The effects of multifocal refractive lenses on occipital extension and forward head posture during a visual task

The purpose of this study was to determine if a change in forward head posture and occipital extension occurred in participants who wore multifocal lenses vs. those persons with non-multifocal lenses while performing an 8-min visual reading task on a visual display unit (VDU). Forty-two healthy human participants were recruited for this study. Thirty-three participants completed the study. Fourteen participants wore multifocal lenses and 19 wore frames with non-multifocal lenses. To evaluate the degree of change of forward head posture and occipital extension digital photographs of cervical posture were taken at four different time intervals: prior to performing the reading task and at 3, 5 and 8 min during the reading task. The digital photographs were analysed utilizing a computer program. Two one-way ANOVA were utilized to determine the degree of change of forward head posture and occipital extension between groups. A significant difference was identified between groups for changes in degrees of forward head posture while performing a visual reading task on a VDU. However, no significant difference between groups was found for occipital extension while performing the same task. Multifocal wearers exhibit greater degrees of change in forward head posture and occipital extension than non-multifocal wearers. These postural changes may place them at a greater risk for musculoskeletal disorders and headaches.     

The nonfixated Austin bunionectomy: a retrospective study of one-hundred procedures

A retrospective evaluation of 64 randomly selected patients with 100 nonfixated Austin bunionectomy procedures was performed. A radiographic and a clinical evaluation were performed, including an analysis of preoperative and postoperative angles as well as postoperative complications. This study demonstrates a similar complication rate for nonfixated Austin bunionectomies as compared with previous studies with internal fixation. Removal of the fibular sesamoid was performed in 90% of the cases and did not increase the incidence of hallux varus. The nonfixated Austin bunionectomy is an acceptable alternative to the correction of hallux valgus. If internal fixation is utilized, the most cost-effective device should be used.     

Three-dimensional analysis of a directional coupler exhibiting aKerr nonlinearity

The propagating beam method is used to carry out a fully three-dimensional analysis of a nonlinear optical waveguide and a directional coupler formed from a pair of nonlinear waveguides. It is shown that, for interesting levels of the index nonlinearity, a beam in a monomode waveguide can undergo mild self-focusing and self-phase modulation. The behavior or the nonlinear coupler, on the other hand, is quantitatively similar to that predicted by coupled-mode theory. On the basis of the calculated power transfer characteristics of the nonlinear coupler, three schemes for using the device as a switch have been proposed. It is found that one of these, which is based on the operation of the coupler at a power close to the critical power, permits a larger power to be switched by a very small one     

Electron-beam lithography of chlorinated polystyrenes with narrow molecular weight distributions

Polystyrenes with narrow molecular weight distributions have been chlorinated with only slight broadening of molecular weight distributions to yield materials that are five to six times more sensitive to electron-beam irradiation. The chlorinated polystyrenes are useful negative resists for electron-beam lithography. At molecular weights of 3-4 × 10⁵g/mole, their threshold sensitivities to 20 keV electrons are 1-2μC/cm². Their lithographic contrasts are ≥ 1.5; in fact, > 2.0 for the narrowest molecular weight distributions. They compare favorably in these regards to polystyrenes of similar molecular weight characteristics. Lithographic relief images that are 80% of the original thickness of the polymer film can be formed at three to four times the threshold dose. The degree of chlorination ranged from 0.65-0.76 Cl/monomer unit. The infrared spectra of the chlorinated materials resemble the spectrum for poly(4-chlorostyrene). Elemental analysis indicated, however that some addition of chlorine had occurred. More extensive chlorination or chlorination of the higher molecular weight starting materials broadened the molecular weight distributions. The chlorinated material, a kind of poly(4-chlorostyrene-costyrene), is less sensitive than poly(4-chlorostyrenc) prepared by addition polymerization by almost a factor of four.     

Coronary revascularization in diabetic patients: a comparison of the randomized and observational components of the Aypass Angioplasty Revascularization Investigation (BARI)

BACKGROUND: Patients with treated diabetes in the randomized-trial segment of the Bypass Angioplasty Revascularization Investigation (BARI) who were randomized to initial revascularization with PTCA had significantly worse 5-year survival than patients assigned to CABG. This treatment difference was not seen among diabetic patients eligible for BARI who opted to select their mode of revascularization. We hypothesized that differences in patient characteristics, assessed and unmeasured, together with the treatment selection in the registry, at least partially account for this discrepancy. METHODS AND RESULTS: Among diabetics taking insulin or oral hypoglycemic drugs at entry, angiographic and clinical presentations were comparable between randomized and registry patients. However, more registry patients were white, and registry diabetics tended to be more educated and more physically active and to report better quality of life. Procedural characteristics and in-hospital complications were comparable. The 5-year all-cause mortality rate was 34.5% in randomized diabetic patients assigned to PTCA versus 19.4% in CABG patients (P=0.0024; relative risk [RR]=1.87); corresponding cardiac mortality rates were 23.4% and 8.2%, respectively (P=0.0002; RR=3.10). The CABG benefit was more apparent among patients requiring insulin. In the registry, all-cause mortality was 14.4% for PTCA versus 14.9% for CABG (P=0.86, RR=1.10), with corresponding cardiac mortality rates of 7.5% and 6. 0%, respectively (P=0.73; RR=1.07). These RRs in the registry increased to 1.29 and 1.41, respectively, after adjustment for all known differences between treatment groups. CONCLUSIONS: BARI registry results are not inconsistent with the finding in the randomized trial that initial CABG is associated with better long-term survival than PTCA in treated diabetic patients with multivessel coronary disease suitable for either surgical or catheter-based revascularization.     

Lateral cracks during sliding indentation on various optical materials

A series of static and sliding indentation (ie, scratching) was performed and characterized on a wide range of optical workpiece materials [single crystals of Al₂O₃ (sapphire), SiC, Y₃Al₅O₁₂ (YAG), CaF₂, and LiB₃O₅ (LBO); a SiO₂–Al₂O₃–P₂O₅–Li₂O glass ceramic (Zerodur); and glasses of SiO₂:TiO₂ (ULE), SiO₂ (fused silica), and P₂O₅–Al₂O₃–K₂O–BaO (Phosphate)] at various applied loads using various indenters (Vickers, 10 µm conical, and 200 µm conical). Despite having different load dependencies, the lateral crack depth formed during sliding indentation quantitatively scales with that formed during static indentation, explaining why static indentation has been historically effective in describing various grinding parameters. Depending on the indenter geometry, the amount of residual trench damage (plastic deformation and local fracturing) during sliding indentation was often enhanced by more than an order of magnitude compared with static indentation. A simple ploughing scratch model, which considers both tangential and normal stresses (where the tangential stress is amplified by relatively small tangential contact area), explains this enhancement and other observed trends. Accounting for the high correlation between residual trench depth and volumetric fracturing, the model is extended to estimate the amount of fracture damage as a function of the material properties of the workpiece, indenter geometry, and applied load. Such a model has utility in the design of optimized grinding processes, particularly the abrasive geometry. Finally, at higher loads (>1 N), lateral cracks were often observed to preferentially propagate in the forward scratching direction, as opposed to perpendicular to the scratch as typically observed. High-speed imaging of the scratch process confirms that these cracks propagate ahead of the sliding indenter during the scratching event. Finite element stress analysis suggests the ploughing frictional forces increase the mode I tensile stresses at the leading edge of the sliding indenter explaining the direction of crack propagation of such cracks.     

An analysis of intersecting diffused channel waveguides

The coupling characteristics of intersecting diffused channel waveguides are computed for realistic three-dimensional diffusion profiles by means of the propagating beam method (PBM). Both TE and TM polarizations are treated for waveguides formed onz-cut LiNbO3. Good agreement between computed and previously reported measured results is found for the TE polarization. Agreement between computed and measured results is not as good for the TM polarization. This is explained by the fact that the applicable2Deltan-waveguide supports four modes, which should make coupling characteristics very sensitive to input conditions.