1,657 research outputs found
Shape memory alloy actuators for active disassembly using ‘smart’ materials of consumer electronic products
This paper reports the preliminary to current development of Shape Memory Alloy (SMA) actuators within their application in ‘Active Disassembly using Smart Materials’ (ADSM). This non-destructive self-dismantling process is to aid recycling of consumer electronic products. Actuators were placed in single and multi-stage hierarchical temperature regimes after being embedded into macro and sub-assemblies of electronic product assemblies. Findings include active disassembly and a hierarchical dismantling regime for product dismantling using developed SMA actuators embedded into candidate products
On the coherence/incoherence of electron transport in semiconductor heterostructure optoelectronic devices
This paper compares and contrasts different theoretical approaches based on incoherent electron scattering transport with experimental measurements of optoelectronic devices formed from semiconductor heterostructures. The Monte Carlo method which makes no a priori assumptions about the carrier distribution in momentum or phase space is compared with less computationally demanding energy-balance rate equation models which assume thermalised carrier distributions. It is shown that the two approaches produce qualitatively similar results for hole transport in p-type Si1-xGex/Si superlattices designed for terahertz emission. The good agreement of the predictions of rate equation calculations with experimental measurements of mid- and far-infrared quantum cascade lasers, quantum well infrared photodetectors and quantum dot infrared photodetectors substantiate the assumption of incoherent scattering dominating the transport in these quantum well based devices. However, the paper goes on to consider the possibility of coherent transport through the density matrix method and suggests an experiment that could allow coherent and incoherent transport to be distinguished from each other
Commission 10: Solar Activity
Commission 10 aims at the study of various forms of solar activity, including networks, plages, pores, spots, fibrils, surges, jets, filaments/prominences, coronal loops, flares, coronal mass ejections (CMEs), solar cycle, microflares, nanoflares, coronal heating etc., which are all manifestation of the interplay of magnetic fields and solar plasma. Increasingly important is the study of solar activities as sources of various disturbances in the interplanetary space and near-Earth “space weather”.
Over the past three years a major component of research on the active Sun has involved data from the RHESSI spacecraft. This review starts with an update on current and planned solar observations from spacecraft. The discussion of solar flares gives emphasis to new results from RHESSI, along with updates on other aspects of flares. Recent progress on two theoretical concepts, magnetic reconnection and magnetic helicity is then summarized, followed by discussions of coronal loops and heating, the magnetic carpet and filaments. The final topic discussed is coronal mass ejections and space weather.
The discussions on each topic is relatively brief, and intended as an outline to put the extensive list of references in context.
The review was prepared jointly by the members of the Organizing Committee, and the names of the primary contributors to the various sections are indicated in parentheses
A tentative derivation of the main cosmological parameters
Based on the assumption that some apparent properties of the observable
universe are accurate at a reasonable level of approximation, a tentative is
made to independently derive the values of the baryon density parameter, the
Hubble constant, the cosmic microwave background temperature and the helium
mass fraction. The obtained values are in excellent agreement with those given
by the most recent observational data.Comment: 13 pages. Accepted for publication in Astrophysics & Space Scienc
The Robinson-Trautman Type III Prolongation Structure Contains K
The minimal prolongation structure for the Robinson-Trautman equations of
Petrov type III is shown to always include the infinite-dimensional,
contragredient algebra, K, which is of infinite growth. Knowledge of
faithful representations of this algebra would allow the determination of
B\"acklund transformations to evolve new solutions.Comment: 20 pages, plain TeX, no figures, submitted to Commun. Math. Phy
Hybrid poplar plantation establishment in Saskatchewan: first year results
Non-Peer ReviewedThe production of Short-Rotation Woody Crops (SRWC) has been growing steadily throughout
North America. In Saskatchewan, interest is focused on developing hybrid poplar (var.
‘Walker’) plantations for an expanding fibre industry, and as a means to diversify farm income
and possibly to increase sequestered carbon. Preliminary results from a small 6 year-old
plantation suggest that there is good potential for operational-scale hybrid poplar production over
a 15 to 20 year rotation period. Larger-scale field trials were established in the spring of 2002 on
two sites in the Meadow Lake region, to assess and compare select silvicultural practices that are
regarded to enhance the growth of hybrid poplars. After one growing season, both types of
rooted stock (cuttings and plugs) showed superior survivability (~92 %) compared to non-rooted
cuttings (~40 %), underscoring the reduced risk in planting rooted stock, especially during dry
years. Measurements of tree growth (tree height, stem volume, total plant biomass and root
production) all indicated a noticeable advantage of rooted versus non-rooted stock.
Observational data pointed to the necessity of thorough site preparation, adherence to proper
planting techniques, and mechanical or chemical weed control for successful plantation
establishment
Localized f electrons in CexLa1-xRhIn5: dHvA Measurements
Measurements of the de Haas-van Alphen effect in CexLa1-xRhIn5 reveal that
the Ce 4f electrons remain localized for all x, with the mass enhancement and
progressive loss of one spin from the de Haas-van Alphen signal resulting from
spin fluctuation effects. This behavior may be typical of antiferromagnetic
heavy fermion compounds, inspite of the fact that the 4f electron localization
in CeRhIn5 is driven, in part, by a spin-density wave instability.Comment: 4 pages, 4 figures, submitted to PR
Mid-infrared entangled photon generation in optimised asymmetric semiconductor quantum wells
The optimal design of asymmetric quantum well structures for generation of entangled photons in the mid-infrared range by spontaneous parametric down- conversion is considered, and the efficiency of this process is estimated. Calcu- lations show that a reasonably good degree of entanglement can be obtained, and that the optical interaction length required for optimal conversion is very short, in the few μm range
The Long-Term Future of Extragalactic Astronomy
If the current energy density of the universe is indeed dominated by a
cosmological constant, then high-redshift sources will remain visible to us
only until they reach some finite age in their rest-frame. The radiation
emitted beyond that age will never reach us due to the acceleration of the
cosmic expansion rate, and so we will never know what these sources look like
as they become older. As a source image freezes on a particular time frame
along its evolution, its luminosity distance and redshift continue to increase
exponentially with observation time. The higher the current redshift of a
source is, the younger it will appear as it fades out of sight. For the popular
set of cosmological parameters, I show that a source at a redshift z=5-10 will
only be visible up to an age of 4-6 billion years. Arguments relating the
properties of high-redshift sources to present-day counterparts will remain
indirect even if we continue to monitor these sources for an infinite amount of
time. These sources will not be visible to us when they reach the current age
of the universe.Comment: Phys. Rev. D, in press (2001
The use of dose quantities in radiological protection: ICRP publication 147 Ann ICRP 50(1) 2021.
The International Commission on Radiological Protection has recently published a report (ICRP Publication 147;Ann. ICRP50, 2021) on the use of dose quantities in radiological protection, under the same authorship as this Memorandum. Here, we present a brief summary of the main elements of the report. ICRP Publication 147 consolidates and clarifies the explanations provided in the 2007 ICRP Recommendations (Publication 103) but reaches conclusions that go beyond those presented in Publication 103. Further guidance is provided on the scientific basis for the control of radiation risks using dose quantities in occupational, public and medical applications. It is emphasised that best estimates of risk to individuals will use organ/tissue absorbed doses, appropriate relative biological effectiveness factors and dose-risk models for specific health effects. However, bearing in mind uncertainties including those associated with risk projection to low doses or low dose rates, it is concluded that in the context of radiological protection, effective dose may be considered as an approximate indicator of possible risk of stochastic health effects following low-level exposure to ionising radiation. In this respect, it should also be recognised that lifetime cancer risks vary with age at exposure, sex and population group. The ICRP report also concludes that equivalent dose is not needed as a protection quantity. Dose limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye will be more appropriately set in terms of absorbed dose rather than equivalent dose
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