Drude weight and total optical weight in a t-t'-J model

We study the Drude weight D and the total optical weight K for a t-t'-J model on a square lattice that exhibits a metallic phase-modulated antiferromagnetic ground state close to half-filling. Within a suitable 1/N expansion that includes leading quantum-fluctuation effects, D and K are found to increase linearly with small hole doping away from the Mott metal-insulator transition point at half-filling. The slow zero-sound velocity near the latter transition identifies with the velocity of the lower-energy branch of the twofold excitation spectrum. At higher doping values, D and K eventually saturate and then start to decrease. These features are in qualitative agreement with optical conductivity measurements in doped antiferromagnets.Comment: 7 pages, REVTEX file (3 Postscript figures). To appear in J. Phys.: Condens. Mattte

Towards a Macroscopic Modelling of the Complexity in Traffic Flow

We present a macroscopic traffic flow model that extends existing fluid-like models by an additional term containing the second derivative of the safe velocity. Two qualitatively different shapes of the safe velocity are explored: a conventional Fermi-type function and a function exhibiting a plateau at intermediate densities. The suggested model shows an extremely rich dynamical behaviour and shows many features found in real-world traffic data.Comment: submitted to Phys. Rev.

Association of the body adiposity index (BAI) with metabolic risk factors in young and older overweight and obese women.

PURPOSE: Body adiposity index (BAI) is a novel index for the assessment of percentage fat mass (FM%). We tested the association between BAI and metabolic outcomes in overweight and obese women of different ages. METHODS: 260 young women (24.7 ± 5.3 years, 31.0 ± 5.0 kg/m(2)) and 328 older women (66.9 ± 4.6 years, 34.8 ± 4.7 kg/m(2)) were recruited. BAI was calculated using hip circumference and height. Bioimpedance analysis was used to measure FM%. Metabolic risk was assessed using a composite z score integrating standardised measurements of fasting glucose, total cholesterol, liver enzymes and triglycerides. RESULTS: The association between BAI and FM% was modest in both young (r = 0.56, p < 0.001) and older (r = 0.49, p < 0.001) groups. BAI was directly associated with metabolic risk in young women (r = 0.29, p < 0.001), whereas it showed a weak, inverse association in the older group (r = -0.14, p = 0.01). CONCLUSIONS: BAI validity needs to be re-assessed in older individuals for better definition of its predictive accuracy

The Expected Perimeter in Eden and Related Growth Processes

Following Richardson and using results of Kesten on First-passage percolation, we obtain an upper bound on the expected perimeter in an Eden Growth Process. Using results of the author from a problem in Statistical Mechanics, we show that the average perimeter of the lattice animals resulting from a very natural family of "growth histories" does not obey a similar bound.Comment: 11 page

Inclusive 2H(3He,t) reaction at 2 GeV

The inclusive 2H(3He,t) reaction has been studied at 2 GeV for energy transfers up to 500 MeV and scattering angles from 0.25 up to 4 degrees. Data are well reproduced by a model based on a coupled-channel approach for describing the NN and N Delta systems. The effect of final state interaction is important in the low energy part of the spectra. In the delta region, the cross-section is very sensitive to the effects of Delta-N interaction and Delta N - NN process. The latter has also a large influence well below the pion threshold. The calculation underestimates the experimental cross-section between the quasi-elastic and the delta peaks; this is possibly due to projectile excitation or purely mesonic exchange currents.Comment: 9 pages, 9 figures, accepted for publication in EPJ

Internal tide acoustic tomography: reliability of the normal modes expansion as a possible basis for solving the inverse problem

Using hydrodynamic and thermodynamic equations appropriate for modelling internal tides, one can predict the current and temperature distributions associated with the ocean's dynamic modes. Comparing such predictions with observations from the INTIMATE'96 experiment, we nd a high degree of correlation between the rst 3 theoretically calculated dynamic modes and corresponding empirical orthogonal functions (EOF's) derived from an ensemble of temperature and current pro les. The implications are twofold. First, this implies that the dominant variability in the INTIMATE'96 experiment is indeed associated with internal tides. Secondly, it suggests that in future tidal experiments a theoretically generated basis may be used as e ectively as an EOF basis (which requires more extensive oceanographic measurements). We have also used the set of dynamic modes to simulate the e ect of the tides on acoustic propagation to understand the relative importance of the usual surface tide (barotropic) and the internal (baroclinic) tides

The relevance of ERTS-1 data to the state of Ohio

There are no author-identified significant results in this report

Single sensor source localization in a range dependent environment

Source localization with a single sensor explores the time spread of the received signal as it travels from the emitter to the receiver. In shallow water, and for ranges larger than a few times the water depth, the received signal typically exhibits a large number of closely spaced arrivals. However, not all the arrivals are equally important for estimating the source position since a number of them convey redundant information. Theoreticaly, identifying the non-redundant arrivals is feasible in a isovelocity range independent waveguide. In previous work, the number of non-redundant arrivals and the dimension of the data sample signal subspace have been related in a range-independent case. This paper addresses the problem of determining the number of significant arrivals for localizing a sound source over a range-dependent environment on the West coast of Portugal during the INTIMATE'96 sea trial.SACLANTCE

Dynamics of acoustic propagation through a soliton wave packet: Observations from the INTIMATE'96 experiment

Experimental observations of acoustic propagation through a Soliton Wave Packet (SWP) show an abnormally large attenuation over some frequencies, that was found to be significantly time dependent and anisotropic. Nevertheless, by considering the problem of signal attenuation, the approach used in most of the studies can be considered as "static" since no additional effects were taken into account as a SWP evolves in range and time. Hydrographic and acoustic data from the INTIMATE'96 experiment clearly exhibit traces of the presence of soliton packets, but in contrast with known observations of attenuation, its frequency response also reveals a sudden increase of signal amplitude, which may be due to a focusing effect. This signal increase coincides with a significant peak found in current and temperature records. However, the correlation of both acoustic and hydrographic features is difficult to support due to the different time scales between the rate of hydrographic data sampling and the rate of signal transmissions. To study the possibility that a SWP could be responsible for the observed signal increase, the INTIMATE'96 hydrographic data was used to generate physically consistent distributions of "soliton-like" fields of temperature and sound velocity, which were used as input for a range-dependent normal-mode model it was found that for a particular soliton field, the set of "dynamic" (i.e., range-dependent and time-dependent) acoustic simulations reveals an acoustic signature similar to that observed in the data. These results contribute to a better understanding of underwater propagation in shallow-water coastal environments and therefore provide a potential basis for range-dependent temperature and sound-speed inversions

Distribution of level curvatures for the Anderson model at the localization-delocalization transition

We compute the distribution function of single-level curvatures, $P(k)$, for a tight binding model with site disorder, on a cubic lattice. In metals $P(k)$ is very close to the predictions of the random-matrix theory (RMT). In insulators $P(k)$ has a logarithmically-normal form. At the Anderson localization-delocalization transition $P(k)$ fits very well the proposed novel distribution $P(k)\propto (1+k^{\mu})^{3/\mu}$ with $\mu \approx 1.58$, which approaches the RMT result for large $k$ and is non-analytical at small $k$. We ascribe such a non-analiticity to the spatial multifractality of the critical wave functions.Comment: 4 ReVTeX pages and 4(.epsi)figures included in one uuencoded packag