Wigner Glass, Spin-liquids, and the Metal-Insulator Transition

Recent experiments on the two dimensional electron gas in various semiconductor devices have revealed an unexpected metal-insulator transition and have challenged the previously held assumption that there is no such transition in two dimensions. While the experiments are still at the stage of rapid development, it is becoming evident that they cannot be understood from the conventional perspective of weak interactions. In the present paper, we propose the following. (1) The low-density insulating state is the Wigner Glass, a phase with quasi-long-range translational order and competing ferromagnetic and antiferromagnetic spin-exchange interactions. (2) The transition is the melting of this Wigner Glass, disorder being the agent allowing the transition to be second order. (3) Within the Wigner Glass phase, there are at least two, distinct magnetic ground-states, a ferromagnetic state at very low electron density and a spin-liquid state with a spin pseudo-gap at higher densities. (4) The metallic side of the transition is a non-Fermi liquid. These conclusions are encapsulated in Figure 1 which presents the proposed phase diagram as a function of disorder strength and density; we also suggest experimental signatures of the various phases and transitions.Comment: Revised manuscript 6 pages, 1 figure redrawn for clarity; discussion of experiments expande

Is reduction in the risk of vision loss the only benefit of photodynamic therapy in predominantly classic subfoveal choroidal neovascularization?

Nicola G Ghazi, rian P Conway, James S Tiedeman, Steven J YoonUniversity of Virginia Health System, Department of Ophthalmology, Charlottesville, VA, USAPurpose: To emphasize the effect of photodynamic therapy (PDT) on the size and progression of the neovascular lesion (NL) and evolution of the disciform scar (DS) in predominantly classic subfoveal choroidal neovascularization (SFCNV).Methods: A retrospective study of 62 eyes treated with PDT for SFCNV was performed. The greatest linear dimension (GLD) before and at last follow-up after treatment and the size of the DS post-PDT were analyzed. A subgroup of patients with DS in their fellow eye at presentation without prior PDT was also studied. The size of the scar in these eyes was compared to that following PDT.Results: After an average follow-up at 9 months, the size of the NL was stabilized or reduced in 64% of the study eyes with absence of fluorescein leakage in 45%. Only 3 eyes (5%) developed DS. At presentation, 14 patients already had DS in their fellow eye, the size of which was significantly larger than that post-PDT (p = 0.044). It was also significantly larger than that of the potential scar in the study eyes of the same subgroup of patients (p = 0.002) and of the rest of the patients (p = 0.0001).Conclusion: This study demonstrates a beneficial effect for PDT on the size of the NL and DS in SFCNV, which might be of great significance, particularly when PDT fails to prevent severe vision loss.Keywords: age-related macular degeneration, choroidal neovascularization, classic choroidal neovascularization, disciform scarring, fluorescein angiography, photodynamic therap

2MASS Studies of Differential Reddening Across Three Massive Globular Clusters

J, H, and K_S band data from the Two Micron All-Sky Survey (2MASS) are used to study the effects of differential reddening across the three massive Galactic globular clusters Omega Centauri, NGC 6388, and NGC 6441. Evidence is found that variable extinction may produce false detections of tidal tails around Omega Centauri. We also investigate what appears to be relatively strong differential reddening towards NGC 6388 and NGC 6441, and find that differential extinction may be exaggerating the need for a metallicity spread to explain the width of the red giant branches for these two clusters. Finally, we consider the implications of these results for the connection between unusual, multipopulation globular clusters and the cores of dwarf spheroidal galaxies (dSph).Comment: 40 pages, 14 figures. Accepted for publication in Oct. 2003 A

Cyclin D activates the Rb tumor suppressor by mono-phosphorylation

The widely accepted model of G1 cell cycle progression proposes that cyclin D:Cdk4/6 inactivates the Rb tumor suppressor during early G1 phase by progressive multi-phosphorylation, termed hypo-phosphorylation, to release E2F transcription factors. However, this model remains unproven biochemically and the biologically active form(s) of Rb remains unknown. In this study, we find that Rb is exclusively mono-phosphorylated in early G1 phase by cyclin D:Cdk4/6. Mono-phosphorylated Rb is composed of 14 independent isoforms that are all targeted by the E1a oncoprotein, but show preferential E2F binding patterns. At the late G1 Restriction Point, cyclin E:Cdk2 inactivates Rb by quantum hyper-phosphorylation. Cells undergoing a DNA damage response activate cyclin D:Cdk4/6 to generate mono-phosphorylated Rb that regulates global transcription, whereas cells undergoing differentiation utilize un-phosphorylated Rb. These observations fundamentally change our understanding of G1 cell cycle progression and show that mono-phosphorylated Rb, generated by cyclin D:Cdk4/6, is the only Rb isoform in early G1 phase. DOI: http://dx.doi.org/10.7554/eLife.02872.00

Kinetics of UV254 inactivation of selected viral pathogens in a static system

Aims:  The objective of this study was to estimate UV254 inactivation constants for four viral pathogens: influenza virus type A, porcine respiratory and reproductive syndrome virus (PRRSV), bovine viral diarrhoea virus (BVDV) and reovirus. Methods and Results:  Viruses in culture medium were exposed to one of nine doses of UV254 and then titrated for infectious virus. Analysis showed that viral inactivation by UV254 was more accurately described by a two-stage inactivation model vs a standard one-stage inactivation model. Conclusions:  The results provided evidence for the existence of two heterogeneous viral subpopulations among the viruses tested, one highly susceptible to UV254 inactivation and the other more resistant. Importantly, inactivation constants based on the one-stage inactivation model would have underestimated the UV254 dose required for the inactivation of these viruses under the conditions of the experiment. Significance and Impact of the Study:  To improve the accuracy of estimates, it is recommended that research involving the inactivation of micro-organisms evaluates inactivation kinetics using both one-stage and two-stage models. These results will be of interest to persons responsible for microbial agents under laboratory or field conditions

Advances in modeling the immune microenvironment of colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and second leading cause of cancer-related death in the US. CRC frequently metastasizes to the liver and these patients have a particularly poor prognosis. The infiltration of immune cells into CRC tumors and liver metastases accurately predicts disease progression and patient survival. Despite the evident influence of immune cells in the CRC tumor microenvironment (TME), efforts to identify immunotherapies for CRC patients have been limited. Here, we argue that preclinical model systems that recapitulate key features of the tumor microenvironment-including tumor, stromal, and immune cells; the extracellular matrix; and the vasculature-are crucial for studies of immunity in the CRC TME and the utility of immunotherapies for CRC patients. We briefly review the discoveries, advantages, and disadvantages of curren

Disorder, pseudospins, and backscattering in carbon nanotubes

We address the effects of disorder on the conducting properties of metal and semiconducting carbon nanotubes. Experimentally, the mean free path is found to be much larger in metallic tubes than in doped semiconducting tubes. We show that this result can be understood theoretically if the disorder potential is long-ranged. The effects of a pseudospin index that describes the internal sublattice structure of the states lead to a suppression of scattering in metallic tubes, but not in semiconducting tubes. This conclusion is supported by tight-binding calculations.Comment: four page

A Petal of the Sunflower: Photometry of the Stellar Tidal Stream in the Halo of Messier 63 (NGC 5055)

We present surface photometry of a very faint, giant arc feature in the halo of the nearby spiral galaxy NGC 5055 (M63) that is consistent with being a part of a stellar stream resulting from the disruption of a dwarf satellite galaxy. This faint feature was first detected in early photographic studies by van der Kruit (1979); more recently by Mart\'inez-Delgado et al. (2010) and as presented in this work, the loop has been realized to be the result of a recent minor merger through evidence obtained by deep images taken with a telescope of only 0.16 m aperture. The stellar stream is confirmed in additional images taken with the 0.5 m of the BlackBird Remote Observatory and the 0.8 m of the McDonald Observatory. This low surface brightness structure around the disk of the galaxy extends ~29 kpc from its center, with a projected width of 3.3 kpc. The stream's morphology is consistent with that of the visible part of a "great-circle" stellar stream originating from the accretion of a ~10^8 M_sun dwarf satellite in the last few Gyr. The progenitor satellite's current position and fate are not conclusive from our data. The color of the stream's stars is consistent with Local Group dwarfs and is similar to the outer regions of M63's disk and stellar halo. We detect other low surface brightness "plumes"; some of these may be extended spiral features related to the galaxy's complex spiral structure and others may be tidal debris associated with the disruption of the galaxy's outer stellar disk as a result of the accretion event. We differentiate between features related to the tidal stream and faint, blue features in the outskirts of the galaxy's disk previously detected by the GALEX satellite. With its highly warped HI gaseous disk (~20 deg), M63 represents one of several examples of an isolated spiral galaxy with a warped disk showing strong evidence of an ongoing minor merger.Comment: 16 pages, 10 figures, 3 tables, Accepted for publication in The Astronomical Journa