101,976 research outputs found
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Improving Screw Compressor Displacement and Efficiency by Increasing the Rotor Profile Depth
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Geometrical Comparison of Conventional and Gerotor-Type Positive Displacement Screw Machines
Approaches to Three-Dimensional Transformation Optical Media Using Quasi-Conformal Coordinate Transformations
We introduce an approach to the design of three-dimensional transformation
optical (TO) media based on a generalized quasi-conformal mapping approach. The
generalized quasi-conformal TO (QCTO) approach enables the design of media that
can, in principle, be broadband and low-loss, while controlling the propagation
of waves with arbitrary angles of incidence and polarization. We illustrate the
method in the design of a three-dimensional "carpet" ground plane cloak and of
a flattened Luneburg lens. Ray-trace studies provide a confirmation of the
performance of the QCTO media, while also revealing the limited performance of
index-only versions of these devices
Coupled quantum wires
We study a set of crossed 1D systems, which are coupled with each other via
tunnelling at the crossings. We begin with the simplest case with no
electron-electron interactions and find that besides the expected level
splitting, bound states can emerge. Next, we include an external potential and
electron-electron interactions, which are treated within the Hartree
approximation. Then, we write down a formal general solution to the problem,
giving additional details for the case of a symmetric external potential.
Concentrating on the case of a single crossing, we were able to explain recent
experinents on crossed metallic and semiconducting nanotubes [J. W. Janssen, S.
G. Lemay, L. P. Kouwenhoven, and C. Dekker, Phys. Rev. B 65, 115423 (2002)],
which showed the presence of localized states in the region of crossing.Comment: 11 pages, 10 figure
Isolation of Cellulolytic Microfungi Involved in Wood-Waste Decomposition: Prospects for Enzymatic Hydrolysis of Cellulosic Wastes
Wood-wastes from dump-sites at Okobaba Saw-mills on the western part of the Lagos lagoon were examined for
cellulolytic microorganisms. Cellulolytic microfungi were isolated from the wastes using minimal salt agar medium containing
0.2% (w/v) crystalline cellulose, sugarcane pulp, corn cob or saw-dust as sole carbon/energy source. The colonies of cellulolytic
microfungi which appeared on the plates increased in size and number as the incubation period (days) increased.
Among the fungal isolates were two pathogenic Aspergilli (A flavus and A fumigatus), three different black Aspergilli (herein
designated as A.niger I, A.niger II and A.niger III), Botrytis cinerea, Fusarium species and Penicillium species. Cell-free filtrates
of 7 – day cultures of A.flavus, A.niger I, A.niger II, B. cinerea and P.species grown on the minimal salt broth supplemented with
crystalline cellulose as sole carbon/energy source showed very significant CM–cellulase activity. P. species gave a very high
value that was over 4 times the value for the closest organism, A.niger II. There is a good propect for cellulase production using
the virgin strain of P. species isolated from the wood-wastes
High energy cosmic ray neutrons
A measurement of the sea level energy spectrum of cosmic ray neutrons in the energy range 50-1000 GeV has been performed. The neutrons interacted in a thick iron absorber, the burst subsequently produced being detected by a scintillation counter. The burst sizes were used to select events and to estimate the energy of the neutrons. The experimental results show a neutron spectrum that is steeper ( Y= 2.95 + 0.1) than might normally be expected. This has been discussed in terms of nucleon propagation in the atmosphere. One possible explanation would be a decrease in the nucleon attenuation length in the atmosphere. An alternative solution is in terras of the charge exchange probability for nucleon interactions. If, as has recently been postulated, the Aleph baryon is produced in high-energy (> 1000 GeV) nucleon collisions, this would lead to a deficit in the expected number of neutrons at sea level in the energy range covered by this experiment. A search for high energy magnetic monopoles has been made using the same apparatus. No events satisfying the selection requirements were observed and the upper limit to the flux at the 909s confidence level is < 9.5- 10(^-11) cm(^-2) sec(^-1) sterad(^-1). An investigation of the characteristics of long cylindrical proportional and sonic spark counters has also been carried out
Interacting Supernovae: Types IIn and Ibn
Supernovae (SNe) that show evidence of strong shock interaction between their
ejecta and pre-existing, slower circumstellar material (CSM) constitute an
interesting, diverse, and still poorly understood category of explosive
transients. The chief reason that they are extremely interesting is because
they tell us that in a subset of stellar deaths, the progenitor star may become
wildly unstable in the years, decades, or centuries before explosion. This is
something that has not been included in standard stellar evolution models, but
may significantly change the end product and yield of that evolution, and
complicates our attempts to map SNe to their progenitors. Another reason they
are interesting is because CSM interaction is an efficient engine for making
bright transients, allowing super-luminous transients to arise from normal SN
explosion energies, and allowing transients of normal SN luminosities to arise
from sub-energetic explosions or low radioactivity yield. CSM interaction
shrouds the fast ejecta in bright shock emission, obscuring our normal view of
the underlying explosion, and the radiation hydrodynamics of the interaction is
challenging to model. The CSM interaction may also be highly non-spherical,
perhaps linked to binary interaction in the progenitor system. In some cases,
these complications make it difficult to definitively tell the difference
between a core-collapse or thermonuclear explosion, or to discern between a
non-terminal eruption, failed SN, or weak SN. Efforts to uncover the physical
parameters of individual events and connections to possible progenitor stars
make this a rapidly evolving topic that continues to challenge paradigms of
stellar evolution.Comment: Final draft of a chapter in the "SN Handbook". Accepted. 25 pages, 3
fig
'Learning together': Sharing international experience on new models of primary care
No abstract available
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Analysis of rolling bearing power loss models for twin screw oil injected compressor
The mechanical losses inside a screw compressor limit the performance of the compressor in terms of efficiency. These losses arise due to relative motion between elements inside the screw compressor. The estimation of mechanical losses predicted in the literature is around 10-15% of the total shaft power. One of the elements which contribute significantly to these losses is rolling element bearings. There are numerous mathematical models available which predict power losses in the rolling bearings. The objective of this paper is to study different models to predict power loss for rolling bearings and to predict the power losses for the bearings used for oil injected, twin screw compressor. A comparison between different power loss models for different operating conditions of compressor is also presented in this paper and results of analysis are compared with available experimental observations. The analysis helps to determine suitable power loss model for different operating conditions and more realistic predictions of the power losses. This allows designers for more accurate estimation of the performance of screw compressors
Variable temperature study of the crystal and magnetic structures of the giant magnetoresistant materials LMnAsO (L=La, Nd)
Peer reviewedPublisher PD
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