Rent Control and Public Housing

Rent control is a snare and a delusion for those who think it will actually help the poor. It reduces the supply of rental housing from the level that would otherwise have obtained, and the poor get the short end of the stick whenever there is a shortage of anything. Housing is no exception to this general rule. Nor is public housing a solution to the needs of the poor. Instead, it boomerangs on this sector of the population. The free enterprise system, with neither of these policies, is the last best option for the poverty stricken

Mechanisms of femtosecond laser-induced refractive index modification of poly(methyl methacrylate)

The mechanisms of refractive index change in poly(methyl methacrylate) by frequency doubled femtosecond laser pulses are investigated. It is demonstrated that positive refractive index modificaton can be caused by a combination of depolymerization and crosslinking

Ultrafast laser beam shaping for material processing at imaging plane by geometric masks using a spatial light modulator

We have demonstrated an original ultrafast laser beam shaping technique for material processing using a spatial light modulator (SLM). Complicated and time-consuming diffraction far-field phase hologram calculations based on Fourier transformations are avoided, while simple and direct geometric masks are used to shape the incident beam at diffraction near-field. Various beam intensity shapes, such as square, triangle, ring and star, are obtained and then reconstructed at the imaging plane of an f-theta lens. The size of the shaped beam is approximately 20 µm, which is comparable to the beam waist at the focal plane. A polished stainless steel sample is machined by the shaped beam at the imaging plane. The shape of the ablation footprint well matches the beam shape

Imaging-based amplitude laser beam shaping for material processing by 2D reflectivity tuning of a spatial light modulator

We have demonstrated an imaging-based amplitude laser-beam-shaping technique for material processing by 2D reflectivity tuning of a spatial light modulator. Intensity masks with 256 gray levels were designed to shape the input laser beam in the outline profile and inside intensity distribution. Squared and circular flattop beam shapes were obtained at the diffractive near-field and then reconstructed at an image plane of a

Femtosecond laser surface texturing of aisi 1045 steel

Morphological changes, including texturing and production of highly oriented periodical surface structures (LIPSS), on AISI 1045 steel were carried out by femtosecond laser pulses. The surface changes, induced by laser, are highly localized with minimal hydrodynamic effects and without the presence of a debris. The produced LIPSS have the periodicity of 700 nm, and were more prominent in case of triple scanning. Elemental analysis of the surface showed chemical changes, due to formation of oxides and diffusion of carbon from the bulk. These changes are also more obvious in case of triple scanning

Experimental and numerical study of multi-pulse picosecond laser ablation on 316 L stainless steel.

An experimental and numerical study on 10 ps laser ablation of 316 L stainless steel up to 400 hundred pulse exposure has been carried out. In this simulation, the material removal threshold temperature has been carefully discussed depending on the different ablation driving mechanisms. The influence of the instantaneous material removal has also been considered which will affect the calculation of the next pulse's absorption. For single-pulse ablation, the simulated ablation threshold Fsim = 0.26 J/cm2 is close to the fitted experimental result F0th = (0.29 ± 0.01) J/cm2. For multi-pulse ablation, the simulated ablation rate Rsim = 11.4 nm/pulse is close to the fitted experimental result Rexp = (12.4 ± 0.1) nm/pulse under 0.9 J/cm2 fluence, while the simulated ablation rate Rsim = 19.8 nm/pulse is slightly larger than the fitted experimental result Rexp = (16.1 ± 0.7) nm/pulse at 2.7 J/cm2, providing good agreement between theory and experiment for both single and multi-pulse ablation. This study could be used to predict the multi-pulse laser processing performance, especially with the help of a machine learning method to find the best parameters automatically