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51.
Professor Peter R. Hobson 《Contemporary Physics》2013,54(3):277-278
The first part considers the theory of the liquid state, discusses the influence of quantum effects on liquid beheviour, and introduces the dimensionless quantum parameter A? which expresses their relative importance. The second part surveys the experimental results for the chief physical properties of liquid rare gases (and also of liquid methane). The observed quantities have been ‘reduced’ for comparison purposes to dimensionless numbers, each being divided by an appropriate parameter of its own dimensions. 相似文献
52.
Chirovsky L.M.F. Hobson W.S. Leibenguth R.E. Hui S.P. Lopata J. Zydzik G.J. Giaretta G. Goossen K.W. Wynn J.D. Krishnmaoorthy A.V. Tseng B.J. Vandenberg J.M. D'Asaro L.A. 《Photonics Technology Letters, IEEE》1999,11(5):500-502
We have fabricated vertical-cavity surface-emitting lasers (VCSELs) which, for the first time, effectively combine a shallow ion implanted aperture, for current confinement under a thin highly conducting lateral current injection layer, and an independent index guide for optical beam confinement (I2-VCSELs). Both features are possible only because they are made before a top dielectric mirror is deposited and patterned, and are photolithographically defined for improved size reproducibility compared to oxide-confined designs. The devices emit near 980 nm and have optical power outputs of 1 mW at 2.5-mA input. The 12-VCSEL design also easily incorporates coplanar contacts allowing us to operate flip-chip bonded I2-VCSEL's on silicon test chips at data rates of nearly 1 Gb/s 相似文献
53.
A. Frommer S. Luryi D. T. Nichols J. Lopata W. S. Hobson 《Fiber and Integrated Optics》1996,15(2):81-88
A method for modulation of semiconductor lasers is demonstrated. The method is based on the modulation of the optical confinement factor. Using this method an enhanced—3-dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. This supports the theoretical predictions, showing an intrinsic 1/f decay rate for the optical confinement factor modulation scheme versus an intrinsic 1/f2 decay for direct modulation. 相似文献
54.
J.P. Hobson 《Surface science》1980,100(1):273-280
This paper reports experimental results on 3 magnetron pump-gauges designed to combine the properties of UHV magnetron pumps and magnetron gauges into a single device with a portable (battery operated) power supply. The pump-gauges had a renewable cathode of Ti and were useful in the pressure range 7 × 10?9 to 1.5 × 10?4 Pa. As gauges, the sensitivities were about 1.5 × 10?2 A Pa?1. As pumps, the speeds were about 0.15 litre s?1 for Kr. 相似文献
55.
The molecule N,N-dimethylacetoacetamide, which is subject to a keto–enol equilibrium process in solution, also exhibits hindered rotation about the amido N? C bond. The hindered rotation rates have been studied by lineshape fit methods of the nuclear magnetic resonance spectra. In spite of some overlap of the keto and enol N-methyl proton signals, the simultaneous measurement of the two distinct energy barriers in the two forms is possible as well as a determination of the keto–enol equilibrium. The differences in free energy of activation between keto and enol forms for the rotation barrier can be related to the conjugation energy of the N? C π system with the enolic hydrogen bonded ring. Appeal to the model compound acetylacetone reveals a consistent set of energies for the keto and enol forms in the ground and transition states for internal rotation. The opportunity has been taken to reexamine and compare the keto–enol system ethylacetoacetate. Long range, solvent, concentration and temperature sensitive scalar couplings 4J(HH) between the enolic –OH and the adjacent methyl group in acetoacetic ester have not hitherto been reported. 相似文献
56.
c.w. X-band Gunn oscillators made with n+ cathode contacts or carefully controlled metal-alloy contacts have good frequency stability against changes of ambient temperature when operated in the appropriate conditions. It is shown that the high stability behaviour is controlled by the ratio of the cavity-controlled frequency to the transit frequency. The optimum ratio is close to that which gives the optimum efficiency. A physical explanation is derived from a finite-difference computer simulation of the depth of r.f. current modulation and its phase relative to the controlling r.f. voltage. 相似文献
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59.
Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ(13) C) and nitrogen (δ(15) N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35-463?cm total length), we found prominent size-related changes in the scute keratin δ(13) C and δ(15) N profiles close to 40 and 119?cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods. 相似文献
60.
In this paper we consider the Skorokhod embedding problem for target distributions with non-zero mean. In the zero-mean case,
uniform integrability provides a natural restriction on the class of embeddings, but this is no longer suitable when the target
distribution is not centred. Instead we restrict our class of stopping times to those which are minimal, and we find conditions
on the stopping times which are equivalent to minimality.
We then apply these results, firstly to the problem of embedding non-centred target distributions in Brownian motion, and
secondly to embedding general target laws in a diffusion.
We construct an embedding (which reduces to the Azema-Yor embedding in the zero-target mean case) which maximises the law
of sups≤TBs among the class of minimal embeddings of a general target distribution μ in Brownian motion. We then construct a minimal embedding of μ in a diffusion X which maximises the law of sups≤Th(Xs) for a general function h. 相似文献