1,251 research outputs found
Spectral and dynamic characteristics of buried-heterostructure single quantum well (Al,Ga)As lasers
We demonstrate that, as predicted, (Al,Ga)As single quantum well (SQW) lasers have substantially narrower spectral linewidths than bulk double-heterostructure lasers. We have observed a further major reduction (>3×) in the linewidth of these SQW lasers when the facet reflectivities are enhanced. This observation is explained theoretically on the basis of the very low losses in coated SQW lasers and the value of the spontaneous emission factor at low threshold currents. We also report on the modulation frequency response parameter of these SQW lasers
Sensitive Chemical Compass Assisted by Quantum Criticality
The radical-pair-based chemical reaction could be used by birds for the
navigation via the geomagnetic direction. An inherent physical mechanism is
that the quantum coherent transition from a singlet state to triplet states of
the radical pair could response to the weak magnetic field and be sensitive to
the direction of such a field and then results in different photopigments in
the avian eyes to be sensed. Here, we propose a quantum bionic setup for the
ultra-sensitive probe of a weak magnetic field based on the quantum phase
transition of the environments of the two electrons in the radical pair. We
prove that the yield of the chemical products via the recombination from the
singlet state is determined by the Loschmidt echo of the environments with
interacting nuclear spins. Thus quantum criticality of environments could
enhance the sensitivity of the detection of the weak magnetic field.Comment: 4 pages, 3 figure
Ultralow threshold graded-index separate-confinement heterostructure single quantum well (Al,Ga)As lasers
Broad area graded‐index separate‐confinement heterostructure single quantum well lasers grown by molecular‐beam epitaxy (MBE) with threshold current density as low as 93 A/cm^2 (520 μm long) have been fabricated. Buried lasers formed from similarly structured MBE material with liquid phase epitaxy regrowth had threshold currents at submilliampere levels when high reflectivity coatings were applied to the end facets. A cw threshold current of 0.55 mA was obtained for a laser with facet reflectivities of ∼80%, a cavity length of 120 μm, and an active region stripe width of 1 μm. These devices driven directly with logic level signals have switch‐on delays <50 ps without any current prebias. Such lasers permit fully on–off switching while at the same time obviating the need for bias monitoring and feedback control
RAFT dispersion polymerization of glycidyl methacrylate for the synthesis of epoxy-functional block copolymer nanoparticles in mineral oil
Epoxy-functional poly(stearyl methacrylate)-poly(glycidyl methacrylate) (PSMA-PGlyMA) diblock copolymer nanoparticles are synthesized via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of glycidyl methacrylate (GlyMA) in mineral oil at 70 °C. This efficient polymerization-induced self-assembly (PISA) formulation yields well-defined spheres of tunable diameter as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies. 1H NMR spectroscopy and gel permeation chromatography (GPC) studies indicate that such non-polar dispersions exhibit greater stability during their long-term storage at 20 °C compared to related epoxy-functional nanoparticles prepared via RAFT aqueous emulsion polymerization. Model epoxy-amine ring-opening reactions using N-methylaniline demonstrate the potential for post-polymerization functionalization of such spherical nanoparticles
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Can Middle-School Students Learn to Reason Statistically Through Simulation Activities?
This paper describes the implementation and quasiexperimental evaluation of a three-week instructional project designed in accordance with theories and assumptions of constructivism and socially situated cognition. Our goal was to develop students' ability to reason about real-life problems, where "good reasoning" was conceptualized in terms of a normative thinking model derived from cognitive research in decision making, probabilistic reasoning, and argumentation. In the spring of 1994, students in two middle school classrooms worked in teams that collected evidence, constructed arguments, and prepared presentations while engaged in activities that culminated in a mock legislative hearing. Through instruction and mentoring, students were encouraged to use statistics and probability as tools for reasoning. The effectiveness of the program was evaluated by comparing the written arguments of students from the two treatment classrooms with those of students from eight comparison classrooms. Students' arguments were scored in terms of how well they captured essential features of model reasoning and avoided particular thinking fallacies. That the reasoning abilities of students developed through social negotiation and shared problem solving was s
Space Shuttle orbiter entry heating and TPS response: STS-1 predictions and flight data
Aerothermodynamic development flight test data from the first orbital flight test of the Space Transportation System (STS) transmitted after entry blackout is given. Engineering predictions of boundary layer transition and numerical simulations of the orbiter flow field were confirmed. The data tended to substantiate preflight predictions of surface catalysis phenomena. The thermal response of the thermal protection system was as expected. The only exception is that internal free convection was found to be significant in limiting the peak temperature of the structure in areas which do not have internal insulation
Block Copolymer Nanoparticles Prepared via Polymerization-Induced Self-Assembly Provide Excellent Boundary Lubrication Performance for Next-Generation Ultralow-Viscosity Automotive Engine Oils
Core cross-linked poly(stearyl methacrylate)–poly(benzyl methacrylate)–poly(ethylene glycol dimethacrylate) [S31–B200–E20] triblock copolymer nanoparticles were synthesized directly in an industrial mineral oil via polymerization-induced self-assembly (PISA). Gel permeation chromatography analysis of the S31–B200 diblock copolymer precursor chains indicated a well-controlled reversible addition–fragmentation chain transfer dispersion polymerization, while transmission electron microscopy, dynamic light-scattering (DLS), and small-angle X-ray scattering studies indicated the formation of well-defined spheres. Moreover, DLS studies performed in THF, which is a common solvent for the S and B blocks, confirmed successful covalent stabilization because well-defined solvent-swollen spheres were obtained under such conditions. Tribology experiments using a mini-traction machine (MTM) indicated that 0.50% w/w dispersions of S31–B200–E20 spheres dramatically reduce the friction coefficient of base oil within the boundary lubrication regime. Given their efficient and straightforward PISA synthesis at high solids, such nanoparticles offer new opportunities for the formulation of next-generation ultralow-viscosity automotive engine oils
Analisis Keamanan Jembatan Rangka Baja Soekarno – Hatta Malang Ditinjau Dari Aspek Kesehatan, Tegangan Pelat Buhul, Dan Simulasi Kebakaran
Salah satu jalur pergerakan transportasi yang patut menjadi perhatian di Kota Malang adalah Jembatan Rangka Baja Soekarno-Hatta, yang merupakan akses utama pengguna jalan menuju ke area pendidikan dan ke arah kota wisata Batu. Jembatan ini dirasa telah mengalami penurunan kualitas. Dalam penelitian ini, pembahasan dalam difokuskan kepada analisis kesehatan jembatan, kondisi pelat buhul akibat distribusi tegangan yang terjadi, dan kondisi jembatan akibat beban termal. Setelah dilakukan uji Rebound Hammer didapatkan nilai karakteristik sebesar 277,66 kg/cm² dan nilai rebound sebesar 46,79. UPV menunjukkan kualitas beton yang rendah (kecepatan gelombang 1633,6 m/s < 3000 m/s). Pada analisis tegangan pelat buhul, perbedaan antara kondisi ideal dan eksisting sangat jelas. Konsentrasi tegangan pada kondisi ideal tidak melebihi tegangan leleh, sedangkan pada kondisi eksisting konsentrasi tegangan melebihi tegangan leleh. Pada analisis kebakaran di atas jembatan, ketika terjadi kebakaran di tengah bentang, total waktu yang dibutuhkan sampai tegangan batang diagonal mencapai leleh adalah setelah menit ke 18.90 (1134 s) dan mencapai titik putus pada menit ke 19.23 (1154 s). Sedangkan, ketika terjadi kebakaran pada bagian pinggir bentang, waktu yang dibutuhkan jembatan untuk mencapai leleh adalah setelah menit ke 15.81 (949 s), dan pada menit ke 17.95 (1077 s) tegangan batang diagonal mencapai titik putus
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