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1.
Appl Opt ; 28(14): 2785-90, 1989 Jul 15.
Article in English | MEDLINE | ID: mdl-20555599

ABSTRACT

Significant improvements can be made in the fabrication of optical thin film structures by using molecular beam and ultrahigh vacuum techniques. These lead to the achievement of more stable films and multilayer coatings with improved morphology, density, and resistance to laser-induced damage. The microstructure of the film can be controlled to a high degree by using quasisuperlattice techniques, which also provide a means of refractive index synthesis. This can be applied to simple graded structures or complex periodic gradings as required for Bragglike structures. Etalon filters fabricated using the technique have been used for optical bistability experiments and have exhibited stable operation for periods of many hours under continuous cycling.

2.
Phys Rev Lett ; 98(3): 034801, 2007 Jan 19.
Article in English | MEDLINE | ID: mdl-17358687

ABSTRACT

We demonstrate a hard-x-ray microscope that does not use a lens and is not limited to a small field of view or an object of finite size. The method does not suffer any of the physical constraints, convergence problems, or defocus ambiguities that often arise in conventional phase-retrieval diffractive imaging techniques. Calculation times are about a thousand times shorter than in current iterative algorithms. We need no a priori knowledge about the object, which can be a transmission function with both modulus and phase components. The technique has revolutionary implications for x-ray imaging of all classes of specimen.

3.
Ultramicroscopy ; 107(2-3): 227-31, 2007.
Article in English | MEDLINE | ID: mdl-16959428

ABSTRACT

We demonstrate experimentally, for the first time, a new form of lensless microscopy. The image we obtain contains the entire wavefunction emanating from the sample. Large scale, quantitative phase information can be measured, unlike in conventional (Zernike) methods. For light optical experiments, we can dispense with expensive high-quality lenses and the very large working distances available would allow remote monitoring of e.g., environmental cells without compromising resolution. In short wavelength microscopy (X-rays and electrons), where lens components are of very limited numerical aperture, the technique has revolutionary implications: objects of any lateral size or shape can be used and, for transmission electron imaging, resolution down to the scale of the wavelength is likely to be limited only by the presence of atomic vibrations.

4.
Soc Sci Med ; 54(5): 827-38, 2002 Mar.
Article in English | MEDLINE | ID: mdl-11999496

ABSTRACT

This paper investigates geographical variations in women's reports of limiting long-term illness in terms of individual inequalities and the contribution of area characteristics among wards and county districts. We use multilevel modelling of linked census data from the Office for National Statistics Longitudinal Study for England and Wales. We follow a random sample of 76.374 women aged between 16 and 45 at the time of the 1971 Census for 20 years to observe their reported limiting long-term illness (LLTI) at the 1991 Census. Car and home ownership were useful markers of social and material advantage, apparently protecting against the risk of reporting LLTI. Migration into the South-East region appeared beneficial, but otherwise there was little difference between those who moved home and those who did not. Differences between county districts persist after adjustment for individual circumstances (education and ethnicity), but almost all of these differences are explained by the social profile of wards in these areas. Geographical differences in LLTI are not, therefore, entirely explained by the distribution of individual characteristics: a woman with the same history may face a different risk of illness in different kinds of area. For women, the social composition of the locality (using the ward as a proxy) is more relevant than the broader economic and industrial classification of the surrounding county district, which is more important for health inequalities among men.


Subject(s)
Chronic Disease/epidemiology , Health Status Indicators , Socioeconomic Factors , Women's Health , Adolescent , Adult , Censuses , England/epidemiology , Female , Humans , Longitudinal Studies , Middle Aged , Models, Statistical , Time Factors , Topography, Medical , Wales/epidemiology
5.
Phys Rev Lett ; 86(11): 2381-4, 2001 Mar 12.
Article in English | MEDLINE | ID: mdl-11289934

ABSTRACT

We report first quantitative measurements by energy-selected imaging in a transmission electron microscope of In segregation within an uncapped islanded In0.25Ga0.75As layer grown epitaxially on GaAs. This layer has the lowest In concentration at which islanding occurs and, then, only after a flat approximately 3 nm alloy layer has been formed. In buildup by segregation at the surface of this initial flat layer is considered the driving force for islanding and, importantly, the segregation process introduces the characteristic delay seen before the Stranski-Krastanow transition. We observe strong inhomogeneous In enrichment within the islands (up to x(In) approximately 0.6 at the apex) and a simultaneous In depletion in the remaining flat layer.

6.
Phys Rev Lett ; 84(4): 733-6, 2000 Jan 24.
Article in English | MEDLINE | ID: mdl-11017359

ABSTRACT

New information on the electron-hole wave functions in InAs-GaAs self-assembled quantum dots is deduced from Stark effect spectroscopy. Most unexpectedly it is shown that the hole is localized towards the top of the dot, above the electron, an alignment that is inverted relative to the predictions of all recent calculations. We are able to obtain new information on the structure and composition of buried quantum dots from modeling of the data. We also demonstrate that the excited state transitions arise from lateral quantization and that tuning through the inhomogeneous distribution of dot energies can be achieved by variation of electric field.

7.
Mem Cognit ; 26(4): 617-32, 1998 Jul.
Article in English | MEDLINE | ID: mdl-9701954

ABSTRACT

In three experiments that used levels of processing and study time manipulations as independent variables in a word fragment completion task, the validity of the assumption of independence between recollection and automatic influences of memory was assessed. This assumption underlies the use of the process dissociation procedure (Jacoby, 1991), a tool suggested for distinguishing the different contributions of recollection and automatic influences of memory. Overall, it appeared that semantic processing, as compared with physical processing at study, positively affected recollection but negatively affected automatic influences of memory in word fragment completion. This negative effect on the automatic influences was reduced when the available study time decreased. The incompatibility of these results with the assumption of independence between recollection and automatic influences of memory and their impact on the applicability of the process dissociation procedure are discussed.


Subject(s)
Cues , Memory/physiology , Adult , Analysis of Variance , Consciousness/physiology , Humans , Mental Recall/physiology , Semantics , Time Factors , Volition/physiology
8.
Ultramicroscopy ; 1(2): 97-112, 1975 Dec.
Article in English | MEDLINE | ID: mdl-1236033

ABSTRACT

An adaptation of the Foucault method for topographical imaging in the transmission electron microscope is described in detail. The image contrast is produced by selection of electrons which have suffered differential phase retardations in the specimen inner potential. Surface or interface displacements produce bright or dark image contrast, and the ultimate resolution approaches that of the atomic scale. The imaging method is applied in studies of both amorphous and crystalline objects. The possibility of performing quantitative measurements is demonstrated by the estimation of the inner potential of crystalline MgO.


Subject(s)
Microscopy, Electron/methods , Crystallography , Surface Properties
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