Discrete structure of ultrathin dielectric films and their surface optical properties

The boundary problem of linear classical optics about the interaction of electromagnetic radiation with a thin dielectric film has been solved under explicit consideration of its discrete structure. The main attention has been paid to the investigation of the near-zone optical response of dielectrics. The laws of reflection and refraction for discrete structures in the case of a regular atomic distribution are studied and the structure of evanescent harmonics induced by an external plane wave near the surface is investigated in details. It is shown by means of analytical and numerical calculations that due to the existence of the evanescent harmonics the laws of reflection and refraction at the distances from the surface less than two interatomic distances are principally different from the Fresnel laws. From the practical point of view the results of this work might be useful for the near-field optical microscopy of ultrahigh resolution.Comment: 25 pages, 16 figures, LaTeX2.09, to be published in Phys.Rev.

Automated ventricular systems segmentation in brain CT images by combining low-level segmentation and high-level template matching

<p>Abstract</p> <p>Background</p> <p>Accurate analysis of CT brain scans is vital for diagnosis and treatment of Traumatic Brain Injuries (TBI). Automatic processing of these CT brain scans could speed up the decision making process, lower the cost of healthcare, and reduce the chance of human error. In this paper, we focus on automatic processing of CT brain images to segment and identify the ventricular systems. The segmentation of ventricles provides quantitative measures on the changes of ventricles in the brain that form vital diagnosis information.</p> <p>Methods</p> <p>First all CT slices are aligned by detecting the ideal midlines in all images. The initial estimation of the ideal midline of the brain is found based on skull symmetry and then the initial estimate is further refined using detected anatomical features. Then a two-step method is used for ventricle segmentation. First a low-level segmentation on each pixel is applied on the CT images. For this step, both Iterated Conditional Mode (ICM) and Maximum A Posteriori Spatial Probability (MASP) are evaluated and compared. The second step applies template matching algorithm to identify objects in the initial low-level segmentation as ventricles. Experiments for ventricle segmentation are conducted using a relatively large CT dataset containing mild and severe TBI cases.</p> <p>Results</p> <p>Experiments show that the acceptable rate of the ideal midline detection is over 95%. Two measurements are defined to evaluate ventricle recognition results. The first measure is a sensitivity-like measure and the second is a false positive-like measure. For the first measurement, the rate is 100% indicating that all ventricles are identified in all slices. The false positives-like measurement is 8.59%. We also point out the similarities and differences between ICM and MASP algorithms through both mathematically relationships and segmentation results on CT images.</p> <p>Conclusion</p> <p>The experiments show the reliability of the proposed algorithms. The novelty of the proposed method lies in its incorporation of anatomical features for ideal midline detection and the two-step ventricle segmentation method. Our method offers the following improvements over existing approaches: accurate detection of the ideal midline and accurate recognition of ventricles using both anatomical features and spatial templates derived from Magnetic Resonance Images.</p

'This was a Conradian world I was entering': Postcolonial river-journeys beyond the Black Atlantic in Caryl Phillips's work

Caryl Phillips has been accused of replicating the stereotyped view of a timeless, ahistorical Africa that Paul Gilroy puts forward in his paradigm of the Black Atlantic. Yet this article shows that Crossing the River and Phillips’s essays about Africa suggest ways in which Gilroy’s important paradigm of the black Atlantic could be broadened to become more inclusive of writing about Africa. Phillips draws inspiration from writers such as V S Naipaul, Chinua Achebe, and especially Joseph Conrad, to update the literary journey upriver and make it relevant to contemporary West African issues. A complex interplay of racial identities occurs when people from the African diaspora travel to Africa; this is a key preoccupation for Phillips when he rewrites Conrad. During the course of his river-journeys, Phillips meditates upon the complexities of being a black Westerner in Africa, examines the memory of slavery, colonialism and postcolonial unrest, problematises diasporan attempts to ‘return’ to Africa, and recognises the longstanding modernity of African countries

Long-term effects of cranial irradiation and intrathecal chemotherapy in treatment of childhood leukemia: a MEG study of power spectrum and correlated cognitive dysfunction

<p>Abstract</p> <p>Background</p> <p>Prophylaxis to prevent relapses in the central nervous system after childhood acute lymphoblastic leukemia (ALL) used to consist of both intrathecal chemotherapy (CT) and cranial irradiation (CRT). CRT was mostly abolished in the eighties because of its neurotoxicity, and replaced with more intensive intrathecal CT. In this study, a group of survivors treated with CRT before 1983 and another group treated without CRT thereafter are investigated 20–25 years later, giving a much stronger perspective on long-term quality of life than previous studies. The outcomes will help to better understand these groups’ current needs and will aid in anticipating late effects of prophylactic CRT that is currently applied for other diseases. This study evaluates oscillatory neuronal activity in these long-term survivors. Power spectrum deviations are hypothesized to correlate with cognitive dysfunction.</p> <p>Methods</p> <p>Resting state eyes-closed magnetoencephalography (MEG) recordings were obtained from 14 ALL survivors treated with CT + CRT, 18 treated with CT alone and 35 controls. Relative spectral power was calculated in the δ, θ, α1, α2, β and γ frequency bands. The Amsterdam Neuropsychological Tasks (ANT) program was used to assess cognition in the executive functions domain. MEG data and ANT scores were correlated.</p> <p>Results</p> <p>In the CT + CRT group, relative θ power was slightly increased (p = 0.069) and α2 power was significantly decreased (p = 0.006). The CT + CRT group performed worse on various cognitive tests. A deficiency in visuomotor accuracy, especially of the right hand, could be clearly associated with the deviating regional θ and α2 powers (0.471 < r < 0.697). A significant association between decreased regional α2 power and less attentional fluctuations was found for CT + CRT patients as well as controls (0.078 < r < 0.666). Patients treated with CT alone displayed a power spectrum similar to controls, except for a significantly increased level of left frontal α2 power (p = 0.030).</p> <p>Conclusions</p> <p>The tendency towards global slowing of brain oscillatory activity, together with the fact that dementia has been reported as a late effect of CRT and the neuropsychological deficiencies currently present, suggest that the irradiated brain might be aging faster and could be at risk for early‐onset dementia. The CT group showed no signs of early aging.</p

A Strategic Orientation Model for the Turkish Local e-Governments

Increased environmental uncertainty and complexity along with budget constraints requires public organizations to manage strategically as never before. The environments of public organizations have become increasingly turbulent and more firmly interconnected. During the past two decades, governments have innovated new management tools such as strategic planning, outsourcing, and performance measurement to deal with complex governance and networks to provide their public services. Meanwhile, the drive to implement e-government has resulted in the formulation of many e-government visions and strategies, driven by their own sets of political, economic, and social factors and requirements. With this regard, recent developments in e-service provision of Turkish Local e-Governments deserve empirical and well-structured research. Building on the recent literature, this study draws a strategic orientation framework and tests it by analyzing the contents of strategic documents of 114 Turkish Local e-Governments

Angular Momentum of Early- and Late-type Galaxies: Nature or Nurture?

We investigate the origin, the shape, the scatter, and the cosmic evolution in the observed relationship between specific angular momentum $j_\star$ and the stellar mass $M_\star$ in early-type (ETGs) and late-type galaxies (LTGs). Specifically, we exploit the observed star-formation efficiency and chemical abundance to infer the fraction f_\rm inf of baryons that infall toward the central regions of galaxies where star formation can occur. We find f_\rm inf\approx 1 for LTGs and $\approx 0.4$ for ETGs with an uncertainty of about $0.25$ dex, consistent with a biased collapse. By comparing with the locally observed $j_\star$ vs. $M_\star$ relations for LTGs and ETGs we estimate the fraction $f_j$ of the initial specific angular momentum associated to the infalling gas that is retained in the stellar component: for LTGs we find $f_j\approx 1.11^+0.75_-0.44$, in line with the classic disc formation picture; for ETGs we infer $f_j\approx 0.64^+0.20_-0.16$, that can be traced back to a $z<1$ evolution via dry mergers. We also show that the observed scatter in the $j_\star$ vs. $M_\star$ relation for both galaxy types is mainly contributed by the intrinsic dispersion in the spin parameters of the host dark matter halo. The biased collapse plus mergers scenario implies that the specific angular momentum in the stellar components of ETG progenitors at $z\sim 2$ is already close to the local values, in pleasing agreement with observations. All in all, we argue such a behavior to be imprinted by nature and not nurtured substantially by the environment