Application of information theory to the design of line-scan imaging systems

Information theory is used to formulate a single figure of merit for assessing the performance of line scan imaging systems as a function of their spatial response (point spread function or modulation transfer function), sensitivity, sampling and quantization intervals, and the statistical properties of a random radiance field. Computational results for the information density and efficiency (i.e., the ratio of information density to data density) are intuitively satisfying and compare well with experimental and theoretical results obtained by earlier investigators concerned with the performance of TV systems

Aliased noise in radiometric measurements

The magnitude of aliased noise that degrades the accuracy of continuous reconstructions of discrete radiometric measurements was evaluated as a function of the spatial response and sampling intervals of the radiometer, and of the resolution of the reconstructed measurements. A Wiener spectrum, representative of a wide range of scenes, was used to characterize the radiance fluctuations

The Arabidopsis mutant feronia disrupts the female gametophytic control of pollen tube reception

Reproduction in angiosperms depends on communication processes of the male gametophyte (pollen) with the female floral organs (pistil, transmitting tissue) and the female gametophyte (embryo sac). Pollen-pistil interactions control pollen hydration, germination and growth through the stylar tissue. The female gametophyte is involved in guiding the growing pollen tube towards the micropyle and embryo sac. One of the two synergids flanking the egg cell starts to degenerate and becomes receptive for pollen tube entry. Pollen tube growth arrests and the tip of the pollen tube ruptures to release the sperm cells. Failures in the mutual interaction between the synergid and the pollen tube necessarily impair fertility. But the control of pollen tube reception is not understood. We isolated a semisterile, female gametophytic mutant from Arabidopsis thaliana, named feronia after the Etruscan goddess of fertility, which impairs this process. In the feronia mutant, embryo sac development and pollen tube guidance were unaffected in all ovules, although one half of the ovules bore mutant female gametophytes. However, when the pollen tube entered the receptive synergid of a feronia mutant female gametophyte, it continued to grow, failed to rupture and release the sperm cells, and invaded the embryo sac. Thus, the feronia mutation disrupts the interaction between the male and female gametophyte required to elicit these processes. Frequently, mutant embryo sacs received supernumerary pollen tubes. We analysed feronia with synergid-specific GUS marker lines, which demonstrated that the specification and differentiation of the synergids was normal. However, GUS expression in mutant gametophytes persisted after pollen tube entry, in contrast to wild-type embryo sacs where it rapidly decreased. Apparently, the failure in pollen tube reception results in the continued expression of synergid-specific genes, probably leading to an extended expression of a potential pollen tube attractant

Mechanisms of Spontaneous Current Generation in an Inhomogeneous d-Wave Superconductor

A boundary between two d-wave superconductors or an s-wave and a d-wave superconductor generally breaks time-reversal symmetry and can generate spontaneous currents due to proximity effect. On the other hand, surfaces and interfaces in d-wave superconductors can produce localized current-carrying states by supporting the T-breaking combination of dominant and subdominant order parameters. We investigate spontaneous currents in the presence of both mechanisms and show that at low temperature, counter-intuitively, the subdominant coupling decreases the amplitude of the spontaneous current due to proximity effect. Superscreening of spontaneous currents is demonstrated to be present in any d-d (but not s-d) junction and surface with d+id' order parameter symmetry. We show that this supercreening is the result of contributions from the local magnetic moment of the condensate to the spontaneous current.Comment: 4 pages, 5 figures, RevTe

Visible inequality breeds more inequality

Experiments suggest that when people can see wealth inequality in their social network, this propels further inequality through reduced cooperation and reduced social connectivity. News & Views comment on Nishi et al, Nature 526, 2015, p. 426-429

Superconducting d-wave junctions: The disappearance of the odd ac components

We study voltage-biased superconducting planar d-wave junctions for arbitrary transmission and arbitrary orientation of the order parameters of the superconductors. For a certain orientation of the superconductors the odd ac components disappear, resulting in a doubling of the Josephson frequency. We study the sensitivity of this disappearance to orientation and compare with experiments on grain boundary junctions. We also discuss the possibility of a current flow parallel to the junction.Comment: 5 pages, 3 figure

Keldysh action for disordered superconductors

Keldysh representation of the functional integral for the interacting electron system with disorder is used to derive microscopically an effective action for dirty superconductors. In the most general case this action is a functional of the 8 x 8 matrix Q(t,t') which depends on two time variables, and on the fluctuating order parameter field and electric potential. We show that this approach reproduces, without the use of the replica trick, the well-known result for the Coulomb-induced renormalization of the electron-electron coupling constant in the Cooper channel. Turning to the new results, we calculate the effects of the Coulomb interaction upon: i) the subgap Andreev conductance between superconductor and 2D dirty normal metal, and ii) the Josephson proximity coupling between superconductive islands via such a metal. These quantities are shown to be strongly suppressed by the Coulomb interaction at sufficiently low temperatures due to both zero-bias anomaly in the density of states and disorder-enhanced repulsion in the Cooper channel.Comment: RevTeX; 39 pages + 10 EPS figure

Building Babies - Chapter 16

In contrast to birds, male mammals rarely help to raise the offspring. Of all mammals, only among rodents, carnivores, and primates, males are sometimes intensively engaged in providing infant care (Kleiman and Malcolm 1981). Male caretaking of infants has long been recognized in nonhuman primates (Itani 1959). Given that infant care behavior can have a positive effect on the infant’s development, growth, well-being, or survival, why are male mammals not more frequently involved in “building babies”? We begin the chapter defining a few relevant terms and introducing the theory and hypotheses that have historically addressed the evolution of paternal care. We then review empirical findings on male care among primate taxa, before focusing, in the final section, on our own work on paternal care in South American owl monkeys (Aotus spp.). We conclude the chapter with some suggestions for future studies.Deutsche Forschungsgemeinschaft (HU 1746/2-1) Wenner-Gren Foundation, the L.S.B. Leakey Foundation, the National Geographic Society, the National Science Foundation (BCS-0621020), the University of Pennsylvania Research Foundation, the Zoological Society of San Dieg