2,096 research outputs found

    D- shallow donor near a semiconductor-metal and a semiconductor-dielectric interface

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    The ground state energy and the extend of the wavefunction of a negatively charged donor (D-) located near a semiconductor-metal or a semiconductor-dielectric interface is obtained. We apply the effective mass approximation and use a variational two-electron wavefunction that takes into account the influence of all image charges that arise due to the presence of the interface, as well as the correlation between the two electrons bound to the donor. For a semiconductor-metal interface, the D- binding energy is enhanced for donor positions d>1.5a_B (a_B is the effective Bohr radius) due to the additional attraction of the electrons with their images. When the donor approaches the interface (i.e. d<1.5a_B) the D- binding energy drops and eventually it becomes unbound. For a semiconductor-dielectric (or a semiconductor-vacuum) interface the D- binding energy is reduced for any donor position as compared to the bulk case and the system becomes rapidly unbound when the donor approaches the interface.Comment: Submitted to Phys. Rev. B on 19 November 200

    Refined EnE_n Chern-Simons theory

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    The partition function of refined Chern-Simons theory on 3d sphere for the exceptional EnE_n gauge algebras is presented in terms of multiple sine functions. Gopakumar-Vafa (BPS) approximation is calculated and presented in the form of some refined topological string partition function.Comment: On the basis of the talk given at the workshop SQS'2

    Two-fold refinement of non simply laced Chern-Simons theories

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    Inspired by the two-parameter Macdonald-Cherednik deformation of the formulae for non simply laced simple Lie algebras, we propose a two-fold refinement of the partition function of the corresponding Chern-Simons theory on S3S^3. It is based on a two-fold refinement of the Kac-Peterson formula for the volume of the fundamental domain of the coroot lattice of non simply laced Lie algebras. We further derive explicit integral representations of the two-fold refined Chern-Simons partition functions. We also present the corresponding generalized universal-like expressions for them. With these formulae in hand, one can try to investigate a possible duality of the corresponding Chern-Simons theories with hypothetical two-fold refined topological string theories.Comment: LaTex, 8 page

    Structured diabetes self-management education and its association with perceived diabetes knowledge, information, and disease distress: Results of a nationwide population-based study

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    Objective: To evaluate, how participation in structured diabetes self-management education (DSME) programs is associated with perceived level of knowledge about diabetes, information needs, information sources and disease distress. Methods: We included 796 ever- and 277 never-DSME participants of the population-based survey “Disease knowledge and information needs - Diabetes mellitus (2017)” from Germany. Data on perceived level of diabetes knowledge (12 items), information needs (11 items), information sources (13 items) and disease distress (2 indices) were collected. Multiple logistic regression analyses were used to examine the association of DSME-participation with these outcomes. Results: DSME-participants showed a higher level of diabetes knowledge compared to never-DSME participants, particularly in aspects concerning diabetes in general (odds ratio 2.53; 95% confidence intervals 1.48–4.33), treatment (2.41; 1.36–4.26), acute complications (1.91; 1.07–3.41) and diabetes in everyday life (1.83; 1.04–3.22). DSME-participants showed higher information needs regarding late complications (1.51; 1.04–2.18) and acute complications (1.71; 1.71–2.48) than DSME never participants. DSME-participants more frequently consulted diabetologists (5.54; 3.56–8.60) and diabetes care specialists (5.62; 3.61–8.75) as information sources. DSME participation was not associated with disease distress. Conclusion: DSME is a valuable tool for improving individual knowledge about diabetes. However, DSME should focus more on psychosocial aspects to reduce the disease burden

    Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor

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    We report on the layer thickness determination on dielectrically coated metal cylinders using terahertz (THz) time-domain spectroscopy. A considerable sensitivity increase of up to a factor of 150 is obtained for layers down to 2.5 um thickness by introducing an experimental geometry based on a two-cylinder waveguide sensor. The layer attached on one metal cylinder is guided in contact with the second metal cylinder in the THz beam waist. This approach uses concepts of adiabatic THz wave compression and the advantages of THz waveguides. The results are compared to measurements on free-standing layers.Peer reviewedElectrical and Computer Engineerin

    Explosions of water clusters in intense laser fields

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    Energetic, highly-charged oxygen ions, Oq+O^{q+} (q6q\leq 6), are copiously produced upon laser field-induced disassembly of highly-charged water clusters, (H2O)n(H_2O)_n and (D2O)n(D_2O)_n, nn\sim 60, that are formed by seeding high-pressure helium or argon with water vapor. ArnAr_n clusters (n\sim40000) formed under similar experimental conditions are found undergo disassembly in the Coulomb explosion regime, with the energies of Arq+Ar^{q+} ions showing a q2q^2 dependence. Water clusters, which are argued to be considerably smaller in size, should also disassemble in the same regime, but the energies of fragment Oq+^{q+} ions are found to depend linearly on qq which, according to prevailing wisdom, ought to be a signature of hydrodynamic expansion that is expected of much larger clusters. The implication of these observations on our understanding of the two cluster explosion regimes, Coulomb explosion and hydrodynamic expansion, is discussed. Our results indicate that charge state dependences of ion energy do not constitute an unambiguous experimental signature of cluster explosion regime.Comment: Submitted to Phys. Rev.

    Continuous-distribution puddle model for conduction in trilayer graphene

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    An insulator-to-metal transition is observed in trilayer graphene based on the temperature dependence of the resistance under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.Comment: 18 pages, 5 figure
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