gap opening, for diluted systems a non-exponential decay is found at low temperatures which is consistent with the thermodynamic scaling of the specific heat established for a Bose-glass phase.Comment: 8 pages, 17 figures, including supplemental material, accepted for PRB rapid communicatio

Correlated Emission of Hadrons from Recombination of Correlated Partons

We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasi-thermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few GeV/c momentum range observed in Au+Au collisions at RHIC.Comment: 4 pages, 2 figures; v2: typo on p.4 correcte

A model of semimetallic behavior in strongly correlated electron systems

Metals with values of the resistivity and the Hall coefficient much larger than typical ones, e.g., of sodium, are called semimetals. We suggest a model for semimetals which takes into account the strong Coulomb repulsion of the charge carriers, especially important in transition-metal and rare-earth compounds. For that purpose we extend the Hubbard model by coupling one additional orbital per site via hybridization to the Hubbard orbitals. We calculate the spectral function, resistivity and Hall coefficient of the model using dynamical mean-field theory. Starting from the Mott-insulating state, we find a transition to a metal with increasing hybridization strength (``self-doping''). In the metallic regime near the transition line to the insulator the model shows semimetallic behavior. We compare the calculated temperature dependence of the resistivity and the Hall coefficient with the one found experimentally for $\rm Yb_4As_3$. The comparison demonstrates that the anomalies in the transport properties of $\rm Yb_4As_3$ possibly can be assigned to Coulomb interaction effects of the charge carriers not captured by standard band structure calculations.Comment: 9 pages RevTeX with 7 ps figures, accepted by PR

EVM and Achievable Data Rate Analysis of Clipped OFDM Signals in Visible Light Communication

Orthogonal frequency division multiplexing (OFDM) has been considered for visible light communication (VLC) thanks to its ability to boost data rates as well as its robustness against frequency-selective fading channels. A major disadvantage of OFDM is the large dynamic range of its time-domain waveforms, making OFDM vulnerable to nonlinearity of light emitting diodes (LEDs). DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are two popular OFDM techniques developed for the VLC. In this paper, we will analyze the performance of the DCO-OFDM and ACO-OFDM signals in terms of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both average optical power and dynamic optical power constraints. EVM is a commonly used metric to characterize distortions. We will describe an approach to numerically calculate the EVM for DCO-OFDM and ACO-OFDM. We will derive the optimum biasing ratio in the sense of minimizing EVM for DCO-OFDM. Additionally, we will formulate the EVM minimization problem as a convex linear optimization problem and obtain an EVM lower bound against which to compare the DCO-OFDM and ACO-OFDM techniques. We will prove that the ACO-OFDM can achieve the lower bound. Average optical power and dynamic optical power are two main constraints in VLC. We will derive the achievable data rates under these two constraints for both additive white Gaussian noise (AWGN) channel and frequency-selective channel. We will compare the performance of DCO-OFDM and ACO-OFDM under different power constraint scenarios

Duality Relation among Periodic Potential Problems in the Lowest Landau Level

Using a momentum representation of a magnetic von Neumann lattice, we study a two-dimensional electron in a uniform magnetic field and obtain one-particle spectra of various periodic short-range potential problems in the lowest Landau level.We find that the energy spectra satisfy a duality relation between a period of the potential and a magnetic length. The energy spectra consist of the Hofstadter-type bands and flat bands. We also study the connection between a periodic short-range potential problem and a tight-binding model.Comment: 6 pages, 3 figures, final version to appear in PR

Stability of the compressible quantum Hall state around the half-filled Landau level

We study the compressible states in the quantum Hall system using a mean field theory on the von Neumann lattice. In the lowest Landau level, a kinetic energy is generated dynamically from Coulomb interaction. The compressibility of the state is calculated as a function of the filling factor $\nu$ and the width $d$ of the spacer between the charge carrier layer and dopants. The compressibility becomes negative below a critical value of $d$ and the state becomes unstable at $\nu=1/2$. Within a finite range around $\nu=1/2$, the stable compressible state exists above the critical value of $d$.Comment: 4 pages, 4 Postscript figures, RevTe

Overview of Hybrid Ventilation Control System and Full Scale Monitoring

Mix-mode or hybrid ventilation systems have been previously shown to reduce cooling and ventilation energy consumption. This paper presents a case study of a new ten story 83,700 ft² (7,780 m²) office building in downtown Tokyo with a hybrid ventilation system that uses only 1.7% of the building footprint for ventilation shafts. The control system design is presented as an example of balancing the comfort expectations of multiple tenants in a mix-mode system. On-site measurements are presented from a three week commissioning project to show: modest temperature differences within the occupied zone with a maximum difference of 1.5 °F (0.83 °C), large differences of up to 6.1 °F (3.4 °C) between the measured outdoor temperature in the control system and the actual inlet temperature for the natural ventilation system, the importance of smooth integration of various design teams, and the use of low-power fans, 1.2-0.60 hp (900-450 W), that leverage the low pressure drop through the building when natural driving forces are insufficient for pure natural ventilation. Practical lessons learned from the design and commissioning of the building are also shared.Hulic Co., Ltd

Liouville Integrability of Classical Calogero-Moser Models

Liouville integrability of classical Calogero-Moser models is proved for models based on any root systems, including the non-crystallographic ones. It applies to all types of elliptic potentials, i.e. untwisted and twisted together with their degenerations (hyperbolic, trigonometric and rational), except for the rational potential models confined by a harmonic force.Comment: 8 pages, LaTeX2e, no figure