Tunable reflection minima of nanostructured antireflective surfaces

Broadband antireflection schemes for silicon surfaces based on the moth-eye principle and comprising arrays of subwavelength-scale pillars are applicable to solar cells, photodetectors, and stealth technologies and can exhibit very low reflectances. We show that rigorous coupled wave analysis can be used to accurately model the intricate reflectance behavior of these surfaces and so can be used to explore the effects of variations in pillar height, period, and shape. Low reflectance regions are identified, the extent of which are determined by the shape of the pillars. The wavelengths over which these low reflectance regions operate can be shifted by altering the period of the array. Thus the subtle features of the reflectance spectrum of a moth-eye array can be tailored for optimum performance for the input spectrum of a specific application

Temperature dependence of the charge carrier mobility in gated quasi-one-dimensional systems

The many-body Monte Carlo method is used to evaluate the frequency dependent conductivity and the average mobility of a system of hopping charges, electronic or ionic on a one-dimensional chain or channel of finite length. Two cases are considered: the chain is connected to electrodes and in the other case the chain is confined giving zero dc conduction. The concentration of charge is varied using a gate electrode. At low temperatures and with the presence of an injection barrier, the mobility is an oscillatory function of density. This is due to the phenomenon of charge density pinning. Mobility changes occur due to the co-operative pinning and unpinning of the distribution. At high temperatures, we find that the electron-electron interaction reduces the mobility monotonically with density, but perhaps not as much as one might intuitively expect because the path summation favour the in-phase contributions to the mobility, i.e. the sequential paths in which the carriers have to wait for the one in front to exit and so on. The carrier interactions produce a frequency dependent mobility which is of the same order as the change in the dc mobility with density, i.e. it is a comparably weak effect. However, when combined with an injection barrier or intrinsic disorder, the interactions reduce the free volume and amplify disorder by making it non-local and this can explain the too early onset of frequency dependence in the conductivity of some high mobility quasi-one-dimensional organic materials.Comment: 9 pages, 8 figures, to be published in Physical Review

Science and instrumentation update from the Palomar testbed interferometer

The Palomar Testbed Interferometer (PTI) is a near-infrared, long-baseline interferometer located at the Palomar Observatory. PTI obtained first fringes in 1995, and has been in routine scientific operations since 1998. PTI was primarily designed as a technology demonstration experiment for the Keck Interferometer, and has been successful in demonstrating 100-uas-class differential astrometry and two-combiner phase referencing. In addition to its engineering development accomplishments, PTI has been extraordinarily scientifically productive, producing more than 25 refereed scientific papers to date. This contribution will provide an update on PTI’s operational, technical, and scientific status

The Integer Valued SU(3) Casson Invariant for Brieskorn spheres

We develop techniques for computing the integer valued SU(3) Casson invariant. Our method involves resolving the singularities in the flat moduli space using a twisting perturbation and analyzing its effect on the topology of the perturbed flat moduli space. These techniques, together with Bott-Morse theory and the splitting principle for spectral flow, are applied to calculate the invariant for all Brieskorn homology spheres.Comment: 50 pages, 3 figure

Helium ion microscopy and energy selective scanning electron microscopy – two advanced microscopy techniques with complementary applications

Both scanning electron microscopes (SEM) and helium ion microscopes (HeIM) are based on the same principle of a charged particle beam scanning across the surface and generating secondary electrons (SEs) to form images. However, there is a pronounced difference in the energy spectra of the emitted secondary electrons emitted as result of electron or helium ion impact. We have previously presented evidence that this also translates to differences in the information depth through the analysis of dopant contrast in doped silicon structures in both SEM and HeIM. Here, it is now shown how secondary electron emission spectra (SES) and their relation to depth of origin of SE can be experimentally exploited through the use of energy filtering (EF) in low voltage SEM (LV-SEM) to access bulk information from surfaces covered by damage or contamination layers. From the current understanding of the SES in HeIM it is not expected that EF will be as effective in HeIM but an alternative that can be used for some materials to access bulk information is presented

Suppression of backscattered diffraction from sub-wavelength ‘moth-eye’ arrays

The eyes and wings of some species of moth are covered with arrays of nanoscale features that dramatically reduce reflection of light. There have been multiple examples where this approach has been adapted for use in antireflection and antiglare technologies with the fabrication of artificial moth-eye surfaces. In this work, the suppression of iridescence caused by the diffraction of light from such artificial regular moth-eye arrays at high angles of incidence is achieved with the use of a new tiled domain design, inspired by the arrangement of features on natural moth-eye surfaces. This bio-mimetic pillar architecture contains high optical rotational symmetry and can achieve high levels of diffraction order power reduction. For example, a tiled design fabricated in silicon and consisting of domains with 9 different orientations of the traditional hexagonal array exhibited a ~96% reduction in the intensity of the ?1 diffraction order. It is suggested natural moth-eye surfaces have evolved a tiled domain structure as it confers efficient antireflection whilst avoiding problems with high angle diffraction. This combination of antireflection and stealth properties increases chances of survival by reducing the risk of the insect being spotted by a predator. Furthermore, the tiled domain design could lead to more effective artificial moth-eye arrays for antiglare and stealth applications

Compassion Inaction: Why President Bush\u27s Faith-Based Initiatives Violate the Establishment Clause

The Administration\u27s Faith-Based Initiatives would fail a constitutional challenge under the Establishment Clause of the First Amendment. Applying the three-pronged test developed in Lemon v. Kurtzman and Zelman v. Simmons-Harris, this Comment concludes that the Initiatives, (1) though purportedly secular, have been enacted for a sectarian purpose and are not neutral toward religion; (2) are coercive and fail to fulfill the condition of private choice because the rural poor, such as those in Franklin County, Washington, whom the Initiatives target, realistically cannot choose between non-religious and sectarian service providers; and (3) to the extent that Initiative funded programs can be kept separate from sectarian influence, they constitute impermissibly excessive entanglement between government and religion. Therefore, federal taxpayers, whose tax dollars fund Faith-Based Initiative programs such as the Compassion Capital Fund for Lourdes Hospital, a Catholic run facility in eastern Washington, have a cause of action under the First Amendment and should succeed in challenging the Initiatives under the Establishment Clause test. Additionally, this Comment identifies serious problems with the Initiative program in light of public policy interests. That this complicated and expansive funding program provides inadequate guidance to religious service providers, lacks transparency in its operations, and contains no obvious oversight provisions, not only undermines the Administration\u27s purported purposes, but also indicates that the program is ripe for abuse. As it crosses the limit of permissible government entanglement with religion, the Bush Administration acknowledges that it is toying with a “delicate” constitutional balance of interests. Yet, it has not demonstrated the capacity to safeguard this balance. Today, as poor Americans become poorer and the national debt continues to rise, we must invoke the Constitution to prevent the Executive branch from oppressing the rural poor, America\u27s most vulnerable demographic sector, with state-sponsored religious coercion that negatively impacts recipients\u27 health and wellbeing. To allow such religious oppression undercuts the intent of the framers of the First Amendment. Part II of this Comment describes one rural Washington community that is indicative of the population that the Initiatives purport to target: the poor and underserved. The policy and structure of the Initiatives are outlined in Part III, including funding streams that reach these rural Washington State residents through Catholic run healthcare programs in Franklin County. In Part IV this Comment briefly surveys the history of Supreme Court Establishment Clause jurisprudence and identifies the test applicable to this set of facts. Part V scrutinizes these Initiative programs under the combined Lemon and Zelman test, and Part VI concludes that the Initiatives entail a government establishment of religion and, therefore violate the First Amendment to the United States Constitution

Compassion Inaction: Why President Bush\u27s Faith-Based Initiatives Violate the Establishment Clause

The Administration\u27s Faith-Based Initiatives would fail a constitutional challenge under the Establishment Clause of the First Amendment. Applying the three-pronged test developed in Lemon v. Kurtzman and Zelman v. Simmons-Harris, this Comment concludes that the Initiatives, (1) though purportedly secular, have been enacted for a sectarian purpose and are not neutral toward religion; (2) are coercive and fail to fulfill the condition of private choice because the rural poor, such as those in Franklin County, Washington, whom the Initiatives target, realistically cannot choose between non-religious and sectarian service providers; and (3) to the extent that Initiative funded programs can be kept separate from sectarian influence, they constitute impermissibly excessive entanglement between government and religion. Therefore, federal taxpayers, whose tax dollars fund Faith-Based Initiative programs such as the Compassion Capital Fund for Lourdes Hospital, a Catholic run facility in eastern Washington, have a cause of action under the First Amendment and should succeed in challenging the Initiatives under the Establishment Clause test. Additionally, this Comment identifies serious problems with the Initiative program in light of public policy interests. That this complicated and expansive funding program provides inadequate guidance to religious service providers, lacks transparency in its operations, and contains no obvious oversight provisions, not only undermines the Administration\u27s purported purposes, but also indicates that the program is ripe for abuse. As it crosses the limit of permissible government entanglement with religion, the Bush Administration acknowledges that it is toying with a “delicate” constitutional balance of interests. Yet, it has not demonstrated the capacity to safeguard this balance. Today, as poor Americans become poorer and the national debt continues to rise, we must invoke the Constitution to prevent the Executive branch from oppressing the rural poor, America\u27s most vulnerable demographic sector, with state-sponsored religious coercion that negatively impacts recipients\u27 health and wellbeing. To allow such religious oppression undercuts the intent of the framers of the First Amendment. Part II of this Comment describes one rural Washington community that is indicative of the population that the Initiatives purport to target: the poor and underserved. The policy and structure of the Initiatives are outlined in Part III, including funding streams that reach these rural Washington State residents through Catholic run healthcare programs in Franklin County. In Part IV this Comment briefly surveys the history of Supreme Court Establishment Clause jurisprudence and identifies the test applicable to this set of facts. Part V scrutinizes these Initiative programs under the combined Lemon and Zelman test, and Part VI concludes that the Initiatives entail a government establishment of religion and, therefore violate the First Amendment to the United States Constitution

The Motherhood Wage Penalty in America

The difference in pay between mothers and otherwise comparable non-mothers is called the family gap. Mothers are paid less than non-mothers on average. Is it because mothers are different than non-mothers or are mothers penalized because of their decisions to have children? Previous studies have found that after controlling for demographic and human capital characteristics, mothers are paid less than non-mothers on average. This study uses 2008 American Community Survey data and finds evidence that the family gap exists in the United States