Proposal for a single-molecule field-effect transistor for phonons

We propose a practical realization of a field-effect transistor for phonons. Our device is based on a single ionic polymeric molecule and it gives modulations as large as -25% in the thermal conductance for feasible temperatures and electric field magnitudes. Such effect can be achieved by reversibly switching the acoustic torsion mode into an optical mode through the coupling of an applied electric field to the dipole moments of the monomers. This device can pave the way to the future development of phononics at the nanoscale or molecular scale

On the magnetic structure of the solar transition region

We examine the hypothesis that ``cool loops'' dominate emission from solar transition region plasma below temperatures of $2\times10^5$K. We compare published VAULT images of H L$\alpha$, a lower transition region line, with near-contemporaneous magnetograms from Kitt Peak, obtained during the second flight (VAULT-2) on 14 June 2002. The measured surface fields and potential extrapolations suggest that there are too few short loops, and that L$\alpha$ emission is associated with the base regions of longer, coronal loops. VAULT-2 data of network boundaries have an asymmetry on scales larger than supergranules, also indicating an association with long loops. We complement the Kitt Peak data with very sensitive vector polarimetric data from the Spectro-Polarimeter on board Hinode, to determine the influence of very small magnetic concentrations on our analysis. From these data two classes of behavior are found: within the cores of strong magnetic flux concentrations ($> 5\times10^{18}$ Mx) associated with active network and plage, small-scale mixed fields are absent and any short loops can connect just the peripheries of the flux to cell interiors. Core fields return to the surface via longer, most likely coronal, loops. In weaker concentrations, short loops can connect between concentrations and produce mixed fields within network boundaries as suggested by Dowdy and colleagues. The VAULT-2 data which we examined are associated with strong concentrations. We conclude that the cool loop model applies only to a small fraction of the VAULT-2 emission, but we cannot discount a significant role for cool loops in quieter regions. We suggest a physical picture for how network L$\alpha$ emission may occur through the cross-field diffusion of neutral atoms from chromospheric into coronal plasma.Comment: Accepted by ApJ, 9 May 200

Mode decomposition and renormalization in semiclassical gravity

We compute the influence action for a system perturbatively coupled to a linear scalar field acting as the environment. Subtleties related to divergences that appear when summing over all the modes are made explicit and clarified. Being closely connected with models used in the literature, we show how to completely reconcile the results obtained in the context of stochastic semiclassical gravity when using mode decomposition with those obtained by other standard functional techniques.Comment: 4 pages, RevTeX, no figure

Provisionally pregnant: uncertainty and interpretive work in accounts of home pregnancy testing

Upon their availability for purchase in the 1970s, home pregnancy testing devices were hailed as a ‘revolution’ for women’s reproductive rights. Some authors, however, have described these technologies as further enabling the medicalisation of pregnancy and as contributing to the devaluing of women’s embodied knowledge. The home pregnancy test is one of many technological devices encountered by women experiencing pregnancy in the United Kingdom today. Existing literature has described how engagement with medical technologies during pregnancy might address uncertainties experienced at this time, providing women with reassurance and alleviating anxieties. Drawing on interviews with women living in Scotland, this article explores accounts of testing for a first pregnancy, and women’s descriptions of the impacts of home pregnancy testing upon experiences of early gestation. Participants engaged with pregnancy tests in varying ways, with uses shaping and shaped by their experiences of early pregnancy more broadly. Particular technical characteristics of the home pregnancy test led many participants to question their interpretation of a positive result, as well as the accuracy of the test itself. Rather than addressing the unknowns of early gestation by confirming a suspected pregnancy, a positive result could thus exacerbate uncertainty. Through participants’ accounts, this article shows how uncertainty is lived out by users of mundane techno-medical artefacts and sheds new light on women’s experiences of the first trimester of pregnancy

Pyrrole-Imidazole Polyamides Distinguish Between Double-Helical DNA and RNA

Groove specificity: Pyrrole-imidazole polyamides are well-known for their specific interactions with the minor groove of DNA (see scheme). However, polyamides do not show similar binding to duplex RNA, and a structural rationale for the molecular-level discrimination of nucleic acid duplexes by minor-groove-binding ligands is presented

The radiating part of circular sources

An analysis is developed linking the form of the sound field from a circular source to the radial structure of the source, without recourse to far-field or other approximations. It is found that the information radiated into the field is limited, with the limit fixed by the wavenumber of source multiplied by the source radius (Helmholtz number). The acoustic field is found in terms of the elementary fields generated by a set of line sources whose form is given by Chebyshev polynomials of the second kind, and whose amplitude is found to be given by weighted integrals of the radial source term. The analysis is developed for tonal sources, such as rotors, and, for Helmholtz number less than two, for random disk sources. In this case, the analysis yields the cross-spectrum between two points in the acoustic field. The analysis is applied to the problems of tonal radiation, random source radiation as a model problem for jet noise, and to noise cancellation, as in active control of noise from rotors. It is found that the approach gives an accurate model for the radiation problem and explicitly identifies those parts of a source which radiate.Comment: Submitted to Journal of the Acoustical Society of Americ

Nonequilibrium Detailed Fluctuation Theorem for Repeated Discrete Feedback

We extend the framework of forward and reverse processes commonly utilized in the derivation and analysis of the nonequilibrium work relations to thermodynamic processes with repeated discrete feedback. Within this framework, we derive a generalization of the detailed fluctuation theorem, which is modified by the addition of a term that quantifies the change in uncertainty about the microscopic state of the system upon making measurements of physical observables during feedback. As an application, we extend two nonequilibrium work relations: the nonequilibrium work fluctuation theorem and the relative-entropy work relation.Comment: 7 pages, 3 figure