405 research outputs found
Origin of the wide-angle hot H2 in DG Tauri: New insight from SINFONI spectro-imaging
We wish to test the origins proposed for the extended hot H2 at 2000K around
the atomic jet from the T Tauri star DGTau, in order to constrain the
wide-angle wind structure and the possible presence of an MHD disk wind. We
present flux calibrated IFS observations in H2 1-0 S(1) obtained with
SINFONI/VLT. Thanks to spatial deconvolution by the PSF and to accurate
correction for uneven slit illumination, we performed a thorough analysis and
modeled the morphology, kinematics, and surface brightness. We also compared
our results with studies in [FeII], [OI], and FUV-pumped H2. The
limb-brightened H2 emission in the blue lobe is strikingly similar to
FUV-pumped H2 imaged 6yr later, confirming that they trace the same hot gas and
setting an upper limit of 12km/s on any expansion proper motion. The wide-angle
H2 rims are at lower blueshifts than probed by narrow long-slit spectra. We
confirm that they extend to larger angle and to lower speed the onion-like
velocity structure observed in optical atomic lines. The latter is shown to be
steady over more/equal than 4yr but undetected in [FeII] by SINFONI, probably
due to strong iron depletion. The H2 rim thickness less/equal than 14AU rules
out excitation by C-shocks, and J-shock speeds are constrained to 10km/s. We
find that explaining the H2 wide-angle emission with a shocked layer requires
either a recent outburst (15yr) into a pre-existing ambient outflow or an
excessive wind mass flux. A slow photoevaporative wind from the dense
irradiated disk surface and an MHD disk wind heated by ambipolar diffusion seem
to be more promising and need to be modeled in more detail
Self-imaging through incoherent to coherent conversion
The self-imaging phenomenon is realized by utilizing an incoherent to coherent converter. For this purpose, a photorefractive BSO crystal that becomes uniformly birefringent due to an external applied voltage is employed. Then, an incoherently illuminated one-dimensional grating that locally modulates the induced birefringence is registered. In the readout process, a linearly polarized plane wave from a He-Ne laser is utilized. The ellipticity of the light exiting the crystal will be determined according to the local birefringence. Then, after passing through a polarizer, the coherent output will reproduce the incoherent input. In this way, under free propagation, coherent replicas of the grating will be obtained
Linking attentional processes and conceptual problem solving: visual cues facilitate the automaticity of extracting relevant information from diagrams
This study investigated links between visual attention processes and conceptual problem solving. This was done by overlaying visual cues on conceptual physics problem diagrams to direct participants’ attention to relevant areas to facilitate problem solving. Participants (N = 80) individually worked through four problem sets, each containing a diagram, while their eye movements were recorded. Each diagram contained regions that were relevant to solving the problem correctly and separate regions related to common incorrect responses. Problem sets contained an initial problem, six isomorphic training problems, and a transfer problem. The cued condition saw visual cues overlaid on the training problems. Participants’ verbal responses were used to determine their accuracy. This study produced two major findings. First, short duration visual cues which draw attention to solution-relevant information and aid in the organizing and integrating of it, facilitate both immediate problem solving and generalization of that ability to new problems. Thus, visual cues can facilitate re-representing a problem and overcoming impasse, enabling a correct solution. Importantly, these cueing effects on problem solving did not involve the solvers’ attention necessarily embodying the solution to the problem, but were instead caused by solvers attending to and integrating relevant information in the problems into a solution path. Second, this study demonstrates that when such cues are used across multiple problems, solvers can automatize the extraction of problem-relevant information extraction. These results suggest that low-level attentional selection processes provide a necessary gateway for relevant information to be used in problem solving, but are generally not sufficient for correct problem solving. Instead, factors that lead a solver to an impasse and to organize and integrate problem information also greatly facilitate arriving at correct solutions
Theory of orientational ordering in colloidal molecular crystals
Freezing of charged colloids on square or triangular two-dimensional periodic
substrates has been recently shown to realize a rich variety of orientational
orders. We propose a theoretical framework to analyze the corresponding
structures. A fundamental ingredient is that a non spherical charged object in
an electrolyte creates a screened electrostatic potential that is anisotropic
at any distance. Our approach is in excellent agreement with the known
experimental and numerical results, and explains in simple terms the reentrant
orientational melting observed in these so called colloidal molecular crystals.
We also investigate the case of a rectangular periodic substrate and predict an
unusual phase transition between orientationnaly ordered states, as the aspect
ratio of the unit cell is changed.Comment: 4 pages, to appear in Phys. Rev. Let
Valid inequalities for a single constrained 0-1 MIP set intersected with a conflict graph
In this paper a mixed integer set resulting from the intersection of a single constrained mixed 0–1 set with the vertex packing set is investigated. This set arises as a subproblem of more general mixed integer problems such as inventory routing and facility location problems. Families of strong valid inequalities that take into account the structure of the simple mixed integer set and that of the vertex packing set simultaneously are introduced. In particular, the well-known mixed integer rounding inequality is generalized to the case where incompatibilities between binary variables are present. Exact and heuristic algorithms are designed to solve the separation problems associated to the proposed valid inequalities. Preliminary computational experiments show that these inequalities can be useful to reduce the integrality gaps and to solve integer programming problems
Measurement of the conductance of a hydrogen molecule
Recent years have shown steady progress in research towards molecular
electronics [1,2], where molecules have been investigated as switches [3-5],
diodes [6], and electronic mixers [7]. In much of the previous work a Scanning
Tunnelling Microscope was employed to address an individual molecule. As this
arrangement does not provide long-term stability, more recently
metal-molecule-metal links have been made using break junction devices [8-10].
However, it has been difficult to establish unambiguously that a single
molecule forms the contact [11]. Here, we show that a single H2 molecule can
form a stable bridge between Pt electrodes. In contrast to results for other
organic molecules, the bridge has a nearly perfect conductance of one quantum
unit, carried by a single channel. The H2-bridge provides a simple test system
and a fundamental step towards understanding transport properties of
single-molecule devices.Comment: 6 pages, 4 figure
Lagrangian relaxation bounds for a production-inventory-routing problem
We consider a single item Production-Inventory-Routing problem with a
single producer/supplier and multiple retailers. Inventory management constraints are considered both at the producer and at the retailers, following a vendor managed inventory approach, where the supplier monitors the inventory at retailers and decides on the replenishment policy for each retailer. We assume a constant production capacity.
Based on the mathematical formulation we discuss a classical Lagrangian relaxation
which allows to decompose the problem into four subproblems, and a new Lagrangian
decomposition which decomposes the problem into just a production-inventory subproblem
and a routing subproblem. The new decomposition is enhanced with valid
inequalities. A computational study is reported to compare the bounds from the two
approaches
Committed to restoring tropical forests: an overview of Brazil’s and Indonesia’s restoration targets and policies
The restoration of tropical forests has become a popular nature-based solution for climate change mitigation, protection of biodiversity, and improving the livelihoods of local populations. The Bonn Challenge and the UN Decade on Ecosystem Restoration underscore the international momentum of the restoration movement, with many countries committing to restore millions of hectares of deforested and degraded land in the next decade. Brazil and Indonesia are among the ones with the most ambitious restoration commitments globally. Since both their economies are highly dependent on the export of agricultural commodities, reconciling economic growth with environmental sustainability will be a major policy challenge. In this paper, we (a) identify the main restoration targets and the policies supporting their implementation in both countries, (b) provide a descriptive overview of these restoration-supportive policies, and (c) discuss the main challenges that Brazil and Indonesia face in the implementation of their restoration commitments. We find that Brazil has an explicit and dedicated strategy to achieve its restoration target, but that recent political developments have weakened environmental governance in the country, affecting the implementation of its restoration commitment. In the case of Indonesia, we find that the government has rather focused and progressed on the restoration of peatlands and mangroves, whereas its commitment to restore forestlands has yet to benefit from a dedicated plan that allows to coordinate policies and agencies’ efforts towards the achievement of its restoration target
Considerations in the determination of orientational order parameters from X-ray scattering experiments
An assessment of the data processing and analysis methods used to obtain the second- and fourth-rank orientational order parameters of liquid crystals from X-ray scattering experiments has been carried out, using experimental data from four extensively studied alkyl-cyanobiphenyls and calculated data generated from two general types of theoretical orientational distribution function. The application of a background subtraction and two different baseline correction methods to the scattering profiles is assessed, along with three different methods to analyse the processed data. The choice of baseline correction method is shown to have a significant effect: an offset to zero overestimates the order parameters from the experimental and calculated data sets, particularly for lower order parameters arising from broad distributions, whereas an offset to a value estimated from regions of low scattering intensity provides experimental values close to those reported from other experimental techniques. By contrast, the three different analysis methods are shown generally to result in relatively small absolute differences between the order parameters. We outline a straightforward general approach to experimental X-ray scattering data processing and analysis for uniaxial phases that results in order parameters that match well with those reported using other experimental techniques
New sulphated flavonoids from Wissadula periplocifolia (L.) C. Presl (Malvaceae)
Wissadula periplocifolia (L.) C. Presl (Malvaceae) is commonly used in Brazil to treat bee stings and as an antiseptic. The antioxidant properties of its extracts have been previously demonstrated, thus justifying a phytochemical investigation for its bioactive phenolic constituents. This has yielded five new sulphated flavonoids: 8-O-sulphate isoscutellarein (yannin) (1a); 4'-O-methyl-7-O-sulphate isoscutellarein (beltraonin) (1b); 7-O-sulphate acacetin (wissadulin) (2a); 4'-O-methyl-8-O-sulphate isoscutellarein (caicoine) (2b) and 3'-O-methyl-8-O-sulphate hypolaetin (pedroin) (3b) along with the known flavonoids 7,4'-di-O-methyl-8-O-sulphate isoscutellarein (4), acacetin, apigenin, isoscutellarein, 4´-O-methyl isoscutellarein, 7,4'-di-O-methylisoscutellarein, astragalin and tiliroside. The compounds were isolated by column chromatography and identified by NMR (¹H, (13)C, HMQC, HMBC and COSY) and LC-HRMS. A cell based assay was carried out to evaluate the preliminary cytotoxic properties of the flavonoids against UVW glioma and PC-3M prostate cancer cells as well as non-tumour cell lines. The obtained results showed that acacetin, tiliroside, a mixture of acacetin + apigenin and the sulphated flavonoids 2a + 2b exhibited inhibitory activity against at least one of the cell lines tested. Among the tested flavonoids acacetin and tiliroside showed lower IC50 values, presenting promising antitumor effects
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