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The objective of this work was to improve our understanding of pulsed laser micropolishing (PLμP) by studying the effects of laser pulse length and feed rate (pulses per millimeter) on surface roughness. PLμP experiments were conducted with a multimode neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm wavelength) that was focused down to approximately 50 μm diameter and scanned over the stationary workpiece surface. Simulation results presented here and previous work suggest that longer laser pulses result in smoother surfaces. Results on microfabricated nickel samples using laser pulse durations of 300 ns and 650 ns test this hypothesis. Polishing with 300 ns and 650 ns pulse durations results in an average surface roughness of 66 nm and 47 nm, respectively; reductions of 30% and 50% compared with the original surface. Furthermore, PLμP is shown to introduce a minor artifact on the sample surface whose spatial frequency (1/mm) is directly related to the laser feed rate (pulses/mm).

The precision of parts created by microfabrication processes is limited by surface roughness. Therefore, as a means of improving surface roughness, pulsed laser micropolishing on nickel was examined numerically and experimentally. A one-dimensional finite element method model was used to estimate the melt depth and duration for single 50–300 ns laser pulses. The critical frequency was introduced to predict the effectiveness of polishing in the spatial frequency domain. A 1064 nm Nd:YAG laser with 300 ns pulses was used to experimentally investigate pulsed laser polishing on microfabricated nickel samples with microscale line features. A microfabricated sample with 2.5 μm wide and 0.2 μm high lines spaced 5 μm apart and one with 5 μm wide and 0.38 μm high lines spaced 10 μm apart were polished with 300 ns long pulses of 47.2 J/cm2 and 44.1 J/cm2 fluences, respectively. The critical frequency for these experimental conditions was predicted and compared with the reduction in the average surface roughness measured for samples with two different spatial frequency contents. The average surface roughness of 5 μm and 10 μm wavelength line features were reduced from 0.112 μm to 0.015 μm and from 0.112 μm to 0.059 μm, respectively. Four regimes of pulsed laser micropolishing are identified as a function of laser fluence for a given pulse width: (1) at low fluences no polishing occurs due to insufficient melting, (2) moderate fluences allow sufficient melt time for surface wave damping and significant smoothing occurs, (3) increasing fluence reduces smoothing, and (4) high fluences cause roughening due to large recoil pressure and ablation. Significant improvements in average surface roughness can be achieved by pulsed laser micropolishing if the dominant frequency content of the original surface features is above the critical spatial frequency for polishing.

Extracellular ATP (eATP), which has now become recognized as a signaling agent in plants, can regulate growth in a variety of plant cell and tissue types. 1 The application of micromolar concentrations of ATP can induce [Ca 2+ ] cyt fluctuations and promote growth-altering accumulation of ROS and NO in diverse tissues of diverse plants. Nitric oxide (NO) and reactive oxygen species (ROS) are important in guard cell responses. In our original study of this signaling response we found that ATPγS-induced stomatal closing was dependent on the production of ROS and NO.2 Importantly we reported that both ABA and light-induced changes in stomatal aperture were preceded by an increase in the eATP levels of guard cells. A subsequent report by Hao et al. (2012) 3 found that applied ATP promoted stomatal opening, but, in contrast to the results we obtained using ATPγS, they did not observe stomatal closing in Arabidopsis or Vicia faba leaves in response to applied ATP. In this study we carry out additional tests that address questions raised by the findings of Hao et al. Regarding eATP-induced stomatal opening, we hypothesized that moderate inhibition of ectoapyrase activity by application of low concentrations of chemical apyrase inhibitors would cause naturally occurring levels of eATP to increase resulting in stomatal opening. We found that, similar to treatment with 15 μM ATPγS, treatment of leaves with two different apyrase inhibitors at a concentration of 1.5 µg/mL also induces stomatal opening (Fig. 1A).We Keywords: extracellular ATP, apyrase, stomata, abscisic acid, ArabidopsisAbbreviations: ABA, abscisic acid; eATP, extracellular ATP; ROS, reactive oxygen species; NO, nitric oxide; RBOHD/F, NADHP oxidase homolog sub-units D/F; DTT, dithiothreitol; DPI, diphenyleneiodonium; GCA2, growth controlled by ABA 2; ABI2, Abscisic Acid-Insensitive2; PA, phosphatidic acid; gpa, α-subunit of the Arabidopsis heterotrimeric G Protein in Arabidopsis leaves there is a bi-phasic dose-response to applied nucleotides; i.e., lower concentrations induce stomatal opening, while higher concentrations induce closure. two mammalian purinoceptor antagonists, PPaDS and rB2, block both nucleotide-induced stomatal opening and closing. these antagonists also partially block aBa-induced stomatal closure and light-induced stomatal opening. there are two closely related Arabidopsis apyrases, ataPY1 and ataPY2, which are both expressed in guard cells. here we report that low levels of apyrase chemical inhibitors can induce stomatal opening in the dark, while apyrase enzyme blocks aBa-induced stomatal closure. We also demonstrate that high concentrations of atP induce stomatal closure in the light. application of atPγS and chemical apyrase inhibitors at concentrations that have no effect on stomatal closure can lower the threshold for aBa-induced closure. the closure induced by atPγS was not observed in gpa1-3 loss-of-function mutants. these results further confirm the role of extracellular atP in regulating stomatal apertures.

The relative surface accuracy (surface roughness/feature size) of meso/micro parts fabricated by emerging meso/micro manufacturing processes is generally worse than that of macro parts fabricated by conventional processes. Meso/micro parts have unique tribology issues and surface roughness strongly impacts their performance, hence there is a demand for effective polishing of their complex shapes. A laser micro polishing method based on rapid surface micromelting is described. To develop a fundamental understanding of the underlying processes, a nickel sample was fabricated using silicon-based microfabrication and electroplating techniques. Results demonstrating the effectiveness of laser polishing using a pulsed 1064 nm Nd:YAG laser are presented. These results show that brief (200–300 ns) laser pulses can significantly improve the sample surface roughness (Ra). Additionally, by examining surface profile data in the spatial frequency domain it is clear that using pulses (up to 300 ns), laser polishing can effectively remove surface roughness features greater than 200 mm−1 in spatial frequency.

Background Little evidence is available regarding the choice of empiric antibiotic therapy in elderly patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). The primary objective of this study is to compare the outcomes of elderly patients receiving broad- versus narrow-spectrum antibiotics during hospitalization for AECOPD. Design A multicenter, retrospective, cohort analysis was performed. Inpatients 65 years and older with a primary discharge diagnosis of AECOPD who received ≥48 hours of antibiotic therapy were included in the study population. Patients were compared based on the spectrum of their antibiotic therapy. Narrow-spectrum antibiotics included: azithromycin, doxycycline, sulfamethoxazole/trimethoprim, or aminopenicillin. The primary outcome was a composite of mechanical ventilation 48 hours after admission, transfer to the intensive care unit 48 hours after admission, 30-day chronic obstructive pulmonary disease (COPD) readmission, and oxygen saturation less than 90% on room air or increased oxygen requirements from baseline 48 hours after admission. Results Two hundred fifty-three patients were included in this analysis; 127 patients were included in the narrow-spectrum group, and 126 patients were included in the broad-spectrum group. Patient demographics and comorbid conditions were similarly distributed in each group. The incidence of the primary composite outcome occurred in 50 (39.3%) and 60 (47.6%) of patients in the narrow- and broad-spectrum groups, respectively ( P = .19). Conclusions and Relevance No difference was found in the primary outcome in inpatients aged ≥65 years with AECOPD who received empiric broad-spectrum or narrow-spectrum antibiotics.

The objective of this work is to improve our understanding of pulsed laser micro polishing (PLμP) by studying the effects of laser pulse length, pulses per mm, and workpiece material on surface roughness. PLμP experiments are conducted with a multi-mode Nd:YAG laser (1064 nm wavelength) that is focused down to approximately 50 μm diameter and scanned over the stationary workpiece surface. Simulation results presented here and previous work suggest that longer laser pulses are better for polishing. Results on microfabricated nickel samples using laser pulse lengths of 300 ns and 650 ns test this hypothesis. Additionally, a surface artifact introduced by the PLμP process will be investigated. Results on the microfabricated nickel sample prove that longer laser pulses yield a higher reduction in surface roughness; 300 ns and 650 ns pulses reduce the Ra of the sample by 30% and 50%, respectively. The artifact introduced by the PLμP is found to be directly related to the number of laser pulses per mm. Successful polishing is achieved on Ti6Al4V and the surface roughness (Ra) of the sample is reduced from 0.250 μm to 0.058 μm. It is also shown that the presence of argon shielding gas is necessary to avoid surface cracks. The results presented here further validate the simplified thermal and fluid flow modeling of the PLμP process and demonstrate the effectiveness of PLμP on a broadly used titanium alloy, Ti6Al4V.

The relative accuracy (accuracy/overall dimension) of meso/micro parts (e.g. dies/molds) generally is far worse than that of macro parts fabricated by conventional manufacturing processes. Meso/micro parts have unique tribology issues, and surface roughness strongly impacts their relative accuracy and performance. There is a high demand for effective polishing of complex shapes in meso/micro engineering. A laser micro polishing method based on rapid surface micro melting is described in this paper. Fundamental understanding of pulse laser micro melting is achieved through a combination of studies of analytical modeling, numerical simulation and experimentation. It is found that a power limit window exists for laser polishing. In the experimental study, a Nd:YAG laser with a wavelength of 355 nm and a pulse of 10 ns is used to polish patterned electroplated nickel surfaces. The experiments show an improvement of surface roughness with repetitive rapid micro melting. These preliminary results show improved surface roughness can be achieved and that laser micro polishing is a viable methodology for automated polishing of 3-D meso/micro complex surfaces of metallic parts.