Log-periodic modulation in one-dimensional random walks

We have studied the diffusion of a single particle on a one-dimensional lattice. It is shown that, for a self-similar distribution of hopping rates, the time dependence of the mean-square displacement follows an anomalous power law modulated by logarithmic periodic oscillations. The origin of this modulation is traced to the dependence on the length of the diffusion coefficient. Both the random walk exponent and the period of the modulation are analytically calculated and confirmed by Monte Carlo simulations.Comment: 6 pages, 7 figure

Atomic resolved material displacement on graphite surfaces by scanning tunnelling microscopy

Atomic scale modifications and subsequent atomic resolution imaging has been achieved on the highly oriented pyrolytic graphite surface in air. Application of short pulse voltages, above a minimum threshold voltage of 3.5 V, across the tunneling gap results in the displacement of a layer or more of atoms to form a hole and create a neighboring mound or ‘‘nanodot’’ from the displaced atoms. We have found a correlation between the hole and ‘‘nanodot’’ volume at the atomic level and observe an asymmetric displacement of material in all cases of feature creation. Nanofeatures as small as four carbon atoms at beta sites have been created. Our experimental observations are consistent with the modification process depending on the gradient in the electric field induced by the rise time of the bias pulse voltage and not the pulse duration. Interesting faceting behavior has also been observed around some hole edges. Tip bias pulsing sometimes induced a tip, and not a surface modification, resulting in a change in the observed tunneling image

The Scatter in the Relationship between Redshift and the Radio-to-Submm Spectral Index

We derive the scatter in the relationship between redshift and radio-to-submm spectral index, alpha^{350}_{1.4}, using the observed spectral energy distributions of 17 low redshift star forming galaxies. A mean galaxy model is derived, along with the rms scatter in alpha^{350}_{1.4}. The scatter is roughly constant with redshift. Constant rms scatter, combined with the flattening of the mean alpha^{350}_{1.4} -- z relationship with increasing redshift, leads to increasing uncertainty for redshift estimates at high redshifts. Normalizing by the dust temperature in the manner proposed by Blain decreases the scatter in alpha^{350}_{1.4} for most of the sample, but does not remove outliers, and free-free absorption at rest frequencies above 1.4 GHz is not likely to be a dominant cause for scatter in the alpha^{350}_{1.4} -- z relationship. We re-derive the cumulative redshift distribution of the 14 field galaxies in a recent submm and radio source sample of Smail et al.. The most likely median redshift for the distribution is 2.7, with a conservative lower limit of z = 2, as was also found by Smail et al. based on the original alpha^{350}_{1.4} -- z models. The normalization and shape of the redshift distribution for the faint submm sources are consistent with those expected for forming elliptical galaxies.Comment: Added Erratum, standard AAS LATEX forma

Transport Equations and Spin-Charge Propagating Mode in the Two Dimensional Hole Gas

We find that the spin-charge motion in a strongly confined two-dimensional hole gas (2DHG) supports a propagating mode of cubic dispersion apart from the diffusive mode due to momentum scattering. Propagating modes seem to be a generic property of systems with spin-orbit coupling. Through a rigorous Keldysh approach, we obtain the transport equations for the 2DHG, we analyze the behavior of the hole spin relaxation time, the diffusion coefficients, and the spin-charge coupled motion

Writing a wrong: Coupled RNA polymerase II transcription and RNA quality control

Processing and maturation of precursor RNA species is coupled to RNA polymerase II transcription. Co-transcriptional RNA processing helps to ensure efficient and proper capping, splicing, and 3' end processing of different RNA species to help ensure quality control of the transcriptome. Many improperly processed transcripts are not exported from the nucleus, are restricted to the site of transcription, and are in some cases degraded, which helps to limit any possibility of aberrant RNA causing harm to cellular health. These critical quality control pathways are regulated by the highly dynamic protein-protein interaction network at the site of transcription. Recent work has further revealed the extent to which the processes of transcription and RNA processing and quality control are integrated, and how critically their coupling relies upon the dynamic protein interactions that take place co-transcriptionally. This review focuses specifically on the intricate balance between 3' end processing and RNA decay during transcription termination. This article is categorized under: RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Processing > 3' End Processing RNA Processing > Splicing Mechanisms RNA Processing > Capping and 5' End Modifications

Field Work Reflections: Journeys in Knowing and Not-Knowing

In this paper, I retrace my interest in narrative forms of inquiry. I begin by revisiting a series of research projects that I conducted early in my career, describing some of my own dissatisfactions with the methods I used at the time. I move on to a detailed reexamination of my first piece of narrative research, completed during my PhD. In that project I used a narrative pointed psychosocial method in an attempt to develop new knowledge in the field of drugs, ‘race’ and ethnicity. In the final section, I consider what I have learned from this approach in terms of knowing and not-knowing and how I have used this experience to explore different approaches to narrative inquiry. I finish by drawing out some lessons I have learned from these different studies, which I hope might be of relevance to other social work researchers

Comparison of three thrust calculation methods using in-flight thrust data

The gross thrust of an experimental airplane was determined by each method using the same flight maneuvers and generally the same data parameters. Coefficients determined from thrust stand calibrations for each of the three methods were then extrapolated to cruise flight conditions. The values of total aircraft gross thrust calculated by the three methods for cruise flight conditions agreed within + or - 3 percent. The disagreement in the values of thrust calculated by the different techniques manifested itself as a bias in the data. There was little scatter (0.5 percent) for the thrust levels examined in flight

Non-Markovian Stochastic Resonance: three state model of ion channel gating

Stochastic Resonance in single voltage-dependent ion channels is investigated within a three state non-Markovian modeling of the ion channel conformational dynamics. In contrast to a two-state description one assumes the presence of an additional closed state for the ion channel which mimics the manifold of voltage-independent closed subconformations (inactivated ``state''). The conformational transition into the open state occurs through a domain of voltage-dependent closed subconformations (closed ``state''). At distinct variance with a standard two-state or also three-state Markovian approach, the inactivated state is characterized by a broad, non-exponential probability distribution of corresponding residence times. The linear response to a periodic voltage signal is determined for arbitrary distributions of the channel's recovery times. Analytical results are obtained for the spectral amplification of the applied signal and the corresponding signal-to-noise ratio. Alternatively, these results are also derived by use of a corresponding two-state non-Markovian theory which is based on driven integral renewal equations [I. Goychuk and P. Hanggi, Phys. Rev. E 69, 021104 (2004)]. The non-Markovian features of stochastic resonance are studied for a power law distribution of the residence time-intervals in the inactivated state which exhibits a large variance. A comparison with the case of bi-exponentially distributed residence times possessing the same mean value, i.e. a simplest non-Markovian two-state description, is also presented