654 research outputs found
How would you integrate the equations of motion in dissipative particle dynamics simulations?
In this work we assess the quality and performance of several novel
dissipative particle dynamics integration schemes that have not previously been
tested independently. Based on a thorough comparison we identify the respective
methods of Lowe and Shardlow as particularly promising candidates for future
studies of large-scale properties of soft matter systems
Integrating modes of policy analysis and strategic management practice : requisite elements and dilemmas
There is a need to bring methods to bear on public problems that are inclusive, analytic, and quick. This paper describes the efforts of three pairs of academics working from three different though complementary theoretical foundations and intervention backgrounds (i.e., ways of working) who set out together to meet this challenge. Each of the three pairs had conducted dozens of interventions that had been regarded as successful or very successful by the client groups in dealing with complex policy and strategic problems. One approach focused on leadership issues and stakeholders, another on negotiating competitive strategic intent with attention to stakeholder responses, and the third on analysis of feedback ramifications in developing policies. This paper describes the 10 year longitudinal research project designed to address the above challenge. The important outcomes are reported: the requisite elements of a general integrated approach and the enduring puzzles and tensions that arose from seeking to design a wide-ranging multi-method approach
The evolution of faint AGN between z~1 and z~5 from the COMBO-17 survey
We present a determination of the optical/UV AGN luminosity function and its
evolution, based on a large sample of faint (R<24) QSOs identified in the
COMBO-17 survey. Using multi-band photometry in 17 filters within 350nm <
lambda_obs < 930nm, we could simultaneously determine photometric redshifts
with an accuracy of sigma_z<0.03 and obtain spectral energy distributions. The
redshift range covered by the sample is 1.2<z<4.8, which implies that even at
z~3, the sample reaches below luminosities corresponding to M_B = -23,
conventionally employed to distinguish between Seyfert galaxies and quasars. We
clearly detect a broad plateau-like maximum of quasar activity around z~2 and
map out the smooth turnover between z~1 and z~4. The shape of the LF is
characterised by some mild curvature, but no sharp `break' is present within
the range of luminosities covered. Using only the COMBO-17 data, the evolving
LF can be adequately described by either a pure density evolution (PDE) or a
pure luminosity evolution (PLE) model. However, the absence of a strong L*-like
feature in the shape of the LF inhibits a robust distinction between these
modes. We present a robust estimate for the integrated UV luminosity generation
by AGN as a function of redshift. We find that the LF continues to rise even at
the lowest luminosities probed by our survey, but that the slope is
sufficiently shallow that the contribution of low-luminosity AGN to the UV
luminosity density is negligible. Although our sample reaches much fainter flux
levels than previous data sets, our results on space densities and LF slopes
are completely consistent with extrapolations from recent major surveys such as
SDSS and 2QZ.Comment: 17 pages, 14 figures, Astronomy & Astrophysics, in print, revised
versio
Dental students’ perceptions of learning communication skills in a forum theatre-style teaching session on breaking bad news
Introduction: Communication skills are an integral component of dental undergraduate education. Due to the complex nature of these skills, didactic teaching methods used in other educational contexts can be limited. Interactive and participative methods rooted in modern adult learning theories, such as Forum Theatre, may be more effective in the teaching of communication skills. Aim: To explore the usefulness of Forum Theatre in teaching clinical undergraduate dental students how to break bad news to their patients.Methods: A purposive sample of 4th-year undergraduate dental students was invited to participate. An evaluation questionnaire was given to the students and collected after the Forum Theatre interactive session. Participants were asked to provide self-reported accounts on the most and least useful parts of the session, as well as the most important learning outcome. Usefulness of the session in clinical work, increasing confidence and ability in breaking bad news, were evaluated via a 5-point Likert-scale type question. Qualitative data were analysed using Framework Analysis to explore the themes found in the open-text component. Descriptive statistics were used to analyse the Likert-scale items.Results: One hundred and fifteen completed questionnaires were collected from the 2015 and 2016 classes. Most students gave the Forum Theatre session a rating of 3 or above on a 5-point Likert scale; indicating that they found it useful. Qualitative results also showed that most participants liked the teaching session thanks to its interactive nature, the use of actors and the input of the facilitators. The majority of students showed preference towards smaller groups which give everyone equal opportunity to participate without unnecessary repetition.Conclusion: The results seem to confirm previous findings. Students rated their learning experience involving Forum Theatre favourably. Smaller groups and trained facilitators are required for the success of this teaching method. Further research is needed to assess the long-term educational benefits of Forum Theatre.</p
BCS to Bose Crossover in Anisotropic Superconductors
In this work we use functional integral techniques to examine the nearest
neighbour attractive Hubbard model on a quasi-2D lattice. It is a simple
phenomenological model for the high-Tc cuprates that allows both extended
(non-local) s- and d-wave singlet superconductivity as well as mixed symmetry
states. The Hartree-Gor'kov mean field theory of the model has a finite
temperature phase diagram which shows a transition from pure s-wave to pure
d-wave superconductivity, via a mixed symmetry s+id state, as a function of
doping. Including Gaussian fluctuations we examine the crossover from
weak-coupling BCS superconductivity to the strong-coupling Bose-Einstein
condensation of composite s- or d-wave bosons and comment on the origin and
symmetry of the pseudogap.Comment: 20 pages inc. 13 figure
Strategies for prompt searches for GRB afterglows: the discovery of the GRB 001011 optical/near-infrared counterpart using colour-colour selection
We report the discovery of the optical and near-infrared counterparts to GRB
001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously
imaged in the near-infrared by the 3.58-m New Technology Telescope and in the
optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we
implement the colour-colour discrimination technique proposed by Rhoads (2001)
and extend it using near-IR data as well. We present the results provided by an
automatic colour-colour discrimination pipe-line developed to discern the
different populations of objects present in the GRB 001011 error box. Our
software revealed three candidates based on single-epoch images. Second-epoch
observations carried out ~3.2 days after the burst revealed that the most
likely candidate had faded, thus identifying it with the counterpart to the
GRB. In deep R-band images obtained 7 months after the burst a faint
(R=25.38+/-0.25) elongated object, presumably the host galaxy of GRB 001011,
was detected at the position of the afterglow. The GRB 001011 afterglow is the
first discovered with the assistance of colour-colour diagram techniques. We
discuss the advantages of using this method and its application to error boxes
determined by future missions.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 16
figure
Deep Ly-alpha imaging of two z=2.04 GRB host galaxy fields
We report on the results of deep narrow-band Ly-alpha, U and I imaging of the
fields of two GRBs at z=2.04 (GRB 000301C and GRB 000926). We find that the
host galaxy of GRB 000926 is an extended, strong Ly-alpha emitter with a
rest-frame equivalent width of 71+20-15 AA. The galaxy consists of two main
components and several fainter knots. GRB 000926 occurred in the western
component, whereas most of the Ly-alpha luminosity (about 65%) originates in
the eastern component. Using archival HST images of the host galaxy we measure
the spectral slopes (f_lambda prop. to lambda^beta) of the two components to
beta = -2.4+-0.3 (east) and -1.4+-0.2 (west). This implies that both components
contain at most small amounts of dust, consistent with the observed strong
Ly-alpha emission. The western component has a slightly redder V-I colour than
the eastern component, suggesting the presence of at least some dust. We do not
detect the host galaxy of GRB 000301C in neither Ly-alpha emission nor in U and
I-band images. We infer a limit of U(AB)>27.7 (2-sigma limit per arcsec^2). The
upper limits on the Ly-alpha flux implies a Ly-alpha equivalent width upper
limit of 150AA. We find 11 and 8 other galaxies with excess emission in the
narrow filter in the fields of GRB 000301C and GRB 000926 respectively. Based
on these detections we conclude that GRB 000926 occurred in one of the
strongest centres of star formation within several Mpc, whereas GRB 000301C
occurred in an intrinsically very faint galaxy far from being the strongest
centre of star formation in its galactic environment. Under the hypothesis that
GRBs trace star formation, the wide range of GRB host galaxy luminosities
implies a very steep faint end slope of the high redshift galaxy luminosity
function.Comment: 13 pages, 7 figures. Accepted for publication in A&
Relative energetics and structural properties of zirconia using a self-consistent tight-binding model
We describe an empirical, self-consistent, orthogonal tight-binding model for
zirconia, which allows for the polarizability of the anions at dipole and
quadrupole levels and for crystal field splitting of the cation d orbitals.
This is achieved by mixing the orbitals of different symmetry on a site with
coupling coefficients driven by the Coulomb potentials up to octapole level.
The additional forces on atoms due to the self-consistency and polarizabilities
are exactly obtained by straightforward electrostatics, by analogy with the
Hellmann-Feynman theorem as applied in first-principles calculations. The model
correctly orders the zero temperature energies of all zirconia polymorphs. The
Zr-O matrix elements of the Hamiltonian, which measure covalency, make a
greater contribution than the polarizability to the energy differences between
phases. Results for elastic constants of the cubic and tetragonal phases and
phonon frequencies of the cubic phase are also presented and compared with some
experimental data and first-principles calculations. We suggest that the model
will be useful for studying finite temperature effects by means of molecular
dynamics.Comment: to be published in Physical Review B (1 march 2000
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Circulating vitamin D concentrations and risk of breast and prostate cancer: a Mendelian randomization study.
BACKGROUND: Observational studies have suggested an association between circulating vitamin D concentrations [25(OH)D] and risk of breast and prostate cancer, which was not supported by a recent Mendelian randomization (MR) analysis comprising 15 748 breast and 22 898 prostate-cancer cases. Demonstrating causality has proven challenging and one common limitation of MR studies is insufficient power. METHODS: We aimed to determine whether circulating concentrations of vitamin D are causally associated with the risk of breast and prostate cancer, by using summary-level data from the largest ever genome-wide association studies conducted on vitamin D (N = 73 699), breast cancer (Ncase = 122 977) and prostate cancer (Ncase = 79 148). We constructed a stronger instrument using six common genetic variants (compared with the previous four variants) and applied several two-sample MR methods. RESULTS: We found no evidence to support a causal association between 25(OH)D and risk of breast cancer [OR per 25 nmol/L increase, 1.02 (95% confidence interval: 0.97-1.08), P = 0.47], oestrogen receptor (ER)+ [1.00 (0.94-1.07), P = 0.99] or ER- [1.02 (0.90-1.16), P = 0.75] subsets, prostate cancer [1.00 (0.93-1.07), P = 0.99] or the advanced subtype [1.02 (0.90-1.16), P = 0.72] using the inverse-variance-weighted method. Sensitivity analyses did not reveal any sign of directional pleiotropy. CONCLUSIONS: Despite its almost five-fold augmented sample size and substantially improved statistical power, our MR analysis does not support a causal effect of circulating 25(OH)D concentrations on breast- or prostate-cancer risk. However, we can still not exclude a modest or non-linear effect of vitamin D. Future studies may be designed to understand the effect of vitamin D in subpopulations with a profound deficiency
Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects
Insect steroid hormones (ecdysteroids) are important for female reproduction in many insect species and are required for the initiation and coordination of vital developmental processes. Ecdysteroids are also important for adult male physiology and behavior, but their exact function and site of synthesis remains unclear, although previous studies suggest that the reproductive system may be their source. We have examined expression profiles of the ecdysteroidogenic Halloween genes, during development and in adults of the flour beetle Tribolium castaneum. Genes required for the biosynthesis of ecdysone (E), the precursor of the molting hormone 20-hydroxyecdysone (20E), are expressed in the tubular accessory glands (TAGs) of adult males. In contrast, expression of the gene encoding the enzyme mediating 20E synthesis was detected in the ovaries of females. Further, Spookiest (Spot), an enzyme presumably required for endowing tissues with competence to produce ecdysteroids, is male specific and predominantly expressed in the TAGs. We also show that prothoracicotropic hormone (PTTH), a regulator of E synthesis during larval development, regulates ecdysteroid levels in the adult stage in Drosophila melanogaster and the gene for its receptor Torso seems to be expressed specifically in the accessory glands of males. The composite results suggest strongly that the accessory glands of adult male insects are the main source of E, but not 20E. The finding of a possible male-specific source of E raises the possibility that E and 20E have sex-specific roles analogous to the vertebrate sex steroids, where males produce primarily testosterone, the precursor of estradiol. Furthermore this study provides the first evidence that PTTH regulates ecdysteroid synthesis in the adult stage and could explain the original finding that some adult insects are a rich source of PTTH
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