93,653 research outputs found
Engines of Liberation - Additional Notes
Get PDFThese short notes supplement the discussion in Greenwood, Seshadri and Yorukoglu (2004) on time-use studies and female labor-force participation.
Health and Wealth in a Life Cycle Model
Get PDFThis paper presents a preliminary model of health investments over the life cycle. Health affects both longevity and provides flow utility. We analyze the interplay between consumption choices and investments in health by solving each household’s dynamic optimization problem to obtain predictions on health investments and consumption choices over the lifecycle. Our preliminary model does a good job of matching the distribution of medical expenses across households in the sample. We illustrate the scope of future model applications by examining the effects of a stylized Medicare program on patterns of wealth and mortality.
Waveguiding and photoluminescence in Er<sup>3+</sup>-doped Ta<sub>2</sub>O<sub>5</sub> planar waveguides
Get PDFThe optimization of erbium-doped Ta2O5 thin film waveguides deposited by magnetron sputtering onto thermally oxidized silicon wafer is described. Optical constants of the film were determined by ellipsometry. For the slab waveguides, background losses below 0.4dB/cm at 633nm have been obtained before post-annealing. The samples, when pumped at 980nm yielded abroad photoluminescence spectrum (FWHM ~50 nm) centred at 1534nm, corresponding to 4 I 13/2 to the 4 I 15/2 transition of Er3+ ion. The samples were annealed up to 600 °C and both photoluminescence power and fluorescence lifetime increase with post-annealing temperature and a fluorescence lifetime of 2.4ms was achieved, yielding promising results for compact waveguide amplifier
Tantalum pentoxide waveguide amplifier and laser for planar lightwave circuits
No full textA planar lightwave circuit (PLC) has been envisioned to provide a new generation of optical networks capable of delivering signal at high speed and bandwidth to the household. High index contrast (HIC) and optical gain in the same material system would substantially enhance integration of different optical devices in a small area and compensate for the losses in the system to realise low cost, dense multi-functional PLCs. This thesis investigates the use of tantala as a HIC material system for realising gain efficient Erbium doped waveguide amplifiers (EDWAs) and lasers to be used at 1.5µm wavelength, towards realising dense multi-functional PLCs.Slab waveguides were fabricated by magnetron sputter deposition under optimised conditions of a powder pressed, Er:Ta2O5 target onto an oxidized silicon substrate. Optimised sputtering process yielded a Er:Ta2O5 thin film with a refractive index of 2.105 @ 1550 nm and a maximum erbium lifetime of 2.3 ms. Single mode rib waveguides were designed and the fabricated using photolithography and argon ion beam milling. A maximum propagation loss of 0.65 ± 0.05 dB/cm at 1600 nm was measured, the peak erbium absorption and emission cross-section was determined to be 4.8 ± 0.2 x 10-21 cm2 and 4.4 ± 0.2 x 10-21 cm2 respectively.Numerical modeling of Er:Ta2O5 based EDWA predicted a maximum gain of 4 dB/cm at 200 mW pump power, in a 5.4cm long waveguide with an erbium concentration of 5.4 x 1020 ions/cm3. Gain measurements were performed on a 2.3cm long rib waveguide with a erbium concentration of 2.7 x 1020 ions/cm3, at a pump power of 200mW, and a net optical gain of 2.25dB/cm peaking at 1531.5 nm was measured in a 2µm wide waveguide. The pump threshold with respect to the launched pump power was measured to be as low as 4.5mW. The cavity was formed by affixing two mirrors at the end facets of the waveguides. Lasing was observed in a single longitudinal and transverse mode peaking between 1556 and 1560nm. The lasing threshold of 14mW with a slope efficiency of 0.3% was measured with respect to the launched power.Finally, a feasibility study for inscribing sub-micron grating structures on the Er:Ta2O5 waveguides were carried out using interferometric ablation. Gratings inscribed with 23 mJ/cm2 energy density and 1000 pulses yielded a maximum reflectivity of 11dB for TE polarisation at 1505nm. This feasibility study shows potential to realise integrated cavity line narrowed lasers and filters. Tantala has long been used for different photonic applications but gain at 1.5 μm is demonstrated for the first time. The results presented in the thesis demonstrate that tantala due to its HIC, net optical gain and other inherent properties that it possesses have the potential to realise low cost, compact PLCs for the short haul networks
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Rainbow Connectivity: Hardness and Tractability
Get PDFA path in an edge colored graph is said to be a rainbow path if no two edges on the path have the same color. An edge colored graph is (strongly) rainbow connected if there exists a (geodesic) rainbow path between every pair of vertices. The (strong) rainbow connectivity of a graph G, denoted by (src(G), respectively)
rc(G) is the smallest number of colors required to edge color the graph such that G is (strongly) rainbow connected. In this paper we study the rainbow connectivity problem and the strong rainbow connectivity problem from a computational point of view. Our main results can be summarised as below:
1) For every fixed k >= 3, it is NP-Complete to decide whether src(G) <= k even when the graph G is bipartite.
2) For every fixed odd k >= 3, it is NP-Complete to decide whether rc(G) <= k. This resolves one of the open problems posed by Chakraborty et al. (J. Comb. Opt., 2011) where they prove the hardness for the even case.
3) The following problem is fixed parameter tractable: Given a graph G, determine the maximum number of pairs of vertices that can be rainbow connected using two colors.
4) For a directed graph G, it is NP-Complete to decide whether rc(G) <= 2
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
Get PDFThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
- …
