6,587 research outputs found
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
Generalized Paraxial Ray Trace Procedure Derived from Geodesic Deviation
Paraxial ray tracing procedures have become widely accepted techniques for
acoustic models in seismology and underwater acoustics. To date a generic form
of these procedures including fluid motion and time dependence has not appeared
in the literature. A detailed investigation of the characteristic curves of the
equations of hydrodynamics allows for an immediate generalization of the
procedure to be extracted from the equation form geodesic deviation. The
general paraxial ray trace equations serve as an ideal supplement to ordinary
ray tracing in predicting the deformation of acoustic beams in random
environments. The general procedure is derived in terms of affine
parameterization and in a coordinate time parameterization ideal for
application to physical acoustic ray propagation. The formalism is applied to
layered media, where the deviation equation reduces to a second order
differential equation for a single field with a general solution in terms of a
depth integral along the ray path. Some features are illustrated through
special cases which lead to exact solutions in terms of either ordinary or
special functions.Comment: Original; 40 pages (double spaced), 1 figure Replaced version; 36
pages single spaced, 7 figures. Expanded content; Complete derivation of the
equations from the equations of hydrodynamics, introduction of an auxiliary
basis for three dimensional wave-front modeling. Typos in text and equations
correcte
Theory of Optical Transmission through Elliptical Nanohole Arrays
We present a theory which explains (in the quasistatic limit) the
experimentally observed [R. Gordon, {\it et al}, Phys. Rev. Lett. {\bf 92},
037401 (2004)] squared dependence of the depolarization ratio on the aspect
ratio of the holes, as well as other features of extraordinary light
transition. We calculated the effective dielectric tensor of a metal film
penetrated by elliptical cylindrical holes and found the extraordinarily light
transmission at special frequencies related to the surface plasmon resonances
of the composite film. We also propose to use the magnetic field for getting a
strong polarization effect, which depends on the ratio of the cyclotron to
plasmon frequencies.Comment: 4 pages, 4 figure
Phycomyces
This monographic review on a fungus is not addressed to mycologists. None of the authors has been trained or has otherwise acquired a general proficiency in mycology. They are motivated by a common interest in the performances of signal handling exhibited by the sense organs of all organisms and by the desire to attack these as yet totally obscure aspects of molecular biology by the study of a microorganism with certain desirable properties.
The sporangiophore of the fungus Phycomyces is a gigantic, single-celled, erect, cylindrical, aerial hypha. It is sensitive to at least four distinct stimuli: light, gravity, stretch, and some unknown stimulus by which it avoids solid objects. These stimuli control a common output, the growth rate, producing either temporal changes in growth rate or tropic responses.
We are interested in the output because it gives us information about the reception of the various signals. In the absence of external stimuli, the growth rate is controlled by internal signals keeping the network of biochemical processes in balance. The external stimuli interact with the internal signals. We wish to inquire into the early steps of this interaction. For light, for instance, the cell must have a receptor pigment as the first
mediator. What kind of a molecule is this pigment? Which organelle contains it? What chemical reaction happens after a light quantum has been absorbed? And how is the information introduced by this primary photochemical event amplified in a controlled manner and processed in the next step? How do a few quanta or a few molecules trigger macroscopic responses? Will we find ourselves confronted with devices wholly distinct from anything now known in biology
Cinematic and aesthetic cartographies of subjective mutation
This article exmaines the use of cinema as a mapping of subjective mutation in the work of Deleuze, Gauttari and Berardi. Drawing on Deleuze's distinciton between the reduction of the art-work to the symptom and the idea of art as symptomatology, the article focuses on Berardi's use of cinematic examples, posing the quesiton in each case of to what extent they function as symptomatologies or mere symptoms of cultural and subjective mutations in examples ranging from Bergman's Persona to Van Sant's Elephant to finish on speculations about Fincher's The Social Network as a cirtical engagement with subjective mutation in the 21st Century
A Torsion Correction to the RR 4-Form Fieldstrength
The shifted quantization condition of the M-theory 4-form G_4 is well-known.
The most naive generalization to type IIA string theory fails, an orientifold
counterexample was found by Hori in hep-th/9805141. In this note we use
D2-brane anomaly cancellation to find the corresponding shifted quantization
condition in IIA. Our analysis is consistent with the known O4-plane tensions
if we include a torsion correction to the usual construction of G_4 from C_3, B
and G_2. The resulting Bianchi identities enforce that RR fluxes lift to
K-theory classes.Comment: 10 Pages, 1 eps figur
Principles of genome evolution in the Drosophila melanogaster species group.
That closely related species often differ by chromosomal inversions was discovered by Sturtevant and Plunkett in 1926. Our knowledge of how these inversions originate is still very limited, although a prevailing view is that they are facilitated by ectopic recombination events between inverted repetitive sequences. The availability of genome sequences of related species now allows us to study in detail the mechanisms that generate interspecific inversions. We have analyzed the breakpoint regions of the 29 inversions that differentiate the chromosomes of Drosophila melanogaster and two closely related species, D. simulans and D. yakuba, and reconstructed the molecular events that underlie their origin. Experimental and computational analysis revealed that the breakpoint regions of 59% of the inversions (17/29) are associated with inverted duplications of genes or other nonrepetitive sequences. In only two cases do we find evidence for inverted repetitive sequences in inversion breakpoints. We propose that the presence of inverted duplications associated with inversion breakpoint regions is the result of staggered breaks, either isochromatid or chromatid, and that this, rather than ectopic exchange between inverted repetitive sequences, is the prevalent mechanism for the generation of inversions in the melanogaster species group. Outgroup analysis also revealed evidence for widespread breakpoint recycling. Lastly, we have found that expression domains in D. melanogaster may be disrupted in D. yakuba, bringing into question their potential adaptive significance
Spectral representation of the effective dielectric constant of graded composites
We generalize the Bergman-Milton spectral representation, originally derived
for a two-component composite, to extract the spectral density function for the
effective dielectric constant of a graded composite. This work has been
motivated by a recent study of the optical absorption spectrum of a graded
metallic film [Applied Physics Letters, 85, 94 (2004)] in which a broad
surface-plasmon absorption band has been shown to be responsible for enhanced
nonlinear optical response as well as an attractive figure of merit. It turns
out that, unlike in the case of homogeneous constituent components, the
characteristic function of a graded composite is a continuous function because
of the continuous variation of the dielectric function within the constituent
components. Analytic generalization to three dimensional graded composites is
discussed, and numerical calculations of multilayered composites are given as a
simple application.Comment: Physical Review E, submitted for publication
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
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