792 research outputs found
Interactions of inert confiners with explosives
The deformation of an inert confiner by a steady detonation wave in an
adjacent explosive is investigated for cases where the confiner is suciently strong
(or the explosive suciently weak) such that the overall change in the sound speed
of the inert is small. A coupling condition which relates the pressure to the deflection
angle along the explosive-inert interface is determined. This includes its dependence
on the thickness of the inert, for cases where the initial sound speed of the inert
is less than or greater than the detonation speed in the explosive (supersonic and
subsonic inert
ows, respectively). The deformation of the inert is then solved by
prescribing the pressure along the interface. In the supersonic case, the detonation
drives a shock into the inert, subsequent to which the
ow in the inert consists
of alternating regions of compression and tension. In this case reverberations or
`ringing' occurs along both the deflected interface and outer edge of the inert. For
the subsonic case, the
flow in the interior of the inert is smooth and shockless.
The detonation in the explosive initially defl
ects the smooth interface towards the
explosive. For sufficiently thick inerts in such cases, it appears that the deflection
of the confiner would either drive the detonation speed in the explosive up to the
sound speed of the inert or drive a precursor wave ahead of the detonation in the
explosive. Transonic cases, where the inert sound speed is close to the detonation
speed, are also considered. It is shown that the confinement affect of the inert on
the detonation is enhanced as sonic conditions are approached from either side
A spherical perfect lens
It has been recently proved that a slab of negative refractive index material
acts as a perfect lens in that it makes accessible the sub-wavelength image
information contained in the evanescent modes of a source. Here we elaborate on
perfect lens solutions to spherical shells of negative refractive material
where magnification of the near-field images becomes possible. The negative
refractive materials then need to be spatially dispersive with and . We concentrate on lens-like solutions for the
extreme near-field limit. Then the conditions for the TM and TE polarized modes
become independent of and respectively.Comment: Revtex4, 9 pages, 2 figures (eps
Thermoelectric properties of co-doped (Bi0.98In0.02)2Te2.7Se0.3 / reduced graphene oxide composites prepared by solid-state reaction
The thermoelectric properties of co-doped (Bi0.98In0.02)2Te2.7Se0.3/reduced graphene oxide composites between 10 - 325 K are presented. X-ray diffraction confirms that the composites adopt a rhombohedral structure with space group R3¯m. Field emission scanning electron microscopy reveals an interface structure of reduced graphene oxide (rGO). N-type conducting behaviour is observed for all the samples, as ascertained by Hall effect and Seebeck coefficient measurements, with a carrier concentration of 1025/m3. The thermal conductivity and electrical resistivity of (Bi0.98In0.02)2Te2.7Se0.3/0.02 wt% reduced graphene oxide composite is found to decrease by 1.6 and 10 times respectively in comparison with that of (Bi0.98In0.02)2Te2.7Se0.3. The power factor is enhanced by 7 times for (Bi0.98In0.02)2Te2.7Se0.3/0.01 wt% rGO compared to that of (Bi0.98In0.02)2Te2.7Se0.3
Cooling rate dependence of the antiferromagnetic domain structure of a single crystalline charge ordered manganite
The low temperature phase of single crystals of NdCaMnO
and GdCaMnO manganites is investigated by squid
magnetometry. NdCaMnO undergoes a charge-ordering
transition at =245K, and a long range CE-type antiferromagnetic state
is established at =145K. The dc-magnetization shows a cooling rate
dependence below , associated with a weak spontaneous moment. The
associated excess magnetization is related to uncompensated spins in the
CE-type antiferromagnetic structure, and to the presence in this state of
fully orbital ordered regions separated by orbital domain walls. The observed
cooling rate dependence is interpreted to be a consequence of the rearrangement
of the orbital domain state induced by the large structural changes occurring
upon cooling.Comment: REVTeX4; 7 pages, 4 figures. Revised 2001/12/0
Amplification of evanescent waves in a lossy left-handed material slab
We carry out finite-difference time-domain (FDTD) simulations, with a
specially-designed boundary condition, on pure evanescent waves interacting
with a lossy left-handed material (LHM) slab. Our results provide the first
full-wave numerical evidence for the amplification of evanescent waves inside a
LHM slab of finite absorption. The amplification is due to the interactions
between the evanescent waves and the coupled surface polaritons at the two
surfaces of the LHM slab and the physical process can be described by a simple
model.Comment: 4 pages, 2 figure
Sedimentation record in the Konkan-Kerala Basin: implications for the evolution of the Western Ghats and the Western Indian passive margin
The Konkan and Kerala Basins constitute a major depocentre for sediment from the onshore hinterland of Western India and as such provide a valuable record of the timing and magnitude of Cenozoic denudation along the continental margin. This paper presents an analysis of sedimentation in the Konkan-Kerala Basin, coupledwith a mass balance study, and numerical modelling of flexural responses to onshore denudational unloading and o¡shore sediment loading in order to test competing conceptual models for the development of high-elevation passive margins. The Konkan-Kerala Basin contains an estimated 109,000 km<sup>3</sup>; of Cenozoic clastic sediment, a volume difficult to reconcile with the denudation of a downwarped rift flank onshore, and more consistent with denudation of an elevated rift flank. We infer from modelling of the isostatic response of the lithosphere to sediment loading offshore and denudation onshore that flexure is an important component in the development of the Western Indian Margin.There is evidence for two major pulses in sedimentation: an early phase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentation can be interpreted in terms of a denudational response to the rifting between India and the Seychelles, whereas the mechanism responsible for the Pliocene pulse is more enigmatic
Decomposition of Differences
This paper examines methods of decomposing a difference in levels between groups for a dependent variable such as income. Applied to regression equations, this technique estimates the contribution to the difference from divergent characteristics and divergent rates of converting characteristics into the dependent variable. The consequences of an "interaction" component being present in the decomposition is examined. The paper, using data from the 1960 Census, shows how ignoring the interaction term can influence results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68707/2/10.1177_004912417500300306.pd
Improved Copper Circularity as a Result of Increased Material Efficiency in the U.S. Housing Stock
Material efficiency (ME) can support rapid climate change mitigation and circular economy. Here, we comprehensively assess the circularity of ME strategies for copper use in the U.S. housing services (including residential buildings and major household appliances) by integrating use-phase material and energy demand. Although the ME strategies of more intensive floor space use and extended lifetime of appliances and buildings reduce the primary copper demand, employing these strategies increases the commonly neglected use-phase share of total copper requirements during the century from 23–28 to 22–42%. Use-phase copper requirements for home improvements have remained larger than the demand gap (copper demand minus scrap availability) for much of the century, limiting copper circularity in the U.S. housing services. Further, use-phase energy consumption can negate the benefits of ME strategies. For instance, the lifetime extension of lower-efficiency refrigerators increases the copper use and net environmental impact by increased electricity use despite reductions from less production. This suggests a need for more attention to the use phase when assessing circularity, especially for products that are material and energy intensive during use. To avoid burden shifting, policymakers should consider the entire life cycle of products supporting services when pursuing circular economy goals
Observability and nonlinear filtering
This paper develops a connection between the asymptotic stability of
nonlinear filters and a notion of observability. We consider a general class of
hidden Markov models in continuous time with compact signal state space, and
call such a model observable if no two initial measures of the signal process
give rise to the same law of the observation process. We demonstrate that
observability implies stability of the filter, i.e., the filtered estimates
become insensitive to the initial measure at large times. For the special case
where the signal is a finite-state Markov process and the observations are of
the white noise type, a complete (necessary and sufficient) characterization of
filter stability is obtained in terms of a slightly weaker detectability
condition. In addition to observability, the role of controllability in filter
stability is explored. Finally, the results are partially extended to
non-compact signal state spaces
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