Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: Bitartrate on Cu(110)

Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces

Label-free segmentation of co-cultured cells on a nanotopographical gradient

The function and fate of cells is influenced by many different factors, one of which is surface topography of the support culture substrate. Systematic studies of nanotopography and cell response have typically been limited to single cell types and a small set of topographical variations. Here, we show a radical expansion of experimental throughput using automated detection, measurement, and classification of co-cultured cells on a nanopillar array where feature height changes continuously from planar to 250 nm over 9 mm. Individual cells are identified and characterized by more than 200 descriptors, which are used to construct a set of rules for label-free segmentation into individual cell types. Using this approach we can achieve label-free segmentation with 84% confidence across large image data sets and suggest optimized surface parameters for nanostructuring of implant devices such as vascular stents

Deep-sea benthic habitats and the impacts of trawling on them in the offshore Greenland halibut fishery, Davis Strait, west Greenland

The offshore Greenland halibut (Reinhardtius hippoglossoides) fishery, west Greenland, employs demersal trawl gear at depths of 800–1400 m. In contrast to many deep-sea fisheries, the target stock appears stable and the fishery is of significant economic importance. Recent Marine Stewardship Council certification of this fishery highlighted the paucity of knowledge of benthic habitats and trawling impacts, which this study aimed to address using a towed benthic video sled. The spatially discrete northern and southern areas of the fishery were found to be distinct in terms of the communities present, which non-metric multidimensional scaling suggests is primarily driven by temperature. Extensive physical evidence of trawling was observed. Trawling effort was significantly linked with community composition, with a negative association between trawling effort and abundance of some taxa, including some vulnerable marine ecosystem (VME) indicator species. Three potential VMEs are identified: (i) Flabellum alabastrum cup coral meadows; (ii) a Halipteris finmarchica sea pen field; and (iii) areas exhibiting mixed assemblages of VME indicators. Of immediate conservation concern is a H. finmarchica field, which seems to be at least regionally rare, is situated within the fringes of existing trawling effort and is currently afforded no protection by management measures

The Association Between Social Networks and Self-rated risk of HIV Infection among Secondary School Students in Moshi Municipality, Tanzania.

Abstract This study describes the social networks of secondary school students in Moshi Municipality, and their association with self-rated risk of human immunodeficiency virus (HIV) infection. A cross-sectional analytical study was conducted among 300 students aged 15-24 years in 5 secondary schools in Moshi, Tanzania. Bonding networks were defined as social groupings of students participating in activities within the school, while bridging networks were groups that included students participating in social groupings from outside of the school environs. A structured questionnaire was used to ask about participation in bonding and bridging social networks and self-rated HIV risk behavior. More participants participated in bonding networks (72%) than in bridging networks (29%). Participation in bridging networks was greater among females (25%) than males (12%, p < .005). Of 300 participants, 88 (29%) were sexually experienced, and of these 62 (70%) considered themselves to be at low risk of HIV infection. Factors associated with self-rated risk of HIV included: type of school (p < .003), family structure (p < .008), being sexually experienced (p < .004), having had sex in the past three months (p < .009), having an extra sexual partner (p < .054) and non-condom use in last sexual intercourse (p < .001), but not the presence or type of social capital. The study found no association between bonding and bridging social networks on self-rated risk of HIV among study participants. However, sexually experienced participants rated themselves at low risk of HIV infection despite practicing unsafe sex. Efforts to raise adolescents' self-awareness of risk of HIV infection through life skills education and HIV/acquired immunodeficiency syndrome risk reduction strategies may be beneficial to students in this at-risk group

The Relationship Between Intermittent Limit Cycles and Postural Instability Associated with Parkinson’s Disease

Background: Many disease-specifc factors such as muscular weakness, increased muscle stiffness, varying postural strategies, and changes in postural refexes have been shown to lead to postural instability and fall risk in people with Parkinson’s disease (PD). Recently, analytical techniques, inspired by the dynamical systems perspective on movement control and coordination, have been used to examine the mechanisms underlying the dynamics of postural declines and the emergence of postural instabilities in people with PD. Methods: A wavelet-based technique was used to identify limit cycle oscillations (LCOs) in the anterior–posterior (AP) postural sway of people with mild PD (n = 10) compared to age-matched controls (n = 10). Participants stood on a foam and on a rigid surface while completing a dual task (speaking). Results: There was no signifcant difference in the root mean square of center of pressure between groups. Three out of 10 participants with PD demonstrated LCOs on the foam surface, while none in the control group demonstrated LCOs. An inverted pendulum model of bipedal stance was used to demonstrate that LCOs occur due to disease-specifc changes associated with PD: time-delay and neuromuscular feedback gain. Conclusion: Overall, the LCO analysis and mathematical model appear to capture the subtle postural instabilities associated with mild PD. In addition, these fndings provide insights into the mechanisms that lead to the emergence of unstable posture in patients with PD

Fermi Surface as a Driver for the Shape-Memory Effect in AuZn

Martensites are materials that undergo diffusionless, solid-state transitions. The martensitic transition yields properties that depend on the history of the material and may allow it to recover its previous shape after plastic deformation. This is known as the shape-memory effect (SME). We have succeeded in identifying the primary electronic mechanism responsible for the martensitic transition in the shape-memory alloy AuZn by using Fermi-surface measurements (de Haas-van Alphen oscillations) and band-structure calculations. This strongly suggests that electronic band structure is an important consideration in the design of future SME alloys

A survey for redshifted molecular and atomic absorption lines I

We are currently undertaking a large survey for redshifted atomic and molecular absorption ... only one clear and one tentative detection were obtained: HI absorption at z = 0.097 in PKS 1555-140 and OH absorption at z =0.126 in PKS 2300-189, respectively... In order to determine why no clear molecular absorption was detected in any of the 13 sources searched, we investigate the properties of the five redshifted systems currently known to exhibit OH absorption. In four of these, molecules were first detected via millimetre-wave transitions and the flat radio spectra indicate compact background continuum sources, which may suggest a high degree of coverage of the background source by the molecular clouds in the absorber. Furthermore, for these systems we find a relationship between the molecular line strength and red optical--near infrared (V-K) colours, thus supporting the notion that the reddening of these sources is due to dust, which provides an environment conducive to the formation of molecules. Upon comparison with the V-K colours of our sample, this relationship suggests that, presuming the reddening occurs at the host galaxy redshift at least in some of the targets, many of our observations still fall short of the sensitivityrequired to detect OH absorption, although a confirmation of the ``detection'' of OH in 2300-189 could contravene this.Comment: 13 pages, loads of figures, accepted by MNRA

Connecting does not necessarily mean learning: Course handbooks as mediating tools in school-university partnerships

This is the author's accepted manuscript (titled "Course handbooks as mediating tools in learning to teach"). The final published article is available from the link below. Copyright @ 2011 American Association of Colleges for Teacher Education.Partnerships between schools and universities in England use course handbooks to guide student teacher learning during long field experiences. Using data from a yearlong ethnographic study of a postgraduate certificate of education programme in one English university, the function of course handbooks in mediating learning in two high school subject departments (history and modern foreign languages) is analyzed. Informed by Cultural Historical Activity Theory, the analysis focuses on the handbooks as mediating tools in the school-based teacher education activity systems. Qualitative differences in the mediating functions of the handbooks-in-use are examined and this leads to a consideration of the potential of such tools for teacher learning in school–university partnerships. Following Zeichner’s call for rethinking the relationships between schools and universities, the article argues that strong structural connections between different institutional sites do not necessarily enhance student teacher learning

Residence Time Statistics for Normal and Fractional Diffusion in a Force Field

We investigate statistics of occupation times for an over-damped Brownian particle in an external force field. A backward Fokker-Planck equation introduced by Majumdar and Comtet describing the distribution of occupation times is solved. The solution gives a general relation between occupation time statistics and probability currents which are found from solutions of the corresponding problem of first passage time. This general relationship between occupation times and first passage times, is valid for normal Markovian diffusion and for non-Markovian sub-diffusion, the latter modeled using the fractional Fokker-Planck equation. For binding potential fields we find in the long time limit ergodic behavior for normal diffusion, while for the fractional framework weak ergodicity breaking is found, in agreement with previous results of Bel and Barkai on the continuous time random walk on a lattice. For non-binding potential rich physical behaviors are obtained, and classification of occupation time statistics is made possible according to whether or not the underlying random walk is recurrent and the averaged first return time to the origin is finite. Our work establishes a link between fractional calculus and ergodicity breaking.Comment: 12 page