On a Order Reduction Theorem in the Lagrangian Formalism

We provide a new proof of a important theorem in the Lagrangian formalism about necessary and sufficient conditions for a second-order variational system of equations to follow from a first-order Lagrangian.Comment: 9 pages, LATEX, no figures; appear in Il Nuovo Cimento

Nonlinear robust controller design for multi-robot systems with unknown payloads

This work is concerned with the control problem of a multi-robot system handling a payload with unknown mass properties. Force constraints at the grasp points are considered. Robust control schemes are proposed that cope with the model uncertainty and achieve asymptotic path tracking. To deal with the force constraints, a strategy for optimally sharing the task is suggested. This strategy basically consists of two steps. The first detects the robots that need help and the second arranges that help. It is shown that the overall system is not only robust to uncertain payload parameters, but also satisfies the force constraints

Size Gap for Zero Temperature Black Holes in Semiclassical Gravity

We show that a gap exists in the allowed sizes of all zero temperature static spherically symmetric black holes in semiclassical gravity when only conformally invariant fields are present. The result holds for both charged and uncharged black holes. By size we mean the proper area of the event horizon. The range of sizes that do not occur depends on the numbers and types of quantized fields that are present. We also derive some general properties that both zero and nonzero temperature black holes have in all classical and semiclassical metric theories of gravity.Comment: 4 pages, ReVTeX, no figure

2D Fourier Transform Spectroscopy of exciton-polaritons and their interactions

We investigate polariton-polariton interactions in a semiconductor microcavity through two-dimensional Fourier transform (2DFT) spectroscopy. We observe, in addition to the lower-lower and the upper-upper polariton self-interaction, a lower-upper cross-interaction. This appears as separated peaks in the on-diagonal and off-diagonal part of 2DFT spectra. Moreover, we elucidate the role of the polariton dispersion through a fine structure in the 2DFT spectrum. Simulations, based on lower-upper polariton basis Gross-Pitaevskii equations including both self and cross-interactions, result in a 2DFT spectra in qualitative agreement with experiments

A comparison of similar aerosol measurements made on the NASA P3-B, DC-8, and NSF C-130 aircraft during TRACE-P and ACE-Asia

Two major aircraft experiments occurred off the Pacific coast of Asia during spring 2001: the NASA sponsored Transport and Chemical Evolution over the Pacific (TRACE-P) and the National Science Foundation (NSF) sponsored Aerosol Characterization Experiment-Asia (ACE-Asia). Both experiments studied emissions from the Asian continent (biomass burning, urban/industrial pollution, and dust). TRACE-P focused on trace gases and aerosol during March/April and was based primarily in Hong Kong and Yokota Air Force Base, Japan, and involved two aircraft: the NASA DC-8 and the NASA P3-B. ACE-Asia focused on aerosol and radiation during April/May and was based in Iwakuni Marine Corps Air Station, Japan, and involved the NSF C-130. This paper compares aerosol measurements from these aircraft including aerosol concentrations, size distributions (and integral properties), chemistry, and optical properties. Best overall agreement (generally within RMS instrumental uncertainty) was for physical properties of the submircron aerosol, including condensation nuclei concentrations, scattering coefficients, and differential mobility analyzer and optical particle counter (OPC) accumulation mode size distributions. Larger differences (typically outside of the RMS uncertainty) were often observed for parameters related to the supermicron aerosols (total scattering and absorption coefficients, coarse mode Forward Scattering Spectrometer Probe and OPC size distributions/integral properties, and soluble chemical species usually associated with the largest particles, e.g., Na+, Cl−, Ca2+, and Mg2+), where aircraft sampling is more demanding. Some of the observed differences reflect different inlets (e.g., low-turbulence inlet enhancement of coarse mode aerosol), differences in sampling lines, and instrument configuration and design. Means and variances of comparable measurements for horizontal legs were calculated, and regression analyses were performed for each platform and allow for an assessment of instrument performance. These results provide a basis for integrating aerosol data from these aircraft platforms for both the TRACE-P and ACE-Asia experiments

Theory of Impurity Effects on the Spin Nematic State

The effect of magnetic bond disorder in otherwise antiferro nematic ordered system is investigated. We introduced triangular-shaped ferromagnetic bond disorder in the S=1 bilinear-biquadratic model on a triangular lattice. It is shown that the coupling between the impurity magnetic moment and nonmagnetic excitation in the bulk yields single-moment anisotropy and long-range anisotropic interaction between impurity magnetic moments. This interaction can induce unconventional spin-freezing phenomena observed in triangular magnet, NiGa2S4.Comment: 19 pages, 14 figure

Co-NMR Knight Shift of NaxCoO2 \dot yH2O Studied in Both Superconducting Regions of the Tc-nuQ3 Phase Diagram Divided by the Nonsuperconducting Phase

In the temperature (T)-nuQ3 phase diagram of NaxCoO2 \dot yH2O, there exist two superconducting regions of nuQ3 separated by the nonsuperconducting region, where nuQ3 is usually estimated from the peak position of the 59Co-NQR spectra of the 5/2-7/2 transition and well-approximated here as nuQ3~3nuQ,nuQ being the interaction energy between the nuclear quadrupole moment and the electric field gradient. We have carried out measurements of the 59Co-NMR Knight shift (K) for a single crystal in the higher-nuQ3 superconducting phase and found that K begins to decrease with decreasing T at Tc for both magnetic field directions parallel and perpendicular to CoO2-planes. The result indicates together with the previous ones that the superconducting pairs are in the spin-singlet state in both phases, excluding the possibility of the spin-triplet superconductivity in this phase diagram. The superconductivity of this system spreads over the wide nuQ3 regions, but is suppressed in the narrow region located at the middle point of the region possibly due to charge instability.Comment: 8 pages, 5 figures, submitted to J. Phys. Soc. Jp

Mean Free Path in Disordered Multichannel Tight-Binding Wires

Transport in a disordered tight-binding wire involves a collection of different mean free paths resulting from the distinct fermi points, which correspond to the various scattering channels of the wire. The generalization of Thouless' relation between the mean free path and the localization length $\xi$ permits to define an average channel mean free path,$\bar\ell$, such that $\xi\sim N\bar\ell$ in an $N$-channel system. The averaged mean free path $\bar\ell$ is expressed exactly in terms of the total reflection coefficient of the wire and compared with the mean free path defined in the maximum entropy approach

SIGGMA: A Survey of Ionized Gas in the Galaxy, Made with the Arecibo Telescope

A Survey of Ionized Gas in the Galaxy, made with the Arecibo telescope (SIGGMA) uses the Arecibo L-band Feed Array (ALFA) to fully sample the Galactic plane (30 < l < 75 and -2 < b < 2; 175 < l < 207 and -2 < b < 1) observable with the telescope in radio recombination lines (RRLs). Processed data sets are being produced in the form of data cubes of 2 degree (along l) x 4 degree (along b) x 151 (number of channels), archived and made public. The 151 channels cover a velocity range of 600 km/s and the velocity resolution of the survey changes from 4.2 km/s to 5.1 km/s from the lowest frequency channel to the highest frequency channel, respectively.RRL maps with 3.4 arcmin resolution and line flux density sensitivity of 0.5 mJy will enable us to identify new HII regions, measure their electron temperatures, study the physics of photodissociation regions (PDRs) with carbon RRLs, and investigate the origin of the extended low density medium (ELDM). Twelve Hn{\alpha} lines fall within the 300 MHz bandpass of ALFA; they are resampled to a common velocity resolution to improve the signal-to-noise ratio (SN) by a factor of 3 or more and preserve the line width. SIGGMA will produce the most sensitive fully sampled RRL survey to date. Here we discuss the observing and data reduction techniques in detail. A test observation toward the HII region complex S255/S257 has detected Hn{\alpha} and Cn{\alpha} lines with SN>10

Nontrivial quantized Berry phases for itinerant spin liquids

Quantized Berry phases as local order parameters in t-J models are studied. A texture pattern of the local order parameters is topologically stable due to the quantization of non-Abelian Berry phases defined by low-energy states below a spin gap, which exists in the large J/t case with a few electrons. We have confirmed that itinerant singlets in the wide class of t-J models carry the nontrivial Berry phase pi. In the large J/t case for the one-dimensional t-J model, Berry phases are uniformly pi when the number of electrons is N =4n +2, ($n=0,1,2,...$).Comment: 8 pages, 4 figure