To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
During the mid to late 1990’s a cluster of Livestock Production Programme (LPP) projects, funded by the Department for International Development (DFID) was established in Zimbabwe, as a representative country of southern sub-Saharan Africa, to develop outputs to increase the livestock contribution to the alleviation of poverty. All stakeholders were involved with the projects from the planning stage and participatory on-farm research was a key feature. Several of the projects addressed one of the major constraints to livestock production in arid and semi-arid areas, dry season feeding, the animal species considered being poultry, donkeys (draught power), goats and milking cows. The benefits of these projects can only be realised through effective dissemination to relevant target groups (farmers, extension staff, which because of failing government extension services in several African countries, must include NGOs, churches and local organizations, and policy makers) and development of relevant training materials.
We present radiocarbon (14C) in tree rings from Mexico City and a reconstruction of fossil CO2 concentrations for the last five decades, as part of a research program to understand the 14C dynamics in this complex urban area. Background values were established by 14C concentrations in tree rings from a nearby clean area. Agreement between background and NH-zone 2 values indicate Taxodium mucronatum is a good biomonitor for annual atmospheric 14C variations. Values for the urban tree rings were significantly lower than background values, indicating a 14C depletion from fossil CO2 emissions. There is an increasing trend of fossil CO2 between 1960 and 1990, in agreement with the population growth and the increasing demand for fossil fuels in Mexico City. Between 1990 and 2000, there is an apparent decrease in fossil CO2 concentration, increasing again after 2000. The decrease in 2000, despite being of the same magnitude as the overall uncertainty, may reflect environmental policies that improved the energy efficiency and reduced CO2 emissions in the area. The increase in fossil CO2 concentration between 2000 and 2010 may be attributable to the significant growth of motor vehicle usage in Mexico City, which made transportation the main energy-demanding and -emitting sector.
We present preliminary results from a programme designed to produce deep images of radio source fields drawn from the Parkes 2700 MHz and Molongolo 408 MHz catalogues using the charge-coupled-device (CCD) camera system built at the Institute of Astronomy, Cambridge. The programme is directed at a search both for faint extensions and nebulosity around radio QSOs and BL Lac objects and for faint objects in otherwise empty radio source fields; a detailed examination of the morphology of selected radio galaxies is also included.
A rapid and dramatic change in our views of the Universe which we have witnessed during the past two decades or so is often compared with what happened at the time of Galileo. Revolutionary role of the optical telescope then may be analogized with that of space-astronomy today which has drastically opened the new observational window to the Universe. The revolution is ongoing with a rapid pace or even being accelerated.
We present preliminary results from a new high resolution optical study of halo gas at the coudé focus of the Canada - France - Hawaii Telescope. Our work is still in progress so two general results are presented here: significant absorption is produced in interstellar gas beyond 500 pc from the galactic plane, and well-resolved halo clouds are identified.
I must admit that, after more than a decade of teaching and researching political parties, I found being selected to and participating in the 1980 Democratic National Convention an exhiliarating experience.
The Alabama delegate-selection process was a very competitive primary with extensive activity by the Carter and Kennedy organizations and by the individual delegate candidates. In varying degrees, the delegate candidates stumped their constituencies with personal appearances, letters, rallies, sample ballots, newspaper ads, group endorsements, and assorted other campaign gimmicks.
The selection process consisted primarily of a statewide primary (1) to allocate Alabama's delegates and alternate delegates among the presidential candidates, and (2) to elect the members of that delegation. Over 500 candidates ran for the 45 delegate and 32 alternate delegate positions in that primary. The primary actually was conducted by congressional district, with 33 candidates running for four delegate and three alternate delegate positions in my CD. The ballot was structured by sex (females listed first) and the voter was instructed to vote for up to four females and up to four males. Delegates were allocated to presidential candidates according to a formula which was roughly proportional; and individual delegates were selected by an equally fair but more complex formula.
We have detected two dominant paramagnetic centers in porous silicon by electron paramagnetic resonance (EPR). One of them is isotropic, assigned to a defect in amorphous silicon oxide in the porous silicon layer. The other is anisotropic, and is very much like a Pb center at a planar Si/SiO2 interface. This EPR center is unambiguously identified as an •Si≡Si3 moiety, a silicon with dangling orbital, back-bonded to three silicon atoms, by 29 Si hyperfine structure (HFS) associated with the dangling orbital, and 29 Si superHFS from three neighboring silicon atoms, as similarly observed in the usual planar surface Pb structure. The dangling orbitals are highly localized and heavily p character. The disposition of dangling orbitals is evidence that the skeletal structure of luminescent porous silicon is crystalline and has a lattice which is aligned and continuous with the wafer substrate. The possibility that these centers are the major photoluminescent killers or quenchers is not supported by our hydrogen annealing experiments.
The standard method to determine the band structure of a condensed phase material is to (1) obtain a single crystal with a well defined surface and (2) map the bands with angle resolved photoelectron spectroscopy (occupied or valence bands) and inverse photoelectron spectroscopy (unoccupied or conduction bands). Unfortunately, in the case of Pu, the single crystals of Pu are either nonexistent, very small and/or having poorly defined surfaces. Furthermore, effects such as electron correlation and a large spin-orbit splitting in the 5f states have further complicated the situation. Thus, we have embarked upon the utilization of unorthodox electron spectroscopies, to circumvent the problems caused by the absence of large single crystals of Pu with well-defined surfaces. Our approach includes the techniques of resonant photoelectron spectroscopy , x-ray absorption spectroscopy [1,2,3,4], electron energy loss spectroscopy [2,3,4], Fano Effect measurements , and Bremstrahlung Isochromat Spectroscopy , including the utilization of micro-focused beams to probe single-crystallite regions of polycrystalline Pu samples. [2,3,6]
Two factors which could affect the image quality of the a-Si:H arrays under development by our collaboration are the temporal drift of the leakage current of the sensors and the capture and release of charge in deep trapping states in the sensors. Data for both of these factors are reported, the implications for imaging are discussed, and strategies for reducing or eliminating their effects are suggested.
Light-sensitive hydrogenated amorphous silicon pixel arrays are now under development for real-time megavoltage and diagnostic fluoroscopic imaging. Such applications place stringent demands upon a variety of array properties including the uniformity of the light-response function of the pixels. It is desirable that the design and fabrication of these imaging arrays maximize such uniformity. The implications of uniformity for imaging are reviewed, and data obtained from small arrays are presented and discussed.
The design and characterization of flat panel a-Si:H arrays for imaging applications in radiotherapy and diagnostic radiology has already begun. Future improvements in design and performance will be heavily reliant on the results of computer simulations capable of accurately predicting the behavior of the arrays in a variety of operating conditions. These results will allow the design of new arrays to be optimized for the particular application before they are committed to fabrication. This paper outlines the results of an investigation into the effects of varying a number of array parameters and operating conditions using a simulation code which models the operation of a-Si:H devices. The results are compared with actual measurements from arrays fabricated at Xerox PARC.
The dynamic response of pixels from an a-Si:H imaging array are investigated and a model is developed to explain their observed behavior. Such arrays are under development for radiotherapy and diagnostic x-ray applications.
Shallow contact metallization of SiGeC was studied in anticipation of this alloys use in low power applications. It has been shown that in the solid state reaction of Co on (100) Si, that Co is the moving species with proper annealing conditions. This prevents the formation of Kirkendal voiding in certain device structures. This work studies the Co and Ti metallization of SiGeC. A bilayer of 44 nm of Co on 7 nm of Ti, were electron beam evaporated onto epitaxially grown Si0.77Ge0.21C0.02. The samples were rapid thermal processed at 600 and 900 °C for up to two minutes in a nitrogen ambient. The analysis techniques used were Rutherford backscattering spectrometry which included the used of the 4.27 MeV 12C(α,α) 12C resonance reaction, glancing angle x-ray diffraction, During annealing at all temperatures, Co diffused through the Ti layer and formed CoSi. This phase was confirmed by x-ray diffraction. The Co displaced the Ti to the surface. At 600 °C, Ge diffused to the surface layer, while at 900 °C it was rejected back into the original SiGeC. The sample annealed at 600 °C was subsequently annealed at 900 °C. The Ge in the surface layer was rejected from the surface layer, diffused across the CoSi and back into the SiGeC.
Zn2SiO4:Mn thin films were deposited and studied as thin film phosphors for flat panel cathodoluminescent displays. Crystallized films with improved electrical conductivity were obtained after conventional and rapid thermal annealings in a N2 environment at 850Xy11100 °C for 0.25 to 60 minutes. A maximum cathodoluminescent efficiency of 1.3 Lm/W was achieved under dc excitation at 1500 volts. The luminescent emission from these thin films was peaked around 525 nm. The decay time of these films was controlled in the range of 2 to 10 ms by varying the deposition and annealing parameters. The fast response time of these thin films overcomes the long decay limitation of the Zn2SiO4:Mn powder phosphor in practical display applications.
The energy and the flux of impinging ions are important factors which determine the properties of deposited films and of exposed surfaces (microstructure, density, hardness, roughness, stress, chemical structure, adhesion etc.). In the present work, we use a multigrid retarding field analyzer to study ion bombardment characteristics in two different systems: a pulsed microwave plasma reactor, and a cold cathode ion source. We have found that the ion energy distribution functions (IEDF) possess specific features for each mode of operation: we evaluate the shape and the maximum and the mean ion energies of the IEDF for different gases such as Ar and N2. These ion characteristics are correlated with surface restructuring of differently treated polymers (polycarbonate and polyethylene terephthalate), analyzed by XPS.
Cathode ray tube (CRT) technology remains the major display component for today's display technologies. The improvements from monochrome displays to today's full color displays have always been accompanied by improvements in the phosphors. The CRT type displays operate at very high voltages (over 10 keV) at relatively low currents, a few microamps/cm2. The phosphors and phosphor coating technology used in CRT based displays have been optimized for operation with these excitation conditions. However, the developments of field emitter displays based on microtip technology, or negative electron affinity technology require phosphors that operate at lower voltages, preferably 10 to 1500 eV at relatively higher current densities. Zn-rich zinc oxide (ZnO:Zn) powders have shown improved low voltage cathodoluminescence (CL) as compared to conventional ZnS based phosphors. ZnO:Zn thin film phosphors for cathodoluminescent displays, compared to conventional powder phosphors, can have the advantages of high electrical and thermal conductivity, high energy saturation limit, and high screen resolution. The photoluminescence (PL), Electroluminescence (EL), and CL from thin ZnO:Zn films were studied. The samples were prepared by Low Pressure Metal Organic Chemical Vapor Deposition (LP MOCVD) and post-annealed at temperatures from 700 °C to 1000 ° C. The PL, EL, and CL spectra have a peak centered at 590 nm that increases with annealing temperatures up to 1000 °C. The CL efficiencies are 0.12 Lm/W at electron voltages and currents as low as 500 V and 64 mA/cm2. The ZnO films have been characterized by X-ray Diffiractometry (XRD), and Sweep Electron Microscope (SEM). These PL, EL, and CL results from ZnO:Zn films show the promise for improved phosphors to meet Field Emitting Device (FED) challenges.
Collaboration is used by the US National Security Council as a means to integrate inter-federal government agencies during planning and execution of common goals towards unified, national security. The concept of collaboration has benefits in the healthcare system by building trust, sharing resources, and reducing costs. The current terrorist threats have made collaborative medical training between military and civilian agencies crucial.
This review summarizes the long and rich history of collaboration between civilians and the military in various countries and provides support for the continuation and improvement of collaborative efforts. Through collaboration, advances in the treatment of injuries have been realized, deaths have been reduced, and significant strides in the betterment of the Emergency Medical System have been achieved. This review promotes collaborative medical training between military and civilian medical professionals and provides recommendations for the future based on medical collaboration.