Minimum energy path for the nucleation of misfit dislocations in Ge/Si(001) heteroepitaxy

A possible mechanism for the formation of a 90{\deg} misfit dislocation at the Ge/Si(001) interface through homogeneous nucleation is identified from atomic scale calculations where a minimum energy path connecting the coherent epitaxial state and a final state with a 90{\deg} misfit dislocation is found using the nudged elastic band method. The initial path is generated using a repulsive bias activation procedure in a model system including 75000 atoms. The energy along the path exhibits two maxima in the energy. The first maximum occurs as a 60{\deg} dislocation nucleates. The intermediate minimum corresponds to an extended 60{\deg} dislocation. The subsequent energy maximum occurs as a second 60{\deg} dislocation nucleates in a complementary, mirror glide plane, simultaneously starting from the surface and from the first 60{\deg} dislocation. The activation energy of the nucleation of the second dislocation is 30% lower than that of the first one showing that the formation of the second 60{\deg} dislocation is aided by the presence of the first one. The simulations represent a step towards unraveling the formation mechanism of 90{\deg} dislocations, an important issue in the design of growth procedures for strain released Ge overlayers on Si(100) surfaces, and more generally illustrate an approach that can be used to gain insight into the mechanism of complex nucleation paths of extended defects in solids

Seed predation is key to preventing population growth of the weed Alopecurus myosuroides

Seed predation can reduce the abundance and spread of unwanted vegetation in agricultural and other semi-natural ecosystems. However, knowledge of how variations in seed predation rates affect plant species population dynamics is needed for decision making and knowledge-based ecosystem management. We developed a stage-classified stochastic matrix population model for Alopecurus myosuroides Huds. (blackgrass), an annual plant species thriving as a weed in temperate agroecosystems of Western and Northern Europe. The model was parameterised using empirical demographic data from long-term experiments in Swedish winter wheat fields, including information on post-dispersal seed losses by vertebrate and invertebrate seed predators. For agroecosystems with highly effective weed control measures (e.g. chemical and mechanical weed control), model simulations showed that seed losses via seed predation need to reach at least 78% at peak seed shedding to suppress population growth of A. myosuroides. The field experiment showed that vertebrates were most important for seed predation in July, at peak seed shedding. In August, after crop harvest, invertebrates were responsible for almost all seed predation. The model indicated that weed seed predation was much more important for weed regulation when it occurred before crop harvest in July. Vertebrates most strongly reduced population growth of A. myosuroides, although both vertebrates and invertebrates were needed to prevent it entirely. Synthesis and applications. We showed that weed seed predation by vertebrate and invertebrate seed predators is key for reducing the population growth of winter annual weeds like A. myosuroides in intensively managed agroecosystems. Therefore, protection of weed seed predators is essential for making management of unwanted vegetation less dependent on chemical and mechanical measures

The Ideal Review Process Is a Three-Way Street

In response to the increasing difficulty of obtaining high quality peer reviews, our invited paper describes the concept of review avoidance and why this phenomenon occurs. In reaffirming the professional responsibilities and potential benefits of reviewing, we also emphasize the interdependent nature of the ideal peer review process. We suggest that the review process is a three-way street where the respective roles and responsibilities of authors, editors and editorial teams, and reviewers are inextricably linked. We present thematic illustrations of undesirable reviewer comments, and a brief synthesis of broad themes in the literature on high-quality reviewing. The synthesis is complemented by a master reviewer’s fine-grained perspective on crafting high quality reviews. A final Appendix presents additional sources that may be informative for prospective reviewers, submitting authors, and those mentors and colleagues who may wish to provide guidance and training to them

Evolution of the vertical profile and flux of large sea-salt particles in a coastal zone

Journal of Geophysical Research, Vol. 106, No. D11, pp. 12,039 - 12,053, June 16, 2001.In the vicinity of the North Carolina Outer Banks we observed both steady onshore flow conditions and a continental air mass transition into a marine boundary layer. Using the CIRPAS Twin Otter aircraft, we measuredc hangesin the columnb urden of sea salt as the air mass was advected out to sea. We also measured the flux of whitecap-generatesde a-saltp articlesi n neutrallys tablea tmospherea t wind speedso f 4, 8, and1 2r n s- •. Productioonf saltp articleass s malla s0 .27/•mi n diametewr aso bserved. Furthermore,w e measureds alt particle size distributionsa t variousw ind speedsd uring alongs horew ind and near steadys tate conditionsU. sing thesem easurementsa s a frame of reference,w e discussth e very large differencesi n the reported size and flux of sea salt presentedi n the literature. The disagreemenitn reported salt fluxesi s larger for smallersizedp articles( almosta n order of magnitude)a nd is most likely due to assumptionms ade when the fluxesw ere computed,e speciallyt he particle dry depositionv elocitya nd air mass history.H owever,f or giant salt particlesw ith short atmosphericli fetimes (>-10/•m in diameter),t here is generala greementb etweenf luxesa nd size distributionsm easuredi n this studya nd previouso nes.R eported salt particle size distributionsin the literature also vary considerablyu nder similar steadyw ind and stability conditions.F rom these and our results it is clear that no more than half of the variance in salt particle concentration can be explainedb y wind speeda lone, suggestingth at the idea of "steadys tate" in the marine boundary layer rarely exists at midlatitudes

The spectral dimension of generic trees

We define generic ensembles of infinite trees. These are limits as $N\to\infty$ of ensembles of finite trees of fixed size $N$, defined in terms of a set of branching weights. Among these ensembles are those supported on trees with vertices of a uniformly bounded order. The associated probability measures are supported on trees with a single spine and Hausdorff dimension $d_h =2$. Our main result is that their spectral dimension is $d_s=4/3$, and that the critical exponent of the mass, defined as the exponential decay rate of the two-point function along the spine, is 1/3

Stigma och de professionella: en undersökning av svenska psykologers grad av stigmatisering av personer med psykisk sjukdom

Studiens syfte var att utifrån en modell av stigma som bestående av komponenterna kunskap, attityder och beteende beskriva psykologers stigmatisering av personer med psykisk sjukdom samt att jämföra psykologers stigmatisering med den övriga befolkningens. Vidare syftade studien till att undersöka vilka faktorer som påverkar psykologers attityder till personer med psykisk sjukdom. Yrkesverksamma psykologer samt psykologstudenter kontaktades via Sveriges psykologförbunds elektroniska nyhetsbrev, via sociala medier samt via klassrumsrekrytering. 371 personer deltog i studien och fyllde i ett webbformulär bestående av tre test som avsåg mäta kunskap, attityder samt beteende. Resultaten visade att psykologer hade god kunskap om psykisk sjukdom, att de hade positiva attityder till personer med psykisk sjukdom, samt att de var positivt inställda till framtida interaktioner med personer med psykisk sjukdom. Erfarenhet av psykisk sjukdom samt kunskap om psykisk sjukdom var de variabler som hade starkast samband med attityder till personer med psykisk sjukdom. Andel förklarad varians var dock liten. Attityder predicerade till viss del inställning till framtida interaktion med personer med psykisk sjukdom. Jämförelse med befolkningsrepresentativt stickprov visade att psykologer hade signifikant mer positiva attityder, dock med små effektstorlekar. Detta tolkades som att psykologer i något lägre grad än den övriga befolkningen stigmatiserar personer med psykisk sjukdom