Simulation and analysis of solenoidal ion sources

We present a detailed analysis and simulation of solenoidal, magnetically confined electron bombardment ion sources, aimed at molecular beam detection. The aim is to achieve high efficiency for singly ionized species while minimizing multiple ionization. Electron space charge plays a major role and we apply combined ray tracing and finite element simulations to determine the properties of a realistic geometry. The factors controlling electron injection and ion extraction are discussed. The results from simulations are benchmarked against experimental measurements on a prototype source

Letter from the Executive Committee of the Alumni Association

Letter concerning copies of a paper and a letter to be distributed at Utah Agricultural College

Linewidths in bound state resonances for helium scattering from Si(111)-(1x1)H

Helium-3 spin-echo measurements of resonant scattering from the Si(111)–(1 × 1)H surface, in the energy range 4–14 meV, are presented. The measurements have high energy resolution yet they reveal bound state resonance features with uniformly broad linewidths. We show that exact quantum mechanical calculations of the elastic scattering, using the existing potential for the helium/Si(111)–(1 × 1)H interaction, cannot reproduce the linewidths seen in the experiment. Further calculations rule out inelastic and other mechanisms that might give rise to losses from the elastic scattering channels. We show that corrugation in the attractive part of the atom–surface potential is the most likely origin of the experimental lineshapes

X-Ray flares in Orion Young Stars. II. Flares, Magnetospheres, and Protoplanetary Disks

We study the properties of powerful X-ray flares from 161 pre-main sequence (PMS) stars observed with the Chandra X-ray Observatory in the Orion Nebula region. Relationships between flare properties, protoplanetary disks and accretion are examined in detail to test models of star-disk interactions at the inner edge of the accretion disks. Previous studies had found no differences in flaring between diskfree and accreting systems other than a small overall diminution of X-ray luminosity in accreting systems. The most important finding is that X-ray coronal extents in fast-rotating diskfree stars can significantly exceed the Keplerian corotation radius, whereas X-ray loop sizes in disky and accreting systems do not exceed the corotation radius. This is consistent with models of star-disk magnetic interaction where the inner disk truncates and confines the PMS stellar magnetosphere. We also find two differences between flares in accreting and diskfree PMS stars. First, a subclass of super-hot flares with peak plasma temperatures exceeding 100 MK are preferentially present in accreting systems. Second, we tentatively find that accreting stars produce flares with shorter durations. Both results may be consequences of the distortion and destabilization of the stellar magnetosphere by the interacting disk. Finally, we find no evidence that any flare types, even slow-rise flat-top flares are produced in star-disk magnetic loops. All are consistent with enhanced solar long-duration events with both footprints anchored in the stellar surface.Comment: Accepted for publication in ApJ (07/17/08); 46 pages, 14 figures, 2 table

Fine structure of alpha decay in odd nuclei

Using an alpha decay level scheme, an explanation for the fine structure in odd nuclei is evidenced by taking into account the radial and rotational couplings between the unpaired nucleon and the core of the decaying system. It is stated that the experimental behavior of the alpha decay fine structure phenomenon is directed by the dynamical characteristics of the system.Comment: 8 pages, 3 figures, REVTex, submitted to Physical Review

Quasi-elastic peak lineshapes in adsorbate diffusion on nearly flat surfaces at low coverages: the motional narrowing effect in Xe on Pt(111)

Quasi-elastic helium atom scattering measurements have provided clear evidence for a two-dimensional free gas of Xe atoms on Pt(111) at low coverages. Increasing the friction due to the surface, a gradual change of the shape of the quasi-elastic peak is predicted and analyzed for this system in terms of the so-called motional narrowing effect. The type of analysis presented here for the quasi-elastic peak should be prior to any deconvolution procedure carried out in order to better extract information from the process, e.g. diffusion coefficients and jump distributions. Moreover, this analysis also provides conditions for the free gas regime different than those reported earlier.Comment: 12 pages, 4 figures (revised version

Molecular modeling and structural analysis of the Myelin basic protein-Q65ZS4.

Schizophrenia (SCZ) is a chronic, debilitating psychotic mental disorder that affects about 1 percent of the population in different countries. Scz is characterized by a series of negative and positive symptoms including psychomotor retardation, attentional impairment, decreased emotional expression, psychomotor agitation, and auditory hallucinations.X-meeting 2007

Ultra-high precision determination of site energy differences using a Bayesian method

Accurate experimental data of adsorbate potential energy landscapes are crucial as benchmarks for the evaluation of first-principles calculations. Here, we present a Bayesian method, analyzing the difference in forward and backward hopping rate in helium spin-echo measurements, that allows us to determine the binding-energy difference between two sites with unprecedented accuracy. Demonstrating the power of the method on the model system cyclopentadienyl/Cu(111), we find an energy difference between fcc and hcp hollow sites of (10.6±1.7) meV

Reading Scepticism Historically. Scepticism, Acatalepsia and the Fall of Adam in Francis Bacon

The first part of this paper will provide a reconstruction of Francis Bacon’s interpretation of Academic scepticism, Pyrrhonism, and Dogmatism, and its sources throughout his large corpus. It shall also analyze Bacon’s approach against the background of his intellectual milieu, looking particularly at Renaissance readings of scepticism as developed by Guillaume Salluste du Bartas, Pierre de la Primaudaye, Fulke Greville, and John Davies. It shall show that although Bacon made more references to Academic than to Pyrrhonian Scepticism, like most of his contemporaries, he often misrepresented and mixed the doctrinal components of both currents. The second part of the paper shall offer a complete chronological survey of Bacon’s assessment of scepticism throughout his writings. Following the lead of previous studies by other scholars, I shall support the view that, while he approved of the state of doubt and the suspension of judgment as a provisional necessary stage in the pursuit of knowledge, he rejected the notion of acatalepsia. To this received reading, I shall add the suggestion that Bacon’s criticism of acatalepsia ultimately depends on his view of the historical conditions that surround human nature. I deal with this last point in the third part of the paper, where I shall argue that Bacon’s evaluation of scepticism relied on his adoption of a Protestant and Augustinian view of human nature that informed his overall interpretation of the history of humanity and nature, including the sceptical schools