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Design for Stable Lasing of an Indirect Injection THz Quantum Cascade Laser Operating at Less Than 2 THz
Tsung-Tse Lin,
Hideki Hirayama
Issue:
Volume 6, Issue 5, September 2017
Pages:
230-234
Received:
4 July 2017
Accepted:
17 July 2017
Published:
11 August 2017
Abstract: In order to realize high temperature lasing of low frequency (< 2 THz) terahertz quantum cascade lasers (THz QCLs), selective carrier injection into an upper lasing level using an indirect injection (II) scheme is an effective method for inducing population inversion. The II scheme is realized with a four-level system. However, a three-level system that operates at low applied bias voltages causes additional lasing at higher frequencies (4～5 THz). By detuning the wave functions at the three lasing levels operating at low bias voltages, we were able to operate an II scheme THz QCL at a single stable frequency. Utilizing the higher injection selectivity, achieved through an indirect scattering-assisted injection process combined with diagonal emission, we were able to demonstrate stable operation of an AlGaAs/GaAs QCL operating at 1.89 THz at temperatures up to 160 K.
Abstract: In order to realize high temperature lasing of low frequency (< 2 THz) terahertz quantum cascade lasers (THz QCLs), selective carrier injection into an upper lasing level using an indirect injection (II) scheme is an effective method for inducing population inversion. The II scheme is realized with a four-level system. However, a three-level sys...
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Peculiarity of Zr in the Neutron Absorption Cross-section and Corrosion Resistance in Water
Issue:
Volume 6, Issue 5, September 2017
Pages:
235-240
Received:
2 August 2017
Accepted:
15 August 2017
Published:
28 August 2017
Abstract: The elements Be, Bi, Mg, Pb, Zr, Al, Ca, Na, Sn, Rb and Ce are the metallic elements of small thermal neutron absorption cross section. Except Be and Zr, they are all soft metals. But the reasons for these small thermal neutron absorption cross-sections are not known. To clarify its mechanism, the thermal neutron absorption cross-sections of elements were plotted on the TC-YM diagram. They lie on a line connecting the elements of low Young’s modulus on the TC-YM diagram. The author at first considered that the neutron absorption characteristics of elements relate to the neutron multiple number which means the number of neutrons per proton in the nucleus. The absorption cross-section of elements roughly increases with increasing neutron multiple number. Among the elements of small neutron absorption cross section, only Zr and Be are the elements of high melting temperature. Zr should not show the small neutron absorption cross section inherently. But in fact, Zr is exceptional both on the TC-YM diagram and in the neutron multiple number. Zr has a small absorption cross-section against the general trends in both the TC-YM diagram and neutron multiple number. On the other hand, the corrosion resistance of Zircaloy is given by the anodic protection provided by the precipitates of metallic compounds containing Fe and Cr. It is fortunate that Fe and Cr belong to the element group of the metals nobler than Zr and that of no solubility in Zr on the TC-YM diagram.
Abstract: The elements Be, Bi, Mg, Pb, Zr, Al, Ca, Na, Sn, Rb and Ce are the metallic elements of small thermal neutron absorption cross section. Except Be and Zr, they are all soft metals. But the reasons for these small thermal neutron absorption cross-sections are not known. To clarify its mechanism, the thermal neutron absorption cross-sections of elemen...
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Effect of Chill Wheel Cooling on Magnetic Properties of Nd15Fe77B8 Alloy Powders Produced by Melt Spinning Method
Sultan Öztürk,
Kürşat Icin,
Bülent Öztürk,
Uğur Topal,
Hülya Kaftelen Odabaşi
Issue:
Volume 6, Issue 5, September 2017
Pages:
241-249
Received:
14 August 2017
Accepted:
25 August 2017
Published:
19 September 2017
Abstract: In this study, effect of wheel cooling on magnetic properties of Nd15Fe77B8 alloy powders produced by melt spinning method has been investigated. The present method includes the cooling of the copper wheel by externally contacting a coolant block which is cooled by internally circulating freon gas. Within this framework, the effect of wheel temperature on the microstructure and magnetic properties of Nd15Fe77B8 powders have been investigated. The temperatures of cooling block and melt spinning wheel were measured as -15°C and -5°C, before experimental run, separately. Produced powders exhibited different morphologies depending on the powder sizes. The smallest size of powders was formed as spherical, ligamental and fiber-like morphologies. As powders get larger, the amount of spherical, ligamental and fiber-like shaped powders decreased and the length of the fibers declined. The microstructural cell sizes for 5 µm and 48 µm size powders were measured as 0.22 µm and 1.23 µm, respectively. The cooling rates of 4 µm, 28 µm and 52 µm sized powders were measured as 5.95 x 106 K/s, 0.85 x 106 K/s and 0.45 x 106 K/s, respectively. The Curie temperature of produced powders was 321.5°C. The coercivity value of melt-spun powders was obtained as 2.842 kOe.
Abstract: In this study, effect of wheel cooling on magnetic properties of Nd15Fe77B8 alloy powders produced by melt spinning method has been investigated. The present method includes the cooling of the copper wheel by externally contacting a coolant block which is cooled by internally circulating freon gas. Within this framework, the effect of wheel tempera...
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Feedstock Recycling of Plastics Waste for Electricity or Fuel: An Exergy Approach
Issue:
Volume 6, Issue 5, September 2017
Pages:
250-259
Received:
5 July 2017
Accepted:
25 July 2017
Published:
26 September 2017
Abstract: Waste plastics contribute to many environmental and social problems due to the loss of natural resources, environmental pollution, depletion of landfill space, and the various demands of an environmentally oriented society. The consumption of plastics waste increases annually, particularly in developing countries. Feedstock recycling of scrap polymers by thermal and chemical methods is well known and environmentally acceptable. However, new technologies for waste utilization as well as the methods that would enable an objective and broad assessment of these processes are strongly needed. Selecting the best method for thermal processing of waste polymers can be done based on a thermodynamic analysis of the process. In the paper, the process of thermal degradation of waste plastics (that is carried out in the new type of a tubular reactor with molten metal) is described and evaluated from the therodynamic poin of view. Depending on the final product (a fuel-like mixture or electricity), the calculated exergy efficiency of the proposed method ranged from 79% to 82%. These results mean that feedstock recycling of this type of waste by thermal degradation is a beneficial process from an energetic and ecological perspective as compared to other processes, particularly incineration.
Abstract: Waste plastics contribute to many environmental and social problems due to the loss of natural resources, environmental pollution, depletion of landfill space, and the various demands of an environmentally oriented society. The consumption of plastics waste increases annually, particularly in developing countries. Feedstock recycling of scrap polym...
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Effect of Cold Work on Creep Rupture Strength of Alloy263
Naoya Kanno,
Yoshiki Shioda,
Keiji Kubushiro
Issue:
Volume 6, Issue 5, September 2017
Pages:
260-268
Received:
13 September 2017
Accepted:
22 September 2017
Published:
13 October 2017
Abstract: Creep rupture strength and the microstructure change during creep deformation of pre-strained Alloy263 were investigated. Creep rupture tests were conducted at 1023, 1073 K at stress range from 120 to 250 MPa. Creep strength of the pre-strained samples was higher than that of the non-strained samples. However, rupture strain of the pre-strained samples was much lower than that of non-strained samples. In the pre-strained samples, Ni3(Al, Ti)- γ’ and M23C6 inside of the grains precipitated finer than the non-strained samples compared at the same creep time. At grain boundaries, the grain boundary shielding ratio covered by M23C6 carbide showed almost same value among each samples. However, diameter of the M23C6 particle decreased in pre-strained samples. Furthermore, dynamic recrystallization was promoted and precipitation free zone (PFZ) was formed around Ni3Ti-η phase at grain boundary. These observations show that increase in creep-strength of pre-strained sample was due to increase in precipitation strengthening in the grain by fine precipitation of γ’ and M23C6. In addition, resistance against crack propagation at grain boundary increased by the fine precipitation of grain boundary M23C6 even though formation of PFZ and promotion of the dynamic recrystallization. It is estimated that Orowan-stress of pre-strained samples was 1.7 times higher than non-strained samples. It is considered that these strengthening effects overcome the weakening effects in the pre-strained samples.
Abstract: Creep rupture strength and the microstructure change during creep deformation of pre-strained Alloy263 were investigated. Creep rupture tests were conducted at 1023, 1073 K at stress range from 120 to 250 MPa. Creep strength of the pre-strained samples was higher than that of the non-strained samples. However, rupture strain of the pre-strained sam...
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