21,885 research outputs found
Optimization of a Non-traditional Unsupervised Classification Approach for Land Cover Analysis
The conditions under which a hybrid of clustering and canonical analysis for image classification produce optimum results were analyzed. The approach involves generation of classes by clustering for input to canonical analysis. The importance of the number of clusters input and the effect of other parameters of the clustering algorithm (ISOCLS) were examined. The approach derives its final result by clustering the canonically transformed data. Therefore the importance of number of clusters requested in this final stage was also examined. The effect of these variables were studied in terms of the average separability (as measured by transformed divergence) of the final clusters, the transformation matrices resulting from different numbers of input classes, and the accuracy of the final classifications. The research was performed with LANDSAT MSS data over the Hazleton/Berwick Pennsylvania area. Final classifications were compared pixel by pixel with an existing geographic information system to provide an indication of their accuracy
Periodically-Poled Silicon [Updated]
We propose a new class of photonic devices based on periodic stress fields in
silicon that enable second-order nonlinearity as well as quasi-phase matching.
Periodically-poled silicon (PePSi) adds the periodic poling capability to
silicon photonics, and allows the excellent crystal quality and advanced
manufacturing capabilities of silicon to be harnessed for devices based on
second-order nonlinear effects. As an example of the utility of the PePSi
technology, we present simulations showing that mid-wave infrared radiation can
be efficiently generated through difference frequency generation from
near-infrared with a conversion efficiency of 50%. This technology can also be
implemented with piezoelectric material, which offers the capability to
dynamically control the X(2) nonlinearity.Comment: 11 pages, 4 figure
Stability of Magneto-optical Traps with Large Field Gradients: Limits on the Tight Confinement of Single Atoms
We report measurements of the stability of magneto-optical traps (MOTs) for neutral atoms in the limit of tight confinement of a single atom. For quadrupole magnetic field gradients at the trap center greater than âŒ1 kG/cm, we find that stochastic diffusion of atoms out of the trapping volume becomes the dominant particle loss mechanism, ultimately limiting the MOT size to greater than âŒ5 ÎŒm. We measured and modeled the diffusive loss rate as a function of laser power, detuning, and field gradient for trapped cesium atoms. In addition, for as few as two atoms, the collisional loss rates become very high for tightly confined traps, allowing the direct observation of isolated two-body atomic collisions in a MOT
Spontaneous radiative decay of translational levels of an atom near a dielectric surface
We study spontaneous radiative decay of translational levels of an atom in
the vicinity of a semi-infinite dielectric. We systematically derive the
microscopic dynamical equations for the spontaneous decay process. We calculate
analytically and numerically the radiative linewidths and the spontaneous
transition rates for the translational levels. The roles of the interference
between the emitted and reflected fields and of the transmission into the
evanescent modes are clearly identified. Our numerical calculations for the
silica--cesium interaction show that the radiative linewidths of the bound
excited levels with large enough but not too large vibrational quantum numbers
are moderately enhanced by the emission into the evanescent modes and those for
the deep bound levels are substantially reduced by the surface-induced red
shift of the transition frequency
Include medical ethics in the Research Excellence Framework
The Research Excellence Framework of the Higher Education
Funding Council for England is taking place in 2013, its three
key elements being outputs (65% of the profile), impact (20%),
and âquality of the research environmentâ (15%). Impact will
be assessed using case studies that âmay include any social,
economic or cultural impact or benefit beyond academia that
has taken place during the assessment period.â1
Medical ethics in the UK still does not have its own cognate
assessment panelâfor example, bioethics or applied
ethicsâunlike in, for example, Australia. Several researchers
in medical ethics have reported to the Institute of Medical Ethics
that during the internal preliminary stage of the Research
Excellence Framework several medical schools have decided
to include only research that entails empirical data gathering.
Thus, conceptual papers and ethical analysis will be excluded.
The arbitrary exclusion of reasoned discussion of medical ethics
issues as a proper subject for medical research unless it is based
on empirical data gathering is conceptually mistaken. âEmpirical
ethicsâ is, of course, a legitimate component of medical ethics
research, but to act as though it is the only legitimate component
suggests, at best, a partial understanding of the nature of ethics
in general and medical ethics in particular. It also mistakenly
places medicine firmly on only one side of the
science/humanities âtwo culturesâ divide instead of in its rightful
place bridging the divide.
Given the emphasis by the General Medical Council on medical
ethics in properly preparing âtomorrowâs doctors,â we urge
medical schools to find a way of using the upcoming Research
Excellence Framework to highlight the expertise residing in
their ethicist colleagues. We are confident that appropriate
assessment will reveal work of high quality that can be shown
to have social and cultural impact and benefit beyond academia,
as required by the framework
The effect of composition on the mechanism of stress-corrosion cracking of titanium alloys in nitrogen tetroxide, and aqueous and hot- salt environments Annual summary report, 1 May 1967 - 30 Apr. 1968
Stress corrosion data for titanium alloys in aqueous, hot salt, and nitrogen dioxide environment
A Study of Feature Extraction Using Divergence Analysis of Texture Features
An empirical study of texture analysis for feature extraction and classification of high spatial resolution remotely sensed imagery (10 meters) is presented in terms of specific land cover types. The principal method examined is the use of spatial gray tone dependence (SGTD). The SGTD method reduces the gray levels within a moving window into a two-dimensional spatial gray tone dependence matrix which can be interpreted as a probability matrix of gray tone pairs. Haralick et al (1973) used a number of information theory measures to extract texture features from these matrices, including angular second moment (inertia), correlation, entropy, homogeneity, and energy. The derivation of the SGTD matrix is a function of: (1) the number of gray tones in an image; (2) the angle along which the frequency of SGTD is calculated; (3) the size of the moving window; and (4) the distance between gray tone pairs. The first three parameters were varied and tested on a 10 meter resolution panchromatic image of Maryville, Tennessee using the five SGTD measures. A transformed divergence measure was used to determine the statistical separability between four land cover categories forest, new residential, old residential, and industrial for each variation in texture parameters
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