Variational Monte-Carlo calculation of the nematic state of the two-dimensional electron gas in a magnetic field

We use a Jastrow-Slater wave function with an elliptical Fermi sea to describe the nematic state of the two-dimensional electron gas in a magnetic field and the Monte Carlo method to calculate a variational energy upper bound. These energy upper bounds are compared with other upper bounds describing stripe-ordered ground states which are obtained from optimized Hartree-Fock calculations and with those which correspond to an isotropic ground state. Our findings support the conclusions drawn in our previous study where the Fermi-hypernetted chain approximation was used instead of the Monte Carlo method. Namely, the nematic state becomes energetically favorable relative to the stripe-ordered Wigner crystal phase for the second excited Landau level and below a critical value of the layer ``thickness'' parameter which is very close to its value in the actual materials.Comment: 6 pages, 8 figure

A stochastic model of the influence of buffer gas collisions on Mollow spectra

In this paper we consider the influence of collisional fluctuations on the Mollow spectra of resonance fluorescence (RF). The fluctuations are taken into account by a simple shift of the constant detuning, involved in a set of optical Bloch equations by collision frequency noise which is modelled by a two-step random telegraph signal (RTS). We consider in detail the Mollow spectra for RF in the case of an arbitrary detuning of the laser frequency, where the emitter is a member of a statistical ensemble in thermodynamic equilibrium with the buffer gas at temperature $T$ which is treated as a colored environment, and velocity $v$ is distributed with the Maxwell-Boltzmann density

Factors Influencing the Intention to Use Open Educational Resources of Students at Universities in Economics and Business Administration in Vietnam

The purpose of this paper is to examine the factors influencing the intention to use Open Educational Resources (OER) of students at universities in Economics and Business Administration in Vietnam. The results showed that Effort Expectancy, Performance Expectancy, Lecturer Influence, and Friend Influence were the factors had higher impact on the intention to use OER of students than other factors namely School Influence and Facilitating Conditions. Furthermore, regression analysis also pointed out that there were no relationship between control variables and students’ intention to use OER. Finally, the paper also proposed several recommendations on how to implement Open Educational Resources initiatives effectively at higher education institutions in Vietnam. Keywords: Intention to Use, Open Educational Resources, Universities in Vietnam. DOI: 10.7176/JESD/11-6-10 Publication date:March 31st 202

Na3Ce(PO4)2:Tb3+ and Na(Mg2–xMnX)LiSi4O10F2:Mn phosphors: a suitable selection for enhancing color quality and luminous flux of remote white light-emitting diodes

This study proposed the TRP, a remote phosphor structure that has 3 phosphor layers, to ehance the chromatic quality and lumen output for white light-emitting diodes devices (WLEDs). The arrangment of phosphor layers is yellow YAG:Ce3+ phosphor, green Na3Ce(PO4)2:Tb3+ phosphor, and red Na(Mg2–xMnX)LiSi4O10F2:Mn phosphor from bottom to top. Red Na(Mg2–xMnX)LiSi4O10F2:Mn phosphor is used for the red light component to boost color rendering index (CRI). The green layer Na3Ce(PO4)2:Tb3+ phosphor is utilized for the green light component to produce higher luminous flux (LF). With the addition of red and green phosphor, the yellow YAG:Ce3+ concentration must decrease to maintain the 6000 K color temperature. The research results show that red phosphor Na(Mg2–xMnX)LiSi4O10F2:Mn concentration is beneficial for CRI, while green phosphor Na3Ce(PO4)2:Tb3+ is detrimental to CRI. Morever, CQS reaction with red and green phosphor is also studied, which show notable improvement when Na(Mg2–xMnX)LiSi4O10F2:Mn concentration is from 10%-14%, regardless of Na3Ce(PO4)2:Tb3+. The luminous flux (LF) can also increase for more than 40% with the reduced light loss and added green phosphor. Research results are valuable references for producers to enhance the color quality and the light emission of WLEDs

SrBaSiO4:Eu2+ phosphor: a novel application for improving the luminous flux and color quality of multi-chip white LED lamps

This paper described in detail the chromatic homogeneity and luminous flux influences in producing better quality white LED devices with various phosphor layers (MCW-LEDs). The method is to let Eu2+-activated strontium–barium silicate (SrBaSiO4:Eu2+) mixed with their phosphor compounding, which results in notable impact on lighting performance. The increase in concentration of yellow-green-emitting SrBaSiO4:Eu2+ phosphor also promotes the color performance and lumen output of WLED devices at high correlated color temperature around 8500K. This is the first time this approach is applied and it results can be utilized for better understanding of optical properties interaction with phosphor materials. Although SrBaSiO4:Eu2+ receives many positive responses, we still need to limit it concentration for high SrBaSiO4:Eu2+ concentration is detrimental to CQS. The appropriate choice of concentration and size of SrBaSiO4:Eu2+ is the principal factor to decide the performance of MCW-LEDs

The application of double-layer remote phosphor structures in increasing WLEDs color rendering index and lumen output

The remote phosphor structure often has inferior color quality but better luminous flux in than conformal or in-cup configurations. Therefore, numerous researches study remote phosphor structure for methods to enhance it chromatic quality. This study introduces the use of dual-layer remote phosphor structure in WLEDs with identical structure but at different color temperature, 6600K and 7700K, to demonstrate their effect on quality indicators. The concept is placing a green phosphor layer (Ce,Tb)MgAl11O19:Ce:Tb or a red phosphor layer MgSr3Si2O8:Eu2+,Mn2+ on the layer of yellow-emitting phosphor YAG:Ce3+ and find the suitable concentration of the additional phosphor to create the best color quality. The results showed that the increase of CRI and CQS are affected by MgSr3Si2O8:Eu2+,Mn2+, in particular, the higher the concentration of red phosphor gets the better CRI and CQS because the emitted red light in enhanced. The green phosphor layer (Ce,Tb)MgAl11O19:Ce:Tb, on the other hand, is beneficial for the luminous flux. The concentration of MgSr3Si2O8:Eu2+,Mn2+ and (Ce,Tb)MgAl11O19:Ce:Tb, however, need to be adjusted properly to avoid decreasing the luminous flux due to overgrowth. The Mie scattering theory and Beer’s law are the verification tools for these conclusions, which gives them the credibility to be applied in producing better quality WLEDs

LaSiO3Cl:Ce3+,Tb3+ and Mg2TiO4:Mn4+: quantum dot phosphors for improving the optical properties of WLEDs

In this research, we focus on the solutions to enhance the lighting properties as well as the heat regulation of the white light-emitting diodes (WLEDs) with conventional phosphor and quantum dots (QDs). Although receiving lots of attention for being an innovative lighting solution with good color rendering index, the potentials of WLEDs conjugated with quantum dots (QDS), especially the QDs-phosphor mixed nanocomposites ones, are restrained due to the lacking performance in the aspects mentioned above. The crucial requirement to produce better WLEDs is finding solutions that improve the lacking aspects, therefore, through observing previous studies and applying advanced technique, this research suggest an effective and unique packaging configuration, in which the nanocomposites QDs-phosphor layer is set horizontally to the WLED. This novel packaging configuration allow WLED performance in terms of lighting and heating to reach it peaks. This is the first time four different types of WLEDs, single-layer phosphor, dual-layer remote phosphor with yellow-red and yellow-green, and triple-layer phosphor, were simulated, utilized and compared in one study to decide the best WLED configuration. The results show that the triple-layer phosphor configurations improve the color rendering ability and lumen output better than the other configurations