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 firstname.lastname@example.org
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.
Phased VLA observations of the Galactic center magnetar J1745-2900 over 8-12 GHz reveal rich single pulse behavior. The average profile is comprised of several distinct components and is fairly stable over day timescales and GHz frequencies. The average profile is dominated by the jitter of relatively narrow pulses. The pulses in each of the four profile components are uncorrelated in phase and amplitude, although the occurrence of pulse components 1 and 2 appear to be correlated. Using a collection of the brightest individual pulses, we verify that the index of the dispersion law is consistent with the expected cold plasma value of 2. The scattering time is weakly constrained, but consistent with previous measurements, while the dispersion measure DM = 1763+3−10 pc cm−3 is lower than previous measurements, which could be a result of time variability in the line-of-sight column density or changing pulse profile shape over time or frequency.
Millisecond pulsars (MSPs) are a class of radio pulsars with extremely stable rotation. Their excellent timing stability can be used to study a wide variety of astrophysical phenomena. In particular, a large sample of these pulsars can be used to detect low-frequency gravitational waves. We have developed a precision pulsar timing backend for the NASA Deep Space Network (DSN), which will allow the use of short gaps in tracking schedules to time pulses from an ensemble of MSPs. The DSN operates clusters of large dish antennas (up to 70-m in diameter), located roughly equidistant around the Earth, for communication and tracking of deep-space spacecraft. The backend system will be capable of removing entirely the dispersive effects of propagation of radio waves through the interstellar medium in real-time. We will describe our development work, initial results, and prospects for future observations over the next few years.
We are developing a purely commensal survey experiment for fast (<5 s) transient radio sources. Short-timescale transients are associated with the most energetic and brightest single events in the Universe. Our objective is to cover the enormous volume of transients parameter space made available by ASKAP, with an unprecedented combination of sensitivity and field of view. Fast timescale transients open new vistas on the physics of high brightness temperature emission, extreme states of matter and the physics of strong gravitational fields. In addition, the detection of extragalactic objects affords us an entirely new and extremely sensitive probe on the huge reservoir of baryons present in the IGM. We outline here our approach to the considerable challenge involved in detecting fast transients, particularly the development of hardware fast enough to dedisperse and search the ASKAP data stream at or near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of the key technologies and survey modes proposed for high time resolution science with the SKA.
A review is given of current efforts to determine the structure of grain boundaries using X-ray diffraction. The general distribution of the diffracted intensity from the thin boundary region in reciprocal space is first described, and then some of the special experimental difficulties with measuring it quantitatively are discussed. These include, weak scattering and poor signal-to-noise ratio, preparation of sufficiently high quality bicrystal specimens, the presence of unwanted allowed and forbidden lattice reflections, double diffraction from the adjoining crystals, and limitations imposed by the scattering geometry. Various strategies for determining the boundary structure are then described. These include the measurement of either relative or absolute structure factors and the determination of structures based on either structure factor measurements alone or the combined use of structure factor measurements and computer modeling. The advantages of measuring absolute structure factors rather than relative structure factors when only a limited number of structure factors is measured is demonstrated. This situation may occur because of the experimental difficulties listed above. Current work, consisting of studies of absolute and/or relative structure factors of a range of  twist boundary structures in gold, is reviewed. Results obtained by the authors represent the first cases where good agreement has been obtained between boundary structures determined by X-ray diffraction and calculation using a physical model (i.e., the Embedded Atom Model). The large displacement model derived by Fitzsimmons and Sass for the Σ5 structure on the basis of relative structure factors is found to be incorrect. It is concluded that future progress will depend to a great extent upon the preparation of improved bicrystal specimens and the measurement of larger numbers of boundary structure factors.
The possibility of studying grain boundary segregation using X-ray diffraction is explored by performing a computer simulation of the diffraction effects expected from the segregation of solute atoms to grain boundaries in two gold alloy systems, i.e. Au-Ag and Au-Ni. Using atomistic Monte-Carlo and molecular statics methods, equilibrium boundary structures are determined and analyzed by computing the grain boundary structure factors. Various changes in both relative and absolute grain boundary structure factors are found which can be directly related to structural and compositional changes due to segregation. In addition, systematic diffraction effects are found as a function of boundary misorientation. The experimental conditions required for verifying these predictions are discussed.
We describe a chemical vapour deposition technique for the controlled growth of ZnO films, containing grain boundaries which are suitable for detailed atomic resolution studies. Using this technique, we have grown; (1) random polycrystalline, (2) highly textured polycrystalline and (3) nominally single crystal films Also, a technique for doping the grain boundaries in these specimens with Bi by an “in-diffusion” method is demonstrated. The grain boundary atomic level structure and chemistry is studied by means of High Resolution Electron Microscopy (HREM) and STEM/EDX microanalysis. Some results obtained from boundaries in textured polycrystalline films which have the c-axes in neighboring grains lined-up to ˜1 ° are described.
Age-related changes in circadian rhythm (e.g., fragmented sleep-wake patterns) occur in many older persons but are particularly pronounced in patients with Alzheimer's disease. In these patients, disruptions of circadian rhythms can be severe enough to increase mental decline, agitation during the day, and restlessness at night. Moreover, patients whose nocturnal restlessness disrupts the sleep of the caregiver are more likely to be institutionalized than those who have cognitive impairment alone.
Two field experiments studied the nitrogen fertilizer requirements of guinea and napier grass on peat. Plants in the control plots, though optimally limed and fertilized with other nutrients, absorbed only 1.7 and 2.4% of total peat N in a year and N fertilization improved DM yield, with an optimum at 900 kg/ha/yr. Further positive response was not observed, probably because of a reduced ratio of N to other nutrients. Optimum N uptake, and N concentration in the DM, were achieved at 600 kg/ha/yr N but N recovery decreased linearly with increasing fertilizer N at the rate of about 2–4% per 100 kg/ha/yr N.
In two field experiments, sweet potato showed symptoms of lime deficiency, and consequently produced extremely low DM, at the natural pH of local peat (3.5–3.7). Liming to increase pH remarkably increased tuber and vine dry matter to pH 5.5 and harvest index to pH 3.8, but higher pH values decreased dry matter and harvest index. Tuber and vine yields generally decreased with continuous monocropping, probably because of increasing infestation with weevils (Cylas formicarius) and other pests, and depletion of available nutrients.
In three field experiments studying the liming needs of cassava on peat, optimum tuber DM was obtained at pH 3.8 and optimum top DM at pH 4.2; liming to higher pH values decreased tuber DM while maintaining top DM. Consequently, the Harvest Index decreased over the whole range of soil pH studied (3.49–5.50). Increases in tuber DM per hectare with liming, and with an increasing growth period, were associated with mean tuber weight (r = 0.86) and with Harvest Index (r = 0.65) rather than with tuber number (r = 0.37).
Email your librarian or administrator to recommend adding this to your organisation's collection.