Magnetic Field-Vector Measurements in Quiescent Prominences via the Hanle Effect: Analysis of Prominences Observed at Pic-Du-Midi and at Sacramento Peak

The Hanle effect method for magnetic field vector diagnostics has now provided results on the magnetic field strength and direction in quiescent prominences, from linear polarization measurements in the He I E sub 3 line, performed at the Pic-du-Midi and at Sacramento Peak. However, there is an inescapable ambiguity in the field vector determination: each polarization measurement provides two field vector solutions symmetrical with respect to the line-of-sight. A statistical analysis capable of solving this ambiguity was applied to the large sample of prominences observed at the Pic-du-Midi (Leroy, et al., 1984); the same method of analysis applied to the prominences observed at Sacramento Peak (Athay, et al., 1983) provides results in agreement on the most probable magnetic structure of prominences; these results are detailed. The statistical results were confirmed on favorable individual cases: for 15 prominences observed at Pic-du-Midi, the two-field vectors are pointing on the same side of the prominence, and the alpha angles are large enough with respect to the measurements and interpretation inaccuracies, so that the field polarity is derived without any ambiguity

Infrared-temperature variability in a large agricultural field

The combined effect of water carved gullies, varying soil color, moisture state of the soil and crop, nonuniform phenology, and bare spots was measured for commercially grown barley planted on varying terrain. For all but the most rugged terrain, over 80% of the area within 4, 16, 65, and 259 ha cells was at temperatures within 3 C of the mean cell temperature. The result of using relatively small, 4 ha instantaneous field of views for remote sensing applications is that either the worst or the best of conditions is often observed. There appears to be no great advantage in utilizing a small instantaneous field of view instead of a large one for remote sensing of crop canopy temperatures. The two alternatives for design purposes are then either a very high spatial resolution, of the order of a meter or so, where the field is very accurately temperature mapped, or a low resolution, where the actual size seems to make little difference

Performance of the SERT 2 spacecraft after 4 and one-half years in space

The SERT 2 satellite, launched in February, 1970, has recently been reactivated after being dormant for a year. The satellite orientation was changed to spin stabilization in 1973 and the satellite is now coning such that the active side of the solar arrays move into and out of the sun every 23 days. There is sufficient power to operate the ion thrusters for seven days of this cycle. The 2 ion thruster system was successfully operated; the electrical short in the accelerating grids had cleared during the year long dormant phase

Natural and anthropogenic forest fires recorded in the Holocene pollen record from a Jinchuan peat bog, northeastern China

Pollen and charcoal particles from a Jinchuan peat (northeastern China) were examined to investigate the fire origin and interaction between climate, vegetation, fire and human activity during the Holocene. Pollen results show that: (i) a broadleaved deciduous forest was dominant during the early Holocene; (ii) from ~5500 cal. yr B.P. there was a gradual increase in coniferous trees (mainly Pinus), and a decrease in broadleaved deciduous trees (e.g. Quercus, Juglans, and Ulmus–Zelkova); (iii) after ~4200 cal. yr B.P., the deciduous forest was replaced by a mixed forest of coniferous and deciduous trees; (iv) coniferous trees including Pinus, Abies and Picea further increased after ~2000 cal. yr B.P., reflecting a cooler and drier climate after ~5500–4200 cal. yr B.P. Two layers of abundant microfossil charcoal particles (250–10 μm) and the coexistence of macrofossil particles (N2 mm) suggest two local fires: fire event 1 (5120±66 cal. yr B.P.) and fire event 2 (1288±8 cal. yr B.P., AD 662±8). Charcoal layer 1, with a large amount of Monolete psilate spores, is superimposed on the long-term trend of vegetation changes, indicating a natural origin for fire event 1 that was probably facilitated by drying environmental conditions since the mid-Holocene. Cerealia-type pollen and a low percentage of Monolete psilate spores were observed in charcoal layer 2, indicating that fire event 2 was caused by clearing. We suggest that fire event 2 may be related to the spread of the Han farming culture accompanied by the territorial expansion of the Tang Dynasty to the studied area in AD 668

The role of monolayer viscosity in Langmuir film hole closure dynamics

We re-examine the model proposed by Alexander et al. (2006) for the closing of a circular hole in a molecularly thin incompressible Langmuir film situated on a Stokesian subfluid. For simplicity their model assumes that the surface phase is inviscid which leads to the result that the cavity area decreases at a constant rate determined by the ratio of edge tension to subfluid viscosity. We reformulate the problem, allowing for a regularizing monolayer viscosity. The viscosity-dependent corrections to the hole dynamics are analyzed and found to be nontrivial, even when the monolayer viscosity is small; these corrections may explain the departure of experimental data from the theoretical prediction when the hole radius becomes comparable to the Saffman-Delbruck length. Through fitting, we find the edge tension could be as much as eight times larger (~5.5 pN) than previously reported under these relaxed assumptions.Comment: 7 pages, 2 figure

Phonon runaway in nanotube quantum dots

We explore electronic transport in a nanotube quantum dot strongly coupled with vibrations and weakly with leads and the thermal environment. We show that the recent observation of anomalous conductance signatures in single-walled carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms of current driven `hot phonons' that are strongly correlated with electrons. Using rate equations in the many-body configuration space for the joint electron-phonon distribution, we argue that the variations are indicative of strong electron-phonon coupling requiring an analysis beyond the traditional uncorrelated phonon-assisted transport (Tien-Gordon) approach.Comment: 8 pages, 6 figure

Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers

We present experimental results on a model system for studying wave propagation in a complex medium exhibiting low frequency resonances. These experiments enable us to investigate a fundamental question that is relevant for many materials, such as metamaterials, where low-frequency scattering resonances strongly influence the effective medium properties. This question concerns the effect of correlations in the positions of the scatterers on the coupling between their resonances, and hence on wave transport through the medium. To examine this question experimentally, we measure the effective medium wave number of acoustic waves in a sample made of bubbles embedded in an elastic matrix over a frequency range that includes the resonance frequency of the bubbles. The effective medium is highly dispersive, showing peaks in the attenuation and the phase velocity as functions of the frequency, which cannot be accurately described using the Independent Scattering Approximation (ISA). This discrepancy may be explained by the effects of the positional correlations of the scatterers, which we show to be dependent on the size of the scatterers. We propose a self-consistent approach for taking this "polydisperse correlation" into account and show that our model better describes the experimental results than the ISA

Light hadron spectroscopy on the lattice with the non-perturbatively improved Wilson action

We present results for the light meson masses and decay constants as obtained from calculations with the non-perturbatively improved (`Alpha') action and operators on a 24^3 \times 64 lattice at beta = 6.2, in the quenched approximation. The analysis was performed in a way consistent with O(a) improvement. We obtained: reasonable agreement with experiment for the hyperfine splitting; f_K=156(17) MeV, f_pi =139(22) MeV, f_K/f_pi = 1.13(4) ; f_{K*}=219(7) MeV, f_rho =199(15) MeV, f_phi =235(4) MeV; f_{K*}^{T}(2 GeV) = 178(10) MeV, f_rho^{T}(2 GeV) =165(11) MeV, where f_V^{T} is the coupling of the tensor current to the vector mesons; the chiral condensate ^\bar{MS} (2 GeV)= - (253 +/- 25 MeV)^3. Our results are compared to those obtained with the unimproved Wilson action. We also verified that the free-boson lattice dispersion relation describes our results very accurately for a large range of momenta.Comment: 29 pages (LaTeX), 14 Postscript figure

Optical Linear Polarization of Late M- and L-Type Dwarfs

(Abridged). We report on the linear polarimetric observations in the Johnson I filter of 44 M6-L7.5 ultracool dwarfs (2800-1400 K). Eleven (10 L and 1 M) dwarfs appear to have significant linear polarization (P = 0.2-2.5%). We have compared the M- and L-dwarf populations finding evidence for a larger frequency of high I-band polarization in the coolest objects, supporting the presence of significant amounts of dust in L-dwarfs. The probable polarizing mechanism is related to the presence of heterogeneous dust clouds nonuniformly distributed across the visible photospheres and the asymmetric shape of the objects. In some young ultracool dwarfs, surrounding dusty disks may also yield polarization. For polarimetric detections, a trend for slightly larger polarization from L0 to L6.5 may be present in our data, suggesting changes in the distribution of the grain properties, vertical height of the clouds, metallicity, age, and rotation speed. One of our targets is the peculiar brown dwarf (BD) 2MASS J2244+20 (L6.5), which shows the largest I-band polarization degree. Its origin may lie in a surrounding dusty disk or rather large photospheric dust grains. The M7 young BD CFHT-BD-Tau 4 and the L3.5 field dwarf 2MASS J0036+18 were also observed in the Johnson R filter. Our data support the presence of a circum(sub)stellar disk around the young accreting BD. Our data also support a grain growth in the submicron regime in the visible photosphere of J0036+18 (1900 K). The polarimetric data do not obviously correlate with activity or projected rotational velocity. Three polarized early- to mid-L dwarfs display I-band light curves with amplitudes below 10 mmag.Comment: Accepted for publication in ApJ (March 2005), 35 pages, 5 figure