1,090 research outputs found
The natural history of bugs: using formal methods to analyse software related failures in space missions
Space missions force engineers to make complex trade-offs between many different constraints including cost, mass, power, functionality and reliability. These constraints create a continual need to innovate. Many advances rely upon software, for instance to control and monitor the next generation ‘electron cyclotron resonance’ ion-drives for deep space missions.Programmers face numerous challenges. It is extremely difficult to conduct valid ground-based tests for the code used in space missions. Abstract models and simulations of satellites can be misleading. These issues are compounded by the use of ‘band-aid’ software to fix design mistakes and compromises in other aspects of space systems engineering. Programmers must often re-code missions in flight. This introduces considerable risks. It should, therefore, not be a surprise that so many space missions fail to achieve their objectives. The costs of failure are considerable. Small launch vehicles, such as the U.S. Pegasus system, cost around 4 million up to 73 million from the failure of a single uninsured satellite. It is clearly important that we learn as much as possible from those failures that do occur. The following pages examine the roles that formal methods might play in the analysis of software failures in space missions
Characterization of Lasiodiplodia theobromae causing leaf blight disease of coconut
Coconut leaf blight pathogen Lasiodiplodia theobromae (Pat.) was characterized based on morphological, cultural characters and Internal Transcribed Spacer (ITS) sequences. Pathogen isolates collected from various coconut growing areas of Tamil Nadu, India showed significant differences in the colony morphology, colour, spore dimensions and fruiting bodies. Molecular characterization by partial sequencing of ITS region confirmed the identity of pathogen as L. theobromae. Among the several methods of inoculation employed to establish the pathogenicity, pinprick method with spraying of conidial suspension (105 spores mL-1) and spot application of mycelial mat (5 mm disc) at the inoculation site produced typical necrotic spots and lesions on coconut leaves of West Coast Tall, Arasampatti Tall, Chowghat Orange Dwarf and Chowghat Green Dwarf. Koch’s postulates were established to confirm pathogenicity. The result of the study helps to streamline the existing management strategies
Bone marrow-derived mesenchymal stem cells become anti-angiogenic when chondrogenically or osteogenically differentiated:implications for bone and cartilage tissue engineering
Osteochondral tissue repair requires formation of vascularized bone and avascular cartilage. Mesenchymal stem cells stimulate angiogenesis both in vitro and in vivo but it is not known if these proangiogenic properties change as a result of chondrogenic or osteogenic differentiation. We investigated the angiogenic/antiangiogenic properties of equine bone marrow-derived mesenchymal stem cells (eBMSCs) before and after differentiation in vitro. Conditioned media from chondrogenic and osteogenic cell pellets and undifferentiated cells was applied to endothelial tube formation assays using Matrigelâ„¢. Additionally, the cell secretome was analysed using LC-MS/MS mass spectrometry and screened for angiogenesis and neurogenesis-related factors using protein arrays. Endothelial tube-like formation was supported by conditioned media from undifferentiated eBMSCs. Conversely, chondrogenic and osteogenic conditioned media was antiangiogenic as shown by significantly decreased length of endothelial tube-like structures and degree of branching compared to controls. Undifferentiated cells produced higher levels of angiogenesis-related proteins compared to chondrogenic and osteogenic pellets. In summary, eBMSCs produce an array of angiogenesis-related proteins and support angiogenesis in vitro via a paracrine mechanism. However, when these cells are differentiated chondrogenically or osteogenically, they produce a soluble factor(s) that inhibits angiogenesis. With respect to osteochondral tissue engineering, this may be beneficial for avascular articular cartilage formation but unfavourable for bone formation where a vascularized tissue is desired
Stepping into the Same River Twice: Field Evidence for the Repeatability of a CO2 Injection Test
A single well characterisation test was conducted at the CO2CRC Otway storage site in Victoria, Australia, in 2011 and repeated in 2014. The near-well permeability was found to have declined nearly 60% since the 2011 test, while the residual saturation inferred from a variety of techniques was lower in 2014. There was a significant change in water chemistry, suggesting an alteration of near-well reservoir properties. Possible reasons for these changes are explored, and the implications for other field tests are discussed
Integer quantum Hall effect for hard-core bosons and a failure of bosonic Chern-Simons mean-field theories for electrons at half-filled Landau level
Field-theoretical methods have been shown to be useful in constructing simple
effective theories for two-dimensional (2D) systems. These effective theories
are usually studied by perturbing around a mean-field approximation, so the
question whether such an approximation is meaningful arises immediately. We
here study 2D interacting electrons in a half-filled Landau level mapped onto
interacting hard-core bosons in a magnetic field. We argue that an interacting
hard-core boson system in a uniform external field such that there is one flux
quantum per particle (unit filling) exhibits an integer quantum Hall effect. As
a consequence, the mean-field approximation for mapping electrons at
half-filling to a boson system at integer filling fails.Comment: 13 pages latex with revtex. To be published in Phys. Rev.
Space-time evolution of hadronization
Beside its intrinsic interest for the insights it can give into color
confinement, knowledge of the space-time evolution of hadronization is very
important for correctly interpreting jet-quenching data in heavy ion collisions
and extracting the properties of the produced medium. On the experimental side,
the cleanest environment to study the space-time evolution of hadronization is
semi-inclusive Deeply Inelastic Scattering on nuclear targets. On the
theoretical side, 2 frameworks are presently competing to explain the observed
attenuation of hadron production: quark energy loss (with hadron formation
outside the nucleus) and nuclear absorption (with hadronization starting inside
the nucleus). I discuss recent observables and ideas which will help to
distinguish these 2 mechanisms and to measure the time scales of the
hadronization process.Comment: 6 pages, 4 figures. Based on talks given at "Hot Quarks 2006",
Villasimius, Italy, May 15-20, 2006, and at the "XLIV internataional winter
meeting on nuclear physics", Bormio, Italy, Jan 29 - Feb 5, 2006. To appear
in Eur.Phys.J.
Efficient use of water for irrigation in the upper midwest
The objectives of this multidisciplinary interinstitutional regional study on the efficient use of water for irrigation in the upper Midwest were: (1) to determine parameters needed for existing or improved models of crop response; (2) to relate yield response to costs and revenues by assessing the water demand for irrigation; and (3) to study the demand for irrigation, present and projected, and its availability as related to public allocation decisions. From this series of studies it was concluded that: (1) There are many areas of the Midwest with sufficient groundwater and surface water resources to support the development of irrigation. (2) Soil moisture models indicate that only moderate yield response to irrigation can be expected on high moisture soils; on lighter soils and claypan soils, yield response is significant, even in regions with relatively high precipitation. (3) Irrigation and drainage on claypan soils can dramatically increase corn yields. (4) It appears economically worthwhile for the individual farmer operating on moderate soils or on claypan soils to evaluate capital investments in irrigation along with other capital investments. (5) Increases in yields and persistence of alfalfa due to irrigation appear to be insignificant when compared to conventional management practices; further research is needed. A potential, however, appears to exist for improving adaptation of a1 fa1 fa varieties to soil water deficits.U.S. Geological SurveyU.S. Department of the InteriorOpe
How to superize Liouville equation
So far, there are described in the literature two ways to superize the
Liouville equation: for a scalar field (for ) and for a vector-valued
field (analogs of the Leznov--Saveliev equations) for N=1. Both superizations
are performed with the help of Neveu--Schwarz superalgebra. We consider another
version of these superLiouville equations based on the Ramond superalgebra,
their explicit solutions are given by Ivanov--Krivonos' scheme. Open problems
are offered
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance
We have made a first measurement of the lepton momentum spectrum in a sample
of events enriched in neutral B's through a partial reconstruction of B0 -->
D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the
Upsilon(4S) resonance by the CLEO II detector, is compared directly to the
inclusive lepton spectrum from all Upsilon(4S) events in the same data set.
These two spectra are consistent with having the same shape above 1.5 GeV/c.
From the two spectra and two other CLEO measurements, we obtain the B0 and B+
semileptonic branching fractions, b0 and b+, their ratio, and the production
ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950
(+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57
+- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes,
tau+/tau0.Comment: 14 page, postscript file also available at
http://w4.lns.cornell.edu/public/CLN
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