14,922 research outputs found
On the growth of the Betti sequence of the canonical module
We study the growth of the Betti sequence of the canonical module of a
Cohen-Macaulay local ring. It is an open question whether this sequence grows
exponentially whenever the ring is not Gorenstein. We answer the question of
exponential growth affirmatively for a large class of rings, and prove that the
growth is in general not extremal. As an application of growth, we give
criteria for a Cohen-Macaulay ring possessing a canonical module to be
Gorenstein.Comment: 12 pages. version 2: includes omitted author contact informatio
Improving ability of tele-operators to complete progressively more difficult mobile robot paths using simple expert systems and ultrasonic sensors
Simple rules to modify pre-planned paths and improve gross robot motions associated with pick & place assembly tasks
Agglomeration Elasticities in New Zealand
This paper analyses the relationship between firms’ multi-factor productivity and the effective employment density of the areas where they operate. Quantifying these agglomeration elasticities is of central importance in the evaluation of the wider economic benefits of transport investments. We estimate agglomeration elasticities using the Statistics New Zealand prototype Longitudinal Business Database: a firm-level panel covering the period 1999 to 2006. We estimate that an area with 10 percent higher effective density has firms with productivity that is 0.69 percent higher, once we control for the industry specific production functions and sorting of more productive firms across industries and locations. We present separate estimates of agglomeration elasticities for specific industries and regions, and examine the interaction of agglomeration with capital, labour, and other inputs.Agglomeration, urban density, transport evaluation, productivity
Efficiency Policies for Salinity Management: Preliminary Research from a Spatial and Dynamic Metamodel
Dryland salinity, as an externality, has an impact on various public assets, including roads, biodiversity and public water supplies. This has been seen as an important justification for government to take action and internalise the pollution. Economic policy instruments have been identified as a potential solution to the problem, as they may achieve environmental goals at least cost to society. This paper presents a spatial and dynamic model which aims to compare economic instruments for land use change to abate the off-site impacts of salinity on public assets. Preliminary research is presented, along with a discussion of the model’s structure.dryland salinity, economic modelling, meta-modelling, policy, Agricultural and Food Policy, Land Economics/Use,
Presentations of rings with non-trivial semidualizing modules
Let R be a commutative noetherian local ring. A finitely generated R-module C
is semidualizing if it is self-orthogonal and satisfies the condition
Hom_R(C,C) \cong R. We prove that a Cohen-Macaulay ring R with dualizing module
D admits a semidualizing module C satisfying R\ncong C \ncong D if and only if
it is a homomorphic image of a Gorenstein ring in which the defining ideal
decomposes in a cohomologically independent way. This expands on a well-known
result of Foxby, Reiten and Sharp saying that R admits a dualizing module if
and only if R is Cohen--Macaulay and a homomorphic image of a local Gorenstein
ring.Comment: 16 pages, uses XY-pic; v.2 reorganized, main theorem revised,
examples adde
Impulsive Heating of Solar Flare Ribbons Above 10 MK
The chromospheric response to the input of flare energy is marked by extended
extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are
usually explained as the result of heating and bremsstrahlung emission from
accelerated electrons colliding in the dense chromospheric plasma. We present
evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon
flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class
event using data from Atmospheric Imaging Assembly (AIA) on board of Solar
Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and
differential emission measure of the flaring regions and investigate the
evolution of the plasma in the flaring ribbons. The ribbons were visible at all
SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 \AA\ filters,
sensitive to temperatures of 8 MK and 12 MK. Time evolution of the emission
measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak
time. The presence of hot plasma in the lower atmosphere is further confirmed
by RHESSI imaging spectroscopy analysis, which shows resolved sources at 11-13
MK associated with at least one ribbon. We found that collisional beam heating
can only marginally explain the necessary power to heat the 10 MK plasma at the
ribbons.Comment: 21 pages, 15 figure
Laser diode initiated detonators for space applications
Ensign Bickford Aerospace Company (EBAC) has over ten years of experience in the design and development of laser ordnance systems. Recent efforts have focused on the development of laser diode ordnance systems for space applications. Because the laser initiated detonators contain only insensitive secondary explosives, a high degree of system safety is achieved. Typical performance characteristics of a laser diode initiated detonator are described in this paper, including all-fire level, function time, and output. A finite difference model used at EBAC to predict detonator performance, is described and calculated results are compared to experimental data. Finally, the use of statistically designed experiments to evaluate performance of laser initiated detonators is discussed
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