Late Quaternary Chorus Frog (Pseudacris) from the Channel Islands, California

Abstract.-Fossil and subfossil remains of the vertebrate faunas from the northern Channel Islands, southern California, have been studied for many decades. Continued interest has focused on skeletal remains of birds, rodents, and mammoths from archaeological and paleontological localities, but considerably less attention has been placed on the detailed description of the herpetofauna (salamanders, anurans [frogs and toads], lizards, and snakes) on the Channel Islands. We present descriptions of an ilium of an anuran from Santa Rosa Island (Larramendy North; radiocarbon dating at least 13,393 calibrated years ago) and two tibiofibulae San Miguel Island (Daisy Cave) dating from earliest and middle late Holocene layers. We identify the fossil ilium as Pseudacris sp. (chorus frog): 1) it is the lowest level that skeletal morphology permits us to attempt, 2) realizing that it appears morphologically closest to P. regilla, and 3) yet realizing that not all species of Pseudacris and Hyla have been directly compared or are understood. The extant amphibian fauna on these islands is depauperate. The remains presented here represent the first description of a fossil anuran from the northern Channel Islands. It is now understood that a chorus frog lived on glacial-age Santa Rosae Island, yet it is not understood when its distribution was reduced to just the present two largest islands, Santa Rosa and Santa Cruz

Cyclical 'flipping' of morphology in block copolymer films

We studied the kinetics of nanopattern evolution in (polystyrene-b-polyethylene oxide) diblock copolymer thin films. Using scanning force microscopy, a highly unexpected cylindrical flipping of morphology from normal to parallel to the film plane was detected during solvent annealing of the film (with average thickness of 30 nm) at high vapor pressure. Using an in situ time-resolved light scattering device combined with an environmental cell enabled us to obtain kinetic information at different vapor pressures. The data indicated that there is a threshold value for the vapor pressure necessary for the structural transition. We propose a swelling and deswelling mechanism for the orientation flipping of the morphology. The cyclic transition occurs faster in thick films (177 nm) where the mass uptake and solvent volume fraction is smaller and therefore the driving force for phase separation is higher. We induced a stronger segregation by confining the chains in graphoepitaxially patterned substrates. As expected, the cyclic transition occurred at higher rate. Our work is another step forward to understanding the structure evolution and also controlling the alignment of block copolymer nanocylinders independently of thickness and external fields

Simulated Fire Behavior and Fine-Scale Forest Structure Following Conifer Removal in Aspen-Conifer Forests in the Lake Tahoe Basin, USA

Quaking aspen is found in western forests of the United States and is currently at risk of loss due to conifer competition at within-stand scales. Wildfires in these forests are impactful owing to conifer infilling during prolonged fire suppression post-Euro-American settlement. Here, restoration cuttings seek to impact wildfire behavior and aspen growing conditions. In this study, we explored how actual and hypothetical cuttings with a range of conifer removal intensity altered surface fuel and overstory structure at stand and fine scales. We then simulated wildfires, examining fire behavior and effects on post-fire forest structures around aspen trees. We found that conifer removal constrained by lower upper diameter limits (\u3c56 cm) had marginal effects on surface fuel and overstory structure, likely failing to enhance resource conditions sufficiently to sustain aspen. Increasing the diameter limit also led to a higher likelihood of fire spread and a higher rate of spread, owing to greater within-canopy wind speed, though crown fire activity decreased. Our simulations suggest heavier treatments could facilitate reintroduction of fire while also dampening the effects of wildfires on forest structure. Cutting specifications that relax diameter limits and remove a substantial portion of conifer overstory could better promote aspen restoration and mitigate fire hazard

Renormalization of gauge invariant composite operators in light-cone gauge

We generalize to composite operators concepts and techniques which have been successful in proving renormalization of the effective Action in light-cone gauge. Gauge invariant operators can be grouped into classes, closed under renormalization, which is matrix-wise. In spite of the presence of non-local counterterms, an ``effective" dimensional hierarchy still guarantees that any class is endowed with a finite number of elements. The main result we find is that gauge invariant operators under renormalization mix only among themselves, thanks to the very simple structure of Lee-Ward identities in this gauge, contrary to their behaviour in covariant gauges.Comment: 35100 Padova, Italy DFPD 93/TH/53, July 1993 documentstyle[preprint,aps]{revtex

Stabilization of black phosphorus by sonication-assisted simultaneous exfoliation and functionalization

Black phosphorus (BP) has extraordinary properties, but its ambient instability remains a critical challenge. Functionalization has been employed to overcome the sensitivity of BP to ambient conditions while preserving its properties. Herein, a simultaneous exfoliation–functionalization process is reported that functionalizes BP flakes during exfoliation and thus provides increased protection, which can be attributed to minimal exposure of the flakes to ambient oxygen and water. A tetrabutylammonium salt was employed for intercalation of BP, resulting in the formation of flakes with large lateral dimensions. The addition of an aryl iodide or an aryl iodonium salt to the exfoliation solvent creates a scalable strategy for the production of functionalized few‐layer BP flakes. The ambient stability of functionalized BP was prolonged to a period of one week, as revealed by STEM, AFM, and X‐ray photoelectron spectroscopy

Evaluating the surface chemistry of black phosphorus during ambient degradation

Black Phosphorus (BP) is emerging as a promising candidate for electronic, optical and energy storage applications, however its poor ambient stability remains a critical challenge. Evaluation of few-layer liquid exfoliated BP during ambient exposure using x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) allows its surface chemistry to be investigated. Oxidation of liquid exfoliated few-layer BP initially occurs through non-bridged oxide species, which convert to bridged oxide species after ambient exposure. We demonstrate the instability of these bridged oxide species which undergo hydrolysis to form volatile phosphorus oxides and evaporate from the BP surface. FTIR spectroscopy, scanning transmission electron microscopy and atomic force microscopy were used to confirm the formation of liquid oxides through a continuous oxidation cycle that results in the decomposition of BP. Furthermore, we show that the instability of few-layer BP originates from the formation of bridged oxide species

Critical Exponents of the Superconducting Phase Transition

We study the critical exponents of the superconducting phase transition in the context of renormalization group theory starting from a dual formulation of the Ginzburg-Landau theory. The dual formulation describes a loop gas of Abrikosov flux tubes which proliferate when the critical temperature is approached from below. In contrast to the Ginzburg-Landau theory, it has a spontaneously broken global symmetry and possesses an infrared stable fixed point. The exponents coincide with those of a superfluid with reversed temperature axis.Comment: Postscript file. For related work see www adress http://www.physik.fu-berlin.de/kleiner_re.html in our homepage http://www.physik.fu-berlin.de/kleinert.htm

Kinematics of the Tucana Dwarf Galaxy: an unusually dense dwarf in the Local Group

We present new FLAMES+GIRAFFE spectroscopy of 36 member stars in the isolated Local Group dwarf spheroidal galaxy Tucana. We measure a systemic velocity for the system of $v_{Tuc}$=216.7$^{+2.9}_{−2.8}$ km s$^{−1}$, and a velocity dispersion of σ$_{v,Tuc}$=14.4$^{+2.8}_{−2.3}$ km s$^{−1}$. We also detect a rotation gradient of $\frac{dvr}{dχ}$=7.6$^{+4.2}_{−4.3}$ km s$^{−1}$ kpc$^{−1}$, which reduces the systemic velocity to $v_{Tuc}$=215.2$^{+2.8}_{−2.7}$ km s$^{−1}$ and the velocity dispersion to σ$_{v,Tuc}$=13.3$^{+2.7}_{−2.3}$ km s$^{−1}$. We perform Jeans modelling of the density profile of Tucana, using the line-of-sight velocities of the member stars. We find that it favours a high central density consistent with ‘pristine’ subhaloes in Λ cold dark matter, and a massive dark matter halo (~10$^{10}$ M$_\odot$) consistent with expectations from abundance matching. Tucana appears to be significantly more centrally dense than other isolated Local Group dwarfs, making it an ideal laboratory for testing dark matter models

Four Fermion Field Theories and the Chern-Simons Field: A Renormalization Group Study

In (2+1) dimensions, we consider the model of a $N$ flavor, two-component fermionic field interacting through a Chern-Simons field besides a four fermion self-interaction which consists of a linear combination of the Gross-Neveu and Thirring like terms. The four fermion interaction is not perturbatively renormalizable and the model is taken as an effective field theory in the region of low momenta. Using Zimmerman procedure for reducing coupling constants, it is verified that, for small values of the Chern-Simons parameter, the origin is an infrared stable fixed point but changes to ultraviolet stable as $\alpha$ becomes bigger than a critical $\alpha_c$. Composite operators are also analyzed and it is shown that a specific four fermion interaction has an improved ultraviolet behavior as $N$ increases.Comment: 9 pages, revte