Sturdier DNA nanotubes via ligation

DNA nanotubes are crystalline self-assemblies of DNA tiles ~10 nm in diameter that readily grow tens of micrometers in length. Easy assembly, programmability, and stiffness make them interesting for many applications, but DNA nanotubes begin to melt at temperatures below 40 °C, break open when deposited on mica or scanned by AFM, and disintegrate in deionized water. These weaknesses can be traced to the presence of discontinuities in the phosphate backbone, called nicks. The nanotubes studied here have five nicks, one in the core of a tile and one at each corner. We report the successful ligation of all four corner nicks by T4 DNA ligase. Although ligation does not change the nanotubes’ stiffness, ligated nanotubes withstand temperatures over 70 °C, resist breaking during AFM, and are stable in pure water for over a month. Ligated DNA nanotubes are thus physically and chemically sturdy enough to withstand the manipulations necessary for many technological applications

Limit curve theorems in Lorentzian geometry

The subject of limit curve theorems in Lorentzian geometry is reviewed. A general limit curve theorem is formulated which includes the case of converging curves with endpoints and the case in which the limit points assigned since the beginning are one, two or at most denumerable. Some applications are considered. It is proved that in chronological spacetimes, strong causality is either everywhere verified or everywhere violated on maximizing lightlike segments with open domain. As a consequence, if in a chronological spacetime two distinct lightlike lines intersect each other then strong causality holds at their points. Finally, it is proved that two distinct components of the chronology violating set have disjoint closures or there is a lightlike line passing through each point of the intersection of the corresponding boundaries.Comment: 25 pages, 1 figure. v2: Misprints fixed, matches published versio

Distributional fixed point equations for island nucleation in one dimension: a retrospective approach for capture zone scaling

The distributions of inter-island gaps and captures zones for islands nucleated on a one-dimensional substrate during submonolayer deposition are considered using a novel retrospective view. This provides an alternative perspective on why scaling occurs in this continuously evolving system. Distributional fixed point equations for the gaps are derived both with and without a mean field approximation for nearest neighbour gap size correlation. Solutions to the equations show that correct consideration of fragmentation bias justifies the mean field approach which can be extended to provide closed-from equations for the capture zones. Our results compare favourably to Monte Carlo data for both point and extended islands using a range of critical island size $i=0,1,2,3$. We also find satisfactory agreement with theoretical models based on more traditional fragmentation theory approaches.Comment: 9 pages, 7 figures and 1 tabl

Band gap control via tuning of inversion degree in CdIn2_2S4_4 spinel

Based on theoretical arguments we propose a possible route for controlling the band-gap in the promising photovoltaic material CdIn$_2$S$_4$. Our \textit{ab initio} calculations show that the experimental degree of inversion in this spinel (fraction of tetrahedral sites occupied by In) corresponds approximately to the equilibrium value given by the minimum of the theoretical inversion free energy at a typical synthesis temperature. Modification of this temperature, or of the cooling rate after synthesis, is then expected to change the inversion degree, which in turn sensitively tunes the electronic band-gap of the solid, as shown here by accurate screened hybrid functional calculations.Comment: In press in Applied Physics Letters (2012); 4 pages, 2 figures, 1 tabl

Measures of gravitational entropy I. Self-similar spacetimes

We examine the possibility that the gravitational contribution to the entropy of a system can be identified with some measure of the Weyl curvature. In this paper we consider homothetically self-similar spacetimes. These are believed to play an important role in describing the asymptotic properties of more general models. By exploiting their symmetry properties we are able to impose significant restrictions on measures of the Weyl curvature which could reflect the gravitational entropy of a system. In particular, we are able to show, by way of a more general relation, that the most widely used "dimensionless" scalar is \textit{not} a candidate for this measure along homothetic trajectories.Comment: revtex, minor clarifications, to appear in Physical Review

Uniqueness of static decompositions

We classify static manifolds which admit more than one static decomposition whenever a condition on the curvature is fullfilled. For this, we take a standard static vector field and analyze its associated one parameter family of projections onto the base. We show that the base itself is a static manifold and the warping function satisfies severe restrictions, leading us to our classification results. Moreover, we show that certain condition on the lightlike sectional curvature ensures the uniqueness of static decomposition for Lorentzian manifolds.Comment: 14 page

Seasonal variations of the vagile fauna associated with Ectopleura crocea (Cnidaria, Hydrozoa) in El Rompido marina (Huelva)

El desarrollo urbano en las zonas costeras se ha visto incrementado notablemente en los últimos años, resultando en un mayor número de estructuras artificiales en los ambientes marinos. Diversos organismos han sido capaces de colonizar las superficies de estos nuevos hábitats, incluyendo al hidrozoo Ectopleura crocea (Agassiz, 1862). Se estudió la epifauna asociada a esta especie a lo largo de un año en Puerto Marina, El Rompido, Huelva, con el objetivo de describir su composición y fluctuaciones temporales. En total, se encontraron 22 especies, mayoritariamente crustáceos anfípodos, siendo los más abundantes Stenothoe tergestina (Nebeski, 1881) y Apocorophium acutum (Chevreux, 1908). No se encontraron diferencias significativas a lo largo del ciclo anual en los valores de abundancia y diversidad, si bien se detectaron cambios en la composición faunística. En general, la diversidad de especies encontrada en Ectopleura crocea fue menor que la citada en otros estudios en hábitats naturales. Se sugiere que ello puede ser debido a características intrínsecas del hábitat artificial, tales como una menor heterogeneidad de sus superficies o a un mayor estrés ambiental. Por ello, para contrastar la consistencia a lo largo del tiempo y la causa de tales patrones, sería necesario estudios futuros que abarcasen un mayor rango temporal.Urban development in coastal areas has increased considerably in recent years, which has resulted in a larger number of artificial structures in coastal marine environments. However, various organisms have been able to colonize the surfaces of these new habitats, including the hydrozoan Ectopleura crocea (Agassiz, 1862). We studied the epifauna associated with this species over a year in Puerto Marina, El Rompido, Huelva, with the objective of describing its composition and temporal fluctuations. In total, 22 species were found, mostly amphipod crustaceans, the most abundant of these being Stenothoe tergestina (Nebeski, 1881) and Apocorophium acutum (Chevreux, 1908). No significant differences were found between the abundance and diversity of epifauna throughout the year, although changes in epifauna composition were detected over time. In general, the diversity found on Ectopleura crocea in the present study was lower than that reported by other studies in natural habitats. It is suggested that this could be due to intrinsic characteristics of the artificial habitat, such as lower heterogeneity of its surfaces or greater environmental stress. To contrast consistency over time and the causes of these patterns future studies carried out over a larger time period will be necessar

Serial diverse imagining task: A new remedy for bedtime complaints of worrying and other sleep-disruptive mental activity

Introduction: A racing mind, worries, and uncontrollable thoughts are common bedtime complaints among poor sleepers. Beaudoin created a Serial Diverse Imagining task (SDIT) that can be used at bedtime to divert attention away from sleep interfering thoughts, An app randomly presents recordings of relatively concrete words one at a time with an 8-second interval between recordings during which the person creates and maintains a mental image of the word until the next recording prompts the next image and so on. Our study is an experimental test of SDIT compared to the standard treatment of Structured Problem-solving (SP) and to the combination of both treatments. A key feature of SP is that it must be done earlier than bedtime and requires about 15 minutes to do it.  SDIT, which is done at bedtime, does not have those constraints.  Method: 154 university students (137 female) who complained of excessive cognitive pre-sleep arousal were randomly assigned to receive SDIT, SP, or both.  At baseline, they completed Pre-Sleep Arousal Scale (Somatic and Cognitive), Sleep Quality Scale, Glasgow Sleep Effort Scale and Sleep Hygiene Index.  Depending on the measure, participants redid it one week and/or one month after starting the intervention.  (They also completed sleep diaries and appraisals of the interventions, which are omitted due to space). Results: Repeated measures ANOVAs indicated that cognitive and somatic pre-sleep arousal , sleep effort, and sleep quality improved significantly relative to baseline (p  < .001; Partial η2 = .43 to .71) even though sleep hygiene worsened ( p  < .001; Partial η2 =  .23). The latter finding is not unexpected because the baseline was done at the start of the academic term before the onset of academic pressures. The fact that we found sleep and arousal improvements in this context are notable. Conclusion: Beaudoin’s Serial Diverse  Imagining Task (SDIT) was as effective as Structured Problem-Solving (SP) in reducing pre-sleep arousal, sleep effort, and poor sleep quality.  One advantage of SDIT is that it can be done at bedtime, unlike SP.&nbsp

Electrical characterisation of highly doped triangular silicon nanowires

A top-down silicon nanowire fabrication using a combination of optical lithography and orientation dependent etching (ODE) has been developed using Silicon-on Insulator (SOI) as the starting substrate. Initially, the samples were doped with phosphorus using the diffusion process resulting in carrier concentration of 2 X 10 18 cm-3. After the silicon nanowires were fabricated, they were measured using a dual configuration method which is similar to the four-point probe measurement technique to deduce its resistivity. The data obtained had suggested that the doping distribution in the silicon nanowires were lower and this may have been affected by the surface depletion effect. In addition, with respect to carrier mobility, the effective mobility of electrons extracted using the four-point probe data had demonstrated that the mobility of carriers in the silicon nanowire is comparable with the bulk mobility. This is most probably due to the fact that in this research, the quantum confinement effect on these nanowires is not significant

Bearing an open “Pandora's Box”:HCI for reconciling everyday food and sustainability

The sustainability of food is a significant global concern with a drastic change required to mitigate complex social, environmental, and economic issues like climate change and food security for an ever increasing population. In this article, we set out to understand the place of food in people's lives, their mundane yet surprisingly complex ways of sourcing their food, and the processes of transition, past and ongoing, that shape these choices. Our goal is to understand the potential role for digital interactions in supporting the various ways that food consumption can be made more sustainable. To inform this exercise, we specifically set out to contrast the journeys of committed sustainable “food pioneers” with more conventional mainstream consumers recruited in branches of a UK supermarket. This contrast highlights for both groups the various values, and “meaningfulness” attached to foods and meals in people's lives, and suggests ways in which food choice and pro-sustainable practices can be supported at least in part by new digital technologies