The reduced-alpha-width of the lowest 1¯ state of ^(16)O

Cross sections for the reaction ¹²C(α,γ)¹⁶O have been measured for a range of center-of-mass alpha particle energies extending from 1.72 MeV to 2.94 MeV. Two 8"x5" NaI (Tℓ) crystals were used to detect gamma rays; time-of-flight technique was employed to suppress cosmic ray background and background due to neutrons arising mainly from the ¹³C(α,n)¹⁶O reaction. Angular distributions were measured at center-of-mass alpha energies of 2.18, 2.42, 2.56 and 2.83 MeV. Upper limits were placed on the amount of radiation cascading through the 6.92 or 7.12-MeV states in ¹⁶O. By means of theoretical fits to the measured electric dipole component of the total cross section, in which interference between the 1¯ states in ¹⁶O at 7.12 MeV and at 9.60 MeV is taken into account, it is possible to extract the dimensionless, reduced-alpha-width of the 7.12-MeV state in ¹⁶O. A three-level R-matrix parameterization of the data yields the width Θ_α,F² = 0.14^+0.10_-0.08. A "hybrid" R-matrix-optical-model parameterization yields Θ_α,F² = 0.11^+0.11_-0.07. This quantity is of crucial importance in determining the abundances of ¹²C and ¹⁶O at the end of helium burning in stars.

Coma measurement by use of an alternating phase-shifting mask mark with a specific phase width

The correlation between the coma sensitivity of the alternating phase-shifting mask (Alt-PSM) mark and the mark's structure is studied based on the Hopkins theory of partially coherent imaging and positive resist optical lithography (PROLITH) simulation. It is found that an optimized Alt-PSM mark with its phase width being two-thirds its pitch has a higher sensitivity to coma than Alt-PSM marks with the same pitch and the different phase widths. The pitch of the Alt-PSM mark is also optimized by PROLITH simulation, and the structure of p - 1.92 lambda/NA and pw = 2p/3 proves to be with the highest sensitivity. The optimized Alt-PSM mark is used as a measurement mark to retrieve coma aberration from the projection optics in lithographic tools. In comparison with an ordinary Alt-PSM mark with its phase width being a half its pitch, the measurement accuracies of Z(7) and Z(14) apparently increase. (C) 2009 Optical Society of America

Varieties generated by modular lattices of width four

A variety (equational class) of lattices is said to be finitely based if there exists a finite set of identities defining the variety. Let M^∞_n denote the lattice variety generated by all modular lattices of width not exceeding n. M^∞₁ and M^∞₂ are both the class of all distributive lattices and consequently finitely based. B. Jónsson has shown that M^∞₃ is also finitely based. On the other hand, K. Baker has shown that M^∞_n is not finitely based for 5 ≤ n ˂ ω. This thesis settles the finite basis problem for M^∞₄. M^∞₄ is shown to be finitely based by proving the stronger result that there exist ten varieties which properly contain M^∞₄ and such that any variety which properly contains M^∞₄ contains one of these ten varieties.

The methods developed also yield a characterization of sub-directly irreducible width four modular lattices. From this characterization further results are derived. It is shown that the free M^∞₄ lattice with n generators is finite. A variety with exactly k covers is exhibited for all k ≥ 15. It is further shown that there are 2^Ӄo sub- varieties of M^∞₄.

A Q-swicthed all-solid-state single-longitudinal-mode laser with adjustable pulse-width and high repetition rate

A single-longitudinal-mode (SLM) laser-diode pumped Nd: YAG laser with adjustable pulse width is developed by using the techniques of pre-lasing and changing polarization of birefingent crystal. The Q-switching voltage is triggered by the peak of the pre-lasing pulse to achieve the higher stability of output pulse energy. The output energy of more than 1 mJ is obtained with output energy stability of 3% (rms) at 100 Hz. The pulse-width can be adjusted from 30 ns to 300 ns by changing the Q-switching voltage. The probability of putting out single-longitudinal-mode pulses is almost 100%. The laser can be run over four hours continually without mode hopping.

Line-width reduction of a laser diode array using an external cavity with two feedback mirrors

A novel Littman-Metcalf external cavity laser diode array with two feedback mirrors is introduced. The line-width broadening effect caused by smile can be reduced by the novel external cavity. At the drive current of 16A, the line-width is narrowed to 0.1nm from free-running width of 1.6nm with output efficiency of 84%.

Generation of 1.5-12 ns width-tunable 532 nm pulses by adopting laser-induced plasma shutter technique

The pulse-shaping technique has found widespread applications in nonlinear optics and material processing. Experimental research on laser-induced plasma shutter to control the 532 nm pulse width is conducted. The impacts of the total pulse output energy on pulse compression are investigated, and a useful conclusion can be drawn that there exists an optimal value of pulse energy at which the shortest output pulse of 3.23 ns can be obtained without a device for delay-time. Once the device for delay-time is employed to change the optical differences between two laser paths, the pulse width can be further shortened to 1.51 ns. In short, the 1.5-12 ns width-tunable 532 nm laser pulses have been obtained by adopting the laser-induced plasma shutter technique. (C) 2007 Elsevier GmbH. All rights reserved.

Prosomal-width-to-weight relationships in American horseshoe crabs (Limulus polyphemus): examining conversion factors used to estimate landings

Horseshoe crabs (Limulus polyphemus) are valued by many stakeholders, including the commercial fishing industry, biomedical companies, and environmental interest groups. We designed a study to test the accuracy of the conversion factors that were used by NOAA Fisheries and state agencies to estimate horseshoe crab landings before mandatory reporting that began in 1998. Our results indicate that the NOAA Fisheries conversion factor consistently overestimates the weight of male horseshoe crabs, particularly those from New England populations. Because of the inaccuracy of this and other conversion factors, states are now mandated to report the number (not biomass) and sex of landed horseshoe crabs. However, accurate estimates of biomass are still necessary for use in prediction models that are being developed to better manage the horseshoe crab fishery. We recommend that managers use the conversion factors presented in this study to convert current landing data from numbers to biomass of harvested horseshoe crabs for future assessments.