Effect of multilayer barriers on the optical properties of GaInNAs single quantum-well structures grown by metalorganic vapor phase epitaxy

We report on the effects of combined strain-compensating and strain-mediating layers of various widths on the optical properties of 1.3 μm GaInNAs∕GaAs single quantum well structures grown by metalorganic vapor phase epitaxy (MOVPE). While the emission wavelength of GaInNAs∕GaAs quantum wells can be redshifted by the adoption of strain-compensated GaNAs layers, the material quality is degraded by the increased stress at the well∕barrier interface. This detrimental effect can be cured by inserting a strain-mediating InGaAs layer between them. Contrary to what is expected, however, the emission wavelength is blueshifted by the insertion of the InGaAs layer, which is attributed to the reduced N incorporation due to the improved interface quality. Our results indicate that the optical properties of MOVPE-grown GaInNAs∕GaAs quantum wells can be optimized in quantum efficiency and emission wavelength by combination of strain-compensating and strain-mediating layers with suitable characteristics

Gauge coupling Unification and SO(10) in 5D

We analyze the gauge unification in minimal supersymmetric SO(10) grand unified theories in 5 dimensions. The single extra spatial dimension is compactified on the orbifold S^1/(Z_2 x Z_2') reducing the gauge group to that of Pati-Salam SU(4)_c x SU(2)_L x SU(2)_R. The Standard Model gauge group is achieved by the further brane-localized Higgs mechanism on one of the fixed points. There are two main different approaches developed in literature. Higgs mechanism can take place on the Pati Salam brane, or on the SO(10) preserving brane. We show, both analytically and numerically, that in the first case a natural and succesfull gauge coupling unification can be achieved, while the second case is highly disfavoured. For completeness, we consider either the case in which the brane breaking scale is near the cutoff scale or the case in which it is lower than the compactification scale.Comment: 18 Pages and 8 PostScript Figure

Spectroscopic characterization of 1.3µm GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy

We report optical studies of high-quality 1.3 μm strain-compensated GaInNAs/GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum

HIGH PRANDTL NUMBER MIXED CONVECTION CAVITY FLOW USING LATTICE BOLTZMANN METHOD

The mixed convection heat transfer and fluid flow behaviors in a lid–driven square cavity filled with high Prandtl number fluids at low Reynolds number have been studied using Thermal Lattice Boltzmann Method (TLBM). The LBM has built up on the D2Q9 model called the Lattice-BGK (Bhatnagar–Gross–Krook) model. The Lattice Boltzmann momentum and energy equations are considered simultaneously to solve the problem. Effects of non dimensional mixed convection parameter, namely buoyancy parameter or Richardson number (Ri) in presence of heat generation (q) with moving lid are discussed to investigate the thermal and fluid flow behaviors. It deals with continuing and comparison study of authors recent published work (Taher et al. 2013). The results are presented as velocity and temperature profiles as well as stream function and temperature contours for 0.50 ≤ Ri ≤ 10.0 and q ranging from 0.0 to 0.10 with other controlling parameters. It is found that LBM has good potential to simulate mixed convection heat transfer and fluid flow problems. The mixed convection parameter, Ri, provides an important measurement of the thermal natural convection forces relative to the mechanically induced lid-driven forced convection with heat generation (q) effects. Moreover, it is found that the overall heat transfer rate in terms of Nusselt number (Nu) are significantly increased with increasing Ri and decreased very slightly with increasing the values of heat generation. Finally, the simulation results have been compared with the previous numerical and experimental results and it is found to be in good agreement

Fermion masses and proton decay in a minimal five-dimensional SO(10) model

We propose a minimal SO(10) model in 5 space-time dimensions. The single extra spatial dimension is compactified on the orbifold S^1/(Z_2 x Z_2') reducing the gauge group to that of Pati-Salam. The breaking down to the standard model group is obtained through an ordinary Higgs mechanism taking place at the Pati-Salam brane, giving rise to a proper gauge coupling unification. We achieve a correct description of fermion masses and mixing angles by describing first and second generations as bulk fields, and by embedding the third generation into four multiplets located at the Pati-Salam brane. The Yukawa sector is simple and compact and predicts a neutrino spectrum of normal hierarchy type. Concerning proton decay, dimension five operators are absent and the essentially unique localization of matter multiplets implies that the minimal couplings between the super-heavy gauge bosons and matter fields are vanishing. Non-minimal interactions are allowed but the resulting dimension six operators describing proton decay are too suppressed to produce observable effects, even in future, super-massive detectors.Comment: 21 pages, 3 figure

Neutrinos in 5D SO(10) Unification

We study neutrino physics in a 5D supersymmetric SO(10) GUT. We analyze several different choices for realizing the See-Saw mechanism. We find that the "natural" scale for the Majorana mass of right-handed neutrinos depends critically on whether the right-handed neutrinos are located in the bulk or localized on a brane. In the former case, the effective Majorana mass is "naturally" of order the compactification scale, about 10^{14} GeV. Note, this is the value necessary for obtaining a light tau neutrino mass approximately 10^{-2} eV which, within the context of hierarchical neutrino masses, is the right order of magnitude to explain atmospheric neutrino oscillations. On the other-hand when the right-handed neutrino is localized on the brane, the effective Majorana mass is typically larger than the compactification scale. Nevertheless with small parameters of order 1/10 - 1/30, an effective Majorana mass of order 10^{14} GeV can be accommodated. We also discuss the constraints on model building resulting from the different scenarios for locating the right-handed neutrinos.Comment: 24 page

Key stakeholder voices:Investigating student perceptions of teachers’ use of assessment for learning

Many schools aim to implement Assessment for Learning (AfL) to stimulate students to take more ownership of their learning and develop self-regulatory skills. This survey-based study is among the few in the field showing how students experience the extent of implementation of AfL, here in English language and mathematics classes in 12 Dutch secondary schools. Analysis showed no differences between the subjects. Students (N = 685) experienced activities to clarify the learning intentions and success criteria and eliciting evidence on their learning progress regularly (between 50–74% of the lessons). Students hardly ever experienced activities aimed at peer- and self-assessment (less than 25% of the lessons). However, cluster analysis revealed three distinct clusters related to the extent of AfL strategy use students experienced. Overall, we can conclude that AfL is not yet fully integrated into teaching practices. Teachers’ skills, knowledge and attitudes required to increase student engagement in AfL practices and strengthen students’ self-regulated learning need more attention in future teacher professional development trajectories.</p

Quark and Lepton Masses in 5D SO(10)

We construct a five dimensional supersymmetric SO(10)$\times$D$_3$ grand unified model with an $S^1/(Z_2 \times Z^\prime_2)$ orbifold as the extra dimension. The orbifold breaks half of the supersymmetry and breaks the SO(10) gauge symmetry down to ${\rm SU(4)}_C \times {\rm SU(2)}_L \times {\rm SU(2)}_R$. The Higgs mechanism is used to break the remaining gauge symmetry the rest of the way to the Standard Model. We place matter fields variously in the bulk and on the orbifold fixed points and the resulting massless fields are mixtures between these brane and bulk fields. A chiral adjoint field in the bulk gets a U(1)$_X$ vacuum expectation value, resulting in an $X$-dependent localization of the bulk matter fields and the Standard Model Higgs field. This Higgs field localization allows us to simultaneously explain the hierarchies $m_u < m_d$ and $m_t \gg m_b$. The model uses 11 parameters to fit the 13 independent low energy observables of the quark and charged lepton Yukawa matrices. The model predicts the values of two quark mass combinations, \f{m_u}{m_c} and $m_d m_s m_b$, each of which are predicted to be approximately $1 \sigma$ above their experimental values. The remaining observables are successfully fit at the 5% level.Comment: 52 pages, published version, includes more discussion of 6D version of mode

The Phase Structure of Supersymmetric Sp(2N_c) Gauge Theories with an Adjoint

We study the phase structure of N = 1 supersymmetric Sp(2N_c) gauge theories with 2N_f fundamentals, an adjoint, and vanishing superpotential. Using a-maximization, we derive analytic expressions for the values of N_f below which the first several gauge-invariant operators in the chiral ring violate the unitarity bound and become free fields. In doing so we are able to explicitly check previous conjectures about the behavior of this theory made by Luty, Schmaltz, and Terning. We then compare this to an analysis of the first two 'deconfined' dual descriptions based on the gauge groups Sp(2N_f+2) x SO(2N_c+5) and Sp(2N_f+2) x SO(4N_f+4) x Sp(2N_c+2), finding precise agreement. In particular, we find no evidence for non-obvious accidental symmetries or the appearance of a mixed phase in which one of the dual gauge groups becomes free.Comment: 18 pages, 2 figures; v2: added references to match JHEP versio

5D seesaw, flavor structure, and mass textures

In the 5D theory in which only 3 generation right-handed neutrinos are in the bulk, the neutrino flavor mixings and the mass spectrum can be constructed through the seesaw mechanism. The 5D seesaw is easily calculated just by a replacement of the Majorana mass eigenvalues, M_i, by 2 M_*tan(h)[\pi RM_i] (M_*: 5D Planck scale, R: compactification radius). The 5D features appear when the bulk mass, which induces the 4D Majorana mass, is the same as the compactification scale or larger than it. Depending on the type of bulk mass, the seesaw scales of the 3 generations are strongly split (the tan-function case) or degenerate (the tanh-function case). In the split case, the seesaw enhancement is naturally realized. The single right-handed neutrino dominance works in a simple setup, and some specific mass textures, which are just assumptions in the 4D setup, can be naturally obtained in 5 dimensions. The degenerate case is also useful for a suitable neutrino flavor structure.Comment: 15 page