338 research outputs found
Phonon transport in large scale carbon-based disordered materials: Implementation of an efficient order-N and real-space Kubo methodology
We have developed an efficient order-N real-space Kubo approach for the
calculation of the phonon conductivity which outperforms state-of-the-art
alternative implementations based on the Green's function formalism. The method
treats efficiently the time-dependent propagation of phonon wave packets in
real space, and this dynamics is related to the calculation of the thermal
conductance. Without loss of generality, we validate the accuracy of the method
by comparing the calculated phonon mean free paths in disordered carbon
nanotubes (isotope impurities) with other approaches, and further illustrate
its upscalability by exploring the thermal conductance features in large width
edge-disordered graphene nanoribbons (up to ~20 nm), which is out of the reach
of more conventional techniques. We show that edge-disorder is the most
important scattering mechanism for phonons in graphene nanoribbons with
realistic sizes and thermal conductance can be reduced by a factor of ~10.Comment: Accepted for publication in Physical Review B - Rapid Communication
Performance Analysis Vapour Absorption Refrigeration Chiller Run by Solar Thermal Energy
Over the past few decades, energy is the backbone of technology and economic development. In addition to men, machines and money, ‘energy' is now the fourth factor of production. The objective of this paper is to design and study an environment friendly ammonia water vapour absorption refrigeration system of unit capacity using Ammonia (R717) as a refrigerant and water as a absorbent working fluids and run by exhaust water Solar Thermal Set Up. The system is designed and tested in Thermal Engineering lab of Agnos College of technology RKDF University Bhopal Madhya Pradesh for various operating conditions using hot water as heat source. In this paper, performance of the fabricated system is outlined with respect to various operating conditions related to heat source, condenser, absorber and evaporator temperatures. The solar heating unit remains idle in the summer months. Also the solar potential is at maximum in the summer other months of year
Effective genes for resistance to stripe rust and virulence of Puccinia striiformis f. sp. tritici in Pakistan
Virulence patterns of wheat stripe rust were studied under the field conditions across four environmentally different locations: Quaid-i-Azam University (Islamabad), Pirsabak (NWFP), Faisalabad (Punjab) and Sakrand (Sindh) by planting trap nursery of tester lines and Pakistan varieties. The results revealed that stripe rust resistance genes Yr3, Yr5, Yr10, Yr15, Yr26, YrSP and YrCV were resistant, while Yr18 showed moderate susceptibility at all locations. Genes YrA-, Yr2, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27 and gene combinations Opata (Yr27+Yr18) and Super Kauz (Yr9, Yr27, Yr18) were found susceptible. Among the fifty-one (51) commercial varieties; Barani70, Marvi2000, Iqbal2000, GA2000 and Seher2006 were found resistant. The genes found effective against stripe rust under natural conditions may be deployed singly or in combination to develop high yielding resistant wheat varieties in Pakistan.Key words: Near-isogenic lines, Puccinia striiformis f. sp. tritici, stripe rust, Triticum aestivum, virulence, Yr genes
Cooperative Scattering by Cold Atoms
We have studied the interplay between disorder and cooperative scattering for
single scattering limit in the presence of a driving laser. Analytical results
have been derived and we have observed cooperative scattering effects in a
variety of experiments, ranging from thermal atoms in an optical dipole trap,
atoms released from a dark MOT and atoms in a BEC, consistent with our
theoretical predictions.Comment: submitted for special issue of PQE 201
Observation of a Cooperative Radiation Force in the Presence of Disorder
Cooperative scattering of light by an extended object such as an atomic
ensemble or a dielectric sphere is fundamentally different from scattering from
many point-like scatterers such as single atoms. Homogeneous distributions tend
to scatter cooperatively, whereas fluctuations of the density distribution
increase the disorder and suppress cooperativity. In an atomic cloud, the
amount of disorder can be tuned via the optical thickness, and its role can be
studied via the radiation force exerted by the light on the atomic cloud.
Monitoring cold atoms released from a magneto-optical trap, we
present the first experimental signatures of radiation force reduction due to
cooperative scattering. The results are in agreement with an analytical
expression interpolating between the disorder and the cooperativity-dominated
regimes
Incidental detection of sinus mucosal abnormalities on CT and MRI imaging of the head
Purpose: To investigate the prevalence of incidental sinus abnormalities on CT and MRI imaging of the head, and identify if there is any correlation between patient symptomatology and image findings. Materials and methods: One hundred and fifteen patients who underwent head CT or MRI for non-sinus related indications were included in this study, with image findings being analysed based on the Lund-Mackay Grading System (LMS). These were compared with their symptomatology based on theSNAQ-11 questionnaire. Two reviewers who were blinded to the patients’ SNAQ-11 scores analysed the images. Patients were also referred to an ENT surgeon for anterior rhinoscopy in an attempt to seek a correlation between symptomatology and/or imaging findings against clinical assessment. Results: The prevalence of incidental sinus abnormalities is between 14.8% and 37% for CT and 29.5%and 85.2% for MRI, depending upon the cutoff LMS used. There was no significant difference in the incidence rate between the different age groups or genders. Asymptomatic patients had a significantly lower incidence rate of sinus mucosal abnormalities (8.2-57.1%) when compared to the symptomatic patients (33.3-66.7%) (P<0.01). A significant correlation was found between the MRI sinus findings and patients’ symptoms (r=0.59, P<0.001) with no correlation demonstrated in the CT group. The mean LM score for the patients with clinical sinusitis was 6.2, while the normal patients had a mean LM score of 2.2. Conclusions: MRI is more sensitive than CT to detect sinus mucosal abnormalities. A significant correlation is noticed between MRI findings and patients’ symptomatology
In situ characterization of mixing and sedimentation dynamics in an impinging jet ballast tank via acoustic backscatter
Impinging jets are utilized in numerous applications, including nuclear waste treatment, for both the erosion of sediment beds and maintaining particulates in suspension. Pulse-echo ultrasonic methods offer great potential for the in situ monitoring of critical mixing and settling dynamics, in concentrated dispersions. A non-active scaled version of a Highly Active Storage Tank at Sellafield, UK, was profiled with an acoustic backscatter system under various jet firing conditions. An advanced analysis technique enabled the direct quantification of dispersion concentration changes from the converted backscatter attenuation. Hence, the erosion and mixing capability of the jets, and settling kinetics were characterized. It was found that jet operation alone provided inadequate localized mixing of eroded sediment. An additional air-lift process operation was required to hinder the rapid re-settling of dispersed particulates
Geometric and homological finiteness in free abelian covers
We describe some of the connections between the Bieri-Neumann-Strebel-Renz
invariants, the Dwyer-Fried invariants, and the cohomology support loci of a
space X. Under suitable hypotheses, the geometric and homological finiteness
properties of regular, free abelian covers of X can be expressed in terms of
the resonance varieties, extracted from the cohomology ring of X. In general,
though, translated components in the characteristic varieties affect the
answer. We illustrate this theory in the setting of toric complexes, as well as
smooth, complex projective and quasi-projective varieties, with special
emphasis on configuration spaces of Riemann surfaces and complements of
hyperplane arrangements.Comment: 30 pages; to appear in Configuration Spaces: Geometry, Combinatorics
and Topology (Centro De Giorgi, 2010), Edizioni della Normale, Pisa, 201
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