The Structure of the [Zn_In - V_P] Defect Complex in Zn Doped InP

We study the structure, the formation and binding energies and the transfer levels of the zinc-phosphorus vacancy complex [Zn_In - V_P] in Zn doped p-type InP, as a function of the charge, using plane wave ab initio DFT-LDA calculations in a 64 atom supercell. We find a binding energy of 0.39 eV for the complex, which is neutral in p-type material, the 0/-1 transfer level lying 0.50 eV above the valence band edge, all in agreement with recent positron annihilation experiments. This indicates that, whilst the formation of phosphorus vacancies (V_P) may be involved in carrier compensation in heavily Zn doped material, the formation of Zn-vacancy complexes is not. Regarding the structure: for charge states Q=+6 to -4 the Zn atom is in an sp^2 bonded DX position and electrons added/removed go to/come from the remaining dangling bonds on the triangle of In atoms. This reduces the effective vacancy volume monatonically as electrons are added to the complex, also in agreement with experiment. The reduction occurs through a combination of increased In-In bonding and increased Zn-In electrostatic attraction. In addition, for certain charge states we find complex Jahn-Teller behaviour in which up to three different structures, (with the In triangle dimerised, antidimerised or symmetric) are stable and are close to degenerate. We are able to predict and successfully explain the structural behaviour of this complex using a simple tight binding model.Comment: 10 pages text (postscript) plus 8 figures (jpeg). Submitted to Phys. Rev.

First-principles study of He in Si

We have performed first-principles calculations for He atoms in a Si lattice. From dynamic total-energy minimization we obtain the relaxations of the Si atoms around the impurity and the corresponding total energies. The calculated heat of solution and the diffusion constant of He in Si are in good agreement with experiment. There is a net attraction between two tetrahedral He interstitials, leading to a binding energy of 0.08 eV for He atoms at neighboring interstices. On the other hand, Si vacancies are found not to trap He atoms. The consequences of these results to He-bubble nucleation and growth are discussed.Peer reviewe

Lateral diatomic two-dimensional artificial molecules: Classical transitions and quantum-mechanical counterparts

Structural properties of a finite number (N=2−20) of point charges (classical electrons) confined laterally in a two-dimensional two-minima potential are calculated as a function of the distance (d) between the minima. The particles are confined by identical parabolic potentials and repel each other through a Coulomb potential. Both ground-state and metastable electron configurations are discussed. Discontinuous transitions from one configuration to another as a function of d are observed for N=6, 8, 11, 16, 17, 18, and 19. We show that the structural transitions have quantum-mechanical counterparts also in the limit of noninteracting electrons.Peer reviewe

Impacts of different climate change regimes and extreme climatic events on an alpine meadow community

Climate variability is expected to increase in future but there exist very few experimental studies that apply different warming regimes on plant communities over several years. We studied an alpine meadow community under three warming regimes over three years. Treatments consisted of (a) a constant level of warming with open-top chambers (ca. 1.9 °C above ambient), (b) yearly stepwise increases in warming (increases of ca. 1.0, 1.9 and 3.5 °C), and (c) pulse warming, a single first-year pulse event of warming (increase of ca. 3.5 °C). Pulse warming and stepwise warming was hypothesised to cause distinct first-year and third-year effects, respectively. We found support for both hypotheses; however, the responses varied among measurement levels (whole community, canopy, bottom layer, and plant functional groups), treatments, and time. Our study revealed complex responses of the alpine plant community to the different experimentally imposed climate warming regimes. Plant cover, height and biomass frequently responded distinctly to the constant level of warming, the stepwise increase in warming and the extreme pulse-warming event. Notably, we found that stepwise warming had an accumulating effect on biomass, the responses to the different warming regimes varied among functional groups, and the short-term perturbations had negative effect on species richness and diversityNFR grant (B-AA/BU 08424) to UM

Metastable defect complexes in GaAs

We have studied the As-vacancy–Si-impurity and the As-vacancy–As-antisite complexes in GaAs using state-of-the-art electronic structure methods. The complexes show metastability as a function of the position of the impurity or the antisite atom similarly to the large-lattice relaxation models for the isolated DX and EL2 centers. Our findings suggest the enlargement of the family of metastable defects in GaAs, and the results enlighten the metastability mechanisms in the large-lattice relaxation model. In order to discuss the possible experimental detection of this type of metastability, we calculate the positron states and annihilation characteristics for the defect complexes.Peer reviewe

Mainostajan perinteisen mediatalon mainos- ja markkinointipalveluista kokeman arvon muutos media-alan murroksessa

Tiivistelmä. Tässä tutkielmassa pyritään ymmärtämään, miten median murros on muuttanut mainostajien perinteisen mediatalon tarjoamista mainos- ja markkinointipalveluista kokemaan arvoon. Aihetta lähestytään arvon yhteisluonnin ja palvelukokemuksen käsitteiden kautta. Median murroksen jatkuessa edelleen on perinteisten mediatalojen tärkeää ymmärtää, millaista arvoa mainostajat heidän palveluistaan kokevat, jotta palveluita voidaan kehittää ja siten varmistaa, että perinteiset mediat säilyvät varteenotettavina vaihtoehtoina mainostajien mediapäätöksissä. Tutkimus on toteutettu laadullisia tutkimusmenetelmiä hyödyntäen syvällisen ymmärryksen muodostamiseksi. Aineisto on kerätty puolistrukturoitujen teemahaastattelujen avulla. Kerätty aineisto on analysoitu teemoittelemalla se teoriaohjautuvan sisällönanalyysin keinoin. Tutkimuksen perusteella median murros on vaikuttanut mainostajien perinteisen mediatalon palveluista kokemaan arvoon mediaympäristössä sekä kuluttajien median käyttötavoissa tapahtuneiden muutosten seurauksena. Tulosten perusteella mainostajan mediatalon palveluista kokema arvo muodostuu palvelukokemuksen lopputuloksen, prosessin sekä erilaisten aika- ja sijaintitekijöiden lopputulemana. Lisäksi koettuun arvoon vaikuttavat erityisesti mainostajan aiemmat, nykyiset, tulevat mutta myös kuvitellut kokemukset perinteisen mediatalon palveluista. Mediaympäristössä tapahtuneet muutokset, kuten uudet viestintäteknologiat ja uudet mediakanavat, ovat haastaneet mainostajien perinteisistä mediataloista kokeman arvon siten, että mainonnan tehokkuuden mittaamisesta on tullut helpompaa ja mainostamisesta edullisempaa kuin perinteisissä kanavissa. Tämä on muuttanut mainostajien kokemaa arvoa perinteisen median palveluista. Kuluttajien mediakäyttötavoissa tapahtuneet muutokset ovat myös muokanneet mainostajien perinteisen mediatalon palveluista kokemasta arvosta. Kuluttajat ovat hajaantuneet useisiin eri medioihin, eikä yhden kanavan kautta enää tavoita koko kohderyhmää. Lisäksi kuluttajien valinnanvara on kasvanut, jonka seurauksena perinteisissä medioissa kulutettu aika on vähentynyt median murroksen myötä, kun taas digimedioissa se on lisääntynyt. Mainostaja joutuu siten aina pohtimaan, missä kanavassa ja millä keinoin on järkevintä pyrkiä tavoittamaan haluttu kohdeyleisö. Tämä on ollut yksi syy siihen, miksi mainostajien panostukset perinteiseen mediaan ovat vähentyneet. Tutkimuksen tuloksia voidaan hyödyntää perinteisten mediatalojen mainostajille suunnattujen palvelujen kehittämisessä vastaamaan paremmin mainostajien tarpeita. Lisäksi tutkimuksen tuloksia voidaan hyödyntää myöhemmässä mainostajien mainospalveluista kokemaa arvoa sekä median murrosta käsittelevässä tutkimuksessa

Comparing connection to theory in Bachelor's theses: Old research university versus new regional university college

Quality of higher education is often assumed to be linked to the size of the faculty. Therefore, this study tested the hypothesis whether Bachelor's theses in ecology at a large, old research university would have more connection to theory than those at a small, young university college. The results revealed no significant difference between the universities. One potential explanation for these results is that theory is more likely to depend on the individual supervisor who may demand a clear connection to theory in Bachelor's theses. However, in the group of theses categorized as without a clear connection to theory, there were significant differences between the two universities regarding whether students were testing/developing a method or performing a case study. At the large, well-equipped research university, Bachelor's theses were significantly more likely to be based on developing/testing methods, while those at the university college more often comprised inexpensive case studies. Further studies including more universities of contrasting sizes, across countries and disciplines, are required to test the general validity of the findings.qscienc

Community and species-specific responses of plant traits to 23 years of experimental warming across subarctic tundra plant communities

To improve understanding of how global warming may affect competitive interactions among plants, information on the responses of plant functional traits across species to long-term warming is needed. Here we report the effect of 23 years of experimental warming on plant traits across four different alpine subarctic plant communities: tussock tundra, Dryas heath, dry heath and wet meadow. Open-top chambers (OTCs) were used to passively warm the vegetation by 1.5–3 °C. Changes in leaf width, leaf length and plant height of 22 vascular plant species were measured. Long-term warming significantly affected all plant traits. Overall, plant species were taller, with longer and wider leaves, compared with control plots, indicating an increase in biomass in warmed plots, with 13 species having significant increases in at least one trait and only three species having negative responses. The response varied among species and plant community in which the species was sampled, indicating community-warming interactions. Thus, plant trait responses are both species- and community-specific. Importantly, we show that there is likely to be great variation between plant species in their ability to maintain positive growth responses over the longer term, which might cause shifts in their relative competitive ability.Scopu

Evidence of boosted 13CO/12CO ratio in early-type galaxies in dense environments

We present observations of $^{13}$CO(1-0) in 17 Combined Array for Research in Millimeter Astronomy (CARMA) Atlas3D early-type galaxies (ETGs), obtained simultaneously with $^{12}$CO(1-0) observations. The $^{13}$CO in six ETGs is sufficiently bright to create images. In these 6 sources, we do not detect any significant radial gradient in the $^{13}$CO/$^{12}$CO ratio between the nucleus and the outlying molecular gas. Using the $^{12}$CO channel maps as 3D masks to stack the $^{13}$CO emission, we are able to detect 15/17 galaxies to $>3\sigma$ (and 12/17 to at least 5$\sigma$) significance in a spatially integrated manner. Overall, ETGs show a wide distribution of $^{13}$CO/$^{12}$CO ratios, but Virgo cluster and group galaxies preferentially show a $^{13}$CO/$^{12}$CO ratio about 2 times larger than field galaxies, although this could also be due to a mass dependence, or the CO spatial extent ($R_{\rm CO}/R_{\rm e}$). ETGs whose gas has a morphologically-settled appearance also show boosted $^{13}$CO/$^{12}$CO ratios. We hypothesize that this variation could be caused by (i) the extra enrichment of gas from molecular reprocessing occurring in low-mass stars (boosting the abundance of $^{13}$C to $^{12}$C in the absence of external gas accretion), (ii) much higher pressure being exerted on the midplane gas (by the intracluster medium) in the cluster environment than in isolated galaxies, or (iii) all but the densest molecular gas clumps being stripped as the galaxies fall into the cluster. Further observations of $^{13}$CO in dense environments, particularly of spirals, as well as studies of other isotopologues, should be able to distinguish between these hypotheses.Comment: 13 pages, 3 tables, 7 figures, accepted by MNRA

Accretion-Inhibited Star Formation in the Warm Molecular Disk of the Green-valley Elliptical Galaxy NGC 3226

We present archival Spitzer photometry and spectroscopy, and Herschel photometry, of the peculiar "Green Valley" elliptical galaxy NGC~3226. The galaxy, which contains a low-luminosity AGN, forms a pair with NGC~3227, and is shown to lie in a complex web of stellar and HI filaments. Imaging at 8 and 16$\mu$m reveals a curved plume structure 3 kpc in extent, embedded within the core of the galaxy, and coincident with the termination of a 30 kpc-long HI tail. In-situ star formation associated with the IR plume is identified from narrow-band HST imaging. The end of the IR-plume coincides with a warm molecular hydrogen disk and dusty ring, containing 0.7-1.1 $\times$ 10$^7$ M$_{\odot}$ detected within the central kpc. Sensitive upper limits to the detection of cold molecular gas may indicate that a large fraction of the H$_2$ is in a warm state. Photometry, derived from the UV to the far-IR, shows evidence for a low star formation rate of $\sim$0.04 M$_{\odot}$ yr$^{-1}$ averaged over the last 100 Myrs. A mid-IR component to the Spectral Energy Distribution (SED) contributes $\sim$20$\%$ of the IR luminosity of the galaxy, and is consistent with emission associated with the AGN. The current measured star formation rate is insufficient to explain NGC3226's global UV-optical "green" colors via the resurgence of star formation in a "red and dead" galaxy. This form of "cold accretion" from a tidal stream would appear to be an inefficient way to rejuvenate early-type galaxies, and may actually inhibit star formation.Comment: Accepted for Publication ApJ Oct 201