Semiclassical effects in black hole interiors

First-order semiclassical perturbations to the Schwarzschild black hole geometry are studied within the black hole interior. The source of the perturbations is taken to be the vacuum stress-energy of quantized scalar, spinor, and vector fields, evaluated using analytic approximations developed by Page and others (for massless fields) and the DeWitt-Schwinger approximation (for massive fields). Viewing the interior as an anisotropic collapsing cosmology, we find that minimally or conformally coupled scalar fields, and spinor fields, decrease the anisotropy as the singularity is approached, while vector fields increase the anisotropy. In addition, we find that massless fields of all spins, and massive vector fields, strengthen the singularity, while massive scalar and spinor fields tend to slow the growth of curvature.Comment: 29 pages, ReVTeX; 4 ps figure

Control of laser induced molecular fragmentation of n-propyl benzene using chirped femtosecond laser pulses

We present the effect of chirping a femtosecond laser pulse on the fragmentation of n-propyl benzene. An enhancement of an order of magnitude for the relative yields of C3H3+ and C5H5+ in the case of negatively chirped pulses and C6H5+ in the case of positively chirped pulses with respect to the transform-limited pulse indicates that in some fragmentation channel, coherence of the laser field plays an important role. For the relative yield of all other heavier fragment ions, resulting from the interaction of the intense laser field with the molecule, there is no such enhancement effect with the sign of chirp, within experimental errors. The importance of the laser phase is further reinforced through a direct comparison of the fragmentation results with the second harmonic of the chirped laser pulse with identical bandwidth

How Reproducible Are Surface Areas Calculated from the BET Equation?

Porosity and surface area analysis play a prominent role in modern materials science, where their determination spans the fields of natural sciences, engineering, geology and medical research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro- and mesoporous materials.[2] Since the BET method was first developed, there has been an explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its widespread use, the manual calculation of BET surface areas causes a significant spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, we have brought together 60 labs with strong track records on the study of nanoporous materials. We provided eighteen already measured raw adsorption isotherms and asked these researchers to calculate the corresponding BET areas. This round-robin exercise resulted in a wide range of values for each isotherm. We demonstrate here that the reproducibility of BET area determination from identical isotherms is a largely ignored issue, raising critical concerns over the reliability of reported BET areas in micro- and mesoporous materials in the literature. To solve this major issue, we have developed a new computational approach to accurately and systematically determine the BET area of nanoporous materials. Our software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol criteria and makes, for the first time, an unambiguous BET area assignment possible