Quantum Theory of Flicker Noise in Metal Films

Flicker (1/f^gamma) voltage noise spectrum is derived from finite-temperature quantum electromagnetic fluctuations produced by elementary charge carriers in external electric field. It is suggested that deviations of the frequency exponent \gamma from unity, observed in thin metal films, can be attributed to quantum backreaction of the conducting medium on the fluctuating field of the charge carrier. This backreaction is described phenomenologically in terms of the effective momentum space dimensionality, D. Using the dimensional continuation technique, it is shown that the combined action of the photon heat bath and external field results in a 1/f^gamma-contribution to the spectral density of the two-point correlation function of electromagnetic field. The frequency exponent is found to be equal to 1 + delta, where delta = 3 - D is a reduction of the momentum space dimensionality. This result is applied to the case of a biased conducting sample, and a general expression for the voltage power spectrum is obtained which possesses all characteristic properties of observed flicker noise spectra. The range of validity of this expression covers well the whole measured frequency band. Gauge independence of the power spectrum is proved. It is shown that the obtained results naturally resolve the problem of divergence of the total noise power. A detailed comparison with the experimental data on flicker noise measurements in metal films is given.Comment: 20 pages, 2 tables, 2 figure

Effect of long-range Coulomb interaction on shot-noise suppression in ballistic transport

We present a microscopic analysis of shot-noise suppression due to long-range Coulomb interaction in semiconductor devices under ballistic transport conditions. An ensemble Monte Carlo simulator self-consistently coupled with a Poisson solver is used for the calculations. A wide range of injection-rate densities leading to different degrees of suppression is investigated. A sharp tendency of noise suppression at increasing injection densities is found to scale with a dimensionless Debye length related to the importance of space-charge effects in the structure.Comment: RevTex, 4 pages, 4 figures, minor correction

Shot Noise Suppression in Avalanche Photodiodes

We identify a new shot noise suppression mechanism in a thin (~100 nm) heterostructure avalanche photodiode. In the low-gain regime the shot noise is suppressed due to temporal correlations within amplified current pulses. We demonstrate in a Monte Carlo simulation that the effective excess noise factors can be <1, and reconcile the apparent conflict between theory and experiments. This shot noise suppression mechanism is independent of known mechanisms such as Coulomb interaction, or reflection at heterojunction interfaces.Comment: Phys. Rev. Lett., accepted for publicatio

Journeys Westward: McGahern, Joyce and Irish Writing

Les nouvelles et romans de James Joyce parcourent, voire hantent, la fiction de John McGahern. Dans cet article, il sera question du dialogue que cette fiction engage avec la nouvelle de Joyce « The Dead », revisitée à maintes reprises par McGahern, y compris à la toute fin de sa carrière dans l’essai « What Is My Language? » Cette étude se construit ainsi en deux parties : la première retrace quelques variations sur le « voyage vers l'ouest ». Ce trope qui sillonne l’ensemble de l’œuvre de McGahern a été initialement introduit par Joyce dans « The Dead ». Dans un deuxième temps, pour mieux l’étudier, ce trope sera ancré dans la nouvelle de McGahern « Swallows ». « Swallows » et « The Dead », qui traitent des voyages propres et métaphoriques vers l'est et l'ouest, se font écho. Il s’avère d’ailleurs que la première nouvelle est une réécriture de la seconde. En tant que réécriture de « The Dead », « Swallows » se lit comme une réflexion métafictionnelle sur la nature de l’écriture irlandaise qui commente quelques aspects persistants du « réalisme » de Joyce, et rend hommage à son amour pour la musique – sujet que McGahern n’a pratiquement jamais abordé dans ses autres écrits. Hanté également par Ulysses, « Swallows » permet enfin à McGahern d’affirmer que pour lui, comme pour Joyce, l’écriture irlandaise constitue une tradition moins « insulaire » qu’internationale

Accumulating Progenitor Cells in the Luminal Epithelial Cell Layer Are Candidate Tumor Initiating Cells in a Pten Knockout Mouse Prostate Cancer Model

The PSA-Cre;Pten-loxP/loxP mouse prostate cancer model displays clearly defined stages of hyperplasia and cancer. Here, the initial stages of hyperplasia development are studied. Immunohistochemical staining showed that accumulated pAkt+ hyperplastic cells overexpress luminal epithelial cell marker CK8, and progenitor cell markers CK19 and Sca-1, but not basal epithelial cell markers. By expression profiling we identified novel hyperplastic cell markers, including Tacstd2 and Clu. Further we showed that at young age prostates of targeted Pten knockout mice contained in the luminal epithelial cell layer single pAkt+ cells, which overexpressed CK8, Sca-1, Tacstd2 and Clu; basal epithelial cells were always pAkt−. Importantly, in the luminal epithelial cell layer of normal prostates we detected rare Clu+Tacstd2+Sca-1+ progenitor cells. These novel cells are candidate tumor initiating cells in Pten knockout mice. Remarkably, all luminal epithelial cells in the proximal region of normal prostates were Clu+Tacstd2+Sca-1+. However, in PSA-Cre;Pten-loxP/loxP mice, the proximal prostate does not contain hyperplastic foci. Small hyperplastic foci in prostates of PSA-Cre;Pten-loxP/+ mice found at old age, showed complete Pten inactivation and a progenitor marker profile. Finally, we present a novel model of prostate development and renewal, including lineage-specific luminal epithelial progenitor cells. It is proposed that Pten deficiency induces a shift in the balance of differentiation to proliferation in these cells

"One time I fell, but I didn't have to cry." A qualitative study on everyday physical complaints in children

OBJECTIVE: Young children experience physical complaints, like abdominal pain or minor injuries from playing, almost every day. These experiences may shape how they deal with health issues later in life. While models exist to explain illness perception in adults, information is lacking on the perspective of young children. This qualitative study aimed to explore important themes in the experience of everyday physical complaints in four- and five-year-old children, using children as informants. STUDY DESIGN: 30 semi-structured interviews were performed in which four- and five-year-old children were questioned about their experiences with everyday physical complaints. The interviews were double coded using Atlas.ti and subsequently qualitative content analysis was used to define themes. RESULTS: All participating children were able to elaborate on their experiences with physical complaints. Three themes emerged from the interviews: causes of complaints, appraisal of complaints, and implications of complaints. In their appraisal of complaints, four- and five-year-old children made a distinction between visible and invisible complaints and real or pretended complaints. CONCLUSION: Four- and five-year-old children can already give details about their experiences with everyday physical complaints. They have developed ideas about the causes and implications of complaints and try to make an appraisal

Statistical theory of shot noise in quasi-1D Field Effect Transistors in the presence of electron-electron interaction

We present an expression for the shot noise power spectral density in quasi-one dimensional conductors electrostatically controlled by a gate electrode, that includes the effects of Coulomb interaction and of Pauli exclusion among charge carriers. In this sense, our expression extends the well known Landauer-Buttiker noise formula to include the effect of Coulomb interaction through induced fluctuations in the device potential. Our approach is based on the introduction of statistical properties of the scattering matrix and on a second-quantization many-body description. From a quantitative point of view, statistical properties are obtained by means of Monte Carlo simulations on a ensemble of different configurations of injected states, requiring the solution of the Poisson-Schrodinger equation on a three-dimensional grid, with the non-equilibrium Green functions formalism. In a series of example, we show that failure to consider the effects of Coulomb interaction on noise leads to a gross overestimation of the noise spectrum of quasi-one dimensional devices