Experimental evidence for a collective insulating state in two-dimensional superconductors

We present the results of an experimental study of the current-voltage characteristics in a strong magnetic field (B) of disordered, superconducting, thin films of amorphous indium oxide. As the B strength is increased superconductivity degrades, until a critical field (B(c)) where the system is forced into an insulating state. We show that the differential conductance measured in the insulating phase vanishes abruptly below a well-defined temperature, resulting in a clear threshold for conduction. Our results indicate that a new collective state emerges in two-dimensional superconductors at high B.     

A free,tricoordinate stannylium cation

Tris(2,4,6-triisopropylphenyl)stannylium tetrakis(pentafluorophenyl)borate constitutes a free, tricoordinate tin cation according to its X-ray structure. There is no coordination between the cation and either solvent or anion, and there are no atoms at apical positions. DFT calculations confirm the structure and indicate that there is no agostic bonding between the ortho isopropyl methinyl hydrogens and the Sn atom. Calculation of the 119Sn chemical shift is in good agreement with the observed value.     

Actions of Cartan subgroups

Using affine Bruhat-Tits buildings, we associate certain subshifts of finite type to systems arising from the action of a Cartan subgroup of ap-adic semisimple Chevalley group on compact quotient spaces Γ\G. These are used to study the resulting dynamical systems. Sponsored in part by the Edmund Landau Center for Research in Mathematical Analysis supported by the Minerva Foundation (Federal Republic of Germany). Research at MSRI supported by NSF grant DMS8505550.     

Catalysis of the kemp elimination by natural coals

Commercially available coals were found to be efficient heterogeneous catalysts of the Kemp elimination reaction in aqueous solutions. A pH-rate profile study suggests that catalysis originates from specific catalytic groups and not simply from the large graphitic surface area. The low-quality lignite coals, which exhibit similar catalytic efficiency per weight to that of molecularly imprinted polymers, are better catalysts for this reaction in comparison with the bituminous coals.     

Diferential Inequalities,Normality and Quasi-normality

We prove that ifD is a domain in C,α 1 and C 0,then the family F of functions f meromorphic in D such that |f′(z)|/1 + |f(z)|α C for every z ∈ D is normal in D.For α = 1,the same assumptions imply quasi-normality but not necessarily normality.     

Self-gravitating ring of matter in orbit around a black hole: the innermost stable circular orbit

We study analytically a black-hole-ring system which is composed of a stationary axisymmetric ring of particles in orbit around a perturbed Kerr black hole of mass $M$ . In particular, we calculate the shift in the orbital frequency of the innermost stable circular orbit (ISCO) due to the finite mass $m$ of the orbiting ring. It is shown that for thin rings of half-thickness $r\ll M$ , the dominant finite-mass correction to the characteristic ISCO frequency stems from the self-gravitational potential energy of the ring (a term in the energy budget of the system which is quadratic in the mass $m$ of the ring). This dominant correction to the ISCO frequency is of order $O(\mu \ln (M/r))$ , where $\mu \equiv m/M$ is the dimensionless mass of the ring. We show that the ISCO frequency increases (as compared to the ISCO frequency of an orbiting test-ring) due to the finite-mass effects of the self-gravitating ring.     

Exceptional functions wandering on the sphere and normal families

We extend Carathéodory’s generalization of Montel’s fundamental normality test to “wandering” exceptional functions (i.e., depending on the respective function in the family under consideration), and we give a corresponding result on shared functions. Furthermore, we prove that if we have a family of pairs (a, b) of functions meromorphic in a domain such that a and b uniformly “stay away from each other,” then the families of the functions a resp. b are normal. The proofs are based on a “simultaneous rescaling” version of Zalcman’s lemma.     

Radioactivity in the Exclusive Economic Zone of east coast Peninsular Malaysia: distribution trends of <Superscript>137</Superscript>Cs in surface seawater

Large volumes of surface seawater samples were collected from thirty locations in the Exclusive Economic Zone (EEZ) of the east coast Peninsular Malaysia on June 2008 to study the activity concentrations of ¹³⁷Cs. The results will serve as additional information to the existing baseline data and is very useful for monitoring fresh input of anthropogenic radionuclide into Malaysian marine environment. In this study, the activity concentrations of ¹³⁷Cs were determined using co-precipitation technique, followed by Gamma Spectrometry measurement. The mean activity concentration of ¹³⁷Cs ranged between 3.40 and 5.89 Bq/m³. Higher activity concentrations were observed at the coastal and towards the south of Peninsular Malaysia and were aligned with the high turbidity. These may due to the rapid diffusion of ¹³⁷Cs from suspended particulates and fine sediments into surface seawater. The activity concentrations of ¹³⁷Cs observed in this study were slightly higher than the concentrations reported in seawater at the Straits of Malacca, Vietnam and Philippines. This might be because the study area received more input of ¹³⁷Cs that originated from global fallout and then deposited on land which later being transported subsequently into the coastal zone due to siltation and erosion processes. It could also be attributed to the intrusion of river waters containing higher concentrations of ¹³⁷Cs.     

Weak cosmic censorship: as strong as ever

Spacetime singularities that arise in gravitational collapse are always hidden inside of black holes. This is the essence of the weak cosmic censorship conjecture. The hypothesis, put forward by Penrose 40 years ago, is still one of the most important open questions in general relativity. In this Letter, we reanalyze extreme situations which have been considered as counterexamples to the weak cosmic censorship conjecture. In particular, we consider the absorption of scalar particles with large angular momentum by a black hole. Ignoring back reaction effects may lead one to conclude that the incident wave may overspin the black hole, thereby exposing its inner singularity to distant observers. However, we show that when back reaction effects are properly taken into account, the stability of the black-hole event horizon is irrefutable. We therefore conclude that cosmic censorship is actually respected in this type of gedanken experiments.