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Combined Numerical Analysis of an Oil-free Twin Screw Compressor Using 3D CFD and 1D Multi-chamber Thermodynamic Model
The application of three-dimensional computational fluid dynamics in twin-screw compressors provides an outstanding opportunity for developers to gain an understanding of the complex internal flow phenomena occurring within the machine. Equipped with this knowledge, design parameters, such as clearances and port geometry, can be optimised, to enhance performance. However, as with all modelling, be it numerical or analytical, a high degree of certainty in the accuracy of the results is necessary.
This paper presents the results of a study of oil-free twin screw compressor in which the results of two modelling techniques are compared. The modelling techniques used are an analytical non-dimensional thermodynamic chamber model and a numerical computational fluid dynamic model. The paper presents an overview of an oil-free twin screw compressor machine, before describing important operating characteristics and the modelling techniques used. To validate, both models are compared against historical test data, this validation indicated the chamber model is more accurate. Following this, the focus will be on the comparison of key performance indicators, including, volume flow rate, volumetric efficiency, indicated power, and discharge temperature at varying duty points. The paper concludes that the difference between both models decreases as the compressor operating speed increases, although the level of variance is dependent on pressure ratio
Detecting flat normal cones using Segre classes
Given a flat, projective morphism from an equidimensional scheme to
a nonsingular curve and a subscheme of , we give conditions under which
specialization of the Segre class of the normal cone of in
implies flatness of the normal cone. We apply this result to study when the
relative tangent star cone of a flat family is flat.Comment: LaTeX, 11 pages, no figure
A portable battery for objective, non-obstrusive measures of human performances
The need for a standardized battery of human performance tests to measure the effects of various treatments is pointed out. Progress in such a program is reported. Three batteries are available which differ in length and the number of tests in the battery. All tests are implemented on a portable, lap held, briefcase size microprocessor. Performances measured include: information processing, memory, visual perception, reasoning, and motor skills, programs to determine norms, reliabilities, stabilities, factor structure of tests, comparisons with marker tests, apparatus suitability. Rationale for the battery is provided
Tangential Quantum Cohomology of Arbitrary Order
J. Kock has previously defined a tangency quantum product on formal power
series with coefficients in the cohomology ring of any smooth projective
variety, and thus a ring that generalizes the quantum cohomology ring. We
further generalize Kock's construction by defining a dth-order contact product
and establishing its associativity.Comment: 18 pages, LaTeX. We correct our paper to work in the correct context,
viz., using numerical equivalence (rather than rational equivalence) and
explicitly mentioning the Novikov rin
Inclusion of transverse shear deformation in the exact buckling and vibration analysis of composite plate assemblies
The problem considered is the development of the necessary plate stiffnesses for use in the general purpose program VICONOPT for buckling and vibration of composite plate assemblies. The required stiffnesses include the effects of transverse shear deformation and are for sinusoidal response along the plate length as required in VICONOPT. The method is based on the exact solution of the plate differential equations for a composite laminate having fully populated A, B, and D stiffness matrices which leads to an ordinary differential equation of tenth order
Motion Sickness Symptomatology of Labyrinthine Defective and Normal Subjects During Zero Gravity Maneuvers
Motion sickness symptomology of labyrinthine defective and normal human subjects during zero gravity maneuver
Epidemiological Baseline of Influenza Virus in Wild Aquatic Birds in Hong Kong during the Pre-H5N1 Endemic Era
Influenza virus surveillance was conducted on wild ducks and shorebirds in Hong Kong at the Mai Po Nature Reserve to determine whether East Asian wild aquatic birds passing through or overwintering in Hong Kong are reservoirs of H5N1 influenza viruses and to establish an epidemiological baseline of influenza virus in wild aquatic birds during the pre-H5N1 endemic era. Three influenza viruses were isolated from 3178 faecal samples collected over three sampling periods from 1988 to 2001 during the southern and northern migration periods. The isolation rates and viruses were, respectively 0.08% (H10N5) in 1988 – 1990, 0.12% (H11N1) in 1998 and 0.09% (H3N8) in 1999 – 2001. Whereas tracheal and intestinal colon explants from representative shorebirds were susceptible to in vitro infection by the H10N5 virus, orally infected shorebirds were apparently not. Genetic analyses indicated that the nucleoprotein, matrix and nonstructural genes of the three viruses were related to those of aquatic bird viruses in Asia, but not to those of the human H5N1 virus. The present study provided epidemiological baseline information for future influenza virus surveillance in wild aquatic birds in southeast China
Approximating the Little Grothendieck Problem over the Orthogonal and Unitary Groups
The little Grothendieck problem consists of maximizing
over binary variables , where C is a
positive semidefinite matrix. In this paper we focus on a natural
generalization of this problem, the little Grothendieck problem over the
orthogonal group. Given C a dn x dn positive semidefinite matrix, the objective
is to maximize restricting to take
values in the group of orthogonal matrices, where denotes the (ij)-th
d x d block of C. We propose an approximation algorithm, which we refer to as
Orthogonal-Cut, to solve this problem and show a constant approximation ratio.
Our method is based on semidefinite programming. For a given , we show
a constant approximation ratio of , where is
the expected average singular value of a d x d matrix with random Gaussian
i.i.d. entries. For d=1 we recover the known
approximation guarantee for the classical little Grothendieck problem. Our
algorithm and analysis naturally extends to the complex valued case also
providing a constant approximation ratio for the analogous problem over the
Unitary Group.
Orthogonal-Cut also serves as an approximation algorithm for several
applications, including the Procrustes problem where it improves over the best
previously known approximation ratio of~. The little
Grothendieck problem falls under the class of problems approximated by a recent
algorithm proposed in the context of the non-commutative Grothendieck
inequality. Nonetheless, our approach is simpler and it provides a more
efficient algorithm with better approximation ratios and matching integrality
gaps.
Finally, we also provide an improved approximation algorithm for the more
general little Grothendieck problem over the orthogonal (or unitary) group with
rank constraints.Comment: Updates in version 2: extension to the complex valued (unitary group)
case, sharper lower bounds on the approximation ratios, matching integrality
gap, and a generalized rank constrained version of the problem. Updates in
version 3: Improvement on the expositio
Immunoreactivity for a calmodulin-dependent protein kinase is selectively increased in macaque striate cortex after monocular deprivation
Immunocytochemical methods were used to localize type II Ca2+/calmodulin-dependent protein kinase in the macaque primary visual cortex. Neurons that stain for the kinase include both pyramidal and nonpyramidal cells and they appear to form a subset of cortical neurons. They are densely packed in layers II and IVB, somewhat more sparse in layers III, IVCß, and VI, and nearly absent in layer V. In normal animals the distribution of kinase-positive cells within each layer is relatively uniform. However, in animals in which one eye is removed 7-14 days before sacrifice or sutured shut for 9 or 11 weeks, the cells in layer IVCß are divided into alternating lightly and darkly stained bands. Comparison of immunocytochemically stained sections with adjacent sections stained for the mitochondrial enzyme, cytochrome oxidase, reveals that the kinase staining increases in ocular dominance columns originally driven by the removed or closed eye. These findings suggest that either the concentration of type II Ca2+/calmodulin-dependent protein kinase or its accessibility to the antibody probe increases dramatically and selectively in neurons of macaque primary visual cortex that have been deprived of their normal visual input. This may indicate that changing levels of activity in cortical neurons can alter their regulatory machinery
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