Proposal for a new magnet lattice for an electron storage ring for a high brightness synchrotron radiation source

A new magnet lattice, named “variable emittance”, for an electron storage ring dedicated to synchrotron radiation is proposed. The lattice has a high flexibility to meet the requirements for a high performance undulator as well as for conventional synchrotron radiation from a bending magnet. Tune shifts due to magnet imperfections were simulated and it is found that the periodic solution of the optics is stable enough except for a very high tune region. The effects of undulators and wigglers on the stored beam were studied and a correction for the tune shift is found necessary for high field wigglers.     

Reduction of mode selectivity in DFB lasers with one cleaved facet by a tapered refractive-index profile

The mode selectivity in DFB lasers with one cleaved facet is analysed considering a tapered refractive-index profile along a laser axis. As a result, it becomes clear that in strong coupled DFB lasers the mode selectivity is reduced remarkably by such a profile.     

Hidden Markov Models for Text Categorization in Multi-Page Documents

In the traditional setting, text categorization is formulated as a concept learning problem where each instance is a single isolated document. However, this perspective is not appropriate in the case of many digital libraries that offer as contents scanned and optically read books or magazines. In this paper, we propose a more general formulation of text categorization, allowing documents to be organized as sequences of pages. We introduce a novel hybrid system specifically designed for multi-page text documents. The architecture relies on hidden Markov models whose emissions are bag-of-words resulting from a multinomial word event model, as in the generative portion of the Naive Bayes classifier. The rationale behind our proposal is that taking into account contextual information provided by the whole page sequence can help disambiguation and improves single page classification accuracy. Our results on two datasets of scanned journals from the Making of America collection confirm the importance of using whole page sequences. The empirical evaluation indicates that the error rate (as obtained by running the Naive Bayes classifier on isolated pages) can be significantly reduced if contextual information is incorporated.     

Effect of tensile strain rate on the mechanical properties of polystyrene and high-impact polystryene

The dependency of the mechanical properties (Young's modulus, maximum load, breaking strain, and breaking energy) of polystyrene (PS) and high-impact polystyrene (HIPS) on the tensile deformation speeds was examined without changing the mode of deformation or the shape of the test specimen. It was found that HIPS has an excellent mechanical balance compared with PS for both low (1.7 × 10^?4 to 2.9 × 10^?2 m/sec) and high (1.3–16m/sec) speeds. This is due to the following two mechanisms ( which have different time responses) originating from the dispersed rubber particles: (1) at low speeds, the generation of large numbers of microcrazes, and (2) at high speeds, tensile-orientation hardening of the rubber and cold-drawing of the PS matrix resulting from the rise in temperature accompanied by the abrupt eleongation of the rubber phases.     

Comparison of polystyrene,poly(styrene/acrylonitrile), high-impact polystryrene,and poly(acrylonitrile/butadiene/styrene) with respect to tensile and impact properties

The tensile behaviors of polystyrene (PS), poly(styrene/acrylonitrile) (SAN), high-impact polystyrene (HIPS), and poly(acrylonitrile/butadiene/styrene) (ABS) were examined systematically in the wide range of strain rate, 1.7 × 10^?4–13.1 m/s. When glassy and brittle PS was a criterion, the incorporation of a polar group (SAN) only strengthened the hardness, and the fracture mode was the same as for PS. The introduction of dispersed rubber particles (HIPS) weakened the hardness a little but offered a new deformation mechanism, i.e., microcrazing (whitening), and contributed to the improvement of impact strength. In the heterogeneous system, the enhancement of matrix strength [e.g., preorientation or blending with poly(phenylene oxide) for HIPS] makes possible another deformation mechanism, i.e., shear band formation (cold drawing), which is superior to microcrazing for achieving higher impact strength. ABS, which incorporates concurrently two factors (polar group to matrix phase and dispersed rubber particles), can be regarded as an enhancement of the matrix strength of HIPS. In spite of the remarkable magnitude of its impact strength compared with that of the other three polymers, the deformation mechanism of ABS was limited to microcrazing. This indicated that only the introduction of a polar group (as nitrile group) could not strengthen the matrix as much as preorientation or blending with poly(phenylene oxide).     

Dependence of Si and Si sputtering yields on residual oxygen impurity

The Si⁺ and Si²⁺ sputtering yields have been measured by time-of-flight (TOF) method under the bombardment of a pulsed 11 keV Ar⁰ beam on a nominally clean Si(1 1 1) surface. Although the residual oxygen impurity is below the detection limit of Auger electron analysis (∼0.01 monolayer), the SiO⁺ ions are clearly observed and its yield can be regarded as a measure of the residual O impurity on the Si surface region. The Si⁺ TOF spectrum changes its shape and the Si⁺ yield increases linearly with the SiO⁺ yield, while the shape of the Si²⁺ TOF spectrum and the Si²⁺ yield remain almost unchanged. The change in the Si⁺ TOF spectrum is attributed to the increasing SiH⁺ yield, which may be caused by the H₂O adhesion to the Si surface during the TOF measurement. The increase in the adsorbing H₂O may also lead to the enhancement of SiO⁺ and Si⁺ yields; Si⁺ ions may be created through the charge exchange process between O and Si due to difference in their electron affinity. The insensitivity of the Si²⁺ yield to the residual O impurity is consistent with the Si²⁺ formation by the Auger ionization process of the excited Si⁺ having the 2p hole, which is produced in the collision cascades.     

Effects of absorbed water on physical properties of polyesters

In previous articles, we reported the change in physical properties of hydrophobic polymers caused by absorption of a very small amount of water. This article describes the changes in physical properties of three polyesters owing to absorption of water. The tested polymers were poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), and polyethylene 2,6-naphthalate (PEN). PBT has more flexible main chains than that of PET, and PEN has more rigid main chains. The dielectric measurements revealed that water absorption results in shortening the relaxation time for PET, while the relaxation time for moist PBT becomes longer. The larger amount of absorbed water yields the higher density of PET and the lower density of PBT. The water absorption of the polyesters also yields increments in dielectric constants and relaxation strength. Distribution of relaxation time of the polyesters is narrowed by absorption of water.