Theoretical He I Emissivities in the Case B Approximation

We calculate the He I case B recombination cascade spectrum using improved radiative and collisional data. We present new emissivities over a range of electron temperatures and densities. The differences between our results and the current standard are large enough to have a significant effect not only on the interpretation of observed spectra of a wide variety of objects but also on determinations of the primordial helium abundance.Comment: Accepted to ApJ

\u3cem\u3eJ\u3c/em\u3e-Resolved He I Emission Predictions in the Low-Density Limit

Determinations of the primordial helium abundance are used in precision cosmological tests. These require highly accurate He I recombination rate coefficients. Here we reconsider the formation of He I recombination lines in the low-density limit. This is the simplest case, and it forms the basis for the more complex situation in which collisions are important. The formation of a recombination line is a two-step process, beginning with the capture of a continuum electron into a bound state and followed by radiative cascade to ground. The rate coefficient for capture from the continuum is obtained from photoionization cross sections and detailed balancing, while radiative transition probabilities determine the cascades. We have made every effort to use today\u27s best atomic data. Radiative decay rates are from Drake\u27s variational calculations, which include QED, fine structure, and singlet-triplet mixing. Certain high-L fine-structure levels do not have a singlet-triplet distinction, and the singlets and triplets are free to mix in dipole-allowed radiative decays. We use quantum-defect or hydrogenic approximations to include levels higher than those treated in the variational calculations. Photoionization cross sections come from R-matrix calculations when possible. We use Seaton\u27s method to extrapolate along sequences of transition probabilities to obtain threshold photoionization cross sections for some levels. For higher n we use scaled hydrogenic theory or an extension of quantum-defect theory. We create two independent numerical implementations to ensure that the complex bookkeeping is correct. The two codes use different (reasonable) approximations to span the gap between lower levels, having accurate data, and high levels, where scaled hydrogenic theory is appropriate. We also use different (reasonable) methods to account for recombinations above the highest levels individually considered. We compare these independent predictions to estimate the uncertainties introduced by the various approximations. Singlet-triplet mixing has little effect on the observed spectrum. While intensities of lines within multiplets change, the entire multiplet, the quantity normally observed, does not. The lack of high-precision photoionization cross sections at intermediate n and low L introduces ~0.5% uncertainties in intensities of some lines. The high-n unmodeled levels introduce ~1% uncertainties for “yrast\u27\u27 lines, defined as those having L=n-1 upper levels. This last uncertainty will not be present in actual nebulae, since such high levels are held in statistical equilibrium by collisional processes. We identify those lines that are least affected by uncertainties in the atomic physics and so should be used in precision helium abundance determinations

Rotational Cooling of Polar Molecules by Stark-tuned Cavity Resonance

A general scheme for rotational cooling of diatomic heteronuclear molecules is proposed. It uses a superconducting microwave cavity to enhance the spontaneous decay via Purcell effect. Rotational cooling can be induced by sequentially tuning each rotational transition to cavity resonance, starting from the highest transition level to the lowest using an electric field. Electrostatic multipoles can be used to provide large confinement volume with essentially homogeneous background electric field.Comment: 10 pages, 6 figure

Death from early colorectal cancer is predicted by the presence of transcripts of the REG gene family

An intrinsic component of colorectal carcinogenesis may be the capacity to activate regenerative responses simultaneously with inhibition of apoptosis. Since apoptosis is known to be inhibited in colorectal cancer, this study sought evidence for the activation of the REG family of genes which are considered to be activated during regeneration of intestinal mucosa. Transcripts for the REG gene were found in 53% of colorectal cancers and for the PAP gene in 60% of colorectal cancers, by RT-PCR. Using in situ hybridization, the REG transcripts were found to be present in the tumour cells themselves rather than inflammatory or stromal cells. There were no significant correlations between the expression of these two genes and tumour stage, age or sex of the patient population or tumour site. However, in patients with non-metastatic disease who underwent ostensibly curative surgery, the expression of REG alone and co-expression of REG with PAP had a highly significantly adverse effect on survival. These data provide support for the concept that, in some tumours, carcinogenesis involves a regenerative process which co-exists with apoptotic inhibition and may provide a valuable selective indicator of the need for adjuvant therapy in those patients with early-stage colorectal cancer whose disease is destined to recur after curative surgery. © 2000 Cancer Research Campaig

Using Neural Networks to Identify Driving Style and Headway Control Behavior of Drivers

This paper illustrates the use of neural network techniques for analyzing headway data collected from a group of 36 driving subjects during normal on-highway driving. Pattern recognition methods are used to identify different types of headway-keeping behavior exhibited by these drivers and their relative distributions. Possibilities for using neural networks to represent longitudinal control behavior of drivers are also considered and discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65024/1/MacAdam_et_al_1998_VSD_NNet_paper.pd

The natural capital of temporary rivers: characterising the value of dynamic aquatic-terrestrial habitats. Valuing Nature Natural Capital Synthesis Reports, VNP12

Temporary rivers naturally transition between flowing, pool and dry states, creating aquatic–terrestrial habitat mosaics that change in space and time. These dynamic habitats are common in the UK's cool, wet climate. Here, they take many forms, from headwater streams that may dominate networks in remote uplands, to winterbourne rivers crossing the chalk of south England. We examine published and unpublished sources to provide an evidence-informed characterisation of the natural assets in temporary rivers

Uncertainties in Theoretical HeI Emissivities: HII Regions, Primordial Abundance, and Cosmological Recombination

A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyze and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call "optimistic" and "pessimistic." We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H II regions and the epoch of cosmological recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than the errors in some recent $Y_p$ calculations, including those derived from CMB observations. We demonstrate a systematic effect on primordial abundance calculations; this effect cannot be reduced by observing a large number of objects. In the cosmological recombination case, the errors are comparable to many of the effects considered in recent calculations.Comment: 5 pages, 3 figures, accepted to MNRAS Letter

Two-species magneto-optical trap with 40K and 87Rb

We trap and cool a gas composed of 40K and 87Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1x10^7 40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review